Mechanisms of Stem Cell Mobilization by Flt-3 Ligand

Nathan Everly, Mentor:Daniel Link M.D.Washington University School of Medicine

Hematopoetic stem cells (HSC) reside in the bone marrow under normal conditions. When these cells are needed, they migrate from the bone marrow to the peripheral blood in a process called stem cell mobilization.

Interestingly, mobilization can be induced using a wide variety of cytokines, chemokines, and chemotherapeutic agents. These agents offer tremendous clinical applications that can minimize the cost, time, and toil associated with stem cell transplants.

Our lab is interested in the pathways these agents use to cause stem cell mobilization. In particular, we are studying the role of the chemokine Stromal cell factor -1 (SDF-1) in mobilization. Recent work supports the hypothesis that SDF-1 signaling plays a key role in the trafficking of hematopoietic cells, including stem cells, to and from the bone marrow. Stem and progenitor cell mobilization is accompanied by a drop in bone marrow SDF-1, suggesting that SDF-1 signaling through its receptor CXCR4 is necessary to retain HSC in the bone marrow at steady state.

I have been involved with studying progenitor cells that have been mobilized by Flt-3 and SCF, two of the agents that are known to cause mobilization. By counting the progenitor cells in the peripheral blood and running colony-forming assays, I can determine the degree of mobilization caused by these agents. I also performed ELISA experiments and an RNA analysis to determine the level of SDF-1 expression during stem cell mobilization. A chemotaxis assay was also performed to estimate the extent of functional CXCR-4 signaling in progenitor cells in the bone marrow and the peripheral blood.

In the future, I hope to develop a flow cytometric assay that will measure the CXCR-4 expression on mobilized progenitor cells. I also would like to determine the signal pathways between Flt-3/SCF and SDF-1/CXCR-4.