Therapy implications of the role of interleukin-2 in cancer

Despite its apparent failure in cancer therapy, IL-2 still remains fundamental in the activation of antitumor immunity. Areas covered: The aim of this review is the reinterpretation of the role of IL-2 in anticancer immunity, according to knowledge gained of the cytokine network, by highlighting its importance in inducing T helper-1 (TH1) cell proliferation, natural killer (NK) actHivation and IL-12 secretion. However, its main negative effect is the stimulation of regulatory T cells (Tregs), which in contrast suppresses anticancer immunity. Expert commentary: Cardiovascular toxicity, which was the main clinical problem at the beginning of IL-2 therapy at high intravenous doses, has almost been completely solved by subcutaneous low-dose IL-2 injection. In order to enhance the anticancer efficacy of IL-2, several strategies have been explored, including chemotherapy and interferon, but up until now no regimen has appeared to be clearly better than IL-2 alone. However, considering the role of immune checkpoints (PD-1 and CTLA-4) in Tregs stimulation, the most effective immunotherapy in the future could be concomitant IL-2 administration, to enhance lymphocyte count, and checkpoint inhibitors, such as anti-PD1 or anti-CTLA-4 monoclonal antibodies, or IL-12, which is also able to counteract IL-2-induced Treg cell generation. Therefore, the time for IL-2 immunotherapy in cancer treatment has finally arrived.