Spatially resolved transcriptomic profiling of myelofibrosis spleen reveals compartment specific niche programs.

Myelofibrosis (MF) splenomegaly reflects not only extramedullary hematopoiesis (EMH) but a compartmental organization of the splenic microenvironment into spatially distinct niches. Using Spatial whole transcriptome profiling on FFPE spleen tissue from three MF patients, we interrogated three anatomically defined compartments: Intravascular (IV), Perivascular (PV) and Red Pulp (RP). Differential expression was estimated through pairwise compartment contrasts with Benjamini-Hochberg false discovery rate correction (FDR < 0.05, |log2FC|≥1), and compartment "core signatures" were defined by directional concordance across the two contrasts relevant to each compartment. IV regions of interest (ROIs) showed an endothelial/adhesion and vascular stress program (e.g., PECAM1, VCAM1; antioxidant enzymes). PV ROIs were characterized by fibro-remodeling and immune-structured signals (COL1A1/COL3A1, LOXL1, MMP2/TIMP1; HLA‑DRA/CD74) including CXCL12, consistent with a PV niche coupling extracellular matrix remodeling to hematopoietic retention cues. RP ROIs captured an EMH-associated erythroid/heme program (ALAS2, FECH, BLVRB) with stress and inflammatory alarmins (S100A8/S100A9). Together, these findings support a compartmental "division of labor" in MF spleen, vascular interface activation, PV remodeling/chemokine niches, and RP EMH/redox stress, providing a spatial framework to interpret splenomegaly as structured niche dependencies and to prioritize candidate microenvironmental dependencies for follow‑up validation.