IMMU-03. DELETION OF RASA2 IN CAR T CELLS OVERCOMES DYSFUNCTIONAL IMMUNE SYNAPSE FORMATION AGAINST DIPGS, ENHANCING IN VITRO AND IN VIVO ANTITUMOR RESPONSE

Abstract

Abstract BACKGROUND Diffuse intrinsic pontine gliomas (DIPGs) are highly lethal pediatric brain tumors and a leading cause of cancer-related death in children. There is currently no cure for DIPG, highlighting an urgent need for novel therapeutics. Chimeric antigen receptor (CAR)-T-cell therapy offers great promise for DIPG treatment; however, several limitations need to be addressed. The goal of this study is to identify why CAR T cells are ineffective against DIPG and overcome this roadblock by improving the immune synapse (IS), or the interaction between tumor and CAR T cells. METHODS In this study, we targeted the tumor associated antigen B7-H3 by generating B7-H3 specific CAR T cells with CD28z signaling domain. We compared in vitro and in vivo antitumor response of CAR T cells against patient derived DIPGs and non-DIPG brain tumors. We contrasted the IS quality in DIPGs against other brain tumors by confocal microscopy. We further generated IS-enhanced CAR T cells by knocking out RASA2 and compared their performance against control KO in terms of IS-quality, killing kinetics, expansion, cytokine secretion, and in vivo tumor control. RESULTS Our data shows that CAR T cells have potent in vitro antitumor activity but fail in vivo against DIPGs which correlates with the formation of deficient IS, reflected by small synapses and poor calcium flux and cell polarity. RASA2 deletion in CAR T cells resulted in improved IS quality evidenced by bigger synapses, increased calcium flux, and CAR clustering upon antigen activation. In concordance, RASA2 KO CAR T cells elicited increased expansion, cytokine secretion, and in vivo antitumor activity against DIPGs compared to control KO. CONCLUSIONS This study shows that poor IS formation contributes to CAR T cell failure against DIPGs. Enhancing the IS formation in CAR T cells improves antitumor activity against DIPGs and should be considered for clinical translation.