Aryl Hydrocarbon Receptor Signaling Controls CD155 Expression on Macrophages and Mediates Tumor Immunosuppression.

Crosstalk between costimulatory and coinhibitory ligands are a prominent node of immune cell regulation. Mounting evidence points toward a critical role for CD155, the poliovirus receptor, in suppressing T cell function, particularly in cancer. However, relative to other known costimulatory/coinhibitory ligands (e.g., CD86, CD80, PD-L1), the physiological functions of CD155 and the mechanisms controlling its expression remain unclear. We discovered that CD155 expression is coregulated with PD-L1 on tumor-associated macrophages, is transcriptionally regulated by persistently active aryl hydrocarbon receptor (AhR), and can be targeted for suppression via AhR inhibition in vivo. Therapeutic inhibition of AhR reversed tumor immunosuppression in an immune competent murine tumor model, and markers of AhR activity were highly correlated with tumor-associated macrophage markers in human glioblastomas. Thus, CD155 functions within a broader, AhR-controlled macrophage activation phenotype that can be targeted to reverse tumor immunosuppression.