CD43 is a checkpoint against KLRG-1⁺CD49d^hi effector CD8⁺ T cell formation

Upon recognition of alloantigen, T cells rely on an array of costimulatory and coinhibitory receptors to shape their activation and function. The surface receptor CD43 has been reported to provide myriad functions on T cell related to adhesion, trafficking, and intracellular signaling. We investigated the role of CD43 on CD8⁺ T cells in vitro and in a fully allogeneic model of acute allograft rejection. Following polyclonal activation, CD43 did not impact the initial proliferation of CD8⁺ T cells, although CD43 deficient CD8⁺ T cells had mildly enhanced expression of IL-2Rα and PD-1 relative to CD43 wild-type CD8⁺ T cells (***p = 0.0008 and **p = 0.006, respectively). Following 7-9 days of in vitro culture, CD43 deficient CD8⁺ T cells had a stronger effector phenotype, displaying greater expression of Granzyme B, CD69, IL-2Rα, and PD-1. Following fully allogeneic skin grafting, alloantigen-specific CD43 deficient CD8⁺ T cells accumulated at greater numbers in the secondary lymphoid tissue and the allograft relative to CD43 wild-type CD8⁺ T cells (draining lymph nodes ***p = 0.007, spleen *p = 0.03). Hierarchical clustering and manual gating of revealed that CD43 deficient had an elevated frequency of effector populations with a CD62L^lo, KLRG-1⁺, and CD49d^hi phenotype, and that CD43 KO CD49d^hi cells preferentially infiltrated the allograft tissue (***p = 0.0001). Together, these data provide evidence that CD43 acts as a checkpoint of alloantigen-specific CD8⁺ T cell differentiation after transplantation.