Functional analysis of NK cells after haplo-HCT. Assays were carried out using cryopreserved PBMCs collected 2 months after haplo-HCT (red boxes, n = 9), MD-HCT (black boxes, n = 9) and from HDs (blue boxes, n = 8). Thawed PBMCs were cultured overnight with media alone or media plus IL-15 (5 ng/mL) and then stimulated with K562 target cells (effector to target ratio = 5:1). (A) Flow cytometry plots from a representative haplo-HCT patient showing surface staining of CD107a and intracellular staining for IFN-γ and TNF-α at baseline (PBMC alone), with target cells (PBMC + K562), and with target cells after priming with IL-15 (IL-15-primed PBMC + K562). (B) Summary data for all samples showing percentage of CD107a⁺, IFN-γ⁺, and TNF-α⁺ NK cells upon coculture with K562 cells in the absence or presence of IL-15 priming. The background staining for CD107a, IFN-γ, and TNF-α present at baseline was subtracted. Box and whisker plots show medians, along with minimum and maximum values. Data were compared using the Wilcoxon signed-rank test for paired comparison (**P < .01; *P < .05).