METHODS AND MATERIALS FOR THE INHIBITION OF TRANSPLANT REJECTION

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Application Serial No. 10/964,215 filed October 12, 2004, pending.

GOVERNMENT SUPPORT CLAUSE

This invention was made with government support under Contract AD 1231, awarded by the National Institutes of Health. The United States Government has certain rights in the invention.

BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION

The present invention is related to transplant rejection. In particular, this invention provides methods and compositions useful for inhibiting transplant rejection. 2. STATE OF THE ART

Current strategies for the treatment of graft rejection after transplantation typically involve the use of immunosuppressive agents such as cyclosporin A (CsA), rapamycin, FK506, corticosteriods, and antibodies to the interleukin (IL)-2 receptor. These drugs are typically taken over a long period of time, result in the global depletion of lymphocytes, and increase the risk of serious infection, nephrotoxicity, and cancer. Furthermore, some patients cannot tolerate doses of these immunosuppressive agents which are sufficient to inhibit transplant rejection.

What is needed are additional inhibitors of transplantation rejection, especially those that do not globally deplete lymphocytes from the individual receiving the inhibitor.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a method of inhibiting transplant rejection in a mammal in need thereof, comprising: administering a therapeutically effective

amount of an antibody to the mammal, wherein the antibody immunoreacts with an extracellular domain of a polypeptide referred to herein as "spleen expressed (SPEX) polypeptide". In certain embodiments, the present method further comprises administering one or more additional transplant rejection inhibitor(s) to the mammal. Examples of additional transplant inhibitors include: CsA, rapamycin, FK506, corticosteriods, and antibodies to the IL-2 receptor

One benefit of using the present anti-SPEX antibody in the inhibition of transplant rejection is that administration of the anti-SPEX antibody to mammals, including a transplant recipient, does not globally deplete lymphocytes in the mammal. Accordingly, one embodiment of the present invention provides a method of inhibiting transplant rej ection in a mammal in need thereof, comprising: administering a therapeutically effective amount of an antibody to the mammal, wherein the antibody immunoreacts with an extracellular domain of a SPEX polypeptide, and wherein the administration of the antibody does not significantly decrease a total CD4 ⁺ T cell count, a total CD8 T cell count, or a total B cell count in the mammal.

One embodiment of the present invention provides a method of decreasing an expression of a spleen expressed (SPEX) polypeptide on a lymphocyte that expresses the SPEX polypeptide, comprising contacting the lymphocyte with an anti-SPEX antibody that immunoreacts with an extracellular domain of a SPEX polypeptide, thereby decreasing the expression of the SPEX polypeptide on the lymphocyte.

One embodiment of the present invention provides a method of identifying an antibody that inhibits transplant rejection in a mammal in need thereof, comprising: providing an amino acid sequence comprising an epitope of an extracellular domain of a SPEX polypeptide, wherein said epitope is at least six amino acids in length; producing antibodies to said amino acid sequence; and screening said antibodies in a model of transplant rejection, thereby identifying said antibody that inhibits transplant rejection.

One embodiment of the present invention provides a method of inhibiting interleukin- 2 (IL-2) secretion by activated lymphocytes, wherein the lymphocytes express a SPEX polypeptide receptor (for example, SEQ ID NO:20 or SEQ ID NO:62), the method comprising contacting the lymphocytes with an antibody that immunoreacts with an extracellular domain of the SPEX polypeptide receptor (SPEX receptor engagement and activation).

One embodiment of the present invention provides a method of inhibiting an

interleukin-2 receptor (CD25) expression by an activated lymphocyte that expresses a spleen expressed polypeptide (SPEX polypeptide) receptor, comprising contacting the lymphocyte with an antibody that immunoreacts with an extracellular domain of the SPEX polypeptide receptor. One embodiment of the present invention provides a method of inhibiting a proliferation of an previously activated lymphocyte that expresses a SPEX polypeptide receptor, comprising contacting said lymphocyte with an antibody the immunoreacts with an extracellular domain of the SPEX polypeptide receptor.

LISTING OF THE FIGURES The drawings form a portion of the specification of the present invention.

FIG. 1 provides a diagram of substantially full-length mouse and human SPEX polypeptides (mSPEX and hSPEX, respectively) having extracellular, transmembrane (crosshatched), and intracellular domains (as labeled). The extracellular domains each include an immunoglobulin (Ig) like domain (horizontally hatched) and optionally have a cleavable signal sequence (dashed areas), wherein the arrows point to the cleavage site. The signal sequence is cleaved during post-translational processing to generate the mature SPEX polypeptide. The intracellular domains each include three tyrosine based motifs (vertically hatched). Each tyrosine based domain, in turn includes a tyrosine amino acid residue (Y, is the one-letter code for tyrosine). The embodiments shown depict that the tyrosine can be optionally phosphorylated (encircled P). The relative position of the SPEX polypeptides in a biological membrane is shown. The stippled areas indicate portions of each polypeptide between the certain functional domains.

FIG. 2 A provides a diagram showing embodiments of the correspondence between selected hSPEX polypeptides and the respective sequence identifier for each selected polypeptide.

FIG. 2B provides a diagram showing embodiments of the correspondence between selected hSPEX polynucleotides and the respective sequence identifier for each selected polynucleotide.

FIG. 2C provides a diagram showing certain embodiments of the correspondence between selected mSPEX polypeptides and the respective sequence identifier for each selected polypeptide.

FIG. 2D provides a diagram showing certain embodiments of the correspondence

between selected mSPEX polynucleotides and the respective sequence identifier for each selected polynucleotide.

FIG. 3 shows syngeneic and allogeneic skin grafts on a control mouse (left panel) at day 9 post transplantation and on a PJl 9.1 monoclonal antibody treated mouse (right panel) at day 13 post transplantation as described in Example 7. The control mouse was injected with PBS on days — 1, 1, 4, and 6 relative to transplantation of the skin grafts. The PJ19.1 monoclonal antibody treated mouse was injected i.p. (intraperitoneal) with 500 μg of the antibody on -1, 1, 4, and 6 relative to transplantation of the skin grafts. The PJl 9.1 monoclonal antibody immunoreacts with the extracellular domain of the mouse SPEX (mSPEX) polypeptide. The control mouse rejected the allogeneic graft by day 9, while maintaining the syngeneic graft. The PJl 9.1 treated mouse maintains both the syngeneic and the allogeneic skin grafts at day 13.

FIG. 4 shows skin graft survival curves for allogeneic skin grafts used as a model system for transplant rejection as described in Example 7. The control mice (square symbols) received syngeneic (data not shown) and allogeneic skin grafts on day 0 and received PBS injections on days — 1, 1, 4, and 6. The PJl 9.1 monoclonal antibody treated mice (diamond symbols) received syngeneic (data not shown) and allogeneic skin grafts on day 0 and received injections of 500 μg of PJ19.1 monoclonal antibody i.p. on days -1, 1, 4, and 6. The percentage of mice with surviving skin grafts is plotted against days post transplantation of the skin grafts. There are five mice in the control group and four mice in the PJl 9.1 antibody treated group.

FIG. 5 shows splenocyte cell counts from a control mouse (left panel) and a PJl 9.1 monoclonal antibody treated mouse (right panel) as described in Example 8. The splenocytes were three color stained for CD4, CD8, and SPEX and analyzed by flow cytometry. Dots representing one count each of CD4+T cells are in the upper left quadrant of each panel, representations of CD8+T cells are shown in the lower right quadrant of each panel, and representations of B cells (CD4 negative and CD 8 negative cells) are shown in the lower left quadrant of each panel. The numbers in each quadrant represent the percentage of each type of cells in the sample. Counts of the CD4+T cells, CD8+T cell, and B cell populations are not significantly increased or decreased in the PJ19.1 monoclonal antibody treated mouse compared to the control mouse.

FIG. 6A shows the effect of SPEX receptor engagement (contacting a SPEX receptor on a lymphocyte with an antibody that immunoreacts with an extracellular domain of the

SPEX receptor) on interleukin-2 (IL-2) secretion from lymphocytes. Supernatants of CD4+ and CD8+ T cells in culture were collected 16 hours after stimulation (activation) of the T cells by anti-CD3 in the presence of rat IgG or PKl 8 and were analyzed for IL-2 secretion (the amount of IL-2 in the supernatants). FIG. 6B shows the effects on the proliferation of T lymphocytes exposed to SPEX receptor engagement with (or without) 800 pg/ml and 80 pg/ml IL-2 supplementation in the cell culture. T cells were stimulated in the presence or absence of PKl 8 as in FIG. 6A with the addition in some cultures of the indicated concentrations of recombinant murine IL-2.

FIG. 6C shows the effects on the IL-2 receptor (CD25) expression on T cells that are treated with rat IgG, and anti-CD3 (gray filled histograms) or PKl 8 and anti-CD3 (bold lines) with the addition of recombinant murine IL-2 (800 pg/ml, high IL-2; 80 pg/ml, low IL-2). On day 2 of culture, cells were harvested and gated populations of CD4+ and CD8+ T cells were analyzed for expression of CD25 by flow cytometry. One representative experiment out of three is shown in the figure. FIG. 7 shows that SPEX receptor engagement with anti-SPEX antibody inhibits the expression of CD25 but not CD69 in lymphocytes. T cells were stimulated (activated) with anti-CD3 and rat IgG (gray filled histograms) or anti-CD3 and PKl 8 (bold lines). Shown is expression of CD69 or CD25 after 16 or 48 hours in culture, respectively, on gated populations of CD4+ or CD8+ T cells, Experiments were repeated three times. FIG. 8 shows that proliferation in pre-activated T cells can be blocked by a secondary •

SPEX signal (activation). CD4+ T cells isolated AND-TCR Tg mice were stimulated over night with a titration of anti-CD3 and transferred to a new plate coated with indicated concentrations of anti-CD3 and rat IgG (all at 10 μg/ml, closed circles) or anti-CD3 and PKl 8 (open circles). Controls were untransferred CD4+ T cells cultured in the presence of anti-CD3 and rat IgG (closed squares) or anti-CD3 and PKl 8 (open squares). Data were displayed as the mean [ ³ H] thymidine incorporation of triplicate cultures (+/-SD) minus cpm of T cells cultured alone (> 1,000 cpm). Experiments were repeated twice.

DETAILED DESCRIPTION OF THE INVENTION

The present inventor discovered, in part, that antibodies which immunoreact with an extracellular domain of a SPEX polypeptide are useful to inhibit transplant rejection and to decrease the expression of a SPEX polypeptide on lymphocytes. The present inventor further discovered, in part, a method of identifying antibodies that inhibit transplant rejection and

that decrease the expression of SPEX on lymphocytes.

1. DEFINITIONS

As used herein, the term "syngeneic" refers to genetically identical or closely related organisms, cells, tissues, organs, and the like. As used herein, a "syngeneic skin graft" refers to a skin graft wherein the host for the skin graft and the source of the skin graft are individuals that are genetically identical or sufficiently closely related such that the graft and the host do not interact antigeneically.

As used herein, the term "allogeneic" refers to organisms, cells, tissues, organs, and the like from, or derived from, individuals of the same species, but wherein the organisms, cells, tissues, organs, and the like are genetically different one from another.

As used herein, the term "xenograft" refers to a transplant in which the donor and recipient are of different species.

As used herein, an "allogeneic skin graft" refers to a skin graft wherein the host for the skin graft and the source of the skin graft are individuals of the same species that are sufficiently unlike genetically such that the graft and the host interact antigeneically. An allogeneic transplant is rejected in time in the absence of an intervention to inhibit transplant rejection.

As used herein, the term "transplant rejection" refers to a partial or complete destruction of a transplanted cell, tissue, organ, or the like on or in a recipient of said transplant.

As used herein, the term "host" refers to an organism (preferably the organism is a mammal), a tissue, organ, or the like that is the recipient of a transplanted cell, tissue, organ, or the like. The terms "host" and "recipient", when referring to transplant hosts or recipients are used interchangeably herein. As used herein, the term "globally depletes lymphocytes" refers to a decrease in the total counts of CD4+ T lymphocytes, CD8+ T lymphocytes, or B lymphocytes by 50% or more by administration of an immunosuppressive agent to a mammal compared to the corresponding lymphocyte counts in a control animal (which does not receive the immunosuppressive agent). The measurement of lymphocyte counts is typically carried out using blood, serum, or plasma samples. An immunosuppressive agent that does not "globally deplete lymphocytes" refers to an agent wherein administration of the agent to a mammal results in more than 50% of the total counts of CD4+ T lymphocytes, CD8+ T lymphocytes,

and B lymphocytes being maintained (preferably 80% or more, more preferably 90% or more, and still more preferably 100% being maintained).

As used herein, an "amount therapeutically effective to inhibit transplant rejection", in regard to an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide, refers to an amount of the antibody that when administered to a transplant recipient, that amount inhibits, either partially or completely, rejection of the transplant over time. The antibody (and, optionally, a second transplant rejection inhibitor) can be administered before, during, and/or after transplantation.

As used herein, a "soluble heterologous polypeptide" is a polypeptide that is different from a SPEX polypeptide in terms of sequence (it is a non-SPEX polypeptide) and is more soluble in aqueous solution than is an extracellular domain of a SPEX polypeptide.

As used herein, the terms "isolated" and "purified" are used interchangeably and mean that the particular compound of interest is separated from other contaminating substances so as to be free, or essentially free, from impurities including toxic matter such as endotoxin. The meaning of "purified" herein discounts solutes, excipients, stabilizers, buffers, salts, acids, acid salts, pharmaceutically acceptable carriers, and the like which are often desirable in combination with an active ingredient (e.g., a monoclonal antibody that immunoreacts with an extracellular domain of a SPEX polypeptide) and are not considered an impurity.

2. SPEX

The discovery of SPEX is described in U.S. Serial No. 10/831,622, filed April 23, 2004 and U.S. Serial No. 06/467,206, filed April 30, 2003; both applications are incorporated herein by reference. SPEX was described in a publication in Nature Immunology (2003, 4(7): 670-679), which is incorporated herein by reference. In the Nature Immunology paper, SPEX is referred to as B and T lymphocyte attenuator (BTLA).

SPEX mRNA and polypeptide is expressed by lymphocytes including B and T lymphocytes, naϊve B and T lymphocytes, thymocytes, activated B and T lymphocytes, splenic macrophages, antigen presenting cells (APCs) and mature bone marrow-derived dendritic cells (see, e.g., Han et al, (2004) Journal of Immunology 172:5931-5939, incorporated herein by reference). The SPEX polypeptide is a multiple domain protein which is observed to be expressed at the cellular membrane. SPEX polypeptide includes an extracellular domain, a single transmembrane domain which is contemplated to anchor the

polypeptide in the cellular membrane, and an intracellular domain. The SPEX polypeptide is a receptor for the B7x ligand (also known as B7-H4 and B7S1). The SPEX extracellular domain includes an immunoglobulin (Ig) like domain and the intracellular domain includes three tyrosine based signaling motifs. The tyrosine based signaling motifs are contemplated herein to be inhibitory signaling motifs which, for example, are contemplated to inhibit, or negatively modulate the activation of lymphocytes. SPEX is contemplated to be a type I receptor phosphoprotein of the immunoglobulin superfamily. A diagrammatic representation of mouse and human SPEX polypeptides is provided in FIG. 1.

Mice deficient in SPEX do not show apparent lymphocyte developmental defects; however, T cells from SPEX deficient mice are hyper responsive to anti-CD3 antibody stimulation of T cell activation. Based, in part, on this observation, SPEX is contemplated to be a negative regulator of lymphocyte activation, proliferation, and function.

3. INHIBITION OF TRANSPLANT REJECTION

The present inventor made the surprising discovery that an antibody which immunoreacts with an extracellular domain of a SPEX polypeptide inhibits transplant rejection in a murine model of transplant rejection. Accordingly, one embodiment of the present invention provides a method of inhibiting transplant rejection in a mammal in need thereof, comprising: administering a transplant rejection inhibiting amount of an antibody to the mammal, wherein the antibody immunoreacts with an extracellular domain of a SPEX polypeptide.

A. SPEX EXTRACELLULAR DOMAIN

As discussed above, the present invention provides that an antibody which immunoreacts with an extracellular domain of a SPEX polypeptide, inhibits transplant rejection. Accordingly, the present invention provides SPEX polypeptides useful, for example, in the manufacture of antibodies that inhibit transplant rejection and SPEX polynucleotides useful, for example, in the manufacture of said SPEX polypeptides. Any SPEX polypeptide is useful as an immunogen for the manufacture of an anti-SPEX antibody. Preferred SPEX polypeptides comprise (or, alternatively, consist essentially of) at least six consecutive amino acids of the extracellular domain of a SPEX polypeptide. A highly preferred SPEX polypeptide comprises (or, alternatively, consists essentially of) an Ig like domain of the SPEX protein (see, e.g., SEQ ID NO:3 (human), 45 (murine), or 88(murine,

allele b, see below)). The Ig like domain is highly preferred as the antigen for manufacturing anti-SPEX antibodies for use in the present invention.

Certain embodiments of the present invention provide a SPEX polypeptide of mouse, human (preferred), or other mammalian origin. Examples of polypeptide, and corresponding polynucleotide sequences, with sequence identifiers, of human SPEX (hSPEX) and mouse SPEX (mSPEX) are set forth diagrammatically in FIGs. 2A-D. An allele of a mSPEX is also disclosed and is referred to herein as mSPEXb (only the extracellular portion of mSPEXb has been sequenced). An example of the unprocessed extracellular domain of mSPEXb is set forth in SEQ ID NO:85 (includes the signal sequence). An example of the processed extracellular domain of mSPEXb is set forth in SEQ ID NO: 86 (without the signal sequence). The preferred Ig like domain of mSPEXb is set forth in SEQ ID NO:88.

As used herein, a highly preferred extracellular domain of a SPEX polypeptide comprises (alternatively, consists essentially of): SEQ ID NO:1, 2, 3, 4, 12, or 13 (from hSPEX). A preferred extracellular domain of a SPEX polypeptide comprises (alternatively, consists essentially of): SEQ ID NO:43, 44, 45, 46, 54 or 55 (from mSPEX) or SEQ ID

NO:85, 86, or 86 (from mSPEXb). A still more highly preferred SPEX polypeptide comprises (alternatively, consists essentially of) the Ig like domain of human SPEX as set forth in SEQ ID N0:3.

In general, a polypeptide including six or more consecutive amino acid residues is capable of eliciting an immune response. Thus, certain embodiments provide an amino acid sequence comprising (or consisting essentially of) six consecutive amino acids of a SPEX extracellular domain (e.g., SEQ ID NO:13, 55, or 85). Typically, increasing the number of consecutive amino acid residues in the SPEX polypeptide enhances the immunogenic response to the peptide. Thus, certain embodiments provide, in increasing order of preference, a SPEX immunogen comprising 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40 or more consecutive amino acids of an extracellular domain of a SPEX polypeptide. Optionally, the SPEX immunogen comprises 6 to 9, 10 to 19, 20 to 29, 30 to 39, or 40 to 50 consecutive amino acids of the SPEX polypeptide. One embodiment of the present invention provides a "SPEX fusion polypeptide" comprising an extracellular domain of a SPEX polypeptide operably linked with a soluble heterologous polypeptide. A preferred soluble heterologous polypeptide comprises a constant region of human IgGl, more preferably the human IgGl hinge CH2, and CH3 domains. In

one embodiment, a solubility promoting heterologous polypeptide comprises SEQ ID NO:97. Another embodiment provides a polypeptide comprising a SPEX polypeptide set forth in SEQ ID NO:3, SEQ ID NC-.45, SEQ ID NO:88, SEQ ID NO: 12, SEQ ID NO:54, or SEQ ID NO: 86 operatively linked to a heterologous polypeptide including a constant region of human IgGl ; preferably the human IgGl hinge, CH2, and CH3 domains. Protein A binds the constant region of IgGl with high affinity. Accordingly, a SPEX-human IgGl fusion can be purified using protein A affinity chromatography.

I. MANUFACTURE OF A SPEX POLYPEPTIDE

In light of the present disclosure, a SPEX polypeptide of this invention can be made using a variety of techniques well known in the art for making a polypeptide. For example, a SPEX polypeptide can be manufactured by purification from natural sources (e.g., lymphocytes or spleen or thymus tissue). In another example, a SPEX polypeptide can be manufactured through expression of a polynucleotide encoding the SPEX polypeptide in a host cell including in bacterial (e.g., K12), eukaryotic, yeast, insect, plant, mammalian, Chinese hamster (e.g., CHO), murine, and human cells (e.g., using transfer of a recombinant SPEX expression system). See FIGs 2B and 2D for examples of sequence identifiers of useful SPEX polynucleotides. In still another example, a SPEX polypeptide is manufactured using synthetic de novo methods. See FIGs 2A and 2C (and SEQ ID NO:85-88) for examples of sequence identifiers of SPEX polypeptides (preferably an extracellular domain thereof) useful herein.

In preferred embodiments, the SPEX polypeptide is purified using methods known in the art for protein separation and purification. For example, in light of the present invention, one of ordinary skill in the art is able to use an anti-SPEX antibody disclosed herein to isolate or purify a SPEX polypeptide including specific fragments and domains thereof through affinity separation. Regarding the SPEX fusion polypeptide discussed above, protein A binds the constant region of IgGl with high affinity. Accordingly, a SPEX-human IgGl fusion can be purified using protein A affinity chromatography. The fusion polypeptide is preferably made using recombinant DNA techniques, polypeptide expression, and purification techniques that are well known in the art. A preferred "operable linkage" comprises a peptide bond. Alternatively, the soluble heterologous polypeptide can be operatively linked to the extracellular domain of the SPEX polypeptide using chemical crosslinking agents, compositions of which and use thereof are well known in the art.

Examples of useful amino acids residues (and nucleotide residues) for the manufacture of a SPEX polypeptide are provided in the World Intellectual Property Organization (WIPO) Handbook on Industrial Property Information and Documentation, Standard ST.25: Standard for the Presentation of Nucleotide and Amino Acid Sequence Listings in Patent Applications (1998), including Tables 1 through 6 in Appendix 2; hereinafter referred to as "WIPO Standard ST.25 of 1998", incorporated herein by reference.

B. ANTIBODIES THAT IMMUNOREACT WITH AN EXTRACELLULAR

DOMAIN OF A SPEX POLYPEPTIDE

One embodiment of the present invention provides an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide. The present antibodies are useful, for example, to decrease lymphocyte SPEX expression and to inhibit transplant rejection. The term "antibody" is meant to include any form of antibody, including intact antibodies molecules and/or an immunologically active portion or fragment of an antibody molecule. Antibodies and active fragments thereof are well known in the art, for example: IgG, IgM, IgE, polyclonal, monoclonal, Fab, Fab', F(ab') ₂ , F(v), single chain antibody (SCA), single chain Fab, humanized, hybrid, and the like antibodies). It is preferred that the antibody is isolated. It is also preferred that the antibody comprises a recombinant, chimeric, or otherwise non-naturally occurring antibody. In certain embodiments it is preferred that the antibody is multivalent (comprises two or more epitope binding sites), for example, a bivalent antibody. A preferred antibody is an anti-SPEX monoclonal antibody, preferably a human or humanized anti-SPEX monoclonal antibody, which immunoreacts with an extracellular domain of the SPEX polypeptide.

I. ANTIBODY MANUFACTURE

Methods of manufacturing an antibody given a specific antigen are well known in the art. The present invention provides SPEX antigens (i.e., immunogen) useful for manufacture of anti-SPEX antibodies that immunoreact with an extracellular domain of a SPEX polypeptide. Thus, in light of the present disclosure, one of ordinary skill in the art is able to manufacture an anti-SPEX antibody useful in the present invention. Antibodies are commonly manufactured, for example: in animals (e.g., rabbit, mouse, hamster, sheep, goat, horse, bovine); in cells, primarily cell culture, (e.g., bacteria, plant, algae, insect, mammalian, murine, hybridoma, and human cells); by phage display; and by epitope cloning into antibody scaffold vectors and gene transfer into any of a variety of cell types (e.g., bacteria, plant,

algae, insect, mammalian, murine, and human).

4. PHARMACEUTICAL COMPOSITIONS

One embodiment of the present invention provides a "SPEX pharmaceutical composition" comprising an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide, wherein the antibody is capable of inhibiting transplant rejection, and wherein the antibody is in an amount therapeutically effective to inhibit transplant rejection. A preferred antibody that immunoreacts with the extracellular domain of a SPEX polypeptide and is capable of inhibiting transplant rejection is PJ19.1 which immunoreacts with the extracellular domain of mSPEX polypeptide (e.g., SEQ ID NO:55). Preferred SPEX pharmaceutical compositions are prepared to minimize contaminants.

Preferred SPEX pharmaceutical compositions are also prepared to minimize allergic and toxic reactions in a recipient to which the compositions are administered. In one embodiment, it is preferred that the SPEX pharmaceutical composition is pyrogen (e.g., endotoxin) free, or essentially pyrogen free. In preferred embodiments, a SPEX pharmaceutical composition further comprises a second transplant rejection inhibitor (meaning one or more transplant rejection inhibitors) in addition to the anti-SPEX antibody). Preferred second transplant rejection inhibitors include, but are not limited to: CsA, rapamycin, FK506, corticosteriods, and antibodies that immunoreact with the IL-2 receptor.

A. PREPARATION OF A PHARMACEUTICAL COMPOSITION

In light of the present invention, a SPEX pharmaceutical composition (comprising an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide) may be manufactured in any manner that is known in the art (including, e.g., by conventional mixing, dissolving, granulating, dragee-making, emulsifying, encapsulating, entrapping, lyophilizing, or suspending processes). It is preferred that manufacture is according to Good

Manufacturing Practice, the procedures and regulations of which are known in the art.

In certain embodiments, the SPEX pharmaceutical composition is manufactured to further include a pharmaceutically acceptable carrier, excipient, auxiliary, preservative, or other ingredient (referred to collectively herein as a "pharmaceutically acceptable carrier"). The term "carrier" refers herein to a "pharmaceutically acceptable carrier". Preferably, a pharmaceutically acceptable carrier is suitable for administration to a human or a non-human

mamma . Further details on techniques for formulation and administration of pharmaceutical compositions may be found in the latest edition of Remington's Pharmaceutical Sciences (Maack Publishing Co., Easton, PA).

Fluid carriers may include aqueous solutions, preferably in physiologically compatible buffers (e.g., Hanks' solution, Ringer's solution, or physiologically buffered saline). Fluid carriers also include non-aqueous and oily suspensions. Suitable lipophilic solvents or vehicles may include fatty oils (e.g., sesame oil, synthetic fatty acid esters, ethyl oleate, triglycerides, or liposomes). Useful liposomes include cationic liposomes, anionic liposomes, and liposomes with neutral charge density. Viscosity enhancing agents may be included (e.g., sodium carboxymethyl cellulose, sorbitol, or dextran). Stabilizers, adhesives, or agents which increase solubility may also be included. Additional inert ingredients may include any or all of gum arabic, syrup, lanolin, or starch. Another excipient which may be used is polyethylene glycol (PEG). PEG can be admixed with the formulation or linked to the anti-SPEX antibody molecule itself. PEG may be useful, for example, as a dehydrating or concentrating agent. Accordingly, carriers may be aqueous, non-aqueous (hydrophobic), or amphophilic. Delayed release and/or sustained release carriers, and the pharmaceutical formulations thereof, are known in the art and can be used in embodiments herein, in light of the present disclosure.

The SPEX pharmaceutical composition may be provided as a salt and can be formed with an acid (e.g., hydrochloric, sulfuric, acetic, lactic, tartaric, malic, succinic, and the like). In other embodiments, the SPEX pharmaceutical composition may be a lyophilized powder which is preferably combined with buffer prior to use.

B. ADMINISTERING A PHARMACEUTICAL COMPOSITION

In certain embodiments of the present invention, a SPEX pharmaceutical composition (comprising an antibody that immunoreacts with a SPEX extracellular domain) is administered to a patient in need of treatment for transplant rejection. The pharmaceutical compositions encompassed by this invention may be administered by any desirable route including, but not limited to, oral, intravenous, intramuscular, nasal, intratracheal, intra¬ articular, intra-arterial, intramedullary, intrathecal, intraventricular, transdermal, subcutaneous, intraperitoneal, intranasal, intraturnoral, enteral., topical, sublingual, vaginal, or rectal routes of administration. In light of the present invention, one of ordinary skill in the art is able to select a suitable route for administering a SPEX pharmaceutical composition to

a patient.

Factors considered for the route of administration may include the location of the transplant and the condition of the patient. Also, in light of the present invention, one of ordinary skill in the art is able to select suitable SPEX pharmaceutical compositions which are desirable for a particular route of administration including formulations with carriers, excipients, auxiliaries, inert ingredients, and the like.

Methods of administering include, but are not limited to injection, infusion, administration by catheter, microinjection, particle mediated (biolistic) transfer, intubation, inhalation, ingestion, diffusion from a matrix, and the like. In one example, the SPEX pharmaceutical composition may be administered by injecting the composition into the afferent blood supply of a transplanted organ or tissue. A preferred method of administering a SPEX pharmaceutical composition comprises intraperitoneal injection.

C . DOSAGE OF A PHARMACEUTICAL COMPOSITION

Pharmaceutical compositions suitable for use in the invention include an antibody that . immunoreacts with an extracellular domain of a SPEX polypeptide in an effective amount, or dose, to achieve an embodied purpose (e.g., in treating a patient having or in need of a transplant). In light of the present invention and knowledge in the art, the determination of an effective dose is well within the capability of those skilled in the art.

A therapeutically effective dose or range can be estimated initially either in cell culture assays or in animal models; usually in mice, rats, rabbits, dogs, pigs, or non-human primates. The animal model may also be used to determine the preferred concentration range and route of administration. Such information can then be used to select preferred doses and routes for administration in humans. A preferred animal model comprising murine skin grafting is discussed below. Therapeutic efficacy and toxicity may be determined by standard pharmaceutical procedures in cell cultures, experimental animals, or other transplant model systems. For example, the ED50 (the dose therapeutically effective in 50% of the population) and the LD50 (the dose lethal to 50% of the population) can be determined in a model system. The dose ratio between toxic and therapeutic effects is the therapeutic index, which may be expressed as the ratio, LD50/ED50. SPEX pharmaceutical compositions which exhibit large therapeutic indices are preferred. The SPEX pharmaceutical composition optionally includes the use of a second transplant rejection inhibitor to enhance or increase the therapeutic index.

The data obtained from the model system(s) is used in formulating a range of dosage for human use. The dosage contained in such compositions is preferably within a range of circulating concentrations that include the ED50 with low toxicity or, more preferably, essentially no toxicity. In one embodiment, the SPEX pharmaceutical composition includes a dose of an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide that includes a therapeutically effective ED50. It is more preferred that the present SPEX pharmaceutical composition includes a toxicity or LD50 that is acceptable for administering the SPEX pharmaceutical composition to a patient (a human or, optionally, a non-human mammal) after taking into account the relative condition of the patient and the need that the patient has for treatment with a transplant rejection inhibitor. Accordingly, the dosage of the SPEX pharmaceutical composition that is used in a patient is preferably determined by the practitioner, in light of factors related to the patient that requires treatment.

Dosage and administration are adjusted to provide sufficient levels of the active moiety(ies) (e.g., circulating and/or local concentration) or to maintain the desired effect. Factors which may be taken into account include the severity of the disease state, general health of the subject, age, weight, gender, diet, time and frequency of administration, drug combination(s), reaction sensitivities, tolerance to therapy, and response to therapy. In general, SPEX pharmaceutical compositions may be administered, for example; once a day, every other day, every 3 to 4 days, every week, once every two weeks, once a month, once every several months, or yearly.

Dosage amounts include, for example, from O.lmg/kg to 20 mg/kg per dose, preferably from 2.5 mg/kg to 20 mg/kg per dose, of an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide.

5. DECREASING LYMPHOCYTE EXPRESSION OF SPEX POLYPEPTIDE One embodiment of the present invention provides a method of decreasing an expression of a SPEX polypeptide on a lymphocyte which expresses the SPEX polypeptide, comprising contacting the lymphocyte with an antibody that immunoreacts with an extracellular domain of the SPEX polypeptide, thereby leading to a down regulation of the SPEX polypeptide on the surface of the lymphocyte. Preferred lymphocytes include, but are not limited to CD4+ T cells, CD8+ T cells, and B cells. A preferred antibody is a monoclonal antibody. It is also preferred that the present antibody is a human or a humanized antibody. The present antibody immunoreacts

with the extracellular domain of the SPEX polypeptide (the antibody is particularly preferred to immunoreact with the Ig like domain), and, optionally, the antibody does not immunoreact with an intracellular domain and/or an intracellular domain of the SPEX polypeptide. In certain embodiments the present antibody immunoreacts with SEQ ID NOs:3, 12, 13, 45, 54, 55, 85, 86, or 88 and, optionally, does not immunoreact with SEQ ID NOs: 17, 18, 59, or 60.

6. IDENTIFYING ANTIBODIES THAT INHIBIT TRANSPLANT REJECTION

One embodiment of the present invention provides a method of identifying an antibody that inhibits transplant rejection in a mammal, comprising: providing an amino acid sequence comprising an epitope of an extracellular domain of a SPEX polypeptide, wherein the epitope is at least six amino acids in length; producing antibodies to the amino acid sequence; and screening the antibodies in a model of transplant rejection to identify antibodies that inhibit transplant rejection.

A. MAMMALIAN MODEL SYSTEM OF TRANSPLANT REJECTION

Techniques are well known to one of ordinary skill in the art for the transplantation of numerous cell, tissue, and organ types including, but not limited to: pancreatic islet transplantation, corneal transplantation, bone marrow transplantation, stem cell transplantation, skin graft transplantation, skeletal muscle transplantation, aortic and aortic valve transplantation, and vascularized organ transplantation including, but not limited to: heart, lung, heart and lung, kidney, liver, pancreas, and small bowel transplantation (see, e.g., Experimental Transplantation Models in Small Animals (1995) Publisher T&F STM, 494 pages). The present invention is not limited by the particular variety of transplantation. In general, transplantation between a non-syngeneic donor and recipient, in the absence of a transplant rejection inhibitor results in transplant rejection characterized by the partial or complete, typically progressive, destruction of the transplanted cells, tissue, or organ(s). Accordingly, any non-syngeneic (e.g., allogeneic or xenogeneic) transplantation is useful herein as a model system of transplant rejection. A preferred model system of transplant rejection inhibition comprises a murine allogeneic skin graft.

In one embodiment, non-syngeneic transplants are performed on two groups of mammals, wherein a first group is not treated (the control group) with a transplant rejection inhibitor and a second group is treated with a SPEX pharmaceutical composition comprising an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide. The

progress of the transplants are monitored over time for the percentage of transplant rejection (destruction of the transplant). The anti-SPEX antibody is capable of inhibiting transplant rejection, for example, if the percentage of transplant rejection is reduced or eliminated for a given time period or if the transplant survives for a longer period of time for a given amount of transplant rejection in the treated versus group the non-treated controls.

In another embodiment, an antibody that imniunoreacts with an extracellular domain of the SPEX polypeptide and a second transplantation rejection inhibitor is administered to a first group of mammals and the second transplantation rejection inhibitor is administered to a second group of mammals (the second inhibitor is not an anti-SPEX antibody). The present embodiment allows, for example, for the detection of a synergistic effect of the anti-SPEX antibody and the second inhibitor in the inhibition of transplant rejection.

7. INHIBITING LYMPHOCYTE INTERLEUKIN-2 SECRETION

It is a discovery of the present invention that an antibody that immunoreacts with the extracellular domain of a SPEX receptor on an activated lymphocyte inhibits interleukin-2 (IL-2) secretion by the activated lymphocyte (see, e.g., Example 11 and Figure 6A).

Lymphocytes can be activated, for example, by contacting the lymphocytes with an antibody to CD3 (αCD3). Accordingly, one embodiment of the present invention provides a method of inhibiting IL-2 secretion by activated lymphocytes, wherein the lymphocytes express a SPEX polypeptide receptor (for example, SEQ ID NO:20 or SEQ ID NO: 62), the method comprising contacting the lymphocytes with an antibody that immunoreacts with an extracellular domain of the SPEX polypeptide receptor (SPEX receptor engagement). Preferably, the antibody comprises an agonist of the SPEX receptor on the lymphocyte and, therefore, stimulates the activation of the SPEX receptor. The SPEX receptor preferably comprises a negative regulator of lymphocyte proliferation and IL-2 secretion; thus, providing a mechanism of action for the inhibition or the IL-2 secretion by the activated lymphocytes.

A preferred antibody comprises a monoclonal antibody or a binding (active) fragment thereof. Preferably, the antibody does not immunoreacts with an intracellular domain of the SPEX polypeptide. In one embodiment, the antibody immunoreacts with an Ig like domain of the SPEX polypeptide (for example, SEQ ID NO:3, SEQ ID NO:45, or SEQ ID NO:88) and, more preferably, does not immunoreacts with an intracellular domain of the SPEX polypeptide. In one embodiment, the antibody immunoreacts a sequence selected from SEQ

ID NOs:3, 12, 13, 45, 54, 55, 85, 86, or, 88. In one embodiment, the antibody does not immunoreacts with a sequence selected from SEQ ID NO:sl7, 18, 59, or 60. hi one embodiment, the antibody immunoreacts with a sequence selected from SEQ ID NOs:3, 12, 13, 45, 54, 55, 85, 86, or, 88; but does not immunoreacts with a sequence selected from SEQ ID NO:sl7, 18, 59, or 60. In one embodiment, the lymphocyte comprises one of a T cell, a CD4+ T cell, or a CD8+ T cell.

It is also an embodiment of the present invention that the proliferation normally observed in activated T cells was not fully restored after contacting the T cells with an antibody that immunoreacts with the extracellular domain of the SPEX receptor (thereby inhibiting IL-2 secretion by the lymphocytes) and by adding IL-2 back to the T cells (see, e.g., Example 11 and Figure 6B).

8. INHIBITING LYMPHOCYTE INTERLEUKIN-2 RECEPTOR EXPRESSION

It is a discovery of the present invention that an antibody that immunoreacts with the extracellular domain of a SPEX polypeptide receptor on an activated lymphocyte inhibits interleukin-2 (IL-2) receptor (CD25) expression by the activated lymphocyte (see, e.g., Example 11 and Figure 6C). Accordingly, the one embodiment of the present invention provides a method of inhibiting an interleukin-2 receptor (CD25) expression by an activated lymphocyte that expresses a spleen expressed polypeptide (SPEX polypeptide) receptor, comprising contacting the lymphocyte with an antibody that immunoreacts with an extracellular domain of the SPEX polypeptide receptor. It is preferred that the antibody activates the SPEX polypeptide receptor. Preferred antibodies, SPEX polypeptides, and lymphocytes are described in section number 7 above.

9. INHIBITING PROLIFERATION OF ALREADY ACTIVATED LYMPHOCYTES

It is a discovery of the present invention that contacting a lymphocyte with an antibody that immunoreacts with an extracellular domain of a SPEX polypeptide inhibits proliferation of the lymphocyte even if the lymphocyte was activated for proliferation before being contacted with the anti-SPEX antibody (see, e.g., Example 11 and Figure 8). Accordingly, one embodiment of the present invention provides a method of inhibiting a proliferation of an activated lymphocyte that expresses a SPEX polypeptide receptor, comprising contacting said lymphocyte with an antibody the immunoreacts with an extracellular domain of said SPEX polypeptide receptor. It is preferred that the antibody

activates the SPEX polypeptide receptor. Preferred antibodies, SPEX polypeptides, and lymphocytes are described in section number 7 above.

The following examples are intended to illustrate, but not limit, the invention.

EXAMPLES

1. IDENTIFICATION AND CLONING OF mSPEX

Positive selection is a developmental process in which immature thymocytes receive maturation signals as a consequence of T cell antigen receptor (TCR) recognition of MHC/self-peptide complexes expressed by thymic stroma. Exposure of immature thymocytes to low concentrations of the pharmacologic activators phorbol ester (e.g., PMA) and/or ionomycin induces the survival and differentiation of double positive (DP) thymocytes in vitro and provides an accepted model system of positive selection of thymocytes in vivo.

Using nucleic acid microarrays, the inventors identified changes in nucleic acid expression during positive selection of thymocytes relative to unstimulated thymocytes. TCRα-chain deficient thymocytes (murine) were cultured in medium in the presence or absence of 0.2 ng/ml PMA and 0.2 mg/ml ionomycin providing activated and non-activated thymocytes respectively. TCRα-chain deficient thymocytes are blocked at the DP stage of development due to a genetic mutation. Gene expression in these cells, after stimulation, is characteristic of developing thymocytes. After incubating the cells for 6 hours, the poly-A+ RNA was isolated using RNeasy RNA and Oligotex mRNA kits (Qiagen). The poly-A+ RNA was subjected to comparative cDNA array analysis using the Mouse 1.02 Array per manufacturer's instructions (Incyte Genomics). Signal analysis of the microarrays was performed using GEMTools analysis software (Incyte Genomics).

The inventors selected two sequences for further study based upon the ratio of expression of the sequences in the stimulated thymocytes over the unstimulated thymocytes. The ratio of expression was determined from the normalized signals of hybridization of each labeled cDNA to the ESTs AA184189 and AA177302, respectively, which ESTs were included on the Mouse Array. The expression of each sequence in the stimulated thymocytes was increased 9.1 fold and 6.6 fold for sequences hybridizing to EST AAl 84189 and EST AA177302, respectively. These ESTs on the Mouse 1.02 Array originated from a murine library called the Soares mouse 3NbMS library which in turn was derived from spleens of 4 week old C57BL/6J mice.

The inventors determined that the ESTs AAl 84189 and AA177302 are linked using

BLAST software (NCBI) to compare the sequences of the ESTs with a database of murine nucleic acid sequences (each EST corresponds to a common sequence in the murine sequence database). Thus, ESTs AA184189 and AA177302 are determined to be part of a more complete nucleic acid. Using the 5'-most EST (AA177302), the inventors cloned a full-length gene by rapid amplification of cDNA ends (SMART RACE cDNA amplification kit,

Clontech) using cDNA prepared from stimulated thymocytes as a template in the reaction. The present gene is designated herein as the mouse spjeen expressed gene (mSPEX gene). An exemplary mSPEX nucleic acid is set forth in SEQ ID NO: 105 and includes a coding region set forth in SEQ ID NO.84. A BLAST search of GenBank reveals that the SPEX cDNA encodes a novel protein. An exemplary mSPEX polypeptide encoded by an mSPEX nucleic acid is set forth in SEQ ID NO:63. A signal sequence (e.g., SEQ ID NO:43) is typically cleaved during cellular processing to form an exemplary mature mSPEX polypeptide set forth in SEQ ID NO:62. Using sequence comparison between the mSPEX polypeptide and the Pfam family of proteins database (NCBI), the inventors identified an immunoglobulin like domain in a predicted extracellular portion of the polypeptide; however, the inventors observed that SPEX lacks close homology to any particular immunoglobulin containing superfamily member.

2. IDENTIFICATION AND CLONING OF A hSPEX cDNA

Using sequence comparisons of the mSPEX sequence to human sequences in the GenBank database the inventors determine that the human ESTs AI792952 and AA931122 align with the mSPEX polynucleotide and that the human ESTs correspond to a single human clone in the GenBank database. A bacterial stab (AI792952) containing the human clone, as well as numerous contaminating clones, was purchased from the IMAGE Consortium (Lawrence Livermore National Laboratory, Livermore, CA). A human gene sequence homologous to mSPEX is purified from the stab, subcloned, and sequenced. An exemplary hSPEX nucleic acid sequence is set forth in SEQ ID NO: 104 and includes a coding region set forth in SEQ ID NO:42. An exemplary hSPEX polypeptide encoded by an hSPEX nucleic acid sequence is set forth in SEQ ID NO:21. A signal sequence (e.g., SEQ ID NO:1) is typically cleaved during cellular processing of hSPEX protein to form an exemplary mature hSPEX polypeptide set forth in SEQ ID NO:20.

3. MANUFACTURE OF RAT ANTI-mSPEX MONOCLONAL ANTIBODIES

An isolated expression vector, referred to herein as p-mSPEX-Ig, was manufactured

comprising a coding region encoding a mSPEX extracellular domain and the hinge, CH2, and CH3 domains of human IgGl. The p-mSPEX-Ig vector is transfected into 293 cells in culture. The p-mSPEX-Ig transfected 293 cells express and secrete the mSPEX-Ig fusion protein (SEQ ID NO:99) as assessed by a Western blot probed with ani-humanlgGl antibody. The mSPEX-Ig fusion protein is purified by protein A affinity chromatography from supernatants of transfected 293 cells.

Rats are immunized in the base of the tail with the purified recombinant mSPEX-Ig emulsified in CFA to produce monoclonal antibodies. Procedures and techniques for the production of antibodies, including monoclonal antibodies, to a given antigen are well known in the art. The medial iliac lymph nodes are harvested two weeks later and fused with YB2/0 cells by standard methods. Antibodies thus produced are screened for immunoreactivity with mSPEX by FACS using DPK and 293 cells that are transfected to express a cell surface mSPEX-YFP fusion protein (YFP is an abbreviation for yellow fluorescent protein). The DPK and 293 cells used for the screening procedure are transfected with an isolated expression vector construct made from cloning a mSPEX gene insert into the pE YEP-Nl vector (Clontech). The pEYEP-Nl vector supplies an YFP tag and expression of a mSPEX insert from pEYEP-Nl results in the expression of a fusion protein including a mSPEX polypeptide operably linked with a YFP tag.

Screening continues until one or more monoclonal antibody that specifically immunoreacts with the extracellular domain of mSPEX is identified in the screening process. The YFP tag allows verification that transfected cells express the mSPEX-YFP fusion protein at the cell surface and allows the correlation of the relative level of cellular antibody binding to mSPEX-YFP fusion protein expression. Three hybridomas: PK3, PKl 8, and PK23 are obtained from a first screening process. The hybridomas are optionally re-cloned and antibody is purified using standard methods.

4. MANUFACTURE OF RAT ANTI-hSPEX MONOCLONAL ANTIBODIES

A monoclonal antibody that immunoreacts with the extracellular domain of a hSPEX polypeptide is prepared using the methods disclosed in Example 3, except that 1) a p-hSPEX- Ig expression vector comprising a hSPEX extracellular domain (including the SPEX signal sequence) and the hinge, CH2, and CH3 domains of human IgGl is prepared and used to produce monoclonal antibodies in rats and 2) a hSPEX polynucleotide encoding the extracellular domain of a hSPEX polypeptide is cloned into a pE YEP-Nl vector and

expressed in DPK and 293 cells to screen for monoclonal antibodies using the FACS-YFP procedure disclosed above. The monoclonal antibodies produced specifically immunoreact with the extracellular domain of hSPEX.

5. MANUFACTURE OF MOUSE ANTI-mSPEX MONOCLONAL ANTIBODIES Because there are multiple alleles known for murine SPEX (mSPEX and mSPEXb) it is possible to raise mouse anti-mouse SPEX antibodies in a mouse host without encountering self-tolerance. To raise a mouse monoclonal antibody against mSPEX, the procedures for Example 3 were followed except that the murine SPEX gene for the p-mSPEX-Ig fusion is derived from C57BL6 mice (which have the mSPEX allele) and immunizations are performed in BALB/c mice (which have the mSPEXb allele). Many anti-mSPEX antibodies with immunoreact with the extracellular domain of mSPEX were produced in a first screening process including, but not limited to: PJ19.1 and PJ196.

6. MANUFACTURE OF MOUSE ANTI-hSPEX MONOCLONAL ANTIBODIES

To raise monoclonal antibodies that immunoreact with an extracellular domain of hSPEX, the procedures of Example 4 are followed except that mice, instead of rats, are immunized with a hSPEX-Ig fusion polypeptide (SEQ ID NO:98). The monoclonal antibodies produced specifically immunoreact with the extracellular domain of hSPEX.

7. INHIBITING GRAFT REJECTION

It is determined that administering an antibody that immunoreacts with the extracellular domain of a SPEX polypeptide inhibits graft rejection. B6 mice (having the mSPEX allele, but not the mSPEXb allele) are injected intraperitoneally with 500 μg of the monoclonal antibody PJ19.1 (which immunoreacts with the extracellular domain of mSPEX, but not mSPEXb) on days -1, 1, 4, and 6 (relative to receiving a skin graft). Age and sex- matched control mice groups received injections of physiologically buffered saline (PBS) or (in parallel experiments) mouse IgG. Individual mice received syngeneic B6 and allogeneic BALB/c skin grafts on day 0. This particular strain combination of skin grafts is highly resistant to the induction of transplantation tolerance; thus, the induction of transplantation tolerance (i.e., the inhibition of transplantation rejection) by a transplantation inhibitor in this system is highly significant. Of note, the PJl 9.1 antibody immunoreacts with the extracellular domain of mSPEX in the B6 transplant recipients, but not the mSPEXb in the allogeneic skin grafts from the BALB/c donors.

Graft rejection as a percentage of the total graft (percentage of graft surface area) was monitored from day 7 through day 16 with photographs taken daily. The day of graft rejection was determined as the day of 90% or more of tissue destruction. As shown in FIG. 3, no rejection of the syngeneic skin grafts was observed during the course of the experiment (sixteen days total). Also as shown in FIG. 3, the allograft (allogeneic skin graft) was rejected in a control mouse (PBS injection) shown at day nine, but rejection of the allograft was inhibited in a mouse treated with the PJl 9.1 monoclonal antibody as described above and shown at day 13.

FIG 4 provides a plot of the percentage of mice in experimental and control groups (see below) with surviving grafts versus the number of days for two groups of mice. A first group of five mice were administered PBS (the control group) at days -1, 1, 4, and 6 relative to each mouse receiving a syngeneic and an allogeneic skin graft, as described above. A second group of four mice were each administered 500 μg of the monoclonal antibody PJl 9.1 (the experimental group) at days -1, 1, 4, and 6 relative to each mouse receiving a syngeneic and an allogeneic skin graft. Photographs of the skin grafts were taken daily until the last graft was rejected. The number of animals with surviving allogeneic skin graphs was recorded on a percentage basis and plotted against days post skin graft. As shown in FIG 4, the median time for rejection (90% or more destruction) of the allogeneic grafts in the control PBS treated mice was day 10 (median), while the median time of rejection of the allogeneic grafts was inhibited in the PJl 9.1 treated mice until day 13.5 (median) which is seven days after the last injection of antibody). Survival fractions were determined using the Kaplan- Meier method. Comparison of survival curves was performed using the logrank test provided by PRISM4 software (statistical software). Median survival is also calculated using the PRISM4 software. The difference between the control and the PJl 9.1 treated mice in terms of median time to rejection is highly significant with a p value of 0.0051. It is contemplated that continuing the treatment with the PJl 9.1 monoclonal antibody beyond day 6 post transplantation (e.g., every day or every other day administration) could result in a continued inhibition of allograft rejection.

8. ANTI-SPEX ANTIBODY DOES NOT GLOBALLY DEPLETE LYMPHOCYTES Example 7 is repeated except that the PBS and PJl 9.1 treated mice are sacrificed 15 days after skin grafting (9 days after the last injection of antibody) and the spleen cells are analyzed for total B, CD4+T and CD8+T cell counts in each group of animals. As shown in

FIG. 5, the frequency and number (data not shown) of CD4+T, CD8+T, and B cells is similar in the control (PBS) and PJl 9.1 antibody treated mice. Accordingly, administration of an antibody that imrnunoreacts with the extracellular domain of a SPEX polypeptide does not globally deplete lymphocyte populations of CD4+T, CD8+T, or B cells.

9. ANTI-SPEX ANTIBODY DOWN-REGULATES LYMPHOCYTE SPEX EXPRESSION

Samples of B, CD4+T, and CD8+T cells from Example 8 (the samples are collected separately from control mice and from PJ19.1 treated mice) above are stained in vitro with PJl 96 (which immunoreacts with the extracellular domain of SPEX) and secondary antibody (with immunoreacts with both PJ19.1 and PJ196 monoclonal antibodies). It is observed, data not shown: 1) that there is no global depletion of B, CD4+T, and CD8+T cells in the PJ19.1 treated mice, 2) that B, CD4+T, and CD8+T cells are coated in vivo with the PJl 9.1 antibody in mice that were treated with PJl 9.1, and 3) that the total cell surface expression of SPEX is decreased on the B, CD4+T, and CD8+T cells in the PJl 9.1 treated mice as compared to the PBS or IgG treated mice. Accordingly, administering a monoclonal antibody that immunoreacts with the extracellular domain of a SPEX polypeptide decreases the expression of SPEX on the surface of lymphocytes including B, CD4+T, and CD8+T cells.

10. IDENTIFICATION OF AMINO ACID RESIDUES IN THE EXTRACELLULAR DOMAIN OF SPEX IMPORTANT TO ANTIBODY IMMUNOREACTIVITY

Example 10 discloses certain, but not necessarily all, of the amino acid residues in the extracellular domain of mSPEX that are important to the immunoreactivity of the PKl 8, PK3, PJl 96 and PJl 9.1 antibodies.

The PK18, PK3, PJ196, and PJ19.1 antibodies are each raised against the mSPEX allele of murine SPEX and immunoreact with the extracellular domain of the mSPEX polypeptide, but do not immunoreact with mSPEXb polypeptide. There are differences in the amino acid sequence of the extracellular domain of the mSPEX allele compared to the mSPEXb allele at eleven amino acid residue positions as indicated in Table 1 below. Mutated mSPEX polypeptides are produced by independently mutating a polynucleotide encoding the mSPEX polypeptide such that a mSPEX polypeptide is produced with substitutions from the mSPEXb sequence at each residue in which there was a difference between the mSPEX and mSPEXb polypeptides (see Table 1 below). The mutations were made independently with the

exception of amino acid residue positions 45 and 47 which were both mutated together forming a T45N/T47K double mutant.

TABLE 1

SEQUENCE DIFFERENCES BETWEEN THE EXTERNAL DOMAINS OF MSPEX AND MSPEXB POLYPEPTIDES

Residue positions 52, 55, 63, 74, 85, 91, and 102 are included in the Ig like domain of the mSPEX polypeptide.

The mutated mSPEX polypeptides are analyzed for changes in the binding of each of the PK18, PK3, PJ196, and PJ19.1 antibodies to demonstrate which of the amino acids that differed between the extracellular domains of mSPEX and mSPEXb polypeptides, respectively, are important to the immunoreactivity of each antibody with the mSPEX polypeptide.

Jurkat T cells (a cell line of human origin) are transfected by electroporation with polynucleotide constructs encoding each mSPEX mutant polypeptide (see Table 1 above) fused at the carboxy-terminus of the mSPEX mutant with a yellow fluorescent protein (YFP). Controls transfections are performed with wild-type mSPEX-YFP fusion polynucleotides as

well. Transfected cells comprising each construct (each mutant mSPEX-YFP or wild-type mSPEX-YFP) are divided into aliquots and then reacted with anti-SPEX antibodies (reacted in separate aliquots with PK18, PK3, PJ196, or PJ19.1) and then all of the samples are reacted with secondary antibodies. The secondary antibodies are linked to PE fluorochrome (FL2, herein) for detection by flow cytometry analysis.

Thus, aliquots of cells are produced wherein each aliquot expresses wild-type mSPEX or one of the mutant mSPEX polypeptides listed in Table 1 above on the cell surface of the Jurkat T cells and aliquots of each of these are reacted separately with PKl 8, PK3, PJ196, or PJl 9.1. FACS analysis is performed by electronically gating the cells on a narrow range of YFP ⁺ cells (fluorochrome 1 positive, or FLl ⁺ ) and then measuring the amount of FL2 fluorescence. A decrease in the amount of FL2 fluorescence for a given primary antibody (PK18, PK3, PJ196, or PJ19.1) immunoreacting with each given mSPEX polypeptide expressing Jurkat T cell indicates that wild-type residue in the mSPEX polypeptide is part of the epitope that specifically immunoreacts with the antibody. The results of the above described experiment are tabulated in Table 2, below.

TABLE 2 RESIDUES OF MSPEX IMPORTANT TO ANTIBODY IMMUNOREACTIVITY

In Table 2, a minus (-) sign indicates that mutation of the respective amino acid position in the extracellular domain of mSPEX does not decrease binding of the antibody for the mutant mSPEX, a plus (+) sign indicates an arbitrary scale (from (+) being the lowest to

(+++) being the greatest) of the extent of decrease in binding of each antibody for a mSPEX mutated at each respective amino acid position in the extracellular domain of the mSPEX polypeptide when compared to wilt-type SPEX.

Based upon the data shown in Table 2 above, it is observed that the PK3 immunoaffinity epitope includes residues 45/47, and 55; the PKl 8 immunoaffinity epitope includes residues 41, 45/47, and 85; the PJ19.1 immunoaffinity epitope includes residues 85 and 91; and the PJl 96 immunoaffinity epitope includes residues 41 and 45/47. The data shown in Table 2 also indicate that residues 85 and 91 of mSPEX are part of the epitope bound by antibody PJl 9.1 which antibody is demonstrated herein to inhibit transplant rejection. In a preferred embodiment an antibody that binds the extracellular domain of a

SPEX polypeptide inhibits transplant rejection. In another preferred embodiment, an antibody that immunoreacts with an epitope that includes residues 85 and 91 in a mSPEX polypeptide (or a corresponding residue in a hSPEX polypeptide) inhibits transplant rejection. In still another preferred embodiment, an antibody that immunoreacts with an Ig like domain of a SPEX polypeptide inhibits transplant rejection. In a further preferred embodiment, an antibody that immunoreacts with an Ig like domain of a SPEX polypeptide (e.g., SEQ ID NO:3, 45, or 88 (most preferably SEQ ID NO:3)), but does not immunoreact with a non-Ig like domain of the SPEX polypeptide (e.g., SEQ ID NO: 1, 2, 4, 5, 6, 7, 8, 9, 10, 11, 43, 44, 46, 47, 48, 49, 50, 51, 52, or 53 (most preferably SEQ ID NO: 1, 2, or 4)) inhibits transplant rejection. In still a further preferred embodiment, an antibody that immunoreacts with an amino acid sequence consisting essentially of a SPEX Ig like domain (e.g., consisting essentially of SEQ ID NO:3, 45, or 88 (most preferably SEQ ID NO:3)), inhibits transplant rejection. In yet another preferred embodiment, an antibody that includes an epitope binding pattern of PJl 9.1 inhibits transplant rejection.

11. INHIBITING IL-2 SECRETION AND CD25 EXPRESSION

A. T Cell Preparation

T cells from spleens or lymph nodes were enriched by negative selection using anti- B220 (clone: RA3-6B2, eBioscience), anti-A ^b class II MHC (clone: Y3P) antibodies and anti- rat IgG magnetic beads (Qiagen, Valencia, CA). All culture experiments were performed in Click's Media (Irvine, Santa Ana, CA) containing 10% heat-inactivated foetal calf serum (GibcoBRL, Carlsbad, CA), penicillin/streptomycin (GibcoBRL), 200 mM glutamine, and 50μM 2-mercaptoethanol (Sigma, St. Louis, MO). Cells were cultured under standard

conditions at 37C in 5% CO ₂ .

B. T Cell Activation

A total of 1 X 10 ⁶ T cells/ml were cultured in 100 μl or 1 ml in 96 well or 24 well flat bottom plates, respectively, coated with 1:1 rations of anti-CD3 (clone: 145-2C11, eBioscience) in combination with rat IgG (JacksonlmmunoResearch, West Grove, PA), PKl 8 or PJl 96 at indicated total Ig-concentrations.

C. Tritiated Thymidine Proliferation Studies

For [ ³ H] thymidine proliferation studies , T cells were cultured in 96 well plates for a total of 72 hours and pulsed with 1 μCi/well [ ³ H] thymidine (PerkinElmer, Boston, MA) for the last 16 hours. Cells were harvested onto glass fibre filters (Brandel Inc., Gaithersburg, MA) and [ ³ H] thymidine incorporation was determined.

D. IL-2 ELISA

Culture supernatants were assayed for mouse IL-2 using a standard sandwich ELISA purchased from eBiosciences. Maxisorb plates (Nunc, Roskilde, Denmark) were coated with anti-IL-2 monoclonal antibodies (niABs) (clone: JES6-1A12), and detection was performed using the corresponding biotinylated mAB. The plates were developed using streptavidin- horseradish peroxidase and tetramethxylbenzidine as substrate. Plates were read on a plate reader at 450 nm and data was analyzed using Softmax software (reader and software from: Molecular Devices Corp., Sunnyvale, CA). Samples were performed in duplicate. The assay was standardized with recombinant murine IL-2 and detection ranged from 1 to 1,000 pg/ml.

E. Inhibition of IL-2 Secretion by Activated Lymphocytes Supernatants of CD4+ and CD8+ T cells in culture were collected 16 hours after stimulation (activation) of the T cells by anti-CD3 in the presence of rat IgG or PKl 8 and were analyzed for IL-2 secretion (the amount of IL-2 in the supernatants). The results are shown in FIG. 6 A. The PKl 8 antibody produced an 80 fold reduction in IL-2 secretion by the activated lymphocytes.

F. Adding IL-2 back to Anti-SPEX Inhibited Lymphocytes Does Not Fully Rescue Proliferation of Activated Lymphocytes

T cells were stimulated in the presence or absence of PK 18 as in FIG. 6 A with the addition in some cultures of the indicated concentrations of recombinant murine IL-2 (800 pg/ml and 80 pg/ml IL-2). The addition of exogenous recombinant IL-2 did not fully rescue the inhibition of lymphocyte proliferation imposed by incubating the lymphocytes with an anti-SPEX antibody that activates SPEX signal transduction (e.g., PKl 8) (see, e.g., FIG. 6B).

This demonstrates that contacting SPEX receptor on a lymphocytes with an antibody agonist of SPEX receptor inhibited the proliferation of the lymphocytes even in the presence of physiological and super physiological concentrations of IL-2.

G. Adding IL-2 back to Lymphocytes Contacted With a SPEX Antibody Agonist Does Not Fully Rescue IL-2 Receptor (CD25) Expression By The

Lymphocytes

CD4+ or CD8+ T cells were stimulated in the presence of PKl 8 and "low IL-2" (80 ρg/ml) or "high IL-2" (800 pg/ml) concentrations and the expression of IL-2 receptor (CD25) was determined by FACS analysis (see, e.g., FIG. 6C). It was determined that CD25 expression was inhibited by SPEX receptor antibody agonist even in the presence of physiological and super physiological concentrations of IL-2 which is normally stimulates the expression of CD25 expression on CD4+ and CD8+ T cells. The inhibition of CD25 expression was observed to be greater in the CD4+ T cells compared to the CD8+ T cells which inhibition positively correlates with the greater expression of SPEX receptor on CD4+ T cells compared to CD 8+ T cells.

H. IL-2 Production, But Not CD69 Induction is Suppressed by SPEX Antibody

Agonist

The induction of proliferation is a relatively late event following T cell activation. To determine whether SPEX receptor antibody agonist (PKl 8 in this example) blocked additional signals mediated by TCR engagement besides IL-2 secretion, the induction of

CD69 expression on T cells was measured. The induction of CD69 expression on both CD4+ and CD8+ T cells was not inhibited by PKl 8 (see, e.g., FIG. 7). In contrast, PKl 8 inhibited subsequent CD25 expression on both CD4+ and CD8+ T cells (see, e.g., FIG. 7). The inhibition of CD25 by PKl 8 was greater on CD4+ T cells than CD8+ T cells, consistent with the greater sensitivity of CD4+ T cells to PKl 8-mediated inhibition of proliferation.

I. Activation of SPEX Receptor Inhibited Proliferation of Pre- Activated T Cells The data in Example 11 H, above, that induction of CD69 expression was not inhibited by PKl 8 indicates that the inhibition of proliferation by SPEX signal transduction was a relatively late event in the activation of T cells. To test this further, isolated naϊve (non- activated) T cells (using AND TCR-Tg mice as an enriched source), were stimulated

overnight with plate bound anti-CD3, and then transferred to fresh plates coated with additional anti-CD3 in combination with PKl 8 or rat IgG (negative control). Surprisingly, PKl 8 was able to inhibit CD4+ T cell proliferation even after an initial overnight activation with anti-CD3 (see, e.g., FIG. 8), similar in magnitude to the inhibition of proliferation observed for cells exposed to PKl 8 for the entire culture period.

Although the invention has been described with reference to the above examples, it will be understood that modifications and variations are encompassed within the spirit and scope of the invention. Accordingly, the invention is limited only by the following claims.