Stem cell expansion: an initial step in functional tissue engineering

Ex vivo cell expansion represents a primary step in the road map of functional tissue engineering. Stem cells are frequently considered the optimal cell type for regenerative cell -based therapies; however they generally represent a small fraction of cells isolated from a biopsy or other cell source. We will present several aspects of expansion that must be considered; 1) the estimated expansion time to obtain the desired number of cells, 2) the changes of functional phenotype with expansion and 3) the possibility that during expansion, cells are brought closer to senescence or, conceivably, transformation. These are just some of the problems that bioengineers must address when stem cells are to be used in such functional regenerative therapies. Here we also present evidence suggesting that muscle-derived stem cells, which have undergone extensive expansion, have reduced ability, as compared to minimally expanded cells, to regenerate muscle in a murine mdx model for Duchenne Muscular Dystrophy.