CONTROL OF CD8 T CELL EXHAUSTION BY EZH2: IMPACT IN ANTI-TUMOR RESPONSE

In chronic infections and cancer, CD8 T cells undergo progressive decrease of effector function, loss of proliferation capacity and gain of inhibitory receptors. This loss of functionality, known as T cell exhaustion, also affects CAR (Chimeric Antigen Receptor) T cells immunotherapy for solid tumors, compromising disease control (Oncogene (2021) 40:421). Our prior data in a viral exhaustion model, the murine LCMV clone 13 infection, revealed that early generated exhausted CD8 T cells expressed lower levels of the epigenetic modulator Ezh2 (Enhancer of zeste homolog 2) which is the catalytic subunit of the Polycomb Repressor Complex 2, that trimethylates histone 3 at the lysine residue 27, and has been reported as critical to CD8 T cell effector differentiation and anti-tumor response (Nat. Immunol. (2015) 17:95). Here, we aimed to evaluate the role of Ezh2 in CD8 T cell exhaustion and the relevance of modulating its levels for advance in experimental immunotherapies. In vitro activated Ezh2 deficient CD8 T cells from Ezh2^fl/fl Cd4 Cre mice exhibited impaired proliferation and production of IFN-γ and TNF, along with increased expression of exhaustion associated molecules PD-1, TIM-3 and CD38. Similar phenotype was replicated by pharmacological inhibition of Ezh2 in wild type CD8 T cells. In vivo, we observed that Ezh2 overexpression in CD8 CAR T cells polarized into a memory-like phenotype and targeting mice B16-hCD19 melanoma led to an increase in Ki67 and granzyme B production, but did not provide significative gain in restraining tumor size when compared to control groups. Lastly, in a preliminary experiment, transfer of effector-like CD8 CAR T cells overexpressing Ezh2 also resulted in increased production of Ki67 and granzyme B, along with a tendency in tumor size reduction (CEUAS: 041/20 and 107/23). Together, our results reinforce Ezh2 cruciality for effector differentiation of CD8 T cells and suggest its modulation for improvements in CAR T cell function.