Jos Domen

A role for Wnt signalling in self-renewal of haematopoietic stem cells

Haematopoietic stem cells (HSCs) have the ability to renew themselves and to give rise to all lineages of the blood; however, the signals that regulate HSC self-renewal remain unclear. Here we show that the Wnt signalling pathway has an important role in this process. Overexpression of activated β-catenin expands the pool of HSCs in long-term cultures by both phenotype and function. Furthermore, HSCs in their normal microenvironment activate a LEF-1/TCF reporter, which indicates that HCSs respond to Wnt signalling in vivo. To demonstrate the physiological significance of this pathway for HSC proliferation we show that the ectopic expression of axin or a frizzled ligand-binding domain, inhibitors of the Wnt signalling pathway, leads to inhibition of HSC growth in vitro and reduced reconstitution in vivo. Furthermore, activation of Wnt signalling in HSCs induces increased expression of HoxB4 and Notch1, genes previously implicated in self-renewal of HSCs. We conclude that the Wnt signalling pathway is critical for normal HSC homeostasis in vitro and in vivo, and provide insight into a potential molecular hierarchy of regulation of HSC development.

The Fetal Liver Counterpart of Adult Common Lymphoid Progenitors Gives Rise to All Lymphoid Lineages, CD45+CD4+CD3− Cells, As Well As Macrophages

We identified an IL-7Rα+Sca-1lowc-Kitlow population in E14 fetal liver, which is the phenotypical analog of common lymphoid progenitors (CLP) in adult bone marrow. After transfer into newborn mice, the IL-7Rα+Sca-1lowc-Kitlow population rapidly differentiated into CD45+CD4+CD3− cells, which are candidate cells for initiating lymph node and Peyer’s patch formation. In addition, this population also gave rise to B, T, NK, and CD8α+ and CD8α− dendritic cells. The fetal liver precursors expressed a significantly lower level of the myeloid-suppressing transcription factor Pax-5, than adult CLP, and retained differentiation activity for macrophages in vitro. We propose that the transition from fetal liver IL-7Rα+Sca-1lowc-Kitlow cells to adult CLP involves a regulated restriction of their developmental potential, controlled, at least in part, by Pax-5 expression.

Bcl-2 Rescues T Lymphopoiesis, but Not B or NK Cell Development, in Common γ Chain–Deficient Mice

The common cytokine receptor gamma chain (gamma(c)) is an indispensable subunit for the formation of lymphoid-related cytokine receptors, including IL-7 and IL-15 receptors, that mediate nonredundant or critical signals for the differentiation of T and B cells and natural killer (NK) cells, respectively. We introduced the bcl-2 transgene driven by E mu or H-2K promoters into gamma(c)-deficient mice that lack all three lymphoid subclasses. The forced expression of Bcl-2 restored all stages of T lymphopoiesis, but not B or NK cell development, indicating that a primary function of gamma(c)-mediated signals in the T lineage might be to maintain cell survival. Therefore, the development of T, B, and NK cells may be influenced by distinct intracytoplasmic signaling cascades that are activated by coupling of gamma(c)-related receptors.

Self-renewal, differentiation or death: regulation and manipulation of hematopoietic stem cell fate

Hematopoietic stem cells (HSCs) are the rare cells from which all hematopoietic cells are derived. The absence of HSCs is not compatible with life because many essential cells, such as myeloid and erythroid cells, are short lived. The hematopoietic system is the first essential organ system that fails following cytotoxic treatments. It is the vulnerability of HSCs that prevents regeneration following treatment and thus long-term survival. Because HSCs have the capacity to regenerate a functional hematopoietic system, the manipulation of these cells in vitro holds many promises for gene-therapeutic and other applications; however, these are severely curtailed by current difficulties in maintaining and expanding HSCs in culture. This review focuses on recent approaches towards understanding how the HSC compartment is regulated in vivo and discusses how this knowledge might be applied to manipulating HSC numbers.

CD8+TCR+ and CD8+TCR− Cells in Whole Bone Marrow Facilitate the Engraftment of Hematopoietic Stem Cells across Allogeneic Barriers

Although purified hematopoietic stem cells (HSC) are sufficient to engraft irradiated allogeneic recipients, bone marrow (BM) contains other cells that facilitate engraftment. Here, several candidate facilitators were tested by cotransplantation with HSC. Both TCR+ and TCR- CD8alpha+ BM subpopulations have facilitative potential. CD8+TCR+ cells are typical T lymphocytes. CD8+TCR- facilitators are CD3 , not CD3+, have a granular morphology, and are CD8beta- and CD11c+; they share phenotypic characteristics with CD8(alpha)alpha lymphoid dendritic cells and veto cells. We also demonstrate that lytic function is nqt necessary for facilitation and that the CD8alpha molecule is either important for facilitation or in the development of facilitators.

From stem cells to lymphocytes; biology and transplantation

Summary: We review the development of the hematopoietic system, focusing on the transition from hematopoietic stem cells (HSCs) to T cell This includes the isolation of HSCs, and recent progress in understanding their ontogeny, homing properties, and differentiation. HSC transplantation is reviewed, including the kinetics of reconstitution, engraftment across histocompatibility barriers, the facilitation of allogeneic engraftment, and the mechanisms of graft rejection. We describe progress in understanding T‐cell development in the bone marrow and thymus as well as the establishment of lymph nodes. Finally, the role of bcl‐2 in regulating homeostasis in the hematopoietic system is discussed.

Role of mesenchymal stem cell therapy in Crohn's disease

Many trials of mesenchymal stem cells (MSCs) have been published in the past 5–6 y. MSCs inhibit T-cell alloreactivity in vitro by soluble factors and direct cell-to-cell contact. They are safe to infuse in humans with no acute toxicity and no ectopic tissue formation. Promising results of MSC infusion for graft-vs.-host disease and fistulizing Crohn’s disease (CD) have been published. Treatment of CD requires a comprehensive treatment approach to maintain symptomatic control, improve health-related quality-of-life measures, and minimize complications from the disease. In this review, we will discuss the results of clinical trials using a novel treatment in the form of MSCs for treatment of CD and related complications. Success of these phase I, II, and III trials have set the stage for usage of this novel treatment for children with CD.

Enforced Expression of Bcl-2 Restores the Number of NK Cells, But Does Not Rescue the Impaired Development of NKT Cells or Intraepithelial Lymphocytes, in IL-2/IL-15 Receptor β-Chain-Deficient Mice

IL-2/IL-15Rβ-deficient mice display impaired development of NK cells, NKT cells, and intraepithelial lymphocytes of the intestine and skin. To determine the role of survival signals mediated by IL-2/IL-15R in the development of these innate lymphocytes, we introduced a bcl-2 transgene into IL-2/IL-15Rβ-deficient mice. Enforced expression of Bcl-2 restored the number of NK cells in IL-2/IL-15Rβ-deficient mice, but the rescued NK cells showed no cytotoxic activity. The numbers of NKT cells and intestinal intraepithelial lymphocytes did not increase significantly, and skin intraepithelial lymphocytes remained undetectable in the bcl-2 transgenic IL-2/IL-15Rβ-deficient mice. These results indicate an essential role of IL-2/IL-15R-mediated survival signals in the development of NK cells, but they also show that additional nonsurvival signals from IL-2/IL-15R are necessary for innate lymphocyte development.

Catecholamines in murine bone marrow derived mast cells

Cultured murine bone marrow derived mast cells (BMMC) were found to store high levels of dopamine (3753+/-844 pg/10(7) cells) and occasionally produce norepinephrine and epinephrine. The catecholamine synthesis inhibitor, alpha-methyl-para-tyrosine, decreased intracellular catecholamine concentrations, and activation with ionomycin stimulated dopamine release. Neither dopaminergic receptor antagonists nor exogenous dopamine < or =10 microM affected IL-3-induced cell proliferation. High exogenous dopamine (20-100 microM) decreased proliferation and increased apoptosis, and the anti-oxidant ascorbic acid prevented these effects. Increased expression of the anti-apoptotic factor Bcl-2 or loss of pro-apoptotic Bax expression attenuated dopamine-induced apoptosis, suggesting the apoptosis proceeds through a mitochondrial pathway.

The role of apoptosis in regulating hematopoietic stem cell numbers

The importance of apoptosis, in combination with proliferation, in maintaining stable populations has become increasingly clear in the last decade. Perturbation of either of these processes can have serious consequences, and result in a variety of disorders. Moreover, as the players and pathways gradually emerge, it turns out that there are strong connections in the regulation of cell cycle progression and apoptosis. Apoptosis, proliferation, and the disorders resulting from aberrant regulation have been studied in a variety of cell types and systems. Hematopoietic stem cells (HSC) are defined as primitive mesenchymal cells that are capable of both self-renewal and differentiation into the various cell lineages that constitute the functioning hematopoietic system. Many (but certainly not all) mature hematopoietic cells are relatively short-lived, sometimes with a half-life in the order of days. Homeostasis requires the production of 108 (mouse) to 1011 (human) cells each day. All of these cells are ultimately derived from HSC that mostly reside in the bone marrow in adult mammals. The study of the regulation of HSC numbers has focussed mainly on the choice between self-renewal and differentiation, symmetric and asymmetric cell divisions. Recently, however, it has been directly demonstrated that apoptosis plays an important role in the regulation of hematopoietic stem cells in vivo.