WO1995035120A1

WO1995035120A1 - Monoclonal antibodies for the reduction of anti-xenogeneic immune responses

Info

Publication number: WO1995035120A1
Application number: PCT/US1995/007556
Authority: WO
Inventors: Eileen Elliott Mueller; Louis A. Matis
Original assignee: Alexion Pharmaceuticals, Inc.
Priority date: 1994-06-17
Filing date: 1995-06-14
Publication date: 1995-12-28
Also published as: AU2828795A

Abstract

Monoclonal antibodies are provided that react with pig antigen presenting cells (APCs), inhibit a human/porcine xenogeneic mixed lymphocyte response (MLR), do not react with human APCs, and do not react with pig major histocompatibility (MHC) molecules. The monoclonal antibodies can be used to reduce the rejection of pig xenografts by the human immune system.

Description

MONOCLONAL ANTIBODIES FOR THE REDUCTION OF

ANTI-XENOGENEIC IMMUNE RESPONSES

I. FIELD OF THE INVENTION

This invention relates to xenotransplantation, and to the modulation of the immune response to the xenotransplant. More specifically, the invention relates to monoclonal antibodies and compositions containing such antibodies that will improve the outcome of the transplantation of porcine cells, tissues, and organs into human recipients. To this end the invention provides methods for the preparation, identification, and isolation of monoclonal antibodies (mAbs) against non-MHC antigens on porcine antigen-presenting cells (APCs) , which mAbs do not react with antigens present on human APCs. These mAbs functionally block the activation of human T cells by porcine APCs. The invention also provides methods for the use of these mAbs.

II. INTRODUCTION

Xenotransplant Rejection: There is an ongoing shortage of human organs for transplant. This shortage has resulted in a long felt and unmet need for organs, and has resulted in attempts to develop xenotransplantation technology.

The primary non-primate candidate donor species for clinical xenotransplantation (e.g., the transplantation of non-human organs into human recipients) are ungulates. Swine, in particular, provide an abundant supply of organs that are similar in size, anatomy, and physiology to their human counterparts (Auchincloss, 1988; Najarian, 1992; and Somervile and d'Apice, 1993). Transplantation of porcine pancreatic islets and of a pig liver into human patients has been reported (Makowka, et al., 1993; Satake, et al., 1993; Tibell, et al., 1993), but the outcomes of these transplants need to be improved. One improvement that is needed is better control (e.g., inhibition) of transplant rejection. Hyperacute rejection: The rejection of xenotransplanted organs typically involves both an extremely rapid, antibody-mediated hyperacute rejection (HAR) phase and a slower cellular rejection phase. HAR of discordant (i.e., non-Old- orld-primate) xenotransplants is initiated by preformed "natural" antibodies that bind to donor organ endothelium and activate complement attack by the recipient immune system (Dalmasso, et al., 1992; and Tuso, et al. , 1993). Such rejection can also be seen in vitro following exposure of the xenogeneic cells to human blood, plasma, serum, lymph, or the like.

Activation of complement leads to the generation of fluid phase (C3a, C5a) and membrane bound (C3b and C5b-9, i.e., C5b, C6, C7, C8, and C9) proteins with chemotactic, procoagulant, proinflammatory, adhesive, and cytolytic properties (Muler-Eberhard, 1988) . Immunohistological analysis of hyperacutely rejected xenotransplants reveals antibody deposition, complement fixation, and vascular thrombosis as well as neutrophil infiltration (Zehr, et al., 1994; Auchincloss, 1988; Najarian, 1992; Somervile and d'Apice, 1993; and Mejia-Laguna, et al., 1972).

While HAR is a major impediment to the xenotransplantation of vascularized organs, some discordantly xenotransplanted tissues (e.g., porcine pancreatic islets) do not appear to be rejected by this mechanism. In addition, methods for the control of HAR are available. These include interference with the antibody antigen reactions responsible for initiating the HAR response, either by removing the antibodies from the circulation or by interfering with the expression of the antigens (see copending U.S. application Serial No. 08/214,580, entitled "Xenotransplantation Therapies", filed by Mauro S. Sandrin and Ian F.C. McKenzie on March 15, 1994, and PCT publication No. 93/03735, entitled "Methods and Compositions for Attenuating Antibody-Mediated Xenograft Rejection") . Inhibition of complement attack on a xenotransplant may be accomplished by several means, including the use of complement inhibitors such as the 18kDa C5b-9 inhibitory protein and monoclonal antibodies against human C5b-9 proteins discussed in U.S. Patent No. 5,135,916, issued August 4, 1992.

Granulocytes and rejection: In order to better understand the xenograft rejection phenomenon, studies have been undertaken to investigate interactions between human white blood cells and xenogeneic cells, particularly xenogeneic APCs, including monocytes and B cells found in isolated PBLs (peripheral blood leukocytes) , dendritic cells, and endothelial cells, including porcine aortic endothelial cells (PAEC) . Various of these APCs are found in pancreatic islets, which thus can be used in experiments requiring APCs.

Granulocytes, specifically neutrophils, are involved in early rejection phenomena. Previous studies have shown that human complement component C3b (C3bi) deposited on PAEC mediates the binding of human granulocytes, specifically neutrophils, to the PAEC through interactions with the heterodimeric neutrophil cell surface receptor CDllb/CDl8 (Vercellotti, et al. , 1991) . Furthermore, blocking HAR by inhibition or depletion of complement results in decreased neutrophil infiltration and increased xenograft survival, providing additional evidence for the role of complement in mediating human neutrophil binding to porcine endothelium. However, a significant neutrophil infiltrate into PAEC monolayers has been observed even in the absence of complement activation (Leventhal, et al., 1993; and Pruitt, et al. , 1991) . The development of such infiltrates is believed to play an important role in early xenograft rejection, and therapeutic approaches have been developed to address this problem (see copending U.S. patent application Serial No. 08/252,493, filed June 1, 1994, entitled "Porcine E-Selectin") . Lymphocytes and rejection: While granulocytes play a major role in early rejection responses, later rejection responses of the host immune system are mediated predominantly by lymphocytes, i.e., T cells and B cells. These cells express antigen receptors that recognize foreign (transplantation) antigens in a highly specific fashion. Recognition of such transplantation antigens leads to lymphocyte activation and the induction of effector mechanisms (e.g., inflammatory cytokine production, cytotoxicity, and antibody production) that mediate the rejection of the graft.

T lymphocytes are central to many of the immune responses that lead to graft rejection, and play a predominant role in mediating long term rejection responses. In addition to the direct cytotoxic activities of T cells, the production of induced, graft- specific antibodies by B cells is dependent on the function of helper T lymphocytes. In the absence of such T cell help, antibody production does not occur.

Examination of the T cells that mediate graft rejection has shown that the immune attack on graft tissue can be the result of effector mechanisms inherent in both of the major subsets of T lymphocytes in the immune system, i.e., the helper, or CD4⁺, and the cytotoxic (killer), or CD8⁺, T cells. Helper function is mediated by T cell production of inflammatory cytokines, such as IL2, gamma interferon, or TNF alpha. These cytokines can destroy grafts both by local inflammatory responses, such as delayed hypersensitivity, and by the induction of the production of factors that activate CD8⁺ T cells.

The paramount role of T cells in mediating the immune system functions responsible for graft rejection has been confirmed experimentally by the demonstration that athymic mice, which have no T cells due to the congenital absence of the thymus, accept allografts (grafts from genetically distinct members of the same species) or even xenografts (grafts from members of other species) without rejection (Manning, et al. , 1973).

Evaluation of T cell activation: The standard in vitro assay of T cell function in cell-mediated immunity is the mixed lymphocyte response, or MLR. This assay measures the activation of T cells after stimulation with foreign antigens in the presence of competent APCs. In this assay, the activation of the T cells is measured either by assessing the magnitude of their proliferation, or alternatively, by the analysis of cytokine production and release by the T cells. Both CD4⁺ and CD8⁺ T cells can be activated in an MLR, although CD4⁺ T cells account for the majority of the response.

MHC antigens and the T cell receptor: Specific antigen recognition by T cells is mediated by a cell surface structure found on T cells that is referred to as the T cell receptor, or TCR. Most antigens are recognized by the TCR in the form of peptide fragments which result from processing of a proteinaceous antigenic molecule by an APC. In order to be recognized by the TCR, these antigen peptides must be associated with major histocompatibility complex (MHC) proteins (also referred to as MHC antigens) on the cell surfaces of APCs.

The predominant basis for the powerful immune response characteristic of graft rejection is believed to be the high frequency of precursor T lymphocytes that specifically recognize transplantation antigens expressed on the surfaces of cells lining the vasculature of the graft. Graft MHC antigens are the primary targets for recognition by these high frequency precursor T lymphocytes; numerous studies have shown that a relatively high percentage of an individual's T cells have the capacity to recognize foreign MHC molecules. This recognition of foreign MHC antigens by host T-cell receptors is atypical in that the TCRs appear to recognize the MHC proteins in their intact form as they normally appear on the cell surface, rather than requiring that the MHC proteins be processed and presented as peptides associated with APC MHCs (i.e., MHC proteins expressed by APCs) .

Costimulatory interactions: In addition to the recognition and engagement of antigens by the TCR, T cell activation and consequent effector functions require interactions between various costimulator molecules on the T cell surface and the specific ligands of these costimulator molecules on APCs. Blocking of such costimulator interactions will block T cell activation. In many cases, blocking only one costimulator interaction of the many involved in T cell stimulation will completely block T cell activation. (As used herein the term "costimulatory factor" refers to a factor that, when blocked, e.g., by binding to a mAb, inhibits T cell activation.)

A number of specific receptor/1igand interactions that amplify or are necessary for allogeneic T cell activation have been characterized. These include CD2/LFA3, LFA-1/ICAMs 1, 2, and 3, CD28/B7 (B7-1) , CD28/B7-2, and VLA-4/VCAM, as well as interactions between receptors on T cells and selectin molecules on APCs.

The efficacy of modulating these interactions as a means to prevent or treat allogeneic transplant rejection has been demonstrated by several experiments. In separate cases, tolerance to heart allografts has been induced by in vivo blockade of the LFA-1/ICAMl interaction (Isobe, et al. , 1992) or the VLA-4/VCAM interaction, using monoclonal antibodies directed at these human cell surface molecules. Stimulation of T cells in vitro while blocking both B7 and B7-2 has also been shown to induce anergy, i.e., the condition in which T cells become relatively unresponsive to stimuli (Chen and Nabavi, 1994) . In addition, tolerance to human islets transplanted into mice has been achieved by blocking the interaction of host T cells with B7 and B7-2 via the administration of an engineered soluble form of a human receptor (CTLA-4Ig) that binds to both molecules. Blockade of T cell activation: As discussed above, treatments that block costimulation can block T cell activation and can thus inhibit graft rejection. Treatments that block costimulator interactions, as compared to treatments that block the primary stimulus provided to T cells by MHC interactions with TCRs, provide especially desirable advantages in the xenotransplant setting. In particular, primary stimulation of T cells by engagement of the T cell receptor alone, in the absence of costimulator interactions (e.g., in the presence of costimulation blockade) , can cause T cells to become anergic over a prolonged period. Induction of anergy in those T cells recognizing xenogeneic transplantation antigens is a desirable outcome in the xenotransplant setting.

In addition, in the xenotransplant setting, costimulation blockade is of general applicability to multiple strains or MHC haplotypes of a given donor species, as costimulator molecules and their ligands generally display very limited variability within a particular species. In contrast, MHC molecules generally represent the most polymorphic proteins in any species. Compounds that react specifically with a particular MHC molecule or group of MHC molecules are therefore often highly specific for restricted sets of individuals. In the case of xenotransplantation, such treatments would only be effective for use in patients receiving donor organs from donor strains expressing a particular MHC molecule.

With regard to costimulatory interactions involved in T cell activation in the xenogeneic immune response, studies have shown that, while many antibodies against human APC costimulatory molecules will not bind to xenogeneic APCs, antibodies that block costimulatory molecules on human T cells can block xenogeneic mixed lymphocyte response assays (MLRs) .

Such blockade of costimulatory molecules on human T cells as an approach to blocking T cell activation by a xenograft is not practical, however, in that it is non¬ specific and will thus produce generalized immunodeficiency in the patient. Thus, known compounds that block allogeneic MLRs (i.e., MLRs containing human APCs and human T cells) are not good candidates for use in the prevention and treatment of xenotransplant rejection. III. SUMMARY OF THE INVENTION

In view of the foregoing, the ideal agent for prevention and treatment of xenotransplant rejection, specifically, porcine xenotransplant rejection, is a compound that 1) blocks the immune response to the porcine antigens expressed by the cells of the transplant without inhibiting the normal responses to non-transplant antigens, and 2) do not bind to porcine MHC molecules, and thus do not prevent the induction of anergy in human T cells that react with porcine MHC antigens. Prior to the present invention, antibodies which could be used as agents of this type were unknown.

In accordance with the invention, methods for screening hybridomas are provided which result in antibodies that only affect the human immune response to xenogeneic antigens expressed by the cells of a porcine transplant without affecting other functions of the human immune system. These antibodies also do not bind to porcine MHC antigens. As a result of these properties, the antibodies provide means for reducing the rejection of porcine xenografts.

Antibodies prepared in accordance with the method of the invention block the activation of human T cells by porcine APCs, but do not inhibit the activation of T cells by human APCs. In their preferred embodiments, these antibodies: l) react with (bind) antigens on porcine APCs, 2) do not react with (bind) porcine MHC molecules, 3) do not react with (bind) antigens on human APCs, and 4) block the human response to porcine antigens as evidenced by the inhibition of MLRs containing porcine APCs and human T cells.

In further preferred embodiments, the antibodies: 1) react with (bind) to porcine APCs from various strains or haplotypes of pig, and/or 2) react with (bind) more than one of the various types of pig APCs, such as, monocytes, B cells, dendritic cells, and endothelial cells. IV. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1-5 show FACS profiles in which the y-axis represents cell number and the x-axis represents fluorescence intensity.

Figure 1A is a FACS profile showing the binding of the mAb obtained from hybridoma 74-11-10 to porcine PBLs obtained from an inbred NIH c/c minipig (referred to herein as "3599 cells") . Hybridoma 74-11-10 was obtained from the ATCC and its mAb binds to a public domain epitope of porcine MHC Class I molecules.

Figure IB is a FACS profile showing the lack of binding of the mAb of hybridoma 74-11-10 to human PBLs. Figure 2A is a FACS profile showing the binding of the mAb obtained from hybridoma 2D10 to 3599 cells.

Figure 2B is a FACS profile showing the lack of binding of the mAb obtained from hybridoma 2D10 to human PBLs.

Figure 2C is a FACS profile showing the binding of the mAb obtained from hybridoma 2D10 to porcine PBLs from an outbred pig identified herein by the number 222 ("222 cells") . Figure 2D is a FACS profile showing the binding of the mAb obtained from hybridoma 2D10 to porcine PBLs from an outbred pig identified herein by the number 1019 ("1019 cells") .

Figure 3A is a FACS profile showing the binding of the mAb obtained from hybridoma 8D1 to 3599 cells. Figure 3B is a FACS profile showing the lack of binding of the mAb obtained from hybridoma 8D1 to human PBLs.

Figure 3C is a FACS profile showing the binding of the mAb obtained from hybridoma 8D1 to 222 cells. Figure 3D is a FACS profile showing the binding of the mAb obtained from hybridoma 8D1 to 1019 cells.

Figure 4A is a FACS profile showing the binding of the mAb obtained from hybridoma 9E6 to 3599 cells.

Figure 4B is a FACS profile showing the binding of the mAb obtained from hybridoma 9E6 to human PBLs.

Figure 5 is a FACS profile showing the binding of mAb H42A to 3599 cells. mAb H42a was obtained from VMRD,

Inc., Pullman, WA, and binds to a public domain epitope on porcine MHC Class II molecules. Figure 6 shows reducing (lane "R") and nonreducing

(lane "NR") SDS-PAGE gels of a porcine costimulatory factor having a molecular weight of approximately 46 kDa which was isolated by immunoprecipitation with the mAb obtained from hybridoma 2D10. Figure 7 shows results of human/porcine xenogenic

MLR assays performed using the hybridoma supernatant produced by hybridoma 1A4 and (i) 3599 cells (NIH MLR) ,

(ii) PAEC (N-PAEC MLR) , or (iii) porcine pancreatic islets (ISLET MLR) . Also shown are results of ELISA and FACS analysis using the supernatant from the same hybridoma and 3599 cells, 222 cells, 1019 cells, or human

PBLs.

Figure 8 shows results of human/porcine xenogenic

MLR assays performed using the hybridoma supernatant produced by hybridoma 2D2 and (i) 3599 cells (NIH MLR) ,

(ii) PAEC (N-PAEC MLR) , or (iii) porcine pancreatic islets (ISLET MLR) . Also shown are results of ELISA and FACS analysis using the same hybridoma supernatant and 3599 cells, 222 cells, 1019 cells, or human PBLs.

The foregoing drawings, which are incorporated in and constitute part of the specification, illustrate certain aspects of the preferred embodiments of the invention and, together with the description, serve to explain certain principles of the invention. It is to be understood, of course, that both the drawings and the description are explanatory only and are not restrictive of the invention.

V. DESCRIPTION OF THE PREFERRED EMBODIMENTS

As discussed above, the present invention relates to the prevention and treatment of the rejection of porcine cells upon exposure to human blood, plasma, serum, lymph, or the like (e.g., upon transplantation into a human patient) . The invention provides methods for the preparation, identification, and isolation of monoclonal antibodies (mAbs) that, among other things, are non- reactive against antigens present on human APCs and block MLRs in which the antigen-presenting cells (APCs) are derived from a pig.

Preparation of porcine and human APCs: Methods for the isolation of APCs of both human and non-human origin are well known in the art. As discussed above, APCs include monocytes and B cells, which are found in PBL preparations, dendritic cells, and endothelial cells, including porcine aortic endothelial cells (PAEC) .

PBLs can be prepared by centrifugation of decoagulated whole blood, followed by careful aspiration of the "buffy coat" of white blood cells on the surface of the red blood cell pellet and transfer of the buffy coat (which consists essentially of PBLs) to a clean container. PBLs can be further purified as described below under the heading "Materials and Methods." If desired, monocytes and B cells can be further purified using techniques known in the art, such as, velocity gradient centrifugation, centrifugal elutriation, affinity chromatography, and the like.

Dendritic cells can be obtained following techniques of the type discussed in Metlay, et al., 1990, Everson et al., 1989, and Miyazaki et al. , 1988. Endothelial cells, including PAEC, are commercially available from, for example, Cell Systems, Inc., Kirkland, WA. Porcine pancreatic islets can be obtained following techniques of the type discussed in Zeng et al., 1993, and Lenschow et al., 1992.

Immunization of antibody-producing animals, production of hybridomas from immunized animals, and screening of hybridomas: Conventional methods for the immunization of animals (in this case with porcine APCs) , isolation of antibody producing cells, fusion of such cells with immortal cells (e.g., myeloma cells) to generate hybridomas secreting monoclonal antibodies, and preparation of hybridoma supernatants are well known by those skilled in the art. General methods for screening hybridoma supernatants or other forms of purified or unpurified monoclonal antibodies for reactivity and/or lack of reactivity of the antibodies with particular antigens (in this case reactivity with porcine APCs and lack of reactivity with, inter alia, human APCs) are also conventional and well known, as are methods for the preparation of quantities of such antibodies, for example from hybridoma supernatants or ascites fluids, and the purification and storage of such monoclonal antibodies. Descriptions of these methods can be found in numerous publications, including: Coligan, et al., eds. Current Protocols In Immunology, John Wiley & Sons, New York, 1992; Harlow and Lane, Antibodies. A Laboratory Manual. Cold Spring Harbor Laboratory, New York, 1988; and Liddell and Cryer, A Practical Guide To Monoclonal Antibodies, John Wiley & Sons, Chichester, West Sussex, England, 1991. Preferred antibody-producing animals for immunization are rodents, with mice being particularly preferred. A particularly preferred method of immunization with porcine APCs is described below under the heading "Materials and Methods". Particularly preferred methods of screening for reactivity with porcine APCs and for lack of reactivity with, inter alia, human APCs are described below under the heading "Materials and Methods" and under the sub-headings "ELISA", "FACS", and "Human/Porcine Xenogeneic MLRs".

As used herein, the terms "monoclonal antibody" and "monoclonal antibodies" refer to immunoglobulins produced by a hybridoma in vivo or in vitro, and antigen binding fragments (e.g., Fab' preparations) of such immunoglobulins, as well as to recombinantly expressed antigen binding proteins, including immunoglobulins, chimeric immunoglobulins, "humanized" immunoglobulins, antigen binding fragments of such immunoglobulins, single chain antibodies, and other recombinant proteins containing antigen binding domains derived from immunoglobulins. Publications describing methods for the preparation of such monoclonal antibodies, in addition to those listed immediately above, include: Reichmann, et al., 1988; Winter and Milstein, 1991; Clackson, et al., 1991; Morrison, 1992; Haber, 1992; and Rodrigues, et al., 1993. Detection of antibodies reactive with human and/or porcine APCs: mAbs reactive or non-reactive with porcine or human APCs are preferably detected using ELISA and/or FACS analysis as described below under the heading "Materials and Methods." Other methods can be used if desired. Positive and negative responses are determined by comparing the responses for test mAbs with the responses obtained for known controls.

For example, as shown in Figure 1, a monoclonal antibody that binds to a public domain epitope of pig MHC Class I molecules can be used as a positive control for binding to porcine APCs and a negative control for binding to human APCs. Test antibodies can be compared to these responses and to responses from no antibody controls to determine if they bind or do not bind to pig APCs and/or human APCs.

Detection of antibodies that inhibit human/porcine xenogeneic MLRs: Antibodies that inhibit human/porcine xenogeneic MLRs can be identified using conventional MLR assay protocols employing human T cells and porcine APCs, rather than human APCs. A typical procedure is described below under the heading "Materials and Methods." Other protocols can be used if desired (see, for example, Murray et al. , 1994, which is incorporated herein by reference) . mAbs that inhibit MLRs are those that provide a substantial reduction (see below) in T cell proliferation and/or cytokine levels as measured in such assays when the antibody is added at a concentration on the order of 50 μg/ml. T cell proliferation can be measured by various methods known in the art, including those described below under the heading "Materials and Methods." Cytokine levels can be measured using, for example, commercially available immunoassays, such as the QUANTIKINE assays manufactured by R&D Systems, Minneapolis, MN. Detection of antibodies reactive with porcine MHC molecules: The mAbs of the invention are typically tested for reactivity with porcine MHC molecules after having been screened for 1) reactivity with porcine APCs, 2) non-reactivity with human APCs, and 3) the ability to inhibit human/porcine xenogeneic MLRs. Reactivity with porcine MHC molecules is detected indirectly using the results of FACS analysis for reactivity with porcine PBLs and MLR analysis for inhibition of human/porcine xenogeneic MLRs. A bimodal FACS profile prepared using pig PBLs is a necessary, but not a sufficient, indication of a mAb which binds to porcine MHC Class II molecules. Accordingly, PBLs of several strains of pig are tested using FACS, and negative reactivity with MHC Class II molecules is identified by the occurrence of a non-bimodal FACS profile for at least one of the strains, provided that the PBLs of that strain positively bind to the mAb being tested.

Negative reactivity with MHC Class I molecules is identified by the occurrence of a greater than about 40% inhibition in the human/porcine xenogeneic MLR assay for the mAb being tested. Rather than using indirect assays for MHC reactivity, direct assays can also be performed by isolating the antigen to which the mAb binds and characterizing its properties. Isolation can be performed using the mAb in a variety of antigen isolation procedures known in the art, including, for example, the immunoprecipitation procedure described below under the heading "Materials and Methods". Characterization of the isolated antigen may include identification of molecular weight, isoelectric point, amino acid sequence, etc., as well as immunological reactivity to antibodies having known specificity to porcine MHC molecules. Results of this characterization is compared to known properties of porcine MHC molecules (see, for example, Lunney and Pescovitz, 1988, which is incorporated herein by reference) to determine if the antigen is a porcine MHC molecule.

Administration of mAbs: As discussed above, the mAbs of the invention can be used therapeutically to reduce the rejection of porcine xenografts. To achieve the desired reduction, the antibodies can be administered in a variety of unit dosage forms. The dose will vary according to the particular antibody. For example, different antibodies may have different masses and/or affinities, and thus require different dosage levels. Antibodies prepared as Fab' fragments will also require differing dosages than the equivalent intact immunoglobulins, as they are of considerably smaller mass than intact immunoglobulins, and thus require lower dosages to reach the same molar levels in the patient's blood.

The dose will also vary depending on the manner of administration, the particular symptoms of the patient being treated, the overall health, condition, size, and age of the patient, and the judgment of the prescribing physician. Dosage levels of the antibodies for human subjects are generally between about 1 mg per kg and about 100 mg per kg per patient per treatment, and preferably between about 5 mg per kg and about 50 mg per kg per patient per treatment.

The dose should provide plasma concentrations equivalent to those that are effective in vitro to substantially inhibit human/porcine xenogeneic MLRs.

Once the concentration of antibody needed to achieve this effect in vitro has been determined, the dosage required to reach the same concentration in a human patient can be readily determined. Subject to the judgement of the physician, a typical therapeutic treatment includes a series of doses, which will usually be administered concurrently with the monitoring of clinical endpoints. For example, in the case of a porcine kidney transplant, such clinical endpoints can include BUN levels, proteinuria levels, etc., with the dosage levels adjusted as needed to achieve the desired clinical outcome.

Administration of the antibodies will generally be performed by an intravascular route, e.g., via intravenous infusion by injection. Other routes of administration may be used if desired. Formulations suitable for injection are found in Remington's Pharmaceutical Sciences, Mack Publishing Company, Philadelphia, PA, 17th ed. (1985) . Such formulations must be sterile and non-pyrogenic, and generally will include a pharmaceutically effective carrier, such as saline, buffered (e.g., phosphate buffered) saline, Hank's solution, Ringer's solution, dextrose/saline, glucose solutions, and the like. The formulations may contain pharmaceutically acceptable auxiliary substances as required, such as, tonicity adjusting agents, wetting agents, bactericidal agents, preservatives, stabilizers, and the like. In addition, the formulations can include conventional immunosuppressive agents, such as cyclosporin.

The formulations of the invention can be distributed as articles of manufacture comprising packaging material and the antibodies of the invention. The packaging material will include a label which indicates that the formulation is for use in the treatment of the rejection of porcine xenografts in general, or of specific porcine xenografts, as the case may be.

Other Applications of the mAbs: In addition to their pharmaceutical applications, the mAbs of the invention can also be used to isolate porcine costimulatory factors and their porcine ligands, which, in turn, can be used to isolate the genes encoding the factors, which, in turn, can be used to modulate the expression of the factors by porcine cells to reduce porcine xenograft rejection. In this regard, Figure 6 shows the isolation of a porcine costimulatory factor having a molecular weight of approximately 46 kDa. This factor was isolated using monoclonal antibody obtained from hybridoma 2D10.

Hybridoma 2D10 was deposited with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Maryland, 20852, United States of America, on June 9, 1994, and has been assigned the designation HB-11648. This deposit were made under the Budapest Treaty on the International Recognition of the Deposit of Micro¬ organisms for the Purposes of Patent Procedure (1977) .

The phrase "substantial reduction" has been used above in connection with describing various assay results. As used herein, an at least 50% reduction will, in general comprise a "substantial reduction". Smaller reductions are also considered "substantial" if they represent a statistically significant reduction, i.e., a reduction that, when obtained in replicate assays and analyzed by a standard statistical test, such as the student's T test, will give a probability value, p, less than or equal to 0.05, and, preferably, less than or equal to 0.015.

• Materials and Methods Hybridoma Production Immunizations and myeloma-splenocyte fusions were performed as described in Coligan et al., supra. Briefly, Balb/c female mice were immunized three times prior to fusion. The first immunization was by IP injection with 2.5 x 10⁷ NIH inbred minipig 3599 cells in TITREMAX adjuvant (Vaxcel, Inc., Norcross, GA) . A second boost followed 5 weeks after the first immunization with 2 x 10⁷ cells injected IP in PBS. Ten days later the mouse was boosted with 1x10^s 3599 cells IV and 5xl0⁶ 3599 cells IP. The cells for immunization were prepared by centrifugation of heparinized peripheral blood over FICOLL gradients. Cells isolated from the interface were washed twice and frozen in 10% DMSO. The cells were thawed and then washed twice prior to use. ELISA lxlO⁵ NIH inbred minipig 3599 cells were added to a

96 well V-bottom plate. The cells were spun into a tight pellet, the supernatant removed and 50μl of hybridoma supernatant added while resuspending the cells. The plates were incubated on ice for 60 min. The cells were washed twice with PBS + 2% FCS. HRP conjugated goat anti-mouse secondary antibody was added and the plates incubated on ice for 60 minutes. The plates were then washed and cells transferred to ELISA 96 well U-bottom plates. The substrate O-phenylenediamine dihydrochloride (Sigma P-8287) was added and the plates read at OD_4go. Positive wells were identified by comparison to negative control wells containing secondary reagent only and positive control wells containing PT85A antibody (VMRD Inc., Pullman, WA) which had previously been identified as positively staining these cells. FACS Those hybridomas which tested positive by ELISA were further screened by FACS staining on the NIH inbred minipig 3599 cells. lxlO⁵ 3599 cells were added to a well and washed once with PBS + 2% FCS. 50μl of hybridoma supernatant was added to the well and incubated for 1 hour on ice. The cells were then washed and the secondary reagent (FITC goat anti-mouse) was added. The plates were incubated on ice for 1 hour. The cells were then washed twice with PBS + 2% FCS and analyzed by FACS. Positive staining hybridomas were identified by comparison to negative controls of the same cells stained with the secondary reagent only. Human/Porcine Xenogeneic MLRs

Human T cells were purified by centrifugation of heparinized peripheral blood over FICOLL gradients followed by purification of T cells using human T cell purification columns (R&D Systems, Minneapolis, MN) . Porcine antigen presenting cells were also purified by centrifugation of heparinized peripheral blood over FICOLL gradients and isolation of PBLs which were then frozen in 10% DMSO/20% serum. The porcine cells were thawed prior to use and washed once with RPMI + 10% FCS. In order to prevent proliferation of the porcine APCs, which would interfere with the measurement of proliferation of the human T cells, the PBLs were mitomycin C treated for 30 minutes at 50μg/ml. These mitomycin C treated cells were washed 3 times to eliminate any remaining mitomycin C before being added to the assay. 2xl0⁵ purified human T cells were incubated with 2xl0⁵ mitomycin treated-NIH inbred 3599 minipig peripheral blood leucocytes (PBLs) in the presence or absence of 50μl of hybridoma supernatant or 25 or 50 μg/ml (final) of purified mAbs in flat bottom 96-well plates. (Where purified mAbs were used, the purification was performed using conventional protein A affinity chromatography.) Each well was pulsed on day 5 with 1 μCi of ³H-thymidine and harvested on day 6. The results were calculated as percent inhibition as compared to negative control wells. In Tables 1 and 2, results obtained using this assay are identified by the rows labelled "Xeno MLR."

Example 1 Isolation and Characterization of mAbs

Three Balb/c female mice were immunized and boosted three times with NIH inbred minipig 3599 PBLs prior to fusion. Nine hundred and ninety-six hybridomas were initially screened by the cell-based ELISA protocol described above for the production of antibodies reactive against the porcine PBLs used for the immunizations. Three hundred and thirty seven hybridomas were identified as positive by the ELISA assay. All the hybridoma supernatants were scored by comparison to the results with secondary antibody only.

The 337 samples were then tested for their reactivity against the 3599 inbred porcine cells by FACS using a FITC-conjugated goat anti-mouse secondary antibody. One hundred and five of the 337 samples were positive by this FACS analysis.

A number of the anti-porcine hybridomas were expanded and antibodies obtained from those hybridomas were purified by conventional protein A affinity chromatography. The hybridoma supernatants or corresponding purified antibodies were further screened by FACS staining of PBLs isolated from several outbred pigs. Figures 2C, 2D, 3C, and 3D illustrate some of the FACS profiles observed when outbred PBLs were stained with the mAbs. The top three rows of Table 1 and Figures 7 and 8 further sets forth the data obtained in these experiments. Purified mAbs were tested in the human/porcine xenogeneic MLR assay described above, where the APCs were 3599 PBLs. The results of these tests are shown in the bottom two rows of Table 1. The results are presented as percentage of proliferation inhibition. The proliferative response in the negative control wells show 0% inhibition.

Selected hybridoma supernatants were tested for their ability to block human/porcine xenogeneic MLRs where the APCs were 3599 PBLs, outbred PAEC, or outbred porcine pancreatic islets. In the PAEC assay, the endothelial cells were activated with 20μg/ml human TNFo. for 20 hours prior to their use. As can be seen in Figures 7 and 8, the hybridoma supernatants were able to significantly block each of the reactions. The results are again presented as percentage of proliferation inhibition. The proliferative response in the negative control wells containing no added antibody again show 0% inhibition. In addition to the foregoing, the antibodies obtained from hybridomas 1A4, 2D10, 8D1, and 9E6 were tested for their ability to inhibit human/human allogenic MLRs. None of these antibodies showed inhibition in these assays. Based on the foregoing, as summarized in Table 2, the antibodies obtained from hybridomas 2D10 and 8D1 are suitable for use in reducing porcine xenograft rejection, with the antibodies obtained from hybridoma 2D10 being most suitable. Example 2

Immunoprecipitation of a Porcine Costimulatory Factor 2xl0⁷ 3599 cells were cell surface biotinylated. The cells were washed twice in serum free media and then incubated with 0.5mg/ml NHS-L-C-biotin (Pierce Chemical Company, Rockford, IL) for 30 minutes at 4°C. Following biotinylation, the cells were washed twice and lysed in RIPA buffer (1% TRITON X100, 1% DOC, 1% SDS 0.15M NaCl, lOmM Tris, lmM EDTA, ImM PMSF, and 0.1 mg/ml aprotinin) . The cells were then incubated on ice for 15 minutes and spun for 15 min at 13,000 rpm. The pellet was removed and 50μl of protein G beads (Sigma) and lOμl of normal mouse serum added to the supernatant lysate. The samples were incubated at 4°C overnight. The beads were spun down and the supernatant transferred to a fresh tube. A second aliquot (50μl) of the protein G beads and purified antibody obtained from hybridoma 2D10 at a final concentration of 50μg/ml were added to the supernatant. (The antibody was purified using conventional protein A affinity chromatography.) The lysate and antibody were incubated with mixing at 4°C for 2-4 hours. The beads were pelleted, washed twice with RIPA buffer and resuspend in either reducing or non-reducing SDS sample buffers.

The samples were placed in a boiling water bath for 3 minutes prior to loading on SDS-PAGE gels. The biotinylated protein was visualized using streptavidan- HRP and a chemiluminescent visualization system (ECL Kit, Amersham, Arlington Heights, IL) and X-ray film recording. The results are shown in Figure 6. As can be seen therein, a single band having a molecular weight of approximately 46 kDa was isolated and resolved on both reducing and nonreducing gels.

Throughout this application various publications and patent disclosures are referred to. The teachings and disclosures thereof, in their entireties, are hereby incorporated by reference into this application to more fully describe the state of the art to which the present invention pertains.

Although specific embodiments of the invention have been described and illustrated, it is to be understood that modifications can be made without departing from the invention's spirit and scope. For example, although the foregoing discussion of the invention is in terms of porcine cells, the principles of the invention are also applicable to other ungulates (i.e., hooved animals) suitable for use in transplantation to humans, including, cows, goats, sheep, donkeys, and the like. A variety of other modifications which do not depart from the scope and spirit of the invention will be evident to persons of ordinary skill in the art from the disclosure herein. The following claims are intended to cover the specific embodiments set forth herein as well as such modifications, variations, and equivalents.

TABLE 1

1A4 2D10 8D1 9E6 H42

FACS-3599

FACS-222 ND ND

FACS-1019 ND ND

FACS-human ND

Xeno MLR 50 μg/ml 59% 54^s, 53% 51% 54^s, mAb

Xeno MLR 16^s 48% 33 ^s 23? ND 25 μg/ml mAb

* NOT COMPLETELY UNIMODAL ** BIMODAL

Table 2

Monoclonal 1A4 2D2 2D10 8D1 9E6 antibody

reactivity Yes Yes Yes Yes Yes with pig Table 1 Fig. Table 1 Table 1 Table 1 APCs Fig. 7 Figs. Figs. Fig. 4A 2A, 2C, 3A, 3C, and 2D and 3D inhibition Yes Yes Yes Yes Yes of Xeno Table 1 Fig. Table 1 Table 1 Table MLR Fig. 7 reactivity No No No No Yes with human Table 1 Fig. Table 1 Table l Table 1 APCs Fig. 7 Fig. 2B Fig. 3B Fig. 4B

reactivity No No No No No with Table 1 Fig. Table 1 Table Table 1 porcine Fig. 7 MHC class I reactivity ND ND No No No with Fig. 2A Fig. 3D Fig 4A porcine

MHC class II reactivity Yes Yes Yes Yes ND with at Fig. 7^* Fig. Table 1 Table 1 least two Figs. Figs. strains or 2A, 2C, 3A, 3C, haplotypes and 2D and 3D of pig reactivity Yes Yes ND ND ND with at Fig. Fig. 8 least two types of pig APCs

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Claims

What is claimed is :

1. A method for the generation of monoclonal antibodies (mAbs) comprising:

(a) immunizing an antibody-producing animal with pig antigen presenting cells (pig APCs) ;

(b) preparing hybridomas producing mAbs from cells obtained from the immunized antibody-producing animal;

(c) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for the presence of antibodies reactive with pig APCs;

(d) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for inhibition of a human/porcine xenogeneic mixed lymphocyte response;

(e) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for reactivity with human APCs;

(f) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for reactivity with pig major histocompatibility molecules of Class I and Class II;

(g) selecting at least one hybridoma which is positive for screens (c) and (d) and negative for screens

(e) and (f) ; and

(h) producing monoclonal antibodies from the at least one selected hybridoma.

2. A method for the generation of monoclonal antibodies (mAbs) comprising:

(a) immunizing an antibod -producing animal with pig antigen presenting cells (pig APCs) ;

(c) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for the presence of antibodies reactive with pig APCs from at least two strains or haplotypes of pig; (d) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for inhibition of a human/porcine xenogeneic mixed lymphocyte response;

(e) and (f) ; and

(h) producing monoclonal antibodies from the at least one selected hybridoma.

3. A method for the generation of monoclonal antibodies (mAbs) comprising:

(c) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for the presence of antibodies reactive with at least two types of pig APCs;

(f) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for reactivity with pig major histocompatibility molecules of Class I and Class II; (g) selecting at least one hybridoma which is positive for screens (c) and (d) and negative for screens (e) and (f) ; and

(h) producing monoclonal antibodies from the at least one selected hybridoma.

4. A method for the generation of monoclonal antibodies (mAbs) comprising:

(d) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for the presence of antibodies reactive with pig APCs of the same or different types from at least two strains or haplotypes of pig;

(e) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for inhibition of a human/porcine xenogeneic mixed lymphocyte response;

(f) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for reactivity with human APCs;

(g) screening supernatants of the hybridomas or antibodies obtained from the hybridomas for reactivity with pig major histocompatibility molecules of Class I and Class II;

(h) selecting at least one hybridoma which is positive for screens (c) , (d) , and (e) and negative for screens (f) and (g) ; and

(i) producing monoclonal antibodies from the at least one selected hybridoma.

5. A hybridoma which produces a monoclonal antibody that is reactive with pig APCs, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

6. A hybridoma which produces a monoclonal antibody that is reactive with pig APCs from at least two strains or haplotypes of pig, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

7. A hybridoma which produces a monoclonal antibody that is reactive with at least two types of pig APCs, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

8. A hybridoma which produces a monoclonal antibody that is reactive with at least two types of pig APCs, is reactive with pig APCs of the same or different types from at least two strains or haplotypes of pig, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

9. A monoclonal antibody that is reactive with pig APCs, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

10. A monoclonal antibody that is reactive with pig APCs from at least two strains or haplotypes of pig, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

11. A monoclonal antibody that is reactive with at least two types of pig APCs, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

12. A monoclonal antibody that is reactive with at least two types of pig APCs, is reactive with pig APCs of the same or different types from at least two strains or haplotypes of pig, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II.

13. Hybridoma 2D10 having ATCC designation HB-11648.

14. A monoclonal antibody produced by the hybridoma of Claim 13.

15. A method of therapeutically reducing the rejection of a porcine xenograft by a patient comprising administration to the patient of a monoclonal antibody that is reactive with pig APCs, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II, in an amount sufficient to reduce rejection of such xenograft by the patient.

16. A method of therapeutically reducing the rejection of a porcine xenograft by a patient comprising administration to the patient of a monoclonal antibody that is reactive with pig APCs from at least two strains or haplotypes of pig, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II, in an amount sufficient to reduce rejection of such xenograft by the patient.

17. A method of therapeutically reducing the rejection of a porcine xenograft by a patient comprising administration to the patient of a monoclonal antibody that is reactive with at least two types of pig APCs, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II, in an amount sufficient to reduce rejection of such xenograft by the patient.

18. A method of therapeutically reducing, the rejection of a porcine xenograft by a patient comprising administration to the patient of a monoclonal antibody that is reactive with at least two types of pig APCs, is reactive with pig APCs of the same or different types from at least two strains or haplotypes of pig, inhibits a human/porcine xenogeneic mixed lymphocyte response, is not reactive with human APCs, and is not reactive with pig major histocompatibility molecules of Class I and Class II, in an amount sufficient to reduce rejection of such xenograft by the patient.

19. A method of therapeutically reducing the rejection of a porcine xenograft by a patient comprising administration to the patient of a monoclonal antibody produced by hybridoma 2D10 having ATCC designation HB- 11648 in an amount sufficient to reduce rejection of such xenograft by the patient.