Exth-85. Targeting Claudin 6 With Car T Cell Therapy for Atypical Teratoid/Rhabdoid Tumor

Abstract

Atypical teratoid/rhabdoid tumor (ATRT) is an aggressive brain tumor that predominantly affects young children and has an average 5-year survival under 50%. Novel, targeted therapies are desperately needed. Claudin 6 (CLDN6) is a tight junction protein present during development and 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 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). Patient-derived ATRT specimens were assessed by RNAseq for CLDN6 expression (mean FPKM= 11.4) and by immunohistochemistry (positive staining in 53% of specimens). Tumor-derived cell lines were validated for CLDN6 expression by flow cytometry. Co-culture of CLDN6-directed mRNA CAR T cells with ATRT cell line 7316-2187 resulted in tumor-specific cytotoxicity compared to CD19-directed control CAR T cells (92% versus 15% at 10:1, p< 0.0001; 86% versus 0% at 5:1, p< 0.0001). Similar results were seen with ATRT cell line 7316-2141 (75% versus 7% at 10:1, p< 0.0001; 53% versus 0% at 5:1, p< 0.0001). Both CLDN6- and CD19-directed CAR T cells showed no cytotoxicity against CLDN6-negative cell line 7316-4149. Patient-derived xenograft models were also created through intracranial injection of multiple ATRT patient cell lines, and ongoing work will evaluate locoregional administration of CLDN6-directed CAR T cells in orthotopic xenograft models to test in vivo efficacy. This work highlights the potential for targeting CLDN6 via CAR T cell therapy in patients with ATRT as a novel therapeutic strategy for these devastating tumors.

mRNA‐based chimeric antigen receptor T cell therapy: Basic principles, recent advances and future directions

“…This development shows the promise of mRNA CAR transfection as a fresh approach to treating solid tumors using cell‐based treatments 19,37 . Subsequently, CAR molecules targeting antigens on solid tumors were generated by T‐cells electroporated with mRNA molecules, suggesting promising results in preclinical models, such as melanoma, 38 mesothelioma, 17f neuroblastoma, 39 lung and breast cancer, 20b,40 glioblastoma, 41 atypical teratoid/rhabdoid tumors, 42 situ medulloblastoma 43 …”