Modulating costimulation in CAR T cells to enhance antitumor efficacy

Project Summary Innovative adoptive cellular therapies have emerged as revolutionary treatment options for patients with hematologic malignancies. One such promising strategy, Chimeric Antigen Receptor (CAR) T cell therapy, involves genetic modification of autologous T cells to express a CAR, redirecting the cytotoxic response of T cells towards hematologic tumors expressing human B cell maturation antigen (hBCMA) on multiple myeloma or CD19 on B cell lymphomas and leukemias. While response rates to CAR T cell therapy are strikingly high in patients with hematologic malignancies, most patients experience disease relapse, highlighting the urgent need to improve CAR T cell efficacy for a durable response. Preliminary data from our lab and published literature indicate that targeting endogenous CD28 on CAR T cells is a viable approach to enhance CAR T cell efficacy. The CAR contains a costimulatory domain (such as CD28), which undergoes activation upon ligation of the target antigen to the CAR, delivering costimulatory signals to contribute to CAR T cell activation, leading to subsequent CAR T cell effector functions. Importantly, as the CAR is integrated into T cells, T cells also express natural endogenous CD28, which can engage CD28 ligands in the tumor microenvironment or on other T cells themselves, providing yet another source of costimulatory signals that contribute to CAR T cell activation. Interestingly preliminary data from our lab show that deletion of endogenous CD28 enhances the functional persistence of CAR T cells in vivo. As such, we hypothesize that endogenous CD28 contributes to the overstimulation of CAR T cells which increases exhaustion, decreases persistence, and hampers efficacy. To test our hypothesis, will rigorously evaluate how knockout of endogenous CD28 using CRISPR/Cas9 technology affects CAR T cell function and efficacy using established preclinical in vitro and in vivo models. These studies have the potential to identify a novel role of endogenous CD28 in hindering CAR T cell efficacy, while highlighting a clinically relevant strategy to improve CAR T cell efficacy.