CD34+ cell selection from frozen cord blood products using the Isolex 300i and CliniMACS CD34 selection devices

Ex vivo expansion of cord blood (CB) cells requires CD34+ cell selection before expansion to obtain optimal numbers of progenitor cells. As a preliminary step to preclinical development of CB expansion, we have evaluated two clinical scale selection devices, the Isolex 300i (Baxter Healthcare, Immunotherapy Division) and the CliniMACS (Miltenyi Biotech Inc.), for CD34+ cell selection from frozen CB products. As expansion of CB results in differentiation of cells, there may be a depletion of stem cells. Therefore, only a fraction of the CB should be expanded while a portion of the CB is maintained unmanipulated for infusion. After thawing of 40% fractions of each CB product, we observed >95% viable cells, with a median total WBC count of 1.8 x 10(8) cells. Use of the Isolex 300i resulted in a median purity of 51% CD34+ cells (n=8) and a median recovery of 34% CD34+ cells. Use of the CliniMACS resulted in a median purity of 54% CD34+ cells (n=10) and a median recovery of 80% CD34+ cells. The absolute number of CD34+ cells recovered after selection varied with samples from 6.7 x 10(4) to 3.2 x 10(6) CD34+ cells. Expansion of CD34+ cells from both systems resulted in >20-fold expansion of CFU-GM, with a median of 44-fold expansion. These data demonstrate the feasibility of selecting small fractions of frozen CB products using clinical scale CD34+ cell selection devices.

Purification of CD34+ cells is essential for optimal ex vivo expansion of umbilical cord blood cells

Allogeneic umbilical cord blood (UCB) cells have recently been used for transplantation following high-dose chemotherapy. However, the numbers of total cells, including progenitor cells, harvested are low compared with bone marrow or peripheral blood progenitor cell harvests. Therefore, we evaluated the potential of UCB cells for their ability to expand granulocyte-macrophage colony-forming cells (GM-CFC) and burst-forming unit-erythroid (BFU-E) cells over 10 days. We used an ammonium chloride lysing buffer to eliminate the majority of contaminating red blood cells. An average recovery of 61% of the starting number of white blood cells was obtained, while retaining 100% of the CD34+ cells. Ex vivo expansion cultures were established in Teflon cell culture bags (American Fluoroseal Corp, Columbia, MD) in 25 ml defined medium (Amgen Inc, Thousand Oaks, CA) containing 100 ng/ml each of stem cell factor (SCF), granulocyte colony-stimulating factor (G-CSF), and megakaryocyte growth and development factor. Either unselected UCB cells or CD34+ UCB cells, selected with Magnetic Activation Cell Sorting technology (Miltenyi Biotech GmbH, Bergisch Gladbach, Germany), were incubated for 10 days at 37 degrees C without refeeding. Unselected UCB cells seeded at 1 X 10(6)/ml produced an average expansion of 1.4-fold in total cells, 0.8-fold in GM-CFC, and 0.3-fold in BFU-E cells. By contrast, CD34+ selected UCB cells seeded at 1.0 X 10(4)/ml produced an average expansion of 113-fold in total cells, 72.6-fold in GM-CFC, and 49-fold in BFU-E cells. These data demonstrate that CD34+ cell selection is necessary for optimal expansion of both GM-CFC and BFU-E cells. The cell numbers thus obtained postexpansion may be sufficient for transplantation in adults.