To date, NK cell trials and ongoing clinical phase I/II studies have shown the feasibility of using freshly purified or IL-2-activated donor NK cells for the treatment of high-risk patients suffering from leukemia or tumors in both non-transplant settings and after haploSCT as an additional immunotherapy (Koehl et al., 2004; Passweg et al., 2004; Miller et al., 2005; Rizzieri et al., 2010; Rubnitz et al., 2010; Curti et al., 2011; Nguyen et al., 2011; Stern et al., 2013). Here, IL2 is linked to leukemia.