Matrix Metalloproteinase Inhibitor COL-3 in the Treatment of AIDS-related Kaposi's Sarcoma: a Phase I AIDS Malignancy Consortium Study

Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. Jan, 2002  |  Pubmed ID: 11773164

Matrix metalloproteinases (MMPs) are involved in tumor invasion and metastasis and are overexpressed in Kaposi's sarcoma (KS) cells. The primary aim was to define the safety and toxicity of the MMP inhibitor COL-3 in patients with AIDS-related KS. Secondary aims were to evaluate tumor response, pharmacokinetics, and changes in blood levels of MMP-2, MMP-9, vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF).

Human HTm4 is a Hematopoietic Cell Cycle Regulator

The Journal of Clinical Investigation. Jan, 2002  |  Pubmed ID: 11781350

Proper control of cell cycle progression is critical for the constant self-renewal, differentiation, and homeostasis of the hematopoietic system. Cells of all types share the common cell cycle regulators. The different expression patterns of common regulators, in a broad sense, define cell-type or lineage specificity. However, there remains the possibility of hematopoietic cell cycle regulators tailored to the demands of the hematopoietic system. Here we describe a novel protein, HTm4, which serves as a hematopoietic cell cycle regulator. Our data indicate that HTm4 is expressed in hematopoietic tissues and is tightly regulated during the differentiation of hematopoietic stem cells. It binds to cyclin-dependent kinase-associated (CDK-associated) phosphatase-CDK2 (KAP-CDK2) complexes, and the three proteins demonstrate similar patterns of cellular expression in human lymphoid tissues. HTm4 stimulates the phosphatase activity of KAP, and its C-terminal region is required for binding to KAP-CDK2 complexes and the modulation of KAP activity. Overexpression of HTm4 can cause cell cycle arrest at the G(0)/G(1) phase. Thus, HTm4 is a novel hematopoietic modulator for the G(1)-S cell cycle transition.

Antitumor Activity of Oral 9-cis-retinoic Acid in HIV-associated Kaposi's Sarcoma

AIDS (London, England). Feb, 2002  |  Pubmed ID: 11834954

To assess the efficacy, safety and tolerance of oral 9-cis-retinoic acid in HIV-infected patients with Kaposi's sarcoma.

Notch1 Activation Increases Hematopoietic Stem Cell Self-renewal in Vivo and Favors Lymphoid over Myeloid Lineage Outcome

Blood. Apr, 2002  |  Pubmed ID: 11895769

Hematopoietic stem cells sequentially pass through a series of decision points affecting self-renewal or lineage-specific differentiation. Notch1 receptor is a known modulator of lineage-specific events in hematopoiesis that we assessed in the context of in vivo stem cell kinetics. Using RAG-1(-/-) mouse stems cells, we documented increased stem cell numbers due to decreased differentiation and enhanced stem cell self-renewal induced by Notch1. Unexpectedly, preferential lymphoid over myeloid lineage commitment was noted when differentiation occurred. Therefore, Notch1 affects 2 decision points in stem cell regulation, favoring self-renewal over differentiation and lymphoid over myeloid lineage outcome. Notch1 offers an attractive target for stem cell manipulation strategies, particularly in the context of immunodeficiency and acquired immunodeficiency syndrome.

Receptor Tyrosine Kinase, EphB4 (HTK), Accelerates Differentiation of Select Human Hematopoietic Cells

Blood. Apr, 2002  |  Pubmed ID: 11929761

EphB4 (HTK) and its ligand, ephrinB2, are critical for angiogenesis and result in fatal abnormalities of capillary formation in null mice. EphB4 was originally identified in human bone marrow CD34(+) cells by us and has since been reported to be expressed in erythroid progenitors, whereas the ligand ephrinB2 is expressed in bone marrow stromal cells. Reasoning that the developmental relationship between angiogenesis and hematopoiesis implies common regulatory molecules, we assessed whether EphB4 signaling influences the function and phenotype of primitive human hematopoietic cells. Ectopically expressed EphB4 in cell lines of restricted differentiation potential promoted megakaryocytic differentiation, but not granulocytic or monocytic differentiation. Primary cord blood CD34(+) cells transduced with EphB4 resulted in the elevated expression of megakaryocytic and erythroid specific markers, consistent with EphB4 selectively enhancing some lineage-committed progenitors. In less mature cells, EphB4 depleted primitive cells, as measured by long-term culture-initiating cells or CD34(+)CD38(-) cell numbers, and increased progenitor cells of multiple cell types. Effects of ectopic EphB4 expression could be abrogated by either targeted mutations of select tyrosine residues or by the tyrosine kinase inhibitor, genistein. These data indicate that EphB4 accelerates the differentiation of primitive cells in a nonlineage-restricted manner but alters only select progenitor populations, influencing lineages linked by common ancestry with endothelial cells. EphB4 enforces preferential megakaryocytic and erythroid differentiation and may be a molecular bridge between angiogenesis and hematopoiesis.

Thymocyte Emigration is Mediated by Active Movement Away from Stroma-derived Factors

The Journal of Clinical Investigation. Apr, 2002  |  Pubmed ID: 11956248

T cells leave the thymus at a specific time during differentiation and do not return despite elaboration of known T cell chemoattractants by thymic stroma. We observed differentiation stage-restricted egress of thymocytes from an artificial thymus in which vascular structures or hemodynamics could not have been playing a role. Hypothesizing that active movement of cells away from a thymic product may be responsible, we demonstrated selective reduction in emigration from primary thymus by inhibitors of active movement down a concentration gradient (chemofugetaxis). Immature intrathymic precursors were insensitive to an emigration signal, whereas mature thymocytes and peripheral blood T cells were sensitive. Thymic stroma was noted to elaborate at least two proteins capable of inducing emigration, one of which was stromal cell-derived factor-1. Thymic emigration is mediated, at least in part, by specific fugetaxis-inducing factors to which only mature cells respond.

A Phase II Randomized Study of HIV-specific T-cell Gene Therapy in Subjects with Undetectable Plasma Viremia on Combination Antiretroviral Therapy

Molecular Therapy : the Journal of the American Society of Gene Therapy. Jun, 2002  |  Pubmed ID: 12027564

Highly active antiretroviral therapy (HAART) can suppress HIV replication to undetectable levels in plasma, but it is unlikely to eradicate cellular reservoirs of virus. Immunotherapies that are cytolytic may be useful adjuncts to drug therapies that target HIV replication. We have generated HIV-specific CD4(+) and CD8(+) T cells bearing a chimeric T-cell receptor (CD4zeta) composed of the extracellular and transmembrane domain of human CD4 (which binds HIVgp120) linked to the intracellular-zeta signaling chain of the CD3 T-cell receptor. CD4zeta-modified T cells can inhibit viral replication, kill HIV-infected cells in vitro, and survive for prolonged periods in vivo. We report the results of a phase II randomized trial of CD4zeta gene-modified versus unmodified T cells in 40 HIV-infected subjects on HAART with plasma viral loads <50 copies/ml. Serial analyses of residual blood and tissue HIV reservoirs were done for 6 months postinfusion. No significant between-group differences were noted in viral reservoirs following therapy. However, infusion of gene-modified, but not unmodified, T cells was associated with a decrease from baseline in HIV burden in two of four reservoir assays and a trend toward fewer patients with recurrent viremia. Both groups experienced a treatment-related increase in CD4(+) T-cell counts.

Absence of Biologically Important Kaposi Sarcoma-associated Herpesvirus Gene Products and Virus-specific Cellular Immune Responses in Multiple Myeloma

Blood. Jul, 2002  |  Pubmed ID: 12091368

Kaposi sarcoma-associated herpesvirus (KSHV) has been associated with several diseases, but the association between KSHV and multiple myeloma (MM) remains controversial. To address this issue, we studied patients with MM for the presence of viral RNA transcripts as well as KSHV-specific cellular immune responses. Highly sensitive reverse transcription-polymerase chain reaction assays for detection of viral transcripts of KSHV open reading frame (ORF) 26, ORF72, and ORF74 did not detect viral gene transcripts in long-term cultures of bone marrow stromal cells from 23 patients with MM. Moreover, sensitive assays for KSHV ORF65-specific and ORF73-specific cytotoxic T-lymphocyte (CTL) activity that readily and routinely detect CTLs specific for ORF65 and ORF73 in patients positive for human immunodeficiency virus and KSHV did not show any specific responses in 16 patients with MM, despite the presence of positive Epstein-Barr virus-specific CTLs in all cases. These data therefore do not show a biologically important association between ongoing KSHV infection and MM.

Cell Cycle Entry of Hematopoietic Stem and Progenitor Cells Controlled by Distinct Cyclin-dependent Kinase Inhibitors

International Journal of Hematology. Jun, 2002  |  Pubmed ID: 12095144

The therapeutic promise of hematopoietic stem cells in medicine has been expanded as broader differentiation potential of the cells has gained experimental support. However, hurdles for stem cell manipulation in vitro and tissue regeneration in vivo remain because of lack of the molecular biology of the stem cells. In particular, elucidating the molecular control of cell cycle entry is necessary for rational stem cell expansion strategies. Understanding how the stem and progenitor cell populations are controlled by negative regulators of cell cycle entry may provide one basis for manipulating these cells. In this mini-review, we focus on the rationale of targeting the cyclin-dependent kinase inhibitors (CKIs) in stem cell biology. Two CKI members, p21(Cip1/Waf1) (p21) and p27kip1 (p27), have been shown to govern the pool sizes of hematopoietic stem and progenitor cells, respectively. Of note, their inhibitory roles in primitive hematopoietic cells are distinct from the action of the inhibitory cytokine, transforming growth factor-beta1 (TGF-beta1). Therefore, the distinct roles of p21, p27, and TGF-beta1 in hematopoietic cells offer attractive targets for specific manipulation of the stem or progenitor cell populations in therapeutic strategies.

Multicenter Trial of Low-dose Paclitaxel in Patients with Advanced AIDS-related Kaposi Sarcoma

Cancer. Jul, 2002  |  Pubmed ID: 12115328

Treatment options are limited for patients with advanced acquired immunodeficiency syndrome (AIDS)-related Kaposi sarcoma (AIDS-KS) whose disease has progressed after receiving therapy with liposomal anthracyclines or combination chemotherapy with doxorubicin (Adriamycin), bleomycin, and vincristine (ABV). This study was performed to assess the safety and efficacy of a novel dose and schedule of paclitaxel in patients with AIDS-KS who failed to respond to previous systemic chemotherapy.

The Protease Inhibitor Ritonavir Inhibits the Functional Activity of the Multidrug Resistance Related-protein 1 (MRP-1)

AIDS (London, England). Sep, 2002  |  Pubmed ID: 12218384

Efflux pumps situated on the plasma membrane, such as P-glycoprotein (Pgp) and the multidrug resistance related-protein 1 (MRP-1), have been shown to extrude HIV protease inhibitors from the cell. MRP-1 is present on many barrier sites throughout the body, such as the blood-brain and blood-testis interfaces and could reduce the concentration of protease inhibitors in these sanctuary sites for HIV-1 replication. Factors that modulate efflux pump function in vivo are poorly defined.

Lack of Antitumor Activity and Intolerance of Interleukin-4 in Patients with Advanced HIV Disease and Kaposi's Sarcoma

Journal of Interferon & Cytokine Research : the Official Journal of the International Society for Interferon and Cytokine Research. Nov, 2002  |  Pubmed ID: 12513914

Kaposi's sarcoma (KS), the most common malignancy associated with HIV infection, is caused by the Kaposi sarcoma herpesvirus (KSHV). Exacerbations of KSHV are associated with increased human interleukin-6 (HuIL-6), and elevated IL-6 could be related to the development of KS. IL-4, a cytokine with pleiotropic effects, suppresses IL-6 in vivo and modestly inhibits AIDS-KS-derived cells in vitro. Suppression of IL-6 by exogenous IL-4 could result in antitumor activity. We report the results of a clinical trial to test this hypothesis. A phase I/II dose escalation safety, tolerance, and efficacy trial was conducted in patients with biopsy-proven AIDS-related KS, at two university medical centers. Patients were scheduled to receive IL-4 (0.5, 1.5, 3.0, or 4.0 microg/kg/day) administered subcutaneously (s.c.) in sequential cohorts. Patients were continued on study as long as the drug was tolerated or the disease progressed. Patients were followed for antitumor activity, effects on viral replication, immune status, and clinical and laboratory toxicity. Seventeen patients were enrolled at two sites over a 21-month period. There were 15 males and 2 females, and 1 patient was Hispanic. All patients had a Karnofsky score >70. Patients enrolled only into the two lower dose cohorts (0.5 and 1.5 microg/kg/day). Both groups had similar baseline characteristics. The median time on treatment was only 7.4 and 8.4 weeks for the 0.5 and 1.5 microg/kg/day dose levels, respectively. There was significant neutropenia, with 6 patients having grade 3 or greater toxicity requiring granulocyte colony-stimulating factor (G-CSF). Three patients on a dose of 1.5 microg/kg/day stopped treatment due to protocol-defined toxicity. There were no appreciable effects on CD4/CD8 counts. HIV viral RNA did not significantly change over time. However, in several people, it appeared to decline with treatment and rebound with discontinuation of treatment. Corresponding changes were noted in the HIV immunocomplex dissociated (ICD) p24 antigen. One patient had a partial response, 11 patients had stable disease, and 5 patients had disease progression during the short period of treatment. The maximum tolerated dose for IL-4 in patients with advanced AIDS-related KS is 1.5 microg/kg/day. At this dose level, IL-4 is poorly tolerated and is not an effective KS treatment. Treatment of the majority of patients is discontinued because of drug-related toxicity or because of disease progression. Future studies of IL-4 should be confined to studies of cytokine manipulation of the underlying HIV infection, as there appears to be little antitumor activity.

Toward Cellular-based Therapies for HIV Infection

Journal of Hematotherapy & Stem Cell Research. Oct, 2002  |  Pubmed ID: 12427282

Infection with HIV-1 progressively erodes immune function, leading ultimately to multiple hematopoietic cytopenias. In advanced HIV disease, anemia, neutropenia, and thrombocytopenia occur in a large fraction of patients and are reflective of a striking inability of the bone marrow to accomplish a compensatory increase in production. No failure of compensatory production is greater than that of the T lymphoid system, where despite apparently effective control of HIV replication, restoration of anti-HIV immunity does not occur. Recent technical developments have provided considerable insight into hematopoietic dysfunction in HIV disease and, in particular, in vivo T cell generation. This article will review some of the mechanisms participating in immune regeneration, the stakes involved in effectively accomplishing full reconstitution, and potential approaches to enhance the limited endogenous regenerative process.

The Contribution of Cytotoxic and Noncytotoxic Function by Donor T-cells That Support Engraftment After Allogeneic Bone Marrow Transplantation

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. 2002  |  Pubmed ID: 12463477

The present studies were designed for investigation of the requirements for cytotoxic function in donor T-cells transplanted to support engraftment after infusion of allogeneic bone marrow. The experiments examined the capacity of donor CD8 T-cells lacking Fas ligand and/or perforin function to facilitate donor B6 congenic (B6-Ly5.1) BM engraftment across major histocompatibility complex class I/II barriers after transplantation. T-cell-depleted BM cells from B6-Ly5.1 donors were transplanted into sublethally irradiated (5.5 Gy) BALB/c recipients together with different lymphocyte populations from wild-type B6 (B6-wt) donors or donors lacking functional cytotoxic pathways. Early presence of lineage-committed donor progenitor cells was assessed by the presence of day 5 splenic colony-forming units-granulocyte-macrophage (CFU-GM). Recipients of BMT without donor T-cells did not demonstrate significant CFU-GM activity 5 days post-BMT. Lineage-committed progenitor cells in recipient spleens could be supported by addition to the BM of wild-type (B6-wt) and cytotoxically single- (perforin, B6-pko or FasL, B6-gld) or double-deficient (B6-cdd) CD8 T-cells. However, B220+-enriched B-cells could not support the presence of day 5 donor CFU-GM. For further assessment of the capacity of cytotoxically impaired T-cells to participate in the engraftment process, the ability of these and normal CD8 cells to support the homing of donor cells to the BM was examined after infusion of carboxyfluorescein diacetete succinimidyl ester-labeled progenitors. In a syngeneic model lacking resistance, cytotoxically impaired donor T-cells supported increased numbers of progenitor cells in the marrow equivalent to the support provided by wild-type donor T-cells. Examination of peripheral chimerism indicated that during the first month after B6-->BALB/c BMT, donor chimerism was detected in BMT recipients receiving unfractionated T-cells or CD8+ T-cells from B6-wt donors, and chimerism was maintained at least 80 days after BMT. In contrast, B6-cdd unfractionated or CD8+ T-cells failed to maintain long-term B6 donor chimerism in the host. Experiments with highly enriched populations of positively selected CD8+ T-cells from B6-pko, B6-gld, or B6-cdd donors demonstrated that although each of these T-cell populations could promote the initial presence of donor CFU-GM early post-BMT, B6-pko and B6-cdd CD8+ T-cell populations were not able to support long-term peripheral chimerism. These results demonstrate that donor T-cells lacking major cytotoxic effector pathways have functions that support initial donor progenitor cell presence in the host hematopoietic compartment after BMT. They also demonstrate that support of long-term donor BM engraftment requires CD8+ T-cells with intact cytotoxic, that is, perforin, function. Finally, syngeneic B6-->B6 BMT suggests activation of CD8+ T-cells posttransplantation apparently is required to support enhanced progenitor cell activity. This study provides new findings concerning the role of cytotoxic function in the process of facilitating allogeneic donor BM engraftment.

Multiple Measures of HIV Burden in Blood and Tissue Are Correlated with Each Other but Not with Clinical Parameters in Aviremic Subjects

AIDS (London, England). Jan, 2003  |  Pubmed ID: 12478069

To determine the levels of residual HIV DNA and RNA in blood and gut reservoirs in aviremic patients, assess correlations among compartmental measurements of HIV burden, and evaluate association with clinical parameters.

AIDS-related Malignancies

Annual Review of Medicine. 2003  |  Pubmed ID: 12525676

Immunodeficiency alters the risk of cancer. Specific types of immune dysfunction are associated with different tumor risks, but most tumors are related to oncogenic viruses. In acquired immunodeficiency due to the human immunodeficiency virus (HIV), HIV itself rarely directly causes cancer; rather, it provides the immunologic background against which other viruses can escape immune control and induce tumors. The most common malignancies are Kaposi's sarcoma and non-Hodgkin's lymphoma. This chapter discusses the pathophysiologic background of these tumors, how they have been affected by the use of anti-HIV medications, and their clinical management.

Ex Vivo Targeting of P21Cip1/Waf1 Permits Relative Expansion of Human Hematopoietic Stem Cells

Blood. Aug, 2003  |  Pubmed ID: 12702511

Relative quiescence is a defining characteristic of hematopoietic stem cells. Reasoning that inhibitory tone dominates control of stem cell cycling, we previously showed that mice engineered to be deficient in the cyclin-dependent kinase inhibitor, p21Cip1/Waf1 (p21), have an increased stem cell pool under homeostatic conditions. Since p21 was necessary to maintain stem cell quiescence and its absence sufficient to permit increased murine stem cell cycling, we tested whether reduction of p21 alone in human adult-derived stem cells could affect stem cell proliferation. We demonstrate here that interrupting p21 expression ex vivo resulted in expanded stem cell number and in vivo stem cell function compared with control, manipulated cells. Further, we demonstrate full multilineage reconstitution capability in cells where p21 expression was knocked down. Therefore, lifting the brake on cell proliferation by altering cell cycle checkpoints provides an alternative paradigm for increasing hematopoietic stem cell numbers. This approach may be useful for relative ex vivo human stem cell expansion.

Myeloid Expression of Cytochrome P450 4F3 is Determined by a Lineage-specific Alternative Promoter

The Journal of Biological Chemistry. Jul, 2003  |  Pubmed ID: 12709424

The cytochrome P450 4F3 (CYP4F3) gene encodes two functionally distinct enzymes that differ only by the selection of exon 4 (CYP4F3A) or exon 3 (CYP4F3B). CYP4F3A inactivates leukotriene B4, a reaction that has significance for controlling inflammation. CYP4F3B converts arachidonic acid to 20-hydroxyeicosatetraenoic acid, a potent activator of protein kinase C. We have previously shown that mRNAs coding for CYP4F3A and CYP4F3B are generated from distinct transcription start sites in neutrophils and liver. We therefore investigated mechanisms that regulate the cell-specific expression of these two isoforms. Initially, we analyzed the distribution of CYP4F3 in human leukocytes and determined a lineage-specific pattern of isoform expression. CYP4F3A is expressed in myeloid cells and is coordinate with myeloid differentiation markers such as CD11b and myeloperoxidase during development in the bone marrow. In contrast, CYP4F3B expression is restricted to a small population of CD3+ T lymphocytes. We identified distinct transcriptional features in myeloid, lymphoid, and hepatic cells that indicate the presence of multiple promoters in the CYP4F3 gene. The hepatic promoter depends on a cluster of hepatocyte nuclear factor sites 123-155 bp upstream of the initiator ATG codon. The myeloid promoter spans 400 bp in a region 468-872 bp upstream of the ATG codon; it is associated with clusters of CACCT sites and can be activated by ZEB-2, a factor primarily characterized as a transcriptional repressor in cells that include lymphocytes. ZEB-2 interacts with C-terminal binding protein and Smads, and this would provide opportunities for integrating environmental signals in myelopoiesis and inflammation.

P2Y-like Receptor, GPR105 (P2Y14), Identifies and Mediates Chemotaxis of Bone-marrow Hematopoietic Stem Cells

Genes & Development. Jul, 2003  |  Pubmed ID: 12842911

Hematopoiesis in mammals undergoes a developmental shift in location from fetal liver to bone marrow accompanied by a gradual transition from highly proliferative to deeply quiescent stem cell populations. P2Y receptors are G-protein-coupled nucleotide receptors participating in vascular and immune responses to injury. We identified a P2Y-like receptor for UDP-conjugated sugars, GPR105 (P2Y14), with restricted expression on primitive cells in the hematopoietic lineage. Anti-GPR105 antibody selectively isolated a subset of hematopoietic cells within the fetal bone marrow, but not in the fetal liver, that was enriched for G0 cell cycle status and for in vitro stem-cell-like multipotential long-term culture capability. Conditioned media from bone marrow stroma induced receptor activation and chemotaxis that was sensitive to G alpha i and anti-receptor antibody inhibition. GPR105 is a G-protein-coupled receptor identifying a quiescent, primitive population of hematopoietic cells restricted to bone marrow. It mediates primitive cell responses to specific hematopoietic microenvironments and extends the known immune system functions of P2Y receptors to the stem cell level. These data suggest a new class of receptors participating in the regulation of the stem cell compartment.

Immune Reconstitution in HIV Infection and Its Relationship to Cancer

Hematology/oncology Clinics of North America. Jun, 2003  |  Pubmed ID: 12852652

HIV infection results in formidable immune dysfunction, widely affecting the immune system, but typified by T lymphopenia. This dysfunction includes a perturbed immune response to several persistent viruses that have a propensity to cause tumors. Effective control of HIV replication by highly active antiretroviral therapy (HAART) results in regeneration of the damaged immune system, and recent advances have allowed this immune reconstitution to be better defined. This article describes the immunodeficiency caused by HIV and the response of the immune system to HAART, with specific reference to the immune response to cancers associated with HIV infection.

Heterologous Cells Cooperate to Augment Stem Cell Migration, Homing, and Engraftment

Blood. Jan, 2003  |  Pubmed ID: 12393569

T-lymphocyte depletion of bone marrow grafts compromises engraftment, suggesting a facilitating mechanism provided by the T cells that has been shown to associate with CD8(+) but not CD4(+) T cells. Explanations for this phenomenon have focused on immune targeting of residual host cells or cytokine production. We provide evidence for an alternative mechanism based on cooperative effects on cell motility. We observed that engraftment of CD34(+) cells in a beta(2)-microglobulin-deficient nonobese diabetic/severe combined immunodeficiency (beta(2)m(-/-) NOD/SCID) mouse model paralleled clinical observations in humans, with an enhancing effect noted from the addition of CD8(+) cells but not CD4(+) cells. This correlated with CD8(+) augmentation of CD34(+) cell homing to the bone marrow in vivo and CD8(+) cell-associated increases of CD34(+) cell transmigration through a bone marrow endothelial cell line in vitro. The cooperative interaction was not sensitive to brefeldin A inhibition of protein secretion. However, cytochalasin D-induced inhibition of CD8(+) cytoskeletal rearrangements abrogated CD34(+) transendothelial migration and impaired CD34(+) cell homing in vivo. CD8(+) cells did not migrate in tandem with CD34(+) cells or alter endothelial barrier integrity; rather, they affected phosphotyrosine-mediated signaling in CD34(+) cells in response to the chemokine stromal derived factor-1alpha (SDF-1alpha). These data demonstrate cell-cell cooperativity between different cell types in mediating chemotactic events and provide one potential explanation for the clinically observed effect of CD8(+) cells on bone marrow transplantation. This modification of cell migration by neighboring cells provides broad possibilities for combinatorial effects between cells of different types to influence cell localization.

Stem Cells and Immune Reconstitution in AIDS

Blood Reviews. Dec, 2003  |  Pubmed ID: 14556777

The hematopoietic system generally has reserve sufficient to tolerate significant insult and regenerative capacity to overcome most damage due to infectious agents. However, HIV infection results in a progressive decline in hematopoietic function and even in the context of potent, anti-retroviral therapy is able to only incompletely reconstitute immune function. The ability of the immune system to respond to HIV itself remains compromised, a defect that leaves infected individuals with a lifelong dependence on medications. The capability of stem cells and the thymus to restore function and their limitations in the context of HIV infection are discussed in this review.

Direct Evidence That the VEGF-specific Antibody Bevacizumab Has Antivascular Effects in Human Rectal Cancer

Nature Medicine. Feb, 2004  |  Pubmed ID: 14745444

The effects of vascular endothelial growth factor (VEGF) blockade on the vascular biology of human tumors are not known. Here we show here that a single infusion of the VEGF-specific antibody bevacizumab decreases tumor perfusion, vascular volume, microvascular density, interstitial fluid pressure and the number of viable, circulating endothelial and progenitor cells, and increases the fraction of vessels with pericyte coverage in rectal carcinoma patients. These data indicate that VEGF blockade has a direct and rapid antivascular effect in human tumors.

The Malignant Side of Successful Transplantation

American Journal of Transplantation : Official Journal of the American Society of Transplantation and the American Society of Transplant Surgeons. Feb, 2004  |  Pubmed ID: 14974933

Regenerative Response in Ischemic Brain Restricted by P21cip1/waf1

The Journal of Experimental Medicine. Apr, 2004  |  Pubmed ID: 15067031

Neural precursor cells from adults have exceptional proliferative and differentiative capability in vitro yet respond minimally to in vivo brain injury due to constraining mechanisms that are poorly defined. We assessed whether cell cycle inhibitors that restrict stem cell populations in other tissues may participate in limiting neural stem cell reactivity in vivo. The cyclin-dependent kinase inhibitor, p21cip1/waf1 (p21), maintains hematopoietic stem cell quiescence, and we evaluated its role in the regenerative response of neural tissue after ischemic injury using the mice deficient in p21. Although steady-state conditions revealed no increase in primitive cell proliferation in p21-null mice, a significantly larger fraction of quiescent neural precursors was activated in the hippocampus and subventricular zone after brain ischemia. The hippocampal precursors migrated and differentiated into a higher number of neurons after injury. Therefore, p21 is an intrinsic suppressor to neural regeneration after brain injury and may serve as a common molecular regulator restricting proliferation among stem cell pools from distinct tissue types.

In Vivo Self-renewing Divisions of Haematopoietic Stem Cells Are Increased in the Absence of the Early G1-phase Inhibitor, P18INK4C

Nature Cell Biology. May, 2004  |  Pubmed ID: 15122268

Self-renewal of stem cells is critical for tissue repair and maintenance of organ integrity in most mammalian systems. The relative asymmetry between self-renewal and differentiation in balance with apoptosis determines the size and durability of a stem-cell pool. Regulation of the cell cycle is one of the fundamental mechanisms underlying determination of cell fate. Absence of p21(Cip1/Waf1), a late G1-phase cyclin-dependent kinase inhibitor (CKI), has previously been shown to enable cell-cycle entry of haematopoietic stem cells, but leads to premature exhaustion of the stem cells under conditions of stress. We show here that deletion of an early G1-phase CKI, p18(INK4C), results in strikingly improved long-term engraftment, largely by increasing self-renewing divisions of the primitive cells in murine transplant models. Therefore, different CKIs have highly distinct effects on the kinetics of stem cells, possibly because of their active position in the cell cycle, and p18(INK4C) appears to be a strong inhibitor limiting the potential of stem-cell self-renewal in vivo.

Direct Vascular Delivery of Primitive Hematopoietic Cells to Bone Marrow Improves Localization but Not Engraftment

Blood. Jun, 2004  |  Pubmed ID: 15178586

Cancer Stem Cells Refined

Nature Immunology. Jul, 2004  |  Pubmed ID: 15224098

Defective Immune Function of Primary Effusion Lymphoma Cells is Associated with Distinct KSHV Gene Expression Profiles

Leukemia & Lymphoma. Jun, 2004  |  Pubmed ID: 15360006

Primary effusion lymphomas (PEL) are uniformly infected with Kaposi's sarcoma-associated herpesvirus (KSHV), and thus likely present both tumor and viral antigens to the immune system. In order to grow unrestricted and cause disease, multiple immune evasion strategies may be utilized by PEL to evade immune surveillance. Using six well-established PEL cell lines and comparing these to Epstein-Barr virus-transformed B cell lines and peripheral blood B cells, significant differences were found in the surface expression of molecules involved in antigen presentation, T cell activation and cell-cell adhesion. Significantly reduced stimulation of cytotoxic T lymphocytes, lowered sensitivity to natural killer cell-mediated lysis and impaired function as antigen presenting cells in mixed leukocyte reactions were found for three PEL cell lines with particularly low CD54, CD58 and CD81 expression. Comparative microarray analysis demonstrated specific patterns of KSHV-encoded gene expression that were associated with the different immune functions of these cell lines. Thus, the present data suggest that distinct patterns of KSHV gene expression may be associated with particular phenotypic and functional characteristics of PEL cells, which may influence PEL pathogenesis.

Ephrin Receptor, EphB4, Regulates ES Cell Differentiation of Primitive Mammalian Hemangioblasts, Blood, Cardiomyocytes, and Blood Vessels

Blood. Jan, 2004  |  Pubmed ID: 12958066

Differentiation of pluripotent embryonic stem (ES) cells is associated with expression of fate-specifying gene products. Coordinated development, however, must involve modifying factors that enable differentiation and growth to adjust in response to local microenvironmental determinants. We report here that the ephrin receptor, EphB4, known to be spatially restricted in expression and critical for organized vessel formation, modifies the rate and magnitude of ES cells acquiring genotypic and phenotypic characteristics of mesodermal tissues. Hemangioblast, blood cell, cardiomyocyte, and vascular differentiation was impaired in EphB4-/- ES cells in conjunction with decreased expression of mesoderm-associated, but not neuroectoderm-associated, genes. Therefore, EphB4 modulates the response to mesoderm induction signals. These data add differentiation kinetics to the known effects of ephrin receptors on mammalian cell migration and adhesion. We propose that modifying sensitivity to differentiation cues is a further means for ephrin receptors to contribute to tissue patterning and organization.

Surrogate Markers for Antiangiogenic Therapy and Dose-limiting Toxicities for Bevacizumab with Radiation and Chemotherapy: Continued Experience of a Phase I Trial in Rectal Cancer Patients

Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. Nov, 2005  |  Pubmed ID: 16258121

Plasmablastic Lymphoma in HIV-positive Patients: an Aggressive Epstein-Barr Virus-associated Extramedullary Plasmacytic Neoplasm

The American Journal of Surgical Pathology. Dec, 2005  |  Pubmed ID: 16327436

AIDS-associated aggressive B-cell lymphomas often have plasmacytoid features. Plasma cell neoplasms in HIV patients were commonly described to have atypical morphology and an aggressive clinical course in the literature. We reviewed 14 cases of neoplasms with marked plasmacytic differentiation in HIV-positive patients to determine their clinicopathologic features. Of these, 13 of 14 had homogeneous morphology and were generally CD45(+), CD20-, PAX-5-, and CD138(+). All were positive for Epstein-Barr virus-encoded RNA (EBER) but lacked EBV late membrane proteins (LMP). Human herpes virus 8 (HHV8) DNA was detected in 6 of 10 cases by nested PCR, but HHV8 latent nuclear antigen (LNA) was absent. The 13 patients ranged in age from 28 to 44 years (median, 41 years) (11 male patients; 2 female patients). All patients had extramedullary and 11 of 13 had extranodal tumor at the initial presentation; 2 had distant marrow involvement. The most commonly involved location was the oral cavity (6 of 13 cases), followed by bone and soft tissue (4 of 13), and the gastrointestinal tract (3 of 13). All 11 patients with follow-up died within 34 months (median, 7 months). The 14th patient who had a nodal disease with more undifferentiated morphology and expression of the HHV8 LNA protein was alive without disease at last follow-up (>72 months), probably representing a novel HHV8(+) lymphoma. We conclude that most plasmacytic tumors in HIV-positive individuals are extramedullary, clinically aggressive EBV(+) tumors identical to plasmablastic lymphoma that does not have the clinical features of plasma cell myeloma.

Angiogenesis Inhibitor IM862 is Ineffective Against AIDS-Kaposi's Sarcoma in a Phase III Trial, but Demonstrates Sustained, Potent Effect of Highly Active Antiretroviral Therapy: from the AIDS Malignancy Consortium and IM862 Study Team

Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. Feb, 2005  |  Pubmed ID: 15598977

IM862 is a synthetic dipeptide (L-glutamine L-tryptophan) with in vitro and in vivo antiangiogenic properties. Phase I/II studies showed minimal toxicity and a response rate of 36% in AIDS-Kaposi's sarcoma. We report a 24-week, randomized, double-blinded, placebo-controlled phase III trial with the phase II dose, 5 mg intranasally every other day.

Anemia in HIV-infected Adults: Epidemiology, Pathogenesis, and Clinical Management

Current Hematology Reports. Mar, 2005  |  Pubmed ID: 15720957

Anemia is the most common cytopenia seen in people with HIV. Independent of CD4 count and HIV-viral load, anemia has been shown to correlate with increased mortality. Furthermore, successful treatment of anemia has been shown to reduce this risk of death in a comparison with patients with similar immunologic and virologic parameters who are not treated. Women, blacks, injection drug users, and people with advanced disease suffer disproportionally from anemia and should be screened. The pathogenesis of anemia in HIV is complex and may result from opportunistic infections, nutritional deficiencies, AIDS-associated malignancies, medications, or alteration in hematopoeisis induced by HIV itself. A careful review of the patient's past medical history, medications, symptoms, and basic laboratory studies often leads to a treatable cause(s). For patients without secondary causes of anemia, a combination of highly active antiretroviral therapy (HAART) and supplemental erythropoietin leads to improved outcomes. Given the importance of completing therapy on adequate doses of both interferon and ribavirin, effective management of anemia in HIV/Hepatitis C (HCV)-coinfected patients is particularly important.

Generic Antiretroviral Efficacy in AIDS-associated Kaposi's Sarcoma in Sub-Saharan Africa

AIDS (London, England). Mar, 2005  |  Pubmed ID: 15750399

Generic antiretroviral drugs are pivotal in the implementation of WHO's '3 by 5' programme. However, clinical experience with generics in sub-Saharan Africa is insufficiently documented. We report on 50 patients with HIV-associated Kaposi's sarcoma treated with generic fixed-dose highly active antiretroviral therapy. At 52 weeks, 74% achieved an undetectable viral load of < 50 copies/ml, 86% achieved < 400 copies/ml, and a 3.1 log10 decline from baseline. Side-effects were minimal. The outcomes support the use of generic antiretroviral therapy.

Kinetic Expression of Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1/CD31) During Embryonic Stem Cell Differentiation

Journal of Cellular Biochemistry. Jun, 2005  |  Pubmed ID: 15786495

Platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) is widely used as a marker during vasculogenesis and angiogenesis from embryonic stem (ES) cells. However, the expression of PECAM-1 isoforms in ES cells has not been determined. The present study was designed to determine the role of PECAM-1 isoforms during in vitro endothelial differentiation of ES cells. It was found that undifferentiated ES cells expressed high level of PECAM-1, which primarily located at cell-cell junction, but the expression of PECAM-1 was sharply down-regulated during early ES cell differentiation. In addition, undifferentiated ES cells were found the expressed all eight known alternatively spliced PECAM-1 isoforms, among them the expression of PECAM-1 isoforms lacking exon 15 or 14&15 was predominant. Quantitative analysis revealed a significant increase in the expression of PECAM-1 isoform lacking exon 12&14&15 as vascular development of ES cells. These results indicate a constitutive expression of PECAM-1 in undifferentiated murine ES cells and suggest a developmental role of PECAM-1 isoform changes during vasculogenesis and angiogenesis.

Haploinsufficiency of GATA-2 Perturbs Adult Hematopoietic Stem-cell Homeostasis

Blood. Jul, 2005  |  Pubmed ID: 15811962

The zinc finger transcription factor GATA-2 plays a fundamental role in generating hematopoietic stem-cells in mammalian development. Less well defined is whether GATA-2 participates in adult stem-cell regulation, an issue we addressed using GATA-2 heterozygote mice that express reduced levels of GATA-2 in hematopoietic cells. While GATA-2+/- mice demonstrated decreases in some colony-forming progenitors, the most prominent changes were observed within the stem-cell compartment. Heterozygote bone marrow had a lower abundance of Lin(-)c-kit(+)Sca-1(+)CD34- cells and performed poorly in competitive transplantation and quantitative week-5 cobblestone area-forming cell (CAFC) assays. Furthermore, a stem-cell-enriched population from GATA1+/- marrow was more quiescent and exhibited a greater frequency of apoptotic cells associated with decreased expression of the anti-apoptotic gene Bcl-xL. Yet the self-renewal potential of the +/- stem-cell compartment, as judged by serial transplantations, was unchanged. These data indicate compromised primitive cell proliferation and survival in the setting of a lower GATA-2 gene dose without a change in the differentiation or self-renewal capacity of the stem-cells that remain. Thus, GATA-2 dose regulates adult stem-cell homeostasis by affecting select aspects of stem cell function.

Quantum Dots Spectrally Distinguish Multiple Species Within the Tumor Milieu in Vivo

Nature Medicine. Jun, 2005  |  Pubmed ID: 15880117

A solid tumor is an organ composed of cancer and host cells embedded in an extracellular matrix and nourished by blood vessels. A prerequisite to understanding tumor pathophysiology is the ability to distinguish and monitor each component in dynamic studies. Standard fluorophores hamper simultaneous intravital imaging of these components. Here, we used multiphoton microscopy techniques and transgenic mice that expressed green fluorescent protein, and combined them with the use of quantum dot preparations. We show that these fluorescent semiconductor nanocrystals can be customized to concurrently image and differentiate tumor vessels from both the perivascular cells and the matrix. Moreover, we used them to measure the ability of particles of different sizes to access the tumor. Finally, we successfully monitored the recruitment of quantum dot-labeled bone marrow-derived precursor cells to the tumor vasculature. These examples show the versatility of quantum dots for studying tumor pathophysiology and creating avenues for treatment.

Rituximab Does Not Improve Clinical Outcome in a Randomized Phase 3 Trial of CHOP with or Without Rituximab in Patients with HIV-associated Non-Hodgkin Lymphoma: AIDS-Malignancies Consortium Trial 010

Blood. Sep, 2005  |  Pubmed ID: 15914552

The addition of rituximab to cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy results in significant improvement in clinical outcome for individuals with non-HIV-associated aggressive B-cell lymphoma. To assess the potential risks and benefits of the addition of rituximab to CHOP for HIV-associated non-Hodgkin lymphoma (HIV-NHL) 150 patients receiving CHOP for HIV-NHL were randomized (2:1) to receive 375 mg/m(2) rituximab with each chemotherapy cycle (n = 99) or no immunotherapy (n = 50) in a multicenter phase 3 trial. The complete response rate (CR + CRu) was 57.6% for R-CHOP and 47% for CHOP (P = .147). With a median follow-up of 137 weeks, time to progression, progression-free survival, and overall survival times were 125, 45, and 139 weeks, respectively, for R-CHOP and 85, 38, and 110 weeks, respectively, for CHOP (P = not significant, all comparisons). Treatment-related infectious deaths occurred in 14% of patients receiving R-CHOP compared with 2% in the chemotherapy-alone group (P = .035). Of these deaths, 60% occurred in patients with CD4 counts less than 50/mm(3). Progression-free survival was significantly influenced by CD4(+) count (P < .001) and International Prognostic Index score (P = .022), but not bcl-2 status. The addition of rituximab to CHOP in patients with HIV-NHL may be associated with improved tumor responses. However, these benefits may be offset by an increase in infectious deaths, particularly in those individuals with CD4(+) lymphocyte counts less than 50/mm(3).

Osteopontin is a Hematopoietic Stem Cell Niche Component That Negatively Regulates Stem Cell Pool Size

The Journal of Experimental Medicine. Jun, 2005  |  Pubmed ID: 15928197

Stem cells reside in a specialized niche that regulates their abundance and fate. Components of the niche have generally been defined in terms of cells and signaling pathways. We define a role for a matrix glycoprotein, osteopontin (OPN), as a constraining factor on hematopoietic stem cells within the bone marrow microenvironment. Osteoblasts that participate in the niche produce varying amounts of OPN in response to stimulation. Using studies that combine OPN-deficient mice and exogenous OPN, we demonstrate that OPN modifies primitive hematopoietic cell number and function in a stem cell-nonautonomous manner. The OPN-null microenvironment was sufficient to increase the number of stem cells associated with increased stromal Jagged1 and Angiopoietin-1 expression and reduced primitive hematopoietic cell apoptosis. The activation of the stem cell microenvironment with parathyroid hormone induced a superphysiologic increase in stem cells in the absence of OPN. Therefore, OPN is a negative regulatory element of the stem cell niche that limits the size of the stem cell pool and may provide a mechanism for restricting excess stem cell expansion under conditions of niche stimulation.

In Vivo Imaging of Specialized Bone Marrow Endothelial Microdomains for Tumour Engraftment

Nature. Jun, 2005  |  Pubmed ID: 15959517

The organization of cellular niches is known to have a key role in regulating normal stem cell differentiation and regeneration, but relatively little is known about the architecture of microenvironments that support malignant metastasis. Using dynamic in vivo confocal imaging, here we show that murine bone marrow contains unique anatomic regions defined by specialized endothelium. This vasculature expresses the adhesion molecule E-selectin and the chemoattractant stromal-cell-derived factor 1 (SDF-1) in discrete, discontinuous areas that influence the homing of a variety of tumour cell lines. Disruption of the interactions between SDF-1 and its receptor CXCR4 inhibits the homing of Nalm-6 cells (an acute lymphoblastic leukaemia cell line) to these vessels. Further studies revealed that circulating leukaemic cells can engraft around these vessels, suggesting that this molecularly distinct vasculature demarcates a microenvironment for early metastatic tumour spread in bone marrow. Finally, purified haematopoietic stem/progenitor cells and lymphocytes also localize to the same microdomains, indicating that this vasculature might also function in benign states to demarcate specific portals for the entry of cells into the marrow space. Specialized vascular structures therefore appear to delineate a microenvironment with unique physiology that can be exploited by circulating malignant cells.

Restoration of Tubular Epithelial Cells During Repair of the Postischemic Kidney Occurs Independently of Bone Marrow-derived Stem Cells

The Journal of Clinical Investigation. Jul, 2005  |  Pubmed ID: 16007251

Ischemia causes kidney tubular cell damage and abnormal renal function. The kidney is capable of morphological restoration of tubules and recovery of function. Recently, it has been suggested that cells repopulating the ischemically injured tubule derive from bone marrow stem cells. We studied kidney repair in chimeric mice expressing GFP or bacterial beta-gal or harboring the male Y chromosome exclusively in bone marrow-derived cells. In GFP chimeras, some interstitial cells but not tubular cells expressed GFP after ischemic injury. More than 99% of those GFP interstitial cells were leukocytes. In female mice with male bone marrow, occasional tubular cells (0.06%) appeared to be positive for the Y chromosome, but deconvolution microscopy revealed these to be artifactual. In beta-gal chimeras, some tubular cells also appeared to express beta-gal as assessed by X-gal staining, but following suppression of endogenous (mammalian) beta-gal, no tubular cells could be found that stained with X-gal after ischemic injury. Whereas there was an absence of bone marrow-derived tubular cells, many tubular cells expressed proliferating cell nuclear antigen, which is reflective of a high proliferative rate of endogenous surviving tubular cells. Upon i.v. injection of bone marrow mesenchymal stromal cells, postischemic functional renal impairment was reduced, but there was no evidence of differentiation of these cells into tubular cells of the kidney. Thus, our data indicate that bone marrow-derived cells do not make a significant contribution to the restoration of epithelial integrity after an ischemic insult. It is likely that intrinsic tubular cell proliferation accounts for functionally significant replenishment of the tubular epithelium after ischemia.

Impact of Kaposi Sarcoma-associated Herpesvirus (KSHV) Burden and HIV Coinfection on the Detection of T Cell Responses to KSHV ORF73 and ORF65 Proteins

The Journal of Infectious Diseases. Aug, 2005  |  Pubmed ID: 16028131

Cellular immune responses to Kaposi sarcoma-associated herpesvirus (KSHV), the etiological agent of KS and several other malignancies, are incompletely characterized. We assessed KSHV-specific interferon- gamma enzyme-linked immunospot responses in a cohort of 154 individuals, using overlapping peptide sets spanning the KSHV-encoded latency-associated nuclear antigen (ORF73) and the minor capsid glycoprotein (ORF65). Among KSHV-seropositive subjects, ORF73-specific responses dominated over responses to ORF65 and were preferentially detected in human immunodeficiency virus-coinfected individuals who had elevated levels of cell-associated KSHV DNA, indicating that the viral antigen burden may have been driving these responses. Responses to both ORF73 and ORF65 were also detected in several KSHV-seronegative subjects who were at increased risk for KSHV infection, which demonstrates that cellular immunity can be found in the absence of detectable humoral responses. These data have implications for the reliable identification of KSHV infection and may help guide the design of immune-based therapeutic and prophylactic interventions.

Oocyte Generation in Adult Mammalian Ovaries by Putative Germ Cells in Bone Marrow and Peripheral Blood

Cell. Jul, 2005  |  Pubmed ID: 16051153

It has been suggested that germline stem cells maintain oogenesis in postnatal mouse ovaries. Here we show that adult mouse ovaries rapidly generate hundreds of oocytes, despite a small premeiotic germ cell pool. In considering the possibility of an extragonadal source of germ cells, we show expression of germline markers in bone marrow (BM). Further, BM transplantation restores oocyte production in wild-type mice sterilized by chemotherapy, as well as in ataxia telangiectasia-mutated gene-deficient mice, which are otherwise incapable of making oocytes. Donor-derived oocytes are also observed in female mice following peripheral blood transplantation. Although the fertilizability and developmental competency of the BM and peripheral blood-derived oocytes remain to be established, their morphology, enclosure within follicles, and expression of germ-cell- and oocyte-specific markers collectively support that these cells are bona fide oocytes. These results identify BM as a potential source of germ cells that could sustain oocyte production in adulthood.

Alpha E Beta 7 (CD103) Expression Identifies a Highly Active, Tonsil-resident Effector-memory CTL Population

Journal of Immunology (Baltimore, Md. : 1950). Oct, 2005  |  Pubmed ID: 16177076

The characterization of antiviral CTL responses has largely been limited to assessing Ag-specific immune responses in the peripheral blood. Consequently, there is an incomplete understanding of the cellular immune responses at mucosal sites where many viruses enter and initially replicate and how the Ag specificity and activation status of CTL derived from these mucosal sites may differ from that of blood-derived CTL. In this study, we show that EBV-specific CTL responses in the tonsils are of comparable specificity and breadth but of a significantly higher magnitude compared with responses in the peripheral blood. EBV-specific, tonsil-resident, but not PBMC-derived, T cells expressed the integrin/activation marker CD103 (alphaEbeta7), consistent with the detection of its ligand, E-cadherin, on tonsillar squamous cells. These CD8-positive, CD103-positive, tonsil-derived CTL were largely CCR7- and CD45RA- negative effector-memory cells and responded to lower Ag concentrations in in vitro assays than their CD103-negative PBMC-derived counterparts. Thus, EBV-specific CTL in the tonsil, a crucial site for EBV entry and replication, are of greater magnitude and phenotypically distinct from CTL in the peripheral blood and may be important for effective control of this orally transmitted virus.

Differential Targeting and Shifts in the Immunodominance of Epstein-Barr Virus--specific CD8 and CD4 T Cell Responses During Acute and Persistent Infection

The Journal of Infectious Diseases. Nov, 2005  |  Pubmed ID: 16206065

The evolution of Epstein-Barr virus (EBV)-specific T cell responses that occurs during the acute and persistent stages of infection remains poorly characterized despite its importance for developing immune interventions for EBV-associated disorders. This study assessed T cell responses to 113 EBV-derived epitopes in 40 subjects with acute or persistent EBV infection. Although no significant differences were seen in the breadth of CD8 and CD4 T cell responses, their magnitude differed significantly over time; acutely infected subjects generated especially strong responses to lytic viral antigens. The cross-sectional shift in immunodominance was also confirmed in subjects followed longitudinally from acute to persistent infection. In addition, human leukocyte antigen-matched siblings with discordant histories of symptomatic EBV infection showed no significant differences in their response patterns, suggesting that symptomatic EBV infection does not lead to unique persistent-stage responses. These data provide an assessment of immunodominance patterns and guidance for developing immunotherapeutic interventions for EBV-associated disorders.

Flowing Cells Through Pulsed Electric Fields Efficiently Purges Stem Cell Preparations of Contaminating Myeloma Cells While Preserving Stem Cell Function

Blood. Mar, 2005  |  Pubmed ID: 15292069

Autologous stem cell transplantation, in the setting of hematologic malignancies such as lymphoma, improves disease-free survival if the graft has undergone tumor purging. Here we show that flowing hematopoietic cells through pulsed electric fields (PEFs) effectively purges myeloma cells without sacrificing functional stem cells. Electric fields can induce irreversible cell membrane pores in direct relation to cell diameter, an effect we exploit in a flowing system appropriate for clinical scale. Multiple myeloma (MM) cell lines admixed with human bone marrow (BM) or peripheral blood (PB) cells were passed through PEFs at 1.35 kV/cm to 1.4 kV/cm, resulting in 3- to 4-log tumor cell depletion by flow cytometry and 4.5- to 6-log depletion by tumor regrowth cultures. Samples from patients with MM gave similar results by cytometry. Stem cell engraftment into nonobese diabetic-severe combined immunodeficient (NOD/SCID)/beta2m-/- mice was unperturbed by PEFs. Flowing cells through PEFs is a promising technology for rapid tumor cell purging of clinical progenitor cell preparations.

Differentiation and Characterization of T Cells

Current Protocols in Immunology / Edited by John E. Coligan ... [et Al.]. Nov, 2005  |  Pubmed ID: 18432955

This paper outlines current standard methods of inducing T lymphopoiesis in vitro and in vivo. Reference is made to both murine and human systems. In addition to differentiation assays, methods to optimally characterize output cells are discussed. In bringing together a number of existing protocols, many techniques important in investigating T cell development can be reviewed in one place.

HOXB4-induced Self-renewal of Hematopoietic Stem Cells is Significantly Enhanced by P21 Deficiency

Stem Cells (Dayton, Ohio). Mar, 2006  |  Pubmed ID: 16210402

Enforced expression of the HOXB4 transcription factor and downregulation of p21(Cip1/Waf) (p21) can each independently increase proliferation of murine hematopoietic stem cells (HSCs). We asked whether the increase in HSC self-renewal generated by overexpression of HOXB4 is enhanced in p21-deficient HSCs. HOXB4 was overexpressed in hematopoietic cells from wild-type (wt) and p21-/- mice. Bone marrow (BM) cells were transduced with a retroviral vector expressing HOXB4 together with GFP (MIGB4), or a control vector containing GFP alone (MIG) and maintained in liquid culture for up to 11 days. At day 11 of the expansion culture, the number of primary CFU-GM (colony-forming unit granulocyte-macrophage) colonies and the repopulating ability were significantly increased in MIGB4 p21-/- BM (p21B4) cells compared with MIGB4-transduced wt BM (wtB4) cells. To test proliferation of HSCs in vivo, we performed competitive repopulation experiments and obtained significantly higher long-term engraftment of expanded p21B4 cells compared with wtB4 cells. The 5-day expansion of p21B4 HSCs generated 100-fold higher numbers of competitive repopulating units compared with wtMIG and threefold higher numbers compared with wtB4. The findings demonstrate that increased expression of HOXB4, in combination with suppression of p21 expression, could be a useful strategy for effective and robust expansion of HSCs.

Evidence for Incorporation of Bone Marrow-derived Endothelial Cells into Perfused Blood Vessels in Tumors

Blood. Apr, 2006  |  Pubmed ID: 16339405

Recent studies have demonstrated that the cellular contribution of the bone marrow to tumor neovascularization is highly complex. In this context, the extent to which bone marrow-derived cells incorporate as bona fide endothelial (nonhematopoietic) cells into perfused tumor vessels, or any new vessels formed postnatally (vasculogenesis), is unclear. To this end, we developed models to characterize local vessel-derived and bone marrow-derived endothelial cells (BMD-ECs). Then, we characterized the BMD-ECs based on a set of endothelial markers and morphology. Finally, we quantified their contribution to perfused blood vessels in tumors using transplanted as well as spontaneous primary and metastatic tumor models. We demonstrate that BMD-ECs incorporate in perfused tumor vessels, and that this contribution varies with organ site and mouse strain.

Stem Cell Engraftment at the Endosteal Niche is Specified by the Calcium-sensing Receptor

Nature. Feb, 2006  |  Pubmed ID: 16382241

During mammalian ontogeny, haematopoietic stem cells (HSCs) translocate from the fetal liver to the bone marrow, where haematopoiesis occurs throughout adulthood. Unique features of bone that contribute to a microenvironmental niche for stem cells might include the known high concentration of calcium ions at the HSC-enriched endosteal surface. Cells respond to extracellular ionic calcium concentrations through the seven-transmembrane-spanning calcium-sensing receptor (CaR), which we identified as being expressed on HSCs. Here we show that, through the CaR, the simple ionic mineral content of the niche may dictate the preferential localization of adult mammalian haematopoiesis in bone. Antenatal mice deficient in CaR had primitive haematopoietic cells in the circulation and spleen, whereas few were found in bone marrow. CaR-/- HSCs from fetal liver were normal in number, in proliferative and differentiative function, and in migration and homing to the bone marrow. Yet they were highly defective in localizing anatomically to the endosteal niche, behaviour that correlated with defective adhesion to the extracellular matrix protein, collagen I. CaR has a function in retaining HSCs in close physical proximity to the endosteal surface and the regulatory niche components associated with it.

CXCR4 and CCR5 Mediate Homing of Primitive Bone Marrow-derived Hematopoietic Cells to the Postnatal Thymus

Experimental Hematology. Mar, 2006  |  Pubmed ID: 16543065

Factors governing the entry of cells into the postnatal thymus are poorly understood. We aimed to define molecular mechanisms mediating the homing of bone marrow cells to the thymus using a sublethally irradiated in vivo murine model. Entry of unfractionated and lineage-depleted bone marrow cells to the thymus, but not bone marrow, was a Galphai-mediated phenomenon. Lineage-depleted cells that had homed to the thymus expressed abundant CXCR4 and CCR5 mRNA, alone of 17 chemokine receptors evaluated by QPCR. Thymic-homed cells were distinct from cells that had homed to bone marrow in expression of CXCR4 and CCR5 by mRNA quantification and cell-surface expression of protein. Abrogation of CXCR4 and CCR5 function by genetic, antibody, or pharmacologic means impaired homing of lineage-depleted cells to the thymus, although not in a synergistic manner, implying interdependency of these receptors in the homing process. Competitive repopulation experiments demonstrated that inhibiting CXCR4-mediated homing adversely affected the double-negative cell pool at 2 weeks, suggesting that cells with prothymocytic activity may in part home via CXCR4. Overall, our data demonstrate differential homing mechanisms governing entry of unfractionated and lineage-depleted cells to irradiated bone marrow or thymus, with thymic homing of immature cells being pertussis-sensitive and mediated by the chemokine receptors CXCR4 and CCR5.

Differential CD146 Expression on Circulating Versus Tissue Endothelial Cells in Rectal Cancer Patients: Implications for Circulating Endothelial and Progenitor Cells As Biomarkers for Antiangiogenic Therapy

Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. Mar, 2006  |  Pubmed ID: 16549839

Circulating endothelial cells (CECs) and progenitor cells are currently evaluated as potential biomarkers of antiangiogenic therapy. CD146 is considered a panendothelial-specific marker, but its utility as a CEC marker in cancer patients remains unclear.

The Hematopoietic Stem Cell in Its Place

Nature Immunology. Apr, 2006  |  Pubmed ID: 16550195

A signature characteristic of stem cells is their ability to self-renew, affording a theoretically limitless ability to produce daughter cells and their descendents. This near-timeless dimension of stem cell function is not free of the constraints of place. The idea that highly specialized 'microenvironmental' cues participate in the regulation of stem cells has evidence in classic embryology and more recently in adult stem cells through the use of model organisms. There is now ample evidence that an anatomically defined, specifically constituted place represents the niche for hematopoietic and other tissue-specific stem cells. This review provides a conceptual framework and detailed account of the hematopoietic stem cell niche as defined at present. The components are assembling into a more complex view of the niche and may now be amenable to examination as a system and possibly to alteration to affect outcomes in immune regeneration.

Stem Cells: Good, Bad and Reformable

Nature. May, 2006  |  Pubmed ID: 16724049

Osteoclasts Eat Stem Cells out of House and Home

Nature Medicine. Jun, 2006  |  Pubmed ID: 16761001

The Stem-cell Niche As an Entity of Action

Nature. Jun, 2006  |  Pubmed ID: 16810242

Stem-cell populations are established in 'niches'--specific anatomic locations that regulate how they participate in tissue generation, maintenance and repair. The niche saves stem cells from depletion, while protecting the host from over-exuberant stem-cell proliferation. It constitutes a basic unit of tissue physiology, integrating signals that mediate the balanced response of stem cells to the needs of organisms. Yet the niche may also induce pathologies by imposing aberrant function on stem cells or other targets. The interplay between stem cells and their niche creates the dynamic system necessary for sustaining tissues, and for the ultimate design of stem-cell therapeutics.

Embryonic Stem Cells Make Human T Cells

Proceedings of the National Academy of Sciences of the United States of America. Aug, 2006  |  Pubmed ID: 16894150

Stem-cell Ageing Modified by the Cyclin-dependent Kinase Inhibitor P16INK4a

Nature. Sep, 2006  |  Pubmed ID: 16957735

Stem-cell ageing is thought to contribute to altered tissue maintenance and repair. Older humans experience increased bone marrow failure and poorer haematologic tolerance of cytotoxic injury. Haematopoietic stem cells (HSCs) in older mice have decreased per-cell repopulating activity, self-renewal and homing abilities, myeloid skewing of differentiation, and increased apoptosis with stress. Here we report that the cyclin-dependent kinase inhibitor p16INK4a, the level of which was previously noted to increase in other cell types with age, accumulates and modulates specific age-associated HSC functions. Notably, in the absence of p16INK4a, HSC repopulating defects and apoptosis were mitigated, improving the stress tolerance of cells and the survival of animals in successive transplants, a stem-cell-autonomous tissue regeneration model. Inhibition of p16INK4a may ameliorate the physiological impact of ageing on stem cells and thereby improve injury repair in aged tissue.

Tumor Stromal-derived Factor-1 Recruits Vascular Progenitors to Mitotic Neovasculature, Where Microenvironment Influences Their Differentiated Phenotypes

Cancer Research. Sep, 2006  |  Pubmed ID: 16982747

Mechanisms underlying tumor vasculogenesis, the homing and engraftment of bone marrow-derived vascular progenitors, remain undefined. We hypothesized that tumor cell-secreted factors regulate vasculogenesis. We studied vasculogenic and nonvasculogenic intracranial murine gliomas. A PCR screen identified stromal-derived factor-1 (SDF-1/CXCL12) and vascular endothelial growth factor (VEGF) expression by vasculogenic glioma cells and spontaneously arising vasculogenic tumors in NF1+/-:Trp53+/- mice, but not by nonvasculogenic glioma cells. Enforced SDF-1, not VEGF, expression in nonvasculogenic cells caused vasculogenesis. Combined SDF-1 and VEGF expression augmented vasculogenesis over SDF-1 expression alone. Blocking SDF-1 receptor CXCR4 reduced short-term homing and long-term engraftment of vascular progenitors. Implanting tumor cells secreting SDF-1 was therefore necessary and sufficient to incorporate marrow-derived precursors into tumor endothelium. SDF-1 seemed to exert these effects by acting locally intratumorally and did not cause an efflux of marrow-derived progenitors into circulation. Tumor microenvironment determined additional fates of marrow-derived cells. Hypoxia, observed with ectopic s.c. murine tumors at levels approximating that of intracranial human glioblastoma, interacted with tumor-secreted SDF-1 to expand engrafted vascular progenitor differentiated phenotypes to include pericytes as well as endothelium. In contrast, less hypoxic orthotopic intracranial murine gliomas contained only marrow-derived endothelium without marrow-derived pericytes. Furthermore, we found that vasculogenesis is significant for tumors because it generates endothelium with a higher mitotic index than endothelium derived from local sources. Although CXCR4 blockade selectively targeted endothelium generated by vasculogenesis, completely inhibiting vessel formation may require combination therapy targeting locally derived and marrow-derived endothelium.

Case Records of the Massachusetts General Hospital. Case 30-2006. A 41-year-old Man with Dyspnea, Fever, and Lymphadenopathy

The New England Journal of Medicine. Sep, 2006  |  Pubmed ID: 17005954

Stromal Cell-derived Factor-1/CXCR4 Signaling Modifies the Capillary-like Organization of Human Embryonic Stem Cell-derived Endothelium in Vitro

Stem Cells (Dayton, Ohio). Feb, 2007  |  Pubmed ID: 17038674

The molecular mechanisms that regulate human blood vessel formation during early development are largely unknown. Here we used human ESCs (hESCs) as an in vitro model to explore early human vasculogenesis. We demonstrated that stromal cell-derived factor-1 (SDF-1) and CXCR4 were expressed concurrently with hESC-derived embryonic endothelial differentiation. Human ESC-derived embryonic endothelial cells underwent dose-dependent chemotaxis to SDF-1, which enhanced vascular network formation in Matrigel. Blocking of CXCR4 signaling abolished capillary-like structures induced by SDF-1. Inhibition of the SDF-1/CXCR4 signaling pathway by AMD3100, a CXCR4 antagonist, disrupted the endothelial sprouting outgrowth from human embryoid bodies, suggesting that the SDF-1/CXCR4 axis plays a critical role in regulating initial vessel formation, and may function as a morphogen during human embryonic vascular development.

AZD2171, a Pan-VEGF Receptor Tyrosine Kinase Inhibitor, Normalizes Tumor Vasculature and Alleviates Edema in Glioblastoma Patients

Cancer Cell. Jan, 2007  |  Pubmed ID: 17222792

Using MRI techniques, we show here that normalization of tumor vessels in recurrent glioblastoma patients by daily administration of AZD2171-an oral tyrosine kinase inhibitor of VEGF receptors-has rapid onset, is prolonged but reversible, and has the significant clinical benefit of alleviating edema. Reversal of normalization began by 28 days, though some features persisted for as long as four months. Basic FGF, SDF1alpha, and viable circulating endothelial cells (CECs) increased when tumors escaped treatment, and circulating progenitor cells (CPCs) increased when tumors progressed after drug interruption. Our study provides insight into different mechanisms of action of this class of drugs in recurrent glioblastoma patients and suggests that the timing of combination therapy may be critical for optimizing activity against this tumor.

Therapeutic Targeting of a Stem Cell Niche

Nature Biotechnology. Feb, 2007  |  Pubmed ID: 17237769

The specialized microenvironment or niche where stem cells reside provides regulatory input governing stem cell function. We tested the hypothesis that targeting the niche might improve stem cell-based therapies using three mouse models that are relevant to clinical uses of hematopoietic stem (HS) cells. We and others previously identified the osteoblast as a component of the adult HS cell niche and established that activation of the parathyroid hormone (PTH) receptor on osteoblasts increases stem cell number. Here we show that pharmacologic use of PTH increases the number of HS cells mobilized into the peripheral blood for stem cell harvests, protects stem cells from repeated exposure to cytotoxic chemotherapy and expands stem cells in transplant recipients. These data provide evidence that the niche may be an attractive target for drug-based stem cell therapeutics.

Primitive Hematopoietic Cells Resist HIV-1 Infection Via P21

The Journal of Clinical Investigation. Feb, 2007  |  Pubmed ID: 17273559

Hematopoietic stem cells are resistant to HIV-1 infection. Here, we report a novel mechanism by which the cyclin-dependent kinase inhibitor (CKI) p21(Waf1/Cip1/Sdi1) (p21), a known regulator of stem cell pool size, restricts HIV-1 infection of primitive hematopoietic cells. Modifying p21 expression altered HIV-1 infection prior to changes in cell cycling and was selective for p21 since silencing the related CKIs, p27(Kip1) and p18(INK4C), had no effect on HIV-1. We show that p21 blocked viral infection by complexing with HIV-1 integrase and aborting chromosomal integration. A closely related lentivirus with a distinct integrase, SIVmac-251, and the other cell-intrinsic inhibitors of HIV-1, Trim5alpha, PML, Murr1, and IFN-alpha, were unaffected by p21. Therefore, p21 is an endogenous cellular component in stem cells that provides a unique molecular barrier to HIV-1 infection and may explain how these cells remain an uninfected "sanctuary" in HIV disease.

Endothelial Cells Derived from Human Embryonic Stem Cells Form Durable Blood Vessels in Vivo

Nature Biotechnology. Mar, 2007  |  Pubmed ID: 17322871

We describe the differentiation of human embryonic stem (hES) cells into endothelial cells using a scalable two-dimensional method that avoids an embryoid-body intermediate. After transplantation into severe combined immunodeficient (SCID) mice, the differentiated cells contributed to arborized blood vessels that integrated into the host circulatory system and served as blood conduits for 150 d.

Lytic and Latent Antigens of the Human Gammaherpesviruses Kaposi's Sarcoma-associated Herpesvirus and Epstein-Barr Virus Induce T-cell Responses with Similar Functional Properties and Memory Phenotypes

Journal of Virology. May, 2007  |  Pubmed ID: 17329344

The cellular immunity against Kaposi's sarcoma-associated herpesvirus (KSHV) is poorly characterized and has not been compared to T-cell responses against other human herpesviruses. Here, novel and dominant targets of KSHV-specific cellular immunity are identified and compared to T cells specific for lytic and latent antigens in a second human gammaherpesvirus, Epstein-Barr virus. The data identify a novel HLA-B57- and HLA-B58-restricted epitope in the Orf57 protein and show consistently close parallels in immune phenotypes and functional response patterns between cells targeting lytic or latent KSHV- and EBV-encoded antigens, suggesting common mechanisms in the induction of these responses.

The Stem Cell Niche in Health and Leukemic Disease

Best Practice & Research. Clinical Haematology. Mar, 2007  |  Pubmed ID: 17336251

That adult stem cells live in a highly specialized complex microenvironment, also known as a niche, is a pedestrian concept about 30 years old. It may, however, represent a relatively novel approach to being able to modify either normal or abnormal stem cells. Our emphasis in the past has been focused on identifying autonomous regulators of the stem cells and in attempting to modify them through the use of exogenous agents like cytokines. The body modulates these cells largely through the complex system that is embodied in the niche. This report discusses studies in which the niche components are modified to observe their effect on stem cells. The niches being investigated lie in the gut, skin, brain and bone. Other sites for hematopoiesis exist in the body, but these specific microenvironments can be localized and each component can be carefully evaluated using mouse models. Studies are ongoing as to how the stem cell microenvironment can support or propagate malignancies. By understanding the signals of this particular microenvironment, we may be able to adapt them to achieve a therapeutic benefit.

A Protocol for Phenotypic Detection and Enumeration of Circulating Endothelial Cells and Circulating Progenitor Cells in Human Blood

Nature Protocols. 2007  |  Pubmed ID: 17446880

Blood circulating endothelial cells (CECs) and circulating hematopoietic progenitor cells (CPCs) represent two cell populations that are thought to play important roles in tissue vascularization. CECs and CPCs are currently studied as surrogate markers in patients for more than a dozen pathologies, including heart disease and cancer. However, data interpretation has often been difficult because of multiple definitions, methods and protocols used to evaluate and count these cells by different laboratories. Here, we propose a cytometry protocol for phenotypic identification and enumeration of CECs and CPCs in human blood using four surface markers: CD31, CD34, CD133 and CD45. This method allows further phenotypic analyses to explore the biology of these cells. In addition, it offers a platform for longitudinal studies of these cells in patients with different pathologies. The protocol is relatively simple, inexpensive and can be adapted for multiple flow cytometer types or software. The procedure should take 2-2.5 h, and is expected to detect 0.1-6.0% viable CECs and 0.01-0.20% CPCs within blood mononuclear cell population.

Kaposi's Sarcoma-associated Herpesvirus-specific Immune Reconstitution and Antiviral Effect of Combined HAART/chemotherapy in HIV Clade C-infected Individuals with Kaposi's Sarcoma

AIDS (London, England). Jun, 2007  |  Pubmed ID: 17545700

Kaposi's sarcoma-associated herpesvirus (KSHV) is endemic in South Africa and the clinical manifestation of AIDS-associated Kaposi's sarcoma (KS) represents a significant clinical problem. Whereas the positive effects of HAART on the regression of KS have been well established, less is known about the role of herpesvirus-specific cellular immunity in disease improvement.

A Microenvironment-induced Myeloproliferative Syndrome Caused by Retinoic Acid Receptor Gamma Deficiency

Cell. Jun, 2007  |  Pubmed ID: 17574023

Myeloproliferative syndromes (MPS) are a heterogeneous subclass of nonlymphoid hematopoietic neoplasms which are considered to be intrinsic to hematopoietic cells. The causes of MPS are largely unknown. Here, we demonstrate that mice deficient for retinoic acid receptor gamma (RARgamma), develop MPS induced solely by the RARgamma-deficient microenvironment. RARgamma(-/-) mice had significantly increased granulocyte/macrophage progenitors and granulocytes in bone marrow (BM), peripheral blood, and spleen. The MPS phenotype continued for the lifespan of the mice and was more pronounced in older mice. Unexpectedly, transplant studies revealed this disease was not intrinsic to the hematopoietic cells. BM from wild-type mice transplanted into mice with an RARgamma(-/-) microenvironment rapidly developed the MPS, which was partially caused by significantly elevated TNFalpha in RARgamma(-/-) mice. These data show that loss of RARgamma results in a nonhematopoietic cell-intrinsic MPS, revealing the capability of the microenvironment to be the sole cause of hematopoietic disorders.

Stem Cells Remember Their Grade

Cell Stem Cell. Aug, 2007  |  Pubmed ID: 18371344

The stem cell state is understood based on what cells do in performance assays, crude measures of a highly refined state. In this issue of Cell Stem Cell, Dykstra et al. (2007) reveal stem cell gradation and the extent to which that gradation is retained in stem cell daughters of hematopoietic stem cells.

Limiting Factors in Murine Hematopoietic Stem Cell Assays

Cell Stem Cell. Sep, 2007  |  Pubmed ID: 18371361

Hematopoiesis arguably provides the most well-defined role of stem cells in tissue development, maintenance, and repair, largely because of the experimental methods developed over decades of investigation. Assays of hematopoietic stem and progenitor cell potential were developed in the late 1950s-1960s with the first reports of in vivo transplantation into lethally irradiated recipients (Ford et al., 1956; McCulloch and Till, 1960) and clonal growth of hematopoietic bone marrow cells in vitro (Bradley and Metcalf, 1966). These two major assays have undergone substantial refinement but remain the foundation for defining hematopoietic stem cell biology. Here, we provide a brief overview of methods commonly used to analyze hematopoietic stem and progenitor cell content in mice, discuss the limitations of these assays, and provide an in-depth review of the limiting dilution assay (Szilvassy et al., 1990), the best single assay for quantitating HSC content.

The Weight of Cell Identity

The Journal of Clinical Investigation. Dec, 2007  |  Pubmed ID: 18060026

Recent studies involving molecular modification of adult somatic cells have pointed to a remarkable plasticity in cell identity. In this issue of the JCI, Koh and colleagues assessed whether bone marrow-derived cells could alter their fate under circumstances conducive to adipocyte generation in vivo (see the related article beginning on page 3684). These cells remained true to their roots, indicating how difficult it will be to exploit cell plasticity for therapeutic purposes.

Analysis of the Hematopoietic Stem Cell Niche

Current Protocols in Stem Cell Biology. Nov, 2007  |  Pubmed ID: 18785177

Hematopoietic stem cells (HSCs) continuously replenish all blood cell lineages not only to maintain the normal rapid turnover of differentiated cells but also to respond to injury and stress. Cell-extrinsic mechanisms are critical determinants of the fine balance between HSC self-renewal and differentiation. The bone marrow microenvironment has emerged as a new area of intense study to identify which of its many components constitute the HSC niche and regulate HSC fate. While HSCs have been isolated, characterized and used in clinical practice for many years thanks to the development of very specific assays and technology (i.e., bone marrow transplants and fluorescence activated cell sorting), study of the HSC niche has evolved by combining experimental designs developed in different fields. In this unit we describe a collection of protocols spanning a wide range of techniques that can help every researcher tackling questions regarding the nature of the HSC niche.

GATA-2 Regulates Granulocyte-macrophage Progenitor Cell Function

Blood. Dec, 2008  |  Pubmed ID: 18840712

The zinc finger transcription factor GATA-2 has been implicated in the regulation of hematopoietic stem cells. Herein, we explored the role of GATA-2 as a candidate regulator of the hematopoietic progenitor cell compartment. We showed that bone marrow from GATA-2 heterozygote (GATA-2(+/-)) mice displayed attenuated granulocyte-macrophage progenitor function in colony-forming cell (CFC) and serial replating CFC assays. This defect was mapped to the Lin(-)CD117(+)Sca-1(-)CD34(+)CD16/32(high) granulocyte-macrophage progenitor (GMP) compartment of GATA-2(+/-) marrow, which was reduced in size and functionally impaired in CFC assays and competitive transplantation. Similar functional impairments were obtained using a RNA interference approach to stably knockdown GATA-2 in wild-type GMP. Although apoptosis and cell-cycle distribution remained unperturbed in GATA-2(+/-) GMP, quiescent cells from GATA-2(+/-) GMP exhibited altered functionality. Gene expression analysis showed attenuated expression of HES-1 mRNA in GATA-2-deficient GMP. Binding of GATA-2 to the HES-1 locus was detected in the myeloid progenitor cell line 32Dcl3, and enforced expression of HES-1 expression in GATA-2(+/-) GMP rectified the functional defect, suggesting that GATA-2 regulates myeloid progenitor function through HES-1. These data collectively point to GATA-2 as a novel, pivotal determinant of GMP cell fate.

Osteoblastic Regulation of B Lymphopoiesis is Mediated by Gs{alpha}-dependent Signaling Pathways

Proceedings of the National Academy of Sciences of the United States of America. Nov, 2008  |  Pubmed ID: 18957542

Osteoblasts play an increasingly recognized role in supporting hematopoietic development and recently have been implicated in the regulation of B lymphopoiesis. Here we demonstrate that the heterotrimeric G protein alpha subunit G(s)alpha is required in cells of the osteoblast lineage for normal postnatal B lymphocyte production. Deletion of G(s)alpha early in the osteoblast lineage results in a 59% decrease in the percentage of B cell precursors in the bone marrow. Analysis of peripheral blood from mutant mice revealed a 67% decrease in the number of circulating B lymphocytes by 10 days of age. Strikingly, other mature hematopoietic lineages are not decreased significantly. Mice lacking G(s)alpha in cells of the osteoblast lineage exhibit a reduction in pro-B and pre-B cells. Furthermore, interleukin (IL)-7 expression is attenuated in G(s)alpha-deficient osteoblasts, and exogenous IL-7 is able to restore B cell precursor populations in the bone marrow of mutant mice. Finally, the defect in B lymphopoiesis can be rescued by transplantation into a WT microenvironment. These findings confirm that osteoblasts are an important component of the B lymphocyte niche and demonstrate in vivo that G(s)alpha-dependent signaling pathways in cells of the osteoblast lineage extrinsically regulate bone marrow B lymphopoiesis, at least partially in an IL-7-dependent manner.

Tumor Necrosis Factor-alpha and Endothelial Cells Modulate Notch Signaling in the Bone Marrow Microenvironment During Inflammation

Experimental Hematology. May, 2008  |  Pubmed ID: 18439488

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.

Differential H3K4 Methylation Identifies Developmentally Poised Hematopoietic Genes

Developmental Cell. May, 2008  |  Pubmed ID: 18477461

Throughout development, cell fate decisions are converted into epigenetic information that determines cellular identity. Covalent histone modifications are heritable epigenetic marks and are hypothesized to play a central role in this process. In this report, we assess the concordance of histone H3 lysine 4 dimethylation (H3K4me2) and trimethylation (H3K4me3) on a genome-wide scale in erythroid development by analyzing pluripotent, multipotent, and unipotent cell types. Although H3K4me2 and H3K4me3 are concordant at most genes, multipotential hematopoietic cells have a subset of genes that are differentially methylated (H3K4me2+/me3-). These genes are transcriptionally silent, highly enriched in lineage-specific hematopoietic genes, and uniquely susceptible to differentiation-induced H3K4 demethylation. Self-renewing embryonic stem cells, which restrict H3K4 methylation to genes that contain CpG islands (CGIs), lack H3K4me2+/me3- genes. These data reveal distinct epigenetic regulation of CGI and non-CGI genes during development and indicate an interactive relationship between DNA sequence and differential H3K4 methylation in lineage-specific differentiation.

Hematopoietic Stem Cell Responsiveness to Exogenous Signals is Limited by Caspase-3

Cell Stem Cell. Jun, 2008  |  Pubmed ID: 18522851

Limited responsiveness to inflammatory cytokines is a feature of adult hematopoietic stem cells and contributes to the relative quiescence and durability of the stem cell population in vivo. Here we report that the executioner Caspase, Caspase-3, unexpectedly participates in that process. Mice deficient in Caspase-3 had increased numbers of immunophenotypic long-term repopulating stem cells in association with multiple functional changes, most prominently cell cycling. Though these changes were cell autonomous, they reflected altered activation by exogenous signals. Caspase-3(-/-) cells exhibited cell type-specific changes in phosphorylated members of the Ras-Raf-MEK-ERK pathway in response to specific cytokines, while notably, members of other pathways, such as pSTAT3, pSTAT5, pAKT, pp38 MAPK, pSmad2, and pSmad3, were unaffected. Caspase-3 contributes to stem cell quiescence, dampening specific signaling events and thereby cell responsiveness to microenvironmental stimuli.

Evolving Concepts on the Microenvironmental Niche for Hematopoietic Stem Cells

Current Opinion in Hematology. Jul, 2008  |  Pubmed ID: 18536566

The hematopoietic stem cell niche is critical for the maintenance and proliferation of hematopoietic stem cells and, as such, is not only essential for steady-state hematopoiesis but may also be relevant to hematologic disease. The present review discusses recent advances in the understanding of interactions within the niche, its potential role in disease pathogenesis and models of its use as a therapeutic target.

MicroRNA-mediated Control of Cell Fate in Megakaryocyte-erythrocyte Progenitors

Developmental Cell. Jun, 2008  |  Pubmed ID: 18539114

Lineage specification is a critical issue in developmental and regenerative biology. We hypothesized that microRNAs (miRNAs) are important participants in those processes and used the poorly understood regulation of megakaryocyte-erythrocyte progenitors (MEPs) in hematopoiesis as a model system. We report here that miR-150 modulates lineage fate in MEPs. Using a novel methodology capable of profiling miRNA expression in small numbers of primary cells, we identify miR-150 as preferentially expressed in the megakaryocytic lineage. Through gain- and loss-of-function experiments, we demonstrate that miR-150 drives MEP differentiation toward megakaryocytes at the expense of erythroid cells in vitro and in vivo. Moreover, we identify the transcription factor MYB as a critical target of miR-150 in this regulation. These experiments show that miR-150 regulates MEP fate, and thus establish a role for miRNAs in lineage specification of mammalian multipotent cells.

Nf2/merlin Regulates Hematopoietic Stem Cell Behavior by Altering Microenvironmental Architecture

Cell Stem Cell. Aug, 2008  |  Pubmed ID: 18682243

Stem cell population size is highly regulated across species and tissue types, and alterations are associated with premature tissue failure or cancer. We assessed whether the tumor suppressor and mediator of cell contact inhibition Nf2/merlin plays a role in governing the hematopoietic stem cell pool by stem cell-autonomous or niche-determined processes. Hematopoietic stem cells in Nf2-deficient mice were increased in number and demonstrated a marked shift in location to the circulation. These changes were entirely dependent on changes in the microenvironment, with a marked increase in trabecular bone and marrow vascularity associated with increased VEGF, but without cell-autonomous alterations in stem cell characteristics. Nf2/merlin is critical for maintaining normal structure and function of the hematopoietic stem cell niche. It limits both bone and vascular components, and our model suggests that it thereby constrains stem cell number and position.

Divided Within: Heterogeneity Within Adult Stem Cell Pools

Cell. Dec, 2008  |  Pubmed ID: 19070570

In this issue, Wilson et al. (2008) demonstrate that there are two functional subsets of hematopoietic stem cells that have distinctive kinetics of cell cycling. They present evidence that cells may transition between the two kinetic states, establishing one subpopulation that is ready to proliferate and another that is a deeply quiescent reserve.

Will Stem Cells Finally Deliver?

Newsweek. Dec, 2008  |  Pubmed ID: 19105310

Dose-reduced Busulfan, Cyclophosphamide, and Autologous Stem Cell Transplantation for Human Immunodeficiency Virus-associated Lymphoma: AIDS Malignancy Consortium Study 020

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Jan, 2008  |  Pubmed ID: 18158962

Intensive chemotherapy for human immunodeficiency virus (HIV)-associated non-Hodgkin lymphoma (NHL) and Hodgkin lymphoma (HL) has resulted in durable remissions in a substantial proportion of patients. High-dose chemotherapy and autologous stem cell transplantation (AuSCT), moreover, has resulted in sustained complete remissions in selected patients with recurrent chemosensitive disease. Based on a favorable experience with dose-reduced high-dose busulfan, cyclophosphamide, and AuSCT for older patients with non-HIV-associated aggressive lymphomas, an AIDS Malignancy Consortium multicenter trial was undertaken using the same dose-reduced busulfan and cyclophosphamide preparative regimen with AuSCT for recurrent HIV-associated NHL and HL. Of the 27 patients in the study, 20 received an AuSCT. The median time to achievement of an absolute neutrophil count (ANC) of >or= 0.5 x 10(9)/L was 11 days (range, 9-16 days). The median time to achievement of an unsupported platelet count of >or= 20 x 10(9)/L was 13 days (range, 6-57 days). One patient died on day +33 posttransplantation from hepatic veno-occlusive disease (VOD) and multiorgan failure. No other fatal regimen-related toxicity occurred. Ten of 19 patients (53%) were in complete remission at the time of their day +100 post-AuSCT evaluation. Of the 20 patients, 10 were alive and event-free at a median of 23 weeks post-AuSCT. Median overall survival (OS) was not reached by 13 of the 20 patients alive at the time of last follow-up. This multi-institutional trial demonstrates that a regimen of dose-reduced high-dose busulfan, cyclophosphamide, and AuSCT is well tolerated and is associated with favorable disease-free survival (DFS) and OS probabilities for selected patients with HIV-associated NHL and HL.

Deconstructing Stem Cell Self-renewal: Genetic Insights into Cell-cycle Regulation

Nature Reviews. Genetics. Feb, 2008  |  Pubmed ID: 18202695

The regulation of stem cell self-renewal must balance the regenerative needs of tissues that persist throughout life with the potential for cell overgrowth, transformation and cancer. Here, we attempt to deconstruct the relationship that exists between cell-cycle progression and the self-renewal versus commitment cell-fate decision in embryonic and adult stem cells. Recent genetic studies in mice have provided insights into the regulation of the cell cycle in stem cells, including its potential modulation by the stem cell niche. Although the dynamics of the embryonic and adult stem cell cycles are profoundly dissimilar, we suggest that shared principles underlie the governance of this important decision point in diverse stem cell types.

Pharmacologic Targeting of a Stem/progenitor Population in Vivo is Associated with Enhanced Bone Regeneration in Mice

The Journal of Clinical Investigation. Feb, 2008  |  Pubmed ID: 18219387

Drug targeting of adult stem cells has been proposed as a strategy for regenerative medicine, but very few drugs are known to target stem cell populations in vivo. Mesenchymal stem/progenitor cells (MSCs) are a multipotent population of cells that can differentiate into muscle, bone, fat, and other cell types in context-specific manners. Bortezomib (Bzb) is a clinically available proteasome inhibitor used in the treatment of multiple myeloma. Here, we show that Bzb induces MSCs to preferentially undergo osteoblastic differentiation, in part by modulation of the bone-specifying transcription factor runt-related transcription factor 2 (Runx-2) in mice. Mice implanted with MSCs showed increased ectopic ossicle and bone formation when recipients received low doses of Bzb. Furthermore, this treatment increased bone formation and rescued bone loss in a mouse model of osteoporosis. Thus, we show that a tissue-resident adult stem cell population in vivo can be pharmacologically modified to promote a regenerative function in adult animals.

Functional Analyses of the Cancer Stem Cell-like Properties of Human Endometrial Tumor Initiating Cells

Cell Cycle (Georgetown, Tex.). Jan, 2008  |  Pubmed ID: 18256549

Recent data suggest that rare stem cell populations with the capacity to self renew and drive tumor formation are a feature of solid tumors. Several investigators have identified putative stem cells from solid tumors and cancer cell lines following isolation of a side population (SP) defined by dye exclusion. We investigated this parameter in our efforts to identify an endometrial cancer (EnCa) stem cell population. Multiple EnCa cell lines were assessed and verapamil sensitive SP and non-SP cells were isolated from two human EnCa cell lines. The functional significance of the SP and non-SP derived from AN3CA was evaluated in vitro and in vivo. SP cells proliferated at a significantly slower rate than the non-SP fraction, and a larger proportion of the SP cells were in the G(1) phase of the cell cycle as compared to the non-SP fraction. The SP fraction was more resistant to the chemotherapeutic agent paclitaxel. The SP comprised -0.02% of the initial AN3CA cell population and this proportion of SP cells was maintained within the larger heterogeneous population following repeated passages of purified SP cells. These findings suggest that SP cells derived from the An3CA cell line have the stem cell properties of low proliferative activity, chemoresistance and self-renewal. We also tested relative tumor formation activity of the SP and non-SP fractions. Only the SP fraction was tumorigenic. Additionally, we identified SP fractions in primary EnCa. Together these results are consistent with the hypothesis that EnCa contain a subpopulation of tumor initiating cells with stem like properties.

Prospects for Stem Cell-based Therapy

Cell. Feb, 2008  |  Pubmed ID: 18295571

Resident pools of somatic stem cells in many organs are responsible for tissue maintenance and repair. The goal of regenerative medicine is to exploit these cells either by transplanting them from an exogenous source or by activating endogenous stem cells pharmacologically. For diseases caused by mutations in a single gene, the therapeutic goal is tissue replacement using stem cells engineered to correct the genetic defect. However, a number of technical hurdles must be overcome before therapies based on pluripotent human stem cells can enter the clinic.

Mutations in the Neutral Sphingomyelinase Gene SMPD3 Implicate the Ceramide Pathway in Human Leukemias

Blood. May, 2008  |  Pubmed ID: 18299447

Ceramide is a lipid second messenger derived from the hydrolysis of sphingomyelin by sphingomyelinases (SMases) and implicated in diverse cellular responses, including growth arrest, differentiation, and apoptosis. Defects in the neutral SMase (nSMase) gene Smpd3, the primary regulator of ceramide biosynthesis, are responsible for developmental defects of bone; regulation of ceramide levels have been implicated in macrophage differentiation, but this pathway has not been directly implicated in human cancer. In a genomic screen for gene copy losses contributing to tumorigenesis in a mouse osteosarcoma model, we identified a somatic homozygous deletion specifically targeting Smpd3. Reconstitution of SMPD3 expression in mouse tumor cells lacking the endogenous gene enhanced tumor necrosis factor (TNF)-induced reduction of cell viability. Nucleotide sequencing of the highly conserved SMPD3 gene in a large panel of human cancers revealed mutations in 5 (5%) of 92 acute myeloid leukemias (AMLs) and 8 (6%) of 131 acute lymphoid leukemias (ALLs), but not in other tumor types. In a subset of these mutations, functional analysis indicated defects in protein stability and localization. Taken together, these observations suggest that disruption of the ceramide pathway may contribute to a subset of human leukemias.

Circadian Rhythms: Stem Cells Traffic in Time

Nature. Mar, 2008  |  Pubmed ID: 18368105

Wnt Signaling in the Niche Enforces Hematopoietic Stem Cell Quiescence and is Necessary to Preserve Self-renewal in Vivo

Cell Stem Cell. Mar, 2008  |  Pubmed ID: 18371452

Wingless (Wnt) is a potent morphogen demonstrated in multiple cell lineages to promote the expansion and maintenance of stem and progenitor cell populations. Wnt effects are highly context dependent, and varying effects of Wnt signaling on hematopoietic stem cells (HSCs) have been reported. We explored the impact of Wnt signaling in vivo, specifically in the context of the HSC niche by using an osteoblast-specific promoter driving expression of the paninhibitor of canonical Wnt signaling, Dickkopf1 (Dkk1). Here we report that Wnt signaling was markedly inhibited in HSCs and, unexpectedly given prior reports, reduction in HSC Wnt signaling resulted in reduced p21Cip1 expression, increased cell cycling, and a progressive decline in regenerative function after transplantation. This effect was microenvironment determined, but irreversible if the cells were transferred to a normal host. Wnt pathway activation in the niche is required to limit HSC proliferation and preserve the reconstituting function of endogenous hematopoietic stem cells.

Stem-cell Ecology and Stem Cells in Motion

Blood. Apr, 2008  |  Pubmed ID: 18398055

This review highlights major scientific developments over the past 50 years or so in concepts related to stem-cell ecology and to stem cells in motion. Many thorough and eloquent reviews have been presented in the last 5 years updating progress in these issues. Some paradigms have been challenged, others validated, or new ones brought to light. In the present review, we will confine our remarks to the historical development of progress. In doing so, we will refrain from a detailed analysis of controversial data, emphasizing instead widely accepted views and some challenging novel ones.

Differential in Vivo Potential of Endothelial Progenitor Cells from Human Umbilical Cord Blood and Adult Peripheral Blood to Form Functional Long-lasting Vessels

Blood. Feb, 2008  |  Pubmed ID: 17993613

Tissue engineering requires formation of a de novo stable vascular network. Because of their ability to proliferate, differentiate into endothelial cells, and form new vessels, blood-derived endothelial progenitor cells (EPCs) are attractive source of cells for use in engineering blood vessels. However, the durability and function of EPC-derived vessels implanted in vivo are unclear. To this end, we directly compared formation and functions of tissue-engineered blood vessels generated by peripheral blood- and umbilical cord blood-derived EPCs in a model of in vivo vasculogenesis. We found that adult peripheral blood EPCs form blood vessels that are unstable and regress within 3 weeks. In contrast, umbilical cord blood EPCs form normal-functioning blood vessels that last for more than 4 months. These vessels exhibit normal blood flow, perm-selectivity to macromolecules, and induction of leukocyte-endothelial interactions in response to cytokine activation similar to normal vessels. Thus, umbilical cord blood EPCs hold great therapeutic potential, and their use should be pursued for vascular engineering.

Forward RNAi Screens in Primary Human Hematopoietic Stem/progenitor Cells

Blood. Apr, 2009  |  Pubmed ID: 19188664

The mechanisms regulating key fate decisions such as self-renewal and differentiation in hematopoietic stem and progenitor cells (HSPC) remain poorly understood. We report here a screening strategy developed to assess modulators of human hematopoiesis using a lentiviral short hairpin RNA (shRNA) library transduced into cord blood-derived stem/progenitor cells. To screen for modifiers of self-renewal/differentiation, we used the limited persistence of HSPCs under ex vivo culture conditions as a baseline for functional selection of shRNAs conferring enhanced maintenance or expansion of the stem/progenitor potential. This approach enables complex, pooled screens in large numbers of cells. Functional selection identified novel specific gene targets (exostoses 1) or shRNA constructs capable of altering human hematopoietic progenitor differentiation or stem cell expansion, respectively, thereby demonstrating the potential of this forward screening approach in primary human stem cell populations.

Role of the Osteoblast Lineage in the Bone Marrow Hematopoietic Niches

Journal of Bone and Mineral Research : the Official Journal of the American Society for Bone and Mineral Research. May, 2009  |  Pubmed ID: 19257832

Haematopoietic Stem Cells Depend on Galpha(s)-mediated Signalling to Engraft Bone Marrow

Nature. May, 2009  |  Pubmed ID: 19322176

Haematopoietic stem and progenitor cells (HSPCs) change location during development and circulate in mammals throughout life, moving into and out of the bloodstream to engage bone marrow niches in sequential steps of homing, engraftment and retention. Here we show that HSPC engraftment of bone marrow in fetal development is dependent on the guanine-nucleotide-binding protein stimulatory alpha subunit (Galpha(s)). HSPCs from adult mice deficient in Galpha(s) (Galpha(s)(-/-)) differentiate and undergo chemotaxis, but also do not home to or engraft in the bone marrow in adult mice and demonstrate a marked inability to engage the marrow microvasculature. If deleted after engraftment, Galpha(s) deficiency did not lead to lack of retention in the marrow, rather cytokine-induced mobilization into the blood was impaired. Testing whether activation of Galpha(s) affects HSPCs, pharmacological activators enhanced homing and engraftment in vivo. Galpha(s) governs specific aspects of HSPC localization under physiological conditions in vivo and may be pharmacologically targeted to improve transplantation efficiency.

P27Kip1 Constrains Proliferation of Neural Progenitor Cells in Adult Brain Under Homeostatic and Ischemic Conditions

Stem Cells (Dayton, Ohio). Apr, 2009  |  Pubmed ID: 19353520

Cell cycle inhibition of neural stem and progenitor cells is critical for maintaining the stability of central nervous system in adults, but it may represent a significant hurdle for neural regeneration after injury. We have previously demonstrated that the cyclin-dependent kinase inhibitor (CKI) p21(cip1/waf1) (p21) maintains the quiescence of neural stem-like cells under cerebral ischemia, as similarly shown for the hematopoietic stem cells. Here, we report the distinct role of another CKI member, p27(kip1) (p27) in neural progenitor cells (NPCs) from adult brain (subventricular zone and hippocampal subgranular zone) under both homeostatic and ischemic conditions. The basal level of NPC proliferation in the p27-/- mice was higher than that in p27+/+ mice. Upon ischemia, the overall proliferation of NPCs continued to be higher in p27-/- mice than that in p27+/+ mice. Moreover, the increase of NPC proliferation in p27-/- mice remained until 2 weeks after ischemia, whereas it resumed back to the basal level in p27+/+ mice. As a result, newly generated neuronal cells in the granular layer of p27-/- brain were more abundant compared with p27+/+ controls. These new data demonstrate that p27 functions as a distinct inhibitor for NPC proliferation under homeostatic as well as ischemic conditions.

The Leukemic Stem Cell Niche: Current Concepts and Therapeutic Opportunities

Blood. Aug, 2009  |  Pubmed ID: 19401558

The genetic events that contribute to the pathogenesis of acute myeloid leukemia are among the best characterized of all human malignancies. However, with notable exceptions such as acute promyelocytic leukemia, significant improvements in outcome based on these insights have not been forthcoming. Acute myeloid leukemia is a paradigm of cancer stem (or leukemia initiating) cells with hierarchy analogous to that seen in hematopoiesis. Normal hematopoiesis requires complex bidirectional interactions between the bone marrow microenvironment (or niche) and hematopoietic stem cells (HSCs). These interactions are critical for the maintenance of normal HSC quiescence and perturbations can influence HSC self-renewal. Leukemia stem cells (LSCs), which also possess limitless self-renewal, may hijack these homeostatic mechanisms, take refuge within the sanctuary of the niche during chemotherapy, and consequently contribute to eventual disease relapse. We will discuss the emerging evidence supporting the importance of the bone marrow microenvironment in LSC survival and consider the physiologic interactions of HSCs and the niche that inform our understanding of microenvironment support of LSCs. Finally, we will discuss approaches for the rational development of therapies that target the microenvironment.

VEGFR2+PDGFRbeta+ Circulating Precursor Cells Participate in Capillary Restoration After Hyperoxia Acute Lung Injury (HALI)

Journal of Cellular and Molecular Medicine. Sep, 2009  |  Pubmed ID: 19426150

The in vivo morphology and phenotype of circulating cells that spontaneously contribute to new vessel formation in adults remain unclear. Here, we use high-resolution imaging and flow cytometry to characterize the morphology and phenotype of a distinct population of circulating mononuclear cells contributing to spontaneous new vessel formation after hyperoxia acute lung injury (HALI). We identify a subpopulation of myeloid (CD11b/Mac1(+)) haematopoietic cells co-expressing vascular endothelial growth factor receptor 2 (VEGFR2) and platelet derived growth factor receptor beta (PDGFRbeta). Moreover, we show that these CD11b(+)VEGFR2(+)PDGFRbeta(+) circulating precursor cells (CPCs) contribute structurally to the luminal surface of capillaries re-forming 2 weeks post-HALI. This indicates that these myeloid CPCs may function, at least transiently, as putative vascular precursors, and has important implications for capillary growth and repair in injury and in pathologies of the lung and other organs.

CD133 Expression Defines a Tumor Initiating Cell Population in Primary Human Ovarian Cancer

Stem Cells (Dayton, Ohio). Dec, 2009  |  Pubmed ID: 19816957

Evidence is accumulating that solid tumors contain a rare phenotypically distinct population of cells, termed cancer stem cells (CSC), which give rise to and maintain the bulk of the tumor. These CSC are thought to be resistant to current chemotherapeutic strategies due to their intrinsic stem-like properties and thus may provide the principal driving force behind recurrent tumor growth. Given the high frequency of recurrent metastasis associated with human ovarian cancer, we sought to determine whether primary human ovarian tumors contain populations of cells with enhanced tumor-initiating capacity, a characteristic of CSC. Using an in vivo serial transplantation model, we show that primary uncultured human ovarian tumors can be reliably propagated in NOD/SCID mice, generating heterogeneous tumors that maintain the histological integrity of the parental tumor. The observed frequency of tumor engraftment suggests only certain subpopulations of ovarian tumor cells have the capacity to recapitulate tumor growth. Further profiling of human ovarian tumors for expression of candidate CSC surface markers indicated consistent expression of CD133. To determine whether CD133 expression could define a tumor-initiating cell population in primary human ovarian tumors, fluorescence-activated cell sorting (FACS) methods were employed. Injection of sorted CD133(+) and CD133(-) cell populations into NOD/SCID mice established that tumor-derived CD133(+) cells have an increased tumorigenic capacity and are capable of recapitulating the original heterogeneous tumor. Our data indicate that CD133 expression defines a NOD/SCID tumor initiating subpopulation of cells in human ovarian cancer that may be an important target for new chemotherapeutic strategies aimed at eliminating ovarian cancer.

Live-animal Tracking of Individual Haematopoietic Stem/progenitor Cells in Their Niche

Nature. Jan, 2009  |  Pubmed ID: 19052546

Stem cells reside in a specialized, regulatory environment termed the niche that dictates how they generate, maintain and repair tissues. We have previously documented that transplanted haematopoietic stem and progenitor cell populations localize to subdomains of bone-marrow microvessels where the chemokine CXCL12 is particularly abundant. Using a combination of high-resolution confocal microscopy and two-photon video imaging of individual haematopoietic cells in the calvarium bone marrow of living mice over time, we examine the relationship of haematopoietic stem and progenitor cells to blood vessels, osteoblasts and endosteal surface as they home and engraft in irradiated and c-Kit-receptor-deficient recipient mice. Osteoblasts were enmeshed in microvessels and relative positioning of stem/progenitor cells within this complex tissue was nonrandom and dynamic. Both cell autonomous and non-autonomous factors influenced primitive cell localization. Different haematopoietic cell subsets localized to distinct locations according to the stage of differentiation. When physiological challenges drove either engraftment or expansion, bone-marrow stem/progenitor cells assumed positions in close proximity to bone and osteoblasts. Our analysis permits observing in real time, at a single cell level, processes that previously have been studied only by their long-term outcome at the organismal level.

Activin A Promotes Multiple Myeloma-induced Osteolysis and is a Promising Target for Myeloma Bone Disease

Proceedings of the National Academy of Sciences of the United States of America. Mar, 2010  |  Pubmed ID: 20194748

Understanding the pathogenesis of cancer-related bone disease is crucial to the discovery of new therapies. Here we identify activin A, a TGF-beta family member, as a therapeutically amenable target exploited by multiple myeloma (MM) to alter its microenvironmental niche favoring osteolysis. Increased bone marrow plasma activin A levels were found in MM patients with osteolytic disease. MM cell engagement of marrow stromal cells enhanced activin A secretion via adhesion-mediated JNK activation. Activin A, in turn, inhibited osteoblast differentiation via SMAD2-dependent distal-less homeobox-5 down-regulation. Targeting activin A by a soluble decoy receptor reversed osteoblast inhibition, ameliorated MM bone disease, and inhibited tumor growth in an in vivo humanized MM model, setting the stage for testing in human clinical trials.

Bone Progenitor Dysfunction Induces Myelodysplasia and Secondary Leukaemia

Nature. Apr, 2010  |  Pubmed ID: 20305640

Mesenchymal cells contribute to the 'stroma' of most normal and malignant tissues, with specific mesenchymal cells participating in the regulatory niches of stem cells. By examining how mesenchymal osteolineage cells modulate haematopoiesis, here we show that deletion of Dicer1 specifically in mouse osteoprogenitors, but not in mature osteoblasts, disrupts the integrity of haematopoiesis. Myelodysplasia resulted and acute myelogenous leukaemia emerged that had acquired several genetic abnormalities while having intact Dicer1. Examining gene expression altered in osteoprogenitors as a result of Dicer1 deletion showed reduced expression of Sbds, the gene mutated in Schwachman-Bodian-Diamond syndrome-a human bone marrow failure and leukaemia pre-disposition condition. Deletion of Sbds in mouse osteoprogenitors induced bone marrow dysfunction with myelodysplasia. Therefore, perturbation of specific mesenchymal subsets of stromal cells can disorder differentiation, proliferation and apoptosis of heterologous cells, and disrupt tissue homeostasis. Furthermore, primary stromal dysfunction can result in secondary neoplastic disease, supporting the concept of niche-induced oncogenesis.

The HSC Niche Concept Has Turned 31. Has Our Knowledge Matured?

Annals of the New York Academy of Sciences. Mar, 2010  |  Pubmed ID: 20392212

The hematopoietic stem cell (HSC) niche is currently defined as the specific microenvironment in the bone marrow (BM) which anatomically harbors HSCs and governs their fate. It plays a pivotal role in regulating the survival and self-renewal ability of HSCs, protecting them from exhaustion while preventing their excessive proliferation. Many different stromal cell types have been proposed as putative constituents of the niche, but their integrated function is still unrevealed. Mechanisms by which stem/progenitor cell behavior is regulated in the niche include cell-to-cell interaction and the production of growth factors, cytokines, and extracellular matrix proteins. The HSC niche is a dynamic entity reflecting and responding to the needs of the organism. An understanding of how the niche participates in the maintenance of tissue homeostasis and repair offers new opportunities for the development of novel therapeutic tools.

MicroRNA MiR-125a Controls Hematopoietic Stem Cell Number

Proceedings of the National Academy of Sciences of the United States of America. Aug, 2010  |  Pubmed ID: 20616003

MicroRNAs influence hematopoietic differentiation, but little is known about their effects on the stem cell state. Here, we report that the microRNA processing enzyme Dicer is essential for stem cell persistence in vivo and a specific microRNA, miR-125a, controls the size of the stem cell population by regulating hematopoietic stem/progenitor cell (HSPC) apoptosis. Conditional deletion of Dicer revealed an absolute dependence for the multipotent HSPC population in a cell-autonomous manner, with increased HSPC apoptosis in mutant animals. An evolutionarily conserved microRNA cluster containing miR-99b, let-7e, and miR-125a was preferentially expressed in long-term hematopoietic stem cells. MicroRNA miR-125a alone was capable of increasing the number of hematopoietic stem cells in vivo by more than 8-fold. This result was accomplished through a differentiation stage-specific reduction of apoptosis in immature hematopoietic progenitors, possibly through targeting multiple proapoptotic genes. Bak1 was directly down-regulated by miR-125a and expression of a 3'UTR-less Bak1 blocked miR-125a-induced hematopoietic expansion in vivo. These data demonstrate cell-state-specific regulation by microRNA and identify a unique microRNA functioning to regulate the stem cell pool size.

Vitamin D Receptor Deletion Leads to Increased Hematopoietic Stem and Progenitor Cells Residing in the Spleen

Blood. Nov, 2010  |  Pubmed ID: 20664059

Bone components participate in the regulation of hematopoietic stem cells in the adult mammal. Vitamin D regulates bone mineralization and is associated with pleiotropic effects in many cell types, including putative roles in hematopoietic differentiation. We report that deletion of the vitamin D receptor (VDR) in hematopoietic cells did not result in cell autonomous perturbation of hematopoietic stem cell or progenitor function. However, deletion of VDR in the microenvironment resulted in a marked accumulation of hematopoietic stem cells in the spleen that could be reversed by calcium dietary supplementation. These data suggest that VDR participates in restricting splenic hematopoiesis through maintenance of bone calcium homeostasis and are consistent with the concept that calcium regulation through VDR is a central participant in localizing adult hematopoiesis preferentially to bone marrow.

Stem Cells and DNA Damage: Persist or Perish?

Cell. Aug, 2010  |  Pubmed ID: 20691895

Stem cells repopulate tissues after injury while also renewing themselves, but this makes them vulnerable to genotoxic damage. Mohrin et al. (2010) and Milyavsky et al. (2010) now show that mouse and human hematopoietic stem cells make opposing decisions about whether to die or to persist in response to DNA damage.

Mesenchymal and Haematopoietic Stem Cells Form a Unique Bone Marrow Niche

Nature. Aug, 2010  |  Pubmed ID: 20703299

The cellular constituents forming the haematopoietic stem cell (HSC) niche in the bone marrow are unclear, with studies implicating osteoblasts, endothelial and perivascular cells. Here we demonstrate that mesenchymal stem cells (MSCs), identified using nestin expression, constitute an essential HSC niche component. Nestin(+) MSCs contain all the bone-marrow colony-forming-unit fibroblastic activity and can be propagated as non-adherent 'mesenspheres' that can self-renew and expand in serial transplantations. Nestin(+) MSCs are spatially associated with HSCs and adrenergic nerve fibres, and highly express HSC maintenance genes. These genes, and others triggering osteoblastic differentiation, are selectively downregulated during enforced HSC mobilization or beta3 adrenoreceptor activation. Whereas parathormone administration doubles the number of bone marrow nestin(+) cells and favours their osteoblastic differentiation, in vivo nestin(+) cell depletion rapidly reduces HSC content in the bone marrow. Purified HSCs home near nestin(+) MSCs in the bone marrow of lethally irradiated mice, whereas in vivo nestin(+) cell depletion significantly reduces bone marrow homing of haematopoietic progenitors. These results uncover an unprecedented partnership between two distinct somatic stem-cell types and are indicative of a unique niche in the bone marrow made of heterotypic stem-cell pairs.

A MicroRNA Regulating Adult Hematopoietic Stem Cells

Cell Cycle (Georgetown, Tex.). Sep, 2010  |  Pubmed ID: 20855952

The Lkb1 Metabolic Sensor Maintains Haematopoietic Stem Cell Survival

Nature. Dec, 2010  |  Pubmed ID: 21124451

Haematopoietic stem cells (HSCs) can convert between growth states that have marked differences in bioenergetic needs. Although often quiescent in adults, these cells become proliferative upon physiological demand. Balancing HSC energetics in response to nutrient availability and growth state is poorly understood, yet essential for the dynamism of the haematopoietic system. Here we show that the Lkb1 tumour suppressor is critical for the maintenance of energy homeostasis in haematopoietic cells. Lkb1 inactivation in adult mice causes loss of HSC quiescence followed by rapid depletion of all haematopoietic subpopulations. Lkb1-deficient bone marrow cells exhibit mitochondrial defects, alterations in lipid and nucleotide metabolism, and depletion of cellular ATP. The haematopoietic effects are largely independent of Lkb1 regulation of AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) signalling. Instead, these data define a central role for Lkb1 in restricting HSC entry into cell cycle and in broadly maintaining energy homeostasis in haematopoietic cells through a novel metabolic checkpoint.

In Vivo Imaging of Transplanted Hematopoietic Stem and Progenitor Cells in Mouse Calvarium Bone Marrow

Nature Protocols. Jan, 2011  |  Pubmed ID: 21212779

In vivo imaging of transplanted hematopoietic stem and progenitor cells (HSPCs) was developed to investigate the relationship between HSPCs and components of their microenvironment in the bone marrow. In particular, it allows a direct observation of the behavior of hematopoietic cells during the first few days after transplantation, when the critical events in homing and early engraftment are occurring. By directly imaging these events in living animals, this method permits a detailed assessment of functions previously evaluated by crude assessments of cell counts (homing) or after prolonged periods (engraftment). This protocol offers a new means of investigating the role of cell-intrinsic and cell-extrinsic molecular regulators of hematopoiesis during the early stages of transplantation, and it is the first to allow the study of cell-cell interactions within the bone marrow in three dimensions and in real time. In this paper, we describe how to isolate, label and inject HSPCs, as well as how to perform calvarium intravital microscopy and analyze the resulting images. A typical experiment can be performed and analyzed in ∼1 week.

Biomimetic Platforms for Human Stem Cell Research

Cell Stem Cell. Mar, 2011  |  Pubmed ID: 21362565

Stem cells are central to developing new treatment options for tissue regeneration and constructing controllable models for biological research. Bioengineered cell culture environments that combine microenvironmental control with tissue-specific transport and signaling are critical tools in our efforts to study tissue development, regeneration, and disease under conditions that predict the human in vivo context. We propose that experimentation at the interfaces of biology, engineering, and medical sciences is critical for unlocking the full potential of stem cells. Here, we focus on the design and utilization of in vitro platforms that recapitulate the environments associated with tissue development, disease, and regeneration.

Inhibition of Bone Morphogenetic Protein Signaling Attenuates Anemia Associated with Inflammation

Blood. May, 2011  |  Pubmed ID: 21393479

Anemia of inflammation develops in settings of chronic inflammatory, infectious, or neoplastic disease. In this highly prevalent form of anemia, inflammatory cytokines, including IL-6, stimulate hepatic expression of hepcidin, which negatively regulates iron bioavailability by inactivating ferroportin. Hepcidin is transcriptionally regulated by IL-6 and bone morphogenetic protein (BMP) signaling. We hypothesized that inhibiting BMP signaling can reduce hepcidin expression and ameliorate hypoferremia and anemia associated with inflammation. In human hepatoma cells, IL-6-induced hepcidin expression, an effect that was inhibited by treatment with a BMP type I receptor inhibitor, LDN-193189, or BMP ligand antagonists noggin and ALK3-Fc. In zebrafish, the induction of hepcidin expression by transgenic expression of IL-6 was also reduced by LDN-193189. In mice, treatment with IL-6 or turpentine increased hepcidin expression and reduced serum iron, effects that were inhibited by LDN-193189 or ALK3-Fc. Chronic turpentine treatment led to microcytic anemia, which was prevented by concurrent administration of LDN-193189 or attenuated when LDN-193189 was administered after anemia was established. Our studies support the concept that BMP and IL-6 act together to regulate iron homeostasis and suggest that inhibition of BMP signaling may be an effective strategy for the treatment of anemia of inflammation.

Guanine Nucleotide Exchange Factor Vav1 Regulates Perivascular Homing and Bone Marrow Retention of Hematopoietic Stem and Progenitor Cells

Proceedings of the National Academy of Sciences of the United States of America. Jun, 2011  |  Pubmed ID: 21606370

Engraftment and maintenance of hematopoietic stem and progenitor cells (HSPC) depend on their ability to respond to extracellular signals from the bone marrow microenvironment, but the critical intracellular pathways integrating these signals remain poorly understood. Furthermore, recent studies provide contradictory evidence of the roles of vascular versus osteoblastic niche components in HSPC function. To address these questions and to dissect the complex upstream regulation of Rac GTPase activity in HSPC, we investigated the role of the hematopoietic-specific guanine nucleotide exchange factor Vav1 in HSPC localization and engraftment. Using intravital microscopy assays, we demonstrated that transplanted Vav1(-/-) HSPC showed impaired early localization near nestin(+) perivascular mesenchymal stem cells; only 6.25% of Vav1(-/-) HSPC versus 45.8% of wild-type HSPC were located less than 30 μm from a nestin(+) cell. Abnormal perivascular localization correlated with decreased retention of Vav1(-/-) HSPC in the bone marrow (44-60% reduction at 48 h posttransplant, compared with wild-type) and a very significant defect in short- and long-term engraftment in competitive and noncompetitive repopulation assays (<1.5% chimerism of Vav1(-/-) cells vs. 53-63% for wild-type cells). The engraftment defect of Vav1(-/-) HSPC was not related to alterations in proliferation, survival, or integrin-mediated adhesion. However, Vav1(-/-) HSPC showed impaired responses to SDF1α, including reduced in vitro migration in time-lapse microscopy assays, decreased circadian and pharmacologically induced mobilization in vivo, and dysregulated Rac/Cdc42 activation. These data suggest that Vav1 activity is required specifically for SDF1α-dependent perivascular homing of HSPC and suggest a critical role for this localization in retention and subsequent engraftment.

Crosstalk Between NOTCH and AKT Signaling During Murine Megakaryocyte Lineage Specification

Blood. Aug, 2011  |  Pubmed ID: 21653327

The NOTCH signaling pathway is implicated in a broad range of developmental processes, including cell fate decisions. However, the molecular basis for its role at the different steps of stem cell lineage commitment is unclear. We recently identified the NOTCH signaling pathway as a positive regulator of megakaryocyte lineage specification during hematopoiesis, but the developmental pathways that allow hematopoietic stem cell differentiation into the erythro-megakaryocytic lineages remain controversial. Here, we investigated the role of downstream mediators of NOTCH during megakaryopoiesis and report crosstalk between the NOTCH and PI3K/AKT pathways. We demonstrate the inhibitory role of phosphatase with tensin homolog and Forkhead Box class O factors on megakaryopoiesis in vivo. Finally, our data annotate developmental mechanisms in the hematopoietic system that enable a decision to be made either at the hematopoietic stem cell or the committed progenitor level to commit to the megakaryocyte lineage, supporting the existence of 2 distinct developmental pathways.

In Vivo Imaging of Treg Cells Providing Immune Privilege to the Haematopoietic Stem-cell Niche

Nature. Jun, 2011  |  Pubmed ID: 21654805

Stem cells reside in a specialized regulatory microenvironment or niche, where they receive appropriate support for maintaining self-renewal and multi-lineage differentiation capacity. The niche may also protect stem cells from environmental insults including cytotoxic chemotherapy and perhaps pathogenic immunity. The testis, hair follicle and placenta are all sites of residence for stem cells and are immune-suppressive environments, called immune-privileged sites, where multiple mechanisms cooperate to prevent immune attack, even enabling prolonged survival of foreign allografts without immunosuppression. We sought to determine if somatic stem-cell niches more broadly are immune-privileged sites by examining the haematopoietic stem/progenitor cell (HSPC) niche in the bone marrow, a site where immune reactivity exists. We observed persistence of HSPCs from allogeneic donor mice (allo-HSPCs) in non-irradiated recipient mice for 30 days without immunosuppression with the same survival frequency compared to syngeneic HSPCs. These HSPCs were lost after the depletion of FoxP3 regulatory T (T(reg)) cells. High-resolution in vivo imaging over time demonstrated marked co-localization of HSPCs with T(reg) cells that accumulated on the endosteal surface in the calvarial and trabecular bone marrow. T(reg) cells seem to participate in creating a localized zone where HSPCs reside and where T(reg) cells are necessary for allo-HSPC persistence. In addition to processes supporting stem-cell function, the niche will provide a relative sanctuary from immune attack.

Differential Niche and Wnt Requirements During Acute Myeloid Leukemia Progression

Blood. Sep, 2011  |  Pubmed ID: 21765021

Hematopoietic stem cells (HSCs) engage in complex bidirectional signals with the hematopoietic microenvironment (HM), and there is emerging evidence that leukemia stem cells (LSCs) may use similar interactions. Using a syngeneic retroviral model of MLL-AF9 induced acute myeloid leukemia (AML), we have identified 2 different stages of leukemia progression, propagated by "pre-LSCs" and established leukemia (LSCs) and compared the homing properties of these distinctive entities to that of normal HSCs. The homing and microlocalization of pre-LSCs was most similar to long-term HSCs and was dependent on cell-intrinsic Wnt signaling. In contrast, the homing of established LSCs was most similar to that of committed myeloid progenitors and distinct from HSCs. Although osteoblast-derived Dickkopf-1, a potent Wnt inhibitor known to impair HSC function, dramatically impaired normal HSC localization within the bone marrow, it did not affect pre-LSCs, LSC homing, or AML development. Mechanistically, cell-intrinsic Wnt activation was observed in human and murine AML samples, explaining the independence of MLL-AF9 LSCs from niche-derived Wnt signals. These data identify differential engagement of HM associated with leukemic progression and identify an LSC niche that is physically distinct and independent of the constraints of Wnt signaling that apply to normal HSCs.

AKT/FOXO Signaling Enforces Reversible Differentiation Blockade in Myeloid Leukemias

Cell. Sep, 2011  |  Pubmed ID: 21884932

AKT activation is associated with many malignancies, where AKT acts, in part, by inhibiting FOXO tumor suppressors. We show a converse role for AKT/FOXOs in acute myeloid leukemia (AML). Rather than decreased FOXO activity, we observed that FOXOs are active in ∼40% of AML patient samples regardless of genetic subtype. We also observe this activity in human MLL-AF9 leukemia allele-induced AML in mice, where either activation of Akt or compound deletion of FoxO1/3/4 reduced leukemic cell growth, with the latter markedly diminishing leukemia-initiating cell (LIC) function in vivo and improving animal survival. FOXO inhibition resulted in myeloid maturation and subsequent AML cell death. FOXO activation inversely correlated with JNK/c-JUN signaling, and leukemic cells resistant to FOXO inhibition responded to JNK inhibition. These data reveal a molecular role for AKT/FOXO and JNK/c-JUN in maintaining a differentiation blockade that can be targeted to inhibit leukemias with a range of genetic lesions.

Diabetes Impairs Hematopoietic Stem Cell Mobilization by Altering Niche Function

Science Translational Medicine. Oct, 2011  |  Pubmed ID: 21998408

Success with transplantation of autologous hematopoietic stem and progenitor cells (HSPCs) in patients depends on adequate collection of these cells after mobilization from the bone marrow niche by the cytokine granulocyte colony-stimulating factor (G-CSF). However, some patients fail to achieve sufficient HSPC mobilization. Retrospective analysis of bone marrow transplant patient records revealed that diabetes correlated with poor mobilization of CD34+ HSPCs. In mouse models of type 1 and type 2 diabetes (streptozotocin-induced and db/db mice, respectively), we found impaired egress of murine HSPCs from the bone marrow after G-CSF treatment. Furthermore, HSPCs were aberrantly localized in the marrow niche of the diabetic mice, and abnormalities in the number and function of sympathetic nerve termini were associated with this mislocalization. Aberrant responses to β-adrenergic stimulation of the bone marrow included an inability of marrow mesenchymal stem cells expressing the marker nestin to down-modulate the chemokine CXCL12 in response to G-CSF treatment (mesenchymal stem cells are reported to be critical for HSPC mobilization). The HSPC mobilization defect was rescued by direct pharmacological inhibition of the interaction of CXCL12 with its receptor CXCR4 using the drug AMD3100. These data suggest that there are diabetes-induced changes in bone marrow physiology and microanatomy and point to a potential intervention to overcome poor HSPC mobilization in diabetic patients.

The Haematopoietic Stem Cell Niche at a Glance

Journal of Cell Science. Nov, 2011  |  Pubmed ID: 22083139

The Bone Marrow at the Crossroads of Blood and Immunity

Nature Reviews. Immunology. Jan, 2012  |  Pubmed ID: 22193770

Progenitor cells that are the basis for all blood cell production share the bone marrow with more mature elements of the adaptive immune system. Specialized niches within the bone marrow guide and, at times, constrain the development of haematopoietic stem and progenitor cells (HSPCs) and lineage-restricted immune progenitor cells. Specific niche components are organized into distinct domains to create a diversified landscape in which specialized cell differentiation or population expansion programmes proceed. Local cues that reflect the tissue and organismal state affect cellular interactions to alter the production of a range of cell types. Here, we review the organization of regulatory elements in the bone marrow and discuss how these elements provide a dynamic means for the host to modulate stem cell and adaptive immune cell responses to physiological challenges.

The Hematopoietic Stem Cell Niche

Frontiers in Bioscience : a Journal and Virtual Library. 2012  |  Pubmed ID: 22201730

Hematopoietic stem cells (HSCs) possess the ability to self-renew and to differentiate to mature progeny along multiple different hematopoietic lineages. The function of HSCs depends upon the signals from surrounding cells found within the highly specialized microenvironment termed the hematopoietic stem cell niche. Understanding and exploiting the HSC niche is a goal of basic scientists and clinicians alike. Recent studies have focused on defining the cellular components and molecular factors critical to this microenvironment. Here we review recent findings, discuss unresolved questions, and examine the clinical implications of our current knowledge of the HSC niche.

NF-Y is Necessary for Hematopoietic Stem Cell Proliferation and Survival

Blood. Feb, 2012  |  Pubmed ID: 22072554

HSC function depends on the tight control of proliferation and the balance between self-renewal and differentiation. Here, we report that the trimeric transcription factor NF-Y is critical for the survival of cycling, but not quiescent HSCs. With the use of a conditional knockout mouse model, we demonstrate that NF-Ya deletion creates an accumulation of HSCs in G(2)/M and prompts apoptosis, causing hematopoietic failure and death of the animal. These defects are accompanied by the dysregulation of multiple genes that influence cell cycle control (cyclin b1 and p21), apoptosis (Bcl-2), and self-renewal (HoxB4, Notch1, Bmi-1) and are independent of p53. Our results identify NF-Y as a pivotal upstream participant in a regu-latory network necessary for the pre-servation of cycling HSCs.