Anti-lymphocyte function-associated antigen-1 monoclonal antibody inhibits CD40 ligand-independent immune responses and vasculopathy in CD40 ligand-deficient mice

Background. Blockade of CD40 ligand (CD40L; CD154, gp39) is a potential treatment for autoimmune disease and allograft rejection. However, CD40L-/- mice are capable of mobilizing cellular immune responses to viral, parasitic, and intracellular bacterial infections as well as rejecting skin grafts with nearly the same efficiency as wild-type mice. CD40L-deficient mice (CD40L-/-) or wild-type mice treated with anti-CD40L develop chronic vasculopathy only 8 weeks after allogeneic heart transplantation. To overcome CD40L-independent immune responses, we used antilymphocyte function-associated antigen monoclonal antibody (LFA)-1, which has previously been shown to inhibit CD8(+) immune responses. Methods. We conducted mixed lymphocyte reactions, cytotoxicity assays, skin transplantation, and vascularized heterotopic heart transplantation in wild-type B6 and CD40L-deficient mice in the presence and absence of anti-LFA-1 to study the effects of anti-LFA-1 in the absence of CD40L signaling. Results. Anti-LFA-1 inhibited proliferation of naive CD40L-/- mixed leukocyte reactions and the lysis of donor targets by CD40L-/- cytotoxic T lymphocytes. Anti-LFA-1-treated CD40L-/- mice that received fully MHC-mismatched skin grafts showed significant prolongation of graft survival, with a median survival time of 55 days (mean 66 days) compared with 13 and 21 days in wild-type and CD40L-/- controls, respectively. CD40L-/- mice that received fully MHC-mismatched vascularized heart transplants treated with four doses of 200 fig of anti-LFA-1 at the time of transplantation did not develop any signs of chronic vasculopathy 150 days after transplantation. Conclusion. These results indicate that anti-LFA-1 can complement CD40L inhibition in the prevention of undesirable immune responses.