Indeed, a recent phase I clinical trial using K562-based feeder cells expressing membrane-bound chimeras of IL-21 (mbIL21) was conducted in patients affected by AML/myelodysplastic syndrome and demonstrated that the infusion of ex vivo–expanded NK cells from BM haplo-donor could control tumor relapse without major toxicity (236). This evidence concerns the gene IL21 and acute myeloid leukemia.