Tumor-associated dendritic cells: molecular mechanisms to suppress antitumor immunity.

Evaluation of: Watkins SK, Zhu Z, Riboldi E et al. FOXO3 programs tumor-associated DCs to become tolerogenic in human and murine prostate cancer. J. Clin. Invest. 121(4), 1361-1372 (2011). Tumor-associated dendritic cells (TADCs) have been described as immune-suppressive cells in cancers, and part of the molecular mechanisms has emerged. The transcription factor FOXO3--one of the tumor suppressors--is overexpressed in TADCs that have been infiltrated in human prostate cancers and TRAMP mouse model of prostate cancers, and induces the expression of immune-suppressive genes including indoleamine-2,3-dioxygenase (IDO1), arginase (ARG1) and TGF-β. Adoptive transfer of T helper cells or silencing of FOXO3 by siRNAs repressed the expression of FOXO3 gene and inhibited the tolerogenicity of TADCs. Therefore, inhibition of FOXO3 signals might be a clue for improvement of cancer immunotherapy.