CD34 is an antigen selectively expressed on human lymphoid and myeloid hematopoietic progenitor/early
precursor cells. The antigen is also expressed on vascular endothelium. We have found that the antibody
that is most reliable in paraffin sections is QBEND10, a monoclonal antibody made in mice against human
endothelial cells. We use the antibody with a microwen-based heat induced epitope retrieval technique.
CD34 works well both in formalin fixed and in B5 fixed material and does not appear to be materially
inhibited by decalcification.
We have had a particular interest in studying CD34 in human bone marrows. The antigen is found expressed in
1-2% of the total nucleated cells in normal human bone marrows. Reactive marrow conditions and the
administration of hematopoietic cytokines which are known to increase the number of CD34+ peripheral blood
cells, do not measurably increase this percentage. About two-thirds of all cases of ALL and about one-third
of AML are CD34+. We and others have demonstrated that there is a good correlation between the percentages
of CD34 positivity in marrow by flow cytometry and immunohistochemistry. As a result, we have found the
CD34 immunostain to be a value in assessing minimal residual disease in patients with acute leukemias that
are CD34+, and have demonstrated that there is good correlation between the presence of minimal residual
disease as documented by cytogenetics and by CD34 immunostaining. In addition we have shown that CD34
immunostain may be used to subclassify the different phases of CML. CD34 immunostain may also be useful in
discriminating between aplastic anemia and hypoplastic myelodysplastic syndrome.
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