In this study, treatment response will be measured by comparing MRD levels before and at several intervals after NK cell infusion.Achievement of MRD negativity in bone marrow, i.e., < 0.01% blasts by flow cytometry or PCR, will be regarded as a complete response. Partial response will be defined as ≥ 1 log decrease in MRD levels, while < 1 log decrease in MRD levels will be regarded as a no response.