Monocyte and Lymphoid Lineages Share a Common Precursor Distinct from Neutrophils in Hematopoiesis

Abstract

During lineage commitment in hematopoiesis, hematopoietic stem cells (HSCs) differentiate into distinct lymphoid and myeloid lineages. Within the myeloid lineages, granulocytes and monocytes have been considered to originate from granulocyte-macrophage progenitors (GMPs) or common myeloid progenitor (CMPs). Single-cell sequencing has refined this hematopoietic hierarchy, revealing that neutrophils and basophils diverge early during commitment. Although current hierarchy models propose that neutrophils and monocytes arise from common neutrophil-macrophage progenitor (NMP) or GMP, their early differentiation trajectories remain inconsistent, leaving the origin relationship between neutrophils and monocytes unclear. This study aimed to clarify the developmental origin of neutrophils and monocytes during hematopoiesis. Leveraging a previously established single-cell atlas of hematopoietic progenitor cells (HPCs), we refined a trilineage hierarchy model, revealing the direct commitment of neutrophils from early multipotent progenitors (MPCs) and their divergence from lymphoid lineages. HOPX was identified as a key regulator during lymphoid lineage commitment. Using HOPX-based lineage tracing, we reconstructed the differentiation trajectory of neutrophils and monocytes. Lineage-tracing results revealed that HOPX-derived tdTomato positive cells contribute extensively to lymphoid lineages and monocytes, but not to neutrophils or erythroid cells. Ex vivo primary macrophage cultures derived from bone marrow cells yielded consistent findings. Our results indicate that monocytes are committed from same precursor with lymphoid lineages, and diverge from neutrophils. Moreover, we propose that classical common lymphoid progenitors (CLPs), redefined as lymphoid-monocyte progenitors (LMPs), rather than GMPs, constitute the likely ancestral source of monocyte lineage. These findings challenge the dogma of hematopoietic hierarchy and open new avenues for understanding lineage specification. Future studies involving conditional knockout of HOPX will provide further mechanistic validation of these conclusions.