(J-393) Investigating RASA2 Overexpression to Reduce CAR T Cell On-Target Off-Tumor Toxicity

Despite the remarkable efficacy of CAR T cell therapies in the treatment of B cell cancers, their ability to effectively treat solid tumors is hindered by many factors, including on-target, off-tumor toxicity. In prostate cancer, malignant cells upregulate prostate-specific membrane antigen (PSMA), which can be targeted by CAR T cells. However, this protein is also present in healthy tissues at a lower density and may partially explain a patient's death in a recent anti-PSMA CAR T trial for prostate cancer1. To combat toxicities associated with CAR T cells targeting off-tumor antigens, this study aims to decrease the sensitivity of anti-PSMA CAR T cells via intracellular signaling modulation. Previous work has shown that knocking out RASA2, a RAS GTPase-activating protein, increases the sensitivity of CAR T cells2. Therefore, we hypothesized that by overexpressing RASA2, CAR T cell sensitivity will be reduced and enable selective killing of high antigen density malignant cells while sparing low antigen density healthy cells. In this work, we found that RASA2 overexpression does not appear to decrease PSMA CAR T cell antigen density threshold and expansion, but it may decrease CAR expression. Although RASA2 overexpression may not be an ideal target to engineer CAR T cell sensitivity, intracellular signaling pathways are complex systems that may yet contain additional targets with the potential to improve CAR T cell therapies for solid tumors.