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.

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.

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.

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.