CD19 and leukemia: There are many studies, aiming at different CAR-T constructs such as EGFR-specific CAR T-cells for non-small-cell lung cancer [30], CD19 CAR T-cells for leukemia/CD19-positive malignancies [12,13,15,31,32,33,34], and CAR T-cells with anti-programmed cell death protein 1 (PD-1) single-chain variable fragment (scfv) [35,36], all showing promising cytotoxic effect in cancer immunotherapy.