Four immunosuppressive cells, myeloid-derived suppressor cell (MDSC), tumor-associated macrophage (TAM), cancer-associated fibroblasts (CAF), and regulatory T cell (Treg), can inhibit the infiltration of immune cells, especially CD8+ T cells, into the TME and suppress their functions within the tumor [34, 35]. The gene discussed is CD8A; the disease is neoplasm.