CD33 and acute myeloid leukemia: In the first, small phase I clinical trials, the repeated infusion of γ-irradiated (10 Gy) CAR-NK-92 cells targeting CD33 at doses up to 5 × 109 cells/patient was reported to be safe in three relapsed/refractory AML patients with no substantial adverse effects, although the clinical efficacy was not found to be significant [22], suggesting a good safety profile of these CAR-NK-92 cells similar to their parental NK-92 cells.