Hematopoietic stem cells
Summary
Hematopoietic stem cells (HSCs) are multipotent, self-renewing cells residing primarily in the bone marrow that give rise to all blood cell lineages—myeloid and lymphoid. They express CD34 surface marker and are the basis for bone marrow/stem cell transplantation. HSCs balance quiescence, self-renewal, and differentiation to maintain lifelong hematopoiesis.
Detail
HSCs originate embryologically from the yolk sac, then aorta-gonad-mesonephros (AGM) region, and finally colonize the fetal liver before settling in bone marrow after birth. They reside in specialized bone marrow niches (endosteal and perivascular) that regulate their quiescence via signals like CXCL12, SCF, and Notch. HSCs undergo asymmetric division, producing one daughter that self-renews and another that differentiates into multipotent progenitors, which further commit to common myeloid progenitors (giving rise to erythrocytes, platelets, granulocytes, monocytes) or common lymphoid progenitors (giving rise to T cells, B cells, NK cells). Key transcription factors include GATA-1 (erythroid/megakaryocytic), PU.1 (myeloid/lymphoid), and Ikaros (lymphoid). Clinically, HSCs are identified by CD34+ CD38- surface markers and are harvested for autologous or allogeneic hematopoietic stem cell transplantation (HSCT) in conditions like leukemia, lymphoma, aplastic anemia, and certain immunodeficiencies. Mobilization agents like G-CSF are used to increase peripheral HSC numbers for collection. Understanding HSC biology is essential for grasping leukemogenesis (clonal expansion of abnormal HSC-derived cells), myelodysplastic syndromes, and the pathophysiology of bone marrow failure syndromes. Board exams often test knowledge of HSC markers, niche interactions, and their role in transplantation medicine.
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Kumar, Abbas, Aster - Robbins Basic Pathology
- Goldman-Cecil Medicine
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