IL21 and leukemia: Remarkably, a phase I study investigating the clinical effect of IL-15 plus IL-21 stimulated CD3-depleted NK cells given 2 and 3 weeks after HCT demonstrated that leukemia progression reduced compared with historical patients who have undergone HCT after the same conditioning regimen without NK cell infusion (hazard ratio 0.527, p = 0.042) [81].