Given the unexplored role of the PD-1/PD-L1 pathway in MDS, and the poorly understood function of PD-1 in non-lymphoid cells, we first examined PD-1 surface receptor expression on HSPCs and erythroid progenitors isolated from the BM of MDS patients (n = 10) compared with normal donors (n = 6) (Supplementary Figure S2). This evidence concerns the gene CD274 and myelodysplastic syndrome.