IGFBP2 Supports ex vivo Expansion of Hematopoietic Stem Cells

The hematopoietic stem cell (HSC), through proliferation and differentiation, gives rise to all lymphoid, myeloid, and erythroid cells. Successful HSC transplantation is often limited by the numbers of HSCs, and robust methods to expand HSCs ex vivo are needed (Bryder et al. 2006; Tse et al. 2008). We demonstrated that insulin-like growth factor binding protein 2 (IGFBP2), secreted by a tumorigenic cell line, enhanced ex vivo expansion of mouse and human HSCs (Huynh et al. 2008; Zhang et al. 2008). We established a completely defined, serum-free culture system for mouse HSCs containing SCF, TPO, FGF-1, Angptl3, and IGFBP2. As measured by competitive repopulation analyses, there was a 48-fold increase in numbers of long-term repopulating mouse HSCs after 21 days of culture. We sought to use a similar condition to culture human cord blood HSCs. We measured the activity of multipotent human SCID-repopulating cells (SRCs) by transplantation into non-obese, diabetic severe combined immunodeficiency (NOD/SCID) mice; secondary transplantation was performed to evaluate the self-renewal potential of SRCs. We showed that a serum-free culture containing SCF, TPO, FGF-1, Angiopoietin-like 5, and IGFBP2 supports a ~20 fold net expansion of repopulating human cord blood HSCs, a number potentially applicable to several clinical processes, including HSC transplantation. This was the first demonstration that IGFBP2 stimulates expansion or proliferation of stem cells. We are studying whether the role of IGFBP2 in regulation of HSCs is IGF-dependent, and whether IGFBP2 regulates the self-renewal and differentiation of HSCs in vivo.