Selective CD28 inhibition modulates alloimmunity and cardiac allograft vasculopathy in anti-CD154-treated monkeys

BACKGROUNDSelective CD28 inhibition is actively pursued as an alternative to B7 blockade using CTLA4-Ig based on the hypothesis that the checkpoint immune regulators CTLA-4 and PD-L1 will induce tolerogenic immune signals. We previously showed that blocking CD28 using a monovalent nonactivating reagent (single chain anti-CD28 Fv fragment linked to alpha-1 anti-trypsinsc28AT) synergizes with calcineurin inhibitors in nonhuman primate (NHP) kidney and heart transplantation. Here, we explored the efficacy of combining a 3-week ‘induction” sc28AT treatment with prolonged CD154 blockade. METHODSCynomolgus monkey heterotopic cardiac allograft recipients received sc28AT (10 mg/kg, d0-20, n=3), hu5C8 (10-30 mg/kg, d0-84, n=4), or combination (n=6). Graft survival was monitored by telemetry. Protocol biopsies and graft explants were graded according to ISHLT AR and CAV scores. Alloantibody, T cell phenotype and Tregs were analyzed by flow cytometry. Immunochemistry and gene expression (Nanostring) characterized intra-graft cellular infiltration. RESULTSRelative to modest prolongation of median graft survival time with sc28AT alone (34 days), hu5C8 (133 days) and sc28AT+hu5C8 (141 days) prolonged survival to a similar extent. CD28 blockade at induction, added to hu5C8, significantly attenuated the severity of acute rejection and cardiac allograft vasculopathy (CAV) during the first 3 months after transplantation relative to hu5C8 alone. These findings were associated with decreased proportions of circulating CD8 and CD3CD28 T cells, and modulation of inflammatory gene expression within allografts. CONCLUSIONSInduction with sc28AT promotes early cardiac allograft protection in hu5C8-treated NHPs. These results support further investigation of prolonged selective CD28 inhibition with CD40/CD154 blockade in NHP transplants.