In-vitro clonogenicity of mobilized peripheral blood CD34-expressing cells: inverse correlation to both relative and absolute numbers of CD34-expressing cells

The determination of CD34-expressing cells by multiparameter flow cytometry is now widely used to estimate the reconstitution potential of cells harvested by cytapheresis for peripheral blood stem cell and progenitor cell transplantation. There is a correlation between the number of CD34-expressing cells collected and committed progenitor cells (CFU-GM and BFU-E) capable of forming colonies in vitro, but there is considerable variation in the proportion of CD34-expressing cells capable of clonogenic growth. The data in this study of 782 cytapheresis samples indicates that there is a negative correlation between the clonogenicity of the CD34-expressing cells and the absolute number or the proportion of CD34-expressing cells within the harvest. In 116 samples the proportion of CD34-expressing cells co-expressing the CD45-RA-antigen (a subset of CD34-expressing cells which includes virtually all clonogenic cells in terms of CFU-GM) was determined, but this did not help to identify the clonogenicity of a given sample. These findings may have clinical relevance, particularly when mobilization is judged to be relatively poor or when a good harvest is to be divided for multiple high-dose procedures.