Abstract PR04: GD2-directed chimeric antigen receptor T cells mediate potent antitumor effect and cure in xenograft models of diffuse intrinsic pontine glioma

Introduction: Diffuse intrinsic pontine glioma (DIPG) is a universally fatal pediatric brainstem tumor with a median survival of less than one year. Despite advances in the understanding of the molecular origins of DIPG, improvement in clinical outcomes has yet to materialize. To date, there has been little target exploration for immunotherapy applications in DIPG. Methods: Patient-derived DIPG cell cultures were screened for expression of more than 350 surface antigens as potential immunotherapeutic targets. The disialoganglioside GD2 was found to have the highest expression across cell cultures and was verified by IHC on post-mortem samples. Chimeric antigen receptor (CAR) T-cell therapy against this target was explored both in vitro and in vivo. Results: We found high levels of the disialoganglioside GD2 expressed on cell cultures derived from post-mortem samples of DIPG. Quantification of the number of GD2 molecules per cell demonstrated higher GD2 expression on DIPG than any other tumors, including neuroblastoma, for which GD2 targeted immunotherapy is part of the standard of care. Most cases of DIPG are caused by a mutation in Histone 3.3 (H3K27M). GD2 is highly and uniformly expressed in patient-derived H3K27M DIPG cultures, whereas H3 wild-type pediatric high-grade gliomas, including those diagnosed as DIPG, do not express significant levels of GD2. The H3K27M mutation is associated with increased levels of enzymes in the ganglioside synthesis pathway, suggesting that expression of the target antigen is driven by H3K27M-induced transcriptional dysregulation. Anti-GD2 CAR T cells with a 4-1BB costimulatory domain demonstrate remarkable preclinical activity against H3K27M DIPG. GD2 CAR T cells specifically kill DIPG cells and produce cytokines IL-2 and IFN- upon coculture with tumor. Systemic administration of anti-GD2 CAR T cells achieves potent and durable cure compared to control T cells in multiple orthotopic xenograft models of DIPG. Using a CAR fluorescent protein fusion construct, we demonstrate significant T-cell trafficking to the brainstem where the antitumor effect is mediated. Universal response was observed across multiple cohorts, and treatment-associated toxicity was transient and tolerated during the period of peak antitumor activity. Conclusion: We have previously demonstrated that antigen density drives CAR efficacy. Extremely high expression of GD2 on DIPG makes this a particularly good disease for CAR T-cell therapy. If these results are predictive of human response, CAR T cells could have a transformative impact upon DIPG outcomes. A clinical trial of second generation anti-GD2 CAR T cells in relapsed and progressive DIPG is planned. Citation Format: Robbie G. Majzner, Christopher Mount, Shree Sundaresh, Evan Arnold, Meena Kadapakkam, Louai Labanieh, Pamelyn Woo, Michelle Monje, Crystal L. Mackall. GD2-directed chimeric antigen receptor T cells mediate potent antitumor effect and cure in xenograft models of diffuse intrinsic pontine glioma [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr PR04.