CD4 and lung carcinoma: At the same time however, KRAS activation in lung cancer is also linked to MEK/ERK/AP-1 mediated secretion of IL-10 and TGF-β1, which regulate recruitment of CD4+, myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Treg) resulting in an immunosuppressive effect via downregulation of MHC-I expression on tumor cells, preventing antigen presentation and T-cells priming (47, 48).