CD4 and hepatocellular carcinoma: The TME of HCC is composed of immune cells (cytotoxic CD4+ T cells, CD8+ T cells, and NK cells), abundant immunosuppressive cells, such as Tregs, myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), stromal cells, the extracellular matrix (ECM), blood vessels, tumor cells, and lymphatic vessels, which play an important role in tumor survival, proliferation, invasion, and metastasis (34).