PDCD1 and myelodysplastic syndrome: Secreted factors in the microenvironment, such as IFN-γ and TNF-α, upregulate PD-L1 expression [142,143] and recently, the role of S100A9, a central molecule in the MDS pathophysiology, as an inducer of PD-1 and PD-L1, has been detected [144].