CTLA4 and cancer: Tregs suppress APC function via down-regulating CD80/CD86 with cytotoxic T lymphocyte associated antigen-4 (CTLA-4) expression, and reduce responder T cells by competitively consuming surrounding interleukin-2 (IL-2), as key mechanisms in cancer immune suppression, proceed effector T cell anergy in antitumor response [36].