IL-2 PROCYTOKINE ANTIBODY FUSION PROTEINS

Cross-Reference to Related Applications

This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63/393,150, filed July 28, 2022, which is incorporated by reference in its entirety.

Statement Regarding the Sequence Listing

The Sequence Listing XML associated with this application is provided in XML file format and is hereby incorporated by reference into the specification. The name of the XML file containing the Sequence Listing XML is PRVA_015_01WO_ST26.xml. The XML file is about 286,496 bytes, was created on July 27, 2023, and is being submitted electronically via USPTO Patent Center.

Background

Technical Field

The present disclosure relates to activatable proprotein homodimers comprising two separate but identical polypeptide chains, each chain comprising a fragment antigen-binding (Fab) region that specifically binds to human PD-1 or human PD-L1 or human B7H3, a hinge/Fc domain, a linker, an IL-2 protein, a protease cleavable linker, and an IL-2Ra protein. Also included are related pharmaceutical compositions and methods of use thereof.

Description of the Related Art

Interleukin-2 (IL-2) immunotherapy has proven utility in the treatment of cancers such as malignant melanoma and renal cell cancer, among others. Programmed cell death protein 1 (PD-1) and programmed death ligand 1 (PD-L1) inhibitor therapy enhances anti-tumor T-cell response and mediates antitumor activity (Dermani et al., J Cell Physiol. 234: 1313-1325, 2019).

However, there are certain problems associated with most IL-2 therapies. For example, current forms of IL-2 therapy have a short half-life in circulation and predominantly expand immunosuppressive regulatory T cells, or T _regs (see, for example, Arenas-Ramirez et al., Trends in Immunology. 36: 763-777, 2015). Also, the effects of IL-2 therapy are predominantly systemic, rather than being localized to target tissues, resulting in many severe side effects such as breathing problems, nausea, low blood pressure, loss of appetite, confusion, serious infections, seizures, allergic reactions, heart problems, renal failure, and vascular leak syndrome. Nonetheless, IL-2 therapy can be effective, and there are strategies for addressing these and other drawbacks (see, for example, WO 2021/011353). However, there is still a need in the art to improve on such strategies.

Embodiments of the present disclosure represent such improvements by providing anti-PD- 1/PD-L1 activatable proproteins comprising IL-2 (procytokine) that can be specifically targeted to, and activated within, the tumor microenvironment (TME). Brief Summary

Embodiments of the present disclosure include an activatable proprotein homodimer, comprising a first polypeptide and a second polypeptide, wherein the first polypeptide and the second polypeptide comprise, in an N- to C-terminal orientation, a fragment antigen-binding (Fab) region that specifically binds to human PD-1 or human PD-L1 or human B7H3, a hinge/Fc domain, a first linker, an IL-2 protein, a second linker, and an IL-2Ra protein, wherein the hinge/Fc domain of the first polypeptide binds to the hinge/Fc domain of the second polypeptide, wherein the IL-2 protein of the first polypeptide binds to the IL-2Ra protein of the second polypeptide, and wherein the IL-2Ra of the first polypeptide binds to the IL-2 protein of the second polypeptide, wherein said binding masks a binding site of the IL-2 protein(s) that otherwise binds to an IL-2Rp/yc and/or IL-2Ra/p/yc chain present on the surface of an immune cell in vitro or in vivo, and wherein the second linker is a cleavable linker.

In some embodiments, the Fab region specifically binds to human PD-1, and optionally comprises the Fab region from an anti-PD- 1 antibody selected from nivolumab, pembrolizumab, cemiplimab, JTX-4014, spartalizumab, camrelizumab, sintilimab, tislelizumab, toripalimab, dostarlimab, MGA012, AMP-22, and AMP-514. In some embodiments, the Fab region specifically binds to human PD-1 and comprises a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 1; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 2; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 3; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 4; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 5; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 6; or a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 7; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 8; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 9; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 10; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 11; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 12; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 13; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 14; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 15; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 16; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 17; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 18; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 19; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 20; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 21; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 22; or a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 23; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 24.

In some embodiments, the VH region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from SEQ ID NOs: 1, 3, 5, 7, 9, 11, 13, 14, 15, 17, 19, 21, and 23, and the VL region respectively comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from SEQ ID NOs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, and 24.

In some embodiments, the Fab region specifically binds to human PD-L1, and optionally comprises the Fab region from an anti-PD-Ll antibody selected from atezolizumab, avelumab, and durvalumab. In some embodiments, the Fab region specifically binds to human PD-L1 and comprises a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 25; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 26; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 27; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 28; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 29; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 30; or a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 31; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 32; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 33; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 34; a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 35; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 36; or a heavy chain variable (VH) region comprising VHCDR1, VHCDR2, and VHCDR3 regions set forth in SEQ ID NO: 37; and a light chain variable (VL) region comprising VLCDR1, VLCDR2, and VLCDR3 regions set forth in SEQ ID NO: 38.

In some embodiments, the VH region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from SEQ ID NOs: 25, 27, 29, 31, 33, 35, and 37, and the VL region respectively comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from SEQ ID NOs: 26, 28, 30, 32, 34, 36, and 38.

In some embodiments, the Fab region specifically binds to human B7H3, wherein the VH region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to SEQ ID NO: 261, and the VL region respectively comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to SEQ ID NO: 262.

In some embodiments, the Fc domain comprises a CH2 domain, a CH3 domain, or a CH2CH3 domain of an immunoglobulin, optionally wherein the immunoglobulin is from an immunoglobulin class selected from IgGl, IgG2, IgG3, IgG4, IgA, IgD, IgE, and IgM. In some embodiments, the hinge comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from Table Fl, and wherein the Fc domain comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from Table Fl. In some embodiments, the Fc domain is a modified Fc domain that does not bind or substantially bind to FcyR, and retains normal or substantially normal binding to FcRn. In some embodiments, the modified Fc domain comprises a modified IgGl CH2 domain with L234A/L235A (“LALA”) mutations and/or a P329A or P329G mutation (EU numbering).

In some embodiments, the IL-2 protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to an amino acid sequence selected from Table SI, optionally amino acids 21-153 of SEQ ID NO: 68 (full-length wild-type human IL-2), optionally comprising a C145X (X is any amino acid) or a C 145 S substitution as defined by SEQ ID NO: 68. In some embodiments, the IL-2 protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 69 (mature human IL-2 with C125S substitution), optionally wherein the IL-2 protein retains the S125 residue as defined by SEQ ID NO: 69. In some embodiments, the IL-2 protein comprises one or more substitutions selected from K35C, R38C, T41C, F42C, E61C, and V69C as defined by SEQ ID NO: 69. In some embodiments, the IL-2 protein of the first polypeptide forms a disulfide bond with the IL-2Ra protein of the second polypeptide, and wherein the IL-2Ra protein of the first polypeptide forms a disulfide bond with the IL-2 protein of the second polypeptide, optionally via one or more of the foregoing cysteines. In some embodiments, the IL-2 protein comprises one or more amino acid substitutions at position 69, 74, and/or 128 as defined by SEQ ID NO: 69, optionally wherein the one or more amino acid substitutions are selected from V69A, Q74P, and I128T as defined by SEQ ID NO: 69.

In some embodiments, the IL-2 protein comprises one or more amino acid substitutions at position T3, R38, F42, K43, Y45, E61, E62, E68, and/or L72 as defined by SEQ ID NO: 69, optionally wherein the one or more amino acid substitutions are selected from T3A; R38A, R38D, and R38K; F42A, F42G, F42S, F42T, F42Q, F42E, F42N, F42D, F42R, F42K, and F42I; K43E; Y45A, Y45G, Y45S, Y45T, Y45Q, Y45E, Y45N, Y45D, Y45R, and Y45K; E61S; E62A and E62L; E68A and E68V; and L72A, L72G, L72S, L72T, L72Q, L72E, L72N, L72D, L72R, and L72K, including combinations thereof, optionally a combination selected from F42A, Y45A, and L72G; R38K, F42Q, Y45N, E62L, and E68V; R38K, F42Q, Y45E, and E68V; R38A, F42I, Y45N, E62L, and E68V; R38K, F42K, Y45R, E62L, and E68V; R38K, F42I, Y45E, and E68V; and R38A, F42A, Y45A, and E62A. In some embodiments, the IL-2 protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 84 or 85 (Human IL-2 mature (26-153)), optionally wherein the IL-2 protein comprises or retains the R38D, K43E, and C125S substitutions of SEQ ID NO: 85.

In some embodiments, the IL-2Ra protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% to an amino acid sequence selected from Table S2, optionally amino acids 22-187 of SEQ ID NO: 86 (full-length wild-type human IL- 2Ra), optionally wherein the IL-2Ra protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% to SEQ ID NO: 90, including wherein the IL- 2Ra protein retains the D6R and/or E29K substitutions. In some embodiments, the IL-2Ra protein comprises one or more cysteine substitutions selected from D4C, D6C, N27C, K38C, S39C, L42C, Y43C, Il 18C, and H120C as defined by SEQ ID NO: 88 (human IL-2Ra Sushi 1 to Sushi 2 domain), and/or a K38S substitution. In some embodiments, the IL-2Ra protein of the first polypeptide forms a disulfide bond with the IL-2 protein of the second polypeptide, and wherein the IL-2Ra protein of the second polypeptide forms a disulfide bond with the IL-2 protein of the first polypeptide, optionally via one or more of the foregoing cysteines and one or more cysteines in the IL-2 protein, optionally one or more cysteine pairs selected from IL2-K35C and IL2Ra-D4C, IL2-R38C and IL2Ra-D6C, IL2-R38C and IL2Ra-H120C, IL2-T41C and IL2Ra-Il 18C, IL2-F42C and IL2Ra-N27C, IL2-E61C and IL2Ra-K38C, IL2-E61C and IL2Ra-S39C, and IL2-V69C and IL2Ra-L42C. In some embodiments, first and second IL-2Ra proteins comprise an alanine substitution at position 49 and/or 68 as defined by SEQ ID NO: 88.

In some embodiments, the hinge of the first polypeptide forms at least one or two disulfide bonds with the hinge of the second polypeptide. In some embodiments, the first linker is a non- cleavable or stable linker, and wherein the cleavable linker comprises a protease cleavage site, optionally wherein the cleavable linker is selected from Table S3. In particular embodiments, the first linker is a non-cleavable or stable linker of 7 or fewer amino acids in length (or 1, 2, 3, 4, 5, 6, 7 amino acids in length), and the cleavable linker comprises a protease cleavage site, optionally wherein the cleavable linker is selected from Table S3, for instance, SEQ ID NO: 93. In specific embodiments, the first linker is a non-cleavable or stable linker, for instance, a 4 amino acid stable linker such as GGGS (SEQ ID NO: 188), and the cleavable linker comprises a protease cleavage site, optionally wherein the cleavable linker is selected from Table S3, for example, SEQ ID NO: 93.

In some embodiments, the protease cleavage site is cleavable by a protease selected from one or more of a metalloprotease, a serine protease, a cysteine protease, and an aspartic acid protease. In some embodiments, protease cleavage site is cleavable by a protease selected from one or more of MMP1, MMP2, MMP3, MMP4, MMP5, MMP6, MMP7, MMP8, MMP9, MMP10, MMP11, MMP12, MMP13, MMP14, TEV protease, matriptase, uPA, FAP, Legumain, PSA, Kallikrein, Cathepsin A, and Cathepsin B. In some embodiments, the first linker and/or the second linker are about 1-50 1-40, 1-30, 1-20, 1-10, 1-5, 1-4, 1-3 amino acids in length, or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 amino acids in length.

In some embodiments, the Fab comprises SEQ ID NOs: 3 (VH) and a human IgGl CHI domain, and SEQ ID NO:4 (VL) and a CL domain (kappa); the Fc domain comprises the IgGl hinge of SEQ ID NO: 42, a modified human IgGl CH2 domain of SEQ ID NO: 57, and a human IgGl CH3 domain of SEQ ID NO: 58; the first linker is a 4 amino acid stable linker of SEQ ID NO: 188; the IL- 2 protein comprises SEQ ID NO: 84 or 85, optionally with R38D, K43E, and C125S mutations; the second linker is a protease cleavable linker of SEQ ID NO: 93; and the IL-2Ra protein comprises SEQ ID NO: 88 or 90, optionally with D6R and E29K mutations.

In certain activatable proprotein homodimers, cleavage, optionally protease cleavage, of the second linker exposes the binding site(s) of the IL-2 proteins that bind to the IL-2Rp/yc chain present on the surface of the immune cell in vitro or in vivo. In some embodiments, the immune cell is selected from one or more of a T cell, a B cell, a natural killer cell, a monocyte, and a macrophage.

In some embodiments, the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to a sequence selected from Table S4 (chains 1 and 2), and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to the corresponding sequence from Table S4 (chains 3 and 4), including wherein: the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 138, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 139; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 140, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 141; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 142, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 143; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 146, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 147; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 148, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 149; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 152, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 153; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 154, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 155; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 156, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 157; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 158, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 159; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 209, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 210; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 211, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 212; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 213, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 214; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 215, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 216; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 217, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 218; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 219, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 220; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 221, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 222; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 223, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 224; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 225, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 226; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 227, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 228; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 229, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 230; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 231, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 232; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 233, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 234; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 235, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 236; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 237, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 238; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 239, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 240; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 241, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 242; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 243, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 244; the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 245, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 246; or the first polypeptide and the second polypeptide comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 247, and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 248.

Certain activatable proprotein homodimers described herein are substantially in homodimeric form in a physiological solution, or under physiological conditions, optionally in vivo conditions.

Also included are one or more recombinant nucleic acid molecules that encode the activatable proprotein homodimers described herein. In some embodiments, a first recombinant nucleic acid molecule encodes the VH/CH1 regions of the Fab region, the hinge/Fc domain, the first linker, the IL- 2 protein, the second linker, and the IL-2Ra protein, and a second nucleic acid molecule encodes the VL/CL regions of the Fab region. Also included are or more vectors comprising the one or more recombinant nucleic acid molecules described herein. Certain embodiments include a host cell comprising the one or more recombinant nucleic acid molecules described herein, or the one or more vectors described herein.

Certain embodiments include methods of producing an activatable proprotein, comprising culturing a host cell described herein under culture conditions suitable for the expression of the activatable proprotein homodimer, and isolating the activatable proprotein from the culture.

Also included are pharmaceutical compositions, comprising an activatable proprotein homodimer described herein, and a pharmaceutically acceptable carrier.

Certain embodiments relate to methods of treating disease in a subject, and/or methods of enhancing an immune response in a subject, comprising administering to the subject a therapeutically effective amount of the pharmaceutical composition described herein. In some embodiments, the disease is a cancer, for instance, a cancer that expresses or overexpresses PD-L1. In some embodiments, the cancer is a primary cancer or a metastatic cancer, and is selected from one or more of melanoma (optionally metastatic melanoma), kidney cancer (optionally renal cell carcinoma), pancreatic cancer, bone cancer, prostate cancer, small cell lung cancer, nonsmall cell lung cancer (NSCLC), mesothelioma, leukemia (optionally lymphocytic leukemia, chronic myelogenous leukemia, acute myeloid leukemia, or relapsed acute myeloid leukemia), multiple myeloma, lymphoma, hepatoma (hepatocellular carcinoma), sarcoma, B-cell malignancy, breast cancer, ovarian cancer, colorectal cancer, glioma, glioblastoma multiforme, meningioma, pituitary adenoma, vestibular schwannoma, primary CNS lymphoma, primitive neuroectodermal tumor (medulloblastoma), bladder cancer, uterine cancer, esophageal cancer, brain cancer, head and neck cancers, cervical cancer, testicular cancer, thyroid cancer, and stomach cancer.

In some embodiments, following administration, the activatable proprotein homodimer is activated through protease cleavage in a cancer cell or cancer tissue, or a tumor microenvironment (TME), which exposes the binding site(s) of the IL-2 proteins that bind to the IL-2Rp/yc chain present on the surface of the immune cell in vitro or in vivo, and thereby generates an activated protein. In some embodiments, the activated protein binds via the IL-2 protein to the IL-2Rp/yc chain present on the surface of an immune cell in vitro or in vivo. In some embodiments, the immune cell is selected from one or more of a T cell, a B cell, a natural killer cell, a monocyte, and a macrophage.

In some embodiments, administration and activation of the activatable proprotein increases an anti-cancer immune response in the subject by about or at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000% or more, relative to a control. In some embodiments, administration and activation of the activatable proprotein increases cancer cell-killing in the subject by about or at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000% or more, relative to a control.

In some embodiments, the pharmaceutical composition is administered to the subject by parenteral administration. In some embodiments, the parenteral administration is intravenous administration.

Certain embodiments include the use of a pharmaceutical composition described herein in the preparation of a medicament for treating a disease in a subject, optionally cancer (e.g., PD-L1 expressing or over-expression cancer), and/or for enhancing an immune response in a subject. Certain embodiments include a pharmaceutical composition described herein for use in treating a disease in a subject, optionally cancer (e.g., PD-L1 expressing or over-expression cancer), and/or for enhancing an immune response in a subject.

Brief Description of the Drawings

Figure 1 shows an exemplary structure of a single polypeptide (IgG-proIL-2 motif), which forms a homodimer (not shown) with a second polypeptide having the same structure. The IgG-proIL- 2 motif is comprised of a high affinity neutralizing antibody (for example, with no FcyR binding and intact FcRn binding) and an IL-2 procytokine module.

Figure 2 shows an exemplary structure of an activatable proprotein homodimer in its inactive (procytokine) state. The dashed lines indicate the cleavable linker. The intact IgG-proIL-2 construct shows little or no IL-2 activity because the IL-2RPy binding site is ‘masked’ in this format.

Figure 3 illustrates the IL-2 “activation” of the homodimer by protease cleavage of the cleavable linker in the TME. The protease cleavable linkers between IL-2 and IL-2Ra are stable in the peripheral blood, but can be cleaved by tumor proteases in the TME, thereby releasing the active IL-2 at the tumor site. Such can reduce the toxicity in peripheral blood and increase the anti -tumor activity.

Figures 4A-4C show ELISA binding activity of PD-l-proIL-2v to (A) human PD-1 or (B) Cyno PD-1 in comparison to PD-1 IgG, and binding activity of (C) PD-Ll-proIL-2v to PD-L1 in comparison to PD-L1 IgG.

Figure 5 shows the results of a mixed lymphocyte reaction that was performed by co-culture of PBMC cells and allogeneic DCs with or without dose titrations of parental PD-1 antibody or PD-1- proIL-2 added at the initiation of the assay. After 5 days, IFN-y secretion in culture supernatants was analyzed by ELISA.

Figures 6A-6B show proliferation of the human acute megakaryoblastic leukemia cell line M-07e induced by (A) MMP2 protease activated PD-l-proIL-2v in comparison to human recombinant IL-2 and intact PD-l-proIL-2v, or (B) MMP2 protease activated PD-Ll-proIL-2v in comparison to human recombinant IL-2 and intact PD-Ll-proIL-2v.

Figures 7A-7D show the results of a STAT5 assay of intact and MMP2 protease activated PD-l-proIL-2v on resting PBMCs of donor 1 (CD4 T-cells (A), CD8 T-cells (B), regulatory T-cell (C), and NK cells (D); Key on 7B).

Figures 8A-8D show the results of a STAT5 assay of intact and MMP2 protease activated PD-Ll-proIL-2v on resting PBMCs of donor 1 (CD4 T-cells (A), CD8 T-cells (B), regulatory T-cell (C), and NK cells (D); Key on 8B).

Figures 9A-9B show in vitro CD4 T cell activation and cytokine release. Shown is the dose dependent (A) GM-CSF and (B) IFN-y secretion by human polyclonal CD4 T cells upon 5 days stimulation with increasing concentrations of either PD- 1 antibody or intact or MMP2 protease activated PD-l-proIL-2v.

Figure 10A shows the averaged tumor volume measured over time in the A375-PBMC xenograft model, which evidences the in vivo anti -tumor activities of PD-Ll-proIL-2v with different linkers compared to anti-PD-Ll antibody at the same molar concentration as single agents in inhibiting tumor growth. Figure 10B shows the averaged tumor volume at Day 24 for the same treatments in 10A. Mice (n=5 or 6) were i.v. injected at Day 0, 3, 7, 10, and 14; the results are expressed as mean ±S.E.M. Figure 11A shows the averaged tumor volume measured over time in HT-29-PBMC xenograft model, which evidences the in vivo anti -tumor activities of PD-Ll-proIL-2v with different linkers compared to anti-PD-Ll antibody at the same molar concentration as single agents in inhibiting the tumor growth. Figure 11B shows the averaged tumor volume at Day 23 for the same treatments in 11A. Mice (n=6 for each group) were i.v. injected at Day 0, 3, 7, and 10; the results of are expressed as mean ±S.E.M.

Figure 12A shows the averaged tumor volume measured over time in A375-PBMC xenograft model, which evidences the in vivo anti-tumor activities of PD-l-proIL-2v with different linkers as single agents in inhibiting the tumor growth. Figure 12B shows the averaged tumor volume at Day 29 for the same treatments in 12A. Mice (n=5 or 6) were i.v. injected at Day 0, 3, 7, and 10; the results are expressed as mean ±S.E.M.

Figure 13A shows the averaged tumor volume measured over time in HT-29-PBMC xenograft model, which evidences the in vivo anti -tumor activities of PD-l-proIL-2v with different linkers compared to anti-PD-1 antibody as single agents in inhibiting the tumor growth. Figure 13B shows the averaged tumor volume at Day 27 for the same treatments in 13 A. Mice (n=5 or 6) were i.v. injected at Day 0, 4, 7, and 11; the results are expressed as mean ±S.E.M.

Figure 14A shows the averaged tumor volume measured over time in A375-PBMC xenograft model, which evidences the in vivo dose-dependent anti-tumor activities of PD-Ll-proIL-2v and PD- l-proIL-2v as single agents in inhibiting the tumor growth. Figure 14B shows the averaged tumor volume at Day 22 for the same treatments in 14A. Mice (n=5 or 6) were i.v. injected at Day 0, 3, 7, 10, and 14; the results are expressed as mean ±S.E.M.

Figure 15A shows the averaged tumor volume measured over time in A375-PBMC xenograft model, which evidences the in vivo anti-tumor activities of B7H3-proIL-2v and PD-l-proIL-2v as single agents in inhibiting the tumor growth. Figure 15B shows the averaged tumor volume at Day 22 for the same treatments in 15A. Mice (n=6) were i.v. injected at Day 0 and 7; the results are expressed as mean ±S.E.M.

Figure 16A shows the averaged tumor volume measured over time in A375-PBMC xenograft model, which evidences the in vivo anti-tumor activities of PD-Ll-proIL-2v and PD-Ll-proIL-2wt as single agents in inhibiting the tumor growth. Figure 16B shows the averaged tumor volume at Day 19 for the same treatments in 16A. Mice (n=5 or 6) were i.v. injected at Day 0, 3, and 7; the results are expressed as mean ±S.E.M.

Figure 17A shows the averaged tumor volume measured over time in A375-PBMC xenograft model, which evidences the in vivo anti-tumor activities of PD-l-proIL-2v and anti-PD-Ll antibody, separately and in combination, in inhibiting the tumor growth. Figure 17B shows the averaged tumor volume at Day 29 for the same treatments in 17A. Mice (n=5 or 6) were i.v. injected at Day 0, 3, 7, and 10; the results are expressed as mean ±S.E.M. Figure 18A shows the concentration of the total drug (procytokine + activated cytokine) and procytokine of PD-l-proIL-2v over time in peripheral blood. Figure 18B shows the concentration of the total drug and procytokine of PD-l-proIL-2v over time in tumor. Figure 18C shows concentration of the activated cytokine of PD-l-proIL-2v over time in tumor. Mice (n=3) were i.v. injected with P41222037 Img/kg at Day 0; the results are expressed as mean ±S.E.M.

Figures 19A-19C show the cell number of CD3 ⁺ (A), CD4 ⁺ (B), and CD8 ⁺ (C) T cells in peripheral blood over time after the treatment of PD-l-proIL-2v in PBMC humanized A375 xenograft model. Mice (n=5) were i.v. injected at Day 0 and 7; the results are expressed as mean ±S.E.M.

Figures 20A-20C show the cell number of CD3 ⁺ (A), CD4 ⁺ (B), and CD8 ⁺ (C) T cells in tumor after the treatment of PD-l-proIL-2v in A375-PBMC xenograft model. Mice (n=3) were i.v. injected at Day 0 and 8, and tumors were harvested at day 12; the results are expressed as mean ±S.E.M.

Figure 21 A shows the concentration of masked or unmasked PD-l-proIL-2v over time in peripheral blood of cynomolgus monkeys. Figure 21B shows the albumin levels over time after treated with masked or unmasked PD-l-proIL-2v in peripheral blood of cynomolgus monkeys. Monkeys (n=2) were i.v. injected with P41222037 or P41252037.

Figures 22A-22C show proliferation of the human acute megakaryoblastic leukemia cell line M-07e induced by protease-activated P41222037 (22A), P45412037 (22B), or P45422037 (22C) constructs in comparison to human recombinant IL-2 and the intact proprotein (without protease activation) P41222037, P45412037, or P45422037 constructs, respectively.

Figure 23A-23D show STAT5 phosphorylation in CD4 T cells, CD8 T cells, and Tregs upon treatment of resting PBMC with both intact and MMP2-cleaved P41222037 (23A), P45412037 (23B), or P45422037 (23C) as determined by flow cytometry in comparison to human recombinant IL-2. STAT5 phosphorylation analysis in CD4 T cells, CD8 T cells, and Tregs upon treatment of resting PBMC with intact proprotein P41222037, P45412037, and P45422037 constructs was plotted together for comparison (23D).

Figures 24A-24C show STAT5 phosphorylation in CD4 T cells, CD8 T cells, and Tregs upon treatment of resting PBMC with P78192037, P78202037, P78212037, P78222037, P78232037, and P78242037 (24A); P78252037, P78262037, P78272037, P78282037, P78292037, and P78302037 (24B); or P78312037, P78322037, P78332037, P78342037, P78352037, and P78362037 (24C) as determined by flow cytometry in comparison to human recombinant IL-2.

Figure 25 shows STAT5 phosphorylation in CD4 T cells, CD8 T cells, and Tregs upon treatment of pre-activated PBMCs with intact proprotein P41222037 construct as determined by flow cytometry.

Figure 26 shows the amino acid sequences of tested constructs at the junction of the fusion between the antibody heavy chain and the IL-2 variants. The exemplary junction sequences include various stable linker lengths, deletions of the C-terminal Lys of the heavy chain, and/or deletions of the N-terminal residues of IL-2. Sequence identifiers: LSPGK (SEQ ID NO: 249); LSPG (SEQ ID NO: 250); GGGS, GGGSGGGS (SEQ ID NO: 188); GGGSGGG (SEQ ID NO: 251); GGGSGG (SEQ ID NO: 252); GGGSG (SEQ ID NO: 253); APASSSTKK (SEQ ID NO: 254); PASSSTKK (SEQ ID NO: 255); ASSSTKK (SEQ ID NO: 256); SSSTKK (SEQ ID NO: 257); SSTKK (SEQ ID NO: 258); STKK (SEQ ID NO: 259); STLT (SEQ ID NO: 260).

Detailed Description

Embodiments of the present disclosure relate to activatable proprotein homodimers, comprising two separate but identical polypeptides, each polypeptide comprising in an N- to C- terminal orientation, a fragment antigen-binding (Fab) region that specifically binds to human PD-1 or human PD-L1, a hinge/Fc domain, a stable linker, an IL-2 protein, a protease cleavable linker, and an IL-2Ra protein. In some instances, the homodimer is formed by the following binding interactions: binding of the hinge/Fc domain of one polypeptide to the hinge/Fc domain of the other polypeptide, and binding of each of the IL-2 proteins of one polypeptide to each of the IL-2Ra proteins of the other polypeptide. These binding interactions form a biologically-inactive (proprotein) homodimer by masking the binding sites of the IL-2 proteins that would otherwise bind to an IL-2Rp/yc and/or IL- 2Ra/p/yc chain present on the surface of an immune cell. The proprotein homodimer remains inactive or substantially inactive in plasma.

In certain instances, the homodimer is targeted to the tumor microenvironment (TME) by the anti -PD-1 or anti-PD-Ll Fab, and then activated within the TME by exposure to tumor-site proteases, which cleave the protease cleavable linker, thereby releasing the IL-2Ra proteins and exposing the active sites of the IL-2 proteins. Such allows enhanced IL-2 signaling activity on PD-1 or PD-L1 expressing cells due to “cis-targeting” effects and/or synergy between the anti-tumor activity of the anti-PD-l/anti-PD-Ll Fab and the immune-stimulating activity of the IL-2 proteins.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the disclosure belongs. Although any methods, materials, compositions, reagents, cells, similar or equivalent similar or equivalent to those described herein can be used in the practice or testing of the subject matter of the present disclosure, preferred methods and materials are described. All publications and references, including but not limited to patents and patent applications, cited in this specification are herein incorporated by reference in their entirety as if each individual publication or reference were specifically and individually indicated to be incorporated by reference herein as being fully set forth. Any patent application to which this application claims priority is also incorporated by reference herein in its entirety in the manner described above for publications and references.

Standard techniques may be used for recombinant DNA, oligonucleotide synthesis, and tissue culture and transformation (e.g., electroporation, lipofection). Enzymatic reactions and purification techniques may be performed according to manufacturer’s specifications or as commonly accomplished in the art or as described herein. These and related techniques and procedures may be generally performed according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification. Unless specific definitions are provided, the nomenclature utilized in connection with, and the laboratory procedures and techniques of, molecular biology, analytical chemistry, synthetic organic chemistry, and medicinal and pharmaceutical chemistry described herein are those well- known and commonly used in the art. Standard techniques may be used for recombinant technology, molecular biological, microbiological, chemical syntheses, chemical analyses, pharmaceutical preparation, formulation, and delivery, and treatment of patients.

For the purposes of the present disclosure, the following terms are defined below.

The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” includes “one element”, “one or more elements” and/or “at least one element”.

By “about” is meant a quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by as much as 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1% to a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length.

The terms “activatable proprotein,” “proprotein”, “activatable procytokine”, “procytokine”, “activatable prodrug”, and “prodrug” or are used interchangeably herein and refer to an activatable proprotein comprising at least a masking moiety and an active domain, or derivatives/ variants therefrom, as described herein. In one embodiment, the proprotein may also comprise one or more protein domains.

The term “antigen” refers to a molecule or a portion of a molecule capable of being bound by a selective binding agent, such as an antibody, and additionally capable of being used in an animal to produce antibodies capable of binding to an epitope of that antigen. An antigen may have one or more epitopes. As used herein, the term “antigen” includes substances that are capable, under appropriate conditions, of inducing an immune response to the substance and of reacting with the products of the immune response. More broadly, the term “antigen” includes any substance to which an antibody binds, or for which antibodies are desired, regardless of whether the substance is immunogenic. For such antigens, antibodies can be identified by recombinant methods, independently of any immune response.

An “antagonist” refers to biological structure or chemical agent that interferes with or otherwise reduces the physiological action of another agent or molecule. In some instances, the antagonist specifically binds to the other agent or molecule. Included are full and partial antagonists.

An “agonist” refers to biological structure or chemical agent that increases or enhances the physiological action of another agent or molecule. In some instances, the agonist specifically binds to the other agent or molecule. Included are full and partial agonists. As used herein, the term “amino acid” is intended to mean both naturally occurring and non- naturally occurring amino acids as well as amino acid analogs and mimetics. Naturally-occurring amino acids include the 20 (L)-amino acids utilized during protein biosynthesis as well as others such as 4-hydroxyproline, hydroxylysine, desmosine, isodesmosine, homocysteine, citrulline and ornithine, for example. Non-naturally occurring amino acids include, for example, (D)-amino acids, norleucine, norvaline, p-fluorophenylalanine, ethionine and the like, which are known to a person skilled in the art. Amino acid analogs include modified forms of naturally and non-naturally occurring amino acids. Such modifications can include, for example, substitution or replacement of chemical groups and moieties on the amino acid or by derivatization of the amino acid. Amino acid mimetics include, for example, organic structures which exhibit functionally similar properties such as charge and charge spacing characteristic of the reference amino acid. For example, an organic structure which mimics arginine (Arg or R) would have a positive charge moiety located in similar molecular space and having the same degree of mobility as the e-amino group of the side chain of the naturally occurring Arg amino acid. Mimetics also include constrained structures so as to maintain optimal spacing and charge interactions of the amino acid or of the amino acid functional groups. Those skilled in the art know or can determine what structures constitute functionally equivalent amino acid analogs and amino acid mimetics.

As used herein, a subject “at risk” of developing a disease, or adverse reaction may or may not have detectable disease, or symptoms of disease, and may or may not have displayed detectable disease or symptoms of disease prior to the treatment methods described herein. “At risk” denotes that a subject has one or more risk factors, which are measurable parameters that correlate with development of a disease, as described herein and known in the art. A subject having one or more of these risk factors has a higher probability of developing disease, or an adverse reaction than a subject without one or more of these risk factor(s).

“Biocompatible” refers to materials or compounds which are generally not injurious to biological functions of a cell or subject and which will not result in any degree of unacceptable toxicity, including allergenic and disease states.

The term “binding” refers to a direct association between two molecules, due to, for example, covalent, electrostatic, hydrophobic, and ionic and/or hydrogen-bond interactions, including interactions such as salt bridges and water bridges.

“Cis-targeting” refers to preferential activity of one function from a multi-functional molecule (including a bispecific or bi-functional molecule) on the same cell where the second function, such as binding activity, has an effect. This approach offers the potential to optimize the use of functional modulators (inhibitor or stimulator of the function of a molecular target) to treat cancer and other diseases by limiting or enhancing their effect to specific cell types. By “coding sequence” is meant any nucleic acid sequence that contributes to the code for the polypeptide product of a gene. By contrast, the term “non-coding sequence” refers to any nucleic acid sequence that does not directly contribute to the code for the polypeptide product of a gene.

Throughout this disclosure, unless the context requires otherwise, the words “comprise,” “comprises,” and “comprising” will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements.

By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of.” Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present. By “consisting essentially of’ is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase “consisting essentially of’ indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present depending upon whether or not they materially affect the activity or action of the listed elements.

The term “endotoxin free” or “substantially endotoxin free” relates generally to compositions, solvents, and/or vessels that contain at most trace amounts (e.g., amounts having no clinically adverse physiological effects to a subject) of endotoxin, and preferably undetectable amounts of endotoxin. Endotoxins are toxins associated with certain micro-organisms, such as bacteria, typically gramnegative bacteria, although endotoxins may be found in gram-positive bacteria, such as Listeria monocytogenes . The most prevalent endotoxins are lipopolysaccharides (LPS) or lipo-oligo- saccharides (LOS) found in the outer membrane of various Gram-negative bacteria, and which represent a central pathogenic feature in the ability of these bacteria to cause disease. Small amounts of endotoxin in humans may produce fever, a lowering of the blood pressure, and activation of inflammation and coagulation, among other adverse physiological effects.

Therefore, in pharmaceutical production, it is often desirable to remove most or all traces of endotoxin from drug products and/or drug containers, because even small amounts may cause adverse effects in humans. A depyrogenation oven may be used for this purpose, as temperatures in excess of 300°C are typically required to break down most endotoxins. For instance, based on primary packaging material such as syringes or vials, the combination of a glass temperature of 250°C and a holding time of 30 minutes is often sufficient to achieve a 3 log reduction in endotoxin levels. Other methods of removing endotoxins are contemplated, including, for example, chromatography and filtration methods, as described herein and known in the art.

Endotoxins can be detected using routine techniques known in the art. For example, the Limulus Amoebocyte Lysate assay, which utilizes blood from the horseshoe crab, is a very sensitive assay for detecting presence of endotoxin. In this test, very low levels of LPS can cause detectable coagulation of the limulus lysate due a powerful enzymatic cascade that amplifies this reaction. Endotoxins can also be quantitated by enzyme-linked immunosorbent assay (ELISA). To be substantially endotoxin free, endotoxin levels may be less than about 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.09, 0.1, 0.5, 1.0, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, or 10 EU/mg of active compound. Typically, 1 ng lipopolysaccharide (LPS) corresponds to about 1-10 EU.

The term “half maximal effective concentration” or “EC50” refers to the concentration of an agent (e.g., activatable proprotein) as described herein at which it induces a response halfway between the baseline and maximum after some specified exposure time; the EC50 of a graded dose response curve therefore represents the concentration of a compound at which 50% of its maximal effect is observed. EC50 also represents the plasma concentration required for obtaining 50% of a maximum effect in vivo. Similarly, the “EC90” refers to the concentration of an agent or composition at which 90% of its maximal effect is observed. The “EC90” can be calculated from the “EC50” and the Hill slope, or it can be determined from the data directly, using routine knowledge in the art. In some embodiments, the EC50 of an agent (e.g., activatable proprotein) is less than about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 200 or 500 nM. In some embodiments, an agent will have an EC5O value of about 1 nM or less.

“Immune response” means any immunological response originating from immune system, including responses from the cellular and humeral, innate and adaptive immune systems. Exemplary cellular immune cells include for example, lymphocytes, macrophages, T cells, B cells, NK cells, neutrophils, eosinophils, dendritic cells, mast cells, monocytes, and all subsets thereof. Cellular responses include for example, effector function, cytokine release, phagocytosis, efferocytosis, translocation, trafficking, proliferation, differentiation, activation, repression, cell-cell interactions, apoptosis, etc. Humeral responses include for example IgG, IgM, IgA, IgE, responses and their corresponding effector functions.

The “half-life” of an agent such as an activatable proprotein can refer to the time it takes for the agent to lose half of its pharmacologic, physiologic, or other activity, relative to such activity at the time of administration into the serum or tissue of an organism, or relative to any other defined time-point. “Half-life” can also refer to the time it takes for the amount or concentration of an agent to be reduced by half of a starting amount administered into the serum or tissue of an organism, relative to such amount or concentration at the time of administration into the serum or tissue of an organism, or relative to any other defined time-point. The half-life can be measured in serum and/or any one or more selected tissues.

The terms “modulating” and “altering” include “increasing” or “enhancing” as well as “decreasing” or “reducing,” typically in a statistically significant or a physiologically significant amount or degree relative to a control. An “increased” or “enhanced” amount is typically a “statistically significant” amount, and may include an amount that is about or at least about 1.1, 1.2, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000-fold or more relative to a control. An “increased” or “enhanced” amount may also include an amount that is about or at least about 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%,

10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% , 19%, 20%, 25%, 30%, 35%, 40%, 45%, 50%,

55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%, 900%, 1000%, 2000%, 3000%, 4000%, 5000% or more of the amount relative to a control. A “decreased” or “reduced” amount is typically a “statistically significant” amount, and may include an amount that is about or at least about 1.1, 1.2, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, or 5000-fold less of the amount relative to a control. A “decreased” or “reduced” amount may also include a 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18% , 19%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%, 900%, 1000%, 2000%, 3000%, 4000%, or 5000% less of the amount relative toa control. Examples of comparisons and “statistically significant” amounts are described herein.

The terms “polypeptide,” “protein” and “peptide” are used interchangeably and mean a polymer of amino acids not limited to any particular length. The term “enzyme” includes polypeptide or protein catalysts. The terms include modifications such as myristoylation, sulfation, glycosylation, phosphorylation and addition or deletion of signal sequences. The terms “polypeptide” or “protein” means one or more chains of amino acids, wherein each chain comprises amino acids covalently linked by peptide bonds, and wherein said polypeptide or protein can comprise a plurality of chains non-covalently and/or covalently linked together by peptide bonds, having the sequence of native proteins, that is, proteins produced by naturally-occurring and specifically non-recombinant cells, or genetically-engineered or recombinant cells, and comprise molecules having the amino acid sequence of the native protein, or molecules having deletions from, additions to, and/or substitutions of one or more amino acids of the native sequence. In certain embodiments, the polypeptide is a “recombinant” polypeptide, produced by recombinant cell that comprises one or more recombinant DNA molecules, which are typically made of heterologous polynucleotide sequences or combinations of polynucleotide sequences that would not otherwise be found in the cell.

The term “polynucleotide” and “nucleic acid” includes mRNA, RNA, cRNA, cDNA, and DNA. The term typically refers to polymeric form of nucleotides of at least 10 bases in length, either ribonucleotides or deoxynucleotides or a modified form of either type of nucleotide. The term includes single and double stranded forms of DNA. The terms “isolated DNA” and “isolated polynucleotide” and “isolated nucleic acid” refer to a molecule that has been isolated free of total genomic DNA of a particular species. Therefore, an isolated DNA segment encoding a polypeptide refers to a DNA segment that contains one or more coding sequences yet is substantially isolated away from, or purified free from, total genomic DNA of the species from which the DNA segment is obtained. Also included are non-coding polynucleotides (e.g., primers, probes, oligonucleotides), which do not encode a polypeptide. Also included are recombinant vectors, including, for example, expression vectors, viral vectors, plasmids, cosmids, phagemids, phage, viruses, and the like.

Additional coding or non-coding sequences may, but need not, be present within a polynucleotide described herein, and a polynucleotide may, but need not, be linked to other molecules and/or support materials. Hence, a polynucleotide or expressible polynucleotides, regardless of the length of the coding sequence itself, may be combined with other sequences, for example, expression control sequences.

The term “isolated” polypeptide or protein referred to herein means that a subject protein (1) is free of at least some other proteins with which it would typically be found in nature, (2) is essentially free of other proteins from the same source, e.g., from the same species, (3) is expressed by a cell from a different species, (4) has been separated from at least about 50 percent of polynucleotides, lipids, carbohydrates, or other materials with which it is associated in nature, (5) is not associated (by covalent or non-covalent interaction) with portions of a protein with which the “isolated protein” is associated in nature, (6) is operably associated (by covalent or non-covalent interaction) with a polypeptide with which it is not associated in nature, or (7) does not occur in nature. Such an isolated protein can be encoded by genomic DNA, cDNA, mRNA or other RNA, of may be of synthetic origin, or any combination thereof. In certain embodiments, the isolated protein is substantially free from proteins or polypeptides or other contaminants that are found in its natural environment that would interfere with its use (therapeutic, diagnostic, prophylactic, research or otherwise).

In certain embodiments, the “purity” of any given agent (e.g., activatable proprotein) in a composition may be defined. For instance, certain compositions may comprise an agent such as a polypeptide agent that is at least 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% pure on a protein basis or a weight-weight basis, including all decimals and ranges in between, as measured, for example and by no means limiting, by high performance liquid chromatography (HPLC), a well-known form of column chromatography used frequently in biochemistry and analytical chemistry to separate, identify, and quantify compounds.

The term “reference sequence” refers generally to a nucleic acid coding sequence, or amino acid sequence, to which another sequence is being compared. All polypeptide and polynucleotide sequences described herein are included as references sequences, including those described by name and those described in the Tables and the Sequence Listing.

Certain embodiments include biologically active “variants” and “fragments” of the proteins/polypeptides described herein, and the polynucleotides that encode the same. “Variants” contain one or more substitutions, additions, deletions, and/or insertions relative to a reference polypeptide or polynucleotide (see, e.g., the Tables and the Sequence Listing). A variant polypeptide or polynucleotide comprises an amino acid or nucleotide sequence with at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% , 99% or more sequence identity or similarity or homology to a reference sequence, as described herein, and substantially retains the activity of that reference sequence. Also included are sequences that consist of or differ from a reference sequences by the addition, deletion, insertion, or substitution of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60,70, 80, 90, 100, 110, 120, 130, 140, 150 or more amino acids or nucleotides and which substantially retain at least one activity of that reference sequence. In certain embodiments, the additions or deletions include C-terminal and/or N- terminal additions and/or deletions.

The terms “sequence identity” or, for example, comprising a “sequence 50% identical to,” as used herein, refer to the extent that sequences are identical on a nucleotide-by-nucleotide basis or an amino acid-by-amino acid basis over a window of comparison. Thus, a “percentage of sequence identity” may be calculated by comparing two optimally aligned sequences over the window of comparison, determining the number of positions at which the identical nucleic acid base (e.g., A, T, C, G, I) or the identical amino acid residue (e.g., Ala, Pro, Ser, Thr, Gly, Vai, Leu, He, Phe, Tyr, Trp, Lys, Arg, His, Asp, Glu, Asn, Gin, Cys and Met) occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison (i.e., the window size), and multiplying the result by 100 to yield the percentage of sequence identity. Optimal alignment of sequences for aligning a comparison window may be conducted by computerized implementations of algorithms (GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package Release 7.0, Genetics Computer Group, 575 Science Drive Madison, Wis., USA) or by inspection and the best alignment (i.e., resulting in the highest percentage homology over the comparison window) generated by any of the various methods selected. Reference also may be made to the BLAST family of programs as for example disclosed by Altschul et al., Nucl. Acids Res. 25:3389, 1997.

The term “solubility” refers to the property of an agent (e.g., activatable proprotein) provided herein to dissolve in a liquid solvent and form a homogeneous solution. Solubility is typically expressed as a concentration, either by mass of solute per unit volume of solvent (g of solute per kg of solvent, g per dL (100 m ), mg/ml, etc.), molarity, molality, mole fraction or other similar descriptions of concentration. The maximum equilibrium amount of solute that can dissolve per amount of solvent is the solubility of that solute in that solvent under the specified conditions, including temperature, pressure, pH, and the nature of the solvent. In certain embodiments, solubility is measured at physiological pH, or other pH, for example, at pH 5.0, pH 6.0, pH 7.0, pH 7.4, pH 7.6, pH 7.8, or pH 8.0 (e.g., about pH 5-8). In certain embodiments, solubility is measured in water or a physiological buffer such as PBS or NaCl (with or without NaPCh). In specific embodiments, solubility is measured at relatively lower pH (e.g., pH 6.0) and relatively higher salt (e.g., 500mM NaCl and lOmM NaPOft. In certain embodiments, solubility is measured in a biological fluid (solvent) such as blood or serum. In certain embodiments, the temperature can be about room temperature (e.g., about 20, 21, 22, 23, 24, 25°C) or about body temperature (37°C). In certain embodiments, an agent has a solubility of at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 40, 50, 60, 70, 80, 90 or 100 mg/ml at room temperature or at 37°C.

A “subject” or a “subject in need thereof’ or a “patient” or a “patient in need thereof’ includes a mammalian subject such as a human subject.

“Substantially” or “essentially” means nearly totally or completely, for instance, 95%, 96%, 97%, 98%, 99% or greater of some given quantity.

By “statistically significant,” it is meant that the result was unlikely to have occurred by chance. Statistical significance can be determined by any method known in the art. Commonly used measures of significance include the p-value, which is the frequency or probability with which the observed event would occur, if the null hypothesis were true. If the obtained p-value is smaller than the significance level, then the null hypothesis is rejected. In simple cases, the significance level is defined at a p-value of 0.05 or less.

“Therapeutic response” refers to improvement of symptoms (whether or not sustained) based on administration of one or more therapeutic agents.

As used herein, the terms “therapeutically effective amount”, “therapeutic dose,” “prophylactically effective amount,” or “diagnostically effective amount” is the amount of an agent (e.g., activatable proprotein, activated protein) needed to elicit the desired biological response following administration.

As used herein, “treatment” of a subject (e.g., a mammal, such as a human) or a cell is any type of intervention used in an attempt to alter the natural course of the individual or cell. Treatment includes, but is not limited to, administration of a pharmaceutical composition, and may be performed either prophylactically or subsequent to the initiation of a pathologic event or contact with an etiologic agent. Also included are “prophylactic” treatments, which can be directed to reducing the rate of progression of the disease or condition being treated, delaying the onset of that disease or condition, or reducing the severity of its onset. “Treatment” or “prophylaxis” does not necessarily indicate complete eradication, cure, or prevention of the disease or condition, or associated symptoms thereof.

The term “wild-type” refers to a gene or gene product (e.g., a polypeptide) that is most frequently observed in a population and is thus arbitrarily designed the “normal” or “wild-type” form of the gene.

Each embodiment in this specification is to be applied to every other embodiment unless expressly stated otherwise.

Activatable Proprotein Homodimers

Certain embodiments relate to activatable proprotein homodimers, comprising a first polypeptide and a second polypeptide, wherein the first polypeptide and the second polypeptide comprise, in an N- to C-terminal orientation, a fragment antigen-binding (Fab) region that specifically binds to human PD-1 or human PD-L1, a hinge/Fc domain, a first linker, an IL-2 protein, a second linker, and an IL-2Ra protein, wherein the hinge/Fc domain of the first polypeptide binds to the hinge/Fc domain of the second polypeptide, wherein the IL-2 protein of the first polypeptide binds to the IL-2Ra protein of the second polypeptide, and wherein the IL-2Ra of the first polypeptide binds to the IL-2 protein of the second polypeptide, wherein said binding masks a binding site of the IL-2 protein(s) that otherwise binds to an IL-2Rp/yc and/or IL-2Ra/p/yc chain present on the surface of an immune cell in vitro or in vivo, and wherein the second linker is a cleavable linker. In some embodiments, the total length of the stable linker effects said binding and masking.

As noted above, the IL-2 protein(s) and the IL-2Ra protein(s) interact or bind together, for example, via non-covalent interactions or certain covalent bonds (e.g., disulfide bonds). In some instances, the binding of the IL-2 protein(s) to the IL-2Ra protein(s) sterically blocks or hinders binding of the IL-2 protein(s) to their cognate IL-2Rp/yc and/or IL-2Ra/p/yc receptor chains expressed on immune cells. Exemplary IL-2 proteins and IL-2Ra proteins are described elsewhere herein.

In some instances, the hinge/Fc domains of the first and second polypeptides dimerize together via at least one non-covalent interaction, at least one covalent bond (for example, at least one disulfide bond), or any combination of non-covalent interactions and covalent bonds, to further stabilize the activatable proprotein and/or to further mask the binding of the IL-2 proteins to their cognate receptors, for example, IL-2Rp/yc and/or IL-2Ra/p/yc receptor chains. Typically, however, the hinge/Fc domains of the first and second polypeptide do not bind together or dimerize via a peptide or amide bond. In some embodiments, the hinge/Fc domains bind together as a homodimer, that is, a homodimer composed of two identical or nearly identical hinge/Fc domains. Thus, the hinge/Fc domains of the first and second polypeptides can be the same (or substantially the same) or different (e.g., knob-in-hole). Exemplary hinge/Fc domains are described herein.

As noted above, the second linker comprises a cleavable linker, for example, a linker cleavable by a protease. In some instances, the first linker is a stable (e.g., physiologically stable) linker. In some instances, the protease is expressed in target tissues or cells, for example, cancer tissues or cancer cells. Cleavage of the linker in that context releases a masking moiety, removes the steric hindrance of the IL-2 protein, and allows selective activation of the IL-2 protein in diseased tissues or cells (e.g., TME), relative to normal or healthy tissues or cells. Such selective and localized activation not only reduces needless consumption of administered IL-2, thereby increasing its halflife, but also enhances tissue penetration and reduces undesirable systemic effects of IL-2, among other advantages. Exemplary linkers are described herein.

In some embodiments, the homodimeric binding between the first and second polypeptides allosterically inhibits the binding of the IL-2 proteins to their target, for example, cognate IL-2Rp/yc and/or IL-2Ra/p/yc receptor chains on the surface of an immune cell. In these and related embodiments, the IL-2 portion of the activatable proprotein shows no binding or substantially no binding to its target, or no more than 0.001%, 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or 50% binding to its target, as compared to the binding of the active domain or the IL-2 protein alone, optionally for at least 2, 4, 6, 8, 12, 28, 24, 30, 36, 48, 60, 72, 84, 96 hours, or 5, 10, 15, 30, 45, 60, 90, 120, 150, 180 days, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 months or greater, optionally as measured in vivo or in a Target Displacement in vitro assay available in the art.

In certain instances, the anti-PD-1 or anti-PD-Ll Fab not only improves targeting of the activatable IL-2 proprotein (or procytokine) module to the TME, but also provides increased anti- cancer/immune-stimulating activity in addition to that of the IL-2 protein, once the latter is activated by protease cleavage of the second linker.

In specific embodiments, the first and second polypeptides of the activatable proprotein homodimer comprise an anti-PD-1 Fab (SEQ ID NOs: 3 and 4) or an anti-PD-Ll Fab (SEQ ID NOs: 25 and 26), together with a human IgGl CHI domain and a CL domain (kappa), an IgGl hinge (SEQ ID NO: 42), a modified IgGl Fc domain with LALA and P329A mutations (see CH2 domain of SEQ ID NO: 57), an IgGl CH3 domain (see CH3 domain of SEQ ID NO: 58), a stable linker (for example, of four amino acids in length such as a GGGS; SEQ ID NO: 188), an IL-2 protein (SEQ ID NO: 84 or 85 optionally with R38D, K43E, C125S mutations), a protease cleavable linker (for example, PLGLAGSGRSDNQGA; SEQ ID NO: 93), and an IL-2Ra protein (SEQ ID NO: 88 or 90, optionally with D6R and E29K mutations), including active or otherwise functional fragments and variants of the foregoing sequences, as described herein.

In specific embodiments, the first and second polypeptides of the activatable proprotein homodimer comprise SEQ ID NO: 146 (anti-PD-1 heavy chain w/modified IgGl Fc domain, stable linker, IL-2, protease cleavable linker, IL-2Ra) and SEQ ID NO: 147 (anti-PD-1 light chain).

The individual components of exemplary activatable proproteins are described in greater detail herein.

Anti-PD-1 and Anti-PD-Ll and Anti-B7H3 Fab Regions. The activatable proproteins described herein comprise at least one fragment antigen-binding (Fab) region that specifically binds to human PD-1 or human PD-L1 or human B7H3. A “Fab” region is composed of one constant and one variable domain of each of the heavy and the light chains of an immunoglobulin molecule, for instance, a VL/CL region or domain bound to a VH/CH1 region or domain that is fused at its C- terminus to the Fc domain optionally via a linker or hinge (hinge/Fc domain). The VL:VH and CL:CH1 regions of the Fab are typically bound together as a covalent heterodimer. In certain embodiments, the CL domain is a kappa chain. In some embodiments, the CL domain is a lambda chain. In some embodiments, the CHI domain is an IgA, IgD, IgE, IgG, IgM domain, for example, an IgAl, IgA2, IgGl, IgG2, IgG2, IgG3, or IgG4 CHI domain. In specific embodiments, the CL domain is a kappa chain and the CHI domain is an IgGl domain. In certain embodiments, an antibody or Fab region as described herein includes a heavy chain and a light chain CDR set, respectively interposed between a heavy chain and a light chain framework region (FR) set which provide support to the CDRs and define the spatial relationship of the CDRs relative to each other. As used herein, the term “CDR set” refers to the three hypervariable regions of a heavy or light chain V region. Proceeding from the N-terminus of a heavy or light chain, these regions are denoted as “CDR1,” “CDR2,” and “CDR3” respectively. An antigen-binding site, therefore, includes six CDRs, comprising the CDR set from each of a heavy and a light chain V region (VHCDR1, VHCDR2, VHCDR3, VLCDR1, VLCDR2, VLCDR3). A polypeptide comprising a single CDR, (e.g., a CDR1, CDR2 or CDR3) is referred to herein as a “molecular recognition unit.” Crystallographic analysis of a number of antigen-antibody complexes has demonstrated that the amino acid residues of CDRs form extensive contact with bound antigen, wherein the most extensive antigen contact is with the heavy chain CDR3. Thus, the molecular recognition units are primarily responsible for the specificity of an antigen-binding site.

As used herein, the term “FR set” refers to the four flanking amino acid sequences which frame the CDRs of a CDR set of a heavy or light chain V region. Some FR residues may contact bound antigen; however, FRs are primarily responsible for folding the V region into the antigenbinding site, particularly the FR residues directly adjacent to the CDRs. Within FRs, certain amino residues and certain structural features are very highly conserved. In this regard, all V region sequences contain an internal disulfide loop of around 90 amino acid residues. When the V regions fold into a binding-site, the CDRs are displayed as projecting loop motifs which form an antigenbinding surface. It is generally recognized that there are conserved structural regions of FRs which influence the folded shape of the CDR loops into certain “canonical” structures — regardless of the precise CDR amino acid sequence. Further, certain FR residues are known to participate in non- co valent interdomain contacts which stabilize the interaction of the antibody heavy and light chains.

In certain embodiments, the Fab regions are humanized. These embodiments refer to a chimeric molecule, generally prepared using recombinant techniques, having an antigen-binding site derived from an immunoglobulin from a non-human species and the remaining immunoglobulin structure of the molecule based upon the structure and/or sequence of a human immunoglobulin. The antigen-binding site may comprise either complete variable domains fused onto constant domains or only the CDRs grafted onto appropriate framework regions in the variable domains. Epitope binding sites may be wild-type or modified by one or more amino acid substitutions. This eliminates the constant region as an immunogen in human individuals, but the possibility of an immune response to the foreign variable region remains (LoBuglio et al., PNAS USA 86:4220-4224, 1989; Queen et al., PNAS USA. 86: 10029-10033, 1988; Riechmann et al., Nature. 332:323-327, 1988). Illustrative methods for humanization of antibodies include the methods described in U.S. Patent No. 7,462,697.

Another approach focuses not only on providing human-derived constant regions, but modifying the variable regions as well so as to reshape them as closely as possible to human form. It is known that the variable regions of both heavy and light chains contain three complementaritydetermining regions (CDRs) which vary in response to the epitopes in question and determine binding capability, flanked by four framework regions (FRs) which are relatively conserved in a given species and which putatively provide a scaffolding for the CDRs. When nonhuman antibodies are prepared with respect to a particular epitope, the variable regions can be “reshaped” or “humanized” by grafting CDRs derived from nonhuman antibody on the FRs present in the human antibody to be modified. Application of this approach to various antibodies has been reported by Sato et al., Cancer Res. 53:851-856, 1993; Riechmann et al., Nature 332:323-327, 1988; Verhoeyen et al., Science 239: 1534-1536, 1988; Kettleborough et al., Protein Engineering. 4:773-3783, 1991; Maeda et al., Human Antibodies Hybridoma 2: 124-134, 1991; Gorman et al., PNAS USA. 88:4181-4185, 1991; Tempest et al., Bio/Technology 9:266-271, 1991; Co et al., PNAS USA. 88:2869-2873, 1991; Carter et al., PNAS USA. 89:4285-4289, 1992; and Co et al., J Immunol. 148: 1149-1154, 1992. In some embodiments, humanized antibodies or Fab regions preserve all CDR sequences (for example, a humanized mouse antibody or Fab which contains all six CDRs from the mouse antibodies). In certain embodiments, humanized antibodies or Fab regions have one or more CDRs (one, two, three, four, five, six) which are altered with respect to the original antibody, which are also termed one or more CDRs “derived from” one or more CDRs from the original antibody.

The binding properties of antibodies and Fab regions can be quantified using methods well known in the art (see Davies et al., Annual Rev. Biochem. 59:439-473, 1990). In some embodiments, an antibody or Fab region specifically binds to a target molecule, for example, a PD-1 or PD-E1 protein or an epitope or complex thereof, with an equilibrium dissociation constant that is about or ranges from about <10 ^-7 M to about 10’ ⁸ M. In some embodiments, the equilibrium dissociation constant is about or ranges from about <10 ^-9 M to about <1O ¹⁰ M. In certain illustrative embodiments, an antibody or antigen-binding fragment thereof has an affinity (Kd or EC50) for a PD-1 or PD-L1 protein (to which it specifically binds) of about, at least about, or less than about, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 40, or 50 nM.

A molecule such as an antibody or Fab region is said to exhibit “specific binding” or “preferential binding” if it reacts or associates more frequently, more rapidly, with greater duration and/or with greater affinity with a particular cell, substance, or particular epitope than it does with alternative cells or substances, or epitopes. An antibody “specifically binds” or “preferentially binds” to a target molecule or epitope if it binds with greater affinity, avidity, more readily, and/or with greater duration than it binds to other substances or epitopes, for example, by a statistically significant amount. Typically one member of the pair of molecules that exhibit specific binding has an area on its surface, or a cavity, which specifically binds to and is therefore complementary to a particular spatial and/or polar organization of the other member of the pair of molecules. Thus, the members of the pair have the property of binding specifically to each other. For instance, an antibody that specifically or preferentially binds to a specific epitope is an antibody that binds that specific epitope with greater affinity, avidity, more readily, and/or with greater duration than it binds to other epitopes. It is also understood by reading this definition that, for example, an antibody (or moiety or epitope) that specifically or preferentially binds to a first target may or may not specifically or preferentially bind to a second target. The term is also applicable where, for example, an antibody is specific for a particular epitope which is carried by a number of antigens, in which case the specific binding member carrying the antigen-binding fragment or domain will be able to bind to the various antigens carrying the epitope; for example, it may be cross reactive to a number of different forms of a target antigen from multiple species that share a common epitope

Immunological binding generally refers to the non-covalent interactions of the type which occur between an immunoglobulin molecule and an antigen for which the immunoglobulin is specific, for example by way of illustration and not limitation, as a result of electrostatic, ionic, hydrophilic and/or hydrophobic attractions or repulsion, steric forces, hydrogen bonding, van der Waals forces, and other interactions. The strength, or affinity of immunological binding interactions can be expressed in terms of the dissociation constant (Kd) of the interaction, wherein a smaller Kd represents a greater affinity. Immunological binding properties of selected polypeptides can be quantified using methods well known in the art. One such method entails measuring the rates of antigen-binding site/antigen complex formation and dissociation, wherein those rates depend on the concentrations of the complex partners, the affinity of the interaction, and on geometric parameters that equally influence the rate in both directions. Thus, both the “on rate constant” (Kon) and the “off rate constant” (Koff) can be determined by calculation of the concentrations and the actual rates of association and dissociation. The ratio of Koff /Kon enables cancellation of all parameters not related to affinity, and is thus equal to the dissociation constant Kd. As used herein, the term “affinity” includes the equilibrium constant for the reversible binding of two agents and is expressed as Kd or EC50. Affinity of an antibody for a PD-1 or PD-L1 protein or epitope can be, for example, from about 100 nanomolar (nM) to about 0.1 nM, from about 100 nM to about 1 picomolar (pM), or from about 100 nM to about 1 femtomolar (fM). As used herein, the term “avidity” refers to the resistance of a complex of two or more agents to dissociation after dilution.

Programmed cell death protein 1 (PD-1; CD279 (cluster of differentiation 279)) refers a protein expressed on the surface of cells that regulates the immune response to the cells of the human body, for example, by down-regulating the immune system and promoting self-tolerance by suppressing T cell inflammatory activity (see Uniprot: Q15116). PD-1 is an immune checkpoint that promotes apoptosis of antigen-specific T-cells in lymph nodes, and reduces apoptosis in regulatory T cells (anti-inflammatory, suppressive T cells). Thus, in certain embodiments, the Fab region specifically binds to the human PD-1 protein sequence described in Uniprot: Q 15116. Anti -PD-1 antibodies are known in the art (see, e.g., U.S. Patent Nos. 8,008,449; 8,993,731; 9,073,994; 9,084,776; 9,102,727; 9,102,728; 9,181,342; 9,217,034; 9,387,247; 9,492,539; 9,492,540; and U.S. Application Nos. 2012/0039906; 2015/0203579). For example, in specific embodiments, the Fab region is from an anti-PD-1 antibody selected from nivolumab, pembrolizumab, cemiplimab, JTX- 4014, spartalizumab, camrelizumab, sintilimab, tislelizumab, toripalimab, dostarlimab, MGA012, AMP-22, and AMP-514.

Programmed death-ligand 1 (PD-L1) is a 40kDatype 1 transmembrane protein that binds to its receptor, PD-1, which is expressed on activated T cells, B cells, and myeloid cells, to modulate activation or inhibition (see Uniprot: Q9NZQ7). In certain embodiments, the Fab region specifically binds to the human PD-L1 protein sequence described in Uniprot: Q9NZQ7. Anti-PD-Ll antibodies are known in the art (see, e.g., U.S. Patent Nos. 9,102,725; 9,393,301; 9,402,899; 9,439,962). For example, in specific embodiments, the Fab region is from an anti-PD-Ul antibody selected from atezolizumab, avelumab, and durvalumab.

In certain embodiments, an anti-PD-1 or anti-PD-Ul Fab region is characterized by or comprises a heavy chain variable (VH) region sequence that comprises complementary determining region VHCDR1, VHCDR2, and VHCDR3 sequences, and a light chain variable (VU) region sequence that comprises complementary determining region VUCDR1, VUCDR2, and VUCDR3 sequences. Exemplary VH, VHCDR1, VHCDR2, VHCDR3, VE, VLCDR1, VLCDR2, and VLCDR3 sequences are provided in Table Pl and Table P2 below.

Thus, in certain embodiments, an anti-PD-1 Fab region thereof comprises a VH region comprising VHCDR1, VHCDR2, and VHCDR3 regions (underlined) from Table Pl, and a corresponding VL region comprising the VLCDR1, VLCDR2, and VLCDR3 regions (underlined) from Table Pl. Also included are variants thereof that bind to human PD-1, for example, variants having 1, 2, 3, 4, 5, or 6 total alterations in the combined CDR regions, for example, the VHCDR1, VHCDR2, VHCDR3, VLCDR1, VLCDR2, and/or VLCDR3 sequences described herein. Exemplary “alterations” include amino acid substitutions, additions, and deletions. In certain embodiments, an anti-PD-1 Fab region comprises a VH region from Table Pl, and the corresponding VL region from Table Pl. In certain embodiments, the VH region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from Table Pl, and the VL region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to the corresponding sequence selected Table Pl. Also included are variants thereof that bind to human PD-1, for example, variants having 1, 2, 3, 4, 5, 6 alterations in one or more framework regions. Exemplary “alterations” include amino acid substitutions, additions, and deletions.

In certain embodiments, an anti-PD-Ll Fab region thereof comprises a VH region comprising VHCDR1, VHCDR2, and VHCDR3 regions (underlined) from Table P2, and a VL region comprising the VLCDR1, VLCDR2, and VLCDR3 regions (underlined) from Table P2. Also included are variants thereof that bind to human PD-L1, for example, variants having 1, 2, 3, 4, 5, or 6 total alterations in the combined CDR regions, for example, the VHCDR1, VHCDR2, VHCDR3, VLCDR1, VLCDR2, and/or VLCDR3 sequences described herein. Exemplary “alterations” include amino acid substitutions, additions, and deletions. In certain embodiments, an anti-PD-Ll Fab region comprises a VH region from Table P2, and the corresponding VL region from Table P2. In certain embodiments, the VH region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from Table P2, and the VL region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to the corresponding sequence selected Table P2. Also included are variants thereof that bind to human PD-L1, for example, variants having 1, 2, 3, 4, 5, 6 alterations in one or more framework regions. Exemplary “alterations” include amino acid substitutions, additions, and deletions.

CD276 (B7H3) is an immune checkpoint molecule that participates in the regulation of T- ce 11 -mediated immune responses, and is expressed on some solid tumors. It plays a protective role in tumor cells, for example, by inhibiting natural-killer mediated cell lysis and potentially other antitumor immune responses. In particular embodiments, the B7H3 is human B7H3, or a domain thereof. In certain embodiments, an anti-B7H3 Fab region specifically binds to a human B7H3 protein, for example, a domain of human B7H3 selected from one or more of the Ig-like V-type 1 domain, Ig-like C2-type 1 domain, Ig-like V-type 2 domain, and an Ig-like C2-type 2 domain. In specific embodiments, a Fab region specifically binds to human BH73 with a KD of about 0.4 or 0.5 nM (400 or 500 pM) or lower.

In certain embodiments, an anti-B7H3 Fab region is characterized by or comprises a VH sequence that comprises complementary determining region VHCDR1, VHCDR2, and VHCDR3 sequences, and a VL sequence that comprises complementary determining region VLCDR1, VLCDR2, and VLCDR3 sequences. Exemplary VH, VHCDR1, VHCDR2, VHCDR3, VL, VLCDR1, VLCDR2, and VLCDR3 sequences are provided in Table P3 below.

Thus, in certain embodiments, an anti-B7H3 Fab region thereof comprises a VH region comprising VHCDR1, VHCDR2, and VHCDR3 regions (underlined) from Table P3, and a corresponding VL region comprising the VLCDR1, VLCDR2, and VLCDR3 regions (underlined) from Table P3. Also included are variants thereof that bind to human B7H3, for example, variants having 1, 2, 3, 4, 5, or 6 total alterations in the combined CDR regions, for example, the VHCDR1, VHCDR2, VHCDR3, VLCDR1, VLCDR2, and/or VLCDR3 sequences described herein. Exemplary “alterations” include amino acid substitutions, additions, and deletions. In certain embodiments, an anti-B7H3 Fab region comprises a VH region from Table P3, and the corresponding VL region from Table P3. In certain embodiments, the VH region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from Table P3, and the VL region comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to the corresponding sequence selected Table P3. Also included are variants thereof that bind to human B7H3, for example, variants having 1, 2, 3, 4, 5, 6 alterations in one or more framework regions. Exemplary “alterations” include amino acid substitutions, additions, and deletions.

Antibodies or Fab regions may be prepared by any of a variety of techniques known to those of ordinary skill in the art. See, e.g., Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988. Monoclonal antibodies specific for a polypeptide of interest may be prepared, for example, using the technique of Kohler and Milstein, Eur. J. Immunol. 6:511-519, 1976, and improvements thereto. Also included are methods that utilize transgenic animals such as mice to express human antibodies or Fab regions. See, e.g., Neuberger et al., Nature Biotechnology 14:826, 1996; Lonberg et al., Handbook of Experimental Pharmacology 113:49-101, 1994; and Lonberg et al., Internal Review of Immunology 13:65-93, 1995. The structures and locations of immunoglobulin variable domains may be determined by reference to Kabat, E. A. et al., Sequences of Proteins of Immunological Interest. 4th Edition. US Department of Health and Human Services. 1987, and updates thereof.

It will be appreciated that any one or more of the foregoing anti-PD-1 Fabs or anti-PD-Ll Fabs or anti-B7H3 Fabs can be combined with any of the other components described herein, for example, CHI domains, hinge/Fc domains, IL-2 proteins, IL-2Ra proteins, and linkers described herein, to generate one or more activatable proproteins.

Hinge/Fc Domains. Certain activatable proprotein homodimers comprises a hinge/Fc domain. The hinge region (found in IgG, IgA, and IgD) acts as a flexible spacerthat allows the Fab portion to move freely in space relative to the Fc domain. In contrast to the constant regions, the hinge regions are structurally diverse, varying in both sequence and length among immunoglobulin classes and subclasses. The hinge region may also contain one or more glycosylation site(s), which include a number of structurally distinct types of sites for carbohydrate attachment. For example, IgAl contains five glycosylation sites within a 17 amino acid segment of the hinge region, conferring significant resistance of the hinge region polypeptide to intestinal proteases. Residues in the hinge proximal region of the CH2 domain can also influence the specificity of the interaction between an immunoglobulin and its respective Fc receptor(s) (see, e.g., Shin et al., Intern. Rev. Immunol. 10: 177- 186, 1993).

The term “Fc domain” or “Fc fragment” or “Fc” refers to a protein that contains one or more of a CH2 domain, a CH3 domain, and/or a CH4 domain from one or more selected immunoglobulin(s), including fragments and variants and combinations thereof. An “Fc domain” may also include one or more hinge region(s) of the heavy chain constant region of an immunoglobulin. In certain embodiments, the Fc domain does not contain one or more of the CHI, CL, VL, and/or VH regions of an immunoglobulin.

The Fc domain can be derived from the CH2 domain, CH3 domain, CH4 domain, and/or hinge region(s) of any one or more immunoglobulin classes, including but not limited to IgA, IgD, IgE, IgG, IgM, including subclasses and combinations thereof. In some embodiments, the Fc domain is derived from an IgA immunoglobulin, including subclasses IgAl and/or IgA2. In certain embodiments, the Fc domain is derived from an IgD immunoglobulin. In particular embodiments, the Fc domain is derived from an IgE immunoglobulin. In some embodiments, the Fc domain is derived from an IgG immunoglobulin, including subclasses IgGl, IgG2, IgG2, IgG3, and/or IgG4. In certain embodiments, the Fc domain is derived from an IgM immunoglobulin. Exemplary hinge and Fc domain sequences are provided in Table Fl below. Thus, in some embodiments, the hinge comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a hinge sequence selected from Table Fl, for instance, an IgAl, IgA2, IgD, IgGl, IgG2, IgG3, IgG4 hinge region selected from Table Fl. In certain embodiments, the Fc domain comprises an amino acid sequence having at least 90%, 95%, 96%, 97%, 98%, 99%, or 100% identity to a sequence selected from Table Fl, for instance, an IgAl CH2, CH3, or combined CH2CH3 sequence, an IgA2 CH2, CH3, or combined CH2CH3 sequence, an IgD CH2, CH3, or combined CH2CH3 sequence, an IgE CH2, CH3, CH4, or combined CH2CH3 or CH2CH3CH4 sequence, an IgGl CH2, CH3, or combined CH2CH3 sequence, an IgG2 CH2, CH3, or combined CH2CH3 sequence, an IgG3 CH2, CH3, or combined CH2CH3 sequence, an IgG4 CH2, CH3, or combined CH2CH3 sequence, or an IgM CH2, CH3, CH4, or combined CH2CH3 or CH2CH3CH4 sequence from Table Fl. In certain embodiments, the hinge is of the same Ig class as the Fc domain.

In certain embodiments, the Fc domain is a modified Fc domain. Such modifications can be employed to alter (e.g., increase, decrease) the binding properties of the Fc region to one or more particular FcRs (e g., FcyRI, FcyRIIa, FcyRIIb, FcyRIIc, FcyRIIIa, FcyRIIIb, FcRn), its pharmacokinetic properties (e.g., stability or half-life, bioavailability, tissue distribution, volume of distribution, concentration, elimination rate constant, elimination rate, area under the curve (AUC), clearance, C _max , tmax, C _m in, fluctuation), its immunogenicity, its complement fixation or activation, and/or the CDC/ADCC/ADCP -related activities of the Fc region, among other properties described herein, relative to a corresponding wild-type Fc sequence.

In some embodiments, the modified Fc domain does not bind or does not substantially bind to FcyR. Examples of FcyRs include FcyRI, FcyRIIa, FcyRIIb, FcyRIIc, FcyRIIIa, and FcyRIIIb. FcyRI (CD64) is expressed on macrophages and dendritic cells and plays a role in phagocytosis, respiratory burst, cytokine stimulation, and dendritic cell endocytic transport. Expression of FcyRI is upregulated by both GM-CSF and y-interferon (y-IFN) and downregulated by interleukin-4 (IL-4). FcyRIIa is expressed on polymorphonuclear leukocytes (PMN), macrophages, dendritic cells, and mast cells. FcyRIIa plays a role in phagocytosis, respiratory burst, and cytokine stimulation. Expression of FcyRIIa is upregulated by GM-CSF and y-IFN, and decreased by IL-4. Fcyllb is expressed on B cells, PMN, macrophages, and mast cells. Fcyllb inhibits immunoreceptor tyrosine-based activation motif (ITAM) mediated responses, and is thus an inhibitory receptor. Expression of FcyRIIc is upregulated by intravenous immunoglobulin (IVIG) and IL-4 and decreased by y-IFN. FcyRIIc is expressed on NK cells. FcyRIIIa is expressed on natural killer (NK) cells, macrophages, mast cells, and platelets. This receptor participates in phagocytosis, respiratory burst, cytokine stimulation, platelet aggregation and degranulation, and NK-mediated ADCC. Expression of FcyRIII is upregulated by C5a, TGF-P, and y-IFN and downregulated by IL-4. Fc y RHIb is a GPI-linked receptor expressed on PMN.

In specific embodiments, the modified Fc domain comprises the L234A/L235A (“LALA”) mutations, and/or the P329A or P329G mutations (EU numbering) (see, for example, CH2 domain SEQ ID NO: 57). In certain embodiments, the Fc domain or modified Fc domain retains normal (wild-type) or substantially normal binding to the neonatal Fc receptor (FcRn). In specific embodiments, the Fc region comprises the IgGl hinge region of SEQ ID NO: 42, the modified IgGl CH2 domain of SEQ ID NO: 57, and the IgGl CH3 domain of SEQ ID NO: 58, including functional or active fragments and variants thereof, as described herein.

It will be appreciated that any one or more of the foregoing hinge and Fc domains can be combined with any of the other components described herein, for example, anti-PD-1 Fabs, anti-PD- L1 Fabs, IL-2 proteins, IL-2Ra proteins, and linkers described herein, to generate one or more activatable proproteins.

IL-2 Proteins. The activatable proproteins described herein comprise at least one “IL-2 protein” (or Interleukin-2 protein), including human IL-2 proteins. IL-2 is a cytokine signals through the IL-2 receptor (IL-2R), a complex composed of up to three chains, termed the a (CD25), (CD122) and yc (CD132) chains. IL-2 is produced by T-cells in response to antigenic or mitogenic stimulation, and is required for T-cell proliferation and other activities crucial to regulation of the immune response. IL-2 can stimulate B-cells, monocytes, lymphokine -activated killer cells, natural killer cells, and glioma cells, among other immune cells.

IL-2 is a 15-16 kDA protein composed of a signal peptide (residues 1-20) and an active mature protein (residues 21-153). Exemplary human IL-2 amino acid sequences are provided in Table

SI below.

Thus, in certain embodiments, an IL-2 protein comprises, consists, or consists essentially of an amino acid sequence selected from Table SI, or an active variant or fragment thereof that is at least 80, 85, 90, 95, 98, or 100% identical to a sequence selected from Table SI. In some embodiments, an “active” IL-2 protein or fragment or variant is characterized, for example, by its ability to bind to an IL-2Rp/yc and/or IL-2Ra/p/yc receptor chain present on the surface of an immune cell in vitro or in vivo, and stimulate downstream signaling activities, absent steric hindrance by the masking moieties described herein. Examples of downstream signaling activities include IL-2 mediated signaling via one or more of the JAK-STAT, PI3 K/Akt/mTOR. and MAPK/ERK pathways, including combinations thereof. Altogether, IL-2 signaling stimulates an array of downstream pathways leading to responses that have a significant role in the development, function, and survival of CD4 T cells, CD8 T cells, NK cells, NKT cells, macrophages, and intestinal intraepithelial lymphocytes, among others.

In particular embodiments, the IL-2 protein is a mature form of IL-2, or an active variant or fragment thereof, which comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to amino acids 21-153 or 26-153 of SEQ ID NO: 68. In some embodiments, the IL-2 protein comprises a C145X substitution, as defined by SEQ ID NO: 68, wherein X is any amino acid. In specific embodiments, the IL-2 protein comprises a C145S substitution as defined by SEQ ID NO: 68.

Certain IL-2 proteins comprise, consist, or consist essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to SEQ ID NO: 69 (mature human IL-2 with C125S substitution). In some embodiments, an active variant or fragment of SEQ ID NO: 69 retains the S125 residue as defined therein.

Certain IL-2 proteins comprise one or more defined amino acid substitutions relative to the exemplary amino acid sequences in Table SI. For example, some IL-2 proteins comprise one or more amino acid substitutions selected from K35C, R38C, T41C, F42C, E61C, and V69C as defined by SEQ ID NO: 69. In some embodiments, the IL-2 protein forms a disulfide bond with the IL-2 binding protein (e.g., IL-2Ra) via one or more of the cysteine substitutions selected from K35C, R38C, T41C, F42C, E61C, and V69C. Certain IL-2 proteins comprise one or more amino acid substitutions at position 69, 74, and/or 128 as defined by SEQ ID NO: 69, including combinations thereof and including, for example, wherein the one or more amino acid substitutions are selected from V69A, Q74P, and I128T as defined by SEQ ID NO: 69. Some IL-2 proteins comprise one or more amino acid substitutions at position R38, F42, K43, Y45, E62, E68, and/or L72 as defined by SEQ ID NO: 69, including combinations thereof and including, for example, wherein the one or more amino acid substitutions are selected from R38A, R38D, and R38K; F42A, F42G, F42S, F42T, F42Q, F42E, F42N, F42D, F42R, F42K, and F42I; K43E; Y45A, Y45G, Y45S, Y45T, Y45Q, Y45E, Y45N, Y45D, Y45R, and Y45K; E62A and E62L; E68A and E68V; and L72A, L72G, L72S, L72T, L72Q, L72E, L72N, L72D, L72R, and L72K, including combinations thereof. Specific examples include where the IL-2 protein comprises one or a combination of amino acid substitutions selected from F42A, Y45A, and L72G; R38K, F42Q, Y45N, E62L, and E68V; R38K, F42Q, Y45E, and E68V; R38A, F42I, Y45N, E62L, and E68V; R38K, F42K, Y45R, E62L, and E68V; R38K, F42I, Y45E, and E68V; and R38A, F42A, Y45A, and E62A. Some IL-2 proteins comprise one or a combination of amino acid substitutions at T3 and/or E61 as defined by SEQ ID NO: 69, for example, T3A and/or E61S. Certain IL-2 proteins (e.g., mature IL-12 or residues 26-153) comprise the combination of R38D and K43E (see, for example, SEQ ID NO: 85). Thus, an IL-2 protein can comprise any one or more of the foregoing amino acid substitutions, including combinations thereof.

It will be appreciated that any one or more of the foregoing IL-2 proteins can be combined with any of the other components described herein, for example, anti-PD-1 Fabs, anti-PD-Ll Fabs, hinge/Fc domains, IL-2Ra proteins, and linkers described herein, to generate one or more activatable proprotein.

IL-2Rq Proteins. The activatable proproteins described herein comprise at least one “IL-2Ra protein” (or Interleukin-2 Receptor-a protein), including human IL-2Ra proteins. The IL-2 receptor is composed of three subunits: IL-2Ra, CD 122, and CD 132. IL-2Ra specifically binds IL-2 with very high affinity, and is capable of binding IL-2 independently of other subunits. Exemplary IL-2Ra protein sequences are provided in Table S2.

Thus, in certain embodiments, an IL-2Ra protein comprises, consists, or consists essentially of an amino acid sequence selected from Table S2, or an active variant or fragment thereof that is at least 80, 85, 90, 95, 98, or 100% identical to a sequence selected from Table S2, and which binds to an IL-2 protein. In some embodiments, the IL-2Ra protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% to amino acids 22-187 or 22-240 of SEQ ID NO: 86 (full-length wild-type human IL-2Ra).

Certain IL-2Ra proteins comprise one or more defined amino acid substitutions relative to the exemplary amino acid sequences in Table S2. For example, in some instances, the IL-2Ra protein comprises one or more amino acid substitutions at D6 and/or E29, for example, D6R and/or E29K as defined by SEQ ID NO: 87 or 88. In some instances the IL-2Ra protein comprises one or more cysteine substitutions selected from D4C, D6C, N27C, K38C, S39C, L42C, Y43C, Il 18C, and H120C as defined by SEQ ID NO: 88 (human IL-2Ra Sushi 1 to Sushi 2 domain). In some instances, the IL- 2Ra protein comprises an alanine substitution at position 49 and/or 68 as defined by SEQ ID NO: 88. In some embodiments, the IL-2Ra protein comprises a K38S substitution as defined by SEQ ID NO: 88. Thus, an IL-2Ra protein can comprise any one or more of the foregoing amino acid substitutions, including combinations thereof. In specific embodiments, the IL-2Ra protein comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% to SEQ ID NO: 90, including wherein the IL-2Ra protein retains the D6R and/or E29K substitutions.

In certain of these and related embodiments, the IL-2Ra protein forms at least one disulfide bond with the IL-2 protein via one or more of the foregoing cysteines and one or more cysteines in the IL-2 protein. In specific embodiments, the IL-2Ra and IL-2 protein form disulfide at least one disulfide bond between one or more cysteine pairs selected from IL2-K35C and IL2Ra-D4C, IL2- R38C and IL2Ra-D6C, IL2-R38C and IL2Ra-H120C, IL2-T41C and IL2Ra-Il 18C, IL2-F42C and IL2Ra-N27C, IL2-E61C and IL2Ra-K38C, IL2-E61C and IL2Ra-S39C, and IL2-V69C and IL2Ra- L42C. In particular embodiments, as noted above, the binding (for example, disulfide binding) between the IL-2 protein and the IL-2Ra protein masks or sterically hinders the binding site of the IL- 2 protein that preferentially binds to the IL-2Ra/p/yc chain expressed on T _regs .

It will be appreciated that any one or more of the foregoing IL-2Ra proteins can be combined with any of the other components described herein, for example, anti-PD-1 Fabs, anti-PD-Ll Fabs, hinge/Fc domains, IL-2 proteins, and linkers described herein, to generate one or more activatable proproteins. Linkers. As noted above, in certain embodiments, each polypeptide comprises at least a first linker and a second linker, typically peptide linkers. In some embodiments, the first linker is a non- cleavable linker, that is, a physiologically-stable linker. In some embodiments, the second linker is a cleavable linker, for example, a cleavable linker that comprises a protease cleavage site.

In some embodiments, the first linker and/or the second linker are about 1-50 1-40, 1-30, 1- 20, 1-10, 1-5, 1-4, 1-3 amino acids in length, or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 ,17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 amino acids in length. In particular embodiments, the first linker is a cleavable linker, and the second linker is a non-cleavable linker. In some embodiments, the first linker is a non-cleavable linker, and the second linker is a cleavable linker. In some embodiments, both linkers are cleavable linkers.

In some embodiments, a cleavable linker comprises at least one protease cleavage site. Suitable protease cleavages sites and self-cleaving peptides are known to the skilled person (see, e.g., Ryan et al., J. Gener. Virol. 78:699-722, 1997; and Scymczak et al., Nature Biotech. 5:589-594, 2004). In some embodiments, the protease cleavage site is cleavable by a protease selected from one or more of a metalloprotease, a serine protease, a cysteine protease, and an aspartic acid protease. In particular embodiments, the protease cleavage site is cleavable by a protease selected from one or more of MMP1, MMP2, MMP3, MMP4, MMP5, MMP6, MMP7, MMP8, MMP9, MMP10, MMP11, MMP12, MMP13, MMP14, TEV protease, matriptase, uPA, FAP, Legumain, PSA, Kallikrein, Cathepsin A, and Cathepsin B.

Exemplary cleavable linker sequences are provided in Table S3.

Thus, in certain embodiment, a cleavable linker is selected from Table S3. Additional examples of cleavable linkers include an amino acid sequence cleaved by a serine protease such as thrombin, chymotrypsin, trypsin, elastase, kallikrein, or subtilisin. Illustrative examples of thrombin- cleavable amino acid sequences include, but are not limited to: -Gly-Arg-Gly-Asp- (SEQ ID NO: 160), -Gly-Gly-Arg-, -Gly- Arg-Gly-Asp-Asn-Pro- (SEQ ID NO: 161), -Gly-Arg-Gly-Asp-Ser- (SEQ ID NO: 162), -Gly-Arg-Gly-Asp-Ser-Pro-Lys- (SEQ ID NO: 163), -Gly-Pro- Arg-, -Val-Pro-Arg-, and -Phe- Vai -Arg-. Illustrative examples of elastase -cleavable amino acid sequences include, but are not limited to: -Ala-Ala-Ala-, -Ala-Ala-Pro-Val- (SEQ ID NO: 164), -Ala-Ala-Pro-Leu- (SEQ ID NO: 165), -Ala-Ala-Pro-Phe-(SEQ ID NO: 166), -Ala-Ala-Pro-Ala- (SEQ ID NO: 167), and -Ala- Tyr-Leu-Val- (SEQ ID NO: 168).

Cleavable linkers also include amino acid sequences that can be cleaved by a matrix metalloproteinase such as collagenase, stromelysin, and gelatinase. Illustrative examples of matrix metalloproteinase -cleavable amino acid sequences include, but are not limited to: -Gly-Pro-Y-Gly- Pro-Z-(SEQ ID NO: 169), -Gly-Pro-, Leu-Gly-Pro-Z-(SEQ ID NO: 170), -Gly-Pro-Ile-Gly-Pro-Z- (SEQ ID NO: 171), and -Ala-Pro-Gly-Leu-Z-(SEQ ID NO: 172), where Y and Z are amino acids. Illustrative examples of collagenase-cleavable amino acid sequences include, but are not limited to: - Pro-Leu-Gly-Pro-D-Arg-Z-(SEQ ID NO: 173), -Pro- Leu-Gly-Leu-Leu-Gly-Z-(SEQ ID NO: 174), - Pro-Gln-Gly-Ile-Ala-Gly-Trp-(SEQ ID NO: 175), -Pro-Leu-Gly-Cys(Me)-His-(SEQ ID NO: 176), - Pro-Leu-Gly-Leu-Tyr-Ala-(SEQ ID NO: 177), -Pro-Leu-Ala-Leu-Trp-Ala-Arg-(SEQ ID NO: 178), and -Pro-Leu-Ala-Tyr-Trp-Ala-Arg-(SEQ ID NO: 179), where Z is an amino acid. An illustrative example of a stromelysin-cleavable amino acid sequence is -Pro-Tyr-Ala-Tyr-Tyr-Met-Arg- (SEQ ID NO: 180); and an example of a gelatinase-cleavable amino acid sequence is -Pro-Leu-Gly-Met-Tyr- Ser-Arg-(SEQ ID NO: 181).

Cleavable linkers also include amino acid sequences that can be cleaved by an angiotensin converting enzyme, such as, for example, -Asp-Lys-Pro-, -Gly-Asp-Lys-Pro-(SEQ ID NO: 182), and - Gly-Ser-Asp-Lys-Pro- (SEQ ID NO: 183). Cleavable linkers also include amino acid sequences that can be degraded by cathepsin B, such as, for example, Val-Cit, Ala-Leu- Ala-Leu-(SEQ ID NO: 184), Gly-Phe-Leu-Gly-(SEQ ID NO: 185) and Phe-Lys.

In particular embodiments, a cleavable linker has a half life at pH 7.4, 25°C, for example, at physiological pH, human body temperature (e.g., in vivo, in serum, in a given tissue), of about or less than about 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 12 hours, 18 hours, 24 hours, 36 hours, 48 hours, 72 hours, or 96 hours, or any intervening half-life.

Typically, at least one of the first or second linker is a non-cleavable linker. Exemplary non- cleavable linkers include those disclosed in Maratea et al., Gene 40:39-46, 1985; Murphy et al., PNAS USA. 83:8258-8262, 1986; U.S. Pat. No. 4,935,233 and U.S. Pat. No. 4,751,180. Particular non- cleavable linker sequences contain Gly, Ser, and/or Asn residues. Other near neutral amino acids, such as Thr and Ala may also be employed in the peptide linker sequence, if desired.

Certain exemplary non-cleavable linkers include Gly, Ser and/or Asn-containing linkers, as follows: [G] _x , [S] _x , [N] _x , [GS] _X , [GGS] _X , [GSS] _X , [GSGS] _X (SEQ ID NO: 186), [GGSG] _X (SEQ ID NO: 187), [GGGS] _X (SEQ ID NO: 188), [GGGGS] _X (SEQ ID NO: 189), [GN] _X , [GGN] _X , [GNN] _X , [GNGN] _X (SEQ ID NO: 190), [GGNG] _X (SEQ ID NO: 191), [GGGN] _X (SEQ ID NO: 192), [GGGGN] _X (SEQ ID NO: 193) linkers, where _x is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 or more. Other combinations of these and related amino acids will be apparent to persons skilled in the art.

Additional examples of non-cleavable linkers include the following amino acid sequences: Gly-Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser- (SEQ ID NO: 194); Gly-Ser-Gly- Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser-Gly- Gly-Gly-Gly-Ser-(SEQ ID NO: 195); Gly-Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser- Gly-Gly-Gly-Gly-Ser-Gly- Gly-Gly-Gly-Ser-Gly-Gly-Gly-Gly-Ser-(SEQ ID NO: 196); Asp-Ala-Ala-Ala-Lys-Glu-Ala-Ala-Ala- Lys-Asp-Ala-Ala-Ala-Arg-Glu-Ala-Ala-Ala-Arg-Asp-Ala-Ala-Ala- Lys-(SEQ ID NO: 197); and Asn- Val-Asp-His-Lys-Pro-Ser-Asn-Thr-Lys-Val-Asp-Lys-Arg-(SEQ ID NO: 198). Further non-limiting examples of non-cleavable linkers include DGGGS (SEQ ID NO: 199); TGEKP (SEQ ID NO: 200) (see, e g., Liu et al., PNAS. 94:5525-5530, 1997); GGRR (SEQ ID NO: 201) (Pomerantz et al. 1995); (GGGGS) _n (SEQ ID NO: 202) (Kim et al., PNAS. 93: 1156-1160, 1996); EGKSSGSGSESKVD (SEQ ID NO: 203) (Chaudhary et al., PNAS. 87: 1066-1070, 1990); KESGSVSSEQLAQFRSLD (SEQ ID NO: 204) (Bird et al., Science. 242:423-426, 1988), GGRRGGGS (SEQ ID NO: 205); LRQRDGERP (SEQ ID NO: 206); LRQKDGGGSERP (SEQ ID NO: 207); LRQKd(GGGS)2 ERP (SEQ ID NO: 208). In specific embodiments, the linker comprises a Gly3 linker sequence, which includes three glycine residues. In particular embodiments, flexible linkers can be rationally designed using a computer program capable of modeling both DNA-binding sites and the peptides themselves (Desjarlais & Berg, PNAS. 90:2256-2260, 1993; and PNAS. 91: 11099-11103, 1994) or by phage display methods.

In some embodiments, the linker comprises a spacer element and a cleavable element so as to make the cleavable element more accessible to the enzyme responsible for cleavage.

It will be appreciated that any one or more of the foregoing linkers can be combined with any one or more of the anti-PD-1 Fabs, anti-PD-Ll Fabs, hinge/Fc domains, IL-2 proteins, and IL-2Ra proteins described herein, to form an activatable proprotein homodimer.

Exemplary activatable proprotein homodimers are provided in Table S4. Thus, in certain embodiments, an activatable proprotein comprises a first and second polypeptide that comprises, consists, or consists essentially of an amino acid sequence that is at least 80, 85, 90, 95, 98, or 100% identical to a sequence selected from Table S4 (i.e., chains 1 and 2), and a VL/CL region polypeptide that is at least 80, 85, 90, 95, 98, or 100% identical to the corresponding sequence from Table S4 (i.e., chains 3 and 4).

In certain additional embodiments, the first polypeptide is different from the second polypeptide, and forms a heterodimeric proprotein. For instance, in some embodiments, the Fc domain from the first polypeptide and Fc domain from the second polypeptide are modified, for example, using knob-and-hole mutations, to promote Fc heterodimerization. In some embodiments, the IL-2 protein of the first polypeptide and the IL-2Ra protein of the second polypeptide are modified (mutated) to form a specific or preferential binding pair, and/or the IL-2 protein of the second polypeptide and IL-2Ra protein of the first polypeptide are modified (mutated) to form a specific or preferential binding pair. In certain of these and related embodiments, modifications to IL- 2 and IL-2Ra proteins discourage homodimer formation between (i) the IL-2/ IL-2Ra of the first polypeptide and (ii) the IL-2/ IL-2Ra proteins of the second polypeptide.

Methods of Use and Pharmaceutical Compositions

Certain embodiments include methods of treating, ameliorating the symptoms of, and/or reducing the progression of, a disease or condition in a subject in need thereof, comprising administering to the subject at least one activatable proprotein, as described herein. Also included are methods of enhancing an immune response in a subject comprising administering to the subject at least one activatable proprotein, as described herein. In particular embodiments, the disease is a cancer. In some embodiments, the cancer expresses or over-expresses PD-L1.

In some embodiments, following administration, the activatable proprotein is activated through protease cleavage in a cell or tissue, which exposes the binding site of the IL-2 protein that binds to an IL-2Rp/yc and/or IL-2Ra/p/yc chain present on the surface of the immune cell in vitro or in vivo, and thereby generates an activated protein. In particular embodiments, the protease cleavage occurs in a cancer cell or cancer tissue. Typically, the activated protein has at least one immune- stimulating IL-2 activity, for example, by binding to an IL-2Rp/yc and/or IL-2Rot/p/yc chain present on the surface of an immune cell in vivo, and thereby stimulating the immune cell. In particular embodiments, the immune cell is selected from one or more of a T cell, a B cell, a natural killer cell, a monocyte, and a macrophage.

In some embodiments, administration and activation of the activatable proprotein, to generate an activated protein, increases an anti-cancer immune response in the subject by about or at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000% or more, relative to a control. In some embodiments, administration and activation of the activatable proprotein, to generate an activated protein, increases cancer cell-killing in the subject by about or at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000% or more, relative to a control.

In certain embodiments, the activated anti-PD-1 Fab/IL-2 protein stimulates an increased (e.g., synergistically increased) anti-cancer immune response relative to either the corresponding anti- PD-1 Fab (or corresponding anti-PD-1 antibody) alone and/or the corresponding IL-2 protein alone, for example, a 2-fold, 2.5-fold, 3-fold, 3.5-fold, 4-fold, 4.5-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, or 10-fold or more increase in the anti-cancer immune response relative to each component alone. In certain embodiments, the activated anti-PD-1 Fab/IL-2 protein stimulates increased (e.g., synergistically increased) cancer cell -killing activity relative to either the corresponding anti-PD-1 Fab (or corresponding anti-PD-1 antibody) alone and/or the corresponding IL-2 protein alone, for example, a 2-fold, 2.5-fold, 3-fold, 3.5-fold, 4-fold, 4.5-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, or 10-fold or more increase in the cancer cell-killing activity relative to each component alone.

In certain embodiments, the activated anti-PD-Ll Fab/IL-2 protein stimulates an increased (e.g., synergistically increased) anti-cancer immune response relative to either the corresponding anti- PD-Ll Fab (or corresponding anti-PD-Ll antibody) alone and/or the corresponding IL-2 protein alone, for example, a 2-fold, 2.5-fold, 3-fold, 3.5-fold, 4-fold, 4.5-fold, 5-fold, 6-fold, 7-fold, 8-fold,

9-fold, or 10-fold or more increase in the anti -cancer immune response relative to each component alone. In certain embodiments, the activated anti-PD-Ll Fab/IL-2 protein stimulates increased (e.g., synergistically increased) cancer cell -killing activity relative to either the corresponding anti-PD-Ll Fab (or corresponding anti-PD-Ll antibody) alone and/or the corresponding IL-2 protein alone, for example, a 2-fold, 2.5-fold, 3-fold, 3.5-fold, 4-fold, 4.5-fold, 5-fold, 6-fold, 7-fold, 8-fold, 9-fold, or

10-fold or more increase in the cancer cell-killing activity relative to each component alone.

In some embodiments, the disease is a cancer, that is, the subject in need thereof has or is suspected of having a cancer. Certain embodiments thus include methods of treating, ameliorating the symptoms of, or inhibiting the progression of, a cancer in a subject in need thereof, comprising administering to the subject at least one activatable proprotein, as described herein. In particular embodiments, the cancer is a primary cancer or a metastatic cancer. In specific embodiments, the cancer is selected from one or more of melanoma (optionally metastatic melanoma), kidney cancer (optionally renal cell carcinoma), pancreatic cancer, bone cancer, prostate cancer, small cell lung cancer, non-small cell lung cancer (NSCLC), mesothelioma, leukemia (optionally lymphocytic leukemia, chronic myelogenous leukemia, acute myeloid leukemia, or relapsed acute myeloid leukemia), multiple myeloma, lymphoma, hepatoma (hepatocellular carcinoma), sarcoma, B-cell malignancy, breast cancer, ovarian cancer, colorectal cancer, glioma, glioblastoma multiforme, meningioma, pituitary adenoma, vestibular schwannoma, primary CNS lymphoma, primitive neuroectodermal tumor (medulloblastoma), bladder cancer, uterine cancer, esophageal cancer, brain cancer, head and neck cancers, cervical cancer, testicular cancer, thyroid cancer, and stomach cancer In some embodiments, as noted above, the cancer is a metastatic cancer. Further to the above cancers, exemplary metastatic cancers include, without limitation, bladder cancers which have metastasized to the bone, liver, and/or lungs; breast cancers which have metastasized to the bone, brain, liver, and/or lungs; colorectal cancers which have metastasized to the liver, lungs, and/or peritoneum; kidney cancers which have metastasized to the adrenal glands, bone, brain, liver, and/or lungs; lung cancers which have metastasized to the adrenal glands, bone, brain, liver, and/or other lung sites; melanomas which have metastasized to the bone, brain, liver, lung, and/or skin/muscle; ovarian cancers which have metastasized to the liver, lung, and/or peritoneum; pancreatic cancers which have metastasized to the liver, lung, and/or peritoneum; prostate cancers which have metastasized to the adrenal glands, bone, liver, and/or lungs; stomach cancers which have metastasized to the liver, lung, and/or peritoneum; thyroid cancers which have metastasized to the bone, liver, and/or lungs; and uterine cancers which have metastasized to the bone, liver, lung, peritoneum, and/or vagina; among others.

In certain embodiments, as noted herein, the cancer expresses or over-expresses PD-L1. PD- L1 expression levels in a sample of tissue (e.g., cancer tissue) can be determined by any variety of methods. For example, PD-L1 protein levels can be determined by immunohistochemistry (IHC) including chromogenic or fluorescent IHC, enzyme linked immunosorbent assay (ELISA), or Western blot on a human AR protein or gene, among other assays. PD-L1 mRNA levels can be measured, for example, by RT-PCR, for example, quantitative competitive (QC) RT-PCR, among other techniques known in the art. Certain embodiments thus include the step of determining or detecting or measuring PD-L1 levels in a tissue sample from a subject in need thereof. Also included is the step of comparing the PD-L1 levels in a tissue sample relative to that of a control or reference. Certain embodiments include the step of determining PD-L1 levels in a sample of cancer tissue from the subject (e.g., biopsy tissue), and administering the activatable proprotein homodimer if the cancer tissue from the subject expresses or over-expresses PD-L1.

The methods for treating cancers can be combined with other therapeutic modalities. For example, a combination therapy described herein can be administered to a subject before, during, or after other therapeutic interventions, including symptomatic care, radiotherapy, surgery, transplantation, hormone therapy, photodynamic therapy, antibiotic therapy, or any combination thereof. Symptomatic care includes administration of corticosteroids, to reduce cerebral edema, headaches, cognitive dysfunction, and emesis, and administration of anti-convulsants, to reduce seizures. Radiotherapy includes whole-brain irradiation, fractionated radiotherapy, and radiosurgery, such as stereotactic radiosurgery, which can be further combined with traditional surgery.

Certain embodiments thus include combination therapies for treating cancers, including methods of treating ameliorating the symptoms of, or inhibiting the progression of, a cancer in a subject in need thereof, comprising administering to the subject at least one activatable proprotein described herein in combination with at least one additional agent, for example, a chemotherapeutic agent, a hormonal therapeutic agent, and/or a kinase inhibitor. In some embodiments, administering the at least one activatable proprotein enhances the susceptibility of the cancer to the additional agent (for example, chemotherapeutic agent, hormonal therapeutic agent, and or kinase inhibitor) by about or at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000% or more relative to the additional agent alone.

Certain combination therapies employ one or more chemotherapeutic agents, for example, small molecule chemotherapeutic agents. Non-limiting examples of chemotherapeutic agents include alkylating agents, anti-metabolites, cytotoxic antibiotics, topoisomerase inhibitors (type 1 or type II), an anti -microtubule agents, among others.

Examples of alkylating agents include nitrogen mustards (e.g., mechlorethamine, cyclophosphamide, mustine, melphalan, chlorambucil, ifosfamide , and busulfan), nitrosoureas (e.g., N-Nitroso-N-methylurea (MNU), carmustine (BCNU), lomustine (CCNU), semustine (MeCCNU), fotemustine, and streptozotocin), tetrazines (e.g., dacarbazine, mitozolomide, and temozolomide), aziridines (e.g., thiotepa, mytomycin, and diaziquone (AZQ)), cisplatins and derivatives thereof (e.g., carboplatin and oxaliplatin), and non-classical alkylating agents (optionally procarbazine and hexamethylmelamine) .

Examples of anti-metabolites include anti-folates (e.g., methotrexate and pemetrexed), fluoropyrimidines (e.g., 5 -fluorouracil and capecitabine), deoxynucleoside analogues (e.g., ancitabine, enocitabine, cytarabine, gemcitabine, decitabine, azacitidine, fludarabine, nelarabine, cladribine, clofarabine, fludarabine, and pentostatin), and thiopurines (e.g., thioguanine and mercaptopurine);

Examples of cytotoxic antibiotics include anthracyclines (e.g., doxorubicin, daunorubicin, epirubicin, idarubicin, pirarubicin, aclarubicin, and mitoxantrone), bleomycins, mitomycin C, mitoxantrone, and actinomycin. Examples of topoisomerase inhibitors include camptothecin, irinotecan, topotecan, etoposide, doxorubicin, mitoxantrone, teniposide, novobiocin, merbarone, and aclarubicin.

Examples of anti-microtubule agents include taxanes (e.g., paclitaxel and docetaxel) and vinca alkaloids (e.g., vinblastine, vincristine, vindesine, vinorelbine).

The skilled artisan will appreciate that the various chemotherapeutic agents described herein can be combined with any one or more of the activatable proproteins described herein, and used according to any one or more of the methods or compositions described herein.

Certain combination therapies employ at least one hormonal therapeutic agent. General examples of hormonal therapeutic agents include hormonal agonists and hormonal antagonists. Particular examples of hormonal agonists include progestogen (progestin), corticosteroids (e.g., prednisolone, methylprednisolone, dexamethasone), insulin like growth factors, VEGF derived angiogenic and lymphangiogenic factors (e.g., VEGF-A, VEGF-A145, VEGF-A165, VEGF-C, VEGF-D, PIGF-2), fibroblast growth factor (FGF), galectin, hepatocyte growth factor (HGF), platelet derived growth factor (PDGF), transforming growth factor (TGF)-beta, androgens, estrogens, and somatostatin analogs. Examples of hormonal antagonists include hormone synthesis inhibitors such as aromatase inhibitors and gonadotropin-releasing hormone (GnRH)s agonists (e.g., leuprolide, goserelin, triptorelin, histrelin) including analogs thereof. Also included are hormone receptor antagonist such as selective estrogen receptor modulators (SERMs; e.g., tamoxifen, raloxifene, toremifene) and anti-androgens (e.g., flutamide, bicalutamide, nilutamide).

Also included are hormonal pathway inhibitors such as antibodies directed against hormonal receptors. Examples include inhibitors of the the IGF receptor (e.g., IGF-IR1) such as cixutumumab, dalotuzumab, figitumumab, ganitumab, istiratumab, and robatumumab; inhibitors of the vascular endothelial growth factor receptors 1, 2 or 3 (VEGFR1, VEGFR2 or VEGFR3) such as alacizumab pegol, bevacizumab, icrucumab, ramucirumab; inhibitors of the TGF-beta receptors Rl, R2, and R3 such as fresolimumab and metelimumab; inhibitors of c-Met such as naxitamab; inhibitors of the EGF receptor such as cetuximab, depatuxizumab mafodotin, futuximab, imgatuzumab, laprituximab emtansine, matuzumab, modotuximab, necitumumab, nimotuzumab, panitumumab, tomuzotuximab, and zalutumumab; inhibitors of the FGF receptor such as aprutumab ixadotin and bemarituzumab; and inhibitors of the PDGF receptor such as olaratumab and tovetumab.

The skilled artisan will appreciate that the various hormonal therapeutic agents described herein can be combined with any one or more of the various activatable proproteins described herein, and used according to any one or more of the methods or compositions described herein.

Certain combination therapies employ at least one kinase inhibitor, including tyrosine kinase inhibitors. Examples of kinase inhibitors include, without limitation, adavosertib, afanitib, aflibercept, axitinib, bevacizumab, bosutinib, cabozantinib, cetuximab, cobimetinib, crizotinib, dasatinib, entrectinib, erdafitinib, erlotinib, fostamitinib, gefitinib, ibrutinib, imatinib, lapatinib, lenvatinib, mubritinib, nilotinib, panitumumab, pazopanib, pegaptanib, ponatinib, ranibizumab, regorafenib, ruxolitinib, sorafenib, sunitinib, SU6656, tofacitinib, trastuzumab, vandetanib, and vemuafenib.

The skilled artisan will appreciate that the various kinase inhibitors described herein can be combined with any one or more of the various activatable proproteins described herein, and used according to any one or more of the methods or compositions described herein.

In some embodiments, the methods and pharmaceutical compositions described herein increase median survival time of a subject by 4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10 weeks, 15 weeks, 20 weeks, 25 weeks, 30 weeks, 40 weeks, or longer. In certain embodiments, the methods and pharmaceutical compositions described herein increase median survival time of a subject by 1 year, 2 years, 3 years, or longer. In some embodiments, the methods and pharmaceutical compositions increase progression-free survival by 2 weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10 weeks or longer. In certain embodiments, the methods and pharmaceutical compositions described herein increase progression-free survival by 1 year, 2 years, 3 years, or longer. In certain embodiments, the methods and therapeutic compositions described herein are sufficient to result in tumor regression, as indicated by a statistically significant decrease in the amount of viable tumor, for example, at least a 10%, 20%, 30%, 40%, 50% or greater decrease in tumor mass, or by altered (e.g., decreased with statistical significance) scan dimensions. In certain embodiments, the methods and therapeutic compositions described herein are sufficient to result in stable disease.

In certain embodiments, the methods and therapeutic compositions described herein are sufficient to result in clinically relevant reduction in symptoms of a particular disease indication known to the skilled clinician.

For in vivo use, as noted above, for the treatment of human or non-human mammalian disease or testing, the agents described herein are generally incorporated into one or more therapeutic or pharmaceutical compositions prior to administration, including veterinary therapeutic compositions.

Thus, certain embodiments relate to pharmaceutical or therapeutic compositions that comprise at least one activatable proprotein, as described herein. In some instances, a pharmaceutical or therapeutic composition comprises one or more of the activatable proproteins described herein in combination with a pharmaceutically- or physiologically-acceptable carrier or excipient. Certain pharmaceutical or therapeutic compositions further comprise at least one additional agent, for example, a chemotherapeutic agent, a hormonal therapeutic agent, and/or a kinase inhibitor as described herein.

Some therapeutic compositions comprise (and certain methods utilize) only one activatable proprotein. Certain therapeutic compositions comprise (and certain methods utilize) a mixture of at least two, three, four, or five different activatable proproteins.

In particular embodiments, the pharmaceutical or therapeutic compositions comprising at least one activatable proprotein is substantially pure on a protein basis or a weight-weight basis, for example, the composition has a purity of at least about 80%, 85%, 90%, 95%, 98%, or 99% on a protein basis or a weight-weight basis.

In some embodiments, the activatable proproteins described herein do not form aggregates, have a desired solubility, and/or have an immunogenicity profile that is suitable for use in humans, as known in the art. Thus, in some embodiments, the therapeutic composition comprising an activatable proprotein is substantially aggregate -free. For example, certain compositions comprise less than about 10% (on a protein basis) high molecular weight aggregated proteins, or less than about 5% high molecular weight aggregated proteins, or less than about 4% high molecular weight aggregated proteins, or less than about 3% high molecular weight aggregated proteins, or less than about 2 % high molecular weight aggregated proteins, or less than about 1% high molecular weight aggregated proteins. Some compositions comprise an activatable proprotein that is at least about 50%, about 60%, about 70%, about 80%, about 90% or about 95% monodisperse with respect to its apparent molecular mass. In some embodiments, the activatable proprotein are concentrated to about or at least about 0.1 mg/ml, 0.2 mg/ml, 0.3 mg/ml, 0.4 mg/ml, 0.5 mg/ml, 0.6, 0.7, 0.8, 0.9, 1 mg/ml, 2 mg/ml, 3 mg/ml, 4 mg/ml, 5 mg/ml, 6 mg/ml, 7 mg/ml, 8 mg/ml, 9 mg/ml, 10 mg/ml, 11, 12, 13, 14 or 15 mg/ml and are formulated for biotherapeutic uses.

To prepare a therapeutic or pharmaceutical composition, an effective or desired amount of one or more agents is mixed with any pharmaceutical carrier(s) or excipient known to those skilled in the art to be suitable for the particular agent and/or mode of administration. A pharmaceutical carrier may be liquid, semi-liquid or solid. Solutions or suspensions used for parenteral, intradermal, subcutaneous or topical application may include, for example, a sterile diluent (such as water), saline solution (e.g., phosphate buffered saline; PBS), fixed oil, polyethylene glycol, glycerin, propylene glycol or other synthetic solvent; antimicrobial agents (such as benzyl alcohol and methyl parabens); antioxidants (such as ascorbic acid and sodium bisulfite) and chelating agents (such as ethylenediaminetetraacetic acid (EDTA)); buffers (such as acetates, citrates and phosphates). If administered intravenously (e.g., by IV infusion), suitable carriers include physiological saline or phosphate buffered saline (PBS), and solutions containing thickening and solubilizing agents, such as glucose, polyethylene glycol, polypropylene glycol and mixtures thereof.

Administration of agents described herein, in pure form or in an appropriate therapeutic or pharmaceutical composition, can be carried out via any of the accepted modes of administration of agents for serving similar utilities. The therapeutic or pharmaceutical compositions can be prepared by combining an agent-containing composition with an appropriate physiologically acceptable carrier, diluent or excipient, and may be formulated into preparations in solid, semi-solid, liquid or gaseous forms, such as tablets, capsules, powders, granules, ointments, solutions, suppositories, injections, inhalants, gels, microspheres, and aerosols. In addition, other pharmaceutically active ingredients (including other small molecules as described elsewhere herein) and/or suitable excipients such as salts, buffers and stabilizers may, but need not, be present within the composition.

Administration may be achieved by a variety of different routes, including oral, parenteral, nasal, intravenous, intradermal, intramuscular, subcutaneous or topical. Preferred modes of administration depend upon the nature of the condition to be treated or prevented. Particular embodiments include administration by IV infusion.

Carriers can include, for example, pharmaceutically- or physiologically-acceptable carriers, excipients, or stabilizers that are non-toxic to the cell or mammal being exposed thereto at the dosages and concentrations employed. Often the physiologically-acceptable carrier is an aqueous pH buffered solution. Examples of physiologically acceptable carriers include buffers such as phosphate, citrate, and other organic acids; antioxidants including ascorbic acid; low molecular weight (less than about 10 residues) polypeptide; proteins, such as serum albumin, gelatin, or immunoglobulins; hydrophilic polymers such as polyvinylpyrrolidone; amino acids such as glycine, glutamine, asparagine, arginine or lysine; monosaccharides, disaccharides, and other carbohydrates including glucose, mannose, or dextrins; chelating agents such as EDTA; sugar alcohols such as mannitol or sorbitol; salt-forming counterions such as sodium; and/or nonionic surfactants such as polysorbate 20 (TWEEN™) polyethylene glycol (PEG), and poloxamers (PLURONICS™), and the like.

In some embodiments, one or more agents can be entrapped in microcapsules prepared, for example, by coacervation techniques or by interfacial polymerization (for example, hydroxymethylcellulose or gelatin-microcapsules and poly-(methylmethacylate)microcapsules, respectively), in colloidal drug delivery systems (for example, liposomes, albumin microspheres, microemulsions, nano-particles and nanocapsules), or in macroemulsions. Such techniques are disclosed in Remington’s Pharmaceutical Sciences, 16th edition, Oslo, A., Ed., (1980). The particle(s) or liposomes may further comprise other therapeutic or diagnostic agents.

The precise dosage and duration of treatment is a function of the disease being treated and may be determined empirically using known testing protocols or by testing the compositions in model systems known in the art and extrapolating therefrom. Controlled clinical trials may also be performed. Dosages may also vary with the severity of the condition to be alleviated. A pharmaceutical composition is generally formulated and administered to exert a therapeutically useful effect while minimizing undesirable side effects. The composition may be administered one time, or may be divided into a number of smaller doses to be administered at intervals of time. For any particular subject, specific dosage regimens may be adjusted overtime according to the individual need.

Typical routes of administering these and related therapeutic or pharmaceutical compositions thus include, without limitation, oral, topical, transdermal, inhalation, parenteral, sublingual, buccal, rectal, vaginal, and intranasal. The term parenteral as used herein includes subcutaneous injections, intravenous, intramuscular, intrastemal injection or infusion techniques. Therapeutic or pharmaceutical compositions according to certain embodiments of the present disclosure are formulated so as to allow the active ingredients contained therein to be bioavailable upon administration of the composition to a subject or patient. Compositions that will be administered to a subject or patient may take the form of one or more dosage units, where for example, a tablet may be a single dosage unit, and a container of a herein described agent in aerosol form may hold a plurality of dosage units. Actual methods of preparing such dosage forms are known, or will be apparent, to those skilled in this art; for example, see Remington: The Science and Practice of Pharmacy, 20th Edition (Philadelphia College of Pharmacy and Science, 2000). The composition to be administered will typically contain a therapeutically effective amount of an agent described herein, for treatment of a disease or condition of interest.

A therapeutic or pharmaceutical composition may be in the form of a solid or liquid. In one embodiment, the carrier(s) are particulate, so that the compositions are, for example, in tablet or powder form. The carrier(s) may be liquid, with the compositions being, for example, an oral oil, injectable liquid or an aerosol, which is useful in, for example, inhalatory administration. When intended for oral administration, the pharmaceutical composition is preferably in either solid or liquid form, where semi-solid, semi-liquid, suspension and gel forms are included within the forms considered herein as either solid or liquid. Certain embodiments include sterile, injectable solutions.

As a solid composition for oral administration, the pharmaceutical composition may be formulated into a powder, granule, compressed tablet, pill, capsule, chewing gum, wafer or the like. Such a solid composition will typically contain one or more inert diluents or edible carriers. In addition, one or more of the following may be present: binders such as carboxymethylcellulose, ethyl cellulose, microcrystalline cellulose, gum tragacanth or gelatin; excipients such as starch, lactose or dextrins, disintegrating agents such as alginic acid, sodium alginate, Primogel, com starch and the like; lubricants such as magnesium stearate or Sterotex; glidants such as colloidal silicon dioxide; sweetening agents such as sucrose or saccharin; a flavoring agent such as peppermint, methyl salicylate or orange flavoring; and a coloring agent. When the pharmaceutical composition is in the form of a capsule, for example, a gelatin capsule, it may contain, in addition to materials of the above type, a liquid carrier such as polyethylene glycol or oil.

The therapeutic or pharmaceutical composition may be in the form of a liquid, for example, an elixir, syrup, solution, emulsion or suspension. The liquid may be for oral administration or for delivery by injection, as two examples. When intended for oral administration, preferred composition contain, in addition to the present compounds, one or more of a sweetening agent, preservatives, dye/colorant and flavor enhancer. In a composition intended to be administered by injection, one or more of a surfactant, preservative, wetting agent, dispersing agent, suspending agent, buffer, stabilizer and isotonic agent may be included.

The liquid therapeutic or pharmaceutical compositions, whether they be solutions, suspensions or other like form, may include one or more of the following adjuvants: sterile diluents such as water for injection, saline solution, preferably physiological saline, Ringer’s solution, isotonic sodium chloride, fixed oils such as synthetic mono or diglycerides which may serve as the solvent or suspending medium, polyethylene glycols, glycerin, propylene glycol or other solvents; antibacterial agents such as benzyl alcohol or methyl paraben; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. Physiological saline is a preferred adjuvant. An injectable pharmaceutical composition is preferably sterile.

A liquid therapeutic or pharmaceutical composition intended for either parenteral or oral administration should contain an amount of an agent such that a suitable dosage will be obtained. Typically, this amount is at least 0.01% of the agent of interest in the composition. When intended for oral administration, this amount may be varied to be between 0.1 and about 70% of the weight of the composition. Certain oral therapeutic or pharmaceutical compositions contain between about 4% and about 75% of the agent of interest. In certain embodiments, therapeutic or pharmaceutical compositions and preparations are prepared so that a parenteral dosage unit contains between 0.01 to 10% by weight of the agent of interest prior to dilution.

The therapeutic or pharmaceutical compositions may be intended for topical administration, in which case the carrier may suitably comprise a solution, emulsion, ointment or gel base. The base, for example, may comprise one or more of the following: petrolatum, lanolin, polyethylene glycols, bee wax, mineral oil, diluents such as water and alcohol, and emulsifiers and stabilizers. Thickening agents may be present in a therapeutic or pharmaceutical composition for topical administration. If intended for transdermal administration, the composition may include a transdermal patch or iontophoresis device.

The therapeutic or pharmaceutical compositions may be intended for rectal administration, in the form, for example, of a suppository, which will melt in the rectum and release the drug. The composition for rectal administration may contain an oleaginous base as a suitable nonirritating excipient. Such bases include, without limitation, lanolin, cocoa butter, and polyethylene glycol.

The therapeutic or pharmaceutical composition may include various materials, which modify the physical form of a solid or liquid dosage unit. For example, the composition may include materials that form a coating shell around the active ingredients. The materials that form the coating shell are typically inert, and may be selected from, for example, sugar, shellac, and other enteric coating agents. Alternatively, the active ingredients may be encased in a gelatin capsule. The therapeutic or pharmaceutical compositions in solid or liquid form may include a component that binds to agent and thereby assists in the delivery of the compound. Suitable components that may act in this capacity include monoclonal or polyclonal antibodies, one or more proteins or a liposome.

The therapeutic or pharmaceutical composition may consist essentially of dosage units that can be administered as an aerosol. The term aerosol is used to denote a variety of systems ranging from those of colloidal nature to systems consisting of pressurized packages. Delivery may be by a liquefied or compressed gas or by a suitable pump system that dispenses the active ingredients. Aerosols may be delivered in single phase, bi-phasic, or tri -phasic systems in order to deliver the active ingredient(s). Delivery of the aerosol includes the necessary container, activators, valves, subcontainers, and the like, which together may form a kit. One of ordinary skill in the art, without undue experimentation may determine preferred aerosols.

The compositions described herein may be prepared with carriers that protect the agents against rapid elimination from the body, such as time release formulations or coatings. Such carriers include controlled release formulations, such as, but not limited to, implants and microencapsulated delivery systems, and biodegradable, biocompatible polymers, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, polyorthoesters, polylactic acid and others known to those of ordinary skill in the art. The therapeutic or pharmaceutical compositions may be prepared by methodology well known in the pharmaceutical art. For example, a therapeutic or pharmaceutical composition intended to be administered by injection may comprise one or more of salts, buffers and/or stabilizers, with sterile, distilled water so as to form a solution. A surfactant may be added to facilitate the formation of a homogeneous solution or suspension. Surfactants are compounds that non-covalently interact with the agent so as to facilitate dissolution or homogeneous suspension of the agent in the aqueous delivery system.

The therapeutic or pharmaceutical compositions may be administered in a therapeutically effective amount, which will vary depending upon a variety of factors including the activity of the specific compound employed; the metabolic stability and length of action of the compound; the age, body weight, general health, sex, and diet of the subject; the mode and time of administration; the rate of excretion; the drug combination; the severity of the particular disorder or condition; and the subject undergoing therapy. In some instances, a therapeutically effective daily dose is (for a 70 kg mammal) from about 0.001 mg/kg (i.e., ~ 0.07 mg) to about 100 mg/kg (i.e., ~ 7.0 g); preferably a therapeutically effective dose is (for a 70 kg mammal) from about 0.01 mg/kg (i.e., ~ 0.7 mg) to about 50 mg/kg (i.e., ~ 3.5 g); more preferably a therapeutically effective dose is (for a 70 kg mammal) from about 1 mg/kg (i.e., ~ 70 mg) to about 25 mg/kg (i.e., ~ 1.75 g). In some embodiments, the therapeutically effective dose is administered on a weekly, bi-weekly, or monthly basis. In specific embodiments, the therapeutically effective dose is administered on a weekly, bi-weekly, or monthly basis, for example, at a dose of about 1-10 or 1-5 mg/kg, or about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 mg/kg.

The combination therapies described herein may include administration of a single pharmaceutical dosage formulation, which contains an activatable proprotein and an additional therapeutic agent (e.g., chemotherapeutic agent, hormonal therapeutic agent, kinase inhibitor), as well as administration of compositions comprising an activatable proprotein and an additional therapeutic agent in its own separate pharmaceutical dosage formulation. For example, an activatable proprotein and additional therapeutic agent can be administered to the subject together in a single oral dosage composition such as a tablet or capsule, or each agent administered in separate oral dosage formulations. Similarly, an activatable proprotein and additional therapeutic agent can be administered to the subject together in a single parenteral dosage composition such as in a saline solution or other physiologically acceptable solution, or each agent administered in separate parenteral dosage formulations. As another example, for cell-based therapies, an activatable proprotein can be mixed with the cells prior to administration, administered as part of a separate composition, or both. Where separate dosage formulations are used, the compositions can be administered at essentially the same time, i.e., concurrently, or at separately staggered times, i.e., sequentially and in any order; combination therapy is understood to include all these regimens.

Also included are patient care kits, comprising (a) at least one activatable proprotein, as described herein; and optionally (b) at least one additional therapeutic agent (e.g., chemotherapeutic agent, hormonal therapeutic agent, kinase inhibitor). In certain kits, (a) and (b) are in separate therapeutic compositions. In some kits, (a) and (b) are in the same therapeutic composition.

The kits herein may also include a one or more additional therapeutic agents or other components suitable or desired for the indication being treated, or for the desired diagnostic application. The kits herein can also include one or more syringes or other components necessary or desired to facilitate an intended mode of delivery (e.g., stents, implantable depots, etc.).

In some embodiments, a patient care kit contains separate containers, dividers, or compartments for the composition(s) and informational material(s). For example, the composition(s) can be contained in a bottle, vial, or syringe, and the informational material(s) can be contained in association with the container. In some embodiments, the separate elements of the kit are contained within a single, undivided container. For example, the composition is contained in a bottle, vial or syringe that has attached thereto the informational material in the form of a label. In some embodiments, the kit includes a plurality (e.g., a pack) of individual containers, each containing one or more unit dosage forms (e.g., a dosage form described herein) of an activatable proprotein and optionally at least one additional therapeutic agent. For example, the kit includes a plurality of syringes, ampules, foil packets, or blister packs, each containing a single unit dose of an activatable proprotein and optionally at least one additional therapeutic agent. The containers of the kits can be air tight, waterproof (e.g., impermeable to changes in moisture or evaporation), and/or light-tight.

The patient care kit optionally includes a device suitable for administration of the composition, e.g., a syringe, inhalant, dropper (e.g., eye dropper), swab (e.g., a cotton swab or wooden swab), or any such delivery device. In some embodiments, the device is an implantable device that dispenses metered doses of the agent(s). Also included are methods of providing a kit, e.g., by combining the components described herein.

Expression and Purification Systems

Certain embodiments include methods and related compositions for expressing and purifying an activatable proprotein described herein. Such recombinant activatable proproteins can be conveniently prepared using standard protocols as described for example in Sambrook, et al., (1989, supra), in particular Sections 16 and 17; Ausubel et al., (1994, supra), in particular Chapters 10 and 16; and Coligan et al., Current Protocols in Protein Science (John Wiley & Sons, Inc. 1995-1997), in particular Chapters 1, 5 and 6. As one general example, activatable proproteins may be prepared by a procedure including one or more of the steps of: (a) preparing one or more vectors or constructs comprising one or more polynucleotide sequences that encode a first and second polypeptide described herein, and a VL/CL region of an anti-PD-1 or anti-PD-Ll Fab region described herein, which are operably linked to one or more regulatory elements; (b) introducing the one or more vectors or constructs into one or more host cells; (c) culturing the one or more host cell to express the first and second polypeptides and the VL/CL regions, which bind together to form an activatable proprotein; and (d) isolating the activatable proprotein from the host cell.

To express a desired polypeptide, a nucleotide sequence encoding a first and/or second polypeptide chain of an activatable proprotein may be inserted into appropriate expression vector(s), i.e., vector(s) which contain the necessary elements for the transcription and translation of the inserted coding sequence. Methods which are well known to those skilled in the art may be used to construct expression vectors containing sequences encoding a polypeptide of interest and appropriate transcriptional and translational control elements. These methods include in vitro recombinant DNA techniques, synthetic techniques, and in vivo genetic recombination. Such techniques are described in Sambrook et al., Molecular Cloning, A Laboratory Manual (1989), and Ausubel et al., Current Protocols in Molecular Biology (1989).

A variety of expression vector/host systems are known and may be utilized to contain and express polynucleotide sequences. These include, but are not limited to, microorganisms such as bacteria transformed with recombinant bacteriophage, plasmid, or cosmid DNA expression vectors; yeast transformed with yeast expression vectors; insect cell systems infected with virus expression vectors (e.g., baculovirus); plant cell systems transformed with virus expression vectors (e.g., cauliflower mosaic virus, CaMV; tobacco mosaic virus, TMV) or with bacterial expression vectors (e.g., Ti or pBR322 plasmids); or animal cell systems, including mammalian cell and more specifically human cell systems.

The “control elements” or “regulatory sequences” present in an expression vector are those non-translated regions of the vector— enhancers, promoters, 5 ’ and 3 ’ untranslated regions— which interact with host cellular proteins to carry out transcription and translation. Such elements may vary in their strength and specificity. Depending on the vector system and host utilized, any number of suitable transcription and translation elements, including constitutive and inducible promoters, may be used. For example, when cloning in bacterial systems, inducible promoters such as the hybrid lacZ promoter of the PBLUESCRIPT phagemid (Stratagene, La Jolla, Calif.) or PSPORT1 plasmid (Gibco BRL, Gaithersburg, Md.) and the like may be used. In mammalian cell systems, promoters from mammalian genes or from mammalian viruses are generally preferred. If it is necessary to generate a cell line that contains multiple copies of the sequence encoding a polypeptide, vectors based on SV40 or EBV may be advantageously used with an appropriate selectable marker.

In bacterial systems, a number of expression vectors may be selected depending upon the use intended for the expressed polypeptide. For example, when large quantities are needed, vectors which direct high level expression of fusion proteins that are readily purified may be used. Such vectors include, but are not limited to, the multifunctional E. coli cloning and expression vectors such as BLUESCRIPT (Stratagene), in which the sequence encoding the polypeptide of interest may be ligated into the vector in frame with sequences for the amino-terminal Met and the subsequent 7 residues of [3-galactosidase so that a hybrid protein is produced; pIN vectors (Van Heeke & Schuster, J. Biol. Chem. 264:5503 5509 (1989)); and the like. pGEX Vectors (Promega, Madison, Wis.) may also be used to express foreign polypeptides as fusion proteins with glutathione S-transferase (GST). In general, such fusion proteins are soluble and can easily be purified from lysed cells by adsorption to glutathione-agarose beads followed by elution in the presence of free glutathione. Proteins made in such systems may be designed to include heparin, thrombin, or factor XA protease cleavage sites so that the cloned polypeptide of interest can be released from the GST moiety at will.

Certain embodiments employ E. coli-based expression systems (see, e.g., Structural Genomics Consortium et al., Nature Methods. 5: 135-146, 2008). These and related embodiments may rely partially or totally on ligation-independent cloning (LIC) to produce a suitable expression vector. In specific embodiments, protein expression may be controlled by a T7 RNA polymerase (e.g., pET vector series). These and related embodiments may utilize the expression host strain BL21(DE3), a XDE3 lysogen of BL21 that supports T7 -mediated expression and is deficient in Ion and ompT proteases for improved target protein stability. Also included are expression host strains carrying plasmids encoding tRNAs rarely used in E. coli, such as ROSETTA™ (DE3) and Rosetta 2 (DE3) strains. Cell lysis and sample handling may also be improved using reagents sold under the trademarks BENZONASE® nuclease and BUGBUSTER® Protein Extraction Reagent. For cell culture, auto-inducing media can improve the efficiency of many expression systems, including high- throughput expression systems. Media of this type (e.g., OVERNIGHT EXPRESS™ Autoinduction System) gradually elicit protein expression through metabolic shift without the addition of artificial inducing agents such as IPTG. Particular embodiments employ hexahistidine tags (such as those sold under the trademark HIS*TAG® fusions), followed by immobilized metal affinity chromatography (IMAC) purification, or related techniques. In certain aspects, however, clinical grade proteins can be isolated from E. coli inclusion bodies, without or without the use of affinity tags (see, e.g., Shimp et al., Protein Expr Purif. 50:58-67, 2006). As a further example, certain embodiments may employ a cold-shock induced E. coli high-yield production system, because over-expression of proteins in Escherichia coli at low temperature improves their solubility and stability (see, e.g., Qing et al., Nature Biotechnology. 22:877-882, 2004).

Also included are high-density bacterial fermentation systems. For example, high cell density cultivation of Ralstonia eutropha allows protein production at cell densities of over 150 g/L, and the expression of recombinant proteins at titers exceeding 10 g/L.

In the yeast Saccharomyces cerevisiae, a number of vectors containing constitutive or inducible promoters such as alpha factor, alcohol oxidase, and PGH may be used. For reviews, see Ausubel et al. (supra) and Grant et al., Methods Enzymol. 153:516-544 (1987). Also included are Pichia pandoris expression systems (see, e.g., Li et al., Nature Biotechnology. 24, 210 - 215, 2006; and Hamilton et al., Science, 301: 1244, 2003). Certain embodiments include yeast systems that are engineered to selectively glycosylate proteins, including yeast that have humanized N-glycosylation pathways, among others (see, e.g., Hamilton et al., Science. 313: 1441-1443, 2006; Wildt et al., Nature Reviews Microbiol. 3: 119-28, 2005; and Gemgross et al., Nature-Biotechnology. 22: 1409 -1414, 2004; U.S. Patent Nos. 7,629,163; 7,326,681; and 7,029,872). Merely by way of example, recombinant yeast cultures can be grown in Fembach Flasks or 15L, 50L, 100L, and 200L fermentors, among others.

In cases where plant expression vectors are used, the expression of sequences encoding polypeptides may be driven by any of a number of promoters. For example, viral promoters such as the 35 S and 19S promoters of CaMV may be used alone or in combination with the omega leader sequence from TMV (Takamatsu, EMBO J. 6:307-311 (1987)). Alternatively, plant promoters such as the small subunit of RUBISCO or heat shock promoters may be used (Coruzzi et al., EMBO J. 3: 1671-1680 (1984); Broglie et al., Science 224:838-843 (1984); and Winter et al., Results Probl. Cell Differ. 17:85-105 (1991)). These constructs can be introduced into plant cells by direct DNA transformation or pathogen-mediated transfection. Such techniques are described in a number of generally available reviews (see, e.g., Hobbs in McGraw Hill, Yearbook of Science and Technology, pp. 191-196 (1992)).

An insect system may also be used to express a polypeptide of interest. For example, in one such system, Autographa califomica nuclear polyhedrosis vims (AcNPV) is used as a vector to express foreign genes in Spodoptera fmgiperda cells or in Trichoplusia cells. The sequences encoding the polypeptide may be cloned into a non-essential region of the vims, such as the polyhedrin gene, and placed under control of the polyhedrin promoter. Successful insertion of the polypeptide-encoding sequence will render the polyhedrin gene inactive and produce recombinant vims lacking coat protein. The recombinant vimses may then be used to infect, for example, S. fmgiperda cells or Trichoplusia cells in which the polypeptide of interest may be expressed (Engelhard et al., Proc. Natl. Acad. Sci. U.S.A. 91:3224-3227 (1994)). Also included are baculovims expression systems, including those that utilize SF9, SF21, and T. ni cells (see, e.g., Murphy and Piwnica-Worms, Curr Protoc Protein Sci. Chapter 5:Unit5.4, 2001). Insect systems can provide post-translation modifications that are similar to mammalian systems.

In mammalian host cells, a number of viral-based expression systems are generally available. For example, in cases where an adenovims is used as an expression vector, sequences encoding a polypeptide of interest may be ligated into an adenovims transcription/translation complex consisting of the late promoter and tripartite leader sequence. Insertion in a non-essential El or E3 region of the viral genome may be used to obtain a viable vims which is capable of expressing the polypeptide in infected host cells (Logan & Shenk, Proc. Natl. Acad. Sci. U.S.A. 81:3655-3659 (1984)). In addition, transcription enhancers, such as the Rous sarcoma vims (RSV) enhancer, may be used to increase expression in mammalian host cells.

Examples of useful mammalian host cell lines include monkey kidney CV1 line transformed by SV40 (COS-7, ATCC CRL 1651); human embryonic kidney line (293 or 293 cells sub-cloned for growth in suspension culture, Graham et al., J. Gen Virol. 36:59 (1977)); baby hamster kidney cells (BHK, ATCC CCL 10); mouse sertoli cells (TM4, Mather, Biol. Reprod. 23:243-251 (1980)); monkey kidney cells (CV1 ATCC CCL 70); African green monkey kidney cells (VERO-76, ATCC CRL-1587); human cervical carcinoma cells (HELA, ATCC CCL 2); canine kidney cells (MDCK, ATCC CCL 34); buffalo rat liver cells (BRL 3A, ATCC CRL 1442); human lung cells (W138, ATCC CCL 75); human liver cells (Hep G2, HB 8065); mouse mammary tumor (MMT 060562, ATCC CCL51); TRI cells (Mather et al., Annals N.Y. Acad. Sci. 383:44-68 (1982)); MRC 5 cells; ES4 cells; and a human hepatoma line (Hep G2). Other useful mammalian host cell lines include Chinese hamster ovary (CHO) cells, including DHER-CHO cells (Urlaub et al., PNAS USA 77:4216 (1980)); and myeloma cell lines such as NSO and Sp2/0. For a review of certain mammalian host cell lines suitable for protein production, see, e.g., Yazaki and Wu, Methods in Molecular Biology, Vol. 248 (B. K.C Lo, ed., Humana Press, Totowa, N.J., 2003), pp. 255-268. Certain preferred mammalian cell expression systems include CHO and HEK293-cell based expression systems. Mammalian expression systems can utilize attached cell lines, for example, in T-flasks, roller bottles, or cell factories, or suspension cultures, for example, in IL and 5L spinners, 5L, 14L, 40L, 100L and 200L stir tank bioreactors, or 20/50L and 100/200L WAVE bioreactors, among others known in the art.

Also included is the cell-free expression of proteins. These and related embodiments typically utilize purified RNA polymerase, ribosomes, tRNA and ribonucleotides; these reagents may be produced by extraction from cells or from a cell-based expression system.

Specific initiation signals may also be used to achieve more efficient translation of sequences encoding a polypeptide of interest. Such signals include the ATG initiation codon and adjacent sequences. In cases where sequences encoding the polypeptide, its initiation codon, and upstream sequences are inserted into the appropriate expression vector, no additional transcriptional or translational control signals may be needed. However, in cases where only coding sequence, or a portion thereof, is inserted, exogenous translational control signals including the ATG initiation codon should be provided. Furthermore, the initiation codon should be in the correct reading frame to ensure translation of the entire insert. Exogenous translational elements and initiation codons may be of various origins, both natural and synthetic. The efficiency of expression may be enhanced by the inclusion of enhancers which are appropriate for the particular cell system which is used, such as those described in the literature (Scharf, et al., Results Probl. Cell Differ. 20: 125-162 (1994)).

In addition, a host cell strain may be chosen for its ability to modulate the expression of the inserted sequences or to process the expressed protein in the desired fashion. Such modifications of the polypeptide include, but are not limited to, post-translational modifications such as acetylation, carboxylation, glycosylation, phosphorylation, lipidation, and acylation. Post-translational processing which cleaves a “prepro” form of the protein may also be used to facilitate correct insertion, folding and/or function. Different host cells such as yeast, CHO, He La, MDCK, HEK293, and W138, in addition to bacterial cells, which have or even lack specific cellular machinery and characteristic mechanisms for such post-translational activities, may be chosen to ensure the correct modification and processing of the foreign protein.

For long-term, high-yield production of recombinant proteins, stable expression is generally preferred. For example, cell lines which stably express a polynucleotide of interest may be transformed using expression vectors which may contain viral origins of replication and/or endogenous expression elements and a selectable marker gene on the same or on a separate vector. Following the introduction of the vector, cells may be allowed to grow for about 1-2 days in an enriched media before they are switched to selective media. The purpose of the selectable marker is to confer resistance to selection, and its presence allows growth and recovery of cells which successfully express the introduced sequences. Resistant clones of stably transformed cells may be proliferated using tissue culture techniques appropriate to the cell type. Transient production, such as by transient transfection or infection, can also be employed. Exemplary mammalian expression systems that are suitable for transient production include HEK293 and CHO-based systems.

Any number of selection systems may be used to recover transformed or transduced cell lines. These include, but are not limited to, the herpes simplex virus thymidine kinase (Wigler et al., Cell 11:223-232 (1977)) and adenine phosphoribosyltransferase (Lowy et al., Cell 22:817-823 (1990)) genes which can be employed in tk- or aprt- cells, respectively. Also, antimetabolite, antibiotic or herbicide resistance can be used as the basis for selection; for example, dhfr which confers resistance to methotrexate (Wigler et al., Proc. Natl. Acad. Sci. U.S.A. 77:3567-70 (1980)); npt, which confers resistance to the aminoglycosides, neomycin and G-418 (Colbere-Garapin et al., J. Mol. Biol. 150: 1- 14 (1981)); and als or pat, which confer resistance to chlorsulfuron and phosphinotricin acetyltransferase, respectively (Murry, supra). Additional selectable genes have been described, for example, trpB, which allows cells to utilize indole in place of tryptophan, or hisD, which allows cells to utilize histinol in place of histidine (Hartman & Mulligan, Proc. Natl. Acad. Sci. U.S.A. 85:8047-51 (1988)). The use of visible markers has gained popularity with such markers as green fluorescent protein (GFP) and other fluorescent proteins (e.g., RFP, YFP), anthocyanins, [3-glucuronidase and its substrate GUS, and luciferase and its substrate luciferin, being widely used not only to identify transformants, but also to quantify the amount of transient or stable protein expression attributable to a specific vector system (see, e.g., Rhodes et al., Methods Mol. Biol. 55: 121-131 (1995)).

Also included are high-throughput protein production systems, or micro-production systems. Certain aspects may utilize, for example, hexa-histidine fusion tags for protein expression and purification on metal chelate-modified slide surfaces or MagneHis Ni-Particles (see, e.g., Kwon et al., BMC Biotechnol. 9:72, 2009; and Lin et al., Methods Mol Biol. 498: 129-41, 2009)). Also included are high-throughput cell-free protein expression systems (see, e.g., Sitaraman et al., Methods Mol Biol. 498:229-44, 2009).

A variety of protocols for detecting and measuring the expression of polynucleotide-encoded products, using binding agents or antibodies such as polyclonal or monoclonal antibodies specific for the product, are known in the art. Examples include enzyme-linked immunosorbent assay (ELISA), western immunoblots, radioimmunoassays (RIA), and fluorescence activated cell sorting (FACS). These and other assays are described, among other places, in Hampton et al., Serological Methods, a Laboratory Manual (1990) and Maddox et al., J. Exp. Med. 158: 1211-1216 (1983).

A wide variety of labels and conjugation techniques are known by those skilled in the art and may be used in various nucleic acid and amino acid assays. Means for producing labeled hybridization or PCR probes for detecting sequences related to polynucleotides include oligolabeling, nick translation, end-labeling or PCR amplification using a labeled nucleotide. Alternatively, the sequences, or any portions thereof may be cloned into a vector for the production of an mRNA probe. Such vectors are known in the art, are commercially available, and may be used to synthesize RNA probes in vitro by addition of an appropriate RNA polymerase such as T7, T3, or SP6 and labeled nucleotides. These procedures may be conducted using a variety of commercially available kits. Suitable reporter molecules or labels, which may be used include radionuclides, enzymes, fluorescent, chemiluminescent, or chromogenic agents as well as substrates, cofactors, inhibitors, magnetic particles, and the like.

Host cells transformed with one or more polynucleotide sequences of interest may be cultured under conditions suitable for the expression and recovery of the protein from cell culture. Certain specific embodiments utilize serum free cell expression systems. Examples include HEK293 cells and CHO cells that can grown on serum free medium (see, e.g., Rosser et al., Protein Expr. Purif. 40:237- 43, 2005; and U.S. Patent number 6,210,922).

An activatable proprotein produced by a recombinant cell may be secreted or contained intracellularly depending on the sequence and/or the vector used. As will be understood by those of skill in the art, expression vectors containing polynucleotides may be designed to contain signal sequences which direct secretion of the encoded polypeptide through a prokaryotic or eukaryotic cell membrane. Other recombinant constructions may be used to join sequences encoding a polypeptide of interest to nucleotide sequence encoding a polypeptide domain which will facilitate purification and/or detection of soluble proteins. Examples of such domains include cleavable and non-cleavable affinity purification and epitope tags such as avidin, FLAG tags, poly-histidine tags (e.g., 6xHis), cMyc tags, V5-tags, glutathione S-transferase (GST) tags, and others.

The protein produced by a recombinant cell can be purified and characterized according to a variety of techniques known in the art. Exemplary systems for performing protein purification and analyzing protein purity include fast protein liquid chromatography (FPLC) (e.g., AKTA and Bio-Rad FPLC systems), high-pressure liquid chromatography (HPLC) (e.g., Beckman and Waters HPLC). Exemplary chemistries for purification include ion exchange chromatography (e.g., Q, S), size exclusion chromatography, salt gradients, affinity purification (e.g., Ni, Co, FLAG, maltose, glutathione, protein A/G), gel filtration, reverse-phase, ceramic HYPERD® ion exchange chromatography, and hydrophobic interaction columns (HIC), among others known in the art. Also included are analytical methods such as SDS-PAGE (e.g., coomassie, silver stain), immunoblot, Bradford, and ELISA, which may be utilized during any step of the production or purification process, typically to measure the purity of the protein composition.

Also included are methods of concentrating activatable proproteins, and composition comprising concentrated soluble activatable proproteina. In some aspects, such concentrated solutions of at least tone activatable proprotein comprise proteins at a concentration of about or at least about 5 mg/mL, 8 mg/mL, 10 mg/mL, 15 mg/mL. 20 mg/mL, or more.

In some aspects, such compositions may be substantially monodisperse, meaning that an activatable proprotein exists primarily (i.e., at least about 90%, or greater) in one apparent molecular weight form when assessed for example, by size exclusion chromatography, dynamic light scattering, or analytical ultracentrifugation.

In some aspects, such compositions have a purity (on a protein basis) of at least about 90%, or in some aspects at least about 95% purity, or in some embodiments, at least 98% purity. Purity may be determined via any routine analytical method as known in the art.

In some aspects, such compositions have a high molecular weight aggregate content of less than about 10%, compared to the total amount of protein present, or in some embodiments such compositions have a high molecular weight aggregate content of less than about 5%, or in some aspects such compositions have a high molecular weight aggregate content of less than about 3%, or in some embodiments a high molecular weight aggregate content of less than about 1%. High molecular weight aggregate content may be determined via a variety of analytical techniques including for example, by size exclusion chromatography, dynamic light scattering, or analytical ultracentrifugation .

Examples of concentration approaches contemplated herein include lyophilization, which is typically employed when the solution contains few soluble components other than the protein of interest. Lyophilization is often performed after HPLC run, and can remove most or all volatile components from the mixture. Also included are ultrafiltration techniques, which typically employ one or more selective permeable membranes to concentrate a protein solution. The membrane allows water and small molecules to pass through and retains the protein; the solution can be forced against the membrane by mechanical pump, gas pressure, or centrifugation, among other techniques.

In certain embodiments, an activatable proprotein in a composition has a purity of at least about 90%, as measured according to routine techniques in the art. In certain embodiments, such as diagnostic compositions or certain pharmaceutical or therapeutic compositions, an activatable proprotein composition has a purity of at least about 95%, or at least about 97% or 98% or 99%. In some embodiments, such as when being used as reference or research reagents, activatable proproteins can be of lesser purity, and may have a purity of at least about 50%, 60%, 70%, or 80%. Purity can be measured overall or in relation to selected components, such as other proteins, e.g., purity on a protein basis. Purified activatable proproteins can also be characterized according to their biological characteristics. Binding affinity and binding kinetics can be measured according to a variety of techniques known in the art, such as Biacore® and related technologies that utilize surface plasmon resonance (SPR), an optical phenomenon that enables detection of unlabeled interactants in real time. SPR-based biosensors can be used in determination of active concentration, screening and characterization in terms of both affinity and kinetics. The presence or levels of one or more biological activities can be measured according to cell-based assays, including those that utilize at least one IL-2 receptor, which is optionally functionally coupled to a readout or indicator, such as a fluorescent or luminescent indicator of biological activity, as described herein.

In certain embodiments, as noted above, an activatable proprotein composition is substantially endotoxin free, including, for example, about 95% endotoxin free, preferably about 99% endotoxin free, and more preferably about 99.99% endotoxin free. The presence of endotoxins can be detected according to routine techniques in the art, as described herein. In specific embodiments, an activatable proprotein composition is made from a eukaryotic cell such as a mammalian or human cell in substantially serum free media. In certain embodiments, as noted herein, an activatable proprotein composition has an endotoxin content of less than about 10 EU/mg of activatable proprotein, or less than about 5 EU/mg of activatable proprotein, less than about 3 EU/mg of activatable proprotein, or less than about 1 EU/mg of activatable proprotein.

In certain embodiments, an activatable proprotein composition comprises less than about 10% wt/wt high molecular weight aggregates, or less than about 5% wt/wt high molecular weight aggregates, or less than about 2% wt/wt high molecular weight aggregates, or less than about or less than about 1% wt/wt high molecular weight aggregates.

Also included are protein-based analytical assays and methods, which can be used to assess, for example, protein purity, size, solubility, and degree of aggregation, among other characteristics. Protein purity can be assessed a number of ways. For instance, purity can be assessed based on primary structure, higher order structure, size, charge, hydrophobicity, and glycosylation. Examples of methods for assessing primary structure include N- and C-terminal sequencing and peptide-mapping (see, e.g., Allen et al., Biologicals. 24:255-275, 1996)). Examples of methods for assessing higher order structure include circular dichroism (see, e.g., Kelly et al., Biochim Biophys Acta. 1751: 119- 139, 2005), fluorescent spectroscopy (see, e.g., Meagher et al., J. Biol. Chem. 273:23283-89, 1998), FT-IR, amide hydrogen-deuterium exchange kinetics, differential scanning calorimetry, NMR spectroscopy, immunoreactivity with conformationally sensitive antibodies. Higher order structure can also be assessed as a function of a variety of parameters such as pH, temperature, or added salts. Examples of methods for assessing protein characteristics such as size include analytical ultracentrifugation and size exclusion HPLC (SEC-HPLC), and exemplary methods for measuring charge include ion-exchange chromatography and isolectric focusing. Hydrophobicity can be assessed, for example, by reverse-phase HPLC and hydrophobic interaction chromatography HPLC. Glycosylation can affect pharmacokinetics (e.g., clearance), conformation or stability, receptor binding, and protein function, and can be assessed, for example, by mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy.

As noted above, certain embodiments include the use of SEC-HPLC to assess protein characteristics such as purity, size (e.g., size homogeneity) or degree of aggregation, and/or to purify proteins, among other uses. SEC, also including gel-fdtration chromatography (GFC) and gelpermeation chromatography (GPC), refers to a chromatographic method in which molecules in solution are separated in a porous material based on their size, or more specifically their hydrodynamic volume, diffusion coefficient, and/or surface properties. The process is generally used to separate biological molecules, and to determine molecular weights and molecular weight distributions of polymers. Typically, a biological or protein sample (such as a protein extract produced according to the protein expression methods provided herein and known in the art) is loaded into a selected size-exclusion column with a defined stationary phase (the porous material), preferably a phase that does not interact with the proteins in the sample. In certain aspects, the stationary phase is composed of inert particles packed into a dense three-dimensional matrix within a glass or steel column. The mobile phase can be pure water, an aqueous buffer, an organic solvent, or a mixture thereof. The stationary-phase particles typically have small pores and/or channels which only allow molecules below a certain size to enter. Large particles are therefore excluded from these pores and channels, and their limited interaction with the stationary phase leads them to elute as a “totally- excluded” peak at the beginning of the experiment. Smaller molecules, which can fit into the pores, are removed from the flowing mobile phase, and the time they spend immobilized in the stationary- phase pores depends, in part, on how far into the pores they penetrate. Their removal from the mobile phase flow causes them to take longer to elute from the column and results in a separation between the particles based on differences in their size. A given size exclusion column has a range of molecular weights that can be separated. Overall, molecules larger than the upper limit will not be trapped by the stationary phase, molecules smaller than the lower limit will completely enter the solid phase and elute as a single band, and molecules within the range will elute at different rates, defined by their properties such as hydrodynamic volume. For examples of these methods in practice with pharmaceutical proteins, see Bruner et al., Journal of Pharmaceutical and Biomedical Analysis. 15: 1929-1935, 1997.

Protein purity for clinical applications is also discussed, for example, by Anicetti et al. (Trends in Biotechnology. 7:342-349, 1989). More recent techniques for analyzing protein purity include, without limitation, the LabChip GXII, an automated platform for rapid analysis of proteins and nucleic acids, which provides high throughput analysis of titer, sizing, and purity analysis of proteins. In certain non-limiting embodiments, clinical grade activatable proproteins can be obtained by utilizing a combination of chromatographic materials in at least two orthogonal steps, among other methods (see, e.g., Therapeutic Proteins: Methods and Protocols. Vol. 308, Eds., Smales and James, Humana Press Inc., 2005). Typically, protein agents (e.g., activatable proprotein) are substantially endotoxin-free, as measured according to techniques known in the art and described herein.

Protein solubility assays are also included. Such assays can be utilized, for example, to determine optimal growth and purification conditions for recombinant production, to optimize the choice of buffer(s), and to optimize the choice of activatable proproteins and variants thereof. Solubility or aggregation can be evaluated according to a variety of parameters, including temperature, pH, salts, and the presence or absence of other additives. Examples of solubility screening assays include, without limitation, microplate-based methods of measuring protein solubility using turbidity or other measure as an end point, high-throughput assays for analysis of the solubility of purified recombinant proteins (see, e.g., Stenvall et al., Biochim Biophys Acta. 1752:6- 10, 2005), assays that use structural complementation of a genetic marker protein to monitor and measure protein folding and solubility in vivo (see, e.g., Wigley et al., Nature Biotechnology. 19: 131- 136, 2001), and electrochemical screening of recombinant protein solubility in Escherichia coli using scanning electrochemical microscopy (SECM) (see, e.g., Nagamine et al., Biotechnology and Bioengineering. 96: 1008-1013, 2006), among others. Activatable proprotein with increased solubility (or reduced aggregation) can be identified or selected for according to routine techniques in the art, including simple in vivo assays for protein solubility (see, e.g., Maxwell et al., Protein Sci. 8: 1908-11, 1999).

Protein solubility and aggregation can also be measured by dynamic light scattering techniques. Aggregation is a general term that encompasses several types of interactions or characteristics, including soluble/insoluble, covalent/noncovalent, reversible/irreversible, and native/denatured interactions and characteristics. For protein therapeutics, the presence of aggregates is typically considered undesirable because of the concern that aggregates may cause an immunogenic reaction (e.g., small aggregates), or may cause adverse events on administration (e.g., particulates). Dynamic light scattering refers to a technique that can be used to determine the size distribution profile of small particles in suspension or polymers such as proteins in solution. This technique, also referred to as photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS), uses scattered light to measure the rate of diffusion of the protein particles. Fluctuations of the scattering intensity can be observed due to the Brownian motion of the molecules and particles in solution. This motion data can be conventionally processed to derive a size distribution for the sample, wherein the size is given by the Stokes radius or hydrodynamic radius of the protein particle. The hydrodynamic size depends on both mass and shape (conformation). Dynamic scattering can detect the presence of very small amounts of aggregated protein (<0.01% by weight), even in samples that contain a large range of masses. It can also be used to compare the stability of different formulations, including, for example, applications that rely on real-time monitoring of changes at elevated temperatures. Accordingly, certain embodiments include the use of dynamic light scattering to analyze the solubility and/or presence of aggregates in a sample that contains an activatable proprotein of the present disclosure.

Although the foregoing embodiments have been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to one of ordinary skill in the art in light of the teachings of this disclosure that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. The following examples are provided by way of illustration only and not by way of limitation. Those of skill in the art will readily recognize a variety of noncritical parameters that could be changed or modified to yield essentially similar results.

Examples

Example 1A

Preparation of PD-Ll-proIL-2 Fusion Proteins

Plasmids coding for PD-Ll-proIL-2v (IL-2 variant) with different protease cleavable linkers or PD-Ll-proIL-2wt or anti-human PD-L1 were constructed by standard gene synthesis, followed by sub-cloning into pTT5 expression vector. Schematics of illustrative IgG-proIL-2 fusion protein formats are depicted in Figures 1-2.

Illustrative proteins of the PD-Ll-proIL-2v (“v” = variant) format with different protease cleavage linkers include P40391942 (SEQ ID NOs: 138 and 139), P40531942 (SEQ ID NOs: 140 and 141), and P40621942 (SEQ ID NOs: 142 and 143). Illustrative proteins of the PD-Ll-proIL-2wt format include P47131942 (SEQ ID NOs: 154 and 155). Illustrative anti-human PD-L1 proteins include P40751942 (SEQ ID NOs: 144 and 145).

PD-Ll-proIL-2 fusion proteins or anti -human PD-L1 were produced by transient transfection in Expi293 cells and purified by one-step purification of MabSelect SuRe chromatography (GE Healthcare). Purified proteins were characterized by SDS-PAGE and high performance liquid chromatography (HPLC) for purity and homogeneity assessment. HPLC analysis was performed using Nanofilm SEC-250 column (Sepax) and Agilent 1260 according to the manufacturer’s instructions. The purified proteins showed high purity on SDS-PAGE gel and good homogeneity based on HPLC results.

Example IB Preparation of PD-l-proIL-2v Fusion Proteins

Plasmids coding for PD-l-proIL-2v with different protease cleavable linkers or PD-l-null- proIL-2v or anti -human PD-1 were constructed by standard gene synthesis, followed by sub-cloning into pTT5 expression vector. Schematics of illustrative IgG-proIL-2 fusion protein formats are depicted in Figures 1-2. Illustrative proteins of PD-l-proIL-2v format with different protease cleavage linkers include P41222037 (SEQ ID NOs: 146 and 147), P43492037 (SEQ ID NOs: 152 and 153). Illustrative proteins of unmasked PD-l-proIL-2v format include P41252037 (SEQ ID NOs: 158 and 159). Illustrative proteins of PD-l-null-proIL-2v format include P54475445 (SEQ ID NOs: 156 and 157). Illustrative proteins of anti-human PD-1 include P42412037 (SEQ ID NOs: 150 and 151).

PD-l-proIL-2v or PD-1 -null -proIL-2v fusion proteins or anti -human PD-1 were produced by transient transfection in Expi293 cells and purified by one-step purification of MabSelect SuRe chromatography (GE Healthcare). Purified proteins were characterized by SDS-PAGE and high performance liquid chromatography (HPLC) for purity and homogeneity assessment. HPLC analysis was performed using Nanofilm SEC-250 column (Sepax) and Agilent 1260 according to the manufacturer’s instructions. The purified proteins showed high purity on SDS-PAGE gel and good homogeneity based on HPLC results.

Example 1C Preparation of B7H3-proIL-2 Fusion Proteins

Plasmid coding for B7H3-proIL-2v was constructed by standard gene synthesis, followed by sub-cloning into pTT5 expression vector. Schematics of illustrative IgG-proIL-2 fusion protein formats are depicted in Figures 1-2.

Illustrative proteins of B7H3-proIL-2v format include P41713699 (SEQ ID NOs: 148 and 149).

B7H3-proIL-2v fusion protein were produced by transient transfection in Expi293 cells and purified by one-step purification of MabSelect SuRe chromatography (GE Healthcare). Purified proteins were characterized by SDS-PAGE and high performance liquid chromatography (HPLC) for purity and homogeneity assessment. HPLC analysis was performed using Nanofilm SEC-250 column (Sepax) and Agilent 1260 according to the manufacturer’s instructions. The purified proteins showed high purity on SDS-PAGE gel and good homogeneity based on HPLC results.

Example 2A

Binding of PD-l-proIL-2 to Both Human and Cynomolgus PD-1

The binding activity of P41222037 and P42412037 was determined by ELISA. Microtitre plates were coated with lOOul 2ug/ml of Streptavidin overnight at 4°C. The next day, plates were washed with PBS and blocked with 2% BSA (2% Bovine Serum Album in PBS). lOOul 2ug/ml of biotinylated huPD-1 or CynoPD-1 was added into corresponding wells and incubated for 1 hr at room temperature to capture biotinylated protein. The plates were washed with PBST (0.01% Tween in PBS) and PBS sequentially.

The indicated samples (PD-1 IgG or PD-l-proIL-2v) used in ELISA assay were prepared in 2% BSA to an initial concentration of lOug/ml, followed by 1/3 serial dilutions. lOOpl diluted protein was added into corresponding wells and incubated at room temperature for Ih. Plates were washed with PBST and PBS sequentially.

Bound antibodies were detected with peroxidase -conjugated anti-human IgG secondary antibody (Jackson Immunoresearch). Plates were washed with PBST and PBS sequentially. 90ul of TMB substrate was added into each well and incubated in dark at room temperature for 5 min. The reaction was terminated with 45ul 2M sulphuric acid and the absorbance was read at 450nm. The data were analyzed by Prism.

As shown in Figures 4A-4B, PD-l-proIL-2v and the corresponding PD-1 IgG bind similarly to human PD-1.

Example 2B Binding of PD-Ll-proIL-2 to Human PD-L1

The binding activity of P40391942 and P40751942 was determined by ELISA. Microtitre plates were coated with lOOul 2ug/ml of Streptavidin overnight at 4°C. The next day, plates were washed with PBS and blocked with 2% BSA (2% Bovine Serum Album in PBS). lOOul 2ug/ml of biotinylated huPD-Ll was added into corresponding wells and incubated for 1 hr at room temperature to capture biotinylated protein. The plates were washed with PBST (0.01% Tween in PBS) and PBS sequentially.

The indicated samples (PD-L1 IgG or PD-Ll-proIL-2v) used in ELISA assay were prepared in 2% BSA to an initial concentration of lOug/ml, followed by 1/3 serial dilutions. lOOpl diluted protein was added into corresponding wells and incubated at room temperature for Ih. Plates were washed with PBST and PBS sequentially.

Bound antibodies were detected with peroxidase -conjugated anti-human IgG secondary antibody (Jackson Immunoresearch). Plates were washed with PBST and PBS sequentially. 90ul of TMB substrate was added into each well and incubated in dark at room temperature for 5 min. The reaction was terminated with 45ul 2M sulphuric acid and the absorbance was read at 450nm. The data were analyzed by Prism.

As shown in Figure 4C, PD-Ll-proIL-2v and the corresponding PD-L1 IgG bind similarly to human PD-L1.

Example 2C PD-l-proIL-2v Restores T cell Function Suppressed by PD-1

Mature DC cells were recovered and treated with Mitomycin C at50ug/ml for 30mins in dark, and were washed with PBS twice. Recovered PBMC (le5 cells/well) and allogeneic DCs (5000 cells/well) were co-cultured with dose titrations of isotope control antibody, parental PD-1 antibody or PD-l-proIL-2 fusion protein at an initial concentration of lOOug/ml. After 5 days incubation at 37°C, IFNy secretion in culture supernatants was analyzed by Human IFNy ELISA Set (Biolegend Cat.430104). The pre-coated Capture Antibody plate was prepared as described in the manufacturer’s instructions and lOOul of diluted standard or sample was added into corresponding well and incubated at room temperature for 2h. Plates were washed 4 times with Wash Buffer, and lOOul of diluted Detection Antibody solution was added to each well and incubate for 30min at room temperature with shaking. Plates were then washed 5 times with Wash Buffer, and lOOul of freshly mixed TMB Substrate solution was added into each well and incubated in dark at room temperature for 20 min. The reaction was terminated with lOOul of Stop Solution and the absorbance was read at 450nm. The data were analyzed by Prism.

As shown in Figure 5, mixed lymphocyte reaction assay data shows that PD-l-proIL-2v restores T cell function suppressed by PD-1.

Example 2D Proliferation of M07-e with PD-l-proIL-2v and PD-Ll-proIL-2v

Human M-07e cells (expressing human IL-2Rp/y) were cultured in RPMI 1640 supplemented with 20% fetal bovine serum (FBS) and 10% of 5637 cells culture supernatant. To measure cytokinedependent cell proliferation, M-07e cells were harvested in their logarithmic growth phase and washed twice with PBS. 90pl of cell suspension (2x 10 ⁴ cells/well) was seeded into 96-well plate and incubated for 4 hours in assay medium (RPMI 1640 supplemented with 10% FBS) for cytokine starvation at 37°C and 5% CO2.

IL-2, P40391942, or P41222037 protein samples used in assays were prepared in assay medium to an initial concentration (300 nM for IL-2, 24300 nM for PD-l/PD-Ll-proIL-2v, and 2700nM for MMP2 protease activated fusion proteins), followed by 1/3 serial dilutions. 10 pl diluted protein was added into corresponding wells and incubated at 37°C and 5% CO2 for 72 hours. Colorimetric assays using a Cell Counting Kit-8 (CCK-8, Dojindo, CK04) were performed to measure the amount of live cells.

Figure 6A shows that PD-l-proIL-2v is not able to induce proliferation of M07-e even at the highest concentration. MMP-2 cleaved PD-l-proIL-2v restored partial IL-2 activity and exhibited ~30 fold lower activity compared with wild type IL-2. Figure 6B shows that PD-Ll-proIL-2v has almost no activity at a high concentration of 810nM. MMP-2 protease activated PD-Ll-proIL-2v induced proliferation of M07-e cells as efficiently as protease-activated PD-l-proIL-2v.

Example 3A

Cell Activation of PBMC with PD-l-proIL-2v (pSTAT5 Assay)

Frozen human PBMCs (SAILYBIO, donor 1) were recovered in RPMI- 1640 added with 10 % FBS, 100 U/ml penicillin and 100 pg/ml streptomycin at 37°C in an atmosphere of 5 % CO2 for ~2 hours. PBMCs were adjusted to 2.6 x 10 ⁶ cells/ml, and plated 4 x 105 cells per well into 96-well plate. The recovered PBMCs were incubated for 15 min at 37 °C with rhIL-2, P41222037 or P54475445. After incubation, cells were immediately fixed with Cytofix buffer (BD Bioscience) to preserve the phosphorylation status for 15 min on ice and wash once with BD Pharmingen™ Stain Buffer (FBS).

For surface staining, cells were incubated with CD3 Alexa Flour 700 (BD 557943), CD4 PerCP-Cytm5.5(BD 560650), CD8 APC-Cytm7 (BD 557760), CD25 BV421(BD562442), CD56 BV510 (BD 744218) for 30min at 4°C. The cells were washed once with IX PBS and centrifuged at 500g for 5min and the supernatant was removed by aspiration. The cells were permeabilized with precold Phosflow Perm buffer III (BD Bioscience) for 30 min at 4°C. Before beginning the intracellular staining, the cells were washed once with IX PBS and centrifuged at 500g for 5min to collect the pellet. The cells were then stained with Foxp3 PE (BD 560046) and Anti-Stat5 (pY694) Alexa Fluor® 647 (BD 562076) for 40min at RT. The cells were washed twice with BD Pharmingen™ Stain Buffer (FBS) and centrifuged at 500g for 5min to pellet the cells and to remove the supernatant. The cell pellet was resuspended in 200ul (per well) BD Pharmingen Stain Buffer (FBS) and analyzed by flow cytometry. STAT5 phosphorylation status in PBMC subsets upon pro-drug treatments was acquired and processed by CytoFLEX (Beckman).

Figures 7A-7D show STAT phosphorylation in CD4 T-cells (7A), CD8 T-cells (7B), regulatory T-cells (7C), and NK cells (7D) upon treatment of resting PBMCs of donor 1 with rhIL-2 as well as intact and protease activated PD-l-proIL-2v. The masked or inactive procytokine form of P41222037 was unable to induce STAT5 phosphorylation in all tested cell subsets. The protease activated form of P41222037 (Matrix metalloproteinase -2 cleaved) was equally effective in activating STAT5 phosphorylation in CD8 and CD4 T cells and less potent in NK cells. In Treg cells, activated P41222037 was over 30X less potent then huIL-2. Thus, compared with wild-type huIL-2, P41222037 no longer preferentially activated Treg cells. Notably, pre-blocking of PD-1 receptor by the parental anti-PD-1 antibody reduced the P41222037 (activated form) potency over 20-folds on PD-1 expressing T cells. Similarly, P54475445 (PD-lnull-IL-2v fusion protein) exhibited 20-fold less potency on CD4+ T cells, CD8+ T cells, and Treg cells. These data validate that preferential cistargeting of PD-l-proIL-2v results in enhanced potency on PD-1 positive T cells.

Example 3B

Cell Activation of PBMC with PD-Ll-proIL-2v (pSTAT5 Assay)

Frozen human PBMCs (SAILYBIO, donor 1) were recovered in RPMI-1640 added with 10 % FBS, 100 U/ml penicillin and 100 pg/ml streptomycin at 37°C in an atmosphere of 5 % CO2 for ~2 hours. PBMCs were adjusted to 2.6 x 10 ⁶ cells/ml, and plated at 4 x 10 ⁵ cells per well into 96-well plate. The recovered PBMCs were incubated for 15 min at 37°C with rhIL-2 and P40391942(both intact and activated forms). After incubation, cells were immediately fixed with Cytofix buffer (BD Bioscience) to preserve the phosphorylation status for 15 min on ice and wash once with BD Pharmingen™ Stain Buffer (FBS). For surface staining, cells were incubated with CD3 Alexa Flour 700 (BD 557943), CD4 PerCP-Cytm5.5(BD 560650), CD8 APC-Cytm7 (BD 557760), CD25 BV421(BD562442), CD56 BV510 (BD 744218) for 30min at 4°C. The cells were washed once with IX PBS and centrifuged at 500g for 5min and the supernatant was removed by aspiration. The cells were permeabilized with precold Phosflow Perm buffer III (BD Bioscience) for 30 min at 4°C. Before beginning the intracellular staining, the cells were washed once with IX PBS and centrifuged at 500g for 5min to collect the pellet. The cells were then stained with Foxp3 PE (BD 560046) and Anti-Stat5 (pY694) Alexa Fluor® 647 (BD 562076) for 40min at RT. The cells were washed twice with BD Pharmingen™ Stain Buffer (FBS) and centrifuged at 500g for 5min to pellet the cells and to remove the supernatant. The cell pellet was resuspended in 200ul (per well) BD Pharmingen Stain Buffer (FBS) and analyzed by flow cytometry. STAT5 phosphorylation status in PBMC subsets upon procytokine treatments was acquired and processed by CytoFLEX (Beckman).

Figures 8A-8D show STAT phosphorylation in CD4 T-cells (8A), CD8 T-cells (8B), regulatory T-cells (8C) and NK cells (8D) upon treatment of resting PBMCs of donor 1 with rhIL-2 as well as intact and activated PD-Ll-proIL-2v. The masked form of P40391942 was unable to induce STAT5 phosphorylation in all tested cell subsets. The activated form of P40391942 (Matrix metalloproteinase -2 cleaved) was equally effective in activating STAT5 phosphorylation in CD8 and CD4 T cells and less potent in NK cells. In Treg cells, activated P40391942 was less potent then huIL-2. Notably, pre-blocking of PD-L1 receptor by the parental anti-PD-Ll antibody reduced the P40391942 (activated form) potency over 100-fold on PD-L1 expressed CD4+ T cells, CD8+ T cells, and Treg cells. These data validate that PD-L1 binding enhances IL-2v potency.

Example 3C

Activated PD-l-proIL-2v Stimulates GM-CSF Secretion by Human CD4 T Cells

Frozen PBMCs were recovered and treated with 10 pg/mL mitomycin C for 2 hrs in dark. After wash 3 times, recovered PBMCs were plated into 96-well plate at 4e5 cells/well with increasing concentrations of parental PD-1 antibody or PD-l-proIL-2 fusion protein (both intact and activated form). Thereafter, suspend the frozen CD4 T cells from the same donor with RPMI1640 with addition of soluble lug/ml aCD3; Seed 4e+5 cells/well CD4 T cells into PBMC 96-well plate.

After 5 days incubation at 37°C, GM-CSF secretion in culture supernatants was analyzed by Human GM-CSF ELISA Set (Biolegend Cat.432004). The pre-coated Capture Antibody plate was prepared as described in the manufacturer instructions and lOOul of diluted standard or sample was added into corresponding well and incubated at room temperature for 2h. Plates were washed 4 times with Wash Buffer, and lOOul of diluted Detection Antibody solution was added to each well and incubate for 30min at room temperature with shaking. Plates were then washed 5 times with Wash Buffer, and lOOul of freshly mixed TMB Substrate solution was added into each well and incubated in dark at room temperature for 20 min. The reaction was terminated with lOOul of Stop Solution and the absorbance was read at 450nm. The data were analyzed by Prism.

As shown in Figure 9A, protease activated PD-l-proIL-2v but not the intact procytokine stimulates production of GM-CSF by CD4 T cells. In contrast, PD-1 blockade alone did not induce any significant level of GM-CSF secretion.

Example 3D

Activated PD-l-proIL-2v Stimulates Production of IFNy Human CD4 T Cells

Frozen PBMCs were recovered and treated with 10 pg/mL Mitomycin C for 2 hrs in dark. After wash 3 times, recovered PBMCs were plated into 96-well plate at 4e5 cells/well with increasing concentrations of parental PD-1 antibody or PD-l-proIL-2 fusion protein (both intact and activated form). Thereafter, suspend the frozen CD4 T cells from the same donor with RPMI1640 with addition of soluble lug/ml aCD3; Seed 4e5 cells/well CD4 T cells into PBMC 96-well plate.

After 5 days incubation at 37°C, the cells were collected for intracellular FACS staining. The accumulation of cytokines in the Golgi complex was induced by re-stimulating the cells with ionomycin (500 ng/ml) and PMA (50 ng/ml) together with protein transport inhibitors (GolgiPlug and GolgiStop, BD) for 5 hours. After incubation, cells were immediately fixed with Cytofix buffer (BD Bioscience) to preserve the phosphorylation status for 15 min on ice and wash once with BD Pharmingen™ Stain Buffer (FBS). For surface staining, cells were incubated with CD3 Alexa Flour 700 (BD 557943) and CD4 PerCP-Cytm5.5 (BD 560650) for 30min at 4°C. The cells were washed once with IX PBS and centrifuged at 500g for 5min and the supernatant was removed by aspiration. The cells were permeabilized with pre-cold Phosflow Perm buffer III (BD Bioscience) for 30 min at 4°C. Before beginning the intracellular staining, the cells were washed once with IX PBS and centrifuged at 500g for 5min to collect the pellet. The cells were then stained with BV605 AntiHuman IFN-y (BD 562974)for 40min at RT. The cells were washed twice with BD Pharmingen™ Stain Buffer (FBS) and centrifuged at 500g for 5min to pellet the cells and to remove the supernatant. The cell pellet was resuspended in 200ul (per well) BD Pharmingen Stain Buffer (FBS) and analyzed using CytoFLEX (Beckman).

As shown in Figure 9B, activated PD-l-proIL-2v, but not the intact procytokine or PD-1 antibody alone, stimulates IFNy production by CD4 T cells.

Example 4

In Vivo Efficacy of PD-Ll-proIL-2v and PD-l-proIL-2v with Different Protease Cleavable Linkers in Tumor-PBMC Xenograft Models

The PD-Ll-proIL-2v and PD-l-proIL-2v with different protease cleavable linkers were tested alone and in comparison to corresponding PD-L1 or PD-1 antibodies for their anti -tumor efficacy in the tumor-PBMC xenograft models. The A375 cells were maintained in vitro in DMEM added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air. The human PBMCs were cocultured with mitomycin C treated A375 tumor cells for 6 days, which maintained in vitro as a suspension cultured in RPMI-1640 added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air.

The HT29 cells were maintained in vitro in McCoy's 5A added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air. The human PBMCs were co-cultured with mitomycin C treated HT29 tumor cells for 6 days, which maintained in vitro as a suspension cultured in RPMI-1640 added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air.

Female NCG mice aged 8—10 weeks at the start of the experiment (GemPharmatech Co., Ltd., Nanjing, China) were maintained under specific-pathogen-free condition with daily cycles of 12 h light/ 12 h darkness. The mice were kept in individual ventilation cages at constant temperature (20-26 °C) and humidity (40-70%) with <6 animals in each cage. Animals had free access to irradiation sterilized dry granule food and sterile drinking water during the entire study period. All the procedures related to animal handling, care and the treatment in this study were performed according to the guidelines approved by the Institutional Animal Care and Use Committee (IACUC) of Shanghai Viva prior to conduct. After arrival, animals were maintained for at least 3 days to get accustomed to the new environment. At the time of routine monitoring, the animals were checked for any effects of tumor growth on normal behavior such as mobility, food and water consumption (by looking only), body weight gain/loss (body weights were measured twice weekly), eye/hair matting and any other abnormal effect.

Mice were inoculated subcutaneously at the right flank with 4 x 10 ⁶ A375 cells and 4 x 10 ⁵ hPBMCs (co-cultured with A375) or 5 x 10 ⁶ HT29 cells and 1 x 10 ⁶ hPBMCs (co-cultured with HT29) in 0.2ml HBSS contained 0. 1ml matrigel (1: 1) for tumor development. One week after the tumor cell inoculation, mice were injected i.v. with PD-Ll-proIL-2v, PD-l-proIL-2v, or PD-L1 and PD-1 antibodies. The mice in the vehicle group were injected with PBS. Tumor volume were measured in two dimensions using a caliper, and the volumes were expressed in mm ³ using the formula: V = 0.5 a x b ² where a and b are the longest and shortest diameters of the tumor, respectively. The tumor volume was then used for calculations TGI and T/C values. Tumor growth inhibition (TGI%) and relative tumor growth inhibition (T/C%) was calculated according to the following equation:

TGI % = (1 - (Tn - To)/ (Vn- Vo)) x 100%

T/C % = (T _n /T _o )/(V _n /Vo) x 100% In the formula, T _n and V _n stands for tumor volume of treatment group and vehicle control group of day n after the start of treatment, respectively. To and Vo stands for tumor volume of corresponding groups on the day of grouping. Results were analyzed using Prism GraphPad.

As the protease cleavable linkers in P40391942 are the easiest to be cleaved, and the linkers in P40531942 are the hardest to be cleaved, Figures 10A-10B and Table 1 show that in A375-PBMC xenograft model, P40391942 showed the best anti -tumor activity, followed by P40621942 >

P40531942 > P40751942 (anti-PD-Ll antibody). 5/5 and 2/6 of the mice treated with P40391942 and P40621942 respectively showed complete responses.

Figures 11A-11B and Table 2 show that in HT-29-PBMC xenograft model, P40391942 showed the best anti -tumor activity, followed by P40621942 > P40531942 > P40751942. 2/6 of the mice treated with P40391942 showed complete responses.

As the protease cleavable linkers in P41222037 are easier to be cleaved than that of in P43492037, Figures 12A-12B and Table 3 show that in A375-PBMC xenograft model, P41222037 showed better anti-tumor activity than that of P43492037.

Figures 13A-13B and Table 4 show that in HT-29-PBMC xenograft model, P41222037 showed the best anti-tumor activity, followed by P43492037 > P42412037 (anti-PD-1 antibody). 3/6 of the mice treated with P41222037 showed complete responses.

Example 5

In Vivo Efficacy of IgG-proIL-2v with Different Target in A375-PBMC Xenograft Models

The PD-Ll-proIL-2v, PD-l-proIL-2v, and B7H3-proIL-2v were tested alone for their antitumor efficacy in the A375-PBMC xenograft models.

The A375 cells were maintained in vitro in DMEM added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air. The human PBMCs were cocultured with mitomycin C treated A375 tumor cells for 6 days, which maintained in vitro as a suspension cultured in RPMI-1640 added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air.

Female NCG mice aged 8—10 weeks at the start of the experiment (GemPharmatech Co., Ltd., Nanjing, China) were maintained under specific-pathogen-free condition with daily cycles of 12 h light/ 12 h darkness. The mice were kept in individual ventilation cages at constant temperature (20-26 °C) and humidity (40-70%) with <6 animals in each cage. Animals had free access to irradiation sterilized dry granule food and sterile drinking water during the entire study period. All the procedures related to animal handling, care and the treatment in this study were performed according to the guidelines approved by the Institutional Animal Care and Use Committee (IACUC) of Shanghai Viva prior to conduct. After arrival, animals were maintained for at least 3 days to get accustomed to the new environment. At the time of routine monitoring, the animals were checked for any effects of tumor growth on normal behavior such as mobility, food and water consumption (by looking only), body weight gain/loss (body weights were measured twice weekly), eye/hair matting and any other abnormal effect.

Mice were inoculated subcutaneously at the right flank with 4 x 10 ⁶ A375 cells and 4 x 10 ⁵ hPBMCs (co-cultured with A375) in 0.2ml HBSS contained 0.1ml matrigel (1: 1) for tumor development. One week after the tumor cell inoculation, mice were injected i.v. with PD-Ll-proIL- 2v, PD-l-proIL-2v, or B7H3-proIL-2v. The mice in the vehicle group were injected with PBS. Tumor volume were measured in two dimensions using a caliper, and the volumes were expressed in mm ³ using the formula: V = 0.5 a x b ² where a and b are the longest and shortest diameters of the tumor, respectively. The tumor volume was then used for calculations TGI and T/C values. Tumor growth inhibition (TGI%) and relative tumor growth inhibition (T/C%) was calculated according to the following equation:

TGI % = (1 - (T _n - To)/ (V _n - Vo)) ^x 100%

T/C % = (T _n /To)/(Vn/Vo) x 100%

In the formula, T _n and V _n stands for tumor volume of treatment group and vehicle control group of day n after the start of treatment, respectively. To and Vo stands for tumor volume of corresponding groups on the day of grouping. Results were analyzed using Prism GraphPad.

Figures 14A-14B and Table 5 show that both of activated PD-Ll-proIL-2v and PD-l-proIL- 2v mediated dose-dependent anti-tumor efficacy in A375-PBMC xenograft model, and PD-l-proIL- 2v demonstrated a superior efficacy compared to PD-Ll-proIL-2v at dose of O.lmg/kg and 0.3mg/kg.

Figures 15A-15B and Table 6 show that PD-l-proIL-2v mediated superior efficacy compared to B7H3-proIL-2v at dose of 0.3mg/kg in A375-PBMC xenograft model. These data showed that compare to other IgG-proIL-2 which target to PD-L1 or B7H3, PD-l-proIL-2v is more potent inhibitor of the tumor growth.

Example 6

In Vivo Efficacy of PD-Ll-proIL-2v and PD-Ll-proIL-2wt in A375-PBMC Xenograft Models

The PD-Ll-proIL-2v and PD-Ll-proIL-2wt were tested alone for their anti-tumor efficacy in the A375-PBMC xenograft models.

The A375 cells were maintained in vitro in DMEM added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air.

Female NCG mice aged 8—10 weeks at the start of the experiment (GemPharmatech Co., Ltd., Nanjing, China) were maintained under specific-pathogen-free condition with daily cycles of 12 h light/ 12 h darkness. The mice were kept in individual ventilation cages at constant temperature (20-26 °C) and humidity (40-70%) with <6 animals in each cage. Animals had free access to irradiation sterilized dry granule food and sterile drinking water during the entire study period. All the procedures related to animal handling, care and the treatment in this study were performed according to the guidelines approved by the Institutional Animal Care and Use Committee (IACUC) of Shanghai Viva prior to conduct. After arrival, animals were maintained for at least 3 days to get accustomed to the new environment. At the time of routine monitoring, the animals were checked for any effects of tumor growth on normal behavior such as mobility, food and water consumption (by looking only), body weight gain/loss (body weights were measured twice weekly), eye/hair matting and any other abnormal effect.

Mice were inoculated subcutaneously at the right flank with 4 x 10 ⁶ A375 cells and 4 x 10 ⁵ hPBMCs in 0.2ml HBSS contained 0.1ml matrigel (1: 1) for tumor development. One week after the tumor cell inoculation, mice were injected i.v. with PD-Ll-proIL-2v, or PD-Ll-proIL-2wt. The mice in the vehicle group were injected with PBS. Tumor volume were measured in two dimensions using a caliper, and the volumes were expressed in mm ³ using the formula: V = 0.5 a x b ² where a and b are the longest and shortest diameters of the tumor, respectively. The tumor volume was then used for calculations TGI and T/C values. Tumor growth inhibition (TGI%) and relative tumor growth inhibition (T/C%) was calculated according to the following equation:

TGI % = (1 - (Tn - To)/ (Vn- Vo)) x 100%

T/C % = (Tn/To)/(Vn/Vo) X 100% In the formula, T _n and V _n stands for tumor volume of treatment group and vehicle control group of day n after the start of treatment, respectively. To and Vo stands for tumor volume of corresponding groups on the day of grouping. Results were analyzed using Prism GraphPad.

Figures 16A-16B and Table 7 show that both of PD-Ll-proIL-2v and PD-Ll-proIL-2wt mediated anti-tumor efficacy in A375-PBMC xenograft model, and PD-Ll-proIL-2wt demonstrated a superior efficacy compared to PD-Ll-proIL-2v at dose of 0.3mg/kg.

Example 7

In Vivo Efficacy of PD-l-proIL-2v and Anti-PD-Ll Antibody as Single Agents and in Combination in A375-PBMC Xenograft Models

The PD-l-proIL-2v and anti-PD-Ll antibody were tested in comparison to their combination for their anti-tumor efficacy in the A375-PBMC xenograft models.

The A375 cells were maintained in vitro in DMEM added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air. The human PBMCs were cocultured with mitomycin C treated A375 tumor cells for 6 days, which maintained in vitro as a suspension cultured in RPMI-1640 added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air.

Female NCG mice aged 8—10 weeks at the start of the experiment (GemPharmatech Co., Ltd., Nanjing, China) were maintained under specific-pathogen-free condition with daily cycles of 12 h light/ 12 h darkness. The mice were kept in individual ventilation cages at constant temperature (20-26 °C) and humidity (40-70%) with <6 animals in each cage. Animals had free access to irradiation sterilized dry granule food and sterile drinking water during the entire study period. All the procedures related to animal handling, care and the treatment in this study were performed according to the guidelines approved by the Institutional Animal Care and Use Committee (IACUC) of Shanghai Viva prior to conduct. After arrival, animals were maintained for at least 3 days to get accustomed to the new environment. At the time of routine monitoring, the animals were checked for any effects of tumor growth on normal behavior such as mobility, food and water consumption (by looking only), body weight gain/loss (body weights were measured twice weekly), eye/hair matting and any other abnormal effect. Mice were inoculated subcutaneously at the right flank with 4 x 10 ⁶ A375 cells and 4 x 10 ⁵ hPBMCs (co-cultured with A375) in 0.2ml HBSS contained 0.1ml matrigel (1: 1) for tumor development. One week after the tumor cell inoculation, mice were injected i.v. with PD-l-proIL-2v, anti-PD-Ll antibody or the combination of PD-l-proIL-2v + PD-L1. The mice in the vehicle group were injected with PBS. Tumor volume were measured in two dimensions using a caliper, and the volumes were expressed in mm ³ using the formula: V = 0.5 a x b ² where a and b are the longest and shortest diameters of the tumor, respectively. The tumor volume was then used for calculations TGI and T/C values. Tumor growth inhibition (TGI%) and relative tumor growth inhibition (T/C%) was calculated according to the following equation:

TGI % = (1 - (T _n - To)/ (V _n - Vo)) ^x 100%

T/C % = (T _n /To)/(Vn/Vo) x 100%

In the formula, T _n and V _n stands for tumor volume of treatment group and vehicle control group of day n after the start of treatment, respectively. To and Vo stands for tumor volume of corresponding groups on the day of grouping. Results were analyzed using Prism GraphPad.

Figures 17A-17B and Table 8 show that the combination of PD-l-proIL-2v and PD-L1 mediated superior efficacy compared to either of the monotherapy in A375-PBMC xenograft model, and all the tumors in the combination group were complete response.

Example 8 Pharmacokinetics and Pharmacodynamics Study of PD-l-proIL-2v

The PD-l-proIL-2v was tested for the pharmacokinetics and pharmacodynamics in peripheral blood and tumors.

The A375 cells were maintained in vitro in DMEM added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air. The human PBMCs were cocultured with mitomycin C treated A375 tumor cells for 6 days, which maintained in vitro as a suspension cultured in RPMI-1640 added with 10% FBS, lOOU/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5% CO2 in air. Female NCG mice aged 8—10 weeks at the start of the experiment (GemPharmatech Co., Ltd., Nanjing, China) were maintained under specific-pathogen-free condition with daily cycles of 12 h light/ 12 h darkness. The mice were kept in individual ventilation cages at constant temperature (20-26 °C) and humidity (40-70%) with <6 animals in each cage. Animals had free access to irradiation sterilized dry granule food and sterile drinking water during the entire study period. All the procedures related to animal handling, care and the treatment in this study were performed according to the guidelines approved by the Institutional Animal Care and Use Committee (IACUC) of Shanghai Viva prior to conduct. After arrival, animals were maintained for at least 3 days to get accustomed to the new environment. At the time of routine monitoring, the animals were checked for any effects of tumor growth on normal behavior such as mobility, food and water consumption (by looking only), body weight gain/loss (body weights were measured twice weekly), eye/hair matting and any other abnormal effect.

For the pharmacokinetics study, mice were inoculated subcutaneously at the right flank with 4 x 10 ⁶ A375 cells and 4 x 10 ⁵ hPBMCs in 0.2ml HBSS contained 0.1ml matrigel (1: 1) for tumor development. 18 days after the tumor cell inoculation, mice were injected i.v. with Img/kg PD-1- proIL-2v. Blood and tumor samples were collected after dose at Ihr, 6hrs, 24hrs, 48hrs, 72hrs, 96hrs, 120hrs and 168hrs. Blood samples will be centrifuged to obtain serum samples (6000rpm, 5min, 4°C) within 30 minutes of collection. Serum samples were stored at -80°C before use. Tumors were weighed, then add twice volume PBS of the tumor weight, homogenized the tissues on ice. The homogenates were then centrifuged at 6000rpm, lOmin, 4°C, supernatant were collected, and stored at -80°C before use.

Total drug (including intact procytokine and cleaved cytokine) and procytokine (intact procytokine) were determined using ELISAs utilizing PD- 1 as the capture antibody and various detection antibodies. HRP conjugated anti -human IgG or anti-IL-2Ra were utilized to detect total cytokine and procytokine levels, respectively. The levels of cleaved cytokine (activated cytokine) were calculated by subtracting procytokine from total drug concentrations.

Figure 18A and Table 9 show that the concentrations of the total drug and procytokine of P41222037 in serum were almost the same, and there was no significant difference in the pharmacokinetics parameters of the total drug and procytokine in serum, which means the P41222037 was very stable in the peripheral blood. Figures 18B-18C show that the intratumoral concentration of total drug and procytokine of P41222037 was peaked at 6 hrs, and the intratumoral concentration of procytokine was lower than that of total drug 48hrs later (Fig. 18B), which means the P41222037 was cleaved in tumor and released the activated cytokine (18C).

For the pharmacodynamics study in peripheral blood, mice were injected i.v. with 5 x 10 ⁶ hPBMC cells. 14 days later, 4 x 10 ⁶ A375 cells in 0.2ml HBSS contained 0.1ml matrigel (1: 1) were inoculated into the right flank of the mice subcutaneously for tumor development. One week after the tumor cell inoculation, mice were injected i.v. with Img/kg PD-l-proIL-2v. The mice in the vehicle group were injected with PBS.

Anticoagulant blood were collected at Ohr, 72hrs, 168hrs, 240hrs, and 336hrs, lysed with red cell lysing buffer. Cells were stained with stain buffer including CD45 (clone HI30, BioLegend), CD3 (clone UCHT1, BioLegend), CD4 (clone RPA-T4, BD Pharmingen), CD8 (clone HIT8a, BioLegend) for 30min at 4°C. Samples were analyzed using a flow cytometer (CytoFLEX S, Beckman coulter) gating on CD45 ⁺ CD3 ⁺ cells (CD3 T cells), CD45 ⁺ CD3 ⁺ CD4 ⁺ cells (CD4 T cells) and CD45 ⁺ CD3 ⁺ CD8 ⁺ cells (CD8 T cells).

Figures 19A-19C show that compared with vehicle control, CD3 ⁺ , CD4 ⁺ , and CD8 ⁺ T cells from the P41222037 Img/kg treatment group had no significant difference or increase overtime in peripheral blood.

For the pharmacodynamics study in tumors, mice were inoculated subcutaneously at the right flank with 4 x 10 ⁶ A375 cells and 4 x 10 ⁴ hPBMCs (co-cultured with A375) in 0.2ml HBSS contained 0.1ml matrigel (1: 1) for tumor development. 18 days afterthe tumor cell inoculation, mice were injected i.v. with Img/kg PD-l-proIL-2v. The mice in the vehicle group were injected with PBS.

At day 12, tumors were collected, weighed, and dissociated using a validated tumor dissociation kit (Miltenyi Biotec) according to the protocol. Then cell suspension were filtered through a 70pm cell strainer. The tumor cells were stained with live/dead (Live/Dead Horizon Fixable Viability Stain 700, BD Pharmingen, for 15min) in PBS, then cells were stained with stain buffer including CD45 (clone HI30, BioLegend), CD3 (clone UCHT1, BioLegend), CD4 (clone RPA-T4, BD Pharmingen), CD8 (clone HIT8a, BioLegend) for 30min at 4°C. Samples were analyzed using a flow cytometer (CytoFLEX S, Beckman coulter) gating on CD45 ⁺ CD3 ⁺ cells (CD3 T cells), CD45 ⁺ CD3 ⁺ CD4 ⁺ cells (CD4 T cells) and CD45 ⁺ CD3 ⁺ CD8 ⁺ cells (CD8 T cells).

Figures 20A-20C show that compared with vehicle control, CD3 ⁺ , CD4 ⁺ and CD8 ⁺ T cells from the P41222037 Img/kg treatment group were all increased at the tumor site.

In summary, these data show that the PD-l-proIL-2v fusion protein P41222037 was very stable, little activated cytokine released in peripheral blood (reduced the toxicity), and could be cleaved in tumors, released the activated cytokine to stimulate the proliferation of CD3 ⁺ , CD4 ⁺ , and CD8 ⁺ T cells, which reduced the toxicity in peripheral blood, and selectively enhanced the anti-tumor activity in the TME. Example 9 Bioactivity of PD-l-proIL-2v in cynomolgus monkeys

The in vivo bioactivity of the masked or unmasked PD-l-proIL-2v was assessed in vivo in cynomolgus monkeys.

To test the safety profde and pharmacodynamics of PD-l-proIL-2v (P41222037) in cynomolgus monkeys, a dose ranging study was performed. Each group, including 1 male and 1 female cynomolgus monkey, received a 5 repeat dose of P41222037 (masked PD-l-proIL-2v) at 3, 10, and 30 mg/kg or P41252037 (unmasked PD-l-proIL-2v) at Img/kg.

Blood samples for pharmacodynamics study were collected before dosing and 5min, Ih, 6hrs, 24hrs, 48hrs, 72hrs, 96hrs, 120hrs, and 168hrs after the 1 ^st dosing. The concentration of P41222037 was determined using ELISAs utilizing PD-1 as the capture antibody and anti-IL-2Ra as the detection antibody. The concentration of P41252037 was determined using ELISAs utilizing PD-1 as the capture antibody and HRP conjugated anti-human IgG as the detection antibody.

Figure 21A shows that the concentrations of P41222037 in serum in cynomolgus monkeys were demonstrated dose-dependent procytokine exposure, and compared to the unmasked PD-1- proIL-2v (P41252037), the T1/2 of the masked PD-l-proIL-2v (P41222037) was longer.

Blood samples for serum chemistry were collected before dosing and 4, 11, 18, 25, and 30 days post-dosing. An automated hematology analyzer was used to monitor the changes in albumin. Figure 21B shows that compared to the vehicle control, there was no significant decrease in albumin level in cynomolgus monkeys treated with P41222037 at 3, 10, and 30 mg/kg. All the monkeys were well tolerant at all three dose of P41222037.

Example 10

Effect of Linker Length and Alterations on Immune Cell Stimulation

Experiments were performed to test the effects of stable linker length (between Fc and IL-2) on the activity of proproteins and activated proteins on cell proliferation and towards specific immune cell subsets. The constructs tested include P41222037 (four amino acid stable linker), P45412037 (eight amino acid stable linker), and P45422037 (12 amino acid stable linker), with and without MMP-2 protease treatment, compared to human IL-2. Figure 26 shows the heavy chain/IL-2 junction of the constructs tested.

Proliferation ofM-07e with PDl-proIL-2v. Human M-07e cells (expressing human IL-2RPy) were cultured in RPMI 1640 supplemented with 20% fetal bovine serum (FBS) and 10% of 5637 cells culture supernatant. To measure cytokine-dependent cell proliferation, M-07e cells were harvested in their logarithmic growth phase and washed twice with PBS. 90pl of cell suspension (2x 10 ⁴ cells/well) was seeded into 96-well plate and incubated for 4 hours in assay medium (RPMI 1640 supplemented with 10% FBS) for cytokine starvation at 37°C and 5% CO2. IL-2, PDl-proIL-2v (P41222037, P45412037 and P45422037) or MMP-2 cleaved PDl-proIL-2v protein samples used in assays were prepared in assay medium to an initial concentration (300 nM for IL-2, 8100 nM for PDl-proIL-2v and 2700 nM for MMP-2 activated PDl-proIL-2v fusion proteins), followed by 1/3 serial dilutions. lOpl diluted protein was added into corresponding wells and incubated at 37°C and 5% CO2 for 72 hours. Colorimetric assays using a Cell Counting Kit-8 (CCK-8, Dojindo, CK04) were performed to measure the amount of live cells.

As shown in Figure 22A, the P41222037 proprotein was not able to induce proliferation of M-07e even at the highest concentration tested; MMP-2 cleavage restored the biological activity of P41222037, but the activity was approximately 30 fold lower relative to wild type IL-2. As shown in Figures 22B-22C, the P45412037 and P45422037 proproteins had no activity at the highest concentration of 810 nM; MMP-2 cleavage restored the activity of P45412037 or P45422037, but the activity was approximately 34-fold or 25-fold lower activity relative to wild type IL-2, respectively.

STAT5 phosphorylation upon treatment with PD-l-proIL2 on resting human PBMC. Frozen human PBMCs (SAILYBIO, donor 1) were recovered in RPMI-1640 added with 10 % FBS, 100 U/ml penicillin and 100 pg/ml streptomycin at 37°C in an atmosphere of 5 % CO2 for ~2 hours. PBMC cells were then adjusted at 2.6 x 10 ⁶ cells/ml, and plated at 4 x 10 ⁵ cells per well into 96-well plate. Recovered PBMCs were incubated for 15 min at 37 °C with rhIL-2, P41222037, PD-l-proIL-2v linker length variants, or MMP-2 activated proteins.

After incubation, cells were immediately fixed with Cytofix buffer (BD Bioscience) to preserve the phosphorylation status for 15 min on ice and wash once with BD Pharmingen™ Stain Buffer (FBS). For surface staining, cells were incubated with CD3 Alexa Flour 700 (BD 557943), CD4 PerCP-Cytm5.5(BD 560650), CD8 APC-Cytm7 (BD 557760), CD25 BV421(BD562442), CD56 BV510 (BD 744218) for 30min at 4°C, washed once with IX PBS, centrifuged at 500g for 5min, and the supernatants were removed by aspiration. Cells were then permeabilized with pre-cold Phosflow Perm buffer III (BD Bioscience) for 30 min at 4°C.

Before beginning the intracellular staining, the cells were washed once with IX PBS and centrifuge cells at 500g for 5min and the cell pellets were collected. The cells were then stained with Foxp3 PE (BD 560046) and Anti-Stat5 (pY694) Alexa Fluor® 647 (BD 562076) for 40min at room temperature. Cells were washed twice with BD Pharmingen™ Stain Buffer (FBS) and centrifuged at 500g for 5min to pellet the cells. Each cell pellet was resuspended in 200ul (per well) BD Pharmingen Stain Buffer (FBS) and data was acquired using a flow cytometry. STAT5 phosphorylation status in PBMC subsets upon pro-drug treatments was acquired and processed by CytoFLEX (Beckman).

Figure 23A shows STAT phosphorylation in CD4 T-cells, CD8 T-cells, and regulatory T- cells upon treatment of resting PBMCs of donor 1 with rhIL-2 as well as intact and activated P41222037. The intact P41222037 proprotein at a concentration as high as 1000 nM was unable to induce STAT5 phosphorylation in all tested cell subsets. The protease-activated form of P41222037 (MMP-2 cleavage) was equally effective in inducing STAT5 phosphorylation in CD8 and CD4 T cells. In Treg cells, however, the activated form of P41222037 was about 30-times less potent than huIL-2. Figures 23B-23C show STAT5 phosphorylation in CD4 T cells, CD8 T cells, and Tregs upon treatment of resting PBMC with intact and MMP2 -cleaved P45412037 or P45422037 in comparison to human recombinant IL-2. Figure 23D shows that unlike P41222037, both intact P45412037 and P45422037 induced STAT5 phosphorylation in CD4 T and regulatory T cells, but not in CD8 T cells.

Figures 24A-24C show the activity of additional proprotein constructs in this assay (see Figure 26). In comparison to human recombinant IL-2, the intact P78192037 and P78342037 proproteins were unable to induce STAT5 phosphorylation in all tested cell subsets. Surprisingly, the intact P78362037 proprotein had significant activity on STAT5 phosphorylation in CD4 T and regulatory T cells, but not in CD8 T cells; and the intact P78352037 proprotein had weaker activity on STAT5 phosphorylation in CD4 T and regulatory T cells. The intact proproteins of P78192037, P78202037, P78212037, P78222037, P78232037, P78242037, P78252037, P78262037, P78272037, P78282037, P78292037, P78302037, P78312037, P78322037, P78332037, and P78342037 did not show activity on STAT5 phosphorylation in CD4 T cells and regulatory T cells.

STAT5 phosphorylation upon treatment with PD-l-proIL2 on pre-activated human PBMC. Frozen human PBMCs (SAILYBIO, donor 1) were recovered in RPMI-1640 added with 10 % FBS, 100 U/ml penicillin and 100 pg/ml streptomycin at 37 °C in an atmosphere of 5 % CO2 for 2 hours. For assays performed in pre-activated PBMC, a 10-cm plate was coated with aCD3 (1 pg/ml, BioLegend) overnight at 4°C. PBMCs suspended in RPMI1640 with addition of soluble aCD28 (1 pg/ml, BioLegend) were cultured for 3 days at 37°C in an atmosphere of 5 % CO2. pre-activated PBMCs were adjusted at cell density of 2.6 x 10 ⁶ cells/ml, and 4 x 10 ⁵ cells/well were plated into 96- well plate.

After incubation with rhIL-2 or P41222037 for 15 min at 37 °C, cells were immediately fixed with Cytofix buffer (BD Bioscience) to preserve the phosphorylation status for 15 min on ice and wash once with BD Pharmingen™ Stain Buffer (FBS). For surface staining, cells were incubated with CD3 Alexa Flour 700 (BD 557943), CD4 PerCP-Cytm5.5 (BD 560650), CD8 APC-Cytm7 (BD 557760) and CD25 BV421 (BD562442) for 30 min at 4°C. Cells were washed once with IX PBS and centrifuge cells at 500 g for 5 min. Cells were permeabilized with pre-chilled Phosflow Perm buffer III (BD Bioscience) for 30 min at 4°C.

Before the intracellular staining, cells were washed once with IX PBS and centrifuged at 500 g for 5 min. The cells were then stained with Foxp3 PE (BD 560046) and Anti-Stat5 (pY694) Alexa Fluor® 647 (BD 562076) for 40 min at RT. Cells were washed twice with BD Pharmingen™ Stain Buffer (FBS) and centrifuged at 500 g for 5 min. Finally, each cell pellet was resuspended in 200 ul (per well) BD Pharmingen Stain Buffer (FBS) for data FACS data acquisition using a flow cytometry. STAT5 phosphorylation status in PBMC subsets upon pro-drug treatments was acquired and processed by CytoFLEX (Beckman). Figure 25 shows STAT phosphorylation in CD4 T-cells, CD8 T-cells, and Treg cells upon treatment of pre-activated PBMCs of donor 1 with rhIL-2 or P41222037. The intact P41222037 proprotein up to 300nM did not induce STAT5 phosphorylation in all tested cell subsets.

Overall, constructs such as the P41222037 proprotein with shorter stable linkers (e.g., 7 amino acids or fewer) between Fc and IL-2 do not stimulate immunosuppressive CD4 T _reg , and certain other immune cells in their proprotein form, and are thus unexpectedly useful relative to constructs with longer stable linkers (e.g., 8 amino acids or more) for treating disease such as cancers, which benefit from highly-controlled activation of anti-tumor immune cell responses.