Combined costimulation blockade prevents rejection of allogeneic islets in mice

There is a need for immunosuppressive protocols in islet transplantation that are neither nephrotoxic nor diabetogenic. We have examined blockade of the CD28-B7, CD40-CD40L and ICAM-LFA-1 pathways in a model of allogeneic islet transplantation in mice to determine the efficacy of this blockade in prolongation of graft survival. Histological evidences of inflammation and function were evaluated in grafts that had been functioning for 100 days. Treatment with a combination of all three drugs, or with CTLA4Ig and anti-CD40L, administered four times during the first six postoperative days, resulted in an excellent graft survival. All animals had a graft survival of >100 days (i.e. indefinitely). Mice treated with CTLA4Ig and anti-CD40L all showed well-preserved islets without signs of degeneration or destruction. There were no signs of rejection, as evidenced by the absence of infiltrating lymphocytes. This group had the least amount of rejection/inflammation changes according to ranking of all grafts. In conclusion, a short induction treatment with anti-CD40L and CTLA4Ig totally prevents rejection and preserves the allogeneic islets transplanted to mice. The addition of anti-LFA-1 did not confer any benefit.