CD274 and myelodysplastic syndrome: It was also reported that overexpression of PD-1 on stroma/non-blast compartment and its ligands (PD-L1 and PD-L2) on CD34+ leukemia cells is associated with more aggressive leukemia and progression from Myelodysplastic syndromes (MDS) to AML or AML relapse [7, 8].