IL15 and melanoma: The inability of ex-vivo isolated human NK cells to completely suppress tumor cell growth despite the presence of Ipilimumab, may be due to a) the low number of NK cells injected (1:1 NK/melanoma cell ratio); b) the lack of cytokines required for an optimal human NK cell activation as IL-2 or IL-15; c) the lack of accessory immune cells that can aid NK cell in eliminating melanoma cells.