Shortened T cell culture with IL-7 and IL-15 provides the most potent chimeric antigen receptor (CAR)-modified T cells for adoptive immunotherapy.

Abstract

Abstract Adoptive T cell immunotherapy involves the isolation, ex vivo expansion and reinfusion of T cells, and is dependent on T cell engraftment and persistence for efficacy. IL-2 is the most commonly used cytokine for ex vivo T cell culture; however, there is renewed interest in IL-7 and IL-15 due to their ability to enhance the survival and proliferation of stem cell memory (Tscm) T cells. Peripheral blood (PB) contains substantial numbers of Tscm, central memory (Tcm) and effector subsets. During ex vivo culture, PB T cells differentiate into cells with a predominantly CD45RO+, CD27−, CCR7− effector phenotype. Exogenous IL-7/15 delays this transition in phenotype and preserves a greater proportion of Tscm and Tcm cells. We hypothesize that limited ex vivo T cell culture in the presence of IL-7/15 rather than IL-2 will enhance engraftment and persistence of T cells in vivo. We show that T cells can be harvested from ex vivo cultures as early as day 3 (d3) following activation. T cells expressing a chimeric antigen receptor targeting CD19 (CART-19) show potent yet specific cytotoxicity in vitro. We investigated the therapeutic potential of cells harvested at d3 versus later time points using a Nalm-6 leukemic cell xenograft mouse model. We demonstrate that d3 CART-19 cells show potent anti-leukemic activity compared to day 5 or day 9 cells. Comparing CART19 cells cultured in IL-2 or IL-7/15 for 3 or 9 days, we show that mice treated with d3 cells cultured in IL-7/15 exhibit the greatest anti-leukemic efficacy at a 10-fold lower dose compared with day 9 cells. In summary, we show that limiting T cell culture ex vivo to the minimum required for lentiviral transduction, in the presence of IL-7/15, provides the most efficacious T cells for adoptive immunotherapy.