Analysis of the epigenetic profiles for HER2 CD8+ CAR T cells cultured under short-term resting conditions and overexpressing FOXO1WT
T cell exhaustion and metabolic dysfunction induced by chronic antigen stimulation within the tumor microenvironment represent formidable obstacles in CAR T cell therapy for solid tumors. Previously, we developed a method to convert effector/exhausted CAR T cells that emerge from repeated antigen stimulation into stem cell memory-like CAR T (termed CAR-iTSCM) cells. These CAR-iTSCM cells exhibit expression of early memory markers and enhanced mitochondrial metabolism after quiescence under culture conditions containing IL-7, CXCL12, and the NOTCH-ligand. However, we noticed that this strategy was effective for CD19-CAR used for blood cancers, but not for HER2 CAR commonly used to treat solid tumors, due to tonic CAR signals. In this study, we developed a new culture condition for CAR iTSCM cells suitable for HER2 CAR and elucidated the mechanism of induction of stemness and mitochondrial fitness. We found that short-term resting condition with IL-7, CXCL12, and pan-tyrosine kinase inhibitor, Dasatinib can induce stem-like CAR T cells at the epigenetic level and enhance mitochondrial metabolism. We identified FOXO1 as a critical regulator in the process of epigenetic and metabolic reprogramming, and anti-tumor activity. We found that overexpression of FOXO1 leads to enhanced mitochondrial metabolism, efficient CAR T cell expansion, and potent anti-tumor effects through epigenetic modifications. These findings suggest that regulating the transcriptional activity of FOXO1 is a promising strategy for engineering effective CAR T cells for treating solid tumors. In this analysis, we aimed to  investigate the effects of the resting conditions (IL-7+CXCL12+IGF-I +Dasatinib) and FOXO1 overexpression on the epigenetic profiles in 4-1BB-based HER2 CAR T cells which exhibit tonic signals-induced exhaustion hallmarks. Overall design: We performed bulk ATAC-seq analysis using four different HER2 CAR T cells (Empty, FOXO1WT, 7/12/I, and 7/12/I + Das). Each CAR T cells were generated from different two healthy donors (n=2).