Interleukin-2, a polypeptide lymphokine that induces proliferation of antigen- or mitogen-stimulated T cells, was first described as "T-cell growth factor" by Morgan et al. in 1976. IL-2 is one of several lymphocyte-produced messenger regulatory molecules that modulate immunocyte function. The main secretory source of IL-2 is the T-helper cell. In 1983, Taniguchi and colleagues isolated a human IL-2 complementary DNA clone from a high-producer Jurkat leukemic cell line, and established its nucleotide sequence. In 1984, Rosenberg et al. described the isolation of cDNA clones of the gene for IL-2 from the Jurkat cell line, its expression in Escherichia coli and its biological characteristics. The mature secreted protein contains 133 amino acids, constituting a calculated molecular weight of 15,420. Since the discovery of IL-2 and its T-cell growth-promoting activity, extensive research has revealed the complex nature of its immunologic effects, both in vitro and in vivo. The immunopotentiating activities, encouraging in vitro results, plus successful therapy of animal tumors in preclinical studies provided the rationale for investigation of IL-2 in patients with advanced malignancy and immunodeficiencies. The IL-2 receptor has been found to have an unexpected by unusual structure in that it is composed of two separate chains designated alpha (p75) and beta (p55). Recently, it has been discovered the 3rd gamma-chain by Sugamura et al. Clinical trials of IL-2 in patients with cancer have been done by many researchers. The clinical trials has reviewed briefly.