498P Generation of CAR T Cells Expressing a Scfv Targeting the Htshr in Thyroid Cancer

The incidences of thyroid cancer increased in many countries within the last 10 years. In patients with Hashimoto’s disease as well as in cancer patients treated with immune checkpoint inhibiting antibodies, a cooperation of this humoral response - together with T cell mediated killing - has been shown to induce effective and often rapid destruction of the thyroid gland. We aim to lay the foundation for therapeutic synthetic immunity targeting thyroid cancer by making use of antigen receptors that naturally occur in autoimmunity and that are specific for the TSH receptor (TSHR). Here we profiled patients with poorly differentiated thyroid cancer (PDTC). We developed a CAR-like construct containing scFv’s in the extracellular moiety and CD28 - 4-1BB as costimulatory domain. scFv’s (single chain fragment varialble rgions)were derived from TSHR autoantibodies identified in patients with Graves‘ and Hashimoto’s disease. Flow Cytometry screened thyroid cancer cell lines 850C, FTC133 and B-PAP for membrane TSHRexpression. Effector/target (E/T) ratios ranging from 5:1 were used in coculture experiments for up to 48 h. Incucyte was used to determine tumor cell cytotoxicity, while a beadbased immunoassay (LEGENDplex) was used to assess the release of IFN-γ by activated CAR-T cells. Poorly differentiated thyroid cancer (PDTC) patients retained higher expression of TSHR compared to healthy controls. FTC133 and B-CPAP cells overexpress hTSHR while 850C was negative. T cell killing experiments showed TSHR-directed CAR-T cells specifically targeting TSHR expressing thyroid cancer cells. Our data support the notion that our TSHR-directed CAR-T cells specifically target TSHR expressing thyroid cancer cells.