Comparison of maximum fold increase in number of circulating NK cells with different agents and dosing schedules. rhIL-15 administered by bolus infusions at the MTD (0.3 μg/kg/d) yielded only a two to threefold increase in NK cells (Conlon et al., 2015). rhIL-15 administered s.c. at the expansion dose of 2 μg/kg/d on days 1–5 and 8–12 produced a 10.8-fold increase in total NK cells and a 39.7-fold increase in CD56^bright NK cells (Miller et al., 2018). ALT-803 mutant (IL-15/IL-15Rα/IgFc) at 10 μg/kg/wk elicited an eightfold increase in NK cells (Romee et al., 2018). rhIL-15 by CIV at 2 μg/kg/d for 10 d resulted in the greatest increase, with a 38-fold increase in circulating total NK cells and a 358-fold increase in CD56^bright NK cells (Conlon et al., 2019).