Dynamics of natural killer cell function upon recurrent stimulation

Natural killer (NK) cells have shown potential for allogeneic cell-based cancer immunotherapies. For development of economical off-the-shelf allogeneic therapies, maximal expansion of the NK cells from each donor must be achieved while maintaining efficacy and uniformity of the cell product. The standard method for robust expansion utilizes weekly stimulation with engineered feeder cells derived from the K562 cell line. However, the effects of repeated stimulation on NK cell growth, metabolism, and function are not well understood. In this study, we demonstrated a distinct shift in growth kinetics and metabolism around week 3-4 of repeated K562 feeder cell stimulation, followed by a change in cytokine secretion and killing ability. Seahorse metabolic flux assays and transcriptomics suggested a transition from glycolytic metabolism to oxidative metabolism after the first week of stimulation, but the shift in growth kinetics generally correlated to reduced metabolic activity. Collectively, these results indicate that serial stimulation sustains large-fold NK cell expansion that can be exploited for NK cell therapy; however, this expansion has important impacts on NK cell growth, metabolism, and function. Careful characterization is critical when developing large-scale biomanufacturing processes to ensure efficacy of the final cellular product.