immune complexes (IL-2C) composed of with low-dose IL-2 and stimulating anti-IL-2 antibody (S4B6) have been shown to enhance immune responses via selective structural interactions. Stimulating IL-2C can preferentially expand memory CD8+ T and NK cells—while more weakly affecting regulatory T cells—via the interaction of anti-IL-2 antibodies (S4B6) and CD25 binding region of IL-2, leading to inhibition of both leukemia and melanoma. Interestingly, the half-life of IL-2 is increased in IL-2C; as such, low-dose IL-2C has immune enhancing effects that are comparable to those of high-dose IL-2 therapy without accompanying serious side effects such as capillary leak syndrome. Low-dose IL-2C therapy is therefore expected to be an effective and safe treatment for immunogenic tumors.