Interleukin-2 (IL-2) is one of the most important regulators in immune system, as it plays an essential part both in immune activation and suppression. However, as the first immunotherapy drug approved for the treatment of cancer, IL-2 is limited in clinical application by the serious adverse reactions. The long-felt needs in clinical practice, including prolonged half-lives, T cell subset specificity, and toxicity reduction can be achieved by polyethylene glycol (PEG) modification, Fc fusing, or protein mutation of IL-2. NKTR-214, the most advanced IL-2 pathway-targeted agent in clinical development for oncology, shows exciting results in treatment of melanoma in combination with nivolumab. At the same time, many more other modified molecules against cancer and autoimmune diseases are being tested in clinical research, an exciting future lying ahead for IL-2 therapeutics.