Variegated levels of alloreactive T cell dysfunction in transplantation tolerance determine graft vulnerability to infection-triggered rejection

Abstract While advances have been made in therapies that achieve tolerance in mouse models of transplantation, successful tolerance remains vulnerable to inflammatory insults, which can trigger graft rejection. To identify strategies for improving the robustness of tolerance, we aim to better understand the mechanisms by which grafts are rejected after donor-specific tolerance is established. In a mouse model of cardiac allograft tolerance in which late infection with Listeria monocytogenes (Lm) can trigger graft rejection, we previously showed that host CD4 +T cells reactive to host MHC-II presenting a donor MHC-I-derived peptide (TCR75 cells) became intrinsically dysfunctional if the alloantigen persisted for 3 weeks or greater. Intriguingly, infection-dependent transplant rejection was not associated with transcriptional or functional reinvigoration of these cells. We hypothesized that there might be heterogeneity in the level of dysfunction of alloreactive T cells depending on duration of their cognate alloantigen persistence. Unlike TCR75 cells, CD4 +T cells specific for host MHC-II presenting a peptide derived from donor MHC Class II (TEa cells), a graft antigen that declines post-transplantation, retained functionality during tolerance induction. Consequently, TEa but not TCR75 cells expanded following Lm-infection, supporting a role for TEa-like cells in driving infection-triggered rejection. Prolonging T cell exposure to cognate alloantigens aggravated TEa dysfunction and rendered grafts resistant to Lm-dependent rejection. These findings demonstrate that inducing dysfunction in a broader array of allospecific T cells, by prolonging exposure to more alloantigens, lessens graft vulnerability to infections. Supported by the UChicago Growth Development and Disabilities Training Program (T32 HD007009). AHA predoctoral fellowships (20PRE35210946, 3PRE14550022 and 15PRE22180007). NIH T32-AI007090. UChicago Cardiovascular Pathophysiology and Biochemistry Training Grant (T32 HL07237). HHMI Med-into-Grad Program training grant (56006772). NIAID Grant P01AI-97113.