GPR15 facilitates recruitment of regulatory T cells to promote colorectal cancer.

Colorectal cancer (CRC) is one of the most frequent malignancies worldwide. Despite considerable progress in early detection and treatment, there is still an unmet need for novel anti-tumor therapies, particularly in advanced CRC. Regulatory T cells (Tregs) are increased in the peripheral blood and tumor tissue of CRC patients. Recently, transient ablation of tumor-associated Tregs was shown to foster CD8+ T cell-mediated anti-tumoral immunity in murine CRC models. However, before considering therapies, targeting Tregs in cancer patients and detailed knowledge of the phenotype and features of tumor-associated Tregs is indispensable. Here we demonstrate in a murine model of inflammation-induced CRC that tumor-associated Tregs are mainly of thymic origin and equipped with a specific set of molecules strongly associated with enhanced migratory properties. Particularly, a dense infiltration of Tregs in mouse and human CRC lesions correlated with increased expression of the orphan chemoattractant receptor GPR15 on these cells. Comprehensive gene expression analysis revealed that tumor-associated GPR15+ Tregs have a Th17-like phenotype, thereby producing IL-17 and TNF-α. Gpr15 deficiency repressed Treg infiltration in CRC, which paved the way for enhanced anti-tumoral CD8+ T cell immunity and reduced tumorigenesis. In conclusion, GPR15 represents a promising novel target for modifying T cell-mediated anti-tumoral immunity in CRC.