Expansion and Differentiation of Human Hematopoietic Cells from Static Cultures through Small‐Scale Bioreactors

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Abstract
Maintenance of the progenitor cells responsible for hematopoiesis has generally been accomplished using a feeder layer of stromal cells in stationary culture. Here, we compared the expansion of the total cell and progenitor cell populations using low‐density mononuclear cells (LDMCs) obtained from human bone marrow in static culture (T‐flasks) and in different cell culture bioreactors designed for the scale‐up of mammalian cells. Static cultures were performed without the presence of a previously established stromal cell layer. Expansion of marrow in all cases was accomplished through the use of added cytokines such as IL‐3, GM‐CSF, and c‐kit ligand. The results for the total cell expansion in static culture ranged from 4.4‐ to 32‐fold. The cell number increase was affected by such factors as patient to patient variability, freeze‐thawing, and the combination of cytokines used. Due to widespread use and the small amount of marrow needed, static cultures were used as a basis for comparison with other expansion systems. The cell culture systems used to evaluate the scale‐up of marrow cultures included suspension, microcarrier, airlift, and hollow fiber bioreactors. Using identical media, cytokines, and feed schedules, LDMCs in the suspension bioreactor expanded to a value of 1.6 compared to a normalized value of 1.0 for static cultures for the two runs investigated. Expansion results for microcarrier cultures averaged 0.75 when compared to static cultures. A cell number increase in the airlift bioreactor resulted in an expansion which was 0.70 of the control static culture. Granulocyte—macrophage and erythroid progenitor assay data were also evaluated for the suspension, microcarrier, and airlift bioreactors. A single run for the hollow fiber system demonstrated no observable expansion of hematopoietic cells when compared to control static cultures. However, this finding may be a reflection of the inefficiency in retrieving cells from the extracapillary space of the hollow fiber bioreactor. Although the expansion results observed here are of limited clinical utility, these studies provide a basis for future development for the scale‐up of hematopoietic cultures.

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