SUMMARY Development of cancer has been linked to chronic inflammation, particularly via interleukin-23 (IL-23) and IL-17 signaling pathways. However, the cellular source of IL-17 and underlying mechanisms by which IL-17-producing cells promote human colorectal cancer (CRC) remain poorly defined. Here, we demonstrate that innate γδT (γδT17) cells are the major cellular source of IL-17 in human CRC. Microbial products elicited by tumorous epithelial barrier disruption correlated with inflammatory dendritic cell (inf-DC) accumulation and γδT17 polarization in human tumors. Activated inf-DCs induced γδT17 cells to secrete IL-8, tumor necrosis factor alpha, and GM-CSF with a concomitant accumulation of immunosuppressive PMN-MDSCs in the tumor. Importantly, γδT17 cell infiltration positively correlated with tumor stages and other clinicopathological features. Our study uncovers an inf-DC-γδT17-PMN-MDSC regulatory axis in human CRC that correlates MDSC-meditated immunosuppression with tumor-elicited inflammation. These findings suggest that γδT17 cells might be key players in human CRC progression and have the potential for treatment or prognosis prediction.

Tumor microenvironment (TME) promotes immune suppression through recruiting and expanding suppressive immune cells such as regulatory T cells (Tregs) to facilitate cancer progression. In this study, we identify a novel CD39 C gdTreg in human colorectal cancer (CRC). CD39 C gdTregs are the predominant regulatory T cells and have more potent immunosuppressive activity than CD4 C or CD8 C Tregs via the adenosine-mediated pathway but independent of TGF-b or IL-10. They also secrete cytokines including IL-17A and GM-CSF, which may chemoattract myeloid-derived suppressive cells (MDSCs), thus establishing an immunosuppressive network. We further demonstrate that tumor-derived TGF-b1 induces CD39 C gdT cells from paired normal colon tissues to produce more adenosine and become potent immunosuppressive T cells. Moreover, CD39 C gdTreg infiltration is positively correlated with TNM stage and other unfavorable clinicopathological features, implicating that CD39 C gdTregs are one of the key players in establishment of immunosuppressive TME in human CRC that may be critical for tumor immunotherapy.

Gamma delta T (γδT) cells are innate-like lymphocytes with strong, MHC-unrestricted cytotoxicity against cancer cells and show a promising prospect in adoptive cellular immunotherapy for various malignancies. However, the clinical outcome of commonly used Vγ9Vδ2 γδT (Vδ2 T) cells in adoptive immunotherapy for most solid tumors is limited. Here, we demonstrate that freshly isolated Vδ1 γδT (Vδ1 T) cells from human peripheral blood (PB) exhibit more potent cytotoxicity against adherent and sphere-forming human colon cancer cells than Vδ2 T cells . We also develop an optimized protocol to preferentially expand Vδ1 T cells isolated from PB of both healthy donors and colon cancer patients by short-term culture with phytohemagglutinin (PHA) and interleukin-7 (IL-7). Expanded Vδ1 T cells highly expressed cytotoxicity-related molecules, chemokine receptors and cytokines with enhanced cytolytic effect against adherent and sphere-forming colon cancer cells in a cell-to-cell contact dependent manner. In addition, PHA and IL-7 expanded Vδ1 T cells showed proliferation and survival advantage partly through an IL-2 signaling pathway. Furthermore, expanded Vδ1 T cells also restrained the tumor growth and prolonged the tumor-burdened survival of human colon carcinoma xenografted mice. Our findings suggest that human PB Vδ1 T cells expanded by PHA and IL-7 are a promising candidate for anticancer adoptive immunotherapy for human solid tumors such as colon cancer.