CD4 and neoplasm: MDSCs within the TME can secrete a range of immunosuppressive factors including IL-35, and in PCA model mice, high IL-35 levels were associated with increases in MDSC and Treg levels and reductions in CD4+ and CD8+ T cell frequencies within the spleen, blood, and TME, and with alterations in tumor growth, metastasis, and worse survival outcomes (19).