CTLA4 and neoplasm: Cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), also known as CD152, is a membrane protein expressed on CD4+ and CD8+ T cells that is involved in the downregulation of T cell immune response at the tumor site upon interaction with CD80/B7.1 and CD86/B7.2 on APC [91,148].