Primary mesenchymal niche in MDS. (A) UMAP overview of total cell populations with highlighted cells of nonhematopoietic origin, magnified and extracted in right panel. (B) Gene expression highlighted in UMAP subspace for the key mesenchymal marker CXCL12 and endothelial marker PECAM1. (C) Epitope density derived from CITE-seq for CD271 and CD31, 2-sided t test. (D) Differential gene expression between pseudobulked MSCs and ECs for MDS/HY comparison. (E-F) Subclustering of n = 418 primary classified MSCs resembles 6 subpopulations that were color-coded. (G) Heat map of marker genes for different MSCs subpopulations, z scored. (H) Gene expression of CXCL12 per MSC subcluster and condition; each dot represents a CXCL12-expressing cell. (I) Quantification of distribution of MSC subpopulations for each donor. FDR, adjusted false discovery rate; NES, normalized enrichment score.