Evaluation of eluents from separations of CD34(+) cells from human cord blood using a commerical, immunomagnetic cell separation system

Human CD34+ cells from cord blood were separated in a two-step process usin g a commercial, immunomagnetic cell retention system. The performance of th e system was evaluated by analyzing a number of eluents from the separation s with a number of analytical techniques. In addition to cell counts and fl ow cytometry analysis, a new experimental technique that is undergoing deve lopment, cell tracking velocimetry (CTV), was used. CTV measures the degree to which a cell is immunomagnetically labeled, known as the magnetophoreti c mobility, of a population of cells on a cell-by-cell basis and presents t he results in the form of a histogram similar to flow cytometry data. The a verage recovery and purity of CD34+ cells from 10 separations was 52% and 6 0%, respectively. CTV analysis indicated that the mean magnetophoretic mobi lity of the positively enriched CD34 cells was 9.64 x 10(-5) mm(3)/T-A-s, w hile the mean mobility from negative eluents was -2.02 x 10(-6) mm(3)/T-A-s , very similar to the mobility of unlabeled cells. Within the positive elue nts, the range of magnetophoretic mobility was approximately 50-fold, repre senting a plausible 50-fold range in surface CD34 antigen expression. CTV a nalysis also indicated that in some separations, positive cells were not re tained by the immunomagnetic cell retention system. Finally, preliminary st udies indicate that monocytes might be a primary cause in the lower puritie s and recoveries seen in this study. It is suggested that the monocytes pha gocytose the magnetic nanobeads and become sufficiently magnetized to be re tained within the Miltenyi column, reducing the purity of the positive elue nt.