IL-21 is an effective inducer of T cell activation in vivo, enhances the antigen affinity of specific CD8+ T cells,25,26 inhibits the development of regulatory T cells (Treg),27 induces the maturation of NK and NKT cells, induces activation and cytolytic potential of NK and NKT cells,28,29 promotes the production of tumor-specific IgG B cells,30 and inhibits angiogenesis by reducing the expression of VEGFR1 and TIE1 in endothelial cells.31 The gene discussed is CD8A; the disease is neoplasm.