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Biomedical subjects

Stephen G Emerson

Publications and source records attributed to Stephen G Emerson.

15 recordsLinked to original sources
PubMed2007

Osteoblasts support B-lymphocyte commitment and differentiation from hematopoietic stem cells.

Early B lymphopoiesis in mammals is induced within the bone marrow (BM) microenvironment, but which cells constitute this niche is not known. Previous studies had shown that osteoblasts (OBs) support hematopoietic stem cell (HSC) proliferation and myeloid differentiation. We now find that purified primary murine OBs also support the differentiation of primitive hematopoietic stem cells through lymphoid commitment and subsequent differentiation to all stages of B-cell precursors and mature B cells. Lin(-)Sca-1(+)Rag-2(-) BM cell differentiation to B cells requires their attachment to OBs in vitro, and this developmental process is mediated via VCAM-1, SDF-1, and IL-7 signaling induced by parathyroid hormone (PTH). Addition of cytokines produced by nonosteoblastic stromal cells (c-Kit ligand, IL-6, and IL-3) shifted the cultures toward myelopoiesis. Confirming the role of OBs in B lymphopoiesis, we found that selective elimination of osteoblasts in Col2.3Delta-TK transgenic mice severely depleted pre-pro-B and pro-B cells from BM, preceding any decline in HSCs. Taken together, these results demonstrate that osteoblasts are both necessary and sufficient for murine B-cell commitment and maturation, and thereby constitute the cellular homolog of the avian bursa of Fabricius.

Animals↗
PubMed2005

Host-reactive CD8+ memory stem cells in graft-versus-host disease.

Graft-versus-host disease (GVHD) is caused by alloreactive donor T cells that trigger host tissue injury. GVHD develops over weeks or months, but how this immune response is maintained over time is unknown. In mouse models of human GVHD, we identify a new subset of postmitotic CD44(lo)CD62L(hi)CD8(+) T cells that generate and sustain all allogeneic T-cell subsets in GVHD reactions, including central memory, effector memory and effector CD8(+) T cells, while self-renewing. These cells express Sca-1, CD122 and Bcl-2, and induce GVHD upon transfer into secondary recipients. The postmitotic CD44(lo)CD62L(hi)CD8(+) T cells persist throughout the course of GVHD, are generated in the initial phase in response to alloantigens and dendritic cells and require interleukin-15. Thus, their long life, ability to self-renew and multipotentiality define these cells as candidate memory stem cells. Memory stem cells will be important targets for understanding and influencing diverse chronic immune reactions, including GVHD.

Animals↗
PubMed2005

NF-Ya activates multiple hematopoietic stem cell (HSC) regulatory genes and promotes HSC self-renewal.

Hematopoietic stem cell (HSC) self-renewal and differentiation are influenced through multiple pathways, including homeobox transcription factors, signaling through beta-catenin and Notch-1, telomerase, and p27. How these multiple pathways interact and are orchestrated is currently unknown. We now report that NF-Ya, the regulatory and DNA-binding subunit of the trimeric transcription factor NF-Y, plays a central, integrating role in several of these HSC pathways. NF-Ya is preferentially expressed in HSC-enriched bone marrow subpopulations, and NF-Ya mRNA rapidly declines with HSC differentiation. Overexpression of NF-Ya in primitive hematopoietic cells activates the transcription of multiple HOX4 paralogs, as well as Notch-1, LEF-1, and telomerase RNA. HSCs overexpressing NF-Ya are biased toward primitive hematopoiesis in vitro and show strikingly increased in vivo repopulating abilities after single or sequential bone marrow transplantation. Thus, NF-Ya is a potent cellular regulator of HSC self-renewal.

Animals↗
PubMed2005

Alloreactive memory T cells are responsible for the persistence of graft-versus-host disease.

Graft-vs-host disease (GVHD) is caused by a donor T cell anti-host reaction that evolves over several weeks to months, suggesting a requirement for persistent alloreactive T cells. Using the C3H.SW anti-C57BL/6 (B6) mouse model of human GVHD directed against minor histocompatibility Ags, we found that donor CD8(+) T cells secreting high levels of IFN-gamma in GVHD B6 mice receiving C3H.SW naive CD8(+) T cells peaked by day 14, declined by day 28 after transplantation, and persisted thereafter, corresponding to the kinetics of a memory T cell response. Donor CD8(+) T cells recovered on day 42 after allogeneic bone marrow transplantation expressed the phenotype of CD44(high)CD122(high)CD25(low), were able to homeostatically survive in response to IL-2, IL-7, and IL-15 and rapidly proliferated upon restimulation with host dendritic cells. Both allogeneic effector memory (CD44(high)CD62L(low)) and central memory (CD44(high)CD62L(high)) CD8(+) T cells were identified in B6 mice with ongoing GVHD, with effector memory CD8(+) T cells as the dominant (>80%) population. Administration of these allogeneic memory CD8(+) T cells into secondary B6 recipients caused virulent GVHD. A similar allogeneic memory CD4(+) T cell population with the ability to mediate persistent GVHD was also identified in BALB/b mice receiving minor histocompatibility Ag-mismatched B6 T cell-replete bone marrow transplantation. These results indicate that allogeneic memory T cells are generated in vivo during GVH reactions and are able to cause GVHD, resulting in persistent host tissue injury. Thus, in vivo blockade of both alloreactive effector and memory T cell-mediated host tissue injury may prove to be valuable for GVHD prevention and treatment.

Animals↗
PubMed2004

Short interfering RNA (siRNA) targeting the Lyn kinase induces apoptosis in primary, and drug-resistant, BCR-ABL1(+) leukemia cells.

We studied the effects of Lyn ablation on the survival of drug-resistant chronic myelogenous leukemia (CML) blast crisis cells using siRNA. Lyn siRNA reduced Lyn protein in both normal hematopoietic cells and BCR-ABL1-expressing (BCR-ABL1(+)) blasts by 80-95%. Within 48 h, siRNA-treated BCR-ABL1(+) blasts underwent apoptosis, whereas normal cells remained viable. This increased dependence on Lyn signaling for BCR-ABL1(+) blast survival provides the basis for rational treatment of drug-resistant CML blast crisis, particularly when lymphoid in nature.

Apoptosis↗
PubMed2004

Graft-versus-leukemia in a retrovirally induced murine CML model: mechanisms of T-cell killing.

The graft-versus-leukemia (GVL) effect, mediated by donor T cells, has revolutionized the treatment of leukemia. However, effective GVL remains difficult to separate from graft-versus-host disease (GVHD), and many neoplasms are GVL resistant. Murine studies aimed at solving these problems have been limited by the use of leukemia cell lines with limited homology to human leukemias and by the absence of loss-of-function leukemia variants. To address these concerns, we developed a GVL model against murine chronic-phase chronic myelogenous leukemia (mCP-CML) induced with retrovirus expressing the bcr-abl fusion cDNA, the defining genetic abnormality of chronic-phase CML (CP-CML). By generating mCP-CML in gene-deficient mice, we have studied GVL T-cell effector mechanisms. mCP-CML expression of Fas or tumor necrosis factor (TNF) receptors is not required for CD8-mediated GVL. Strikingly, maximal CD4-mediated GVL requires cognate interactions between CD4 cells and mCP-CML cells as major histocompatibility complex-negative (MHC II(-/-)) mCP-CML is relatively GVL resistant. Nevertheless, a minority of CD4 recipients cleared MHC II(-/-) mCP-CML; thus, CD4 cells can also kill indirectly. CD4 GVL did not require target Fas expression. These results suggest that CPCML's GVL sensitivity may in part be explained by the minimal requirements for T-cell killing, and GVL-resistance may be related to MHC II expression.

Animals↗
PubMed2004

Dendritic cell-activated CD44hiCD8+ T cells are defective in mediating acute graft-versus-host disease but retain graft-versus-leukemia activity.

Graft versus host disease (GVHD) is triggered by host antigen-presenting cells (APCs) that activate donor T cells to proliferate and differentiate, but which APC-activated donor T-cell subsets mediate GVHD versus beneficial antitumor effects is not known. Using a CD8(+) T cell-dependent mouse model of human GVHD, we found that host dendritic cell (DC)-induced CD44(hi)CD8(+) effector/memory T cells were functionally defective in inducing GVHD, whereas CD44(lo)CD8(+) naive phenotype T cells were extremely potent GVHD inducers. Depletion of CD44(lo)CD8(+) T cells from host DC-stimulated T cells before transplantation prevented GVHD without impairing their antitumor activity in vivo. Compared with CD44(lo)CD8(+) T cells, CD44(hi)CD8(+) T cells expressed high levels of Fas and were efficiently deleted in vivo following transplantation. These results suggest that ex vivo allogeneic DC stimulation of donor CD8(+) T cells may be useful for the prevention of GVHD and for optimizing antitumor therapies in vivo.

Acute Disease↗
PubMed2004

A new bone to pick: osteoblasts and the haematopoietic stem-cell niche.

Two recent publications highlight the role of bone-forming cells, the osteoblasts, in controlling the development of neighboring haematopoietic stem cells (HSCs).1,2 Using two distinct transgenic mouse models, one using the conditional deletion of the Bone Morphogenetic Protein Receptor 1A (BMPR1A) gene, the other using over-expression of an active PTH/PTHrP receptor (PPR) mutant within osteoblasts, the authors show parallel, concordant increases in the generation of trabecular osteoblasts and the number of HSCs. In situ staining showed that rarely cycling HSCs sporadically attach to endosteal osteoblasts, while in vitro assays indicated that ligation of Jag1 on osteoblasts by Notch1 on HSCs promotes HSC proliferation. These two independent works have revived and revitalized the notion that osteoblasts are a major, defining component of the HSC niche within the bone marrow (BM). This minireview discusses these results in the context of other recent studies of mesenchymal cells within the BM microenvironment, presents one potential unified model of the functional anatomy of the BM HSC niche, and highlights new questions raised by these and other studies of osteoblasts and HSCs.

Animals↗
PubMed2004

Molecular pathways regulating the self-renewal of hematopoietic stem cells.

Hematopoietic stem cells (HSC) self-renew throughout life, but the molecular mechanisms by which this process occurs and is regulated are imprecisely understood. We review the published data from overexpression and knockout studies describing genes that influence stem cell self-renewal, including transcription factors, cell cycle regulators, and genes that influence chromosome structure. One model suggesting how some of these disparate classes of molecular regulators might be integrated is presented, focusing on the role of G1/S progression in the developmental switch toward stem cell self-renewal vs differentiation. Experimental exploration of this model and other related hypotheses will hopefully lead to a more complete description of HSC self-renewal and its regulation, both in normal physiology and in applied therapeutics.

Animals↗
PubMed2004

Stem cell transplantation (cord blood transplants).

Allogeneic stem cell transplantation is an accepted treatment modality for selected malignant and non-malignant diseases. However, the ability to identify suitably matched related or unrelated donors can be difficult in some patients. Alternative sources of stem cells such as cord blood provide a readily available graft for such patients. Data accumulated over the past several years have demonstrated that the use of cord blood is an accepted source of stem cells for pediatric patients. Since the cell numbers of hematopoietic progenitors in cord blood is limited and the collection can occur only in a single occasion, its use in adult patients can be more problematic. Here, new developments in the use of cord blood for adults and studies aimed at expansion of cord blood cells and immune reconstitution are described. In Section I, Dr. Nelson Chao describes the early data in cord blood transplantation in adult patients. The patient outcomes are reviewed and analyzed for various factors such as cell dose, HLA typing, and patient selection that could have contributed to the final outcome of these adult patients. Myeloablative as well as nonmyeloablative approaches are presented. Discussion of the various benefits and risks are presented. More recent data from multiple single institutions as well as larger registry data comparisons are also provided. Analyses of these studies suggest methods to improve on the outcome. These newer data should lead to a logical progression in the use of cord blood cells in adult patients. In Section II, Dr. Stephen Emerson describes the historical efforts associated with expansion of hematopoietic stem cells, specifically with cord blood cells. These efforts to expand cord blood cells continue with novel methods. Moreover, a better understanding of stem cell biology and signaling is critical if we are to be able to effectively expand these cells for clinical use. An alternative, more direct, approach to expanding stem cells could be achieved by specific genetic pathways known or believed to support primitive HSC proliferation such as Notch-1 receptor activation, Wnt/LEF-1 pathway induction, telomerase or the Homeobox (Hox) gene products. The clinical experience with the use of expanded cord blood cells is also discussed. In Section III, Dr. Kenneth Weinberg describes immune reconstitution or lack thereof following cord blood transplantation. One of the hallmarks of successful hematopoietic stem cell transplantation is the ability to fully reconstitute the immune system of the recipient. Thus, the relationship between stem cell source and the development of T lymphocyte functions required for protection of the recipient from infection will be described, and cord blood recipients will be compared with those receiving other sources of stem cells. T cell development is described in detail, tracking from prethymic to postthymic lymphocytes with specific attention to umbilical cord blood as the source of stem cells. Moreover, a discussion of the placenta as a special microenvironment for umbilical cord blood is presented. Strategies to overcome the immunological defects are presented to improve the outcome of these recipients.

Adult↗
PubMed2003

NF-Y cooperates with USF1/2 to induce the hematopoietic expression of HOXB4.

The transcription factor homeobox B4 (HOXB4) is preferentially expressed in immature hematopoietic cells and implicated in the transition from primitive hematopoiesis to definitive hematopoiesis as well as in immature hematopoietic cell proliferation and differentiation. We previously identified Hox response element 1 (HxRE-1) and HxRE-2/E-box as 2 critical DNA-binding sites of the HOXB4 promoter active in hematopoietic cells and demonstrated that upstream stimulating factor 1 and 2 (USF1/2) activate HOXB4 transcription through their binding to the E-box site. Here we report that the trimeric regulatory complex nuclear factor Y (NF-Y) is the factor that recognizes HxRE-1 and activates the HOXB4 promoter in hematopoietic cells. We further show that NF-Y interacts biochemically with USF1/2 on the HOXB4 promoter, and that the formation of this NF-Y/USF1/2 complex is required for the full activity of the HOXB4 promoter. Most important, NF-Ya subunit protein levels are found to be lower in c-Kit-Gr-1+ granulocytic bone marrow (BM) cells than in c-Kit+ immature BM cells, in parallel with a reduction of NF-Y occupancy on the HOXB4 promoter as shown by chromatin immunoprecipitation (ChIP) assay. These results suggest that NF-Y is a developmentally regulated inducer of the HOXB4 gene in hematopoietic cells.

Animals↗
PubMed2002

APCs in the liver and spleen recruit activated allogeneic CD8+ T cells to elicit hepatic graft-versus-host disease.

Host APCs are required for initiating T cell-dependent acute graft-vs-host disease (GVHD), but the role of APCs in the effector phase of acute GVHD is not known. To measure the effect of tissue-resident APCs on the local development of acute GVHD, we selectively depleted host macrophages and DCs from the livers and spleens, but not from the skin, peripheral lymph nodes (PLN), or mesenteric lymph nodes (MLN), of C57BL/6 (B6) mice by i.v. administration of liposomal clodronate before allogeneic bone marrow transplantation. Depletion of host hepatic and splenic macrophages and DCs significantly inhibited the proliferation of donor C3H.SW CD8(+) T cells in the spleen, but not in the PLN or MLN, of B6 mice. Such organ-selective depletion of host tissue APCs also markedly reduced the trafficking of allogeneic CD8(+) T cells into the livers and spleens, but not PLN and MLN, of B6 recipients compared with that of the control mice. Acute hepatic, but not cutaneous, GVHD was inhibited as well, resulting in improved survival of liposomal clodronate-treated B6 recipients. When C3H.SW CD8(+) T cells were activated in normal B6 recipients, recovered, and adoptively transferred into secondary B6 recipients, activated donor CD8(+) T cells rapidly migrated into the livers and spleens of control B6 recipients but were markedly decreased in B6 mice that were depleted of hepatic and splenic macrophages and DCs. Thus, tissue-resident APCs control the local recruitment of allo-reactive donor T cells and the subsequent development of acute GVHD.

Acute Disease↗
PubMed2002

Hematopoietic cytokines, transcription factors and lineage commitment.

The past two decades have witnessed significant advances in our understanding of the cellular physiology and molecular regulation of hematopoiesis. At the heart of stem cell self-renewal and lineage commitment decisions lies the relative expression levels of lineage-specific transcription factors. The expression of these transcription factors in early stem cells may be promiscuous and fluctuate, but ultimately comes under the influence of extracellular regulatory signals in the form of hematopoietic cytokines. In this review, we first summarize our current understanding of the phenotypic characterization of hematopoietic stem cells. Next, we describe key known transcription factors which govern stem cell self-renewal and lineage commitment decisions. Finally, we review data concerning the role of specific cytokines in influencing these decisions. From this review, a picture emerges in which stem cell fate decisions are governed by the integrated effects of intrinsic transcription factors and external signaling pathways initiated by regulatory cytokines.

Apoptosis↗
PubMed2002

Preterminal host dendritic cells in irradiated mice prime CD8+ T cell-mediated acute graft-versus-host disease.

To understand the relationship between host antigen-presenting cells (APCs) and donor T cells in initiating graft-versus-host disease (GVHD), we followed the fate of host dendritic cells (DCs) in irradiated C57BL/6 (B6) recipient mice and the interaction of these cells with minor histocompatibility antigen- (miHA-) mismatched CD8+ T cells from C3H.SW donors. Host CD11c+ DCs were rapidly activated and aggregated in the T cell areas of the spleen within 6 hours of lethal irradiation. By 5 days after irradiation, <1% of host DCs were detectable, but the activated donor CD8+ T cells had already undergone as many as seven divisions. Thus, proliferation of donor CD8+ T cells preceded the disappearance of host DCs. When C3H.SW donor CD8+ T cells were primed in vivo in irradiated B6 mice or ex vivo by host CD11c+ DCs for 24-36 hours, they were able to proliferate and differentiate into IFN-gamma-producing cells in beta(2)-microglobulin-deficient (beta(2)m(-/-)) B6 recipients and to mediate acute GVHD in beta(2)m(-/-) --> B6 chimeric mice. These results indicate that, although host DCs disappear rapidly after allogeneic bone marrow transplantation, they prime donor T cells before their disappearance and play a critical role in triggering donor CD8+ T cell-mediated GVHD.

Animals↗