XCL1 and neoplasm: Besides these factors, the activated NK cells have been reported to produce several other factors, including immunoregulatory cytokines such as IL-5, IL-8, IL-10, IL-13, FLT3LG, TGF-α, the chemokines MIP-1α, MIP-1β, XCL1/2, CCL3/4/5 and RANTES, and several growth factors, including GM-CSF, G-CSF, M-CSF, which recruit other immune cells and regulate their anti-tumor responses [57,58,59,60,61,62,63].