IMMU-20. EVALUATION OF B7-H3 NANOBODY CAR-T CELLS IN PEDIATRIC GLIOBLASTOMA

Chimeric antigen receptor (CAR)-T cell therapies are an undoubted success in childhood acute lymphoblastic leukemia; however, this success has not translated clinically to any childhood solid tumor. B7-H3 has been found to be highly expressed in pediatric brain tumors and correlates with tumor progression and poor prognosis. We utilized a novel nanobody based CAR-T cell which can bind tumor antigens with high affinity. We hypothesize that anti-B7-H3 nanobody CAR-T cells mediate more potent antitumor effects both in vitro and in vivo compared to existing antibody-based B7-H3 CAR-T cells. High expression of B7-H3 was confirmed on the surface of two pediatric glioblastoma cell lines by flow cytometry and Quantibrite staining. B7-H3 nanobodies isolated from camel phage libraries were cloned into lentiviral CAR-T cell constructs. We manufactured CAR-T cells by lentiviral transduction of human T cells. Glioblastoma tumor cells were co-cultured with B7-H3 CAR-T cells vs. control T cells. We confirmed B7-H3 specific cytokine release by CAR-T cells via ELISA and effective tumor cell killing via two different cytotoxicity assays (impedance or luciferase based). Nanobody based B7-H3 CAR-T cells exhibited statistically significant higher cytokine release and cytotoxicity compared to antibody based B7-H3 CAR-T cells. In vivo studies are currently evaluating the efficacy of intracerebroventricular delivery of B7-H3 CAR-T cells against two orthotopic glioblastoma models utilizing multiple human donor T cells in immunocompromised mice. We are simultaneously developing a syngeneic orthotopic glioblastoma model to evaluate the nanobody based B7-H3 CAR-T cell cross-reactive in mice utilizing an immunocompetent model. Careful investigation of CAR-T cell therapy in appropriate immunocompetent in vivo models is needed to develop effective immunotherapy for clinical application.