Photo of William H. Fleming, M.D., Ph.D.

William H. Fleming M.D., Ph.D.

    • Professor of Pediatrics School of Medicine
    • Cancer Biology Graduate Program School of Medicine
    • Cell and Developmental Biology Graduate Program School of Medicine
    • Program in Molecular and Cellular Biosciences School of Medicine

Over the past several years, my laboratory has been interested in functional relationship between hematopoiesis and blood vessel formation. Recently, we have found that adult vascular endothelial cells are an important component of the hematopoietic microenvironment. Specifically, endothelial cells can produce signals that protect hematopoietic stem cells (HSCs) from radiation induced cell death. Classical  studies in embryology demonstrated the existence of the hemangioblast, a stem cell that can give rise to both hematopoiesis and blood vessels. To address the question of whether bone marrow derived cells with hemangioblast activity exist in the adult, the vascular compartment of bone marrow transplanted mice and humans was carefully evaluated for the presence of donor derived cells. A similar frequency of bone marrow derived endothelial cells was detected in both mouse and human transplant recipients. A single HSC can give rise to both hematopoietic and endothelial cells in vivo providing direct evidence for the existence of an adult hemangioblast. Additional studies demonstrate that endothelial cells can arise from hematopoietic progenitors cells committed to the myelomonocytic cell lineages. These functional interactions between HSCs and blood vessels represent a new area of investigation that has important implications for our understanding of both normal and malignant hematopoiesis.

  • Residency:

    • 1987- 89 Stanford University Hospital, Stanford
  • Fellowship:

    • 1989- 93 Stanford University Hospital, Stanford
  • Certifications:

    • Internal medicine, medical oncology

Memberships and associations

  • Internal medicine, 1995

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