Transient persistence of donor cells following haploidentical NK-cell infusions without in vivo expansion after Lo-Cy/mPred. Each donor/recipient pair was evaluated for a unique class I MHC allele present in the donor but not the recipient. After reverse transcription, PCR primers were chosen to amplify donor-derived informative transcripts without cross reactivity with recipient alleles. A standard curve was established using donor cell dose titration, while showing little or no product in the control sample that does not contain donors cells. Patient PBMC samples were analyzed in a similar manner at various time points after infusion. Shown is a representative donor/recipient pair where HLA-A1 was informative (β-actin control for equal sample loading). There was persistence of donor cells through day 5 (D5) after NK-cell infusion but none at later time points. There was no consistent increase in band density after infusion, suggesting that in vivo expansion did not occur. A similar pattern demonstrating persistence of donor cells through day 5 was seen in 5 of 6 donor/recipient pairs tested.