ERBB2 and neoplasm: Conventional single-antigen CAR-T therapies, such as those targeting HER2 or SSEA-4, have demonstrated potent antitumor effects but often induce severe off-tumor cytotoxicity due to the expression of these antigens in healthy tissues, as evidenced by preclinical findings where SSEA-4-directed CAR-T cells caused severe toxicity through recognition of normal progenitor cells [53].