Interleukin 15 (IL-15) is a pleiotropic cytokine with a wide spectrum of activity. The significant role of IL-15 in the pathogenesis of inflammatory and autoimmune processes, infectious diseases and cancer suggests a possibility of a therapeutic intervention by blocking the biological activity of this cytokine. The methods of blocking IL-15, which have been already developed, are based either on the administration of anti-IL-15 and anti-IL-15 receptor antibodies or on the modifications leading to a soluble receptor molecule or a mutated IL-15, exhibiting properties of competitive antagonists.