Enumeration of CD34+ hematopoietic progenitor cells in peripheral blood and leukapheresis products by microvolume fluorimetry: A comparison with flow cytometry

There is increasing interest in both standardization and simplification of methods for enumeration of CD34+ hematopoietic progenitor cells (HPC) to facilitate cellular therapies and to improve interinstitutional comparison of clinical and laboratory results. We evaluated a novel method for CD34+ cell enumeration based on microvolume fluorimetry (MVF) compared with our laboratory's routine flow cytometric method on samples of peripheral blood and leukapheresis products. The MVF method is semiautomated and uses a 633-nm light from a helium-neon laser to scan fluorochrome-labeled cells held in stasis in a capillary of known volume. The performance of the MVF assay for enumeration of CD34+ cells was found to be comparable to our routine flow cytometric assay in linearity and accuracy in the range of 5-1500 cells per microliter. Precision of MVF for replicate assays on the same instrument was demonstrated by coefficient of variation (CV) values of 8.4% at a CD34+ cell concentration of 284/mu l for a sample volume of 0.8 mu l, and 15.7% at 12/mu l for a sample volume of 3.2 mu l. Precision among three different instruments was demonstrated, using sample volumes of 1.6 mu l, by CV values of 44% at 6 cells/mu l and 4.6% at 733 cells/mu l. In a field sample evaluation, precision of the entire assay system for paired measurements on 0.8-mu l sample volumes was demonstrated by CV values of 50%, 31%, and 15% for peripheral blood samples with concentrations of 0-10, 10-20, and 20-100 CD34+ cells/mu l, respectively, and 6.3%, 8.1% and 6.5% for leukapheresis samples with concentrations of 0-100, 100-1000, and 1000-2500 CD34+ cells/mu l, respectively. The MVF assay was easy to perform, required minimal technical training time, and had a turnaround time of 40 min, of which less than 10 min was actual technical time. These observations suggest that the MVF method for CD34+ cell enumeration may prove useful to clinical laboratories providing support for HPC collection, processing, and transplantation services that require relatively simple, rapid assays for product quality control or to guide real-time clinical decisions.