CD33 and neoplasm: The CAR/TCR/NKR triple-targeting mechanism of Allo15CAR33-NKT cells was validated through a series of in vitro tumor cell killing assays using six human AML cell lines, each representing different scenarios of tumor antigen expression levels: THP1 (CD33+CD1dhigh), KG1 (CD33+CD1dmedium), HL60 (CD33+CD1dlow/-), THP1CD33-/- (CD33-CD1d+), THP1CD1d-/- (CD33+CD1d-), and THP1CD33/CD1d-/- (CD33-CD1d-) (Fig. 3a–c).