Cross Reference

This application claims priority to U.S. Provisional Patent Application Serial No. 62/696142 filed My 10, 2019, incorporated by reference herein it is entirety.

Statement of Government Support

This invention was made with government support under Grant # A1123131 awarded by the National Institutes of Health. The government has certain rights in the invention.

Background

T cell immune responses are tightly controlled by co-stimulatory and co-inhibitory molecules. The co-stimulatory molecules contribute to the development of immune responses against cancers and foreign pathogens, while the co-inhibitory molecules are critical for peripheral tolerance to avoid autoimmunity, GVHD and transplant rejection.

Summary

In one aspect, the disclosure provides methods for treating cancer, comprising administering to a subject in need thereof an antibody that selectively binds to a protein selected from the group consisting of CD300c, BTN5 (Erythroid membrane-associated protein), TAPBPL (antigen processing (TAP) binding protein like protein), Skint8 (selection and upkeep of intraepithelial T cells 8 protein), and/or CD300f in an amount effective to treat the cancer. In various embodiments, the antibody selectively binds to an extracellular domain (ECD) of CD300c, BTN5, TAPBPL, SkintS, and/or CD300f. In other embodiments, the antibody selectively binds to an IgV domain of CD300c, BTN5, TAPBPL, SkintS, and/or CD300f.

In another aspect, the disclosure provides an isolated anti-human CD300c antibody, or fragment thereof, comprising 1, 2, 3, 4, 5, or all 6 complementarity determining regions (CDRs) selected from the group consisting of:

Heavy chain CDR1 (H-CDR.1) comprising the amino acid sequence at least 80%,

85%, 90%, 95%, or 100% identical to the amino acid sequence IYGMN (SEQ ID NO: 10); Heavy chain CDR2 (H-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence WINTYT (SEQ ID NO: 11);

Heavy chain CDR3 (H-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence ARSRFAY (SEQ ID NO: 12).

Light chain CDR1 (L-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence KASQNVGTNVA (SEQ ID NO: 13);

Light chain CDR2 (L-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence SASYRYS (SEQ P) NO: 14); and Light chain CDR3 (L-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence QQYNSYPLT (SEQ ID NO: 15).

In one embodiment, the isolated anti-human CD300c antibody, or fragment thereof, comprises (a) a heavy chain comprising the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO: 16;

and/or

(b) a light chain comprising the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO: 17.

In a further aspect, the disclosure provides an isolated anti-human TAPBPL antibody, or fragment thereof, comprising 1, 2, 3, 4, 5, or all 6 complementarity determining regions (CDRs) selected from the group consisting of:

Heavy chain CDR1 (H-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the ammo acid sequence GYFWH (SEQ ID NO: 18);

Heavy chain CDR2 (H-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence YISYSGTTNYNPSLKN (SEQ ID NO: 19);

Heavy chain CDR3 (H-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence DDWDWFAY (SEQ ID NO:20);

Light chain CDR1 (L-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence SASSSVNYMH (SEQ ID NO:21); Light chain CDR2 (L-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence DTSKLAS (SEQ ID NO:22); and Light chain CDR3 (L-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence FQGSGYPLT (SEQ ID NO:23).

In one embodiment, the isolated anti-human TAPBPL antibody, or fragment thereof, comprises a heavy chain comprising the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:24:

and/or

(b) a light comprising the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:25.

In various embodiments, the antibody comprises a monoclonal antibody, or fragment thereof; the antibody comprises a humanized antibody, or fragment thereof; the antibody or fragment thereof further comprises a detectable label; and/or the isolated antibody or fragment thereof further comprises a therapeutic agent, including but not limited to a chemotherapeutic, conjugated to the antibody or fragment thereof.

In one aspect, the disclosure provides a method for treating an autoimmune disorder, comprising administering to a subject in need thereof an amount effective to treat the autoimmune disorder of one or more of:

(a) an IgV domain from a protein selected from the group consisting of CD300c, BTN5, TAPBPL, Skint8, and CD300f; and/or

(b) an expression vector comprising a promoter operatively linked to a nucleic acid sequence encoding a protein selected from the group consisting of CD300c, BTN5, TAPBPL, Skint8, and CD300f. In one embodiment, the autoimmune disease is selected from the group consisting of multiple sclerosis, type I diabetes, arthritis including but not limited to rheumatoid arthritis, systemic lupus erythematosus, Crohn’s disease, scleroderma, sarcoidosis, ulcerative colitis, ankylosing spondylitis, autoimmune hepatitis, autoimmune myocarditis, dermatomyositis, Graves’ disease, Sjogren’s syndrome, and vitiligo, and other autoimmune diseases. In a further embodiment, the method further comprises administering to the subject an amount effective of an immune regulator to stimulate T cell function, including but not limited to anti-CD3 antibodies.

In another aspect, the disclosure provides a fusion molecule comprising (a) a first polypeptide comprising an IgV domain from a protein selected from the group consisting of CD300c, BTN5, TAPBPL, Skint8, and CD300f; and

(b) a heterologous molecule.

In one embodiment, the first polypeptide does not include any portion of CD300c, BTN5, TAPBPL, SkintS, or CD300f outside of the ECM domain. In another embodiment, the heterologous molecule comprises a second polypeptide selected from the group consisting of a constant region of an immunoglobulin or a fragment thereof (including but not limited to CHI, CH2, and/or CH3; and Fc regions from immunoglobulins, including but not limited to native IgGl, IgG2, or IgG4). In another embodiment, the heterologous molecule comprises an organic molecule of interest.

In another aspect, the disclosure provides nucleic acids encoding the fusion molecule, wherein the heterologous molecule is a second polypeptide, or the antibodies of the disclosure. In other aspects, the disclosure provides expression vectors comprising the nucleic acids operatively linked to a promoter, and recombinant host cell comprising the nucleic acid and/or expression vectors.

Description of the Figures

Figure 1. The effects of hCD300c-Ig protein on the proliferation and activation of mouse and human T cells in vitro. (A, B) T cells were isolated from the spleen of C57BL/6 mice and cultured with (A, B) plate-bound anti-CD3 antibody ( 1 mg/ml) and (B) anti-CD28 antibody (0.5mg/ml) in the presence of graded doses of hCD300c-Ig protein (800, 1600, and 3200 ng/ml) or equimolar amounts of control Ig protein for 3 days. Cell proliferation was measured by [^H] thymidine incorporation. (C-F) Mouse splenic cells were labelled with CFSE and cultured with anti-CD3 antibody (1 mg/ml) and graded doses of hCD300c-Ig protein (1600, and 3200 ng/ml) or equimolar amounts of control Ig protein for 3 days. The cells were stained with anti-CD4 and CDS antibodies, and analyzed for

CFSE levels by CD4 ⁺ and CD8 ⁺ T cells. (C, E). Representative flow cytometric profiles, and (D, F) statistical analysis of CFSE* ⁰ proliferating CD4 ⁺ or CD8 ⁺ T cells. (G-J) Mouse splenic cells were cultured with anti-CD3 antibody and graded doses of hCD300c-Ig protein or control Ig protein as (C) for 24 hours. The cells were then analyzed for CD69 expression by CD4 ⁺ and CD8 ⁺ T cells. (G, I) Representative flow cytometric profiles, and (H, J) statistical analysis of CD69 ⁺ cells in CD4 ⁺ or CD8 ⁺ T cells. (K) Purified human CD3 ⁺ T cells were cultured with plate-bound anti-human CDS antibody (1 mg/ml) in the presence of graded doses of hCD300c-Ig protein (1500, and 3000 ng/ml) or control Ig protein for 3 days. Cell proliferation was measured by [¾] thymidine incorporation. (L,

M) Purified human CD3 ⁺ T cells were cultured with plate-bound anti-human CD3 antibody (1 mg/ml) in the presence of graded doses of hCD300c-Ig protein (1600, and 3200 ng/ml) or control Ig protein for 1 days. The cells were then analyzed for human CD69 expression by CD4 ⁺ and CD8 ⁺ T cells. The data were pooled from 3 independent experiments and expressed as mean +JSD. * PO.05 compared with control Ig.

Figure 2. The effects of mCD300c-Ig protein on the proliferation and activation of mouse T cells in vitro. (A, B) CD3 ⁺ T cells were isolated from the spleen of C57BL/6 mice and cultured with (A, B) plate-bound anti-CD3 antibody (1 mg/ml) and (B) anti-CD28 antibody (0.5 mg/ml) in the presence of graded doses of mCD300c2-Ig protein (800, 1600, and 3200 ng/ml) or equimolar amounts of control Ig protein for 3 days. Cell proliferation was measured by [^H] thymidine incorporation. (C-F) Mouse splenic cells were labelled with CFSE and cultured with anti-CD3 antibody ( 1 mg/ml) and graded doses of mCD300c2- Ig protein or control Ig protein as (A). The cells were then stained with anti-CD4 and CDS antibodies and analyzed for CFSE levels by CD4 ⁺ and CD8 ⁺ T cells. (C, E) Representative flow cytometric analysis of CFSE distribution of CD4 ⁺ or CD8 ⁺ T cells. (D, F) statistical analysis of CFSE^ ⁰ proliferating CD4 ⁺ or CD8 ⁺ T cells. (G-Q) Mouse splenic cells were cultured wife (G-Q) anti-CD3 antibody and (I, L) anti-CD28 antibody in the presence of graded doses of mCD300c2-Ig or control Ig protein as (A, B). The cells were analyzed for the expression of (G-L) CD6924 hours later, (M-Q) CD44 and CD62L 72 hours later. (G, J, M) Representative flow cytometric profiles, and (H, I, K, L, N-Q) statistical analyses of the percentages of CD69 ⁺ , CD44^ ^0W CD62L^' naive, and CD44^CD62L ^low effector memory CD4 and CDS T cells. The data were pooled from 3 independent experiments and expressed as mean +_SD. * PO.05 compared with control Ig.

Figure 3. mCD300c2 suppresses cytokine production from T cells. Purified murine T cells were cultured with plate-bound anti -CDS antibody (1 mg/ml) in the presence of graded doses of mCD300c2-Ig protein or control Ig protein for 3 days as Figure 3A. The levels of IFNy, TNFo, IL-2, IL-17A and IL-10 in the supernatant were measured by ELISA kits. The data were pooled from 3 independent experiments and expressed as mean +_SD. * P<0.05 compared with control Ig.

Figure 4. Analysis of the expression of mCD300c2 on immune cells. Splenocytes from C57BIV6 mice were freshly harvested and used for resting immune cells. To initiate T cell activation, splenocytes were incubated with anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/rnl) antibodies for 3 days. For activated B cells, DCs, monocytes and macrophages, splenocytes were incubated with LPS (10 mg/ml) for 3 days. The resting and activated immune cells were stained with anti- mCD300c2 antibody (Ab) (open histograms) or isotype Ab (shaded histograms), as well as anti- CD4, CDS, B220, CD 11c, CD 1 lb, or F4/80 Ab to identify immune cells. (A) Representative flow cytometric profiles and (B) statistical analysis showing the expression of mCD300c2 on resting and activated immune cells. (B) The data were pooled from 3 independent experiments and presented as relative fluorescence intensity (RFI) for the expression of mCD300c2 on activated cells versus resting cells. * P<0.05 compared with isotype Ab. ** P<0.05 compared with resting cells. (C) Immunohistochemical analysis of hCD300c expression in normal and tumor human tissues by immunohistochemistry using an anti-hCD300c Ab. The data are representative of 3 independent experiments.

Figure 5. The expression pattern of the putative mCD300c2 counter-receptor. (A, B) Murine resting and activated immune cells were harvested or generated as in Figure 5 A. The cells were stained with biotinylated mCD300c2-Ig (open histograms) or control Ig (shaded histograms), followed by streptavidin-PE. The binding of mCD300c2 to its putative receptor on immune cells was determined by flow cytometry. (A) Representative flow cytometric profiles and (B) statistical analysis showing the binding of mCD300c2-Ig or control Ig to resting and activated immune cells. (B) Data are presented as relative fluorescence intensity (RFI) for cell binding of mCD300c2-lg versus control Ig. The data were pooled flora 3 independent experiments. (A, B) * P<0.05 compared with control Ig. ** PO.05 compared with resting cells. (C, D) HEK-293 cells were transfected with an expression vector containing the mouse CD28, CTLA-4, PD-1, BTLA, or ICOS gene. The transfected cells were stained with (C) antibodies against the respective CD28, CTLA-4, PD-1, BTLA, or ICOS protein (open histograms) or isotype Ab (shaded histograms), or (D) biotinylated mCD300c2-Ig (open histograms) or control Ig protein (shaded histograms), and analyzed by flow cytometry. Representative flow cytometric profiles showing the binding of (A, D) mCD300c-Ig or control Ig, or (C) indicated antibodies to (A) resting and activated immune cells, or (C, D) transfected HEK-293 cells. Figure 6. hCD300c-Ig ameliorates GVHD in mice. Lethally irradiated BALB/c recipients were injected i.v. with 5X10^ BM and 2.5X10^ spleen cells from C57BL/6 mice at day 0 and i.p. with 20 mg hCD300c-Ig, or control Ig every 3 days for 6 times . (A-C) Recipients were monitored for (A) survival, (B) weight change, and (C) clinical GVHD. (D, E) In separate experiments, recipients given 20 mg hCD300c-Ig or control Ig at 3-day intervals from days 0-12 were euthanized 2 weeks after BMT. (D, E) The liver, SI and lung were analyzed for histologic damage. (D) Representative photomicrographs (the magnification was X200), and (E) mean ofhistopathology scores. (F-M) hCD300c-Ig

inhibits T-cell proliferation and activation in response to alloantigens in vivo. Lethally irradiated BALB/c mice were injected i.v. with 5X10 ^b BM 10X10 ^b splenic cells from C57BL/6 mice. The recipients were injected i.v. on day 0 and i.p. on day 2 with 20 mg hCD300c-Ig, or control lg. On Day 4 post-transplant, the percentage of (F-I) KΪ67 , (J, K)

CD44 ^hi , and (L, M) CD62L ¹⁰ cells in donor T cells (H2 ^b+ CD4 ⁺ , or H2 ^b+ CD8 ⁺ ) of the spleens were examined by flow cytometry. (F, H, J, L) Representative flow cytometric profiles and (G, I, K, M) statistical data are shown. (J, L) Dash lines: control Ig; solid lines: hCD300c. Pooled data from 2 separate experiments are represented; with 5-6 mice per group in each experiment. * P<0.05 compared with control lg-treated mice.

Figure 7: hCD300c-Ig attenuates autoimmune diseases EAE and CIA in mice. (A) C57BL/6 mice were immunized with 200 mg MOG35-55 emulsified in CFA and 500 ng of purified Bordetella pertussis toxin. The mice were injected i.p. with 25 mg hCD300c-Ig or control Ig protein 3 times per week for 5 weeks. EAE development was monitored. (B) DBA/1 mice were injected s.c. with the emulsion of CII in CFA on day 0. On day 14, tire mice will receive a booster injection of the CII/IFA emulsion. When CIA symptom occurred (day 48), the mice were injected i.p. with 25 mg hCD300c-Ig, or control Ig once every 3 days for 6 times. The CIA clinical scores were measured over time. Mean clinical scores are shown.

Figure 8. In vivo administration of anti-hCD300c mAh inhibits local growth of melanoma and colon cancer. (A-E) BALB/c mice were injected s.c. with 2x10 ^s CT-26 colon cancer cells, followed by injections with anti-hCD300c mAb or isotype antibody control into the tumor injection site 3 times each week. Tumor sizes were measured over time. (A) The mean tumor volume (mm ³ ) +.S.D. at the indicated time points are shown. (B-E) At the end of studies, the mice were euthanized and the colon tumors were removed. Single-cell suspensions from the tumors were analyzed by flow cytometry for the percentages of (B, C)

CD4 ⁺ and (D, E) CD8 ⁺ T cells. (F) C57BL/6 mice were injected s.c. with lxlO^ B16F10 melanoma cells followed by intratumoral injections with anti-hCD300c mAb or isotype antibody control three times a week. Tumor sizes were measured over time.

Figure 9. The expression patterns of TAPBPL protein. (A, B) Analysis of TAPBPL protein expression on immune cells. Splenocytes from C57BL/6 mice were freshly harvested and analyzed for TAPBPL protein expression on resting immune cells. To obtain activated T cells, the splenocytes were incubated with anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/ml) antibodies for 3 days. To obtain activated B cells, DCs, monocytes and macrophages, the splenocytes were incubated with LPS (10 mg/ml) for 3 days. The resting and activated immune cells were stained with anti-TAPBPL or isotype antibody (Ab), as well as anti-CD4, CDS, CDllb, F4/80, CD1 lc, B220 or CD19 antibody to identify immune cells. (A) Representative flow cytometric profiles and (B) statistical analysis showing the expression of TAPBPL protein on resting and activated immune cells. (C) Determination of TAPBPL protein expression in normal and tumor human tissues by immunohistochemistry using anti-

TAPBPL or isotype Ab. (D) Analysis of TAPBPL protein expression on neuro-2a, Lewis lung, P388, CT26, and B16 cancer cell lines by flow cytometry. The data are representative of 3 independent experiments. (B) * P<0.05 compared with isotype Ab. ** P<0.05 compared with resting cells.

Figure 10. The effects of hTAPBPL-Ig protein on T cell proliferation in vitro. (A, B) T cells were purified from splenocytes of C57BL/6 mice by magnetic separation. The cells were cultured on plates pre -coated with (A) anti-CD3 antibody (1 mg/ml) or (B) anti-CD3 (1 mg/ml) and anti- CD28 (0.5 mg/ml) antibodies in the presence of graded doses of hTAPBPL- Ig (10 and 15 mg/ml) or equimolar amounts of control Ig (3.75 and 5.63 mg/ml) for 3 days. [¾] thymidine (1 pCi/well) was added to the cultures 12 hours before harvest. T cell proliferation was measured by [^H] thymidine incorporation. (C-E) Splenic cells were labelled with CFSE and cultured in 96-well plates that were precoated with anti-CD3 antibody and hTAPBPL-Ig or control Ig for 3 days as in Figure 3A. The cells were analyzed for CFSE levels by CD4 ⁺ and CD8 ⁺ T cells. (C) Representative flow cytometric analysis of CFSE distribution of CD4 ⁺ and CD8 ⁺ T cells, and (D, E) statistical analysis of (D) CD4 and (E) CDS T cell proliferation. (F) Purified human T cells were cultured with plate-bound anti- human CD3 antibody (1 mgZml) in the presence of graded doses of hTAPBPL-Ig (1.5 and 3 mg/tnl) or control Ig protein (1.5 and 3 mg/ml) for 3 days. Cell proliferation was measured by

[¾] thymidine incorporation. The data are expressed as mean +_SD and representative of 3 independent experiments. * P<0.05 compared with control Ig.

Figure 11. The effects of hTAPBPL-Ig protein on T cell activation in vitro. Splenic cells from C57BL/6 mice were cultured with (A, B, E, F, I, J) anti-CD3 antibody (1 mg/ml) or (C, D, G, H, K, L) anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/ml) antibodies in the presence of graded doses of hTAPBPL-Ig (10 and 15 mg/ml) or equimolar amounts of control Ig (3.75 and 5.63 mg/ml) for (A-D) 1 day or (E-L) 3 days. The cells were analyzed for the percentages of (A-D) CD69+, (E-I,K) CD44 ^hi CD62L ^lo and (E, G, I-L)

CD44 ^lo CD62L ^hi cells in CD4 and CD8 T cells. (A, C, E, G, I, K) Representative flow cytometric and (B, D, F, H, J, L) statistical analyses of the percentages of CD69 ⁺ ,

CD44 ^h *CD62L ^, ° and CD44 ^lo CD62L ^hi cells in CD4 and CDS T cells. The data are expressed as mean +.SD and representative of 3 independent experiments. * P<0.05 compared with control Ig.

Figure 12: hTAPBPL-Ig attenuates autoimmune disease EAE in mice. C57BL/6 mice were immunized with 200 mg MOG35-55 emulsified in CFA and 500 ng of purified

Bordetella pertussis toxin. (A) Mice were injected i.p. with 25 mg hTAPBPL-Ig or control Ig protein 3 times per week from day 0. Mean clinical scores. (B-O) When EAE symptoms occurred, the mice were injected i.p. with 25 mg hTAPBPL-Ig or control Ig protein 3 times per week. (B) Mean clinical scores (C-O) At the end of the study, spleens were harvested and analyzed for (C and D) CD4 ⁺ T cells, (E and F) CD4 ⁺ CD25 ⁺ FoxP3 ⁺ Tregs, (G and H) CD69 expression by CD4~ T cells, and (I, J) CD4 ⁺ CD44 ^hi CD62L ¹⁰ effector memory and

CD4TD44 ¹⁰ CD62L ^hi naive T cells. (K-N)The CNS-infiltrating (K and L) CD4 ⁺ T cells and (M and N) CD4 ⁺ CD25 ⁺ FoxP3 Tregs were analyzed. (O) Splenocytes were cultured with graded doses of MOG _33-55 for 72 horns. [ ³ H] thymidine (1 pCiAvell) was added to the cultures

12 hours before harvest. T cell proliferation was measured by [ ³ H] Thymidine incorporation. The data are expressed as mean + SD and representative of 3 independent experiments with n= 8/group. * P<0.05 compared with control Ig.

Figure 13. Anti-hTAPBPL mAb inhibits tumor growth in vivo. (A) Anti-hTAPBPL mAb (clone 54) neutralize the proliferation inhibitory of hTAPBPL-Ig on T cells in vitro. (B-

H) DBA/2J mice were injected s.c. with lx 10 ⁵ P388 leukemia cells followed by injection with anti-hTAPBPL mAb (lOOmg) or control-Ig(lOOmg) 3 times per week. (B) Tumors size was measured over time. The mean tumor diameter (mm ³ ) + S.D. at the indicated time points are shown. (C-H) At the end of the studies, tumors were harvested. Single-cell suspension of the tumors was analyzed for the percentage of (C, D) CD4 ¹ T cells, (E, F) CD8 ⁺ T cells, and (G and H) CD4 ⁺ CD25 ⁺ FoxP3~ Tregs by flow cytometry. The data are expressed as mean + SD and representative of 2 independent experiments with similar results. * P<0.05 compared with isotype antibody.

Figure 14. The expression pattern of SkintS mRNA in tissues and immune cells. (A) RNA was isolated from indicated tissues of C57BL/6 mice. The expression of SkintS mRNA was determined by RT-PCR. GAPDH was used as a loading control. (B) CD4 ⁺ and CD8 ⁺ T cells, B220 ⁺ B cells, CD1 lb ⁺ monocytes, F4/80 ⁺ macrophages, and CD1 lc ⁺ DCs were magnetically isolated from splenocytes. (C) To activate T cells, purified CD4 ⁺ or CD8 ¹ T cells were incubated with anti-CD3 (1 mg/rnl) and anti-CD28 (0.5 mg/ml) antibodies for 3 days. To activate B cells, monocytes, macrophages, or DCs, the purified immune cells were incubated with LPS (10 mg/ml) for 3 days. RNA was isolated from the (B) resting and (C) activated immune cells. The expression of SkintS mRNA was determined by RT-PCR (D) The expression of SkintS mRNA was determined by qRT-PCR Each column was normalized with GAPDH. *P<0.05 compared with resting cells. The data are representative of 3 independent experiments.

Figure 15. The expression pattern of the SkintS putative receptor. (A, B) Spleen cells were harvested from C57BL/6 mice. To obtain activated T cells, the spleen cells were incubated with anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/ml) antibodies for 3 days. To obtain activated B cells, monocytes and DCs, the spleen cells were incubated with LPS (10 mg/ml) for 3 days. The freshly harvested and activated immune cells were stained with biotinylated SkintS-Ig or control Ig, followed by streptavidin-PE, as well as anti-CD4, CDS, B220, CD1 lb, or CD1 lc antibodies to identify the immune cells. (A) Representative flow cytometric profiles and (B) Statistical analysis showing the binding of SkintS-Ig or control Ig to freshly harvested and activated immune cells. (B) Data are presented as relative fluorescence intensity (RFI) for cell binding of SkintS-Ig versus control Ig. (C) HEK-293 cells were transfected with an expression vector containing the murine PD-1, CD28, BTLA, CTLA-4, or ICOS gene and screened for cells stably expressing each gene. The transfected cells were stained with antibody against the respective PD-1, CD28, BTLA, CTLA-4, or ICOS protein (open histograms) or isotype antibody (shaded histograms). Representative flow cytometric profiles showing the expression of each receptor. (D) PD-1, CD28, BTLA, CTLA-4, or ICOS gene-transfected HEK-293 cells were stained wife biotinylated SkintS-Ig or control Ig, followed by streptavidin-PE. Representative flow cytometric profiles showing the binding of Skint8-Ig (open histograms) or control Ig protein (shaded histograms) to the transfected cells. The data are representative of 3 independent experiments.

Figure 16. The effects of Skint8-Ig protein on T cell proliferation and activation in vitro. (A) T cells were purified from spleen cells of C57BL/6 mice by magnetic separation. The cells were cultured on plates pre -coated with (A) anti -CDS antibody (1 mg/ml) and graded doses of SkintS- Ig (1840, 3728, 7456 ng/ml) or equimolar amounts of control Ig (990, 1980, 3960 ng/ml) protein, or (B) anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/ml) antibodies in the presence of Skint8-Ig or equimolar amount of control Ig lor 3 days. [1H] thymidine (1 pCi/well) was added to the cultures 12 hours before harvest. T cell proliferation was measured by [¾] thymidine incorporation. (C-E) Spleen cells were labelled with CFSE and cultured in anti -CDS antibody precoated 96-well plates in the presence of indicated doses of Skint8-Ig or control Ig for 3 days. The cells were analyzed for

CFSE levels by CD4 ⁺ and CD8 ⁺ T cells. (C) Representative flow cytometric analysis of CFSE distribution of CD4 ⁺ and CD8 ⁺ T cells, and (D, E) statistical analysis of T cell proliferation. (F, G) Purified CD4 ⁺ or CD8 ⁺ T cells were cultured with anti-CD3 antibody and graded doses of Skint8-Ig or equimolar amounts of control Ig protein for 3 days. T cell proliferation was measured by [ ³ H] thymidine incorporation as in (A). (H-L) Spleen cells were cultured with (H, I) anti-CD3 antibody or (J-L) anti-CD3 and anti-CD28 antibodies in the presence of Skint8-Ig or control Ig. The cells were analyzed for the expression of CD69 24 hours later. (H, J) Representative flow cytometric profiles, and (I, K, L) statistical analyses of the percentages of CD69 ⁺ cells in CD4 ⁺ or CD8 ⁺ T cells. The data are expressed as mean +JSD and representative of 3 independent experiments. * P<0.05 compared with control Ig.

Figure 17. The effects of Skint8-Ig protein on cytokine production from T cells in vitro. Purified murine T cells were cultured with plate-bound (A-C) anti-CD3 antibody (1 mg/ml) in the presence of Skint8-Ig (3728 ng/ml) or equimolar amount of control Ig (1980 ng/ml), or (D, E) anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/ml) antibodies in the presence of Skint8-Ig (6 mg/ml) or equimolar amount of control Ig for 3 days. (A) The levels of IRNg, and TNFo, (mg/ml) in the supernatant were measured by ELISA kits. (B-E) The T cells were stimulated with phorbol myri state acetate and ionomycin 4 hours before harvesting, and then stained with antibodies against CD4, IRNg, and TNFo,. The percentages of the cytokine positive cells in CD4 ⁺ T cells were determined by flow cytometry. (B, D)

Representative flow cytometric profiles, and (C, E) statistical analyses of the percentages of cytokines in CD4 ⁺ T cells. The data are expressed as mean + SD and representative of 3 independent experiments. * P<0.05 compared with control Ig.

Figure 18. Skint8-Ig attenuates EAE in mice. C57BL/6 mice were immunized with 200 mg MOG ₃₅ - ₅₅ emulsified in CFA and 500 ng of purified Bordetella pertussis toxin. The mice were injected i.p. with 25 mg Skint8-Ig or control Ig protein 3 times per week from day 0. EAE development was monitored. (A) Mean clinical scores, (B-E) Thirty five days after immunization, spleens were harvested and analyzed for (B, C) CD69 expression by CD4 T cells, and (D, E) CD44 ^to CD62L ^hi naive and CD44 ^h ‘CD62L ^k> effector memory CD4 T cells. (F-S) In separate experiments, groups of EAE mice were sacrificed at (F-I, N) prime time (day 10) or (J-M, O, P-S) peak time (day 22) of EAE. (F, G, J, K) The percentage of CD4 ⁺ T cells in the spleen, and (H, I, L, M) the percentage of CD4~CD25 ^t Foxp3 ⁺ Tregs in CD4 ⁺ T cells were examined. (N, O) The splenic CD4 ⁺ T cells were stimulated with MOG (20 mg/ml) in vitro for 3 days; the supernatant was analyzed for the production of the indicated cytokines by ELISA. (P-S) The CNS infiltrating (P, Q) CD4 ¹ T cells and (R, S)

CD4~CD25 ⁺ Foxp3 ⁺ Tregs were analyzed. The data are pooled from 2 independent experiments (n=8 for Skint8-Ig or control Ig groups each). * P<0.05 compared with control Ig-treated mice.

Figurel9. The expression pattern of BTN5 protein. (A) Analysis of mBTN5 protein expression on immune cells. Splenocytes from C57BL/6 mice were freshly harvested and analyzed for mBTN5 protein expression on resting immune cells. To obtain activated B cells, DCs, monocytes and macrophages, splenocytes were incubated with LPS (10 mg/ml) for 3 days. To obtain activated T cells, splenocytes were incubated with anti-CD3 antibody (1 mg/ml) and anti-CD28 antibody (0.5 mg/ml) for 3 days. The resting and activated immune cells were stained with anti-BTN5 or isotype antibody, as well as anti-CD4, CDS, B220,

CDl lc, or CD1 lb antibody to identify immune cells. Representative flow cytometric profiles showing the expression of mBTN5 protein on resting and activated immune cells. (B, C) Determination of hBTN5 protein expression in human (B) normal and (C) cancer tissues by immunohistochemistry. (D) Analysis of BTN5 protein expression on neuro-2a, Lewis lung, P388, K562, CT26, and B16 tumor cell lines by flow cytometry. The data are representative of 3 independent experiments. Figure 20. The expression pattern of the mBTN5 putative receptor. (A) Splenocytes from C57BL/6 mice were freshly harvested and analyzed for resting immune cells. For T cell activation, splenocytes were incubated with anti-CD3 (1 mg/ml) and anti-CD28 (0.5 mg/ml) antibodies for 3 days. For the activation of B cells, DCs and monocytes, splenocytes were incubated with LPS (10 mg/ml) for 3 days. The resting and active immune cells were stained with anti-CD4, CDS, B220, CD1 lc, or CD1 lb antibodies, and biotinylated mBTN5-Ig or control Ig, followed by streptavidin-PE. Representative flow cytometric profiles showing the binding of mBTN5-Ig or control Ig to resting and activated immune cells. (B, C) HEK-293 cells were transfected with an expression vector containing murine PD-1, CD28, BTLA, CTLA-4, or ICOS gene. The transfected cells were stained with (B) antibodies against the respective PD-1, CD28, BTLA, CTLA-4, or ICOS protein, (C) biotinylated mBTN5-Ig or control Ig, followed by streptavidin-PE. Representative flow cytometric profiles showing the binding of (B) the antibodies or (C) mBTN5-Ig to the transfected cells. Representative of 3 independent experiments.

Figure 21. The effects of mBTN5-Ig protein on murine T cell proliferation and activation in vitro. (A) T cells were purified from splenocytes of C57BL/6 mice by magnetic separation. The cells were cultured on plates pre-coated with anti-CD3 antibody (1 mg/ml) and indicated doses of mBTN5-Ig or control Ig for 3 days. [ ³ H] thymidine (1 pCi/well) was added to the cultures 12 hours before harvest. T cell proliferation was measured by [ ³ H] thymidine incorporation. Results are expressed as counts per mmute (CPM). (B-D) Splenic cells from C57BL/6 mice were labelled with CFSE and cultured in 96-well plates that were precoated with anti-CD3 antibody and indicated doses of mBTN5-Ig or control Ig for 3 days. The cells were analyzed for CFSE levels by CD4 ⁺ and CD8 ¹ T cells. (B) Representative flow cytometric analysis of CFSE distribution of CD4 ¹ and CD8 ⁺ T cells, and (C, D) statistical analysis of the percentages of proliferating CD4 and CDS T cells. (E-K) Splenic cells were cultured with anti-CD3 antibody in the presence of mBTN5-Ig or control Ig (1728 ng/ml).

The cells were analyzed for the expression of (E, F) CD6924 hours later, (G-K) and the expression of CD44 and CD62L 72 hours later. (E, G) Representative flow cytometric and (F, H-K) statistical analyses of the percentages of (F) CD69 ⁺ , (H, I) CD44 ^l0 CD62L ^hi naive CD4 and CDS T cells and (J, K) CD44 ^hi CD62L ^l ° effective memory CD4 and CDS T cells. The data are expressed as mean + SD and representative of 3 independent experiments. * P<0.05 compared with control Ig. Figure 22. The effects of hBTN5-Ig protein on murine and human T cells in vitro.

(A) T cells were purified from splenocytes of C57BL/6 mice and cultured on plates precoated with anti-CD3 antibody (1 mg/ml) and indicated doses of hBTN5-Ig or control Ig for 3 days. [ ³ H] thymidine (1 pCi/well) was added to the cultures 12 horns before harvest, and T cell proliferation was measured by [ ³ H] thymidine incorporation. (B-D) Murine splenic cells were labelled with CFSE and cultured in 96-well plates that were precoated with anti-CD3 antibody and indicated doses of hBTN5-Ig or control Ig for 3 days. The cells were analyzed for CFSE levels by CD4 ⁺ and CD8 ⁺ T cells. (B) Representative flow cytometric analysis of CFSE distribution of CD4 ⁺ and CD8 ⁺ T cells, and (C, D) statistical analysis of CD4 ⁺ and CD8 ¹ T cell proliferation. (E) Purified human T cells were cultured with plate-bound anti- human CD3 antibody (1 mg/ml) in the presence of indicated doses of hBTN5-Ig protein or control Ig protein for 3 days. Cell proliferation was measured by [ ³ H| thymidine

incorporation. (F) hBTN5-Ig protein suppresses cytokine production from T cells. Purified murine T cells were cultured with plate-bound anti -CDS antibody (1 mg/ml) in the presence of 6.4 mg/ml hBTN5-Ig protein or control Ig protein for 3 days. The levels of IFNy, TNFo,

IL-2, and IL-10 in the supernatant were measured by ELISA kits. The data are expressed as mean + SD and representative of 3 independent experiments. * P<0.05 compared with control

Ig.

Figure 23. The effects of hBTN5 on macrophage function and differentiation in vitro and tumor growth in vivo. (A, B) Macrophages were generated from BM of C57BL/6 mice. K562 cancer cells were labeled with CFSE and cultured with the macrophages in the presence of anti-hBTN5 or control antibody (10 mg/ml) for 2 hours. (A) Representative flow cytometric profiles and (B) statistical data showing the percentages of CFSE ⁺ cells in F4/80 ⁺ macrophages. (C, D) M0 macrophages were induced to differentiate into M2 in the presence of hBTN5 or control Ig (5 or 10 mg/ml). (C) Representative flow cytometric profiles and (D) statistical data the percentages of CD206 ^hl MHC P ¹⁰ M2 macrophages in F4/80 ⁺ cells. (E) CT-26 colon cancer cells were transfected with an expression vector containing the full- length hBTN5 gene and screened for the cancer cells that stably expressed BTN5. A representative flow cytometric profile showing the expression of HBTN5 protein on the cell surface. (F-H) BALB/c mice were injected s.c. with 2x10 ^s hBTN 5 -transfected CT-26 cells. When the tumors were palpable, the mice were injected intratumorally with anti -hBTN 5 or control polyclonal antibody (25 mΐ) twice each week from days 10-28 after tumor inoculation. (F) The mean tumor volume (mm ³ ) + S.D. at the indicated time points are shown. (G, H) Thirty days after CT26 cell inoculation, the mice were euthanized and the tumors were removed. Single-cell suspensions from the tumors were analyzed by flow cytometry for (G) CD4 ¹ and CD8 ⁺ T cells; and (H) M2 macrophages. * P<0.05 compared with control group. The data are representative of 2 independent experiments with 4-6 mice per group.

Figure 24: hBTN5-Ig attenuates autoimmune disease EAE in mice. C57BL/6 mice were immunized with 200 mg MOG35.55 emulsified in CFA and 500 ng of purified Bordetella pertussis toxin. The mice were injected i.p. with 25 mg/ml hBTN5-Ig or control Ig protein 3 times per week for 5 weeks. EAE development was monitored for 42 days. (A) Mean clinical scores, and (B) a Kaplan-Meier plot of the proportion of disease-free mice are shown. (C-P) Forty two days after immunization, spinal cords and spleens were harvested. (C, D)

Histological sections of the spinal cords were stained with H&E, LFB and BSI. (C)

Representative stained histological sections (the magnification was 200 *), and (D) histological scores are shown. (E-H) The splenocytes were analyzed for CD44 ^k> CD62L ^hi naive, CD44 ^hi CD62L ^l ° effective memory, and CD44 ^hi CD62L ^hl central memory (G) CD4 and (H) CDS T cells; (I, J) CD4 ⁺ CD25lFoxP3 ⁺ Tregs; and (K, L) arginase ⁺ and CD206 ^hi MHC ¹ °

M2, as well as CD206 ^k> MHC ^hi Ml macrophages. (M, N) Splenocytes were labelled with CFSE and stimulated with varying doses of PMOG35-35 in vitro. CFSE dilution was analyzed 3 days later to determineCD4 ¹ and CDS ¹ T cell proliferative responses. (O, P) Splenocytes were stimulated with PMOG35-55 in vitro for 3 days. The cells were analyzed for the percentages of cytokine-producing cells by flow cytometry. The data are expressed as mean + SD and representative of 3 independent experiments. * P<0.05 compared with control Ig- treated mice.

Figure25: hBTN5-Ig treatment ameliorates T1D in mice. 22 week-old female NOD mice were injected i.p. with 30 mg hBTN5-Ig or control Ig protein at 2-day intervals for 3 weeks. At week 30, the mice were euthanized. (A) The pancreases were stained with hematoxylin and eosin (H&E). Representative sections (200X). (B-G) the spleens were analyzed for (B-E) T cell and (F, G) macrophage subsets. (B, D, F) Representative flow cytometric profiles and (C, E, G) statistical analysis of (B-E) CD44 ^to CD62L ^hl naive, CD44 ^M CD62L ^l0 effective memory, and CD44 ^hi CD62L ^hi central memory CD4 and CDS T cells, as well as (F, G) CD206 ^M MHC ^|0 M2 and CD206 ^lo MHC“ Ml macrophages. The data are expressed as mean + SD and representative of 2 independent experiments per group. * P<0.05 compared with control Ig-treated mice. Figure 26. Anti-hBTN-5 mAbs enhance macrophage-mediated phagocytosis of cancer cells in vitro. Macrophages were generated from BM of C57BL/6 mice. K562 cancer cells were labeled with CFSE and cultured with the macrophages in the presence of anti- hBTN5 mAbs (clones D4 and D16) for 2 horns. (A) Representative flow cytometric profiles (anti-hBTN5 mAbs: open histograms; control mAbs: shaded histograms) and (B) statistical data of the percentages of CFSE ^* cells in F4/80* macrophages. The data are expressed as mean + SD and pooled from 3 independent experiments. * P<0.05 compared with control mAbs.

Figure 27. CD300f-Ig protein inhibits lymphocyte proliferation in vitro.

Splenocytes from C57B1V6 mice were cultured with plate-bound anti-CD3 antibody (1 mg/ml) in the presence of graded doses of CD300f-Ig protein (800, 1600, and 3200 ng/ml) or equimolar amounts of control Ig protein for 3 days. Cell proliferation was measured by [^H] thymidine incorporation. The data are expressed as mean + SD and representative of 3 independent experiments.

Figure 28. CD300f-Ig protein inhibits T cell proliferation in vitro. Splenocytes from C57BL/6 mice were labelled with CFSE and cultured with anti-CD3 antibody (1 mg/ml) in the presence of graded doses of CD300f-Ig protein (800, 1600, and 3200 ng/ml) or equimolar amounts of control Ig protein for 3 days. The cells were stained with anti-CD4 and

CDS antibodies, and analyzed for CFSE levels by CD4 ⁺ and CD8 ⁺ T cells. (A, C)

Representative flow cytometric profiles, and (B, D) statistical analysis of CFSE* ⁰ proliferating (A, B) CD4 ⁺ and (C, D) CD8 ⁺ T cells. (B, D) The data are expressed as mean + SD and representative of 3 independent experiments.

Figure 29. CD300f-Ig protein inhibits T cell activation in vitro. Splenocytes from C57B1V6 mice were cultured with plate-bound anti-CD3 antibody (1 mg/ml), or anti- CD3 antibody (1 mg/ml) and (B) anti-CD28 antibody (0.5 mg/ml) in the presence of graded doses of CD300f-Ig protein (800, 1600, and 3200 ng/ml) or equimolar amounts of control

Ig protein. The cells were analyzed for the expression of CD69 by (A, B) CD4 ⁺ and (C,

D) CD8 ⁺ T cells 24 hours later. (B, D)The data are expressed as mean + SD and representative of 3 independent experiments.

Detailed Description As used herein and unless otherwise indicated, the terms“a” and“an” are taken to mean“one”,“at least one” or“one or more”. Unless otherwise required by context, singular terms used herein shall include pluralities and plural terms shall include the singular.

Unless the context clearly requires otherwise, throughout the description and the claims, the words‘comprise’,‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. Words using the singular or plural number also include the plural or singular number, respectively. Additionally, the words“herein,”“above” and "below" and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application.

As used herein, the amino acid residues are abbreviated as follows: alanine (Ala; A), asparagine (Asn; N), aspartic acid (Asp; D), arginine (Arg; R), cysteine (Cys; C), glutamic acid (Glu; E), glutamine (Gin; Q), glycine (Gly; G), histidine (His; H), isoleucine (He; I), leucine (Leu; L), lysine (Lys; K), methionine (Met; M), phenylalanine (Phe; F), praline (Pro; P), serine (Ser; S), threonine (Thr; T), tryptophan (Trp; W), tyrosine (Tyr; Y), and valine (Val; V).

All embodiments of any aspect of the invention can be used in combination, unless the context clearly dictates otherwise.

In a first aspect, the disclosure provides methods for treating cancer, comprising administering to a subject in need thereof an antibody that selectively binds to a protein selected from the group consisting of CD300c, BTN5 (Erythroid membrane-associated protein), TAPBPL (antigen processing (TAP) binding protein like protein), SkintS (selection and upkeep of intraepithelial T cells 8 protein,), and/or CD300f in an amount effective to treat the cancer. The methods may be used to treat any suitable cancer. In various non- limiting embodiments, the cancer may be selected from the group consisting of breast cancer, lung cancer, colon cancer, prostate cancer, leukemia, neuroblastoma, liver, lymphoma, cervical cancer, ovarian cancer, gastric cancer, and esophageal cancer, etc.

Tumor progression is often accompanied by profound immune suppression that interferes with an effective antitumor response and tumor elimination. In contrast, graft- versus-host disease (GVHD) and autoimmune diseases, such as type 1 diabetes (T1D), arthritis, including but not limited to rheumatoid arthritis (RA), and multiple sclerosis (MS), arise when the immune system actively targets and destroys self-tissues. In order to elicit protective immunity to cancer and infection, and to prevent an overactive immune system, immune responses need to be tightly controlled by immune cell stimulatory and inhibitory molecules. Many cancers protect themselves from the immune system by producing inhibitory molecules to inhibit T cell function.

As disclosed in the examples herein, the inventors have identified CD300c, BTN5, TAPBPL, SkintS, and CD300f as targets for treating cancer, and as therapeutics for treating autoimmune disease.

As used herein, the term“treat,”‘treatment,” or“treating,” means to reverse, alleviate, ameliorate, inhibit, slow down or stop the progression or severity of a symptom or condition of the disorder being treated. The term“treating” includes reducing or alleviating at least one adverse effect or symptom of a condition. Treatment is generally“effective” if one or more symptoms are reduced. Alternatively, treatment is“effective” if the progression of a condition is reduced or halted. That is,“treatment” may include not just the improvement of symptoms, but also a cessation or slowing of progress or worsening of symptoms that would be expected in the absence of treatment. Beneficial or desired clinical results include, but are not limited to, alleviation of one or more symptom(s), diminishment of extent of the deficit, stabilized (i.e., not worsening) state of a tumor, malignancy, or autoimmune disease; delay or slowing of tumor growth and/or metastasis or autoimmune disease effects, and an increased lifespan as compared to that expected in the absence of treatment.

As used herein, the term“administering,” refers to the placement of a therapeutic into a subject by a method or route deemed appropriate. The therapeutic can be administered by any appropriate route which results in an effective treatment in the subject including orally, parentally, by inhalation spray, rectally, or topically in dosage unit formulations containing conventional pharmaceutically acceptable carriers, adjuvants, and vehicles. The term parenteral as used herein includes, subcutaneous, intravenous, intra-arterial, intramuscular, intrastemal, intratendinous, intraspinal, intracranial, intrathoracic, infusion techniques or intraperitoneally. Dosage regimens can be adjusted to provide the optimum desired response (e.g., a therapeutic response). A suitable dosage range may, for instance, be 0.1 ug/kg-100 mg/kg body weight; alternatively, it may be 0.5 ug/kg to 50 mg/kg; 1 ug/kg to 25 mg/kg, or 5 ug/kg to 10 mg/kg body weight. The therapeutic can be delivered in a single bolus, or may be administered more than once (e.g., 2, 3, 4, 5, or more times) as determined by an attending physician.

As used herein, the phrase“amount effective” or“the like refers to an amount that provides a therapeutic benefit in the treatment, of cancer or autoimmune disease. Determination of a therapeutically effective amount is well within the capability of those skilled in the art. Generally, a therapeutically effective amount can vary with the subject's history, age, condition, sex, as well as the severity and type of the medical condition in the subject, and administration of other pharmaceutically active agents.

As used herein, the term "antibody" refers to binding proteins having at least one antigen-binding domain and includes monoclonal antibodies fragments and/or variants thereof including recombinant polypeptides, fusion proteins, and immunoconjugates. Thus, the terms "antibody," "antibody fragment," and "antibody variant" are used interchangeably herein. Examples of antibody fragments of the invention include, but are not limited to, the Fab fragment, consisting of VL, VH, CL and CHI domains; the Fc fragment, consisting of the VH and CHI domains; the Fv fragment consisting of the VL and VH; the dAb fragment consisting of a VH domain; isolated CDR regions; F(ab')2 a bivalent fragment comprising two linked Fab fragments; and single chain Fv molecules (scFv). The antibodies provided herein may be generated from any species including, but not limited to, mouse, rat, rabbit, primate, llama and human. The antibodies may be chimeric, humanized, or felly human antibodies. In one specific embodiment, the antibody is a monoclonal antibody. In other specific embodiments, the antibody may be the anti-CD300c and/or anti-TAPBPL antibodies disclosed and claimed herein.

As used herein, selective binding or specific binding means the antibody specifically bound to its target antigen is not displaced by a non-similar competitor and preferentially recognizes its target antigen in a complex mixture of proteins and/or macromolecules.

Antibodies and fragments thereof that are selective for the target antigens described herein bind the target antigen with greater affinity (i.e., a lower binding affinity Kd value) than any other target. In non-limiting embodiments, the antibodies and fragments or variants thereof may have a binding affinity Kd value for target antigen in the range of about 0.01 tiM to about 500 nM, about 0.02 nM to about 250 nM, about 0.02 to about 200 nM, about 0.05 to about 100 nM, about 0.05 to about 50 nM. The antibodies and fragments thereof may have a binding affinity Kd value for target antigen of about 500 nM, about 250 nM, about 200 nM, about 150 nM, about 100 nM, about 75 nM, about 50 nM, about 25 nM, about 10 nM, about 5 nM, about 1 nM, about 500 pM, about 250 pM, about 100 pM, about 50 pM, or about 10 pM. The antibodies and fragments thereof may have a binding affinity Kd value for target antigen of about 100 nM or less, about 75 nM or less, about 50 nM or less, about 10 nM or less, about 1 nM or less, about 500 pM or less, or about 100 pM or less. In one embodiment, the antibody selectively binds to an extracellular domain (BCD) of CD300c, including but not limited to an BCD of human CD300c within amino acid residues 21-138. In another embodiment, the antibody selectively binds to an IgV domain of

CD300c, including but not limited to an IgV domain of human Cd300c within anmino add residues 20-135. Exemplary Cd300c sequences are shown below:

Mouse CD300c2 amino acid sequences (ECM region: 22-187, IgV: 24-116); the IgV domain is predicted from aa20-28 to aal 12-140:

MIPRVIRLWLPSALFLSQVPGCVPLHGPSTITGTVGKSLSVSCQYEEKFKTKDKFWCRGS LKVLCKDIVKT SSSEEVRNGRVTIRDHPDNLTFTVTYESLTLEDADTYMCAVDISLFDGSLGFDKYFKIEL SWPSEDPVTG SSLESGRDILESPTSSVGHTHPSVTTDDTIPTPCPQPRSLRSSLYFRVLVSLKLFLFLSM LGAVLWVNRPQ KCSGGSSTQPCYENQ (SEQ ID NO: 01)

Human CD300c amino acid sequences (ECM region: 21-183, IgV: 22-128); the IgV domain is predicted from aa20-28 to aal 14-135:

1 MTARAWASWR SSALLLLLVP GYFPLSHPMT VAGPVGGSLS VQCRYEKEHR TLNKFWCRPP 61 QILRCDKIVE TKGSAGKRNG RVSIRDSPAN LSFTVTLENL TEEDAGTYWC GVDTPWLRDF 121 HDPIVEVEVS VFPAGTTTAS SPQSSMGTSG PPTKLPVHTW PSVTRKDSPE PSPHPGSLFS 181 NVRFLLLVLL ELPLLLSMLG AVLWVNRPQR SSRSRQNWPK GENQ (SEQ ID NO: 02)

In one embodiment, the antibody selectively binds to an extracellular domain of BTN5, including but not limited to an BCD of human BTN5 within amino acid residues 30-

155. In another embodiment, the antibody selective binds to an IgV domain of BTN5, including but not limited to an IgV domain of human BTN within amino acid residues 17- 150. Exemplary BTN5 sequences are shown below: Mouse BTN5 amino acid sequences (Signal peptides: 1-47; ECM region: 48-271, IgV: 49- 165); the IgV domain is predicted from amino acid (aa)49-68 to aal51-l 70.

1 MLKRLKKHW AWKMCVMPHS RKMSVHMERP SPCGSWLVGC LFTIAVFQPP VQVLGDAGKV 61 YIAPLRDTAN LPCPLFLWPN MVLSEMRWYR PGHLPRTQAV HVFRDGQDRD EDLMPEYKGR 121 TALVRDAHKE SYILQISNVR LEDRGLYQCQ VWVGNSSRED NVTLQVAVLG SDPYIHVKGY 181 DAGWIELLCQ SVGWFPKPWT EWRDTTGRAL LSLSEVHSLD ENGLFRTAVS SRIRDNALGN 241 VSCTIHNEAL GQEKTTAMII GAPERGSLSS PAVALSWLP VLGLLILLGI WLICKQKKSK 301 EKLLYEQAME VENLLEDHAK EKGRLHKALK KLRSELKLKR AAANAGWRRA RLHFVAVTLD 361 PDTAHPKLIL SEDRRCVRLG DRKRPVPDNP ERFDFWSVL GSEYFTTGCH YWEVYVGEKT 421 KWILGVCSES VSRKGKVTAS PANGHWLVRQ SRGNEYEALT SPQTSFRLKE SPKCVGIFLD 481 YEAGIISFYN VTDKSHIFTF THSFSSPLRP FFEPCLHDEG KNTAPLIICT ELQKSEESIV 541 PKQEGKDRAN GDVSLKMNPS LLSPQGSELF LLNDTWPSNL GPALKGLKVP SL

(SEQ ID NO: 03)

Human BINS amino acid sequences (ECM 30-155, IgV: 30-144); the IgV domain is predicted from aal 7-45 to aal43-150:

1 MEMASSAGSW LSGCLIPLVF LRLSVHVSG H AGDAGKFHVA LLGGTAELLC

PLSLWPGTVP

61 KEVRWLRSPF PQRSQAVHIF RDGKDQDEDL MPEYKGRTVL VRDAQEGSVT LQILDVRLED 121 QGSYRCLIQV GNLSKEDTVI LQVAAPSVGS LSPSA VALAV ILPVLVLLIM

VCLCLIWKQR

181 RAKEKLLYEH VTEVDNLLSD HAKEKGKLHK AVKKLRSELK LKRAAANSGW RRARLHFVAV 241 TLDPDTAHPK LILSEDQRCV RLGDRRQPVP DNPQRFDEW SILGSEYFTT GCHYWEVYVG 301 DKTKWILGVC SESVSRKGKV TASPANGHWL LRQSRGNEYE ALTSPQTSFR LKEPPRCVGI 361 FLDYEAGVIS FYNVTNKSHI FTFTHNFSGP LRPFFEPCLH DGGKNTAPLV ICSELHKSEE 421 SIVPRPEGKG HANGDVSLKV NSSLLPPKAP ELKDIILSLP PDLGPALQEL KAPSF (SEQ ID NO: 04)

In one embodiment, the antibody selectively binds to an extracellular domain of

TAPBPL, including but not limited to an ECD of human TAPBPL within amino acid residues 19-405. In another embodiment, the antibody selective binds to an IgV domain of

TAPBPL, including but not limited to an IgV domain of human TAPBPL within amino acid residues 181-300. Exemplary TAPBPL sequences are shown below:

Mouse TAPBPL amino acid sequences (ECM region: 21-412, IgV: 196-305); the IgV domain is predicted from aal96-210 to aa301-306.

1 mglepswyll lclavsgaag tdpptaptta erqrqptdii ldcflvtedr hrgafassgd 61 rerallvlkq vpvlddgsle gitdfqgste tkqdspvife asvdlvqipq aeallhadcs 121 gkavtceisk yflqarqeat fekahwfisn mqvsrggpsv smvmktlrda evgavrhptl 181 nlplsaqgtv ktqvefqvts etqtlnhllg ssvslhcsfs mapgldltgv ewrlqhkgsg 241 qlvyswktgq gqakrkgatl epeellragn asltlpnltl kdegnyicqi stslyqaqqi 301 mplnilappk iqlhlankdp lpslvcsiag yypldvgvtw ireelggipa qvsgasfssl 361 rqstmgtysi sstvmadpgp tgatytcqva hvsleepltt smrvlpnpeq rgtlgvifas 421 iiflsalllf lglhrqqass srstrpmrhs g (SEQ ID NO: 05)

Human TAPBPL amino acid sequences (ECM region: 19-405, IgV: 198-300); the IgV domain is predicted from aal8l-198 to aa297-300:

1 mgtqegwcll lclalsgaae tkphpaegqw ravdwldcf lakdgahrga lassedrara 61 slvlkqvpvl ddgsledftd fqggtlaqdd ppiifeasvd lvqipqaeal lhadcsgkev 121 tceisryflq mtettvktaa wfmanmqvsg ggpsislvmk tprvtkneal whptlnlpls 181 pqgtvrtave fqvmtqtqsl sfllgssasl dcgfsmapgl dlisvewrlq hkgrgqlvys 241 wtagqgqavr kgatlepaql gmardasltl pgltiqdegt yicqittsly raqqiiqlni 301 qaspkvrlsl aneallptli cdiagyypld vwtwtreel ggspaqvsga sfsslrqsva 361 gtysissslt aepgsagaty tcqvthisle eplgastqvv pperrtalgv ifasslflla 421 lmflglqrrq aptglgllqa erwettscad tqsshlhedr tarvsqps (SEQ ID

NO: 06)

In one embodiment, the antibody selective binds to an extracellular domain of SkintS, including but not limited to an ECD of mouse SkintS within amino acid residues 26-233. In another embodiment, the antibody selective binds to an IgV domain of SkintS, including but not limited to an ECD of mouse Skint 8 within amino acid residues 18-142. An exemplary' SkintS sequence is shown below:

Mouse Skint8 amino acid sequences (ECM region: 26-233, IgV: 29-140); the IgV domain is predicted from aaI8-35 to aal 40-142:

1 mmkpefshff gfcvyflflq vmasseklrv ttptrhllar vggqaelscq vipphsvmhm 61 evrwfrsghs qpvylyrggh kmseeaapey anrtefvkea igegkvslri yninilddgp 121 yqcsfndsgf idvaimnlnv tavgleteih vqapdadgvm vecntggwfp rpqmewrdsk 181 gatlphslks ysqdearffh mkmtllltnm shgsiiccis npvtgeekqt siilanelfn 241 qdylwvgifp fsvlslilfg vlpfinsffr sqgcasgcls kclpwtswp vqivhflvcs 301 gvlfavylph ryrvslsdpq fplynnwite llivilflti cfvlpitvll liklsptcla 361 kweknkddim dsqlglgkar eastlyeeqs rksweqek (SEQ ID NO: 07)

In one embodiment, the antibody selective binds to an extracellular domain of

CD300f, including but not limited to an ECD of human CD300f within amino acid residues

20-155. In another embodiment, the antibody selective binds to an IgV domain of CD300f, including but not limited to an IgV domain of human CD300f within amino acid residues 2- 140. An exemplary CD300f sequence is shown below:

Human CD300F amino acid sequences (ECM region: 20-155, IgV: 24-125); the IgV domain is predicted from aa2-25 to aal 25-140:

1 mplltlylll fwlsgysivt qitgpttvng lergsltvqc vyrsgwetyl kwwcrgaiwr 61 dckilvktsg seqevkrdrv sikdnqknrt ftvtmedlmk tdadtywcgi ektgndlgvt 121 vqvtidpapv tqeetssspt ltghhldnrh kllklsvllp liftilllll vaasllawrm 181 mkyqqkaagm speqvlqple gdlcyadltl qlagtspqka ttklssaqvd qveveyvtma 241 slpkedisya sltlgaedqe ptycranghls shlpgrgpee pteystisrp

(SEQ ID NO: 08)

In another aspect the disclosure provides isolated anti-human CD300c antibodies, or antigen binding fragments thereof, comprising 1, 2, 3, 4, 5, or all 6 complementarity determining regions (CDRs) selected from the group consisting of:

Heavy chain CDR1 (H-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence IYGMN (SEQ ID NO: 10);

Heavy chain CDR2 (H-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence WINTYT (SEQ ID NO: 1 1);

Heavy chain CDR3 (H-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence ARSRFAY (SEQ ID NO: 12).

Light chain CDR1 (L-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence KASQNVGTNVA (SEQ ID

NO: 13);

Light chain CDR2 (L-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence SASYRYS (SEQ P) NO: 14); and Light chain CDR3 (L-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence QQYNSYPLT (SEQ ID NO: 15).

As shown in the examples that follow, the disclosed antibodies are the first antibodies shown to have the ability to neutralize the inhibitory' effects of CD300c on T cells. The sequences of these antibodies have been determined, including the complementarity determining regions (CDRs) disclosed herein. As will be understood by those of skill in the art, the CDRs are the key factor in antigen-binding selectivity, and thus other regions of the antibody amino acid sequence may be substantially modified. In a further embodiment, the anti-human CD300c antibody, or antigen-binding fragment thereof comprises:

(a) a heavy chain comprising the amino acid sequence having at least 60%, 65%,

70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO: 16

QIQLVQSGPELRKPGETVKISCKASGYTFTIYGMNWMKQAPGKGLKWMGWINTYTGEPTY AD DFKGRFAFSLETSASTAFLQINNLTNEDTATYFCARSRFAYWGQGTLVTVSA (SEQ ID NO: 16; CDRs are highlighted) ; and/or

(b) a light chain comprising the amino acid sequence having at least 60%, 65%,

70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the foil length of the amino acid sequence of SEQ ID NO: 17.

DIVMTQSQKFMSTSVGDRVSVTCKA3QWVGTNVAWYQQKPGQSPKAl·IYSASYRYSGV PDRF TGSRSGTDFTLTISNVQSEDLAEYVCQQYNSYPLTFGAGTKLELK (SEQ ID NO: 17; CDRs are highlighted).

In one embodiment, variability compared to the reference sequence is present only outside the CDRs.

In another aspect the disclosure provides isolated anti-human TAPBPL antibodies, or antigen binding fragments thereof, comprising 1, 2, 3, 4, 5, or all 6 complementarity determining regions (CDRs) selected from the group consisting of:

Heavy chain CDR1 (H-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence GYFWH (SEQ P) NO: 18);

Heavy chain CDR2 (H-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence YISY SGTTNYNPSLKN (SEQ ID NO: 19);

Heavy chain CDR3 (H-CDR3) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence DDWDWFAY (SEQ ID NO:20);

Light chain CDR1 (L-CDR1) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence SASSSVNYMH (SEQ ID NO:21);

Light chain CDR2 (L-CDR2) comprising the amino acid sequence at least 80%, 85%, 90%, 95%, or 100% identical to the amino acid sequence DTSKLAS (SEQ ID NO:22); and Light chain CDR3 (L-CDR3) comprising the amino acid sequence at least 80%, 85%,

90%, 95%, or 100% identical to the amino acid sequence FQGSGYPLT (SEQ ID NO:23).

As shown in the examples that follow, the disclosed antibodies are the first antibodies shown to have the ability to neutralize the inhibitory effects of TAPBPL on T cells. The sequences of these antibodies have been determined, including the complementarity

determining regions (CDRs) disclosed herein. In a further embodiment, the anti-human

TAPBPL antibody, or antigen-binding fragment thereof comprises:

(a) a heavy chain comprising the amino acid sequence having at least 60%, 65%,

70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:24:

DVQLQESGPGLVKPSQTLSLTCSVTGYSLTSGYFWHWIRQFPGNKLEWMGYISYSGTTNY NP SLKNRISITHDSSKNQFFLNLNSVTAEDTATYFCAGDDWDWEAYWGQGTLVTVSA (SEQ ID NO: 24 ; CDRs are highlighted) ; and/or

(b) a light chain comprising the amino acid sequence having at least 60%, 65%,

70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:25).

ENVLTQSPAIMSASPGEKVTMTC3A333VNYMHWYQQKSSTSPKLWIYDTSKLASGVPGR FS GSGSGNSYSLTISSMEAEDVATYYCPQGSGYPLTFGSGTKLEIK (SEQ ID NO: 25; CDRs are highlighted).

In one embodiment, variability compared to the reference sequence is present only outside the CDRs.

In one specific embodiment of these aspects, the antibody may be a monoclonal antibody or antigen-binding fragments thereof, and/or may be a humanized antibody or antigen-binding fragment thereof.

In some embodiments, the antibodies and fragments thereof (in the compositions or methods of the disclosure) are conjugated to one or more agents selected from the group including an additional therapeutic agent, such as a chemotherapeutic agent. A

"chemotherapeutic agent" is a chemical compound useful in the treatment of cancer.

Examples of chemotherapeutic agents include alkylating agents such as thiotepa and cyclosphosphamide; alkyl sulfonates such as busulfan, improsulfan and piposulfan; aziridines such as benzodopa, carboquone, meturedopa, and uredopa; ethylenimines and

methylamelamines including altretamine, triethylenemelamine, triethylenephosphoramide, triethylenethiophosphoramide and trimethylolomelamine; acetogenins (especially bullatacin and bullatacinone); a camptothecin (including the synthetic analogue topotecan); biyostatin; callystatin; CC-1065 (including its adozelesin, carzelesin and bizelesin synthetic analogues); cryptophycins (particularly cryptophycin 1 and ciyptophycin 8); dolastatin; duocarmycin (including the synthetic analogues, KW-2189 and CB1-TM1); eleutherobin; pancratistatin; a sarcodictyin; spongistatin; nitrogen mustards such as chlorambucil, chlomaphazine, cholophosphamide, estramustine, ifosfamide, mechlorethamine, mechlorethamine oxide hydrochloride, melphalan, novembichin, phenesterine, prednimustine, trofosfamidc, uracil mustard; nitrosureas such as carmustine, chlorozotocin, fotemustine, lomustine, nimustine, and ranimustine; antibiotics such as the enediyne antibiotics (e. g., calicheamicin, especially calicheamicin gamma 11 and calicheamicin omega 11 (see, e.g., Agnew, Chem Inti. Ed.

Engl., 33: 183-186 (1994)); dynemicin, including dynemicin A; bisphosphonates, such as clodronate; an esperamicin; as well as neocarzinostatin chromophore and related

chromoprotein enediyne antibiotic chromophores), aclacinomysins, actinomycin, authramycin, azaserine, bleomycins, cactinomycin, carabicin, carminomycin, carzinophilin, chromomycinis, dactinomycin, daunorubicin, detorubicin, 6-diazo-5-oxo-L-norleucine, doxombicin (including moipholino-doxorubicin, cyanomoipholino-doxombicin, 2-pyrrolino- doxorubicin and deoxydoxombicin), epimbicin, esombicin, idarubicin, marcellomycin, mitomycins such as mitomycin C, mycophenolic acid, nogalamycin, olivomycins, peplomycin, potfiromycin, puromycin, quelamycin, rodombicin, streptonigrin, streptozocin, tubercidin, ubenimex, zinostatin, zorubicin; anti-metabolites such as methotrexate and 5- fluorouracil (5-FU); folic acid analogues such as denopterin, methotrexate, pteropterin, trimetrexate; purine analogs such as fludarabine, 6-mercaptopurine, thiamiprine, thioguanine; pyrimidine analogs such as ancitabine, azacitidine, 6-azauridine, carmofur, cytarabine, dideoxyuridine, doxifluridine, enocitabine, floxuridine; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone; anti-adrenals such as aminoglutethimide, mitotane, trilostane; folic acid replenisher such as frolinic acid;

aceglatone; aldophosphamide glycoside; aminolevulinic acid; eniluracil; amsacrine;

bestrabucil; bisantrene; edatraxate; defofamine; demecolcine; diaziquone; clfomithine;

elliptinium acetate; an epothilone; etoglucid; gallium nitrate; hydroxyurea; lentinan;

lonidainine; maytansinoids such as maytansine and ansamitocins; mitoguazone;

mitoxantrone; mopidanmol; nitraerine; pentostatin; phenamet; pirarubicin; losoxantrone; podophyllinic acid; 2-ethylhydrazide; procarbazine; polysaccharide complex (JHS Natural Products, Eugene, Oreg.); razoxane; rhizoxin; sizofiran; spirogermanium; tenuazonic acid; triaziquone; 2,2 ^, ,22"-trichlorotriethylamine; trichothecenes (especially T-2 toxin, verracurin A, roridin A and anguidine); urethan; vindesine; dacarbazine; mannomustine; mitobronitol; mitolactol; pipobroman; gacytosine; arabinoside ("Ara-C"); cyclophosphamide ; thiotepa; taxoids, e.g., paclitaxel, ABRAXANE® Cremophor-ftee, albumin-engineered nanoparticle formulation of paclitaxel (American Pharmaceutical Partners, Schaumberg, Ill.), and doxetaxel; chloranbucil; gemcitabine; 6-thioguanine; mercaptopurine; methotrexate; platinum analogs such as cisplatin and carboplatin; vinblastine; platinum; etoposide (VP-16);

ifosfamide; mitoxantrone; vincristine; vinorelbine; novantrone; teniposide; edatrexate;

daunomycin; aminopterin; xeloda; ibandronate; CPT-11; topoisomerase inhibitor RFS 2000; difluorometlhylomithine (DMFO); retinoids such as retinoic acid; capecitabine; and pharmaceutically acceptable salts, acids or derivatives of any of the above. Also included in the definition are proteasome inhibitors such as bortezomib (Velcade), BCL-2 inhibitors, IAP antagonists (e.g. Smac mimics/xIAP and cIAP inhibitors such as certain peptides, pyridine compounds such as (S)— N-{6-benzo[l,3]dioxol-5-yl-l-[5-(4-fluoro-benzoyl)-pyridin-3 - ylmethy- l]-2-oxo-l ,2-dihydro-pyridin-3-yl }-2-methylamino-propionamide, xIAP antisense), HDAC inhibitors (HDACI) and kinase inhibitors (Sorafenib).

In other embodiments, the antibodies and fragments thereof are linked to a detectable label, such as a radiolabel, an enzyme, a fluorescent label, a luminescent label, a

bioluminescent label, a magnetic label, and/or biotin.

In some embodiments, the agent and/or detectable label is conjugated directly to the antibodies or fragments thereof. In other embodiments, the agent and/or detectable label is conjugated to the antibodies or fragments thereof via a linker. Suitable linkers include, but are not limited to, amino acid and polypeptide linkers disclosed herein. Linkers may be cleavable ornon-cleavable.

In another aspect, the disclosure provides methods for treating an autoimmune disorder, comprising administering to a subject in need thereof an amount effective to treat the autoimmune disorder of one or more of:

(a) an IgV domain from a protein selected from the group consisting of CD300c, BTN5 (Erythroid membrane-associated protein), TAPBPL (antigen processing (TAP) binding protein like protein), SkintS (selection and upkeep of intraepithelial T cells 8 protein), and CD300f; and/or

(b) an expression vector comprising a promoter operatively linked to a nucleic acid sequence encoding a protein selected from the group consisting of CD300c, BTN5 (Erythroid membrane-associated protein), TAPBPL (antigen processing (TAP) binding protein like protein), SkintS (selection and upkeep of intraepithelial T cells 8 protein), and CD300f.

In one embodiment, the IgV domain comprises an IgV domain from CD300c. In another embodiment, the IgV domain comprises amino acids 28-114 of human CD300c. In a further embodiment, the IgV domain comprises amino acids 22-128 of human CD300c. In one embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding, residues 21-183 of human CD300c. Exemplary CD300c sequences are SEQ ID NOs: 1-2. In a further embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%,

93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity' along the full length of the amino acid sequence of SEQ ID NO:26.

Human CD300c-Igfitsion protein amino acid sequences (hCD300c : lower case, Ig: upper): Mtvagpvggslsvqcryekehrtlnkfwcrppqilrcdkivetkgsagkrngrvsirdsp anlsftvt lenlteedagtywcgvdtpwlrdfhdpivevevsvfpagtttasspqssmgtsgpptklp vhtwpsvt rkdspepsphmgslfsnvrPRGPTIKPCPPCKCPAPNLLGGPSVFIFPPKIKDVLMISLS PIVTCVW DVSEDDPDVQISWFVNNVEVHTAQTQTHREDYNSTLRWSALPIQHQDWMSGKEFKCKVNN KDLPAPI ERTISKPKGSVT^PQVYVLPPPEEEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELNYK NTEPVLDS DGSYFMYSKLRVEKKNWVERNSYSC8VVHEGLHNHHTTK85'SRTPGK (SEQ ID NO:26)

In one embodiment, tire IgV domain comprises an IgV domain from BTN5. In another embodiment, the IgV domain comprises amino acids 45-143 of human BTN5. In a further embodiment, the IgV domain comprises amino acids 30-144 of human BTN5. In one embodiment, the method comprises administering the subject a polypeptide comprising residues 30-155 of human BTN5 or an expression vector comprising a promoter operatively linked to a nucleic acid sequence encoding a polypeptide comprising residues 30-155 of human BTN5. Exemplary BTN5 amino acid sequences are provided in SEQ ID NOS: 3-4. In a further embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:27.

Human BTN5-Igfiision protein amino acid sequences (hBTN5: lower case, Ig: upper): hagdagkfhvallggtaellcplslwpgtvpkevrwlrspfpqrsqavhifrdgkdqded lmpeykgrtvlvrda qegsvtlqildvrledqgsyrcliqvgnlskedtvilqvaaPRGPTlKPCPPCKCPAPNL LGGPSVFlFPPKIK! VLMISLSFIVTCWVDV5EDDFDVQISWFVNNVEVHTAQTQTHREDYNSTLRWSALPIQHQ DWMSGKEFKCKVN NKDLPAPIERTISKPKGSVRAPQVYVLPPPEEEMTKKQVTLTCMVTDEMPEDIYVEWTNN GKTELNYKNTEPVLD SDGSYFMYSKLRVEKKNWVERNSYSCSWHEGLHNHHTTKSFSRTPGK (SEQ ID NO: 27)

In one embodiment, the IgV domain comprises and IgV domain from TAPBPL. In another embodiment, the IgV domain comprises amino acids 198-297 of human TAPBPL. In a further embodiment, the IgV domain comprises amino acids 198-300 of human TAPBPL.

In one embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding, residues 19-405 of human TAPBPL.

Exemplary TAPBPL amino acid sequences are provided in SEQ ID NOS: 5-6. In a further embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:28.

Human TAPBPL-Ig fusion protein amino acid sequences (hTAPBPL: lower case, Ig: upper case):

Kphpaegqwravdwldcflakdgahrgalassedraraslvlkqvpvlddgsledftdfq ggtlaqddppiife asvdlvqipqaeallhadcsgkevtceisryflqmtettvktaawfmanmqvsgggpsis lvmktprvtknealw hptlnlplspqgtvrtavefqvmtqtqslsfllgssasldcgfsmapgldlisvewrlqh kgrgqlvyswtagqg qavrkgatlepaqlgmardasltlpgltiqdeg tyicqittslyraqqiiqlniqaspkvrlslaneallptlic diagyypldwvtwtreelggspaqvsgasfsslrqsvagtysisssltaepgsagatytc qvthisleeplgas tqwpperrtPRGPTIKPCPPCKCPAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCWVDVS EDDPDVQISWFVN NVEVHTAQTQTHREDYNSTLRWSALPIQHQDWMSGKEFKCKVNNKDLPAPIERTISKPKG SVRAPQVYVLPPPE EEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELNYKNTEPVLDSDGSYFMY3KLRVEKK NWVERN3YSCSWHE GLHNHHTTKSFSRTPGK (SEQ ID NO: 28)

In one embodiment, the IgV domain comprises and IgV domain from SkintS. In another embodiment, the IgV domain comprises amino acids 35-140 of SkintS. In a further embodiment, tire IgV domain comprises amino acids 29-140 of SkintS. In one embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding residues 26-233 of SkintS. An exemplary SkintS amino acid sequence is provided in SEQ ID NO:7. In a further embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:29

Mouse Skint8-Ig fiision protein amino acid sequences ( mouse Skint8: lower case, Ig: upper case):

eklrvttptrhllarvggqaelscqvipphsvmhmevrwfrsghsqpvylyrgghkm seeaapeyanrtefvkea igegkvslriyninilddgpyqcsfndsgfidvaimnlnvtavgleteihvqapdadgvm vecntggwfprpqme wrdskgatlphslksysqdearffhmkmtllltnmshgsiiccisnpvtgeekqtsiiPR GPTIKPCFPCKCPAF NLLGGPSVFIFPPKIKDVLMISLSPIVTCWVDVSEDDPDVQISWEVNNVEVHTAQTQTHR EDYNSTLRWSALP IQHQDWMSGKEFKCKVNNKDLPAPIERTISKPKGSVRAPQVYVLPPPEEEMTKKQVTLTC MVTDEMPEDIYVEWT NNGKTELNYKNTEPVLDSDGSYEMYSKLRVEKKNWVERNSYSCSWHEGLHNHHTTKSFSR TPGK ( SEQ ID NO:29)

In one embodiment, the IgV domain comprises an IgV domain from CD300f. In another embodiment, the IgV domain comprises amino acids 2-140 of human CD300f. In a further embodiment, the IgV domain comprises amino acids 24-125 of human CD300f. In one embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding, residues 20-155 of human CD300f. An exemplary CD300f amino acid sequence is provided in SEQ ID NO:8. In a further embodiment, the method comprises administering the subject a polypeptide comprising, or an expression vector encoding the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:9

Human CD300F-Igfiision protein amino acid sequences (hCD300F: lower case, Ig: upper case):

tqitgpttvnglergsltvqcvyrsgwetylkwwcrgaiwrdckilvktsgseqevk rdrvsikdnqknrt ftvtmedlmktdadtywcgiektgndlgvtvqvtidpapvtqeetsssptltghhldnrh kllklPRGFTIKPCF PCKCPAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCVWDVSEDDPDVQISWFVNNVEVHT AQTQTHREDYNSTL RW3ALPIQHQDWMSGKEEKCKVNNKDLFAPIERTISKPKGSVRAPQVYVLPPPEEEMTKK QVTLTCMVTDFMPE DIYVEWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKKNWVERNSYSCSWHEGLHNHH TTKSFSRTPGK

(SEQ ID NO: 09)

In all of these embodiments, the methods may be used to treat any suitable autoimmune disorder. In various non-limiting embodiments, the autoimmune disease may be selected from the group consisting of multiple sclerosis, type I diabetes, arthritis including but not limited to rheumatoid arthritis, systemic lupus erythematosus, Crohn’s disease, scleroderma, sarcoidosis, ulcerative colitis, ankylosing spondylitis, autoimmune hepatitis, autoimmune myocarditis, dermatomyositis, Graves’ disease, Sjogren’s syndrome, and vitiligo, and other autoimmune diseases. In one embodiment, the methods further comprise administering to the subject an amount effective of an immune regulator to stimulate T cell function. Any suitable immune regulator may be used, including but not limited to anti-CD3 antibodies.

In another aspect, the disclosure provides fusion molecules comprising

(a) a first polypeptide comprising an IgV domain from a protein selected from the group consisting of CD300c, BTN5 (Erythroid membrane-associated protein), TAPBPL (antigen processing (TAP) binding protein like protein), SkintS (selection and upkeep of intraepithelial T cells 8 protein), and CD300f and

(b) a heterologous molecule.

In one embodiment, the first polypeptide does not include any portion of CD300c, BTN5, TAPBPL, SkintS, or CD300f outside of the ECM domain. In another embodiment, the heterologous molecule comprises a second polypeptide selected from the group consisting of a constant region of an immunoglobulin or a fragment thereof (including but not limited to CHI, CH2, and/or CH3; Fc regions from immunoglobulins, including but not limited to native IgGl, IgG2, or IgG4). In this embodiment, the immunoglobulin or a fragment thereof adds functionality to the by, for example, helping target the first polypeptide to a cell type that has a cell surface receptor to which the immunoglobulin or a fragment thereof selectively binds. As a result, fusion molecules of this embodiment are particularly useful for therapeutic applications. As will be understood by those of skill in the art, any suitable immunoglobulin or a fragment thereof can be employed that targets a cell or tissue of interest. The immunoglobulin or a fragment thereof may be recombinantly expressed as part of the polypeptide. In another embodiment, the heterologous molecule comprises an organic molecule of interest.

The fusion molecules disclosed herein may be used, for example, in the methods of the invention. In a specific embodiment, a fusion molecule is a fusion protein comprising the first polypeptide and a second polypeptide sequence. In one embodiment, the second polypeptide is a constant region of an immunoglobulin or a fragment thereof (e.g., CHI,

CH2, and/or CH3). In various non-limiting embodiments, Fc regions from immunoglobulins including but not limited to IgGl, IgG2, or IgG4 can be used to produce such a fusion protein. In various further embodiments, hybrid IgGl/IgG4 Fc domains can be used to produce such a fusion protein as can modified IgGl Fc domains (e.g., IgGl modified to improve binding to certain Fc gamma receptors; IgGl modified to minimize effector function; IgGl with altered/no glycan; and IgGl with altered pH-dependent binding to FcRn) and modified IgG4 Fc domains (e.g., IgG4 modified to prevent binding to Fc gamma receptors and/or complement). In other embodiments, the first polypeptide may act as a targeting moiety to target a therapeutic second polypeptide to a cell or tissue target of interest; non-limiting embodiments of such therapeutic second polypeptides include but are not limited to interferon^, interferon-b, interferon-a, interleukin-2 ("IL-2"), interleukin-7 ("IL-7"), interleukin 9 ("IL-9"), interleukin- 10 ("IL-10"), interleukin- 12 ("IL-12"), interleukin- 15 ("IL-15"), interleukin-23 ("IL-23"), granulocyte macrophage colony stimulating factor ("GM-CSF"), granulocyte colony stimulating factor ("G-CSF")), or growth factors.

In other embodiments, the fusion molecule is a fusion protein or a conjugate (such as via a linker) comprising the first polypeptide and an organic molecule of interest. In this embodiment, the first polypeptide may, for example, act as a targeting moiety to target the organic molecule to which it is fused or conjugated to particular organs or tissues (e.g., lymphoid organs or tissues). The attached appendices provide information regarding the organs and tissues expressing the first polypeptide. The organic molecule fused or conjugated to the first polypeptide may be a molecule that one skilled in the art is interested in targeting to a particular organ(s) or tissue(s) (e.g., a cytokine, drug, marker, etc.).

In one embodiment, the first polypeptide comprises an IgV domain from CD300c. In another embodiment, the IgV domain comprises amino acids 28-114 of human CD300c. In a further embodiment, the IgV domain comprises amino acids 22-128 of human CD300c. In one embodiment, the first polypeptide comprises residues 21-183 of human CD300c.

Exemplary CD300c amino acid sequences are provided in SEQ ID NOs: 1-2. In another embodiment, the fusion molecule comprises the amino acid sequence having at least 60%,

65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or

100% identify along the full length of the amino acid sequence of SEQ ID NO:26.

Human CD300c-Ig fiision protein amino acid sequences (hCD300c: lower case, Ig: upper case):

Mtvagpvggslsvqcryekehrtlnkfwcrppqilrcdkivetkgsagkrngrvsirdsp anlsftvtlenltee dagtywcgvdtpwlrdfhdpivevevsvfpagtttasspqssmg tsgpptklpvhtwpsvtrkdspepsphpgsl fsnvrPRGPTIKPCPPCKCPAPNLLGGPSVFIFPPKIKBVLMISLSFIVTCWVDVSEBOF BVQISWFVNNVEVH 7AQTQTHREDYNSTLRWSALFIQHQBWMSGKEFKCKVNNK0LFAPIER7ISKPKGSVRAP QVYVLPPPEEEMTK KQVTLTCMVTDFMPEDIYVEWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKKNWVER NSYSCSWHEGLHNH HTTKSFSP.TPGK (SEQ IB NO:26)

In one embodiment, the first polypeptide comprises an IgV domain from BTN5. In another embodiment, the IgV domain comprises amino acids 45-143 of human BTN5. In a further embodiment, the IgV domain comprises amino acids 30-144 of human BTN5. In one embodiment, the first polypeptide comprises residues 30-155 of human BTN5. Exemplary BTN5 amino acid sequences are provided in SEQ ID NOs:3-4. In another embodiment, the fiision molecule comprises the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:27. Human BTN5-Ig fusion protein amino acid sequences (hBTN5: lower case, Ig: upper case): hagdagkfhvallggtaellcplslwpgtvpkevrwlrspfpqrsqavhifrdgkdqded lmpeykgrtvl vrdaqegsvtlqildvrledqgsyrcliqvgnlskedtvilqvaaPRGPTIKPCPPCKCP APNLLGGPSVFIFPP KIKDVLMISLSPIVTCWVDVSEDDPDVQISWFVNNVEVHTAQTQTHREDYNSTLRWSALP IQHQDWMSGKEFK CKVNNKDLPAFIERTISKFKGSVRAFQVYVLFFPEEEMTKKQVTLTCMVTDFMFEDIYVE WTNNGKTELNYKNTE PVLDSDGSYEMYSKLKVEKKNWVERNSYSCSWHEGLHNHHTTKSFSRTPGK (SEQ ID NO: 27 )

In one embodiment, the first polypeptide comprises an IgV domain from TAPBPL. In another embodiment, the IgV domain comprises amino acids 198-297 of human TAPBPL. In a further embodiment, the IgV domain comprises amino acids 198-300 of human TAPBPL.

In one embodiment, the first polypeptide comprises residues 19-405 of human TAPBPL.

Exemplary TAPBPL amino acid sequences are provided in SEQ ID NO:5-6. In another embodiment, the fusion molecule comprises the amino acid sequence having at least 60%,

65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:28.

Human TAPBPL-Ig fusion protein amino acid sequences (hTAPBPL: lower case, Ig: upper case):

Kphpaegqwravdvvldcflakdgahrgalassedraraslvlkqvpvlddgsledftdf qggtlaqddppiife asvdlvqipqaeallhadcsgkevtceisryflqmtettvktaawfmarunqvsgggpsi slvmktprvtknealw hptlnlplspqgtvrtavefqvmtqtqslsfllgssasldcgfsmapgldlisvewrlqh kgrgqlvyswtagqg qavrkgatlepaqlgmardasltlpgltiqdegtyicqittslyraqqiiqlniqaspkv rlslaneallptlic diagyypldvvvbwtreelggspaqvsgasfsslrqsvag tysisssltaepgsagatytcqvthisleeplgas tqwpperrtPRGPT!KPCPPCKCPAPNLLGGPSVF!FPPKIKDVLMISLSPIVTCVWDVS EDDPDVQISWFVN NVEVHTAQTQTHREDYNSTLRVVSALPIQHQDWMSGKEFKCKVNNKDLPAPIERTISKPK GSVRAPQVYVLPPPE EEMTKKQVTLTCMVTDFMPEDIYVEWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKK NWVERNSYSCSWHE GLHNHHTTKSFSRTPGK (SEQ ID NO: 28)

In one embodiment, the first polypeptide comprises an IgV domain from SkintS. In another embodiment, the IgV domain comprises amino acids 35-140 of SkintS. In a further embodiment, the IgV domain comprises amino acids 29-140 of SkintS. In one embodiment, the first polypeptide comprises residues 26-233 of SkintS. An exemplary SkintS amino acid sequence is provided in SEQ ID NO:7. In another embodiment, the fusion molecule comprises the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:29.

Mouse Skint8-Ig fusion protein amino acid sequences (lower case, Ig: upper case):

eklrvttptrhllarvggqaelscqvipphsvmhmevrwfrsghsqpvylyrgghkm seeaapeyanrtefvkea igegkvslriyninilddgpyqcsfndsgfidvaimnlnvtavgleteihvqapdadgvm vecntggwfprpqme wrdskgatlphslksysqdearffhmkmtllltnmshgsiiccisnpvtgeekqtsiiPR GPTIKPCPPCKCPAP NLLGGPSVFIFPPKIKDVLMISLSPIVTCVWDVSEDDPDVQISWFVNNVEVHTAQTQTHR EDYNSTLRWSALP IQHQDWMSGKEFKCKVNNKDLPAPIERTISKPKGSVRAPQVYVLPPPEEEMTKKQVTLTC MVTDFMPEDIYVEWT NNGKTELNYKNTEPVLDSDGSYEWYSKLRVEKKNWVERNSYSCSWHEGLHNHHTTKSFSR TPGK (SEQ ID NO:29)

In one embodiment, the IgV domain comprises an IgV domain from CD300f. In another embodiment, the IgV domain comprises amino acids 2-140 of human CD300f. In a further embodiment, the IgV domain comprises amino acids 24-125 of human CD300f. In one embodiment, the first polypeptide comprises residues 20-155 of human CD300f. An exemplary CD300f amino acid sequence is provided in SEQ ID NO:8. In one embodiment, the fusion molecule comprises the amino acid sequence having at least 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity along the full length of the amino acid sequence of SEQ ID NO:9.

Human CD300F-Igfiision protein amino acid sequences (hCD300F: lower case, Ig: upper case):

tqitgpttvnglergsltvqcvyrsgwetylkwwcrgaiwrdckilvktsgseqevk rdrvsikdnqknrt ftvtmedlmktdadtywcgiektgndlgvtvqvtidpapvtqeetsssptltghhldnrh kllklPRGFTIKPCF PCKCPAPNLLGGPSVFIFPPKIKDVLMISLSPIVTCVWDVSEDDPDVQISWFVNNVEVHT AQTQTHREDYNSTL RWSALPIQHQDimSGKEFKCKVNNKDLPAPIERTISKPKGSVRAPQVYVLPPPEEEMTKK QVTLTCMVTDFMPE DIYVEWTNNGKTELNYKNTEPVLDSDGSYFMYSKLRVEKKNWVERNSYSCSWHEGLHNHH TTKSFSRTPGK

(SEQ ID NO: 09)

As used throughout the present application, the term "polypeptide" is used in its broadest sense to refer to a sequence of subunit amino acids, whether naturally occurring or of synthetic origin. The polypeptides of the invention may comprise L-amino acids, D-amino acids (which are resistant to L-amino acid-specific proteases in vivo), or a combination of D- and L-amino acids. The polypeptides described herein may be chemically synthesized or recombinantly expressed. The polypeptides may be linked to other compounds to promote an increased half-life in vivo, such as by PEGylation, HESylation, PASylafion, or glycosylation. Such linkage can be covalent or non-covalent as is understood by those of skill in the art.

The polypeptides may be linked to any other suitable linkers, including but not limited to any linkers that can be used for purification or detection (such as FLAG or His tags).

In another aspect, the present disclosure provides nucleic acids encoding the antibodies or fusion molecules in which the heterologous molecule is a polypeptide of any aspect or embodiment of the invention. The nucleic acid sequence may comprise RNA or DNA. Such nucleic acid sequences may comprise additional sequences useful for promoting expression and/or purification of the encoded protein, including but not limited to polyA sequences, modified Kozak sequences, and sequences encoding epitope tags, export signals, and secretory signals, nuclear localization signals, and plasma membrane localization signals. It will be apparent to those of skill in the art, based on the teachings herein, what nucleic acid sequences will encode the antibodies or fusion molecules disclosed herein.

In a further aspect, the present disclosure provides nucleic acid expression vectors comprising the nucleic acid of any embodiment of the disclosure operatively linked to a suitable control sequence. "Recombinant expression vector" includes vectors that operatively link a nucleic acid coding region or gene to any control sequences capable of effecting expression of the gene product. “Control sequences” operably linked to the nucleic acid sequences of the disclosure are nucleic acid sequences capable of effecting the expression of the nucleic acid molecules. The control sequences need not be contiguous with the nucleic acid sequences, so long as they function to direct the expression thereof. Thus, for example, intervening untranslated yet transcribed sequences can be present between a promoter sequence and the nucleic acid sequences and the promoter sequence can still be considered "operably linked" to the coding sequence. Other such control sequences include, but are not limited to, polyadenylation signals, termination signals, and ribosome binding sites. Such expression vectors can be of any type known in the art, including but not limited plasmid and viral-based expression vectors. The control sequence used to drive expression of the disclosed nucleic acid sequences in a mammalian system may be constitutive (driven by any of a variety of promoters, including but not limited to, CMV, SV40, RSV, actin, EF) or inducible (driven by any of a number of inducible promoters including, but not limited to, tetracycline, ecdysone, steroid-responsive. The expression vector must be replicable in the host organisms either as an episome or by integration into host chromosomal DNA. In one, the expression vector comprises a plasmid; in another embodiment a viral vector, including but not limited to adenoviral vectors or rAAV vectors.

In another aspect, the present disclosure provides recombinant host cells comprising the nucleic acid expression vectors of the disclosure. The host cells can be either prokaryotic or eukaryotic. The cells can be transiently or stably transfected or transduced. Such transfection and transduction of expression vectors into prokaryotic and eukaryotic cells can be accomplished via any suitable technique . A method of producing the antibodies or fusion molecules of the disclosure is also provided herein. The method comprises the steps of (a) culturing a host according to this aspect of the disclosure under conditions conducive to the expression of the antibodies or fusion molecules, and (b) optionally, recovering the expressed antibodies or fusion molecules. The expressed antibodies or fusion molecules can be recovered from the cell free extract, cell pellet, or recovered from the culture medium. In a further aspect, the present disclosure provides pharmaceutical compositions, comprising the antibodies or fusion molecules, nucleic acids, nucleic acid expression vectors, or recombinant host cells, of any aspect or embodiment of the disclosure, and a

pharmaceutically acceptable carrier. The pharmaceutical compositions of the disclosure can be used, for example, in the methods of the disclosure. The pharmaceutical composition may comprise in addition to the polypeptides, nucleic acids, etc. of the disclosure (a) a lyoprotectant; (b) a surfactant; (c) a bulking agent; (d) a tonicity adjusting agent; (e) a stabilizer; (f) a preservative and/or (g) a buffer.

In some embodiments, the buffer in the pharmaceutical composition is a Tris buffer, a histidine buffer, a phosphate buffer, a citrate buffer or an acetate buffer. The pharmaceutical composition may also include a lyoprotectant, e.g. sucrose, sorbitol or trehalose. In certain embodiments, the pharmaceutical composition includes a preservative e.g. benzalkonium chloride, benzethonium, chlorohexidine, phenol, m-cresol, benzyl alcohol, methylparaben, propylparaben, chlorobutanol, o-cresol, p-crcsol, chlorocrcsol, phcnylmercuric nitrate, thimerosal, benzoic acid, and various mixtures thereof. In other embodiments, the pharmaceutical composition includes a bulking agent, like glycine. In yet other embodiments, the pharmaceutical composition includes a surfactant e.g., polysorbate-20, polysorbate-40, polysorbate- 60, polysorbate-65, polysorbate-80 polysorbate-85, poloxamer-188, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan trilaurate, sorbitan tristearate, sorbitan trioleaste, or a combination thereof. The

pharmaceutical composition may also include a tonicity adjusting agent, e.g., a compound that renders the formulation substantially isotonic or isoosmotic with human blood.

Exemplary tonicity adjusting agents include sucrose, sorbitol, glycine, methionine, mannitol, dextrose, inositol, sodium chloride, arginine and arginine hydrochloride. In other embodiments, the pharmaceutical composition additionally includes a stabilizer, e.g., a molecule which, when combined with a protein of interest substantially prevents or reduces chemical and/or physical instability of the protein of interest in lyophilized or liquid form. Exemplary stabilizers include sucrose, sorbitol, glycine, inositol, sodium chloride, methionine, arginine, and arginine hydrochloride.

The antibodies or fusion molecules, nucleic acids, etc. of the disclosure may be the sole active agent in the pharmaceutical composition, or the composition may further comprise one or more other active agents suitable for an intended use. The pharmaceutical compositions described herein generally comprise a combination of a therapeutic described herein and a pharmaceutically acceptable carrier, diluent, or excipient. Such compositions are substantially free of non-pharmaceutically acceptable components, i.e., contain amounts of non-pharmaceutically acceptable components lower than permitted by US regulatory requirements at the time of filing this application. In some embodiments of this aspect, if the compound is dissolved or suspended in water, the composition further optionally comprises an additional pharmaceutically acceptable carrier, diluent, or excipient. In other embodiments, the pharmaceutical compositions described herein are solid pharmaceutical compositions (e.g, tablet, capsules, etc.).

These compositions can be prepared in a manner well known in the pharmaceutical art, and can be administered by any suitable route. In a preferred embodiment, the pharmaceutical compositions and formulations are designed for oral administration.

Conventional pharmaceutical carriers, aqueous, powder or oily bases, thickeners and the like may be necessary or desirable.

The pharmaceutical compositions can be in any suitable form, including but not limited to tablets, pills, powders, lozenges, sachets, cachets, elixirs, suspensions, emulsions, solutions, syrups, aerosols (as a solid or in a liquid medium), ointments containing, for example, up to 10% by weight of the active compound, soft and hard gelatin capsules, sterile injectable solutions, and sterile packaged powders.

Example 1. CD300c

In this example, we describe CD300c as a novel T cell co-inhibitory molecule that shares significant sequence homology with existing B7 family members. CD300c protein is expressed on professional antigen-presenting cells (APC), including B cells, monocytes, macrophages and dendritic cells (DCs). The putative CD300c counter-receptor is expressed on CD4 and CDS T cells, and the expression levels are upregulated upon activation. Soluble human and mouse CD300c-Fc fusion proteins significantly inhibit the proliferation, activation, and cytokine production by CD4 and CDS T cells in vitro.

Administration of CD300c-Fc protein attenuates graft-versus-host disease (GVHD) in mice, and autoimmune diseases including experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA), animal models for human multiple sclerosis (MS) and rheumatoid arthritis (RA). Furthermore, anti-CD300 antibodies inhibit tumor growth in melanoma and colon cancer mouse models, which is related to the neutralization of the inhibitory activity of CD300c on T cells and other immune cells. Our results demonstrate that therapeutic interaction with the CD300c inhibitory pathway represents a new strategy to modulate T cell-mediated immunity for the treatment of GVHD and autoimmune disease, as well as cancer.

Materials and Methods \

Cloning and purification of hCD300c and mCD300c2

The extracellular domains of hCD300c (aa29-183) and mCD300c2 (aa22-193) were cloned and fused into a pCMV6-AC-FC-S expression vector containing the constant region of mouse IgG2a (ORIGENE). The vectors were transfected into

HEK293F cells. The fusion proteins were purified for supernatant using Protein G

Sepharose 4 Fast Flow™ according to the manufacturer’s instructions (GE Healthcare). Purified proteins were verified by SDS-PAGE, Coomassie Staining and Western blot.

Protein was quantified using the Pierce™ BCA Protein Assay Kit (Pierce, Rockford, IL). Control Ig (recombinant mouse IgG2a Fc protein) was purchased from BXCell (West Lebanon, NH).

SDS-PAGE and Western blot

Purified CD300c-Ig was loaded on a 12% SDS-PAGE, and stained with Coomassie blue or transferred to apolyvinylidene fluoride membrane. The protein containing membrane was incubated with HRP conjugated anti-mouse IgG2 antibody, or anti- hCD300c antibody (Novus Biologicals, Littleton, CO) followed by HRP conjugated second antibody, and then developed with Super Signal® West Pico chemiluminescent Substrate (Thermo Scientific). Flow Cytometry analysis

Single cell suspensions of organs were stained with the fluorochrome-conjugated antibodies protein as described [35; 36; 37; 38] For intracellular staining, the cells were first permeabilized with a BD Cytofix/Cytoperm solution for 20 minutes at 4 °C. Direct or indirect staining of fluorochrome-conjugated antibodies included: CD4, CDS, CD 19, B220, CD1 lc, CD1 lb, F4/80, H2 ^b , Annexin V, Ki67, CD44, CD62L, CD69, CTLA-4, CD28, PD- 1, BTLA, and ICOS and mCD300c2 (BioLegend, or BD Biosciences, San Jose, CA, San Diego, CA). mCD300c2-Ig and hCD300c-Ig were biotinylated with sulfo-NHS-LC-Biotin (Pierce). The samples were analyzed on a FACSCalibur™ or LSRFortessa™ X-20 Cell Analyzer (BD Biosciences). Data analysis was done using FlowJo™ software (Ashland, OR).

Limulus Amebocyte Lysate (LAL) assay

The endotoxin level in the purified proteins was determined by the endpoint chromogenic LAL test according to the manufacturer’s instructions (Lonza, Walkersville,

MD) [39]

In vitro T cell proliferation assays

Normal human peripheral blood CD3 ⁺ Pan T Cells that were negatively isolated from mononuclear cells using an indirect immunomagnetic Pan-T labeling system were purchased from ALLCELLS, LLC (Alameda, CA). Murine CD3 ⁺ T cells were purified from C57BL/6 mice by an immunomagnetic system (Miltenyi, Auburn, CA), and the purity of the cells was usually >95%. T cells were stimulated with anti-CD3 and/or anti-CD28 antibodies (Biolegend) in the presence of CD300c-Ig or control Ig. Proliferative response was assessed by pulsing the culture with 1 pCi of [¾] thymidine (PerkinElmer, Inc.,

Downers Grove, IL) 12 hours before harvest. Incorporation of [¾] thymidine was measured by liquid scintillation spectroscopy (PerkinElmer, Inc.). For carboxyfluorescein diacetate succinimidyl ester (CFSE) assay, splenocytes were labeled with CFSE

(ThermoFisher Scientific) and stimulated with anti-CD3 in the presence of CD300c-Ig or control Ig. The cells were analyzed by flow cytometry.

Mice

Four-week-old female C57BL/6 and BALB/c mice were purchased from Jackson

Laboratory. The mice were used in accordance with a protocol approved by the

Institutional Animal Care and Use Committee of the University of Connecticut.

GVHD model

BALB/c recipients received 900 cGy total body irradiation from a 137Cs source (Gammator-50 Gamma Irradiator; Radiation Machinery Corporation, Parsippany, NJ). Two to four hours later, the mice were injected intravenously (i.v.) with BM and spleen cells from C57BL/6 mice. The recipients were injected i.p. with hCD300c-Ig, or control Ig. The severity of GVHD was evaluated with a clinical GVHD scoring system. In brief, GVHD recipients in coded cages were individually scored every week for five clinical parameters on a scale from 0 to 2: weight loss, posture, activity, fur texture and skin integrity. A clinical GVHD index was generated by summation of the five criteria scores (maximum index = 10).

GVHD target organs were harvested for histopathological analysis. The organs were formalin-preserved, paraffin-embedded, sectioned and hematoxylin/eosin (H&E)- stained. Assessment of tissue damage was performed based on scoring systems

previously described [40] Briefly, liver GVHD was scored on the number of involved tracts and severity of liver cell necrosis; the maximum score is 10. Gut GVHD was scored on the basis of crypt apoptosis and lamina propria inflammation; the maximum score is 8. Lung GVHD was scored on the periluminal infiltrates, pneumonitis, and the severity of lung tissues involved; the maximum score is 9. Induction and assessment of EAE

Mouse MOG35-55 (GL Biochem, Shanghai, China) was emulsified in complete Freud’s adjuvant (Sigma-Aldrich, St Louis, MO, USA) supplemented with Mycobacterium tuberculosis H37Ra (Difco Laboratories, Detroit, MI). Mice were injected s.c. with the MOG at 4 points in the dorsal flank on day 0. The mice were also injected i.p. with 500 ng of purified Bordetella pertussis toxin (Sigma-Aldrich). The mice were injected i.p. with hCD300c-Ig, or control Ig, and observed for clinical scores based on the following scale: 0, normal; 0.5, partially limp tail; 1, paralyzed tail; 2, loss in coordinated movement, hind limb paresis; 2.5, one hind limb paralyzed; 3, both hind limbs paralyzed; 3.5, hind limbs paralyzed, weakness in forelimbs; 4, forelimbs paralyzed; 5, moribund or dead. As required by animal ethics, mice were euthanized beyond a clinical score of 4.

Induction and assessment of collagen-induced arthritis (CIA)

Type II collagen (CII) (2 mg/ml) was emulsified with an equal volume of complete Freund's adjuvant (CFA). DBA/1 mice were injected s.c. 1 cm from the base of the tail with 50 ul of the emulsion on day 0. On day 14, the mice were receive a booster injection of the

CH/incomplete Freund's adjuvant (IF A) emulsion s.c. around the base of the tail. When CIA symptom occured, the mice were injected i.p. with hCD300c-Ig, or control Ig. The development of CIA was assessed over time. The clinical severity of arthritis in each paw was quantified according to a graded scale from 0 to 4 as follows: 0, no swelling; 1, swelling in one digit or mild edema; 2, moderate swelling affecting several digits; 3, severe swelling affecting most digits; and 4, the most severe swelling and/or ankyloses. Generation of anti-hCD300c polyclonal and monoclonal Antibodies

BALB/c mice were immunized with 100 mg hCD300c-Ig protein emulsified in complete Freund's adjuvant (CFA) on day 0 and boosted on day 14 and day 21 in the same protein quantity in incomplete Freund's adjuvant (IFA). The mice were boosted with 100 ^ hCD300c-Ig without IFA 3 times (days 28, 29, and 30). On day 31, the serum that contain anti-CD300c polyclonal antibody was harvested.

To make anti-hCD300c monoclonal antibodies, the spleens were also harvested from the immunized mice on day 31. Single-cell suspension of the splenocytes were fused to X63- Ag8.653 myeloma cells to produce hybridomas. ELISA was performed to identify the hybridomas that could produce mAbs that reacted with hCD300c-Ig, but not with control Ig protein. These hybridoma clones were subcloned by limiting dilution. The anti- hCD300c mAbs were further screened for the ability to neutralize the inhibitory activity of hCD300c on T cell proliferation and activation. The anti-hCD300c mAbs were purified for supernatant of the hybridomas using Protein G Sepharose 4 Fast Flow according to the manufacturer’s instructions (GE Healthcare).

Evaluation of local tumor growth

Murine CT-26 colon cancer cells and B16F10 melanoma cells were obtained from the National Cancer Institute and ATCC. The cancer cells were injected s.c. into syngeneic BALB/c or C57BL/6 mice. Anti-hCD300c or control mAb was then injected into the tumor injection site. Tumor size (volume) was determined every other day by caliper

measurements of the shortest (A) and longest (B) diameter, using the formula V = (A2B)/2.

Statistical analysis

P-values were based on tire two-sided Student’s t test. A confidence level above 95% (p<0.05) was determined to be significant.

Results:

hCD300c inhibits the proliferation and activation of mouse and human T cells in vitro

To investigate whether CD300c protein can affect T cell function, we produced an hCD300c-Ig fusion protein by cloning the extracellular domain of the hCD300c gene into an expression vector containing the constant region of the mouse IgG2a. The expression vector was then transfected into human HEK-293 cells to produce hCD300c-Ig fusion protein that was then purified from the supernatant of the cells. A relatively high purity of hCD300c-Ig protein was obtained, as determined by Coomassie blue-stained SDS-PAGE. The identity of the fusion protein was verified by Western blot using anti-IgG2a antibody or anti-hCD300c antibody. The actual molecular weight (MW) of the hCD300c-Ig was higher than the predicted MW, suggesting that the recombinant protein was glycosylated. The endotoxin level was less than 0.01 EU/ml of 1 mg of purified protein.

We then determined whether hCD300c-Ig protein affected T cell proliferation. To do this, CD3 ¹ T cells were purified from splenocytes of C57BL/c mice, and cultured on plates pre-coated with anti-CD3 antibody in the presence of graded doses of hCD300-Ig (800, 1600, and 3200 ng/ml) for 3 days. Since the molecular weight of hCD300-Ig fusion protein is ~1 5-fold higher than that of control Ig protein, we used equimolar amounts of the control Ig as a control. T cell proliferation was measured by [ ³ H] thymidine incorporation. As shown in Figure 1A, hCD300c- Ig inhibited anti-CD3 -activated T cell proliferation in a dose-responsive manner, with ~32%, 72% and 78% inhibition by 800, 1600, and 3200 ng/ml hCD300c-Ig, respectively, as compared to equimolar amounts of control Ig. We also determined whether hCD300c could inhibit anti- CD3 and anti-CD28 antibody-activated T cell proliferation. Similarly, hCD300c-Ig reduced anti- CD3 and anti-CD28-activated T cell proliferation in a dose-dependent manner, although to a lesser extent than that with anti-CD3 activation only (Figure IB).

To confirm the effect on T cell proliferation and to determine whether hCD300c affects CD4 and/or CDS T cells, we performed a carboxyfluorescein diacetate

succinimidyl ester (CFSE) dilution assay. Murine splenocytes were labelled with CFSE, and then cultured with anti-CD3 antibody in the presence of graded doses of hCD300c-Ig or control Ig. T cell proliferation was measured by CFSE fluorescent dilution in CD4 and CDS T cells. As shown in Figure 1C-F, hCD300c-Ig inhibited anti-CD3-activated proliferation of both CD4 and CDS T cells in a dose-dependent manner.

We next determined whether hCD300c-Ig affects the activation of T cells in vitro. CD69 is an early activation marker. After splenocytes were cultured with anti-CD3 antibody and hCD300c-Ig or contiol Ig, the expression of the CD69 on CD4 and CDS T cells was analyzed 24 hours later. As shown in Figure 1G-J, hCD300c-lg at the dose of 3200 ng/ml significantly reduced the expression of CD69 on both CD4 and CDS T cells. The results suggest that hCD300c also inhibits the activation of CD4 and CDS T cells.

Having demonstrated that hCD300c-Ig inhibited murine T cells proliferation in vitro, we examined whether hCD300c-Ig affected human T cells. Purified human T cells were cultured with anti-CD3 antibody in the presence of graded doses of hCD300-Ig or control Ig, and T cell proliferation was measured by [ ³ H] thymidine incorporation.

Similarly, hCD300c-Ig markedly inhibited human T cell proliferation with ~53% and 77% inhibition by 1500, and 3000 ng/ml hCD300c-Ig, respectively (Figure IK). Furthermore, hCD300c-Ig at both 1600 ng/ml and 3200 ng/ml doses significantly reduced the expression of CD69 on both human CD4 and CDS T cells (Figure 1L, M).

Taken together, our results indicate that hCD300c-Ig inhibits TCR-mediated proliferation and/or activation of both mouse and human T cells in vitro. hCD300c has similar inhibitory effects in both human and mouse primary T cells, suggesting that its binding partner and its conferred function on T cells may be conserved across species. mCD300c2 inhibits the proliferation and activation of mouse T cells in vitro

We also produced a mCD300c2-Ig protein by fusing the extracellular domain of mCD300c2 to the mouse IgG2a constant region, and analyzed the effects of purified mCD300c2-Ig fusion protein on mouse T cell proliferation and activation in vitro. We found that mCD300c2-Ig markedly inhibited anti-CD3-induced T cell proliferation, with more than 90% inhibition by 800, 1600, or 3200 ng/ml of mCD300c2-Ig (Figure 2A). mCD300c2-Ig also inhibited anti-CD3 and anti-CD28 antibody-induced T cell proliferation, with ~81%, 85% and 94% inhibition by 800, 1600, and 3200 ng/ml hCD300c-Ig, respectively (Figure

2B). CFSE dilution assay confirmed that mCD300c2-Ig inhibited anti -CD3 -induced proliferation of both CD4 ¹ and CD8 ¹ T cells (Figure 2C-F).

Like hCD300c-Ig, mCD300c2-Ig significantly reduced the expression of CD69 on both CD4 ¹ and CD8 ¹ T cells induced by either anti-CD3 antibody, or anti-CD3 plus anti- CD28 antibodies, and the reduction was also in dose-dependent manner (Figure 2G-L). To further confirm that mCD300c2-Ig inhibits T cell activation, we analyzed the expression of CD44 and CD62L by CD4 ¹ and CD8 ¹ T cells. It has been reported that naive T cells are CD44 ^low CD62L ^hi , while effective memory T cells are CD44 ^ld CD62L ^low . As shown in Figure 2M-Q, mCD300c2-Ig significantiy increased the percentages of CD44 ^low CD62L ^hi naive cells in anti -CDS -activated CD4 ⁺ and CD8 ⁺ T cells, but decreased the percentages of CD44 ^hi CD62L ^k,w effector memory T cells. The results further suggest that mCD300c2-Ig inhibits the activation of CD4 ⁺ and CD8 ¹ T cells.

Collectively, our results indicate that both hCD300c-lg and mCD300c2-Ig inhibit TCR- mediated proliferation and activation of both CD4 and CDS T cells in vitro, providing further evidence that CD300c has T cell co-inhibitory properties.

mCD300c2 inhibits cytokine production from T cells

We then determined the effect of mCD300c2 on cytokine production from T cells in vitro. CD3 ⁺ T cells were purified from the spleens of C57BL/6 mice and stimulated with anti- CD3 antibody in the presence of graded doses of mCD300c2-Ig or control Ig protein for 3 days. The contents of cytokines in the supernatants were measured by ELISA. As shown in Figure 3, mCD300c2-Ig inhibited the production of IFNy, IL-2, IL-17A and IL-10, but not TNFa. The results indicate that mCD300c2-Ig suppresses certain

Thl /Th2/Thl7 cytokine production by T cells induced by TCR signaling.

The expression pattern of CD300c on murine immune cells and in normal and human tumor tissues

We analyzed cell surface expression of mCD300c2 protein on murine immune cells by flow cytometry using a monoclonal antibody against mCD300c2 (clone TX52). We found that resting splenic CD4 ⁺ and CD8 ⁺ T cells scarcely expressed mCD300c2 protein (Figure 4A, B). After activation by anti-CD3 and anti- CD28 antibodies, a small percentage of activated CD4 ⁺ and CD8 ⁺ T cells expressed mCD300c2. We then examined the expression of mCD300c2 protein on other immune cells, and found that resting and activated B220 ⁺ B cells, CD1 lb ⁺ monocytes and F4/80 ⁺ macrophages expressed various levels of mCD300c2 (Figure 4A, B). The expression level of mCD300c2 on macrophages was upregulated upon activation. In addition, although CD300c protein was scarcely expressed on resting CD1 lc ⁺ DCs, it was induced upon activation by LPS (Figure 4A, B). These results indicate that CD300c is expressed on a variety' of APCs.

We then determined the expression of hCD300c protein in normal and tumor human tissues by immunohistochemistry . As shown in Figure 4C, hCD300c was weakly or not at all expressed in normal breast, colon, and liver tissues. The expression levels of hCD300c in breast, colon, and liver tumor tissues were higher than the respective normal tissues, whereas the expression levels of hCD300c in normal and tumor tissues of lung were similar (Figure 4C). hCD300c protein was largely confined to the plasma membrane or cytoplasm of epithelial cells. The expression of the putative CD300c counter-receptor

To determine the expression pattern of the CD300c counter-receptor, purified mCD300c2-Ig and control Ig proteins were biotinylated. Splcnocytes from C57BL/c mice were stained with the biotinylated proteins, followed by streptavidin-PE. Flow cytometric analysis showed that mCD300c2-Ig bound to resting CD4 ¹ and CD8 ⁺ T cells, and the binding was increased when CD4 ⁺ and CD8 ⁺ T cells were activated by anti-CD3 and anti- CD28 antibodies (Figure 5 A, B).

We also analyzed the expression of the CD300c counter-receptor on other immune cells. We found that mCD300c2-Ig bound to both resting and activated B220 ⁺ B cells,

CD1 lc ¹ DCs, CDl lb ¹ monocytes and G4/80 ¹ macrophages (Figure 5 A, B). The expression levels of the putative mCD300c counter-receptor on these immune cells were not significantly changed upon activation by LPS.

To determine whether mCD300c binds to molecules previously identified as receptors of the known B7 family members, HEK-293 cells were transfected with an expression vector containing the mouse CD28, CTLA-4, PD-1, BTLA or ICOS gene. The expression of these receptors on the transfected 293 cells was confirmed by flow cytometric analysis with the antibodies against the respective receptors (Figure 5C). The binding of mCD300c to the transfected HEK-293 cells was then analyzed. As shown in Figure 5D, mCD300c2 did not bind to the CD28, CTLA-4, PD-1, BTLA or ICOS transfected cells.

Taken together, our results indicate that the mCD300c2 counter-receptor is expressed on resting and activated CD4 and CDS T cells, B cells, DCs, monocytes, and macrophages. The expression levels of the receptor on activated CD4 and CDS T cells is upregulated. The mCD300c counter-receptor seems to be distinct from CD28, PD-1, CTLA-4, PD-1, or BTLA.

hCD300c-Ig protein ameliorates GVHD in mice

Although bone marrow (BM) transplantation (BMT) has been widely used in the treatment of many diseases, GVHD remains a major complication after allogeneic BMT. Acute GVDH is primarily caused by T cells in donor transplants attacking recipient's tissues. We used a well-defined MHC-mismatched [C57BL/6 (H2^) ® BALB/c (H2½ GVHD mouse model to validate the effect of CD300c on T cells in vivo. BALB/c mice were lethally irradiated and injected i.v. with BM and splenic cells from allogeneic C57BL/6 mice. The recipients were then injected i.p. with hCD300c-Ig, or control Ig. The development of GVHD was monitored over time. As shown in Figure 6A-C, control Ig- treated GVHD recipients revealed gradual body weight loss and all succumbed by day 35 after BMT. hCD300c-Ig treatment significantly reduced the mortality and morbidity of GVHD, with 45% of the mice still surviving at day 40 post transplantation (Figure 6A-C). GVHD severity was confirmed by pathologic analysis, showing that pathology scores of the liver, small intestine (SI), and lung in hCD300c-Ig-treated recipients were significantly lower than those in control Ig-trcated recipients (Figure 6D, E). These data indicate that hCD300c-Ig treatment attenuates GVHD in vivo.

We then analyzed T cell proliferation, survival, and activation in hCD300c-Ig- or control Ig-treated GVHD mice. Lethally irradiated BALB/c recipients were injected i.v. with BM and splenic cells from C57BL/6 mice. The mice were injected i.v. on day 0 and i.p. on day 2 with 20 mg hCD300c-Ig or control Ig protein. The recipients were euthanized and the spleens were harvested on day 4. We analyzed for the expression of Ki67, a cell marker of proliferation. As shown in Figure 6F-I, the percentages of KΪ67 ¹ cells in donor CD4 ⁺ and CD8 ⁺ T cells of hCD300c-Ig-treated recipients were significantly lower than those in control Ig-treated mice. We also analyzed the survival of donor CD4 ⁺ and CD8 ⁺ T cells, and found that the percentages of annexin V ⁺ 7-ADD ^" apoptotic CD4 ⁺ or CD8 ⁺ T cells were not significantly different between hCD300c-Ig- and control Ig-treated groups (data not shown). We next examined the expression of activation markers by CD4 ⁺ and CD8~ T cells. Although the percentages of CD69 ⁺ cells in donor CD4 ⁺ and CD8 ⁺ T cells w'erc not significantly different between hCD300c-Ig- and control Ig-treated groups (data not shown), the percentages of CD44 ^M cells and CD62L ¹⁰ cells in donor CD4 ¹ and CD8 ¹ T cells were significantly reduced in hCD300c-Ig-treated GVHD mice (Figure 6J-M).

Taken together, our data indicate that hCD300c-Ig treatment attenuates GVHD, likely by inhibition of the proliferation and activation of donor T cells in response to alloantigen stimulation.

Administration of hCD300c-Ig fusion protein ameliorates EAE and CIA in mice

Since hCD300c-Ig fusion protein inhibits T cell proliferation, activation and cytokine production in vitro, we set out to investigate whether in vivo administration of hCD300c-Ig could ameliorate autoimmune diseases that are caused by an overactive immune system. Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, and EAE is a common animal model for MS. To determine whether hCD300c-Ig attenuates EAE, C57BL/6 mice were immunized with pMOG peptide to induce EAE development. The mice were then treated with hCD300c-Ig or control Ig protein. As shown in Figure 7A, hCD300c-

Ig treatment reduced the mean clinical scores throughout the entire 57 day time course.

CIA is an animal model for human RA. We also determined the ability of hCD300c- Ig to treat CIA. Similarly, hCD300c-Ig treatment reduced the mean clinical scores of CIA (Figure 7B). Our data suggest that hCD300c-Ig treatment ameliorates autoimmune diseases including EAE and CIA.

Generation of anti-hCD300c monoclonal antibodies (mAbs)

To generate anti-hCD300c mAbs, BALB/c mice (8-10 weeks of age) were immunized with hCD300c-Ig protein in complete Freund's adjuvant (CFA) on day 0 and boosted on day 14 and day 21 in the same protein quantity in incomplete Freund's adjuvant (IFA). The mice were boosted with hCD300c-Ig (no adjuvant, add 100ml lxPBS instead) three times three days in a row (days 28, 29, 30). The spleens were harvested from the mice on day 31. Single-cell suspension of the splenocytes were fused to X63-Ag8.653 myeloma cells to produce hybridomas. ELISA was performed to identify the hybridomas that could produce mAbs reacting with hCD300c-Ig but not with control Ig protein.

We then determined the ability of anti-hCD300c mAbs to neutralize the ability of hCD300c to inhibit the proliferation and activation of T cells. We found that an anti- hCD300c mAb (clone B47-1D2) significantly inhibited the proliferation and activation of T cells. The heavy and light chain amino acid sequences of the B47-1D2 anti-hCD300c mAb were as follows

Heavy chain ( complementarity regions highlighted):

OIOLVOSGPELRKPGETVKISCKASGYTFnYGMNWMKQAPGKGLKWMGWINTYT GEPTYADDFKGRFAFSLETSASTAFLOINNLTNEDTATYFCARSRFAYWGOGTLVTV SA (SEQ ID NO: 16).

Light chain (complementarity regions highlighted):

DIVMTOSOKFMSTSVGDRVSVTCKASONVGTNVAWYOOKPGOSPKALIYSASYRY SGVPDRFTGSRSGTDFTLTISNVOSEDLAEYVCOOYNSYPLTFGAGTKLELK (SEP ID NO: 17).

We then determined the ability of the anti-hCD300c mAb (clone B47-1D2) to inhibit tumor growth in mouse models. We found that the mAh significantly reduced colon cancer cell growth in a CT-26 mouse model (Figure 8A). The antitumor activity of the anti-CD300c antibodies was related to increased infiltration of CD4+ and CD8+ T cells, NK cells and B cells, as well as enhanced activation of B cells and monocytes in the tumors (Figure 8B-E, and data not shown). Similarly, the anti-CD300c rtiAb significantly inhibited melanoma cell growth in a B16/F16 melanoma model (Figure 8F). Taken together, our data demonstrates that the anti-CD300c mAb can inhibit tumor growth in vivo.

Discussion:

The present study describes CD300c as a novel T cell co-inhibitory molecule.

CD300c protein is expressed on A PCs and its counter-receptor is expressed on T cells. Functionally, CD300c-Ig protein inhibits the proliferation, activation and cytokine production of T cells.

Both human and mouse CD300c have only one IgV domain in the extracellular region. It has been reported that the interaction site in the Ig superfamily members is often mapped to the distal Ig domain, which would be the IgV domain in the CD300c.

We have shown that the mCD300c2 protein is expressed on the cell surface of a variety of APCs, including B cells, monocytes, macrophages and DCs. Our results demonstrate that the mCD300c3 counter-receptor is expressed on resting and activated CD4 and CDS T cells, B cells, DCs, monocytes, and macrophages. The expression levels of the counter-receptor on activated CD4 and CDS T cells is upregulated upon activation, while the expression levels of the mCD300c counter-receptor on resting and activated B cells, DCs, monocytes, and macrophages were not significantly different. mCD300c2 protein did not bind to CD28, PD-1, CTLA-4, PD-1, or BTLA-expressing cells, indicating that the mCD300c2 counter-receptor is distinct from known members of the CD28 receptor family.

The expression of CD300c protein on APCs and its counter-receptor on T cells suggests that CD300c affects T cells. Indeed, we have demonstrated that both hCD300c and mCD300c2 significantly inhibit the proliferation, activation, and/or cytokine production of CD4 and CDS T cells in vitro.

We have also shown that hCD300c-Ig treatment attenuates acute GVHD in mice. To the best of our knowledge, this is the first report that CD300c is able to inhibit T cell function and treat GVHD. The effect of CD300c on GVHD is associated with the inhibition of T cell function in vivo. In agreement with the in vitro data, hCD300c-Ig inhibits T cell proliferation and activation in the GVHD model. However, although both mCD300c2-Ig and hCD300c-Ig inhibit the expression of CD69 in T cells in vitro, we did not observe that hCD300c-Ig treatment reduced CD69 expression by donor T cells in vivo. This

inconsistency is most likely caused by time differences in analyzing this marker. CD69 is an early activation marker. We analyzed the expression of this marker 1 day after activation by anti-CD3 antibody or anti-CD3 and anti- CD28 antibodies in vitro, but 4 days after activation by allogeneic antigens in the GVHD model. hCD300c-Ig may inhibit the expression of CD69 in vivo at early time points, but this inhibition was not in effect 4 days later. This notion is supported by our results that hCD300c-lg reduced the percentages of two other T cell activation markers CD44 ^hi cells and CD62L ¹⁰ cells, in CD4 ¹ and CD8 ⁺ T cells in vitro 3 days (Figure 2M-Q) and in vivo 4 days (Figure 6J-M) after activation.

In summary, CD300c protein is expressed on APCs, and its counter-receptor is expressed on T cells. Soluble human or mouse CD300c-Ig fusion proteins significantly inhibit T cell proliferation, activation, and cytokine production in vitro. Administration of hCD300c-lg protein attenuates GVHD and autoimmune diseases in mice. Anti-CD300c mAb inhibits tumor growth in vivo. Therefore, CD300c protein has can be used in the treatment of GVHD, autoimmune disease, and transplant rejection, as well as cancer.

Abbreviations: APC, antigen-presenting cells; DCs, dendritic cells; GVHD, graft-versus- host disease; ICOSL, T cell co-stimulator ligand; Ig, immunoglobulin; CD300c-Ig, CD300c- IgG2a Fc; CFSE, carboxyfluorescein diacetate succinimidyl ester; human CD300c, hCD300c; mCD300c, mouse CD300c; CLM-6, CMRF-35-like molecule-6; LMIR2, leukocyte mono-Ig-like receptor 2, DIgRI, dendritic cell-derived Ig-like receptor 1; MAIR- P, myeloid-associated Ig-like receptor II; MW, molecular weight; BM, bone marrow; BMT, BM transplantation; SI, small intestine

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In this example, we identify a novel T cell co-inhibitory molecule

TAPBPL/TAPBPR, whose amino acid sequence shares homolog with known B7 family members. TAPBPL protein is expressed on resting and activated T cells, B cells, monocytes and dendritic cells (DCs), as well as in tumor tissues. A soluble recombinant human TAPBPL-IgG Fc (hTAPBPL-Ig) fusion protein inhibits the proliferation and activation of CD4 and CDS T cells in vitro. In vivo administration of hTAPBPL-Ig protein attenuates experimental autoimmune encephalomyelitis (EAE) in mice. Furthermore, anti- TAPBPL antibody can neutralize tire inhibitory activity of hTAPBPL-Ig on T cells, and inhibit tumor growth in a tumor animal model. Our results indicate that therapeutic intervention of the TAPBPL inhibitory pathway represents a new strategy to modulate T cell-mediated immunity for the treatment of cancer, infection, autoimmune disease, and transplant rejection.

TAPBPL is a member of the Ig superfamily [18-21] The TAPBPL gene encodes a signal peptide in the N terminus, an extracellular region, a transmembrane domain, and an intracellular region. The B7 family members typically contain IgV and IgC domains in the extracellular portion. The extracellular region of TAPBPL also contains an IgV domain and an IgC domain. TAPBPL is highly conserved among vertebrates, and human and mouse TAPBPL proteins have 69% homology' [19, 21]

TAPBPL protein is expressed on the cell surface of APCs and T cells, and in some tumor tissues

We used a commercial available anti-TAPBPL monoclonal antibody (clone 5D7) to determine whether TAPBPL protein is expressed on APC and/or T cells. Although the antibody was raised against hTAPBPL, it cross-reacted with mTAPBPL (data not shown). As shown in Figure 9A and B, TAPBPL was expressed on the cell surface of CD4 ⁺ and

CD8 ⁺ T cells at low levels. The expression level of TAPBPL on CD8 ⁺ T cells was slightly increased upon activation by anti-CD3 and anti-CD28 antibodies. TAPBPL protein was also detected on APCs including CD1 lb ⁺ monocytes, F4/80 ⁺ macrophages, CD1 lc ⁺ dendritic cells (DCs), and B220 ⁺ or CD19 ⁺ B cells.

The expression levels of TAPBPL on monocytes and DCs, but not on macrophages and B cells, were increased upon activation by LPS. The results suggest that TAPBPL protein is constitutively expressed on the cell surface of APCs and T cells, and the expression of TAPBPL is upregulated on monocytes, DCs cells, and CDS T cells after activation.

We then detennined the expression of TAPBPL protein in normal and tumor human tissues by immunohistochemistry. As shown in Figure 9C, TAPBPL protein was detected in normal breast, colon, liver, lung and prostate tissues at low levels, as compared to isotype antibody staining. TAPBPL protein was expressed in liver, lung and prostate cancer tissues at medium to high levels (Figure 9C). Therefore, the expression levels of TAPBPL in liver, lung and prostate cancer tissues was higher than the respective normal tissues. TAPBPL protein was largely located to the plasma membrane or cytoplasm of epithelial cells.We also examined TAPBPL protein expression on some cancer cell lines by flow cytometry. As shown in Figure 9D, TAPBPL was expressed highly on the cell surface of murine neuro-2a neuroblastoma and P388 leukemia cells, and weakly expressed on murine Lewis Lung Carcinoma, CT-26 colon cancer and B16F10 melanoma cells. We have also found that TAPBPL is expressed on human K562 and HL60 leukemia cell lines (data not shown).

TAPBPL inhibits T cell proliferation in vitro

Since TAPBPL shares sequence homolog with tire B7 family members and TAPBPL is expressed on APCs, we hypothesized that TAPBPL has regulatory roles on T cells. We produced an hTAPBPL-Ig fusion protein by cloning the extracellular domain of human TAPBPL into an expression vector containing the constant region of mouse IgG2a. The vector was transfected into HEK-293 cells to produce a recombinant hTAPBPL-Ig fusion protein. We then purified hTAPBPL-Ig protein from the supernatant of HEK-293 cells. A relative high purity of hTAPBPL-Ig fusion protein was obtained as shovra by SDS-PAGE and confirmed by Western blot. To determine whether TAPBPL-Ig protein affects T cell proliferation, CD3 ⁺ T cells were purified from splenocytes of C57BL/c mice, and cultured on plates pie -coated with anti-CD3 antibody in the presence of graded doses of hTAPBPL-Ig for 3 days. Since the molecular weight of hTAPBPL-Ig is ~2.7-fold higher than that of control Ig, we used equimolar amounts of recombinant mouse IgG2a (control Ig) protein as a control. T cell proliferation was measured by [^H] thymidine incorporation. As shown in Figure 10A, TAPBPL-Ig inhibited anti-CD3 -induced T cell proliferation in a dose-dependent manner, with ~70% and 81% inhibition in the presence of 10 and 15 mg/ml hTAPBPL-Ig, respectively, as compared to equimolar amounts of control Ig. We also determined whether hTAPBPL-Ig could inhibit ani-CD3 and anti-CD28 antibody- induced T cell proliferation. Similarly, hTAPBPL-Ig inhibited the T cell proliferation in a dose- dependent manner, with ~66% and 70% inhibition in the presence of 10 and 15 mg/ml hTAPBPL-Ig, respectively (Figure 10B).

To confirm the inhibitory effect on T cell proliferation and to determine whether hTAPBPL-Ig inhibits CD4 and/or CDS T cells, splenocytes were labelled with

caiboxyfluorescein diacetate succinimidyl ester (CFSE), and cultured with anti-CD3 antibody and graded doses of TAPBPL-Ig or equimolar amounts of control Ig. T cell proliferation was analyzed for CFSE fluorescent intensity in CD4 ⁺ or CD8 ⁺ T cells by flow cytometry. Consistent with results from the [ ³ HJ thymidine incorporation assay, hTAPBPL-Ig inhibited anti-CD3- induced proliferation of both CD4 ⁺ and CDS ¹ T cells (Figure 10C-E).

Having shown that hTAPBPL-Ig inhibits murine T cell proliferation in vitro, we next determined whether hTAPBPL-Ig also inhibits the proliferation of human T cells. Purified hitman T cells were cultured with anti-human CD3 antibody in the presence of graded doses of hTAPBPL-Ig or control Ig for 3 days. T cell proliferation was measured by

[ ³ H] thymidine incorporation. As shown in Figure 10F, hTAPBPL-Ig also significantly inhibited the proliferation of human T cells. When compared to the doses of hTAPBPL-Ig that have an effect on murine T cells, the doses for human T cells were lower (Figure 10F vs A). Collectively, our results indicate that hTAPBPL-Ig can inhibit the proliferation of both mouse and human primary T cells. TAPBPL inhibits T cell activation in vitro

We then determined whether hTAPBPL-Ig affects T cell activation in vitro. After splenocytes were cultured with anti-CD3 antibody and hTAPBPL-Ig or control Ig, T cells were analyzed for the expression of an early activation marker CD69 24 hours later. As shown in Figure 11 A and B, TAPBPL-Ig reduced anti-CD3-activated CD69 expression on both CD4 and CDS T cells. Similarly, the expression levels of CD69 on both CD4 and CDS T cells activated by both anti-CD3 and anti-CD28 antibodies were also significantly decreased by TAPBPL-Ig (Figure 11C and D).

T cells can be divided into nai ^' ve (CD44*°CD62L^) and effective memory

(CD44^CD62 L^°) T cells based on the expression levels of CD44 and CD62L. We next analyzed the effect of mBTN5-Ig on these T cell subsets. We found that the percentages of

CD44^CD62L^° CD4 and CDS effective memory T cells were significantly lower in the presence of hTAPBPL-Ig than those in the control group (Figure 11E-I, K). In contrast, the percentages of CD44^°CD62L^ CD4 and CDS T naive cells were significantly higher in the presence of hTAPBPL-Ig (Figure 11E-G, I-L). The results further suggest that hTAPBPL-Ig inhibits the activation of CD4 and CDS T cells. Taken together, our results indicate that hTAPBPL-Ig inhibits TCR-mediated proliferation and activation of both CD4 and CDS T cells in vitro. Administration of hTAPBPL-Ig fusion protein ameliorates EAE in mice

We then determined whether in vivo administration of hTAPBPL-Ig fusion protein could ameliorate multiple sclerosis (MS) that is an autoimmune disease of the central nervous system. EAE induced by autoantigen pMOG peptide is a well-established animal model for MS. C57BL/6 mice were injected with pMOG peptide to induce EAE. To determine whether hTAPBPL-Ig could prevent EAE development, mice were injected with 25 mg/ml hTAPBPL-Ig or control Ig protein beginning from the day that EAE was induced (day 0). EAE development was monitored over time. As shown in Figure 12A, hTAPBPL-Ig significantly reduced the mean clinical scores throughout the entire 42-day time course. To determine whether hTAPBPL-Ig could treat established EAE, mice were injected with hTAPBPL-Ig or control Ig protein after the mice had developed EAE. hTAPBPL-lg also significantly reduced the mean clinical scores in the treatment model (Figure 12B). At end of the studies, the spleen and spinal cord were harvested from the mice. hTAPBPL-Ig-treated mice had decreased proportion of CD4 ⁺ T cells and increased percentage of CD4 ⁺ CD25 ⁺ FoxP3 ⁺ Tregs in the spleen (Figure 12C-F). CD4 T cell activation in hTAPBPL-Ig-treated mice was also significantly reduced, as indicated by reduced expression of CD69, decreased percentage of effector memory T cells, but increased percentage of naive T cells (Figure 12G-J). Furthermore, CNF-infiltrating CD4 T cells were decreased, but Tregs were increased. In addition, when the splonocytes from hTAPBPL-Ig-treated mice were stimulated with MOP in vitro, the cell proliferation was reduced, indicating that hTAPBPL inhibits antigen-specific proliferation.

Taken together, our results suggest that in vivo administration of hTAPBPL-Ig can prevent and treat EAE. This is associated with decreased proportion of CD4 T cells and increased Tregs in the spleen and CNS, and reduced activation of CD4 T cells.

Anti-hTAPBPL mAb inhibits tumor growth in vivo

Since TAPBPL is highly expressed in some tumor tissues and hTAPBPL-Ig inhibits T cell functions, we hypothesized that anti-TAPBPL antibody could block the inhibitory effect of TAPBPL, thereby enhancing antitumor immunity and inhibiting tumor growth in vivo. We produced anti-hTAPBPL mAbs by immunizing BALB/c mice with hTAPBPL-Ig protein.

The splenocytes were fused to X63-Ag8.653 myeloma cells to produce hybridomas. ELISA was performed to identify the clones of hybridomas that could produce anti-hTAPBPL mAbs reacting with hTAPBPL-Ig fusion protein but not with control Ig protein. We also screened the mAbs by determining their ability to neutralize the inhibitory activity of hTAPBPL on T cells in vitro. As shown in Figure 13A, an anti-hTAPBPL mAb (clone 54) neutralized the inhibitory activity of hTAPBPL on T cell proliferation.

We then determined the ability of the mAb to treat cancer in a leukemia mouse model that was injected s.c. with P388 cells. Anti-hTAPBPL mAb at 25 and 50 mg doses inhibited tumor growth in the model although at some time points the differences did not reach statistical significance (data not shown). Anti-hTAPBPL mAb at 100 mg dose significantly inhibited tumor growth for most of time points (Figure 13B). Analyses of tumor infiltrating lymphocytes show that anti-hTAPBPL mAb significantly increased the percentages of (Figure 13C-F) CD4 ⁺ and CD8 ⁺ T cells, but decreased the percentage of CD4 ⁺ CD25 ⁺ FoxP3 ⁺ Tregs (Figure 13G, H). Together, our results suggest that the anti-TAPBPL mAb can inhibit tumor growth in vivo, which is related to neutralizing the inhibitory activity of TAPBPL on tumor infiltrating T cells.

Heavy chain: DVOLOESGPGLVKPSOTLSLTCSVTGYSLTSGYFWHWIRQFPGNKLEWMGYISYSG TTNYNPSLKNRISIIHDSSKNOFFLNLNSVTAEDTATYFCAGDDWDWFAYWGOGT LVTVSA (SEQ ID NO:24); Light chain

ENVLTOSPAIMSASPGEKVTMTCSASSSVNYMHWYOOKSSTSPKLWrYDTSKLASG VPGRFSGSGSGNSYSLTISSMEAEDVATYYCFOGSGYPLTFGSGTKLEIK (SEQ ID NO:25)

In summary, we described TAPBPL as a novel T cell co-inhibitory molecule.

TAPBPL protein is expressed on APCs and in tumor tissues. TAPBPL-Ig fusion protein inhibits T cell proliferation and activation in vitro. In vivo administration of TAPBPL-Ig protein attenuates EAE. Anti-TAPBPL antibody inhibits tumor growth in a mouse model. Therefore, targeting the TAPBPL has can be used in the treatment of autoimmune diseases (such as MS) and transplant rejection, as well as cancer and infection.

Materials and Methods

Cloning and purification of TAPBPL

The extracellular domains of hTAPBPL (aa22-406) were cloned and fused into a pCMV6-AC-FC-S expression vector containing the constant region of mouse IgG2a

(ORIGENE, Rockville, MD). The vectors were transfected into HEK-293 cells. The fusion proteins were purified for the supernatant using Protein G Sepharose 4 Fast Flow according to the manufacturer's instructions (GE Healthcare). Purified proteins were verified by SDS- PAGE, Coomassie Staining and Western blot. Protein was quantified using the Pierce™ BCA Protein Assay Kit (Pierce, Rockford, IL). Control Ig (recombinant mouse IgG2a Fc protein) was purchased from BXCell (West Lebanon, NH).

Mice

C57BL/6 mice were purchased from Jackson Laboratory. The mice were used in accordance with protocols approved by the Institutional Animal Care and Use Committee of the University of Connecticut.

Flow Cytometry analysis

Single cell suspensions of organs and tumors were stained with the fluorochrome- conjugated antibodies protein as described [24-27], For intracellular staining, the cells were first permeabilized with a BD Cytofix/Cytoperm solution for 20 minutes at 4 °C. Direct or indirect staining of fluorochrome-conjugated antibodies included: CD4, CDS, CD 19, B220, CDllc, CDllb, F4/80, CD44, CD62L, CD69, CTLA-4, CD28, PD-1, BTLA, and ICOS (BioLegend, or

BD Biosciences, San Jose, CA, San Diego, CA). Anti-TAPBPL monoclonal antibodies were purchased from LifeSpan Biosciences, Inc (Seattle, WA). The samples were analyzed on a FACSCalibur™ or LSRFortessa™ X-20 Cell Analyzer (BD

Biosciences). Data analysis was done using FlowJo™ software (Ashland, OR).

Histopathology

Human Multiple Normal and Tumor Tissue Arrays were purchased from BioChain (Newark, CA). The tissues were subjected to antigen unmasking, and then incubated with anti- TAPBPL monoclonal antibody, followed by ImmPRESS™ VR Polymer HRP antimouse IgG reagent, and developed with peroxidase substrate solution (Vector Laboratories) according to the manufacturer's instructions.

In vitro T cell assays

Normal human peripheral blood CD3 ⁺ Pan T Cells that were negatively isolated from mononuclear cells using an indirect immunomagnetic Pan-T labeling system were purchased from ALLCELLS, LLC (Alameda, CA). Murine CD3 ⁺ T cells were purified from C57BL/6 mice by an immunomagnetic system (Miltenyi, Auburn, CA), and the purity of the cells was usually >95%. T cells were stimulated with anti-CD3 and/or anti-CD28

(Biolegend) in the presence of hTAPBPL-Ig or control Ig. Proliferative response was assessed by pulsing the culture with 1 pCi of [ H] thymidine (PerkinElmer, Inc., Downers

Grove, IL) 12 hours before harvest. Incorporation of [ H] thymidine was measured by liquid scintillation spectroscopy (PerkinElmer, Inc.). For the carboxyfluorescein diacetate succinimidyl ester (CFSE) assay, splenocytes were labeled with CFSE (ThermoFisher Scientific) and stimulated with anti-CD3 in tire presence of hTAPBPL-Ig or control Ig. The cells were analyzed by flow cytometry.

Induction and assessment of EAE

Mouse MOG35-55 (GL Biochem, Shanghai, China) was emulsified in complete Freud’s adjuvant (Sigma-Aldrich, St Louis, MO, USA) supplemented with Mycobacterium tuberculosis H37Ra (Difco Laboratories, Detroit, MI). Mice were injected s.c. with the MOG at 4 points in the dorsal flank on day 0. The mice were also injected i.p. with 500 ng of purified Bordetella pertussis toxin (Sigma-Aldrich). The mice were injected i.p. with hTAPBPL-Ig, or control Ig, and observed for clinical scores based on the following scale:

0, normal; 0.5, partially limp tail; 1, paralyzed tail; 2, loss in coordinated movement, hind limb paresis; 2.5, one hind limb paralyzed; 3, both hind limbs paralyzed; 3.5, hind limbs paralyzed, weakness in forelimbs; 4, forelimbs paralyzed; 5, moribund or dead. As required by animal ethics, mice were euthanized beyond a clinical score of 4.

Generation of hTAPBPL monoclonal Antibodies (mAbs)

BALB/c mice were immunized with 50 mg hTAPBPL-lg protein emulsified in complete Freund's adjuvant (CFA) on day 0 and boosted on day 14 and day 21 in the same protein quantity in incomplete Freund's adjuvant (IFA). The mice were boosted with 50 mg hTAPBPL-Ig without IFA 3 times (days 28, 29, and 30). On day 31, the spleens were harvested from the immunized mice. Single-cell suspension of the splenocytes were fused to X63-Ag8.653 myeloma cells to produce hybridomas. ELISA was performed to identify the hybridomas that could produce anti- hTAPBPL mAbs but not with control Ig protein. These hybridoma clones were further subcloned by limiting dilution. The anti- hTAPBPL mAbs were further screened for the ability to neutralize the inhibitory' activity of hTAPBPL-Ig on T cell proliferation and activation. The anti- hTAPBPL mAbs were purified for supernatant of the hybridomas using Protein G Sepharose 4 Fast Flow according to the manufacturer’s instructions (GE Healthcare).

Evaluation of local tumor growth

Murine P388 leukemia cells were obtained from ATCC. The cancer cells were injected

s.c. into syngeneic DBA/2a mice. Anti- hTAPBPL or control mAb was then injected into the tumor injection site. Tumor size (volume) was determined by caliper measurements of the shortest (A) and longest (B) diameter, using the formula V = (A2B)/2.

Statistical analysis

P-values were based on the two-sided Student’s t test. A confidence level above 95% (p<0.05) was determined to be significant. References

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Example 3. SkintS

In this example, we identify SkintS as a new member of T cell co-inhibitory group, whose extracellular domains share significant homology with existing B7 family members. SkintS mRNA is expressed in resting and activated B cells, monocytes, and CD4 T cells. The SkintS putative receptor is expressed on activated CD4 and CDS T cells, B cells, monocytes and dendritic cells (DCs). Recombinant SkintS-IgG Fc (SkintS- Ig) fusion protein inhibits T cell proliferation, activation, and cytokine production in vitro. In vivo administration of SkintS-Ig reduces T cell activation and ameliorates experimental autoimmune encephalomyelitis (EAE) in mice.

Results

The expression pattern of SkintS mRNA We first evaluated the expression of SkintS rtiKNA in various tissues by using RT- PCR analysis. As shown in Figure 14A, SkintS mRNA was expressed in the heart, skin, spinal cord, kidney, spleen and thymus with the highest expression level in the thymus.

We then examined the expression of SkintS mRNA in purified immune cells. We found that SkintS was expressed in testing CD4 ⁺ T cells, B220 ⁺ B cells, and CD1 lb ⁴ monocytes, but not in resting CD8 ⁺ T cells, F4/80 ⁺ macrophages, and CD1 lc ⁺ DCs (Figure 14B). The expression of SkintS mRNA in CD4 ⁺ T cells, B220 ⁺ B cells, and CD1 lb ⁺ monocytes was not significantly altered upon activation (Figure 14C). The expression of SkintS mRNA was induced in CD8 ⁺ T cells, and slightly upregulated in F4/80 ⁴ macrophages upon activation (Figure 14C). The data suggest that SkintS transcript was constitutively expressed in CD4 T cells, B cells, and monocytes and induced in CDS T cells and macrophages.

To confirm the expression of SkintS mRNA in immune cells, we also performed real- time quantitative RT-PCR (qRT-PCR). The expression levels of SkintS mRNA were not significantly different between resting and activated CD4 ⁴ T cells, B220 ⁴ B cells, and CD1 lb ⁴ monocytes. However, the expression of SkintS mRNA was induced in CD8 ⁺ T cells and F4/80 ⁴ macrophages upon activation (Figure 14D). The qRT-PCR data were consistent with tire RT-PCR results. The putative SkintS receptor is expressed on activated T cells, B cells, monocytes, and DCs

In order to determine the expression pattern of the putative SkintS receptor, we cloned and expressed Skint8-Ig fusion protein in which the extracellular domain of SkintS was fused to the constant region of mouse IgG2a. SkintS-Ig fusion protein was purified from the expression system. A relatively high purity of SkintS-Ig protein was obtained, as determined by Coomassie blue-stained SDS-PAGE. The identity of the fusion protein was verified by Western blot using anti-IgG2a antibody. The actual molecular weight (MW) of the SkintS -Ig was higher than the predicted MW, suggesting that the recombinant protein was glycosylated.

Purified SkintS-Ig and control mouse IgG2a Fc (control Ig) proteins were then biotinylated. Spleen cells from C57BL/6 mice were stained with the biotinylated Skint8-Ig or control Ig, followed by streptavidin-PE. The binding of Skint8-Ig or control Ig to immune cells was analyzed by flow cytometry. As shown in Figure 15A and B, SkintS bound to a small fraction of freshly harvested CD4 ⁺ or CD8 ⁺ T cells. It has been reported that naive T cells are CD44^ ^0W CD62L^, while effective memory T cells are

CD44^CD62L ^low . We found that there were not CD44^ ^0W CD62L^ naive T cells in the

CD4 ⁺ and CD8 ⁺ T cells that bound to SkintS (data not shown). In contrast, significant percentages of the freshly harvested CD4 ⁺ and CD8 ⁺ T cells that did bind to SkintS were naive T cells (data not shown). Our data indicate that resting CD4 ⁺ and CD8 ⁺ T cells did not express the putative SkintS receptor. We also analyzed the binding of SkintS to other immune cells and found that SkintS bound weakly to freshly harvested B220 ⁺ B cells,

CD1 lb ⁺ monocytes, and CD1 lc ⁺ DCs.

We then determined the binding of SkintS to activated immune cells. We activated CD4 ⁺ and CD8 ⁺ T cells by anti-CD3 and anti-CD28 antibodies. After the activation, there were few CD44^ ^0W CD62L^ naive CD4 ⁺ and CD8 ⁺ T cells in the cultures (data not shown), confirming that the T cells were activated. The binding of SkintS to CD4 ⁺ and CD8 ⁺ T cells was significantly increased upon the activation (Figure 15A, B).

To determine whether the IgV- and IgC-like domains are required for SkintS ligand binding, we produced SkintS IgV-Ig and SkintS IgC-lg fusion proteins. We found that SkintS IgV-Ig could bind to both activated CD4 ⁺ and CD8 ⁺ T cells, whereas SkintS IgC-lg did not (data not shown). The data suggest that the IgV-like domain is required for the SkintS ligand binding.

We also analyzed the binding of SkintS to other activated immune cells. After activation by LPS, the binding of SkintS to activated B cells, monocytes and DCs was also significantly enhanced (Figure 15A, B). Taken together, our data suggest that activated CD4 and CDS T cells, B cells, monocytes and DCs express high levels of the putative SkintS receptor, whereas the resting immune cells express the putative receptor at low levels or not at all.

To determine whether the putative SkintS receptor is a known receptor for B7 family members, HEK-293 cells were transfected with an expression vector containing the murine PD- 1, CD28, BTLA, CTLA-4, or ICOS gene. The expression of PD-1, CD28, BTLA, CTLA-4, and ICOS proteins on the transfected cells was confirmed by flow cytometric analysis with antibodies against the respective receptors (Figure 15C). The binding of SkintS to the transfected cells was then analyzed. As shown in Figure 15D, SkintS did not bind to the PD-1, CD28, BTLA, CTLA-4, or ICOS transfected cells. The data indicate that SkintS binds to a receptor distinct from PD-1, CD28, BTLA, CTLA-4, or ICOS.

Skint8-Ig fusion protein inhibits T cell proliferation and activation in vitro

The expression of the SkintS putative receptor on T cells suggests that SkintS may have an effect on T cell function. We first evaluated whether SkintS -Ig affected T cell proliferation in vitro. CD3 ⁺ T cells were purified from spleen cells of CSTBIVc mice, and cultured on plates pre- coated with or without anti-CD3 antibody in the presence of graded doses of Skint8-Ig for 3 days. Since Skint8-Ig has a 1.88-fold higher molecular weight than control Ig, we used equimolar amounts of Ig as a control. T cell proliferation was measured by [ H] thymidine incorporation. Skint8-Ig did not affect the proliferation of T cells in the absence of anti-CD3 antibody stimulation (data not shown). However, Skint8-Ig inhibited anti-CD3-activated T cell proliferation in a dose-dependent manner, with -10%, 47% and 61% inhibition in the presence of 1864, 3728, and 7456 ng/ml Skint8-Ig, respectively, as compared to equimolar amounts of control Ig (Figure 16A). We then determined whether Skint8-Ig could inhibit anti-CD3 and anti- CD28 antibody-activated T cell proliferation. As shown in Figure 16B, Skint8-Ig also reduced anti-CD3 and anti-CD28-activated T cell proliferation although Skint8-Ig at a low dose (1864 ng/ml) did not have the effect.

To confirm the inhibitory effect of Skint8-Ig on T cell proliferation and to determine whether Skint8-Ig inhibits CD4 and/or CDS T cells, spleen cells were labelled with carboxyfluorescein diacetate succinimidyl ester (CFSE), and cultured with anti- CD3 antibody and equimolar amounts of Skint8-Ig or control Ig. T cell proliferation was assessed by CFSE intensity that is diluted with each cell division. As shown in Figure 16C-E, Skint8-Ig inhibited anti-CD3-activated proliferation of CD4 ¹ and CD8 ¹ T cells.

The inhibition was further confirmed by [ ³ H| thymidine incorporation with purified CD4 ⁺ and CD8 ⁺ T cells (Figure 16F, G).

We then determined whether Skint8-Ig affects T cell activation in vitro. Murine spleen cells were cultured with anti-CD3 antibody in the presence of Skint8-Ig or control Ig. The expression of CD69 that is an early marker of T cell activation was analyzed by flow cytometry 24 hours later. As shown in Figure 16H and I, the expression levels of CD69 on both CD4 and CDS T cells were significantly reduced by Skint8-Ig. Similarly, Skint8-Ig at high doses also inhibited the expression levels of CD69 on anti-CD3 and CD28 antibody- activated CD4 and CDS T cells (Figure 16J-L). Collectively, our results suggest that SkintS- Ig inhibits TCR-mediated proliferation and activation of both CD4 and CDS T cells in vitro.

Skint8-Ig fusion protein inhibits cytokine production from T cells in vitro

We next examined whether Skint8-Ig affects cytokine production from T cells in vitro. Murine purified T cells were stimulated with anti-CD3 antibody in the presence of SkintS-Ig or control Ig protein for 3 days. The cytokines in the supernatants were measured by ELISA. As shown in Figure 17 A, Skint8-Ig inhibited the production of IFNy and TNFa. The results suggest that SkintS -Ig can also inhibit TCR-mediated cytokine production from T cells in vitro.

We then used flow cytometry to determine whether Skint8-Ig inhibited Thl cytokine production by CD4 ⁺ or CD8 ⁺ T cells. Skint8-Ig significantly inhibited the production of IFNy and TNFa by anti-CD3-, or anti -CD 3- and anti-CD28-stimulated CD4 ⁺ T cells (Figure 17B- E). Skint8-Ig also significantly reduced the production of TNFa, but not IFNy by anti-CD3- or anti-CD3 and CD28-stimulated CD8 ⁺ T cells (data not shown). Administration of Skint8-Ig fusion protein ameliorates EAE in mice

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system and is caused by an overactive immune system. EAE is a common animal model for MS. We determined whether in vivo administration of SkintS-Ig protein could ameliorate EAE.

C57BL/6 mice were induced for EAE and injected with SkintS-Ig or control Ig protein. As shown in Figure 18 A, hBTN5-Ig treatment delayed EAE onset, and reduced the mean clinical scores throughout the entire 35 day time course.

Since EAE is primarily mediated by CD4 T cells, we analyzed CD4 T cell activation in the mice. SkintS-Ig reduced the expression of CD69 by CD4 ¹ T cells (Figure 18B, C). In addition, SkintS-Ig increased the percentages of CD44 ^lo CD62L ^hi naive CD4 T cells, but decreased the percentages of CD44 ^hi CD62L ^l0 effector memory CD4 T cells (Figure 18D. E).

We also examined the percentages of CD4 ⁺ T cells and CD4 ⁺ CD25~Foxp3 ⁺ regulatory T cells (Tregs) in the spleen at both prime (day 10) and peak (day 22) times. The percentages of CD4 ⁺ T cells in SkintS-Ig-treated mice were decreased, whereas those of Tregs were increased at both time points (Figure 18F-M). We then analyzed antigen-specific T cell responses. After MOG in vitro stimulation, the production of TNFo, IFNy, and IL-17 was decreased, whereas that of IL-10 was increased by splenic CD4 ⁺ T cells in SkintS-Ig-treated EAE mice (Figure 18N, O). Similar trends were also observed in the draining lymph nodes (data not shown). In addition, we found that the percentage of the CNS infiltrating CD4~ T cells was decreased, whereas that of CD4 ^* CD25 ⁺ Foxp3 Tregs was increased in SkintS-Ig- treated EAE mice (Figure 18P-S).

Taken together, our results indicate that in vivo administration of SkintS-Ig ameliorates EAE in mice. This is related to reduced CD4 T cell activation, and a decreased proportion of CD4 T cells and an increased percentage of Tregs in the lymphoid organs and

CNS. Furthermore, SkintS-Ig inhibits antigen-specific T cell responses.

Discussion

In this example we characterize a novel T cell inhibitory molecule SkintS that shares ~20% identity in the extracellular region with several existing members of the B7 family. Like B7 family molecules, the extracellular region of SkintS contains one IgV-like and one IgC-like domain. Although SkintS has a higher sequence identify with the BTN molecules than with the B7 members, unlike most of BTN members, SkintS does not have the intracellular B30.2 domain. Therefore, SkintS appear to be a novel member of tire extended B7 family or a B7 family-related molecule.

We analyzed its expression in purified immune cells and found that SkintS mRNA was expressed in purified CD4 T cells, B cells and monocytes. The expression levels of SkintS mRNA in these immune cells were not significantly altered upon activation of these cells. The constitutive expression of SkintS transcript in APCs including B cells and monocytes is in accordance with its functions in regulating T cell proliferation and/or activation.

The SkintS putative receptor is not expressed on resting CD4 and CDS T cells, but is induced upon activation by anti-CD3 and anti-CD28 antibodies. This expression pattern is similar to the receptors for other BTN and BTNL proteins, such as BTN1A1, BTN2A2, BTNL2, BTNL1 and BTN3 (24, 26, 29, 31), as well as some B7 family molecules, such as ICOSL, PDL1/PDL2, B7-H3, B7-H4 (11, 13). SkintS protein did not bind the PD-1, CD28, BTLA, CTLA-4, or ICOS gene transfected cells, suggesting that the putative SkintS receptor is distinct from the receptors for the known B7 family ligands.

The expression of the SkintS putative receptor on activated T cells indicates that SkintS may affect T cells that have already been activated and provides a negative signal that limits the effector phase, akin to the activity of PD-L1. Indeed, we have demonstrated that Skint8-Ig protein inhibits anti-CD3 or anti-CD3 plus anti-CD28-induced proliferation, activation and cytokine production from T cells. Furthermore, in vivo administration of Skint8-Ig inhibits T cell activation and attenuates EAE in mice. In addition to the expression on activated T cells, the SkintS putative receptor is expressed on activated B cells, DCs and monocytes.

In summaiy, we have identified SkintS as a novel T cell inhibitory molecule. SkintS mRNA is expressed on APCs, and the SkintS putative receptor is expressed on activated T cells, and APCs. Skint8-Ig fusion protein inhibits the proliferation, activation, and cytokine production of T cells in vitro and ameliorates EAE in vivo, and thus is a target for regulation of immune responses, which has implications for the treatment of many immune-associated diseases. Materials and Methods Bioinformatics analysis of SkintS.

Sequence alignment of the extracellular domains of SkintS and existing B7 family members was analyzed via the Clustal W™ program in Mac Vector™ 16.0.5

(Mac Vector, Inc.). Phylogenic tree analysis was also performed via the Clustal W™ program in MacVector™.

Cloning and purification of SkintS

The IgV- and IgC-like domains in the extracellular region of SkintS (aa 26-233) were cloned and fused into a pCMV6-AC-FC-S expression vector containing the constant region of mouse IgG2a (ORIGENE, Rockville, MD). Separately, the IgV-like domain (aa 26-142) or IgC- like domain (aa 159-233) alone was cloned and fused into the vector. The vectors were transfected into HEK-293 cells. The fusion proteins were purified from the supernatant using Protein G Sepharose 4 Fast Flow according to the manufacturer’s instructions (GE Healthcare). Purified proteins were verified by SDS-PAGE, Coomassie Staining and Western blot. Proteins were quantified using the Pierce™ BCA Protein Assay Kit (Pierce, Rockford, IL). Control Ig (recombinant mouse IgG2a Fc protein) was purchased from BXCell (W est Lebanon, NH).

Mice

Four-week-old female C57BL/6 mice were purchased from Jackson Laboratory. The mice were used in accordance with protocols approved by the Institutional Animal Care and Use Committee of the University of Connecticut

RT-PCR and qRT-PCR

Total RNA from cells was isolated from tissues or cells, and cDNA was synthesized as described (37). Equal amounts of cDNAs were used for RT-PCR. PCR products were viewed after running through an agarose gel. qRT-PCRs were performed with the Power SYBR™ green mastermix (Applied Biosystems, UK) using the 7500 realtime PCR system (Applied Biosystems, UK).

Flow Cytometry analysis

Single cell suspensions of organs were stained with the fluorochrome-conj ugated antibodies protein as described (38-41). Direct or indirect staining of fluorochrome- conjugated antibodies included: CD4, CDS, B220, CDl lc, CDl lb, F4/80, CD69, CD44, CD62L, IFNy, TNFa, IL-2, IL-10, CD28, CTLA-4, PD-1, BTLA, and ICOS (BioLegend, or BD Biosciences, San Jose, CA, San Diego, CA). Skint8-Ig, SkintS IgV-Ig or SkintS IgC- Ig proteins were biotinylated with sulfo-NHS-LC-Biotin (Pierce) and detected by streptavidin-PE. The samples were analyzed on a FACSCalibur or LSRFortessa X-20 Cell Analyzer (BD Biosciences). Data analysis was done using FlowJo software (Ashland, OR). In vitro T cell assays

Murine CD3 ⁺ , CD4 ⁺ or CD8 ⁺ T cells were purified from C57BL/6 mice by an immunomagnetic system (Miltenyi, Auburn, CA), and tire purity of the cells was usually >95%. T cells were stimulated with anti-CD3 antibody, or anti-CD3 and anti-CD28 antibodies (Biolegend) in the presence of Skint8-Ig or control Ig. Proliferative response was assessed by pulsing the culture with 1 pCi of [ H] thymidine (PerkinElmer, Inc., Downers

Grove, IL) 12 hours before harvest. [¾] thymidine incorporation was measured by liquid scintillation spectroscopy (PerkinElmer, Inc.). For the carboxyfluorescein diacetate succinimidyl ester (CFSE) assay, splenocytes were labeled with CFSE (ThermoFisher

Scientific, Grand Island, NY) and stimulated with anti-CD3 in the presence of Skint8-Ig or control Ig. The cells were analyzed by flow cytometry.

ELISA

The concentration of cytokines IFNy, TNFa, IL-2, and IL-10 was determined by its respective ELISA Kit (Biolegend) according to the manufacturer's instructions. Induction and assessment of EAE

Mouse MOG35-55 (GL Biochem, Shanghai, China) was emulsified in complete Freud’s adjuvant (Sigma-Aldrich, St Louis, MO, USA) supplemented with Mycobacterium tuberculosis H37Ra (Difco Laboratories, Detroit, MI). Mice were injected s.c. with the MOG in the dorsal flank on day 0. The mice were also injected i.p. with 500 ng of purified Bordetella pertussis toxin (Sigma-Aldrich). The mice were then observed for clinical scores based on the following scale: 0, normal; 0.5, partially limp tail; 1, paralyzed tail; 2, loss in coordinated movement, hind limb paresis; 2.5, one hind limb paralyzed; 3, both hind limbs paralyzed; 3.5, hind limbs paralyzed, weakness in forelimbs; 4, forelimbs paralyzed; 5, moribund or dead. As required by animal ethics, mice were euthanized beyond a clinical score of 4.

Statistical analysis

P-values were based on the two-sided Student’s t test. A confidence level above 95% (p<0.05) was determined to be significant.

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Example 4. BTN5

In this example, we identify BTN5, previously called erythroid membrane-associated protein (ERMAP), as a novel T cell inhibitory molecule. BTN5 protein is expressed on the cell surface of resting and activated antigen presenting cells (APCs), and in tumor tissues. The BTN5 putative receptor is expressed on activated CD4 and CDS T cells, and macrophages. Both mouse and human BTN5-IgG2a Fc (BTN5-Ig) fusion proteins inhibit T cell proliferation, activation, and/or cytokine production in vitro. Administration of BTN5-Ig protein ameliorates autoimmune diseases including experimental autoimmune

encephalomyelitis (EAE) and type 1 diabetes (T1D) in mice. BTN5 also affects macrophage function because anti-BTN5 blocking antibody enhances macrophage phagocytosis of cancer cells in vitro. Furthermore, administration of the anti -BTN 5 antibody inhibits tumor growth in mice, likely by blocking the inhibitory effects of BTN5 on T cells and macrophages. These results demonstrate that therapeutic interaction of the BTN5 inhibitory pathway represents a novel strategy for treating patients with autoimmune disease or cancer.

Results:

BTN5 shares sequence and structural similarity to existing B7 family members in the extracellular region

B7-H3 is a B7 family member whose putative receptor is expressed on activated T cells. B7-H3 has been shown to have either a stimulatory or an inhibitory effect on T cells.

By a series of genome-wide database searches, we found that the extracellular region of mouse BTN5 (mBTN5) shares a strong similarity with that of B7-H3 with 25% identity and 15% similarity, including a conserved pattern of 4 cysteines in identical positions. mBTN5 also has a significant homology with other B7 family members, sharing 20%, 17%, 24%, 20%, 22% and 22% identity in the extracellular region with mouse PD-L1, PD-L2, B7-1, B7-

2, B7-H2, B7-H4, respectively (data not shown). These levels of identity are similarly observed among the known B7 family members, suggesting that BTN5 is a new B7 family member or B7-related molecule. BTN5 is highly conserved among vertebrates, and human BTN5 (hBTN5) shares a striking homology with rtiBTNS (73% identity and 14% similarity; data not shown). Both mBTN5 and hBTN5 proteins contain an extracellular region, a transmembrane domain, and an intracellular region. The extracellular region in rtiBTNS contains an lgV domain and an IgC domain, whereas hBTN5 has an IgV domain, but no IgC domain [37, 38, 41] BTN5 also shares a significant homology across its entire length to other BTN molecules [37] Phylogenic tree analysis shows that the extracellular region of rtiBTNS is closer to that of B7-H3, B7-H4, PD-L1 and PD-L2 than that of B7.1 and B7.2.

BTN5 is expressed on APCs, and some cancer tissues and tumor cell lines We evaluated the expression of mBTN5 tnRNA in various tissues by using RT-PCR analysis. mBTN 5 tnRNA was detected in the lymph node, thymus and lung. mBTNS mRNA was also weakly expressed in other organs including the spleen, pancreas, blood, liver, heart, and kidney.

It has been reported that BTN5 protein was predominately located on cell surfaces of BTN5 gene transfected cells [37, 38, 41] We analyzed the expression of mBTN protein on the cell surface of immune cells by flow cytometry. As shown in Figure 19A, mBTN5 protein was not expressed on the cell surface of resting CD19 ⁺ or B220 ⁺ B cells, CD1 lb ⁺ monocytes, F4/80 ^* macrophages, and CD1 lc ⁺ dendritic cells (DCs), but was induced upon activation by LPS. (Figure 19A). mBTN5 protein was also expressed weakly on resting CD4 ⁺ and CD8 ⁺ T cells, and the expression levels were upregulated upon activation by anti-CD3 and CD28 antibodies (Figure 19A). These results suggest that endogenous mBTN5 is an integral cell surface protein that is expressed on activated APCs, resting and activated T cells.

We then determined the expression of hBTN5 protein in normal and cancer human tissues by immunohistochemistry. As shown in Figure 19B and C, control isotype antibody did not stain any normal or cancer tissues. In contrast, an anti-hBTN5 antibody detected hBTN5 protein expression in normal breast, lung, liver, colon, and prostate tissues at low levels (Figure 19B). HBTN5 protein was also detected in cancer tissues, and the expression levels of hBTN5 in breast, lung, liver, colon, and prostate tumor tissues were higher than those of the respective normal tissues (Figure 19C vs 19B). hBTN5 protein was largely confined to the plasma membrane or cytoplasm of epithelial cells.

We also examined BTN5 protein expression on some tumor cell lines by flow cytometry'. As shown in Figure 19D, BTN5 protein was expressed highly on the cell surface of murine neuro-2a neuroblastoma cells, Lewis lung carcinoma, P388 leukemia, and human erythroleukemia line K562. BTN5 protein was weakly or not expressed on murine CT-26 colon cancer cells and B16F10 melanoma cells.

The expression of the putative BTN5 receptor

To determine the expression pattern of the putative BTN5 receptor, we constructed an mBTN5-Ig fusion protein that contains the IgV domain of mBTN5 and the constant region of mouse lgG2a. Purified mBTN5-Ig fusion protein and control mouse lgG2a Fc (control Ig) were biotinylated. Splenocytes from C57BL/6 mice were stained with the biotinylated proteins, followed by Streptavidin-PE. The binding of mBTN5-Ig or control Ig to immune cells was analyzed by flow cytometry. As shown in Figure 20A and B, mBTN5 scarcely bound to resting CD4 ⁺ and CD8 ⁺ T cells, but bound significantly to anti-CD3 and anti-CD28 antibody-activated CD4 ¹ and CD8 ⁺ T cells (Figure 20A). The results indicate that activated CD4 and CDS T cells express the putative BTN5 receptor.

We also analyzed the expression of the putative BTN5 receptor on other immune cells. We found that mBTN5 bound to a proportion of resting B220 ⁺ B cells, CDl lc ⁺ DCs, CD1 lb ¹ monocytes, and F4/80 ¹ macrophages (Figure 20A). After activation by LPS, the mBTN5 binding to B cells, DCs, monocytes and macrophages was increased (Figure 20A). The data suggest that resting B cells, DCs, monocytes and macrophages also express the putative BTN5 receptor and the expression levels on these cells are uprcgulated upon activation.

To determine whether the putative BTN5 receptor is a known B7 member receptor, HEK-293 cells were transfected with an expression vector containing the murine PD-1, CD28, BTLA, CTLA-4, or ICOS gene. The expression of PD-1, CD28, BTLA, CTLA-4, or ICOS protein on the transfected cells was confirmed by flow cytometric analysis with the antibodies against the respective receptors (Figure 20B). The binding of mBTN5 to the transfected cells was then analyzed. mBTN5 did not bind to the PD-1, CD28, BTLA, CTLA- 4, or ICOS transfected cells (Figure 20C). The results suggest that mBTN5 binds to a receptor distinct from PD-1, CD28, BTLA, CTLA-4, or ICOS. mBTN5-Ig fusion protein inhibits T cell proliferation and activation in vitro

The data that mBTN5 protein is expressed on APCs and its putative receptor is expressed on activated T cells suggest a potential function of mBTN5 on T cells. We therefore investigated the effect of mBTN5-Ig on T cell proliferation in vitro. CD3 ¹ T cells were purified from splenocytes of C57BL/c mice, and cultured on plates pre-coated with or without anti-CD3 antibody in the presence of graded doses of mBTN5-Ig or control Ig for 3 days. T cell proliferation was measured by [ ³ HJ thymidine incorporation. mBTN5-Ig in the absence of anti-CD3 antibody did not affect the proliferation of T cells (data not shown). However, mBTN5-Ig inhibited anti-CD3-induced T cell proliferation in a dose-dependent manner, with ~22%, 52% and 79% inhibition in the presence of 1434, 2868, and 5736 ng/ml mBTN5-Ig, respectively, as compared to respective amounts of control Ig (Figure 21 A).

To confirm the T cell inhibitory effect and to determine whether mBTN5 inhibits CD4 and/or CDS T cells, splenocytes were labelled with caiboxyfluorescein diacetate succinimidyl ester (CFSE), and cultured with anti-CD3 antibody and graded doses of mBTN5-Ig or control Ig. T cell proliferation was analyzed for CFSE fluorescent intensity in CD4 ¹ or CD8 ⁺ T cells by flow cytometry. Consistent with the results from the [ ³ H| thymidine incorporation assay, mBTN5-Ig inhibited anti -CD3 -activated proliferation of CD4 ¹ and CD8 ⁺ T cells in a dose-dependent manner (Figure 21 B-D) .

We then determined whether mBTN5-Ig affects T cell activation in vitro.

Splenocytes were cultured with anti-CD3 antibody and mBTN5-Ig or control Ig. Since CD69 is an early marker of T cell activation, the expression of CD69 was analyzed after 24 hours. As shown in Figure 21E and F, the expression levels of CD69 on both CD4 and CDS T cells were significantly reduced in the presence of mBTN5-Ig. The results suggest that mBTN5-Ig inhibits the activation of CD4 and CDS T cells.

T cells can be divided into naive and effective memory T cells based on the expression levels of CD44 and CD62L. We next analyzed the effect of mBTN5-Ig on these T cell subsets. We found that the percentages of CD44 ^l0 CD62L ^hi CD4 and CDS T naive cells were significantly higher in the presence of mBTN5-Ig than those in the control group (Figure 21G-I). In contrast, the percentages of CD44 ^hi CD62L ^l0 CD4 and CDS effective memory T cells were significantly lower in the presence of mBTN5-Ig (Figure 21, G, J, K). The results further suggest that mBTN5-Ig inhibits the activation of CD4 and CDS T cells. Taken together, our results suggest that mBTN5-Ig inhibits TCR-mediated proliferation and activation of both CD4 and CDS T cells in vitro. hBTN5-Ig fusion protein inhibits T cell proliferation and cytokine production in vitro Having demonstrated that mBTN5-Ig protein inhibits the proliferation and activation of murine T cells in vitro, we wished to know whether hBTN5 has similar effects. Like mBTN5-Ig, we cloned and expressed hBTN5-Ig fusion protein containing the IgV domain of hBTN5 and the constant region of mouse IgG2a. hBTN5-Ig protein was then purified from the expression system until a relatively high purity, as determined by Coomassie blue-stained SDS-PAGE. The identity of the fusion protein was verified by Western blot using anti-IgG2a antibody. [ ³ H] thymidine incorporation assay showed that hBTN5-Ig also inhibited tire proliferation of murine T cells in a dose-dependent manner, with ~15%, 61 % and 85% inhibition in the presence of 1434, 2868, and 5736 ng/ml hBTN5-Ig , respectively (Figure 22A). CFSE dilution assay showed that hBTN5-Ig inhibited the proliferation of both CD4 ⁺ and CD8 ⁺ T cells (Figure 22B-D). We also determined whether hBTN5-Ig inhibits the proliferation of human T cells. Purified human T cells were cultured with anti-human CD3 antibody in the presence of hBTN5-Ig or control Ig, and T cell proliferation was measured by [¾] thymidine incorporation. As shown in Figure 22E, hBTN5-Ig significantly inhibited the proliferation of human T cells. Collectively, hBTN5 inhibits the proliferation of both mouse and human primary T cells, suggesting that its binding partner and its conferred function on T cells may be conserved across species.

We next examined whether hBTN5-Ig affects cytokine production from T cells in vitro. Purified T cells were stimulated with anti-CD3 antibody in the presence of hBTN5-Ig or control Ig protein for 3 days. The cytokines in the supernatants were measured by ELISA.

As shown in Figure 22F, hBTN5-Ig inhibited the production of IFNy, TNFa, IL-2, and IL-10 from T cells. Taken together, the results suggest that hBTN5-Ig can inhibit TCR-mediated proliferation and/or cytokine production from mouse and human T cells in vitro Aniti-hBTNS antibody enhances macrophage phagocytosis of cancer cells in vitro and inhibits tumor growth in vivo.

It has been reported that CD47 is expressed on erythroid cells and cancer cells, and represents a“don’t eat me” signal that protects these cells from phagocytosis by macrophages [42, 43] Conversely, anti-CD47 blocking antibodies enhance macrophage phagocytosis of cancer cells [43 J. Since BTN5 is also expressed on erythroid cells and cancer cells, we determined whether BTN5 could affect macrophage phagocytosis of cancer cells. We made anti-hBTN5 polyclonal antibody by immunizing hBTN5-Ig in mice. K562 cancer cells that express hBTN5 were labelled with CFSE. BM-derived macrophages were incubated with the K562 cells in the presence of the anti-hBTN5 or control antibody for 2 horns. The cells were then harvested, washed, and analyzed for the percentages of CFSE ¹ cells, which represents phagocytosis of the cancer cells by macrophages. As shown in Figure 23 A and B, macrophage-mediated phagocytosis of cancer cells was significantly augmented in the presence of the anti-BTN5 antibody.

Macrophages are composed of distinct subsets, including the classically activated Ml and alternatively activated M2 macrophages. Ml macrophages are proinflammatory, whereas M2 macrophages are anti-inflammatory or protumor. We investigated whether BTN5-Ig protein affects the differentiation of Ml or M2 in vitro. BM cells were first induced to generate proliferative nonactivated macrophages (also named MO macrophages) in vitro according to published protocols [44] The MO macrophages were then induced to differentiate into Ml or M2 as described [44] in the presence of hBTN5-Ig or control Ig protein. We found that hBTN-Ig significantly increased the generation of CD206 ^hi MHC II ¹⁰ M2 macrophages (Figure 23C, D), but did not affect the generation of MHC II¾O206 ¹⁰ Ml macrophages (data not shown).

Having observed that BTN5-lg fusion protein inhibits T cell proliferation, activation, and cytokine production in vitro, and that anti-hBTN5 blocking antibody enhances macrophage phagocytosis of cancer cells, we hypothesized that administration of anti-hBTN5 antibody could block the inhibitory effects of BINS on T cells and macrophages, resulting in enhanced antitumor immunity and the inhibition of tumor growth in vivo. We transfected murine CT-26 colon cancer cells with an expression vector containing the full-length hBTN5 gene and screened for the cancer cells that stably expressed BTN5. As shown in Figure 23E, transfected CT-26 cells expressed hBTN5 protein on the cell surface. We then injected the hBTN5-exprcssing CT-26 cells s.c. into syngeneic BALB/c mice. When the tumors were palpable, the mice were injected at the tumor site with same amounts of mouse anti-hBTN5 or control polyclonal antibody. As shown in Figure 23F, the anti-hBTN5 antibody significantly inhibited the growth of CT-26 cancer cells, as compared to control antibody treatment. Analysis of tumor-infiltrating immune cells shows that there were significantly higher percentages of (Figure 23G) CD4 and CDS T cells, and lower percentages of (Figure 23H) M2 macrophages in hBTN5-Ig-treated tumors.

Taken together, our results suggest that hBTN5 protein induces the production of M2 macrophages that may promote tumor growth. Conversely, anti-hBTN5 blocking antibody enhances macrophage phagocytosis of cancer cells in vitro, and inhibits the growth of BTN5 expressing cancer cells in vivo. The in vivo antitumor activity is likely due to the anti-BTN5 antibody blocking the inhibitory effects of BTN5 on T cells and macrophages.

Administration of hBTN5-Ig fusion protein ameliorates EAE in mice

Since BTN5-Ig fusion protein inhibits T cell proliferation, activation and cytokine production in vitro, we set out to investigate whether in vivo administration of BTN5-Ig could ameliorate autoimmune diseases that are caused by an overactive immune system. Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, and EAE is a common animal model for MS. To determine whether BTN5 attenuates EAE, C57BL/6 mice w'ere immunized with pMOG peptide to induce EAE development. The mice were then treated with hBTN5-Ig or control Ig protein. As shown in Figure 24A, hBTN5-Ig treatment delayed EAE onset, and reduced the mean clinical scores throughout the entire 42 day time course. In addition, the percentage of disease-free mice in hBTN5-Ig-treated group was increased (Figure 24B). Furthermore, histological evaluation showed a significant reduction in inflammatory lesions, with little or no demyelination and/or axonal damage or loss in hBTN5-Ig-treated group (Figure 24C). Consequently, the histological scores were significantly reduced in the hBTN5-Ig-treated mice, as compared to those in the control group (Figure 24D).

We then analyzed T cell subsets in the spleen of the EAE mice. As shown in Figure 246E-H, the percentages of CD44 ^k> CD62L ^M naive CD4 and CDS T cells were increased, while the percentages of CD44 ^hl CD62L ^l ° effective memory CD4 and CDS T cells were decreased in hBTN5-Ig-treated mice, although the percentages of CD44 ^hi CD62L ^hi CD4 and CDS central memory T cells were not significantly different between the hBTN5-Ig and control groups. The results are in agreement with our in vitro data that BTN5-Ig protein inhibits T cell activation.

Since Tregs are involved in immune tolerance induction and CD4 ^l CD25 ^l FoxP3 ¹ cells are the most profoundly characterized Tregs [45], we evaluated CD4 ⁺ CD25 ⁺ FoxP3 ⁺ Tregs. We found that hBTN5-Ig treatment increased the percentage of Tregs in the spleen (Figure 241, J). Furthermore, the percentages of arginase ¹ and CD206 ^hi MHC ^k> M2 macrophages were increased, while the percentage of MHC ^hi CD206 ^to Ml macrophages was not altered in hBTN5-Ig-treated mice (Figure 24K, L).

We next investigated T cell proliferation and cytokine production after MOG stimulation in vitro. As shown in Figure 24M and N, the proliferation of CD4 T cells from hBTN5-Ig-treated mice was reduced in response to pMOG.15-55 stimulation, although the proliferation of CDS T cells was not significantly different between control- and hBTN5-Ig- groups. hBTN5-Ig treatment also reduced the production of Thl cytokines IFNy and TNFo, as well as Thl7 cytokine, but increased the production of Th2-type cytokine IL-10 from CD4 T cells (Figure 24 O, P).

Administration of hBTN5-Ig fusion protein attenuates T1D in mice

Type 1 diabetes (T1D) is an autoimmune disease caused by the destruction of insulin- secreting islet b-cells by autoreactive T cells. The NOD mouse is the most commonly used animal model for human T1D [46], We also investigated whether hBTN5-Ig could attenuate T1D. Female 22 week-old NOD mice were divided into two groups and 33% of the mice in each group had T1D. The mice were injected with 30 mg hBTN5-Ig or control Ig protein at 2- day intervals for 3 weeks. At 30 weeks 67% control Ig-treated mice had T1D, while none of hBTN5-Ig-treated mice had T1D. Histological analysis showed that inflammation and loss of islets in BTN5 -Ig-treated mice were significantly lower than control Ig-treated group (Figure 25A). We then examined T cells and macrophages in the spleen. Like the EAE mice, hBTNS-

Ig treatment resulted in increased percentages of naive CD4 and CDS naive T cells, although the percentages of CD44 ^hi CD62L ¹ ° effective memory and CD44 ^hi CD62L ^hi central memory CD4 and CDS T cells were not significantly different between hBTN5-Ig and control groups (Figure 25B-E). Furthermore, the percentage of M2 macrophages was increased, and that of Ml macrophages were decreased in hBTN5-Ig-treated NOD mice (Figure 25F, G). Taken together, our results suggest that hBTN5-Ig treatment ameliorates EAE and T1D, probably by inhibiting the proliferation and activation of autoreactive T cells, as well as increasing the number of M2 macrophages. Generation of anti-hBTNS-Ig monoclonal antibodies (mAbs)

To generate anti-hBTN5 mAbs, B ALB/c mice (8-10 weeks of age) were immunized with 100 mg hBTN5-Ig protein in complete Freund's adjuvant (CFA) on day 0 and boosted on day 14 and day 21 in the same protein quantity in incomplete Freund's adjuvant (IF A). The mice were boosted with 100 mg hBTN5-Ig (no adjuvant, add 100ml lxPBS instead) three times three days in a row (days 28, 29, 30). The spleens were harvested from the mice on day 31. Single-cell suspension of the splenocytes were fused to X63-Ag8.653 myeloma cells to produce hybridomas. ELISA was performed to identify the hybridomas that could produce anti-hBTN5 mAbs but not with control Ig protein. These hybridoma clones were further subcloned. A total of 9 hybridoma lines that can produce anti-hBTNS mAbs have been generated.

We then determined whether the anti-hBTNS mAbs could enhance macrophage- mediated phagocytosis of cancer cells. BM-derived macrophages were incubated with the K562 cells that had been labelled with CFSE as in Figure 23A. The anti-hBTNS mAbs were added to the cultures for 2 hours. The cells were then analyzed for the percentages of CFSE ⁺ cells. As shown in Figure 26, macrophage-mediated phagocytosis of cancer cells was significantly augmented by two anti-hBTNS mAbs (clones D4 and D16). We are

investigating the ability of the mAbs to treat tumors in several tumor animal models. Discussion:

The present study identifies BTN5 as a novel inhibitory molecule for T cells and macrophages. BTN5 shares significant sequence and structural homolog with existing B7 family members in the extracellular region. Like B7 family molecules, the extracellular region in mBTN5 contains an lgV-like and an IgC-like domain. Although hBTN5 are highly homologous to mBTN5, hBTN5 contains only an IgV-like domain, and no IgC-like domain. However, the absence of the IgC-like domain in hBTN5 seems not to affect its functions. We have shown that hBNT5-Ig protein inhibits T cell proliferation and cytokine production in vitro and ameliorates autoimmune diseases in vivo. The mBTN5-Ig protein that we produced contains the IgV-like domain only, but also significantly inhibits T cell proliferation and activation in vitro.

By using flow cytometric analysis, we show that mBTN5 protein was expressed on the cell surface of activated APCs including DCs, monocytes, macrophages and B cells, as well as resting and activated T cells. The expression of BTN5 protein on the cell surface of APCs is also in accordance with its functions in regulating T cell proliferation and/or activation.

BTN5-Ig protein binds to activated CD4 and CDS T cells, but not to resting T cells, suggesting that tire putative BTN5 receptor is expressed on activated T cells. BTN5 joins ICOS, PDL1/2, B7-H3, B7-H4, BTN1A1, BTN2A2, BTNL2, BTNL1 and BTN3, to recognize receptors induced after T cell activation [24, 26, 29, 31] However, BTN5 protein did not bind the CD28, CTLA-4, PD-1, BTLA or ICOS transfected cells. Therefore, the putative BTN5 receptor appears distinct from CD28, PD-1, CTLA-4, BTLA, or ICOS.

In addition to inhibiting T cell functions, BTN5 also affects macrophages. We have shown that anti-BTN5 antibody enhances macrophage-mediated phagocytosis of BTN5 expressing cancer cells. The IgV domain in both mBTN5 and hBTN5 contains a Clq recognition sequence that is a macrophage membrane protein. The interaction between macrophages and BTN5 expressing cancer cells may be mediated by the Clq recognition sequence.

Our immunohistochemical analyses show that hBTN5 protein was expressed in breast, colon, lung, liver and prostate tumor tissues at medium to high levels, whereas only low levels of hBTN5 protein was detected in the respective normal tissues.. Furthermore, we detected the expression of BTN5 protein on the cell surface of several cancer cell lines. The expression pattern indicates that BTN5 is involved in immune evasion of cancer cells. Indeed, we have demonstrated that in vivo administration of anti-BTN5 polyclonal antibody inhibits the growth of BTN5 expressing colon cancer cells in mice.

We have also demonstrated that in vivo administration of BTN5-Ig protein ameliorates EAE. We have shown that T cells from BTN5-treated EAE mice have a reduced proliferation in response to in vitro MOG stimulation. Furthermore, splenocytes from BTN5- treated EAE mice secreted decreased amounts of the Thl cytokines TNFa, IFNy, and IL-2 in response to MOG, but increased amount of the Th2 cytokine IL-10. Interestingly, BTN5 increased IL-10 amounts in the serum of EAE mice, but inhibited IL-10 production in vitro.

In addition to inhibition of T cell proliferation and activation, BTN5 -induced production of Tregs and M2 macrophages is involved in the beneficial effects of BTN5 in autoimmune diseases

BTN5-Ig protein treatment also attenuates T1D in NOD mice. Although the mechanisms by which BTN5-Ig inhibits EAE and T1D are similar, there are also some differences. For examples, BTN5-Ig not only increased the percentages of naive T cells, but also decreased the percentages of effective memory cells in the EAE model, whereas BTN5-

Ig only increased the percentages of naive T cells in the T1D model. In addition, BTN5-Ig increased the percentages of M2 macrophage and decreased the percentages of inflammatory Ml macrophages in the T1D model, but only increased the percentages of M2 macrophages in the EAE model. These differences are probably due to the different animal models and/or different doses and duration of hBTN5-Ig used.

In summary, we have identified BINS as a novel inhibitor)' molecule for T cells and macrophages. BTN5 protein is expressed on APCs, and some tumor tissues and cancer cells. The BTN5 putative receptor is expressed on activated T cells, and resting and activated macrophages. BTN5-Ig fusion protein inhibits the proliferation, activation, and cytokine production of T cells, and increases the generation of anti-inflammatory M2 macrophages in vitro. In vivo administration of hBTN5-Ig attenuates autoimmune diseases including EAE and T1D. Conversely, anti-BTN5 antibody enhances macrophage-mediated phagocytosis of cancer cells in vitro, and administration of the antibody inhibits tumor growth in vivo.

Therefore, targeting the BTN5 pathway is an innovative approach for the treatment of autoimmune diseases, cancer and infections.

Materials and Methods

Bioinformatics analysis of BTN5. Sequence alignments of the extracellular domains of mBTN5 and existing B7 family members, as well as the full sequences of mBTN5 and hBTNS proteins were analyzed via the Clustal W program in MacVector 16.0.5 (MacVector, Inc.). Phylogenic tree analysis was also performed via the Clustal W program in MacVector. The transmembrane, and Ig-like domain were predicted with TMHMM server version 2.0, and InterPro.

Cloning and purification of mBTN5 and hBTNS

The extracellular domains of mBTN5 (aa48-156) and hBTNS (aa30-145) were cloned and fused into a pCMV6-AC-FC-S expression vector containing the constant region of mouse IgG2a (ORIGENE, Rockville, MD). The vectors were transfected into HEK-293 cells. The fusion proteins were purified for the supernatant using Protein G Sepharose 4 Fast Flow according to the manufacturer’s instructions (GE Healthcare). Purified proteins were verified by SDS-PAGE, Coomassie Staining and Western blot. Protein was quantified using the Pierce™ BCA Protein Assay Kit (Pierce, Rockford, IL). Control Ig (recombinant mouse IgG2a Fc protein) was purchased from BXCell (West Lebanon, NH). The endotoxin levels of the recombinant proteins were less than 0.01 EU/ml of 1 mg of purified protein.

Mice

BALB/c, C57BL/6 and NOD/LU NOD mice were purchased from Jackson

Laboratory. The mice were used in accordance with protocols approved by the Institutional Animal Care and Use Committee of the University of Connecticut.

Flow Cytometry analysis

Single cell suspensions of organs and tumors were stained with the fluorochrome- conjugated antibodies protein as described [53-56] For intracellular staining, the cells were first permeabilized with a BD Cytofix/Cytoperm solution for 20 minutes at 4 °C. Direct or indirect staining of fluorochrome-conjugated antibodies included: CD4, CDS, CD 19, B220,

CD1 lc, CD1 lb, F4/80, CD44, CD62L, CD69, FoxP3, CD206, MHC P, IFNy, TNFct, IL- 17A, IL-10, CTLA-4, CD28, PD-1, BTLA, and ICOS (BioLegend, or BD Biosciences, San Jose, CA, San Diego, CA). Anti-arginase 1 antibody, anti-hBTN5 monoclonal antibody were purchased from R&D System (Minneapolis, MN). mBTN5-Ig was biotinylated with sulfo- NHS-LC-Biotin (ThermFisher, Grand Island, NY). The samples were analyzed on a

FACSCalibur or LSRFortessa X-20 Cell Analyzer (BD Biosciences). Data analysis was done using FlowJo software (Ashland, OR).

ELISA The concentration of cytokines IFNy, TNFo, IL-2, and IL-10 was determined respectively by ELISA Kit (Biolegend) according to the manufacturer's instructions.

Histopathology

Spinal cords and pancreata were removed from mice and fixed with 10%

formaldehyde for 24 hours. Segments of the tissues were embedded in paraffin, and sections were prepared. The sections were stained with hematoxylin-eosin (H&E). The sections of spinal cords were also stained with Luxol fast blue (LFB) and Bielschowslti silver impregnation (BSI) to assess demyelination, and axonal damage, respectively. The histological stained sections were semiquantitatively scored blind as described [57J.

Human Multiple Normal and Tumor Tissue Arrays were purchased from BioChain (Newark, CA). The tissues were subjected to antigen unmasking, and then incubated with anti-hBTN5 monoclonal antibody (R&D system), followed by ImmPRESS VR Polymer HRP anti-mouse lgG reagent, and developed with peroxidase substrate solution (Vector

Laboratories) according to the manufacturer's instructions.

In vitro T cell assays

Normal human peripheral blood CD3 ⁺ Pan T Cells that were negatively isolated from mononuclear cells using an indirect immunomagnetic Pan-T labeling system were purchased from ALLCELLS, LLC (Alameda, CA). Murine CD3 ⁺ T cells were purified from C57BL/6 mice by an immunomagnetic system (Miltenyi, Auburn, CA), and the purity of the cells was usually >95%. T cells were stimulated with anti-CD3 and/or anti-CD28 (Biolegend) in the presence of BTN5-Ig or control Ig. Proliferative response was assessed by pulsing the culture with [ ³ H] thymidine (1 pCi/well) (PetkinElmer, Inc., Downers Grove, IL) 12 hours before harvest. Incorporation of [ ³ H] thymidine was measured by liquid scintillation spectroscopy (PetkinElmer, Inc.). For carboxyfluorescein diacetate succinimidyl ester (CFSE) assay, splenocytes were labeled with CFSE (ThermoFisher Scientific) and stimulated with anti-CD3 in the presence of BTN5-Ig or control Ig. The cells were analyzed by flow cytometry.

Reverse transcription polymerase chain reaction (RT-PCR)

Total RNA from cells was isolated from tissues and cDNA was synthesized as described [58] Equal amounts of cDNAs were used for RT-PCR. PCR products were viewed by agarose gel.

Culturing of BM-derived macrophages BM was harvested from C57BL/6 mice and cultured in medium containing M-CSF for 7 days to differentiate into MO macrophages [44], The MO macrophages were induced to differentiate into Ml and M2 as described [44] in the presence of mBTN5-Ig or control Ig.

For the macrophage phagocytosis assay, cancer cells were labeled with CFSE, and cultured with MO macrophages in the presence of anti-hBTN5 antibody or isotype antibody for 2 horns. Phagocytosis was measured by flow cytometric analysis of CFSE ¹ cells.

Generation of anti-hBTNS polyclonal and monoclonal Antibodies

BALB/c mice were immunized with 100 mg hBTN5-Ig protein emulsified in complete Freund's adjuvant (CFA) on day 0 and boosted on day 14 and day 21 in the same protein quantity in incomplete Freund's adjuvant (IF A). The mice were boosted with 100 mg hBTN5-

Ig without IFA 3 times (days 28, 29, and 30). On day 31, the serum that contain anti-hBTNS polyclonal antibody was harvested.

To make anti-hBTNS monoclonal antibody, the spleens were also harvested from the immunized mice on day 31. Single-cell suspension of the splenocytes were fused to X63- Ag8.653 myeloma cells to produce hybridomas. ELISA was performed to identify the hybridomas that could produce anti-hBTNS mAbs but not with control Ig protein. These hybridoma clones were further subcloned by limiting dilution.

Evaluation of local tumor growth

Murine CT-26 colon cancer cells were obtained from the ATCC. The cancer cells that had been transfected with a vector containing the hBTNS gene were injected subcutaneously (s.c.) into the flank of syngeneic BALB/c mice. Mouse anti-hBTNS or control polyclonal antibody were then injected into the tumor injection site. Tumor size (volume) was determined every other day by caliper measurements of the shortest (A) and longest (B) diameter, using the formula V = (A2B)/2.

Induction and assessment of EAE

Mouse MOG35-55 (GL Biochem, Shanghai, China) was emulsified in complete Freud’s adjuvant (Sigma-Aldrich, St Louis, MO, USA) supplemented with Mycobacterium tuberculosis H37Ra (Difco Laboratories, Detroit, MI). Mice were injected s.c. with the MOG at 4 points in the dorsal flank on day 0. The mice were also injected i.p. with 500 ng of purified

Bordetella pertussis toxin (Sigma-Aldrich). The mice were then observed for clinical scores based on the following scale: 0, normal; 0.5, partially limp tail; 1, paralyzed tail; 2, loss in coordinated movement, hind limb paresis; 2.5, one hind limb paralyzed; 3, both hind limbs paralyzed; 3.5, hind limbs paralyzed, weakness in forelimbs; 4, forelimbs paralyzed; 5, moribund or dead. As required by animal ethics, mice were euthanized beyond a clinical score of 4.

Assessment of T1D

Female NOD mice were injected i.p. with hBTNL5-Ig, or control Ig protein. The blood glucose levels of mice were determined by test strips (Advanced glucose meter, CVS health, USA). Mice with a blood glucose measurement of greater than 250 mg/dL on two consecutive readings were considered diabetic.

Statistical analysis

P-values were based on the two-sided Student’s t test. A confidence level above 95% (p<0.05) was determined to be significant.

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Example 5. CD300f

We have demonstrated that both mouse and human CD300c-Fc fusion proteins significantly inhibit T cell functions in vitro. Administration of CD300c-Fc protein attenuates graft-versus-host disease (GVHD) and autoimmune diseases including experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis (CIA), murine models for human multiple sclerosis (MS) and rheumatoid arthritis (RA).

Furthermore, anti-CD300c antibodies inhibit tumor growth in mouse tumor models.

Since CD300 family contains other members, we have cloned and expressed CD300f-Fc fusion protein. The extracellular domain of human CD300f (aa22-125) was cloned and fused into a pCMV6-AC-FC-S expression vector containing the constant region of mouse IgG2a (ORIGENE). The vector was transfected into HEK293F cells. The fusion protein was purified for supernatant using Protein G Sepharose 4 Fast Flow according to the manufacturer’s instructions (GE Healthcare). Purified protein was verified by SDS-PAGE, Coomassie Staining and Western blot. Protein was quantified using the Pierce™ BCA Protein Assay Kit (Pierce, Rockford, IL).

After we obtained purified CD300f-Fc fusion protein, we determined whether CD300f-lg protein affected lymphocyte and T cell proliferation. Splenocytes from C57BL/c mice were cultured on plates pre-coated with anti-CD3 antibody in the presence of graded doses of CD300f- Ig (800, 1600, and 3200 ng/ml) for 3 days. Since the molecular weight of CD300-lg fusionprotein is ~1.5-fold higher than that of control Ig protein, we used equimolar amounts of the control Ig (533, 1066, and 2133 ng/ml) as a control. T cell proliferation was measured by [¾] thymidine incorporation. As shown in Figure 27, CD300f-Ig inhibited anti-CD3 -activated T cell proliferation in a dose-responsive manner, as compared to equimolar amounts of control Ig. We also determined whether CD300f could inhibit anti-CD3 and anti-CD28 antibody-activated T cell proliferation. Similarly, CD300f- Ig reduced anti-CD3 and anti-CD28-activated T cell proliferation (data not shown).

To confirm the effect on T cell proliferation and to determine whether CD300f affects CD4 and/or CDS T cells, we performed a carboxyfluorescein diacetate

succinimidyl ester (CFSE) dilution assay. Murine splenocytes were labelled with CFSE, and then cultured with anti-CD3 antibody in the presence of graded doses of CD300f-Ig or control Ig as in Figure 27. T cell proliferation was measured by CFSE fluorescent dilution in CD4 and CDS T cells. As shown in Figure 28, CD300f-Ig inhibited anti-CD3- activated proliferation of both CD4 and CDS T cells in a dose-dependent manner.

We next determined whether CD300f-Ig affects the activation of T cells in vitro. CD69 is an early activation marker. After splenocytes were cultured with anti-CD3 antibody or anti-CD3 plus anti-CD28 antibodies in the presence of graded doses of CD300f-Ig or control Ig. The expression of the CD69 on CD4 and CDS T cells was analyzed 24 hours later. As shown in Figure 29, CD300f-Ig reduced the expression of

CD69 on both CD4 and CDS T cells in a dose- responsive manner. The results suggest that CD300f also inhibits the activation of CD4 and CDS T cells.

To further confirm that CD300f2-Ig inhibits T cell activation, we analyzed the expression of CD44 and CD62L by CD4 ⁺ and CD8 ⁺ T cells. It has been reported that naive T cells are CD44^ ^0W CD62L^, while effective memory T cells are

CD44*“CD62LJ ^0W . We found that CD300f- Ig significantly increased the percentages of CD44^ ^0W CD62L^ naive cells in anti-CD3-activated CD4 ⁺ and CD8 ⁺ T cells, but decreased the percentages of CD44^CD62]J ^0W effector memory' T cells (data not shown).

Collectively, our results indicate that CD300f-Ig inhibits both TCR-mediated proliferation and activation of both CD4 and CDS T cells in vitro. Like CD300c, therapeutic interaction with the CD300f inhibitory pathway has the potential to be used in the treatment of GVHD and autoimmune disease, as well as cancer.