Induction of operational tolerance to allografts and xenografts

Abstract: Inhibition of the costimulatory molecules B7 and CD40L with CTLA4Ig and anti-CD40L administered only during the first week after transplantation induces indefinite survival of allo- and xenogeneic heart transplants and significantly prolongs skin grafts in C3H mice. However, this treatment protocol is not as effective in C57BL/6 mice which reject skin transplants with nearly the same median survival time as untreated controls. This has been shown to be due to the ability of CD8+ T cells to be activated autonomously of B7 or CD40L costimulation. LFA-1 is an important signaling molecule for CD8+ T cell function and we therefore hypothesized that its inhibition may compliment B7 and CD40L blockade and induce indefinite survival of transplants in mice. Anti-LFA-1 combined with CTLA4Ig induced indefinite survival of heart transplants after one week of treatment. Anti-LFA-1 also prevented immune responses and chronic vasculopathy in CD40L -/- mice. When CTLA4Ig was combined with anti-LFA-1 and given to CD40L -/- mice, dopaminergic porcine xenografts were accepted without any signs of rejection. The combination of anti-CD40L, CTLA4Ig and anti-LFA-1 induced permanent acceptance of dopaminergic porcine grafts in wild-type C57BL/6 mice. Surprisingly these recipients could be induced to rejected their grafts if challenged with glia cells of donor origin indicating that regulatory T cells maybe involved in the acceptance of these transplants. In order to ascertain the importance of regulatory T cells, IL-10 deficient mice were transplanted with allogeneic heart transplants and treated with costimulation blockade. A majority of these hearts stopped beating two days after transplantation succumbing to a massive neutrophilic infiltrate resembling myocardial infarction. The remaining hearts were rejected with in 50 days after transplantation. These results indicate that anti-LFA-1 can compliment CTLA4Ig and anti-CD40L in the induction of operational tolerance and that this state is facilitated by IL-10 and indirectly regulatory T cells.