Hematopoiesis is a finely tuned process involving self-renewal or proliferation/differentiation of hematopoietic stem cells (HSC) to respectively produce more HSC, or hematopoietic progenitor cells (HPC). HSC and HPC functions are controlled by cytokines, chemokines, and interactions with the bone marrow (BM) microenvironment. During the past grant period where we assessed the role of SIRT1, a member of the sirtuin family of deacetylases, on regulation of HSC and HPC we fortuitously came upon a phenomenon that we termed: extra physiologic oxygen shock/stress (EPHOSS). It is known that HSC and HPC reside in the BM in a more hypoxic (? 5% oxygen) environment than that of ambient air (~18-20 oxygen; normoxia), yet most investigators still study hematopoiesis and HSC/HPC function under normoxia. However, our work, over the last 28 years, and that of others evaluating effects of lowered oxygen tension on growth of HSC and HPC were based on experiments in which cells removed from mice and man were subjected to normoxia, prior to placing the cells under hypoxia. We reasoned that even a relatively short interval of minutes to hours in normoxia might change the phenotypic characteristics and functional activities of HSC and HPC. We hypothesized that maintaining cells under hypoxic conditions during removal from mice and man, without the cells being subjected to normoxia at all, would greatly enhance numbers of phenotypically-defined HSC collected, and perhaps enhance their functional capabilities. We present preliminary data that suggests this is the case. Our goal is to substantiate and better define the EPHOSS phenomenon, and mechanisms inherent in it. Towards this goal, we propose two specific aims: (1) Evaluate our newly designated phenomenon of EPHOSS at a cell and molecular level for HSC and HPC. Use this information to obtain greater numbers of HSC/HPC with increased functional activity and enhanced engrafting activity and for their increased expansion ex-vivo and in-vivo. (2) Enhance generation capacity of fully vs. partially reprogrammed induced pluripotent stem (iPS) cells and their differentiation towards the hematopoietic lineage, by blocking or counteracting EPHOSS.