CTLA4 and myelodysplastic syndrome: As myeloid derived suppressor cells (MDSC) are expanded in AML and MDS [43,44], a reduction in Ly6C+/Ly6G+ cells in this model may indicate a reduction in MDSCs after 5-Aza treatment, although, as with the CD4+ and CD8+ T-cells, increased expression of PD-L1 and CTLA-4 on MDSC may intensify their suppressive function leading to eventual resistance.