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. 2021 Mar 30;13(7):1577. doi: 10.3390/cancers13071577

Figure 2.

Figure 2

Memory-like NK cells exhibit higher anti-tumor cytotoxicity compared to NK activated ON with IL-2. (A) Schematic representation of the approach for ex vivo induction and expansion of memory-like NK cells. The protocol included 16-h activation with IL-12, IL-15 and IL-18 followed by 6-day culture in the presence of 40 U/ml IL-2 and 1 ng/mL IL-15. After 6 days in the maintenance phase, the cells were recovered or alternatively reactivated for 6-h with 10 ng/mL IL-2 and 100 ng/mL IL-15. Alternatively, purified NK cells were stimulated overnight (ON) with 100 U/mL of IL-2 (control NK). After each step, the cells were evaluated for cellular recovery and cytotoxic activity. (B) The means and SDs of cell recovery of NK cells recovered at day 7 (no reactivation) or at day 8 after 6-h reactivation and 16-h maintenance (reactivation), * p < 0.05. (C) The means and SDs of cytotoxic activity of memory-like NK cells obtained at day 7 (♦), at day 8 (■) and of control NK cells (activated ON with rhIL-2) (▲). Results derived from five independent experiments performed with NK cells derived from healthy donors and tested against THP-1 cell lines at various E:T ratios ranging from 30:1 to 1.7:1 are reported.