BLOCKADE OF THE CD40-CD154 PATHWAY USING A CHIMERIC ANTI-HUMAN CD40 MONOCLONAL ANTIBODY SYNERGIZES WITH CD28 BLOCKADE TO PROLONG ISLET ALLOGRAFT SURVIVAL (2004)

O457* Intro: Islet transplantation is emerging as an increasingly viable treatment option for type I diabetes. Further application of this therapy is limited in part by the side effects associated with the immunosuppressive agents currently used to prevent rejection. In recent years reagents have been developed that specifically target signals critical for effective T cell activation and function. Manipulation of the CD28/B7 and CD40/CD154 pathways has exhibited extraordinary promise particularly when the pathways are blocked simultaneously. Despite the reported efficacy of anti-CD154 in rodents and higher models its future clinical use is uncertain due to reported thromboembolic events in clinical trials. To circumvent this potential complication we developed and evaluated a chimeric antibody targeting CD40 as an alternative to CD154. Methods: Total pancreatectomy was used as a model of insulin dependent diabetes in Rhesus macaques. Donor/recipient pairs were selected from divergent colonies and class I/II disparity documented by molecular typing. Islets were prepared and >10,000 IEQ/kg were transplanted via intra-portal infusion. Animals received either LEA29Y alone (0,4,7,14, then every 2 wks for three months then monthly through 6 months), anti-CD40 alone (2wk course), or LEA29Y and anti-CD40 (same regimens). Rituximab (anti-human CD20, 2wk course) Results: The anti-CD40 was tested alone and in combination with a high-affinity mutant form of CTLA4-Ig, LEA29Y, in non-human primate model of islet transplantation. While either agent alone only modestly prolonged islet survival (anti-CD40 alone 14, 16, and 84 days, LEA29Y alone 58 and 60 days), the combination (LEA29Y and anti-CD40) dramatically induced long-term survival (237, 237, 220, >185, and 172 days). Recent published work has suggested that the mechanism of action of anti-CD154 is in part depletional. The chimeric anti-CD40 Ab used in this study profoundly depleted peripheral B cells. To investigate whether the prolonged survival induced by the anti-CD40/LEA29Y was dependent on B cell depletion we tested LEA29Y in combination with Rituximab (anti-human CD20) which effectively depleted B cells. We found that the effects of the anti-CD40 treatment were not mediated by deletion of CD20 bearing cells as animals treated with anti-CD20 and LEA29Y rejected quickly following transplantation (14 and 16 days). We also found despite profound depletion of peripheral B cells the combined therapy (LEA29Y/anti-CD40)did not significantly impair established anti-viral immunity. Conclusions: Rodent data has demonstrated immunosuppressive synergy when both the CD40 and CD28 pathways are targeted. Here we report for the first time synergistic activity when anti-CD40 mAb is combined with LEA29Y. Anti-CD40 avoids the potential thromboembolic complications associated with anti-CD154 and thus could be a viable option for clinical application in transplantation. Such a regimen provides effective immunosuppression while avoiding many of the side effects associated with current conventional immunosuppressive therapies thereby potentially expanding the number of patients who could benefit from islet transplantation.