Local IL-21 Promotes the Therapeutic Activity of Effector T cells by Decreasing Regulatory T Cells Within the Tumor Microenvironment.

The eradication of tumors by the immune system depends on the generation of antigen-specific T cells which can migrate to sites of tumor growth and maintain their effector functions despite local tumor-derived T-cell inhibitory factors. Interleukin-21 (IL-21) is an IL-2-related cytokine that has shown limited evidence of antitumor activity in murine models and early phase clinical trials. Effect of local IL-21 on T-cell responses within the tumor microenvironment, however, has not been extensively evaluated. Thus, we developed a stably transfected IL-21-secreting B16 melanoma cell line to test the effects of local IL-21 on endogenous and adoptively transferred T-cell responses. Tumors expressing IL-21 exhibited delayed growth in vivo, which was associated with an increase in activated systemic effector and memory CD8+ T–cell responses. Local IL-21 also enhanced the therapeutic effects of adoptively transferred gp100-specific T cells and was synergistic with IL-2. The effect was also associated with an increased proliferation of local CD8+ T cells and decreased accumulation of regulatory CD4+FOXP3+ T cells within the tumor microenvironment. These data suggest that local IL-21 enhances endogenous and adoptively transferred T-cell immunity through increased effector CD8+ T cells and decreased CD4+ regulatory T cells in the tumor microenvironment.Molecular Therapy (2009) 17 2, 380–388 doi:10.1038/mt.2008.249 [ABSTRACT FROM AUTHOR]