Blockade of OX40/OX40L pathway combined with ethylene-carbodiimide-fixed donor splenocytes induces donor-specific allograft tolerance in presensitized recipients

Background: Memory T cells (Tms) are the major barrier preventing long-term allograft survival in presensitized transplant recipients. The OX40/OX40L pathway is important in the induction and maintenance of Tms. Methods: In this study, we added anti-OX40L mAb to ethylene-carbodiimide-fixed donor splenocytes (ECDI-SPs)-a method which is effective in inducing allograft tolerance in non-presensitized mouse heart transplant model. Recipient mice received heart transplantation after 6 weeks of donor skin presensitization and were treated with anti-OX40L mAb, ECDI-SPs or anti-OX40L mAb + ECDI-SPs, respectively. Results: Our data showed that the combination of ECDI-SPs and anti-OX40L mAb induced donor-specific tolerance in skin-presensitized heart transplant recipients, with the mechanism for this being associated with suppression of Tms and upregulation of CD4(+)CD25(+)Foxp3(+) T regulatory cells (Tregs). Importantly, CD25(+) T-cell depletion in the combined therapy-treated recipients broke the establishment of allograft tolerance, whereas adoptive transfer of presensitization-derived T cells into tolerant recipients suppressed Tregs expansion and abolished established tolerance. Conclusions: Blockade of OX40/OX40L pathway in combination with ECDI-SPs appears to modulate the Tms/Tregs imbalance so as to create a protective milieu and induce graft tolerance in presensitized recipients.