Submitted August 15, 2007
Accepted December 5, 2007
Expansion of multipotent and lymphoid-committed human progenitors through intracellular dimerization of Mpl
Hisham Abdel-Azim, Yuhua Zhu, Roger Hollis, Xiuli Wang, Shundi Ge, Qian-Lin Hao, Goar Smbatyan, Donald B. Kohn, Michael Rosol, and Gay M. Crooks*
Division of Research Immunology/Bone Marrow Transplantation, Childrens Hospital Los Angeles, Los Angeles, CA, United States
Department of Radiology, Childrens Hospital Los Angeles, Los Angeles, CA, United States
* Corresponding author; email: gcrooks{at}chla.usc.edu.
Self-renewal capacity is rapidly lost during differentiation of hematopoietic stem cells to lineage-committed progenitors. We demonstrate here that regulated intracellular signaling through the cytokine receptor Mpl induces profound expansion of not only multipotent (i.e. lympho-myeloid) but also lymphoid-committed human hematopoietic progenitors. A fusion protein containing the intracellular signaling domain of Mpl and a dimerization domain was constitutively expressed in populations enriched in human lympho-myeloid progenitor/stem cells (CD34+CD38-Lin-CD7-) and multi-lymphoid progenitors (CD34+CD38-Lin-CD7+). Intracellular dimerization of Mpl in target cells was induced by in vitro or in vivo administration of a diffusible synthetic ligand. In vitro, Mpl dimerization produced divisions of clonogenic, multilineage CD34+ cells able to engraft immune deficient mice. When dimerization was induced in vivo after transplantation of either lympho-myeloid or multi-lymphoid progenitors, donor-derived hematopoiesis was sustained for at least 12 weeks and primitive CD34+Lin- progenitors were expanded >1000 fold. Lineage potential of progenitors was not altered and differentiation was not prevented by synthetically induced Mpl signaling. These data demonstrate that dimerization of a single cytokine receptor can deliver a profound expansion signal in both uncommitted and lymphoid-committed human hematopoietic progenitors.
