Regulatory T cells (Tregs) can express CTLA-4 constitutively, which is considered to be dominant for their suppressive functions.120 In tumor models, suppressive functions of Tregs can be impaired by genetic CTLA-4 deficiency.121 One of the mechanisms of Tregs controlling effector T cells is downregulating B7 ligands on antigen-presenting cells (APCs), and then reducing CD28 costimulation.122. Here, CTLA4 is linked to neoplasm.