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Biomedical subjects

John E Dick

Publications and source records attributed to John E Dick.

At least 19 recordsLinked to original sources
PubMed2025

Transcriptional activation of regenerative hematopoiesis via microenvironmental sensing.

Transition between activation and quiescence states in hematopoietic stem and progenitor cells (HSPCs) is tightly governed by cell-intrinsic means and microenvironmental co-adaptation. Although this balance is fundamental for lifelong hematopoiesis and immunity, the underlying molecular mechanisms remain poorly defined. Multimodal analysis divulging differential transcriptional activity between distinct HSPC states indicates the presence of Fli-1 transcription factor binding motif in activated hematopoietic stem cells. We reveal that Fli-1 activity is essential during regenerative hematopoiesis in mice. Fli-1 directs activation programs while priming cellular sensory and output machineries, enabling HSPCs co-adoptability with a stimulated vascular niche through propagation of niche-derived angiocrine Notch1 signaling. Constitutively induced Notch1 signaling is sufficient to recuperate functional hematopoietic stem cells impairments in the absence of Fli-1, without leukemic transformation. Applying FLI-1 transient modified-mRNA transduction into latent adult human mobilized HSPCs, enables their niche-mediated expansion and superior engraftment capacities. Thus, decryption of stem cell activation programs offers valuable insights for immunological regenerative medicine.

Animals↗
PubMed2006

A human colon cancer cell capable of initiating tumour growth in immunodeficient mice.

Colon cancer is one of the best-understood neoplasms from a genetic perspective, yet it remains the second most common cause of cancer-related death, indicating that some of its cancer cells are not eradicated by current therapies. What has yet to be established is whether every colon cancer cell possesses the potential to initiate and sustain tumour growth, or whether the tumour is hierarchically organized so that only a subset of cells--cancer stem cells--possess such potential. Here we use renal capsule transplantation in immunodeficient NOD/SCID mice to identify a human colon cancer-initiating cell (CC-IC). Purification experiments established that all CC-ICs were CD133+; the CD133- cells that comprised the majority of the tumour were unable to initiate tumour growth. We calculated by limiting dilution analysis that there was one CC-IC in 5.7 x 10(4) unfractionated tumour cells, whereas there was one CC-IC in 262 CD133+ cells, representing >200-fold enrichment. CC-ICs within the CD133+ population were able to maintain themselves as well as differentiate and re-establish tumour heterogeneity upon serial transplantation. The identification of colon cancer stem cells that are distinct from the bulk tumour cells provides strong support for the hierarchical organization of human colon cancer, and their existence suggests that for therapeutic strategies to be effective, they must target the cancer stem cells.

AC133 Antigen↗
PubMed2006

Individual stem cells with highly variable proliferation and self-renewal properties comprise the human hematopoietic stem cell compartment.

Hematopoiesis requires tight regulation of the hematopoietic stem cell (HSC) population; however, the dynamics of HSC use at steady state are uncertain. Over 3-7 months, we evaluated the repopulation and self-renewal of more than 600 individual human 'severe combined immunodeficiency mouse-repopulating cells' (SRCs), tracked on the basis of lentiviral integration sites, in serially transplanted immune-deficient mice, as well as of SRC daughter cells that migrated to different marrow locations in a single mouse. Our data demonstrate maintenance by self-renewing SRCs after an initial period of clonal instability, a result inconsistent with the clonal succession model. We found wide variation in proliferation kinetics and self-renewal among SRCs, as well as between SRC daughter cells that repopulated equivalently, suggesting that SRC fate is unpredictable before SRCs enter more rigid 'downstream' developmental programs.

ADP-ribosyl Cyclase 1↗
PubMed2006

Targeting of CD44 eradicates human acute myeloid leukemic stem cells.

The long-term survival of patients with acute myeloid leukemia (AML) is dismally poor. A permanent cure of AML requires elimination of leukemic stem cells (LSCs), the only cell type capable of initiating and maintaining the leukemic clonal hierarchy. We report a therapeutic approach using an activating monoclonal antibody directed to the adhesion molecule CD44. In vivo administration of this antibody to nonobese diabetic-severe combined immune-deficient mice transplanted with human AML markedly reduced leukemic repopulation. Absence of leukemia in serially transplanted mice demonstrated that AML LSCs are directly targeted. Mechanisms underlying this eradication included interference with transport to stem cell-supportive microenvironmental niches and alteration of AML-LSC fate, identifying CD44 as a key regulator of AML LSCs. The finding that AML LSCs require interaction with a niche to maintain their stem cell properties provides a therapeutic strategy to eliminate quiescent AML LSCs and may be applicable to other types of cancer stem cells.

ADP-ribosyl Cyclase 1↗
PubMed2006

Low rhodamine 123 retention identifies long-term human hematopoietic stem cells within the Lin-CD34+CD38- population.

Progress to uncover the molecular and cellular regulators that govern human hematopoietic stem cell (HSC) fate has been impeded by an inability to obtain highly purified fractions of HSCs. We report that the rhodamine 123 (Rho 123) dye effluxing fraction of the Lin-CD34+CD38- population contains SCID-repopulating cells (SRCs) capable of long-term repopulation in primary nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Purification based on Rho uptake led to a 4-fold enrichment of SRCs in the Lin-CD34+CD38- fraction, with a frequency of 1 SRC in 30 Lin-CD34+CD38-Rholo cells. The Lin-CD34+CD38-Rholo fraction also possesses long-term self-renewal capacity as measured by serial transplantation totaling more than 20 weeks. We conclude that Rho dye efflux provides an additional means of purifying human HSCs in the quest to achieve homogeneous populations of primitive cells for both experimental and therapeutic applications.

ADP-ribosyl Cyclase 1↗
PubMed2005

Generation of hematopoietic repopulating cells from human embryonic stem cells independent of ectopic HOXB4 expression.

Despite the need for alternative sources of human hematopoietic stem cells (HSCs), the functional capacity of hematopoietic cells generated from human embryonic stem cells (hESCs) has yet to be evaluated and compared with adult sources. Here, we report that somatic and hESC-derived hematopoietic cells have similar phenotype and in vitro clonogenic progenitor activity. However, in contrast with somatic cells, hESC-derived hematopoietic cells failed to reconstitute intravenously transplanted recipient mice because of cellular aggregation causing fatal emboli formation. Direct femoral injection allowed recipient survival and resulted in multilineage hematopoietic repopulation, providing direct evidence of HSC function. However, hESC-derived HSCs had limited proliferative and migratory capacity compared with somatic HSCs that correlated with a distinct gene expression pattern of hESC-derived hematopoietic cells that included homeobox (HOX) A and B gene clusters. Ectopic expression of HOXB4 had no effect on repopulating capacity of hESC-derived cells. We suggest that limitations in the ability of hESC-derived HSCs to activate a molecular program similar to somatic HSCs may contribute to their atypical in vivo behavior. Our study demonstrates that HSCs can be derived from hESCs and provides an in vivo system and molecular foundation to evaluate strategies for the generation of clinically transplantable HSC from hESC lines.

Animals↗
PubMed2005

Human short-term repopulating stem cells are efficiently detected following intrafemoral transplantation into NOD/SCID recipients depleted of CD122+ cells.

The nonobese diabetic/severe combined immune deficiency (NOD/SCID) xenotransplantation model has emerged as a widely used assay for human hematopoietic stem cells; however, barriers still exist that limit engraftment. We previously identified a short-term SCID-repopulating cell (SRC) following direct intrafemoral injection into NOD/SCID mice, whereas others characterized similar SRCs using NOD/SCID mice depleted of natural killer (NK) cell activity. To determine the model that most efficiently detects short-term SRCs, we compared human engraftment in 6 different xenotransplantation models: NOD/SCID-beta2-microglobulin-null mice, anti-CD122 (interleukin-2 receptor beta [IL-2Rbeta])-treated or unmanipulated NOD/SCID mice, each given transplants by intravenous or intrafemoral injection. Human cell engraftment was highest in intrafemorally injected anti-CD122-treated NOD/SCID mice compared to all other groups at 2 and 6 weeks after transplantation. These modifications to the SRC assay provide improved detection of human stem cells and demonstrate that CD122+ cells provide barriers to stem cell engraftment, a finding with potential clinical relevance.

Animals↗
PubMed2005

Dynamic changes in cellular and microenvironmental composition can be controlled to elicit in vitro human hematopoietic stem cell expansion.

OBJECTIVE: The absence of effective strategies for the ex vivo expansion of human hematopoietic stem cells (HSCs) limits the development of many cell-based therapies. Prior attempts to stimulate HSC expansion have focused on media supplementation using cytokines and growth factors. In these cultures, cellular and microenvironmental compositions change with time. In this study, the impact of controlling these dynamic changes on HSC output is determined. MATERIALS AND METHODS: Cord blood-derived lin(-) cells were cultured for 8 days in serum-free medium supplemented with stem cell factor, Flt3 ligand, and thrombopoietin. Functional, phenotypic, and molecular (gene and protein) analyses were used to characterize dynamic changes in cellular and microenvironmental composition. The effects of these changes and the mechanism behind their effects on HSC expansion were assessed using a selection/media exchange-based global culture manipulation (GCM) technique. RESULTS: We show that the direct secretion of negative regulators by culture-generated lin(+) cells, and the indirect stimulation of cells to secrete negative regulators by culture-conditioned media, limits in vitro HSC generation. The GCM strategy was able to abrogate these effects to produce elevated numbers of LTC-ICs (14.6-fold relative to input), migrating rapid NOD/SCID repopulating cells (12.1-fold), and long-term NOD/SCID repopulating cells (5.2-fold). CONCLUSIONS: Cellular and microenvironmental changes that occur during all in vitro HSC cultures can significantly affect HSC output through the direct or indirect secretion of negative regulators. This study provides insight into the mechanisms regulating HSC fate in vitro and describes a novel methodology to regulate overall in vitro microenvironmental dynamics to enable the generation of clinically relevant numbers of HSCs.

Animals↗
PubMed2005

Cancer stem cells: lessons from leukemia.

A fundamental problem in cancer research is identification of the cell type capable of initiating and sustaining growth of the tumor--the cancer stem cell (CSC). While the existence of CSCs was first proposed over 40 years ago, only in the past decade have these cells been identified and characterized in hematological malignancies. Recent studies have now described CSCs in solid tumors of the breast and brain, raising the possibility that such cells are at the apex of all neoplastic systems. An appreciation of the biological distinctness of CSCs is crucial not only for the design of studies to understand how tumorigenic pathways operate but also for the development of specific therapies that effectively target these cells in patients.

Animals↗
PubMed2005

Acute myeloid leukemia stem cells.

A fundamental problem in cancer research is identification of the cells within a tumor that sustain the growth of the neoplastic clone. The concept that only a subpopulation of rare cancer stem cells (CSCs) is responsible for maintenance of the neoplasm emerged nearly 50 years ago; however, conclusive proof for the existence of a CSC was obtained only relatively recently. The evidence for the existence of CSCs was first derived from the study of human acute myeloid leukemia (AML), largely because of the availability of quantitative stem cell assays for the leukemic stem cell (LSC). These studies showed that only rare cells within the leukemic clone had the capacity to initiate AML growth after transplant into NOD/SCID mice, establishing the hierarchical organization of AML. Recent clonal-tracking studies showed that the LSC compartment is composed of different classes of LSCs, which can be distinguished on the basis of self-renewal potential. These findings have important implications for our understanding of the leukemogenic process as well as the design of more effective therapies to eliminate AML based on eradication of the LSCs. These studies are briefly reviewed here.

Animals↗
PubMed2005

Biology of normal and acute myeloid leukemia stem cells.

The substantial understanding that has been gained over the past 5 decades of the biology of blood formation is largely due to the development of functional quantitative assays for cells at all stages of differentiation, from multipotential stem cells to mature cells. The majority of studies have involved the mouse because the ease with which repopulation studies can be carried out with this animal model allows the assay of complete lineage development from stem cells. In the past decade, advances in repopulation assays for human stem cells using xenotransplantation have greatly enhanced our understanding of human stem cell biology. Importantly, the xenotransplantation methodology has also been used to identify the cancer stem cell that initiates and sustains leukemic proliferation, providing key evidence for the cancer stem cell hypothesis. This hypothesis argues that cancer cells are functionally heterogeneous and hierarchically organized such that only specific cells are capable of sustaining tumor growth and continuously producing the cells that make up the bulk of the tumor. Recent studies have also brought into focus the importance of the intimate relationship between the stem cell (normal or leukemic) and its microenvironment. Coming into view are the molecular players involved in stem cell homing, migration, and adhesion, as well as the cellular components of the microenvironmental niche. Here we review recent studies that have begun, to elucidate the interplay between normal and leukemic human stem cells and their microenvironment.

Animals↗
PubMed2004

Concepts of human leukemic development.

Two fundamental problems in cancer research are identification of the normal cell within which cancer initiates and identification of the cell type capable of sustaining the growth of the neoplastic clone. There is overwhelming evidence that virtually all cancers are clonal and represent the progeny of a single cell. What is less clear for most cancers is which cells within the tumor clone possess tumorigenic or 'cancer stem cell' (CSC) properties and are capable of maintaining tumor growth. The concept that only a subpopulation of rare CSC is responsible for maintenance of the neoplasm emerged nearly 50 years ago. Testing of this hypothesis is most advanced for the hematopoietic system due to the establishment of functional in vitro and in vivo assays for stem and progenitor cells at all stages of development. This body of work led to conclusive proof for CSC with the identification and purification of leukemic stem cells capable of repopulating NOD/SCID mice. This review will focus on the historical development of the CSC hypothesis, the mechanisms necessary to subvert normal developmental programs, and the identification of the cell in which these leukemogenic events first occur.

Acute Disease↗
PubMed2004

Acute myeloid leukemia originates from a hierarchy of leukemic stem cell classes that differ in self-renewal capacity.

Emerging evidence suggests cancer stem cells sustain neoplasms; however, little is understood of the normal cell initially targeted and the resultant cancer stem cells. We show here, by tracking individual human leukemia stem cells (LSCs) in nonobese diabetic-severe combined immunodeficiency mice serially transplanted with acute myeloid leukemia cells, that LSCs are not functionally homogeneous but, like the normal hematopoietic stem cell (HSC) compartment, comprise distinct hierarchically arranged LSC classes. Distinct LSC fates derived from heterogeneous self-renewal potential. Some LSCs emerged only in recipients of serial transplantation, indicating they divided rarely and underwent self-renewal rather than commitment after cell division within primary recipients. Heterogeneity in LSC self-renewal potential supports the hypothesis that they derive from normal HSCs. Furthermore, normal developmental processes are not completely abolished during leukemogenesis. The existence of multiple stem cell classes shows the need for LSC-targeted therapies.

Animals↗
PubMed2004

Hematopoietic cell fate and the initiation of leukemic properties in primitive primary human cells are influenced by Ras activity and farnesyltransferase inhibition.

The Ras pathway transduces divergent signals determining normal cell fate and is frequently activated in hematopoietic malignancies, but the manner in which activation contributes to human leukemia is poorly understood. We report that a high level of activated H-Ras signaling in transduced primary human hematopoietic progenitors reduced their proliferation and enhanced monocyte/macrophage differentiation. However, the exposure of these cells to a farnesyltransferase inhibitor and establishment of a moderate level of Ras activity showed increased proliferation, an elevated frequency of primitive blast-like cells, and progenitors with enhanced self-renewal capacity. These results suggest that the amplitude of Ras pathway signaling is a determinant of myeloid cell fate and that moderate Ras activation in primitive hematopoietic cells can be an early event in leukemogenesis.

Alkyl and Aryl Transferases↗
PubMed2003

Lentivector-mediated clonal tracking reveals intrinsic heterogeneity in the human hematopoietic stem cell compartment and culture-induced stem cell impairment.

Knowledge of the composition and interrelationship of the various hematopoietic stem cells (HSCs) that comprise the human HSC pool and the consequence of culture on each class is required for effective therapies based on stem cells. Clonal tracking of retrovirally transduced HSCs in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice revealed heterogeneity in the repopulation capacity of SCID-repopulating cells (SRCs). However, it is impossible to establish whether HSC heterogeneity is intrinsic or whether the culture conditions required for retroviral transduction induce qualitative and quantitative alterations to SRCs. Here, we report establishment of a clonal tracking method that uses lentivectors to transduce HSCs with minimal manipulation during overnight culture without cytokine stimulation. By serial bone marrow (BM) sampling of mice receiving transplants, short-term SRCs (ST-SRCs) and long-term SRCs (LT-SRCs) were identified on the basis of repopulation dynamics demonstrating that their existence is not an experimental artifact but reflects the state of the HSC pool. However, 4 days of culture in conditions previously used for SRC retroviral transduction significantly reduced SRC number as assessed by clonal analysis. These studies provide a foundation to understand the molecular and cellular determinants of human HSC development and to develop therapies targeted to specific HSC classes.

Animals↗