CTLA-4 is considered to be a necessary suppressor of the adaptive immune response, and is capable of maintaining peripheral tolerance, binding to CD80/CD86 on activated T cells, competitively inhibiting CD28, and binding to B7 co-stimulatory molecules expressed on antigen-presenting or tumor cells; this reduces the binding of B7 to CD28 and downregulates the expression of T cells [60]. Here, CD28 is linked to neoplasm.