First, S100A9 expression appears unaffected by the epigenetic drug 5-azacytidine [40], and S100A9-directed induction of PD-1/PD-L1 may contribute to therapeutic resistance of MDS to 5-azacytidine, which also induces the expression of these immune checkpoints [15]. Here, S100A9 is linked to myelodysplastic syndrome.