Artificial Hematopoietic Stem Cell Niches-Dimensionality Matters

Hematopoietic stem cell niches are perhaps the best described niche system in mammals. The niches themselves, as well as their cellular and structural constituents and factors that play a role in maintaining the niche structure and function, are being refined on a more or less daily basis. Despite this, it seems as if the more we know the harder it gets to mimic the in vivo-situation using in vitro-systems. This is due to the fact that hematopoiesis is a multi step maturation process leading to HSC heterogeneity. Subpopulations of HSCs and niche supporting cells can be defined depending on characteristics such as their potency of leading to successful reconstitution of sub lethally irradiated mice in serial transplantation experiments or, with less scientific impact, clonogenic assays. Since the bone marrow obviously provides all necessary information to maintain the stem cell pool constant and to adapt the number of blood cells according to physiologic needs, it has been the goal to engineer artificial niches that display at least one or several of the major characteristics of the in vivo-situation to make use of these systems for not only fundamental research purposes but, moreover, also for clinical applications. ... mehrThis review will give an overview of approaches to engineering artificial hematopoietic niches with a focus on the complexity/dimensionality of the systems used.