STAT3 and cancer: - Tregs, MDSCs and cancer cells-Adenosine released by cancer cells stimulates Tregs and MDSCs mediated suppression-By the action of immunosuppressive mediators (IDO1, PD-L1, COX-2, STAT3) released by cancer cells- By the action of TNF-α, TGF-β, IL-6.-Inhibitory checkpoints (CTLA-4, PD-1, etc.)