IM-7 Identification of novel glioblastoma specific antigen using patient derived tumor cell for CAR-T cell therapy

Chimeric antigen receptor T (CAR-T) cell therapy is a newly developed antitumor immunotherapy presenting remarkable clinical response with leukemia, and is expected to be applied to other malignant solid tumors including glioblastoma (GBM). However, for development of CAR-T therapy against GBM, identification of novel and suitable tumor specific antigen is required to expect higher therapeutic efficacy. Herein, we developed our original method to detect novel GBM specific antigen using patient derived GBM (PD-GBM) cells. First, BALB/c mice were immunized by footpad injection of PD-GBM cells. B cells were extracted from lymph nodes of the mice, fused with murine myeloma cells, and then cultured to produce monoclonal antibodies for GBM cells. About 500 GBM binding monoclonal antibody lines were established, and then each antibody was again analyzed by flow cytometry with multiple PD-GBM cells and human non-tumor brain cells to find out GBM specific antibodies. Consequently, two GBM specific antibody lines were selected and genetically analyzed to identify the recognized antigen. CAR-T cells targeting the detected antigens were successfully generated, and the cytotoxicity against GBM cells was confirmed by chromium releasing assay and bioluminescent cytokine assay. Remarkably, one of the identified tumor specific antigens proved to be B7-H3, which is known pan-cancer antigen expected to be one CAR-T therapeutic target for malignant solid tumors, also expressed in most GBM cells. This result confirms that our experimental method using murine antigen-antibody reaction is feasible for detecting antigen as a novel CAR-T therapeutic target for GBM. Moreover, this method can also detect antigens derived from post-translational conformational changes such as glycosylation, which might have been overlooked by conventional methods. In addition, these results suggest our method using PD-GBM cells can identify potential targets of CAR-T therapy for each GBM patients respectively, thus leading to precision immunotherapy for GBM.