Can be expressed on antigen presenting cells (APCs) or tumor cells;Interacts with both co-stimulatory (CD28) and coinhibitory receptors (cytotoxic T lymphocytes, antigen 4 (CTLA-4)) and regulates the immune response;The low level of CD80 expression serves as a tumor escape mechanism due to the higher affinity and therefore preferential binding of CTLA-4 to CD80 compared to CD28;In contrast, CD80 overexpression promotes T cell activation and tumor rejection, and CD80 deficiency also increases the immunogenicity of tumor cells. Here, CTLA4 is linked to neoplasm.