CD4 and cancer: Through cancer immunoediting, CD4+ Treg cells and programmed cell death 1 (PD-1)-ligand 1 (PD-L1) play an important role in promoting the escape phase of tumor growth in an immunosuppressive tumor microenvironment [1], while interaction between PD-1 and PD-L1 may be involved in the production of CD4+ Tregs [4].