Transient Foxp(3+) Regulatory T-Cell Depletion Enhances Therapeutic Anticancer Vaccination Targeting The Immune-Stimulatory Properties Of Nkt Cells

The natural killer T (NKT) cell ligand, alpha-galactosylceramide (alpha-GalCer), represents a potential adjuvant to boost immunotherapeutic vaccination strategies against poorly immunogenic cancers. The objective of this study was to assess the therapeutic potential of an alpha-GalCer-loaded tumor-cell vaccine against solid tumors in mice and to enhance the effectiveness of this approach by removing immune suppression associated with the activity of Foxp(3+) regulatory T cells (Tregs). In the B16F10 melanoma model, we show that single vaccination with irradiated, alpha-GalCer-loaded tumor cells resulted in suppression of established subcutaneous (s.c.) B16F10 tumor growth, which was mediated by NKT cell-dependent IFN-gamma production and enhanced in the absence of IL-17 A. Selective depletion of Foxp3(+) Tregs in transgenic DEpletion of REGulatory T cells (DEREG) mice led to significant inhibition of B16F10 tumor growth and enhanced survival of mice receiving vaccination. Shortterm elimination of Foxp3(+) Tregs (<7 days) was sufficient to boost vaccine-induced immunity. Enhanced antitumor activity with combination therapy was associated with an increase in systemic NK cell and effector CD8(+) T-cell activation and IFN-gamma production, as well as infiltration of effector CD8(+) T cells into the tumor. Overall, these findings demonstrate that transient depletion of Foxp(3+) Tregs constitutes a highly effective strategy to improve the therapeutic efficacy of anticancer vaccination with NKT cell adjuvants. Immunology and Cell Biology (2013) 91, 105-114; doi:10.1038/icb.2012.58; published online 23 October 2012