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Extent of variability inherent in measurements of CD34-positive cells in different human haemopoietic tissues.

Estimation of CD34 expression is widely used to detect and quantify progenitor cells in haemopoietic tissues used as stem cell sources for transplantation. Mouse monoclonal antibodies to CD34 recognise different epitopes of the mucin-like sialoglycoprotein. These epitopes can be grouped into three classes by their differing sensitivities to the enzymes: neuraminidase, chymopapain and glycoprotease. We have compared the expression, by flow cytometry, of the three CD34 epitopes on normal adult and fetal haemopoietic tissue and in chronic myeloid leukaemia, and have used four antibodies from each class to assess variability of staining within and between epitope classes. The results reveal variable expression of CD34 both within and between tissue types and antibody classes. As a result of the different levels of detection by different antibodies, the apparent number of CD34-positive cells vary by approximately 6-fold. Enrichment for CD34 cells using magnetic bead technology shows a significant difference in the percentage of CD34 cells detected for two of the epitope types.