Alcohol remodels the immunosuppressive tumor microenvironment by targeting myeloid-derived suppressor cells

The tumor immunosuppressive microenvironment plays an important role in tumor progression. Alcohol is well-known as a regulator of the immune system and several studies have also reported that chronic alcohol intake can activate the immune system. However, it is unclear whether alcohol can affect liver cancer progression by regulating the immunosuppressive microenvironment. In this study, we investigated the effects of different alcohol concentrations on the growth of liver cancer and tumor immune microenvironment. We examined the growth of tumors in mice provided with water, or alcohol (for 2 weeks before tumor injection, and for 3 weeks after tumor injection). We found that alcohol consumption at 5% and 20% inhibited the growth of subcutaneous tumors in hepatocellular carcinoma-bearing mice, whereas 2% alcohol concentration did not significantly inhibit liver cancer growth. The ratio of myeloid-derived suppressor cells (MDSCs) in peripheral blood and spleen of mice treated with 5% or 20% alcohol for 2 weeks before tumor inoculation was downregulated. After tumor inoculation, the proportion of MDSCs in peripheral blood, spleen, and tumor of mice treated with 5% or 20% alcohol for another 3 weeks also decreased and the proportion of CD4+ T cells and CD8+ T cells increased. In addition, Alcohol consumption of 20% reduced levels of the inflammatory factor IL-6 by inhibiting JAK/STAT3 signaling. These results indicate that chronic alcohol consumption may inhibit the growth of liver cancer by regulating MDSCs.