Targeting poorly differentiated thyroid cancer with bispecific antibodies and CAR T cells from the human anti-TSHR autoantibody repertoire
Background: Poorly differentiated thyroid carcinoma (PDTC) has no effective systemic treatment option once radioactive iodine and tyrosine kinase inhibitors fail. The thyroid-stimulating hormone receptor (TSHR) is highly tissue-restricted and the anti-TSHR autoantibody repertoire of thyroid autoimmunity offers sequence-defined, fully human binders. We asked whether this repertoire can be converted into an off-the-shelf T cell-redirecting therapy for PDTC. Methods: TSHR expression was profiled on a 151-case thyroid cancer tissue microarray (TMA), 50 healthy controls and on fresh tumor material. Eight anti-TSHR clones, four of human autoimmune origin (M22, K1-18, K1-70, 5C9) and four murine (IRI-SAb2, IRI-SAb3, 9D33, 1H7), were reformatted as CD3-engaging bispecific antibodies (bsAbs; anti-TSHR Fab x anti-CD3 scFv) and, for leading clones, as chimeric antigen receptor (CAR) T cells. Activity was compared in vitro, across graded and mixed antigen densities and in a CAL-62-Luc-TSHR xenograft model, using healthy-donor (HD) or thyroid cancer-patient T cells. Results: TSHR was retained on a substantial fraction of PDTC, including metastatic lesions. Both formats mediated potent, antigen-selective killing and the leading bsAbs suppressed xenograft growth in vivo. For CAR T cells, scFv heavy/light-chain orientation was decisive. Anti-TSHR bsAbs cleared mixed cultures far beyond the antigen-positive fraction matching mosunetuzumab and indicating a modality-intrinsic bystander effect. Patient-derived T cells obtained on or after oncological treatment retained full effector function. Conclusions: The anti-TSHR autoantibody repertoire provides a promising source of binders for off-the-shelf bispecific antibodies targeting TSHR-positive thyroid cancer, while CAR T cells offer an autologous alternative.