CTLA4, which is up-regulated after T cell activation (2), is homologous to the T cell costimulatory protein CD28, and bind to its ligands CD80 and CD86 on many tumors and on cells within the tumor microenvironment (TME), such as antigen-presenting cells, B cells, macrophages, and the stromal cell subset (4). The gene discussed is CTLA4; the disease is neoplasm.