CTLA4 and cancer: Hypoxia also exerts multifaceted immunosuppressive effects: it decreases the expression of MHC molecules on cancer cells, thereby impairing antigen presentation; it upregulates the expression of immune checkpoint molecules such as CTLA‐4 and PD‐1 on relevant cells [160], and it promotes the accumulation or expansion of immunosuppressive cells within the TME [161].