Isolation of CD34⁺ cells from blood stem cell components using the Baxter Isolex system

Abstract

The CD34 antigen is expressed by human hematopoietic progenitor and stem cells. These cells are capable of reconstituting marrow function after marrow-ablative chemo-radiotherapy. Several different technologies have been developed for the separation of CD34⁺ cells from bone marrow or peripheral blood stem cell (PBSC) components. We used an immunomagnetic separation technique to enrich CD34⁺ cells from PBSC components in anticipation of autologous transplantation for patients with B lymphoid malignancies. Twenty-nine patients enrolled on this study and received mobilization chemotherapy followed by G-CSF. Of these, 21 achieved a peripheral blood CD34⁺ cell level of at least 2.0 × 10⁴/l required by protocol for separation of the stem cell components. A median of three components per patient was collected for processing. The average CD34⁺ cell concentration in the components after apheresis was 1.0 ± 1.2%. After the CD34⁺ cell selection, the enriched components contained 0.6 ± 0.6% of the starting nucleated cells. The recovery of CD34⁺ cells, however, averaged 58.4 ± 19.2% of the starting cell number, with a purity of 90.8 ± 6.5%. Overall depletion of CD34⁻ cells was 99.96 ± 0.06%. Nineteen patients were treated with marrow-ablative conditioning regimens and received an average of 6.2 ± 2.0 × 10⁶ CD34⁺ cells/kg body weight. These patients recovered to an ANC >0.5 × 10⁹/l at a median of 11 days (range 8–14), and platelet transfusion independence at a median of 9 days (range 5–13). Four patients died of transplant-related complications or relapse before 100 days after transplantation. No patient required infusion of unseparated cells because of failure of sustained bone marrow function. These data demonstrate that peripheral blood-derived CD34⁺ cells enriched by use of an immunomagnetic separation technique are capable of rapid engraftment after autologous transplantation.