Treatment with the humanized CD154-specific monoclonal antibody, hu5C8, prevents acute rejection of primary skin allografts in nonhuman primates.

BACKGROUND: Allogeneic skin transplantation remains a rigorous test of any immune intervention designed to prevent allograft rejection. To date, no single, clinically available immunosuppressant has been reported to induce long-term primary skin allograft survival in primates. We have previously shown that treatment with the humanized CD154-specific monoclonal antibody, humanized 5C8 (hu5C8), induces long-term renal allograft survival in nonhuman primates. In this study, we evaluated the efficacy of hu5C8 in preventing primary skin allograft rejection in rhesus monkeys. METHODS: Ten rhesus monkeys were transplanted with full-thickness skin allografts mismatched at both class I and class II major histocompatibility loci. Of these, two were given no treatment, five were treated with hu5C8 alone, and three received hu5C8 combined with whole blood donor-specific transfusion (DST). All recipients also received skin autografts for comparison. Animals were followed by inspection, serial biopsy, mixed lymphocyte culture, and alloantibody determination. RESULTS: Treatment with hu5C8 alone or hu5C8 plus DST greatly prolonged allograft survival. Rejection occurred in the untreated group within 7 days. Mean allograft survival in the monotherapy hu5C8 group was >236 days and in the DST group was >202 days; these differences were not significant. Rejection eventually occurred in most animals. Allograft survival was not correlated with the development of T cell hyporesponsiveness in mixed lymphocyte culture. Rejection was not predicted by the development of donor-specific alloantibody. CONCLUSION: These results show that treatment with the CD154-specific monoclonal antibody, hu5C8, greatly delays the onset of acute skin allograft rejection.

Induction therapy with monoclonal antibodies specific for CD80 and CD86 delays the onset of acute renal allograft rejection in non-human primates.

CD80 and CD86 (also known as B7-1 and B7-2, respectively) are both ligands for the T cell costimulatory receptors CD28 and CD152. Both CD80 and CD86 mediate T cell costimulation, and as such, have been studied for their role in promoting allograft rejection. In this study we demonstrate that administering monoclonal antibodies specific for these B7 ligands can delay the onset of acute renal allograft rejection in rhesus monkeys. The most durable effect results from simultaneous administration of both anti-B7 antibodies. The mechanism of action does not involve global depletion of T or B cells. Despite in vitro and in vivo evidence demonstrating the effectiveness of the anti-B7 antibodies in suppressing T cell responsiveness to alloantigen, their use does not result in durable tolerance. Prolonged therapy with murine anti-B7 antibodies is limited by the development of neutralizing antibodies, but that problem was avoided when humanized anti-B7 reagents are used. Most animals develop rejection and an alloantibody response although still on antibody therapy and before the development of a neutralizing antibody response. Anti-B7 antibody therapy may have use as an adjunctive agent for clinical allotransplantation, but using the dosing regimens we used, is not a tolerizing therapy in this non-human primate model.