CD4 and cancer: In the tumor microenvironment (TME) of several types of cancers, constitutive expression of LAG-3 has been observed in tumor-infiltrating lymphocytes (TILs), especially in CD4 + and CD8 + T lymphocytes, Treg cells, NK cells, NKT cells, and B lymphocytes, as well as in tumor-associated macrophages (TAMs) [2, 56–60].