Aldehyde Dehydrogenase-Positive Hematopoetic Progenitor Cells in Peripheral Blood and Progenitor Cell Apheresis Products: Characterization and Correlation with Kinetics of Engraftment.

Hematopoietic progenitor cells are rich in aldehyde dehydrogenase (ALDH) activity, allowing their identification using fluorogenic substrates (Aldefluor^®, StemCo Biomedical, Durham, North Carolina) and Fluorescence-activated cell sorting (FACS). We compared the numbers of ALDH⁺ cells in peripheral blood and progenitor cell harvests with the numbers of CD34-positive cells. Furthermore, we compared the numbers of ALDH⁺ cells with the kinetics of hematopoietic engraftment following high-dose chemotherapy (HDCT) and transplantation of autologous stem cell harvests (SCT).

25 Patients (Multiple Myeloma, n=10, Hodgkin’s disease, n=3, mantle cell lymphoma, n=3, follicular lymphoma, n=2, T-cell lymphoma, n=3, Burkitt-like lymphoma, n=3) were included in treatment protocols involving high-dose chemotherapy, and received mobilization chemotherapy and G-CSF (10 μg/kg/d s.c.). The numbers of CD34-positive cells were determined daily, and peripheral blood progenitor cell apheresis was initiated when adequate. PBPC collections were performed on an AS 104 cell separator (Fresenius AG, St. Wendel, Germany). Samples of peripheral blood and of progenitor cell harvests were routinely tested for the numbers of CD34-positive cells and ALDH⁺ cells. The enrichment of CD34-positive cells was calculated and compared to the numbers of ALDH⁺ cells. 20 patients (Multiple Myeloma, n=10, Hodgkin’s disease, n=3, mantle cell lymphoma, n=3, follicular lymphoma, n=2, T-cell lymphoma, n=2) proceeded to HDCT followed by reinfusion of progenitor cell harvests. The enrichment of ALDH⁺ cells in the course of apheresis exceeded the enrichment of CD34-positive cells slightly (18,3fold +/−12,8 vs. 15,7fold +/−10,2). The percentage of CD34-negative cells among ALDH+ cells was comparable in peripheral blood and in the harvest, whereas the population of CD34-positive, ALDH−negative cells varied substantially in the peripheral blood (CD34−/ ALDH⁺: 7,53% +/−5,2% (pB) vs. 6,52% +/−3,9 (harvest); CD34+/ALDH−: 24,6% +/−12,3% (pB) vs. 11,9% +/−9,3% (harvest).

Following HDCT and SCT, the numbers of ALDH⁺ cells and of CD34⁺ cells in the peripheral blood on the day of apheresis and in the harvests were compared with the reconstitution of the peripheral blood count. In a regression analysis, the number of ALDH⁺ cells in the peripheral blood on the day of apheresis (p=0,005), the number of ALDH⁺ cells transfused (p=0,01) and the number of CD34-positive cells transfused (p=0,012) were independent predictors of early recovery of the leukocyte counts. CD34-positive and ALDH⁺ cells appear to comprise partially different subsets of hematopoietic progenitor cells. The quantitation of ALDH⁺ cells may allow a more reliable prediction of the numbers of early hematopoietic progenitor cells than the assessment of CD34-positive cells and thus may be of predictive value for the recovery of leukocytes following SCT.