Summary:over, plasma factors (eg paraprotein) may also have some impact. In summary, the Isolex 50 provides a high Immunomagnetic separation with anti-CD34 monopurity of CD34 ؉ cells and depletion of tumor cells was clonal antibodies and paramagnetic microbeads has efficient. However, calculated and experimental purging been used to enrich hematopoietic stem cells from efficiencies are not necessarily identical. human bone marrow (BM) or mobilized peripheral Keywords: immunomagnetic separation; CD34 + hematoblood mononuclear cells (PBMNC). The introduction of poietic cells; peripheral blood mononuclear cells; tumor this technique also constitutes a new principle of tumor cell purging; breast cancer cells; cloning assay cell purging. The efficiency in terms of purging tumor cells from PBMNC was evaluated in seven different experiments. Mobilized (chemotherapy and G-CSF) PBMNC were collected from patients with solid tumors Autologous reinfusion of peripheral blood mononuclear (n = 6) and multiple myeloma (n = 1) by leukapheresis cells (PBMNC) after high-dose chemotherapy constitutes using an automated MNC separation system and conan important alternative to autologous bone marrow transtaminated with 1% (n = 5) or 10% (n = 2) tumor cells plantation in patients with hematologic malignancies or from different epithelial cell lines being CD34-negative.solid tumors. 1-6 The cell mixture was sensitized with anti-CD34 (9C5)There are multiple advantages of PBMNC reinfusion vs antibodies and sheep anti-mouse IgG1 paramagnetic autologous bone marrow transplants. The collection promicrospheres and enriched for CD34 ؉ cells using an cedure with a central i.v. line is much easier abrogating any Isolex 50 magnetic separator. Purity of CD34 ؉ cells was need for general anesthesia for the donor. Hematological studied by flow cytometry (FACScan) and tumor cell reconstitution in the recipient is faster 4-7 which contributes depletion was evaluated by comparative human tumor to applicability of high-dose protocols. cloning assays (HTCA) containing methylcellulose and Although the rate of tumor cell contamination in agar. We achieved a median purity of CD34 ؉ cells of PBMNC has been reported to be significantly lower than 85.9% (range 69.8-92.9%) and a median yield of 48.1% in bone marrow transplants 8 the circulation of tumor cells (range 21.0-85.2%). From these data in each case the in the PBMNC transplant remains a major concern regardestimated log depletion of tumor cells was calculated ing the prognosis of patients. [9][10][11][12][13][14][15][16] Brenner et al 15 showed and compared with the experimentally achieved with genetic markers that residual tumor cells in autologous (HTCA) log depletion (log ⌬ depletion = log experibone marrow transplants can contribute to disease recurmental depletion − log calculated depletion). In our rence. Moreover, mobilization of hematopoietic stem cells experiments we achieved a median depletion of 2.75 log into peripheral blood by applying chemotherapy followed (range 1.55-3.69 log). When corr...

+ : 12.8%) and Isolex300/Isolex50 (n = 2; TCD: 3.8 log; yield CD34 + : 43.2%). Furthermore, we have established and tested a new simultaneous ؉/؊ selection method by using CD34-specific releasing agent PR34؉ in the Isolex300i. With this method we have obtained a mean total yield-corrected TCD of 4.7 log (n = 4; range: 4.1-6.0 log) with high CD34 + cell yield (mean: 69.8%) and CD34 + cell purity (mean: 92.8%). Since this new simultaneous ؉/؊ purging procedure is safe, applicable within a closed system (GMP-like) and most effective, we recommend it for further testing in a clinical setting.