Tumor cells induce neural DKK1 expression to promote MDSC infiltration and subsequent T cell suppression

Nerves are often overlooked as key components of the tumor microenvironment. However, the molecular mechanisms underlying the reciprocal interactions between tumors and nerves remain largely unknown. In this study, we analyzed data from The Cancer Genome Atlas (TCGA) and identified a significant association between DKK1 expression and poor prognosis, as well as a correlation between DKK1 expression and myeloid-derived suppressor cell (MDSC) infiltration in head and neck squamous cell carcinoma (HNSCC) and pancreatic ductal adenocarcinoma (PDAC), two cancer types characterized by pronounced tumor-nerve interactions. Based on these findings, we hypothesize that tumors may induce DKK1 expression in nerves, and that nerve-derived DKK1 may promote MDSC infiltration and immunosuppression. To test this hypothesis, we employed a combination of experimental approaches, including in vitro co-culture of trigeminal ganglia with tumor cells, multiplex immunohistochemistry, and in vivo administration of DKK1 neutralizing antibodies. Our results indicate that tumor cells significantly induce DKK1 expression in ganglia in co-culture experiments. Additionally, in vivo orthotopic tumor models revealed that DKK1 levels were markedly elevated in both the plasma and ganglia of tumor-bearing mice. Neutralization DKK1 in vivo led to a reduction in MDSC levels and impaired MDSC-mediated T cell suppression in both HNSCC and PDAC orthotopic models. Furthermore, conditional deletion of neuronal DKK1 elucidated its role in MDSC infiltration and immune suppression. Our findings establish a novel molecular axis in which tumor cells modulate the immune microenvironment by inducing the expression of secreted proteins in nerves, thereby enriching the research landscape of the tumor microenvironment.