Different inflammatory, fibrotic, and immunologic signatures between pre-fibrotic and overt primary myelofibrosis.

Primary myelofibrosis (PMF) is a myeloid proliferative neoplasm (MPN) characterized by bone marrow (BM) fibrosis. Pre-fibrotic PMF (pre-PMF) progresses to overt PMF. Megakaryocytes (MKs) play a primary role in PMF; however, the functions of MK subsets and those of other hematopoietic cells during PMF progression remain unclarified. Therefore, we analyzed BM aspirates in pre-PMFs, overt PMFs, and other MPNs using single-cell RNA sequencing (scRNA-seq). We identified 14 cell types with subsets, including hematopoietic stem and progenitor cells (HSPCs) and MKs. HSPCs in overt PMF were MK-biased and inflammation/fibrosis-enriched. Among MKs, the epithelial-mesenchymal transition (EMT)-enriched subset was abruptly increased in overt PMF. MKs in non-fibrotic/non-PMF MPN were MK differentiation-enriched, whereas those in fibrotic/non-PMF MPN were inflammation/fibrosis-enriched. Overall, the inflammation/fibrosis signatures of the HSPC, MK, and CD14+ monocyte subsets increased from pre-PMF to overt PMF. Cytotoxic and dysfunctional scores also increased in T and NK cells. Clinically, MK and HSPC subsets with high inflammation/fibrosis signatures were frequent in the patients with peripheral blood blasts ≥1%. scRNA-seq predicted higher cellular communications of MK differentiation, inflammation/fibrosis, immunologic effector/dysfunction, and tumor-associated signaling in overt PMF than pre-PMF. However, no decisive subset emerged during PMF progression. Our study demonstrated that HSPCs, monocytes, and lymphoid cells contribute to PMF progression, and subset specificity existed regarding inflammation/fibrosis and immunologic dysfunction. PMF progression may depend on multiple cell types' alterations, and EMTenriched MKs may be potential targets for the diagnosis and therapy of the progression.