More recently, a phase I/II clinical trial of haploidentical NK cell infusion given with recombinant human IL-15 resulted in remission in 35% of patients with refractory AML, with in vivo NK cell expansion (Cooley et al., 2019), indicating that persistence and expansion of these NK cells in vivo is key for achieving a clinical response and that IL-15 alone is powerful enough to make this happen. Here, IL15 is linked to acute myeloid leukemia.