IL-21 is an immunomodulatory cytokine produced by natural killer (NK) cells and T cells that has pleiotropic roles in immune and nonimmune cells. IL-21 can modulate innate and specific immunity activities. It is a potent stimulator of T and natural killer cell-mediated antitumor immunity but also has pro-inflammatory functions in many tissues and is involved in oncogenesis. It is important to understand IL-21 biology in these different situations to ensure the maximal benefit of therapeutic strategies targeting this cytokine. This chapter summarizes IL-21 characteristics and signaling, its role in immune system components, and its use in cancer immunotherapies.
Keywords: Antitumor activity; Cytokine; ERK pathway; Immune cells; JAK-STAT pathways; Lymphocytes; Myeloid cells; PI3-kinase pathway; Pro-tumoral activity; Regulation; Signaling pathways; Transcription factors; Tumor microenvironment; γc Cytokine family.