Persistent STAT5 signaling in polyfunctional CD4 T cells and its application in adoptive T cell therapy

Project summary/abstract Recent advances in adoptive T-cell therapy (ACT), especially CD19-targeting chimeric antigen receptor (CAR) T-cell therapy (CD19CART), have highlighted the potential of immunotherapy to achieve durable and curative patient outcomes. However, even for the well-developed CD19CART, many patients have failed to respond to the treatment or succumbed to late relapse. Moreover, so far ACT in general has not been effective in treating most solid tumors. The major barriers to effective ACT include deficiencies in donor T cell expansion, persistence and tumor- infiltration, as well as loss of T-cell effector function - a process termed exhaustion. There is increasing demand for novel strategies that can overcome these barriers to improve the efficacy of ACT. The presence of CD4 T cells with a polyfunctional phenotype, characterized by concomitant production of multiple inflammatory cytokines, has been associated with favorable therapeutic outcomes in preclinical models and cancer patients. However, how to generate polyfunctional CD4 (pfCD4) T cells suitable for ACT remains elusive. We previously reported that CD4 T cells exposed to interleukin 7 (IL7) during antigenic stimulation can acquire polyfunctionality in a STAT5-dependent manner. Our recent work demonstrated that ectopic expression of a constitutively active form of STAT5 (CASTAT5) in CD4 T cells induces genome- wide transcriptional and epigenetic remodeling in tumor-specific CD4 T cells, endowing these cells polyfunctionality, exhaustion-resistance and tumor-infiltrating capability. Importantly, CASTAT5 can markedly improve the expansion and persistence of CD19CAR T cells, resulting in high cure rate in mice with advanced lymphoma. These new findings form the basis of our central hypothesis that CASTAT5-induced epigenetic remodeling endows CD4 T cells polyfunctionality and exhaustion-resistance, and these features equip CD4 T cells with superior helper activities to orchestrate potent antitumor immune responses. This cross-disciplinary multi- PI project will employ our well-characterized ACT model systems in conjunction with cutting-edge epigenomics and single cell RNA sequencing technologies to advance our understanding of the ontogeny, heterogeneity, regulatory circuitry and mechanism of action of pfCD4 T cells. Specifically, we will investigate how persistent STAT5 signaling induces and maintains pfCD4 T cells (Aim 1), how CASTAT5-induced pfCD4 T cells potentiate ACT (Aim 2), and the potential utility of CASTAT5 in human CD19CAR T cells (Aim 3). Successful completion of this project will establish CASTAT5 as a clinically applicable strategy to overcome the barriers impeding effective ACT including CAR T cell therapy.