ICOS-expressing CAR-T cells mediate durable eradication of triple-negative breast cancer and metastasis.

Triple-negative breast cancer (TNBC) remains one of the most aggressive and therapeutically challenging breast cancer subtypes. In their recent study, Cao et al introduced a B7H3-specific chimeric antigen receptor (CAR)-T cell with constitutive inducible co-stimulator (ICOS) expression (ICOS-B7H3-CAR-T), which demonstrated eradication of TNBC, including metastases, in preclinical models. These CAR-T cells exploit the expression of ICOS ligand on TNBC cells, enhancing antitumor cytotoxicity through ICOS signaling. Compared with conventional B7H3-CAR-T cells, the ICOS-B7H3-CAR-T cells exhibited superior antitumor efficacy, increased cytokine secretion, and prolonged survival in xenograft murine models. This study highlights ICOS as a promising co-stimulatory molecule for improving CAR-T therapy against solid tumors and underscores the critical role of ICOS signaling in enhancing therapeutic outcomes. Here, we discuss the implications of these findings for TNBC treatment, the importance of understanding and exploiting ICOS biology in immunotherapies, and future directions for optimizing ICOS CAR-T cell therapies in solid tumor immunotherapy.