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Simultaneous Immunomagnetic CD34+ Cell Selection and B-Cell Depletion in Peripheral Blood Progenitor Cell Samples of Patients Suffering from B-Cell Non-Hodgkin’s Lymphoma¹

Departments of Medicine/Hematology and Oncology [M. M., F. D., E. H., E. O., M. Z., K. K., A. N., C. S., H. S., J. K., W. E. B.] and Transfusion Medicine [D. Ö., U. C., W. S.], University of Münster, D-48129 Münster, Germany

The reduction of residual tumor cells is one of the main targets of leukapheresis product (LP) processing. Immunomagnetic enrichment/selection of CD34+ progenitor cells (Baxter Isolex 300i) can achieve a reduction of contaminating B-cells of approximately 2–3 logs in B-cell non-Hodgkin’s lymphoma patients. Specific release of the enriched CD34+ cells (stem cell releasing agent PR34+; Baxter) and the use of antibody-coated immunobeads targeted against B-cell markers (CD10, CD19, CD20, CD22, CD23, and CD37) during this procedure allows the GMP-like simultaneous capture of residual B cells within a closed system. This combination of two purging techniques enhances the B-cell depletion capacity up to 4.5 logs. By performing 10 clinical-scale purging procedures, we could show that the simultaneous immunomagnetic purging method is easy to perform and highly efficient. We evaluated B-cell log depletion by flow cytometry for cases with marker-positive cells detectable before and after the purging procedure. The mean reduction of B-cells in these cases was 3.5 logs; the mean CD34+ cell yield and purity were 47 and 92%. Using three LPs, we tested the procedure on a modified Baxter Isolex 300i device with software adaptations for this procedure (software version 2.0) in direct comparison with CD34+ cell selection only, using the former version (version 1.12). The CD34+ cell yield was 49% (40–54%) for the CD34+ cell selection and 51% (19–72%) for simultaneous double selection. The mean purity was 96% for CD34+ cell selection and 98% for simultaneous double selection. B-cell depletion was 1.9 logs for CD34+ cell selection, and after simultaneous double selection, the B-cell content was decreased by 3.7 log steps (P = 0.0495). Clinical application of double-purged cells has not prolonged the hematopoietic recovery times after high-dose therapy as compared with nonpurged peripheral blood progenitor cell autotransplants. In conclusion, we could show that the simultaneous double selection protocol developed leads to a highly increased B-cell purging efficacy when compared with CD34+ cell selection without any negative effects regarding CD34+ cell yield and engraftment times after high-dose therapy.

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