Atrt-17. car t cell therapy targeting claudin-6 is effective in cellular and xenograft models of atypical teratoid/rhabdoid tumor

Abstract Novel therapies are needed to for the treatment of atypical teratoid/rhabdoid tumor (ATRT), an aggressive brain tumor that predominantly affects young children and has an average 5-year survival under 50%. Claudin-6 (CLDN6) is a tight junction protein present during development and is expressed in up to 70% of ATRT specimens but not in normal tissue, making it a promising immunotherapeutic target. CLDN6-targeted chimeric antigen receptor (CAR) T cells in combination with a CAR T cell-amplifying mRNA vaccine have demonstrated antitumor activity against other CLDN6-expressing cancers in pre-clinical and a phase I adult trial (NCT04503278; Haanen J et al AACR, 2022). To assess the effectiveness of CLDN6-targeted CAR T cells against ATRT, we utilized a second-generation mRNA CAR with a 4-1BB costimulatory domain and single-chain variable fragment against CLDN6 (Reinhard et al, 2020). CLDN6 expression in patient-derived ATRT specimens was profiled by RNAseq (mean FPKM 11.4) and immunohistochemistry (positive staining in 53% of specimens). Tumor-derived cell lines were assessed for CLDN6 expression by flow cytometry. Co-culture of CLDN6-directed mRNA CAR T cells resulted in tumor-specific cytotoxicity compared to CD19-directed control CAR T cells in CLDN6-positive ATRT cell lines 7316-2187 (92% versus 15% at 10:1, p < 0.0001; 86% versus 0% at 5:1, p<0.0001) and 7316-2141 (75% versus 7% at 10:1, p<0.0001; 53% versus 0% at 5:1, p< 0.0001). Patient-derived, orthotopic xenograft ATRT models were created through intracranial injection of tumor cells into the cerebellum of NSG mice. Following engraftment with 7316-2141, repeated intratumoral administration of mRNA CLDN6 CAR T cells resulted in significant tumor regression (-1.9x108 vs. +2.4x109 p/sec/cm2/sr, p<0.001) and improved survival compared to mRNA CD19 CAR T cells (median OS not reached vs. 13 days, p=0.002). This work highlights the potential for targeting CLDN6 via CAR T cell therapy in patients with ATRT as a novel therapeutic strategy.