CTLA4 and cancer: Thus, clinically significant cancers have multiple immunosuppressive mechanisms, including an increase in various immunosuppressive cells (e.g., Treg cells and tumor-associated macrophages), an increase in the expression of various immunosuppressive molecules (e.g., CTLA-4), and a decrease in the expression of cancer antigens, resulting in the inability of CD8+ T cells to recognize cancer cells.