IL-6 blockade prevents costimulation blockade-resistant allograft rejection by promoting intragraft regulation in T cell-depleted recipients [GIL]

The efficacy of costimulation blockade (CTLA4Ig/belatacept) in transplantation is reduced by an increased incidence of T cell-mediated rejection, which also persists after induction therapy with anti-thymocyte globulin (ATG). Herein, we investigate why ATG fails to prevent costimulation blockade-resistant rejection and how this barrier can be overcome. ATG did not prevent graft rejection in a murine heart transplant model of CTLA4Ig therapy and induced a pro-inflammatory cytokine environment. While ATG improved the balance between Tregs and effector T cells in the peripheral compartment, it had no such effect within cardiac allografts, which showed signs of inflammation. Neutralizing IL-6 alleviated inflammation, increased intragraft Treg frequencies long-term, and enhanced intragraft IL-10 and Th2 cytokine expression. IL-6 blockade together with ATG led to long-term, rejection-free heart graft survival under CTLA4Ig therapy. Combining ATG with IL-6 blockade prevents costimulation blockade-resistant rejection, thereby eliminating a major impediment to clinical use of costimulation blockers in transplantation. Overall design: to investigate the effects of IL-6 blockade on intragraft leukocyte signaling patterns, we performed gene expression profiling of data obtained via RNAseq of flow sorted graft infiltrating leukocytes isolated from fully mismatched murine cardiac allografts explanted from recipients treated with or without IL-6 blockade explanted 14 days after transplantation.