Like CD28, CTLA-4, which is expressed on antigen-presenting cells (APCs), has B7 ligands (CD80 and CD86), which have been shown to exhibit upregulated expression in acute myelocytic leukemia (AML) cells [85], and the affinity of CTLA-4 for the B7 ligands is higher than that of CD2 8[86]. Here, CTLA4 is linked to acute myeloid leukemia.