CAR NK cell production from human cord blood cells is enhanced by stimulation of the IL15 receptor on NK progenitor cells

Human cord blood (CB)-derived CAR NK cells have demonstrated significant anti-tumor efficacy in clinical trials. We recently reported that CB-derived CAR NK cells are mainly derived from CD7+CD56-CD34-HLA-DR-Lin- NK precursors. Here we show that CAR NK cell production from human CB cells can be enhanced by stimulation of the IL15 receptor on NK precursors. In CB CD56-CD34-HLADR-Lin- cells, the IL15 receptor was expressed exclusively on the CD7+ NK cell precursors but not on the CD7- population. The production of mature NK cells from the purified NK cell precursors or CD3- CB cells was significantly enhanced by using K562 feeder cells expressing membrane-bound (mb) IL15 in addition to 4-1BB ligand and mbIL21. The in vitro and in vivo anti-tumor efficacy of CAR NK cells generated using K562 feeder cells expressing 4-1BBL, mbIL15 and mbIL21 was comparable to that of CAR NK cells generated using the K562 feeder cells expressing only 4-1BBL and mbIL21. These results suggest that the use of K562 feeder cells expressing mbIL15 in addition to 4-1BBL and mbIL21 increases the yield of CAR NK cell production from CB cells, while the clinical efficacy and safety of the CAR NK cells generated should be tested in the future.