Anti-CTLA-4 Treatment Abrogates Co-stimulation Blockade-induced Acceptance of Transgenic Porcine Islets in Humanized Mice.

Background: In previous studies, we showed that beta cell-specific overexpression of high-affinity variant of human CTLA-4 (LEA29Y), a high-affinity variant of cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4)-immunoglobulin, prevented porcine islet rejection in humanized mouse models. We here investigate whether long-term xenograft function and survival is maintained after neutralization of LEA29Y-mediated co-stimulation blockade.

Methods: Diabetic humanized NOD-SCID IL2rγ-/- mice were transplanted with transgenic neonatal porcine islet-like clusters expressing LEA29Y under control of the porcine insulin promoter. After development of normal glucose tolerance, mice were treated with blocking anti-CTLA-4 antibody (Ab) or isotype control Ab. Reoccurrence of diabetes, plasma cytokines/chemokines and graft histology were analyzed.

Results: Systemic treatment with an inhibitory anti-humanized CTLA-4 Ab led to a significant increase of pro-inflammatory plasma cytokine production (interferon gamma, monokine induced by interferon gamma; P < 0.05) at day 14 and reoccurrence of diabetes in 100% of the animals within 40 d after Ab application (P = 0.01). Strong infiltration with human CD45+ cells consisting mainly of CD4+ and CD8+ T cells and some B lymphocytes and few destructed remaining beta cells were observed in the treatment group indicating rapid and severe graft rejection.

Conclusions: The present data demonstrate that long-lasting acceptance of LEA29Y transgenic porcine islet grafts is dependent on CTLA-4/LEA29Y signaling even several months after transplantation. This finding has important implications on safety of pig islet xenotransplantation in patients with type 1 diabetes because it provides a potent tool for graft elimination in case of medical indication.