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

Primary myelofibrosis (PMF) is a myeloid proliferative neoplasm (MPN) characterized by bone marrow fibrosis. Pre-fibrotic PMF (pre-PMF) progresses to overt PMF. Megakaryocytes play a primary role in PMF; however, the functions of megakaryocyte subsets and those of other hematopoietic cells during PMF progression remain unclear. We, therefore, analyzed bone marrow aspirates in cases of pre-PMF, overt PMF, and other MPN using single-cell RNA sequencing. We identified 14 cell types with subsets, including hematopoietic stem and progenitor cells (HSPC) and megakaryocytes. HSPC in overt PMF were megakaryocyte-biased and inflammation/fibrosis-enriched. Among megakaryocytes, the epithelial-mesenchymal transition (EMT)-enriched subset was abruptly increased in overt PMF. Megakaryocytes in non-fibrotic/non-PMF MPN were megakaryocyte differentiation-enriched, whereas those in fibrotic/non-PMF MPN were inflammation/fibrosis-enriched. Overall, the inflammation/fibrosis signatures of the HSPC, megakaryocyte, and CD14+ monocyte subsets increased from pre-PMF to overt PMF. Cytotoxic and dysfunctional scores also increased in T and NK cells. Clinically, megakaryocyte and HSPC subsets with high inflammation/fibrosis signatures were frequent in the patients with peripheral blood blasts ≥1%. Single-cell RNA-sequencing predicted higher cellular communication of megakaryocyte differentiation, inflammation/fibrosis, immunological effector/dysfunction, and tumor-associated signaling in overt PMF than in pre-PMF. However, no decisive subset emerged during PMF progression. Our study demonstrated that HSPC, monocytes, and lymphoid cells contribute to the progression of PMF, and subset specificity existed regarding inflammation/fibrosis and immunological dysfunction. PMF progression may depend on alterations of multiple cell types, and EMT-enriched megakaryocytes may be potential targets for diagnosing and treating the progression.