Measuring stem cell function in vivo
Because in vitro tests do not duplicate the environment within an animal, we use a series of in vivo assays to analyze the function of hematopoietic stem cells (HSCs) in healthy mice. In the vital readouts of cell function, we test for confounding effects of enrichment. We measure functional abilities relative to a standard marrow pool, as proportions of myeloid and lymphoid cell types produced in the recipients by the cells of interest vs. the standard. Using small precursor numbers with 20–40 recipients, we use Poisson statistics to test numbers of stem cells and functional ability per stem cell.
A major advantage of our competitive methods that test HSCs in vivo is the unambiguous measure of stem cell exhaustion as clonal instability. Recipients are repopulated with HSCs of 2 distinguishable glucophosphate isomerase (GPI) types, using low cell numbers and many recipients, so that variances are high and correlations are accurate. Because the same HSCs continue to produce descendants proportionally within each recipient, the proportion of donor-type blood cells remains stable after 3–4 months. Correlation coefficients between times are very high (0.7–0.9).
Following is an overview of the way we measure stem cell function in vivo. The overview is divided into 3 parts.