Summary:Primitive haemopoietic cells are required for studies in both the clinical and research fields and a number of systems have been developed to facilitate isolation of these haemopoietic cell populations. We have analysed the results from several European centres using positive selection of CD34 ؉ cells from haemopoietic tissues (n ؍ 110). Four selection techniques including immunoaffinity columns (Ceprate LC), immunomagnetic beads (Dynabeads, Baxter Isolex 50) and submicroscopic magnetic beads (MACS) were used and the selected CD34 ؉ cells were assessed for purity, yield and enrichment of colony-forming cells (CFC). The mean purities for all samples ranged from 68.4-78.4% for MACS, 33.9-69.9% for Dynabeads, 46.9-66.8% for Ceprate LC and 43.2-65% for Baxter Isolex 50. Yields were variable with all techniques. On average CFC enrichment using the immunoaffinity columns was greater than that observed for the other systems. Some techniques appear to be problematic and may require further expertise to improve the results. Nevertheless, the study demonstrates that highly purified CD34 ؉ cells can be isolated from various haemopoietic sources, though yield and CFC enrichment varies significantly depending on the technique selected. This extends our previous report indicating that not all selection methods generate similar results and that there are differences in the purity, number and colony-forming ability of the cells recovered. Keywords: CD34 + cells; positive selection; colony-forming cells; peripheral blood progenitor cells; umbilical cord blood; bone marrow Peripheral blood progenitor cells (PBPC) are used to reconstitute haemopoiesis after high-dose chemotherapy in both the autologous and allogeneic settings. As the time to engraftment is generally shorter than when bone marrow is used, the number of PBPC transplants performed each year has increased rapidly and they are gradually replacing auto- logous bone marrow transplants. Interest has also focussed on umbilical cord blood as another rich source of cells for transplantation and, to date, more than 600 of these transplants have been performed, primarily in children.
1-3The CD34 antigen is expressed on virtually all haemopoietic progenitor cells and their precursors and normal bone marrow, umbilical cord blood and PBPC grafts contain varying numbers of CD34 + cells. The isolated CD34 + cells can reconstitute haemopoiesis in humans following myeloablative chemotherapy, indicating that the cells responsible for short-term and long-term engraftment must reside within the CD34 + compartment. 4 This led to the use of CD34-positive cell selection as a method for durable engraftment after highdose chemotherapy. [4][5][6] The functional properties of CD34 + cells have been widely studied and many transplant centres now rely only on the enumeration of CD34 + cells as an indicator for both optimal timing of PBPC harvests and haemopoietic reconstitutive capacity. 7,8 There are many scientific and clinical applications for the isolated cells. Mechanisms involved...