Feeder cell training shapes the phenotype and function of in vitro expanded natural killer cells

Natural killer (NK) cells are candidates for adoptive cell therapy, and the protocols for their activation and expansion profoundly influence their function and fate. The complexity of NK cell origin and feeder cell cues impacts the heterogeneity of expanded NK (eNK) cells. To explore this, we compared the phenotype and function of peripheral blood-derived NK (PB-NK) and umbilical cord blood-derived NK (UCB-NK) cells activated by common feeder cell lines, including K562, PLH, and 221.AEH. After first encounter, most PB-NK cells showed degranulation independently of cytokines production. Meanwhile, most UCB-NK cells did both. We observed that each feeder cell line uniquely influenced the activation, expansion, and ultimate fate of PB eNK and UCB eNK cells, determining whether they became cytokine producers or killer cells. In addition, they also affected the functional performance of NK cell subsets after expansion, that is, expanded conventional NK (ecNK) and expanded FcRγ^- NK (eg-NK) cells. Hence, the regulation of eNK cell function largely depends on the NK cell source and the chosen expansion system. These results underscore the significance of selecting feeder cells for NK cell expansion from various sources, notably for customized adoptive cell therapies to yield cytokine-producing or cytotoxic eNK cells.