Cutibacterium acnes Induces the Expression of Immunosuppressive Genes in Macrophages and is Associated with an Increase of Regulatory T-Cells in Prostate Cancer.

Tumors and infectious agents both benefit from an immunosuppressive environment. Cutibacterium acnes () is a bacterium in the normal skin microbiota, which has the ability to survive intracellularly in macrophages and is significantly more common in prostate cancer tissue compared with normal prostate tissue. This study investigated if prostate cancer tissue culture positive for has a higher infiltration of regulatory T-cells (Tregs) and if macrophages stimulated with induced the expression of immunosuppressive genes that could be linked to an increase of Tregs in prostate cancer. Real-time PCR and enzyme-linked immunosorbent spot assay (ELISA) were used to examine the expression of immunosuppressive genes in human macrophages stimulated with , and associations between the presence of and infiltration of Tregs were investigated by statistically analyzing data generated in two previous studies. The results demonstrated that macrophages stimulated with significantly increased their expression of PD-L1, CCL17, and CCL18 mRNA and protein (0.05). In the cohort, Tregs in tumor stroma and tumor epithelia were positively associated with the presence of (0.0004 and 0.046, respectively). Since the macrophages stimulated with increased the expression of immunosuppressive genes, and prostate cancer patients with prostatic infection had higher infiltration of Tregs than their noninfected counterparts, we suggest that may contribute to an immunosuppressive tumor environment that is vital for prostate cancer progression. In an immune suppressive tumor microenvironment constituted by immunosuppressive cells and immunosuppressive mediators, tumors may improve their ability to give rise to a clinically relevant cancer. In the present study, we found that might contribute to an immunosuppressive environment by recruiting Tregs and by increasing the expression of immunosuppressive mediators such as PD-L1, CCL17, and CCL18. We believe that our data add support to the hypothesis of a contributing role of in prostate cancer development. If established that stimulates prostate cancer progression it may open up avenues for targeted prostate cancer treatment.