CTLA4 and neoplasm: Hypoxic conditions facilitate the recruitment of immunosuppressive cells through chemokine secretion and enhance the expression of immune checkpoint molecules including cytotoxic T-lymphocyte-associated protein 4 (CTLA4) and lymphocyte-activation gene 3 (LAG3) on regulatory T-cells (Tregs), as well as programmed cell death 1 ligand 1 (PD-L1) on myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), and tumor cells [28].