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Hematopoietic stem cells in coculture with mesenchymal stromal cells - modelling the niche compartments in vitro

¹ Medical Clinic and Policlinic I, University Hospital, Dresden, Germany
² Biotechnology Center, Technical University, Dresden, Germany

Correspondence: Rainer Ordemann, Medical Clinic and Policlinic I, University Hospital Dresden 01307 Dresden, Germany. Phone: international +493514588114. E-mail: rainer.ordemann{at}uniklinikum-dresden.de

ABSTRACT

Background: Hematopoietic stem cells located in the bone marrow are interacting with a specific microenvironment referred to as the stem cell niche. Data derived from ex vivo coculture systems using mesenchymal stromal cells as feeder cell layer suggest that cell-to-cell contact has a significant impact on hematopoietic stem cells expansion, migratory potential and stemness. Here we investigated in more detail the spatial relationship between hematopoietic stem cells and mesenchymal stromal cells during ex-vivo expansion.

Design and Methods: In the coculture system, we have defined three distinct localizations of HSCs relative to MSC layer: (i) those in supernatant (non-adherent cells); (ii) cells adhering on the surface of mesenchymal stromal cells (phase-bright cells) and (iii) cells beneath the mesenchymal stromal cells (phase-dim cells). Cell cycle, proliferation, cell division and immunophenotype of these three cell fractions were evaluated from day 1 to 7.

Results: Phase-bright cells contained the highest proportion of cycling progenitors during coculture. In contrast, phase-dim cells divided much slower and retained a more immature phenotype compared to the remaining cell fractions. The phase-dim compartment was soon enriched for CD34+/CD38- cells. Migration beneath the mesenchymal stromal cell layer could be hampered by inhibiting integrin ß1 or CXCR4.

Conclusions: Our data suggest that the mesenchymal stromal cell surface is the dominant location where hematopoietic stem cells proliferate, whereas the compartment beneath the mesenchymal stromal cell layer seems to be mimicking the stem cell niche for more immature cells. The SDF-1/CXCR4 interaction and integrin-mediated cell adhesion play important roles in the distribution of hematopoietic stem cells in the coculture system.