CD274 and neoplasm: MDSCs contribute to creating an immunosuppressive environment enhancing the expansion and the activation of T-regs, CD4+ T lymphocytes that can inhibit the function of tumor-specific T lymphocytes producing immunosuppressive cytokines (IL-10 and TGF-β), expressing negative costimulatory molecules (CTLA-4, PD-1 and PD-L1) and consuming IL-2, a cytokine essential for the proliferation of cytotoxic T lymphocytes [84,85].