
<ArticleTitle>The impact of ex vivo cytokine stimulation on engraftment of primitive hematopoietic cells in a non-human primate model.</ArticleTitle>
<AbstractText>The impairment of engraftment ability after ex vivo or in vivo stimulation of hematopoietic stem cells, potentially related to induction of active cell cycling, has recently been a topic of intense interest. Our group has used the non-human primate autologous transplantation model and genetic marking to investigate a number of questions in hematopoiesis with direct relevance to human clinical applications. The issue of a potential reversible engraftment defect would have many implications for gene therapy and allogeneic or autologous transplantation. Initial in vitro studies with rhesus <prot>CD34</prot>+ cells indicated that after 4 days of stimulatory culture in <prot>stem cell factor</prot> (<prot>SCF</prot>), <prot>megakaryocyte growth and development factor</prot> (<prot>MDGF</prot>), and <prot>flt3</prot> ligand (<prot>FLT</prot>), transfer of the cells to <prot>SCF</prot> alone on <prot>retronectin</prot> (<prot>FN</prot>) support resulted in decreased active cycling and a halt to proliferation, without a loss of viability or induction of apoptosis. We then directly compared the engraftment potential of cytokine-stimulated cells versus those transferred to <prot>SCF</prot> on <prot>FN</prot> alone before reinfusion, <prot>SCF</prot>/<prot>G-CSF</prot> mobilized <prot>CD34</prot>+ cells from three animals were split into two parts and transduced with either of two retroviral marking vectors for 4 days in the presence of <prot>SCF</prot>/<prot>FLT</prot>/<prot>MGDF</prot> on <prot>FN</prot>. One aliquot was cryopreserved, and the other was continued in culture without transduction for 2 days in the presence of <prot>SCF</prot> alone on <prot>FN</prot>. After total body irradiation, both aliquots were thawed and reinfused into each animal. In all animals, the level of marking from the fraction continued in culture for 2 days with <prot>SCF</prot> on <prot>FN</prot> was significantly higher than the level of marking from the aliquot transduced for 4 days without the 2-day period in <prot>SCF</prot> alone. This approach may allow more efficient engraftment of successfully transduced or ex vivo expanded cells by avoiding active cell cycling at the time of reinfusion.</AbstractText>
