Anti-Leukocyte Function-Associated Antigen 1 Therapy in a Nonhuman Primate Renal Transplant Model of Costimulation Blockade-Resistant Rejection.

Costimulation blockade with the fusion protein belatacept provides a desirable side effect profile and improvement in renal function compared with calcineurin inhibition in renal transplantation. This comes at the cost of increased rates of early acute rejection. Blockade of the integrin molecule leukocyte function-associated antigen 1 (LFA-1) has been shown to be an effective adjuvant to costimulation blockade in a rigorous nonhuman primate (NHP) model of islet transplantation; therefore, we sought to test this combination in an NHP renal transplant model. Rhesus macaques received belatacept maintenance therapy with or without the addition of LFA-1 blockade, which was achieved using a murine-derived LFA-1-specific antibody TS1/22. Additional experiments were performed using chimeric rhesus IgG1 (TS1/22R1) or IgG4 (TS1/22R4) variants, each engineered to limit antibody clearance. Despite evidence of proper binding to the target molecule and impaired cellular egress from the intravascular space indicative of a therapeutic effect similar to prior islet studies, LFA-1 blockade failed to significantly prolong graft survival. Furthermore, evidence of impaired protective immunity against cytomegalovirus was observed. These data highlight the difficulties in translating treatment regimens between organ models and suggest that the primarily vascularized renal model is more robust with regard to belatacept-resistant rejection than the islet model.

Islet transplantation in type 1 diabetics using an immunosuppressive protocol based on the anti-LFA-1 antibody efalizumab.

The applicability of islet transplantation as treatment for type 1 diabetes is limited by renal and islet toxicities of currently available immunosuppressants. We describe a novel immunosuppressive regimen using the antileukocyte functional antigen-1 antibody efalizumab which permits long-term islet allograft survival while reducing the need for corticosteroids and calcineurin inhibitors (CNI). Eight patients with type 1 diabetes and hypoglycemic unawareness received intraportal allogeneic islet transplants. Immunosuppression consisted of antithymocyte globulin induction followed by maintenance with efalizumab and sirolimus or mycophenolate. When efalizumab was withdrawn from the market in mid 2009, all patients were transitioned to regimens consisting of mycophenolate and sirolimus or mycophenolate and tacrolimus. All patients achieved insulin independence and four out of eight patients became independent after single-islet transplants. Insulin independent patients had no further hypoglycemic events, hemoglobin A1c levels decreased and renal function remained stable. Efalizumab was well tolerated and no serious adverse events were encountered. Although long-term follow-up is limited by discontinuation of efalizumab and transition to conventional imunnosuppression (including CNI in four cases), these results demonstrate that insulin independence after islet transplantation can be achieved with a CNI and steroid-free regimen. Such an approach may minimize renal and islet toxicity and thus further improve long-term islet allograft survival.

Co-stimulation with LFA-1 triggers apoptosis in gamma delta T cells on T cell receptor engagement.

Stimulation of T cells through the T cell receptor (TcR) initiate activation pathways, and paradoxically can also result in activation-induced cell death. Many factors influence a stimulated cell's decision to manifest one or the other. Here we show that co-stimulation with LFA-1 plays a key role in the choice between the two fates, differentiating between alpha beta and gamma delta T cells. Peripheral gamma delta. T cells but not alpha beta T cells undergo apoptosis upon co-cross-linking of TcR and LFA-1 in MRL lpr/lpr mice as well as +/+ mice. Our results suggest that apoptosis of gamma delta T cells is inducible by combined stimuli independent of the Fas-mediated pathway.