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

Abstract

γδT cells are unconventional T cells particularly abundant in mucosal tissues that play an important role in tissue surveillance, homeostasis and cancer. γδT cells recognize stressed cells or cancer cells through the NKG2D receptor to kill these cells and maintain normality. Contrary to the well-established anti-tumor function of these NKG2D-expressing γδT cells, we show here that, in mice, NKG2D regulates a population of pro-tumor γδT cells capable of producing IL-17A. 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 reduced 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 increased 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.

NKG2D Fine-Tunes the Local Inflammatory Response in Colorectal Cancer

“…To probe the requirement for NKG2D in TIL activation in this model, we used NKG2D-deficient mice on the Apc min background. We previously reported that Apc min/+ mice deficient for Klrk1 ( Apc min/ ;Klrk1 −/− ) survive longer than Apc min/+ ;Klrk1 +/+ mice and displayed a lower tumor burden [ 30 ]. When comparing the frequencies of IFNγ-producing CD8 + T cells in Apc min/+ ;Klrk1 +/+ and Apc min/+ ;Klrk1 −/− mice, we found that the frequency of CD8 + T cells was significantly decreased in the absence of NKG2D ( Figure 4 a,b) demonstrating the importance of NKG2D in CD8 + T cells enrichment.…”

“…IFNγ is typically an indicator of good prognosis in colorectal cancer [ 37 ], yet studies have suggested that low concentrations of IFNγ can negatively impact the anti-tumor response, whereas high levels lead to tumor regression [ 38 ]. To understand the mechanism resulting in IFNγ-mediated tumor progression, we used a mouse model of colorectal cancer where we previously showed that NKG2D-deficiency improved survival [ 30 ]. We observed that T cells expanded and/or accumulated at late stages of disease in an NKG2D-dependent manner where they produced high levels of IFNγ.…”

“…We observed that T cells expanded and/or accumulated at late stages of disease in an NKG2D-dependent manner where they produced high levels of IFNγ. We have previously shown that NKG2D ligands are highly expressed in that model and that similarly, NKG2D-expressing γδT cells that secrete IL-17A accumulate in the TME, contributing to a pro-tumorigenic microenvironment that sustains tumor growth [ 30 ]. These conclusions are supported by in vitro studies that use colorectal cancer spheroids to show that blocking NKG2D decreases immune cell infiltration [ 39 ], suggesting that immune cells infiltrate the TME in an NKG2D-dependent manner.…”

“…As previously described [ 30 ], NKG2D-heterozygous ( Klrk1 +/− ) mice were crossed with Apc min/+ mice to generate Klrk1 +/+ ;Apc min/+ , Klrk1 −/− ;Apc min/+ , Klrk1 +/+ ;Apc +/+ and Klrk1 −/− ;Apc +/+ mice and to study the impact of NKG2D-deficiency in the intestine. The health status of Apc min/+ mice was checked and evaluated frequently.…”

“…In line with this, high expression levels of certain human NKG2D ligands were associated with poor prognosis in advanced-stage hepatocellular carcinoma [ 29 ]. In the gut tissue, we recently showed that NKG2D-mediated immune activation contributes to tumor progression [ 30 ]. Specifically, in the Apc min/+ model of intestinal tumorigenesis, we demonstrated a role for NKG2D in IL-17A-producing γδT cells, a particular subset defined as CD27 - Vγ6 T cells with pro-tumor function.…”