The mechanisms of cancer immune escape mainly include: reducing the expression of tumor antigens; increasing co-inhibitor expression (e.g., PD-L1, CTLA-4) (20) (Figure 2); secreting suppressive cytokines (e.g., TGF-β and IL-10); and lastly orchestrating an immunosuppressive microenvironment (21, 22). Here, CTLA4 is linked to neoplasm.