Intratumoral enrichment and suppressive activity of DP8α regulatory T cells in human colorectal cancer

Colorectal cancer (CRC) progression is driven by dynamic interactions among tumor cells, immune infiltrates, and the gut microbiota. While regulatory T cells (Tregs) may contribute to immune suppression in CRC, the role of non-conventional Tregs remains poorly defined. We identified a non-conventional population of microbiota-induced Tregs in the human colonic mucosa that co-expressed CD4, CD8α, CXCR6, and CCR6, termed DP8α Tregs, that exert potent immunomodulatory properties in different inflammatory settings. Their status and role in CRC, however, have not been investigated. Here, using multiparametric flow cytometry in a prospective cohort of CRC patients, we showed that DP8α Tregs are significantly enriched in tumors compared to paired non-tumoral colonic mucosa. Tumor-infiltrating DP8α Tregs displayed elevated expression of the CD39/CD73 ectonucleotidases, as well as CCR5, consistent with a suppressive phenotype within the tumor microenvironment. Functional co-culture assays further demonstrated that sorting DP8α Tregs from CRC tumors inhibited both CD4 and CD8 T-cell proliferation, an effect largely reversed by pharmacological inhibition of CD39 and CD73, which was associated with reduced IL-2 levels. Together, these findings show that DP8α Tregs enriched in the CRC tumor microenvironment, are able to suppress effector T-cell responses through the purinergic pathway and support further investigation of their contribution to immune regulation in CRC.