CD80 and cancer: A second immunomodulatory system hijacked by cancer cells is the one composed by CTLA-4 (Cytotoxic T-Lymphocyte Antigen 4) receptor, known to be exclusively inducible expressed in T lymphocytes, and constitutively expressed in regulatory T cells (Tregs).98 Normally, this system attenuates effector T cells (CD4+CD25-) and enhances regulatory T cells (CD4+CD25+).99–101 It is physiologically activated by antigen-presenting cells expressing CD80 (also known as B7.1) and CD86 (also known as B7.2), known CTLA-4-ligands.