Flow Cytometric Aldehyde Dehydrogenase Assay Enables a Fast and Accurate Human Umbilical Cord Blood Hematopoietic Stem Cell Assessment

OBJECTIVE: Colony-forming units of granulocytes/macrophages (CFU-GM) analysis is the most widely used method to determine the hematopoietic stem cell (HSC) content of human umbilical cord blood (CB) for prediction of engraftment potential. The measurement of aldehyde dehydrogenase (ALDH) activity is a more recent method for HSC qualification. Our aim was to correlate phenotypic and functional assays to find the most predictive method. MATERIALS AND METHODS: In this study, flow cytometric quantitation of CD34(+) cells and ALDH positivity along with CFU-GM capacity were assessed in fresh and post-thaw CB units. RESULTS: Among 30 post-processing samples, for each CB unit the mean total number of nucleated cells (TNCs) was (93.8±30.1)x10(7), CD34(+) cells were (3.85±2.55)x10(6), ALDH(+) cells were (3.14±2.55)x10(6), and CFU-GM count was (2.64±1.96)x10(5). Among an additional 19 post-thaw samples the cell counts were as follows: TNCs, (32.79±17.27)x10(7); CD34(+), (2.18±3.17)x10(6); ALDH(+), (2.01±2.81)x10(6); CFU-GM, (0.74±0.92)x10(5). Our findings showed that in fresh samples TNCs, CD34(+) cells, and ALDH correlated highly with counts of CFU-GM, CFU-erythroids/granulocytes-macrophages/megakaryocytic cells (GEMM), and burst forming units of erythroids (BFU-E) as follows: TNCs, r=0.47, r=0.35, r=0.41; CD34+, r=0.44, r=0.54, r=0.41; and ALDH, r=0.63, r=0.45, r=0.6, respectively. In terms of post-thaw samples, the correlations were as follows: TNCs, r=0.59, r=0.46, r=0.56; CD34(+), r=0.67, r=0.48, r=0.61; and ALDH, r=0.61, r=0.67, r=0.67, for CFU-GM, CFU-GEMM, and BFU-E, respectively. All correlations were statistically significant. CONCLUSION: In our experience, HSC assessment by ALDH activity yields the highest correlation with conventional analytical methods, particularly for post-thaw samples. Thus, this fast, inexpensive method has the potential to overcome the weaknesses of other techniques.