Blockade of CD28-B7, but not CD40-CD154, prevents costimulation of allogeneic porcine and xenogeneic human anti-porcine T cell responses

Despite increasing use of swine in transplantation research, the ability to block costimulation of allogeneic T cell responses has not been demonstrat ed in swine, and the effects of costimulatory blockade on xenogeneic human anti-porcine T cell responses are also not clear, We have compared the in v itro effects of anti-human CD154 mAb and human CTLA4IgG4 on allogeneic pig T cell responses and xenogeneic human anti-pig T cell responses. Both anti- CD154 mAb and CTLA4IgG4 cross-reacted on pig cells. While anti-CD154 mAb an d CTLA4IgG4 both inhibited the primary allogeneic pig MLRs, CTLA4IgG4 (7.88 mu g/ml) was considerably more inhibitory than anti-CD154 mAb (100 mu g/ml ) at optimal doses. Anti-CD154 mAb inhabited the production of IFN-gamma by 75%, but did nut inhibit IL-10 production, while CTLA4IgG4 completely inhi bited the production of both IFN-gamma and IL-10, In secondary allogeneic p ig MLRs, CTLA4IgG4, but not anti-CD154 mAb, induced Ag-specific T cell aner gy, CTLAIgG4 completely blocked the indirect pathway of allorecognition, wh ile anti-CD154 mAb blocked the indirect response by approximately 50%, The generation of porcine CTLs was inhibited by CTLA4IgG4, but not by anti-CD15 4 mAb, Human anti-porcine xenogeneic MLRs were blocked by CTLA4IgG4, but on ly minimally by anti-CD154 mAb, Finally, CTLA4IgG4 prevented secondary xeno geneic human anti-porcine T cell responses. These data indicate that blocka de of the B7-CD28 pathway was more effective than blockade of the CD40-CD15 4 pathway in inhibiting allogeneic pig T cell responses and xenogeneic huma n anti-pig T cell responses in vitro, These findings have implications for inhibiting cell-mediated immune responses in pig-to-human xenotransplantati on.