Single-cell analyses reveal aberrant pathways for megakaryocyte-biased hematopoiesis in myelofibrosis and identify mutant clone-specific targets

Myelofibrosisis a severe myeloproliferative neoplasmcharacterised by increased numbers of abnormal bone marrow megakaryocytesthat induce progressive fibrosis, destroying the hematopoietic microenvironment. To determine the cellular and molecular basis for aberrant megakaryopoiesis in myelofibrosis, we performed high-throughput single-cell transcriptome profiling of 50,538 hematopoietic stem/progenitor cells (HSPCs), single-cell proteomics, genomics and functional assays. We identified an aberrant pathway for direct megakaryocytedifferentiation from the earliest stages of hematopoiesis in myelofibrosisand associated aberrant molecular signatures, including surface antigens selectively expressed by JAK2-mutant HSPCs. Myelofibrosis megakaryocyteprogenitors were heterogeneous, with distinct expression of fibrosis and proliferation-associated genes and putative therapy targets. We validated the immunoglobulin receptor G6B as a promising JAK2-mutant clone-specific antigen warranting further development as an immunotherapy target. Our study paves the way for selective targeting of the myelofibrosisclone and more broadly illustrates the power of single-cell multi- omicsto discover tumor-specific therapeutic targets and mediators of tissue fibrosis.