Third generation CAR T cells form polyfunctional long-lived memory and protect from solid-tumor relapse in an immunocompetent murine model

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Abstract Effector CAR T cell persistence and transition to memory have been widely associated with long-term protection from hematological tumor relapse. In the context of solid tumors, anti-tumor T cell exhaustion in the tumor microenvironment (TME) leads to T cell dysfunction and impaired memory formation. However, in solid tumor models a vast number of infused CAR T cells traffic to lymphoid organs (such as spleen and nondraining lymph nodes), which are bereft of CAR-antigen. The fate of these CAR T cells which have undergone ex vivo activation, viral transduction, and expansion regimens prior to transfer back into patients remains unclear. Using a third generation CAR targeting human(h)CD19t, and syngeneic murine tumor lines expressing hCD19t tumor-associated antigen, we show that CAR T cells residing in antigen-free sites of tumor-bearing immunocompetent mice transition to fully functional memory cells. Using viral infection-induced memory T cells as a benchmark, memory CAR T cells displayed hallmark memory characteristics including homeostatic proliferation, rapid polyfunctional cytokine production upon restimulation, and secondary expansion in response to cognate antigenic stimulation. Finally, memory CAR T cells in naive mice, or in mice with primary tumor remission, were protected against lethal rechallenge with heterologous hCD19t-expressing tumors. Results from this study are among the first to directly compare canonical virus-induced memory T cells with memory CAR T cells, and provide valuable insight into the characteristics and function of memory CAR T cells in an immunocompetent model for solid tumors. Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number F32CA265056, and the Pediatric Cancer Research Foundation