EPEN-04. DEVELOPMENT OF B7-H3-TARGETED CAR T CELL THERAPY FOR EPENDYMOMA

Targeted treatment options are desperately needed for ependymomas (EPN). Chimeric antigen receptor (CAR) T cells have immense potential to positively transform treatment outcomes; however, little is known regarding antitumor efficacy of CAR T cells against EPNs. We found that B7-H3 is highly expressed on pediatric brain tumor patient-derived orthotopic xenografts from EPN patients, making it a promising target for CAR-T cells. The project’s goal is to develop a safe, effective B7-H3 targeted CAR T cell immunotherapy for EPN. We generated second generation human B7-H3-CAR T cells and examined their anti-EPN cytolytic activity, expansion, and cytokine production. We found that B7-H3-CAR T cells had potent in vitro antitumor activity against all EPN cell lines tested (1425, ST1, CPITT, ST2, EPI, L6SJ). In repeated-stimulation assays, CAR T cells expanded 7-10 times, and up to one million-fold when co-cultured with EPN cells. Interestingly, while the EPN cells were found to secrete high levels of C-C motif chemokine ligand 2 (CCL2) which is consistent with published data, our Multiplex analysis of co-culture supernatants shows that CCL2 production increased up to 10-fold when EPN cells were co-cultured with CAR T cells. Finally, we demonstrate that B7-H3-CAR T cells had antitumor activity in a supratentorial-EPN xenograft mouse model (1425 cell line) without apparent toxicities, although 4 out of 12 tumors re-lapsed. Recurrent tumor analysis is underway. Together, our data shows establishment of a clinically relevant model to study resistance to CAR T cell therapy in EPN, and preliminary mechanistic insight into CAR T cell persistence and modulation through CCL2 signaling. Given that little is known about the function of CCL2 and its receptor, C-C chemokine receptor type 2 (CCR2) in EPNs or CAR T cells, future work will focus on defining these biological mechanisms, enabling us to develop improvements to B7-H3-CAR T cells for EPN.