In Vivo Anti-Cd45rb Antibody-Induced Regulatory T Cells Demonstrate Species-Specific Tolerance To Discordant Human Xenogenic Islets

Organ transplantation-Sichuan Youth Science and Technology Innovation Research Team. Background: Although islet xenotransplantation has been proven to be a promising strategy for treatment of type 1 diabetes, it’s application in clinical setting would have to overcome acute cellular rejection and challenging species barrier. The aim of this study was to determine the role of Foxp3+ regulatory T cells (Treg) in anti-CD45RB induced dominant and specific tolerance to human islet cells in mice. Methods: One thousand and five hundred IEQ human islets were isolated from deceased donors and transplanted under the kidney capsule of B6 diabetic mice, B6µMT-/- mice and thymectomized µMT-/- mice. The recipients were then temporarily treated with low dose anti-CD45RB. CD4+Foxp3+Tregs were identified in the blood, spleen, draining lymph nodes and within the graft of tolerant and rejecting mice by FCM and immunohistochemistry. Additional anti-CD25 mAb was applied in the tolerant B6µMT-/-mice, which received another human islets simultaneously. The CD4+CD25+ Tregs sorted from the tolerant mice were adoptively transferred to diabetic Scid mice which were grafted with another human islets to assess the suppressive function. Results: In vitro, CD4+CD25-Foxp3-T cells which were activated with anti-CD3/anti-CD28 beads and cultured with anti-CD45RB demonstrated significant increase in Foxp3+ expression. In vivo, an increase of Foxp3+ T cells was observed in treated mice and more significant increase in tolerant mice, compared with a negligible increase in rejected mice. Anti-CD45RB alone allowed indefinite graft survival in 26.6% of B6 mice and 88.9% in µMT-/- mice, whereas none of xenografts were accepted in these mice treated simultaneously with anti-CD25. µMT-/-mice which were thymectomized and treated by anti-CD45 yielded 100% of grafts with long-term survival, which indicated that the transplant tolerance was thymus-derived Tregs independent. Moreover, the µMT-/-mice which tolerated to the first human islets accepted the re-transplanted second party of islets from another human, whereas the tolerance was hampered by anti-CD25 treatment. Adoptive cell transfer model showed the CD4+CD25+ Tregs from the mice tolerant to the first human islets prolonged survival of the second human islets, compared to natural Tregs (p < 0.05). Conclusions: These data suggest that anti-CD45RB-induced tolerance in islet xenotransplantation is mediated by Tregs expansion. These tolerant Tregs had the potent capacity to transfer dominant and species-specific tolerance. The National Natural Science Foundation of China (No. 81172832, 81771723). Sichuan Youth Science and Technology Foundation (2013JQ0020). Special Program for Sichuan Youth Science and Technology Innovation Research Team (2014TD0010).