Generation of large numbers of functional NK cells without feeders or serum

Abstract

Abstract Natural killer (NK) cells are innate lymphocytes that modulate immune responses by secreting proinflammatory cytokines, and provide antitumor and antivirus activity. The ability to generate therapeutically relevant numbers of functional NK cells is critical for the development of advanced cellular immunotherapies. We have developed a streamlined culture workflow that enables expansion of functional NK cells without using either feeder cells or serum. Fresh human NK cells were isolated from peripheral blood using EasySep™, then cultured in ImmunoCult™ NK Cell Expansion Medium in plates coated with ImmunoCult™ NK Cell Expansion Coating Material. NK cells were fed, harvested, and replated on days 7 and 10 – 11 prior to phenotyping and functional assessment on day 14. The average frequency of CD56+CD3− NK cells was 88% (range 75 – 96%, n=34), 74% (range 49 – 92%) of which expressed CD16, with an average expansion of 88 fold (range 3 – 454). Expanded NK cells were stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin, or co-cultured with K562 cells. As detected by intracellular flow cytometry, the average frequency of interferon-γ+ among NK cells was 68% (range 41 – 90%, n=7) and 43% (range 12 – 55%) when stimulated by PMA/ionomycin or K562 cells, respectively. Similarly, the frequency of degranulated NK cells (CD107a+) was 81% (range 35 – 97%, n=7) and 64% (range 35 – 97%), respectively. The ability of expanded NK cells to kill target K562 cells was visualized by activated caspase in co-cultures with labeled K562 cells using the Incucyte® imaging system. At an effector:target ratio of 1:1, an average of 50% of K562 cells were killed (range 45 – 56, n=3). These results show large numbers of functional NK cells can be generated.