In vivo expansion of haploidentical NK cells. After establishing a standard curve between donor and recipient using the informative HLA-B7 allele, postinfusion samples were analyzed in a patient receiving Hi-Cy/Flu. In contrast to patients receiving Lo-Cy/mPred, Hi-Cy/Flu not only increased the persistence of donor cells but also facilitated in vivo expansion as demonstrated by the increased band density beyond day 2 (D2) (β-actin control for equal sample loading). In another patient, after establishing HLA-B31 as an informative allele, NK cells, T cells, and B cells were sorted from blood (PB) and marrow (BM). From this patient, essentially 100% of NK cells, but not T or B cells, were of donor origin.