Suppression of Antitumor Immunity by Stromal Cells Expressing Fibroblast Activation Protein–α

Tumor Vaccination Success Vaccination with tumor-specific antigens is one of several attempted therapies seeking to harness the immune system, but—unfortunately—this strategy has been unsuccessful, possibly because of the immunosuppressive properties of the tumor microenvironment. Kraman et al. (p. 827 ; see the Perspective by Schreiber and Rowley ) have identified immunosuppressive cells of mesenchymal origin in mice comprising 2% of the tumor stromal cell population. They were identified by expression of the fibroblast activation protein–α. Deletion of these cells in lung or pancreatic cancers in mice allowed successful therapeutic vaccination against the tumors, which was dependent on the adaptive immune system and the cytokines interferon-γ and tumor necrosis factor–α. These findings reveal that multiple cell types contribute to the immunosuppressive tumor microenvironment and will inform therapeutic cancer vaccine design.