ASSAY OF HUMAN STEM-CELLS BY REPOPULATION OF NOD SCID MICE/

The only conclusive method to assay stem cells is to follow their abil ity to repopulate conditioned recipients, making it difficult to study human stem cells, The development of systems to transplant human hema topoietic cells into immune-deficient mice lays the foundation for suc h an experimental repopulation assay for primitive human cells, Cell p urification and gene marking studies have shown that the repopulating cells, termed severe-combined immunodeficiency (SCID) mouse-repopulati ng cells (SRC), are primitive and distinct from most of the progenitor s that are detected using short and long-term in vitro culture assays, The SRC are exclusively CD34(+)CD38(-) and poorly infected with retro virus vectors, These gene marking data are reminiscent of the human cl inical trials establishing that the SRC assay is a good surrogate to d evelop improved transduction methods, Limiting dilution analysis has b een used to establish a quantitative assay for SRC that can be used to precisely determine the effect of various cytokine cocktails on the p roliferation and differentiation of SRC during in vitro culture.