NKG2D signaling regulates IL-17A-producing γδT cells to promote cancer progression

γδT cells are unconventional T cells particularly abundant in mucosal tissues that play an important role in tissue surveillance and homeostasis. γδT cell activation is mediated by the T cell receptor composed of γ and δ chains, as well as activating receptors for stress-induced ligands, such as NKG2D. Contrary to the well-established anti-tumor function of γδT cells, recent studies have shown that γδT cells can promote tumor development in certain contexts. However, the mechanisms leading to this diseasepromoting role remain poorly understood. Here, we show that mice lacking γδT cells survive longer in a mouse model of intestinal cancer, further supporting their pro-tumoral role. In a surprising conceptual twist, we found that these pro-tumor γδT cells are regulated by NKG2D signaling, a receptor normally associated with cancer cell killing. Germline deletion of Klrk1 , the gene encoding NKG2D, reduced the frequency of γδT cells in the tumor microenvironment and delayed tumor progression. We further show that blocking NKG2D reduces the capability of γδT cells to produce IL-17A in the pre-metastatic lung and that co-culture of lung T cells with NKG2D ligand-expressing tumor cells specifically increases the frequency of γδT cells. Together, these data support the hypothesis that in a tumor microenvironment where NKG2D ligands are constitutively expressed, γδT cells accumulate in an NKG2D-dependent manner and drive tumor progression by secreting pro-inflammatory cytokines, such as IL-17A. ### Competing Interest Statement The authors have declared no competing interest.