MSLN and neoplasm: At present, the majority of CAR T-cell targets in solid tumors are overexpressed tumor-associated antigens (TAA) with lower-level expression in normal tissues as compared to tumor tissues, such as HER2, GPC-3, EGFR, mesothelin, PSMA, and IL13Ra2, which greatly limits the maximum safety dosage in order to avoid on-target off-tumor side effect and consequently results in unsatisfactory clinical efficacy (1, 8, 9).