Specifically, IL15, a potent stimulant of CD8+ T cells and natural killer (NK) cells [18, 19], is a promising cancer immunotherapeutic agent being explored by several companies. ALT-803, the lead IL15 analogue in the field, is a complex of an IL15 superagonist N72D mutant and a dimeric IL15 receptor α Su/IgG1 Fc fusion protein that was found to exhibit enhanced biologic activity and potent anti-tumor efficacy in vivo with a substantially longer serum half-life than recombinant IL15 [20–22]. This evidence concerns the gene IL15 and cancer.