Highly efficient ex vivo expansion of human hematopoietic stem cells using Delta1-Fc chimeric protein

Tumor necrosis factor-alpha and endothelial cells modulate Notch signaling in the bone marrow microenvironment during inflammation

OBJECTIVE

Homeostasis of the hematopoietic compartment is challenged and maintained during conditions of stress by mechanisms that are poorly defined. To understand how the bone marrow (BM) microenvironment influences hematopoiesis, we explored the role of Notch signaling and BM endothelial cells in providing microenvironmental cues to hematopoietic cells in the presence of inflammatory stimuli.

MATERIALS AND METHODS

The human BM endothelial cell line (BMEC) and primary human BM endothelial cells were analyzed for expression of Notch ligands and the ability to expand hematopoietic progenitors in an in vitro coculture system. In vivo experiments were carried out to identify modulation of Notch signaling in BM endothelial and hematopoietic cells in mice challenged with tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS), or in Tie2-tmTNF-alpha transgenic mice characterized by constitutive TNF-alpha activation.

RESULTS

BM endothelial cells were found to express Jagged ligands and to greatly support progenitor's colony-forming ability. This effect was markedly decreased by Notch antagonists and augmented by increasing levels of Jagged2. Physiologic upregulation of Jagged2 expression on BMEC was observed upon TNF-alpha activation. Injection of TNF-alpha or LPS upregulated three- to fourfold Jagged2 expression on murine BM endothelial cells in vivo and resulted in increased Notch activation on murine hematopoietic stem/progenitor cells. Similarly, constitutive activation of endothelial cells in Tie2-tmTNF-alpha mice was characterized by increased expression of Jagged2 and by augmented Notch activation on hematopoietic stem/progenitor cells.

CONCLUSIONS

Our results provide the first evidence that BM endothelial cells promote expansion of hematopoietic progenitor cells by a Notch-dependent mechanism and that TNF-alpha and LPS can modulate the levels of Notch ligand expression and Notch activation in the BM microenvironment in vivo.

Cytokines regulating hematopoietic stem cell function

PURPOSE OF REVIEW

Regulation of the multiple fates of hematopoietic stem cells - including quiescence, self-renewal, differentiation, apoptosis, and mobilization from the niche - requires the cooperative actions of several cytokines and other hormones that bind to receptors on these cells. In this review we discuss recent advances in the identification of novel hematopoietic stem cell supportive cytokines and the mechanisms by which they control hematopoietic stem cell fate decisions.

RECENT FINDINGS

Several extrinsic factors that stimulate ex-vivo expansion of hematopoietic stem cells were recently identified by a number of experimental approaches, including forward genetic screening and transcriptional profiling of supportive stromal cells. Recent experiments in which multiple cytokine signaling pathways are activated or suppressed in hematopoietic stem cells reveal the complexity of signal transduction and cell-fate choice in hematopoietic stem cells in vivo and in vitro.

SUMMARY

The study of genetically modified mice and improvements in the in-vitro hematopoietic stem cell culture system will be powerful tools to elucidate the functions of cytokines that regulate hematopoietic stem cell function. These will further reveal the complex nature of the mechanisms by which extrinsic factors regulate signal transduction and cell-fate decisions of hematopoietic stem cells.

Canonical notch signaling is dispensable for the maintenance of adult hematopoietic stem cells

Gain-of-function experiments have demonstrated the potential of Notch signals to expand primitive hematopoietic progenitors, but whether Notch physiologically regulates hematopoietic stem cell (HSC) homeostasis in vivo is unclear. To answer this question, we evaluated the effect of global deficiencies of canonical Notch signaling in rigorous HSC assays. Hematopoietic progenitors expressing dominant-negative Mastermind-like1 (DNMAML), a potent inhibitor of Notch-mediated transcriptional activation, achieved stable long-term reconstitution of irradiated hosts and showed a normal frequency of progenitor fractions enriched for long-term HSCs. Similar results were observed with cells lacking CSL/RBPJ, a DNA-binding factor that is required for canonical Notch signaling. Notch-deprived progenitors provided normal long-term reconstitution after secondary competitive transplantation. Furthermore, Notch target genes were expressed at low levels in primitive hematopoietic progenitors. Taken together, these results rule out an essential physiological role for cell-autonomous canonical Notch signals in HSC maintenance.

Angiopoietin-like 5 and IGFBP2 stimulate ex vivo expansion of human cord blood hematopoietic stem cells as assayed by NOD/SCID transplantation

Hematopoietic stem cells (HSCs) are the basis of bone marrow transplantation and are attractive target cells for hematopoietic gene therapy, but these important clinical applications have been severely hampered by difficulties in ex vivo expansion of HSCs. In particular, the use of cord blood for adult transplantation is greatly limited by the number of HSCs. Previously we identified angiopoietin-like proteins and IGF-binding protein 2 (IGFBP2) as new hormones that, together with other factors, can expand mouse bone marrow HSCs in culture. Here, we measure the activity of multipotent human severe combined immunodeficient (SCID)-repopulating cells (SRCs) by transplantation into the nonobese diabetic SCID (NOD/SCID) mice; secondary transplantation was performed to evaluate the self-renewal potential of SRCs. A serum-free medium containing SCF, TPO, and FGF-1 or Flt3-L cannot significantly support expansion of the SRCs present in human cord blood CD133+ cells. Addition of either angiopoietin-like 5 or IGF-binding protein 2 to the cultures led to a sizable expansion of HSC numbers, as assayed by NOD/SCID transplantation. A serum-free culture containing SCF, TPO, FGF-1, angiopoietin-like 5, and IGFBP2 supports an approximately 20-fold net expansion of repopulating human cord blood HSCs, a number potentially applicable to several clinical processes including HSC transplantation.

Notch ligand Delta-1 differentially modulates the effects of gp130 activation on interleukin-6 receptor alpha-positive and -negative human hematopoietic progenitors

Interleukin (IL)-6 plays pleiotropic roles in human hematopoiesis and immune responses by acting on not only the IL-6 receptor-alpha subunit (IL-6Ralpha)(+) but also IL-6Ralpha(-) hematopoietic progenitors via soluble IL-6R. The Notch ligand Delta-1 has been identified as an important modulator of the differentiation and proliferation of human hematopoietic progenitors. Here, it was investigated whether these actions of IL-6 are influenced by Delta-1. When CD34(+)CD38(-) hematopoietic progenitors were cultured with stem cell factor, flt3 ligand, thrombopoietin and IL-3, Delta-1, in combination with the IL-6R/IL-6 fusion protein FP6, increased the generation of glycophorin A(+) erythroid cells but counteracted the effects of IL-6 and FP6 on the generation of CD14(+) monocytic and CD15(+) granulocytic cells. Although freshly isolated CD34(+)CD38(-) cells expressed no or only low levels of IL-6Ralpha, its expression was increased in myeloid progenitors after culture but remained negative in erythroid progenitors. It was found that Delta-1 acted in synergy with FP6 to enhance the generation of erythroid cells from the IL-6Ralpha(-) erythroid progenitors. In contrast, Delta-1 antagonized the effects of IL-6 and FP6 on the development of monocytic and granulocytic cells, as well as CD14(-)CD1a(+) dendritic cells, from the IL-6Ralpha(+) myeloid progenitors. These results indicate that Delta-1 interacts differentially with gp130 activation in IL-6Ralpha(-) erythroid and IL-6Ralpha(+) myeloid progenitors. The present data suggest a divergent interaction between Delta-1 and gp130 activation in human hematopoiesis.