The epigenetic regulation of alloimmune stem-like CD4+ T cells

About This Grant

Summary T cells are central to transplant rejection, driving allograft destruction through differentiation into effector cells. However, the mechanisms by which effector T cells sustain persistent alloimmune responses remain unclear. Our recent studies have identified a subset of “stem-like” T cells within the alloreactive pool. These stem-like T cells possess two fundamental features: self-renewal and the capacity for continuous differentiation into effector T cells. Importantly, terminal effector T cells, despite having all the cardinal features of effector activity, rapidly undergo apoptosis and fail to sustain graft rejection in vivo. This underscores the critical role of stem-like T cells, which continuously generate effector T cells to drive allograft rejection. Understanding the fundamental mechanisms regulating T cell stemness is a key question with significant therapeutic implications. Our preliminary data reveal that T cell stemness is epigenetically regulated by enhancer of zeste homolog 2 (EZH2), the catalytic subunit of the Polycomb Repressive Complex 2 (PRC2). EZH2 functions as a histone methyltransferase, catalyzing the trimethylation of histone H3 at lysine 27 (H3K27me3), a key marker of gene repression. Deletion of Ezh2 in T cells completely abrogates their differentiation into effector cells. Furthermore, mice with T cell-specific EZH2 deletion (Ezh2fl/flCd4-Cre) or WT mice transiently treated with an EZH2 inhibitor (DZNep) accepted heart allografts long term (>100 days). These results suggest that EZH2 deletion/inhibition disrupts the stemness of alloreactive T cells, rendering them unable to sustain graft rejection. The central goal of this proposal is to elucidate how EZH2, an epigenetic repressor, regulates T cell stemness. We hypothesize that EZH2 preserves two key features of stem-like T cells: maintaining their long-term functional persistence and enabling their differentiation into effector cells. This hypothesis will be tested through two aims: Aim 1: Investigate whether EZH2-mediated repression of key transcription regulators is required for the differentiation of stem-like T cells into effector cells. Aim 2: Investigate whether EZH2 preserves T cell stemness by epigenetically repressing genes involved in apoptosis, cell cycle arrest, and functional exhaustion. Successful completion of these studies will uncover the epigenetic mechanisms governing stem-like T cell persistence and effector differentiation, providing a foundation for novel therapeutic strategies to improve transplant outcomes.