Toward modeling the bone marrow niche using scaffold-based 3D culture systems.

In the bone marrow, specialized microenvironments, called niches, regulate hematopoietic stem cell (HSC) maintenance and function through a complex crosstalk between different cell types. Although in vivo studies have been instrumental to elucidate some of the mechanisms by which niches exert their function, the establishment of an in vitro model that recapitulates the fundamental interactions of the niche components in a controlled setting would be of great benefit. We have previously shown that freshly harvested bone marrow- or adipose tissue-derived cells can be cultured under perfusion within porous scaffolds, allowing the formation of an organized 3D stromal tissue, composed by mesenchymal and endothelial progenitors and able to support hematopoiesis. Here we describe 3D scaffold-based perfusion systems as potential models to reconstruct ex vivo the bone marrow stem cell niche. We discuss how several culture parameters, including scaffold properties, cellular makeup and molecular signals, can be varied and controlled to investigate the role of specific cues in affecting HSC fate. We then provide a perspective of how the system could be exploited to improve stem cell-based therapies and how the model can be extended toward the engineering of other specialized stromal niches.