EXPRESSION OF CD44 ISOFORMS BY HIGHLY ENRICHED CD34-POSITIVE CELLS INCORD-BLOOD, BONE-MARROW AND LEUKAPHERESES

CD34-positive cells were isolated from cord blood (n = 8), bone marrow (n = 4) and leukapheresed material (n = 7), using an immunomagnetic i solation technique, MACS (Miltenyi Biotec, Bergisch Gladbach, Germany) . In flow cytometric analysis, cell populations after enrichment revea led a fraction of 96.1% (cord blood), 96.2% (bone marrow) and 98.6% (l eukapheresis material) CD34-positive cells. Cells were further stained with antibodies specific for CD44 isoforms: CD44s (SFF-2), CD44v5 (VF F-8) and CD44v6 (VFF-18). CD44-positive cells were detected by directl y (FITC, fluorescein isothiocyanate) or indirectly (streptavidin-PE, p hycoerythrin)-conjugated fluorochromes in flow cytometric analysis. An alysis was restricted to CD34-positive cells. A high expression of CD4 4s was noted in all kinds of material under investigation with mean va lues in the range of 98.6-100%. There was little expression of CD44v6 (mean values in the range of 1.5-3.6%) and very slight expression of C D44v5 (mean values in the range of 0.6-1.4%). The finding that CD34-po sitive hematopoietic stem cells express CD44v5 and CD44v6 to a very sm all extent offers the possibility of using antibodies specific to CD44 v5 and CD44v6 in immunopurging in the course of autologous stem cell t ransplantation.