B7-H3 and CSPG4-targeted CAR T cells as potent effectors in anaplastic thyroid cancer.

Background: Anaplastic thyroid cancer (ATC) is a rare and aggressive malignancy with poor survival and no available effective therapy. This unmet clinical need led us to investigate chimeric antigen receptor (CAR) T cells s as potential treatment option for this malignant disease. As target tumor antigens of our CAR T cell therapy, we selected the chondroitin sulfate proteoglycan 4 (CSPG4) and the B7-homolog 3 (B7-H3), as they are both highly and homogeneously expressed on different types of thyroid carcinoma cell lines and tissues, including ATC. Importantly, both CSPG4 and B7-H3 have a low distribution on normal tissues, thus limiting 'on-target off-tumor' CAR T-related toxicities.

Methods: We generated CSPG4-specific and B7-H3-specific CAR T cells by utilizing a second-generation CAR construct comprised of a CD28 costimulatory domain and tested their antitumor activity in vitro and in an orthotopic xenograft murine model of ATC.

Results: We demonstrated that thyroid cancer cells are specifically recognized and effectively eradicated in vitro by CSPG4-targeted and B7-H3-targeted CAR T cells. Additionally, both CAR T cell types were able to mediate significant control or complete eradication of primary ATC tumors when mice were treated with CSPG4 CAR T cells or B7-H3 CAR T cells, respectively.

Conclusion: Overall, in this study we identified CSPG4 and B7-H3 as valuable target antigens in thyroid cancer and demonstrated that CAR T cell immunotherapy can be a valuable therapeutic option for ATC patients. Our findings provide the translational basis for exploring CAR T cell immunotherapies targeting CSPG4 and B7-H3 with ATC patients who do not respond or relapse after first line treatment.