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BACKGROUND:  The information regarding the minimum number of CD34+ cells that are necessary to reconstitute hematopoiesis in patients undergoing peripheral blood progenitor cell transplantation is quite controversial. Some of the differences in these figures might be due to the selection of antibodies, staining protocols, and acquisition strategies for the flow cytometric enumeration of these cells.

STUDY DESIGN AND METHODS:  Twenty-seven human umbilical cord blood samples and 33 leukapheresis products were consecutively collected for this study. Cells were stained following two different protocols, both using monoclonal antibodies to CD45 and CD34, and analyzed by the same operator in two different flow cytometers to enumerate the percentage of CD34+ mononuclear cells.

RESULTS:  Relevant differences in the proportion of cells were encountered, and the correlation between the results yielded by both instruments and protocols, although statistically valid, was suboptimal.

CONCLUSIONS:  Both interinstrument and interprotocol variation can provide additional explanation for the redundantly reported discrepancies concerning the numbers of CD34 cells that suffice to secure hemopoietic grafting. These results point to the need for new and different standardization approaches in this clinically relevant field.