CTLA4 and acute lymphoblastic leukemia: Although, we did not find statistical differences in intracellular/surface frequency of CTLA-4+ cells among ALL+ (37.5 ± 6.5) and ALL− (15.1 ± 2) T helper cells (P = 0.05) (data not shown); the percentage of TGF-β+ cells was statistically higher in ALL+CD4+ T cells (98%) than in ALL−CD4+ T cells (51%) (P = 0.02) (Figure 5(c)).