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Biomedical subjects

I L Weissman

Publications and source records attributed to I L Weissman.

At least 37 records · Page 2Linked to original sources
PubMed2001

BCL-2 cooperates with promyelocytic leukemia retinoic acid receptor alpha chimeric protein (PMLRARalpha) to block neutrophil differentiation and initiate acute leukemia.

The promyelocytic leukemia retinoic acid receptor alpha (PMLRARalpha) chimeric protein is associated with acute promyelocytic leukemia (APL). PMLRARalpha transgenic mice develop leukemia only after several months, suggesting that PMLRARalpha does not by itself confer a fully malignant phenotype. Suppression of apoptosis can have a central role in tumorigenesis; therefore, we assessed whether BCL-2 influenced the ability of PMLRARalpha to initiate leukemia. Evaluation of preleukemic animals showed that whereas PMLRARalpha alone modestly altered neutrophil maturation, the combination of PMLRARalpha and BCL-2 caused a marked accumulation of immature myeloid cells in bone marrow. Leukemias developed more rapidly in mice coexpressing PMLRARalpha and BCL-2 than in mice expressing PMLRARalpha alone, and all mice expressing both transgenes succumbed to leukemia by 7 mo. Although both preleukemic, doubly transgenic mice and leukemic animals had abundant promyelocytes in the bone marrow, only leukemic mice exhibited thrombocytopenia and dissemination of immature cells. Recurrent gain of chromosomes 7, 8, 10, and 15 and recurrent loss of chromosome 2 were identified in the leukemias. These chromosomal changes may be responsible for the suppression of normal hematopoiesis and dissemination characteristic of the acute leukemias. Our results indicate that genetic changes that inhibit apoptosis can cooperate with PMLRARalpha to initiate APL.

Animals↗
PubMed2001

Molecular cloning and characterization of a novel regulator of G-protein signaling from mouse hematopoietic stem cells.

A novel regulator of G-protein signaling (RGS) has been isolated from a highly purified population of mouse long-term hematopoietic stem cells, and designated RGS18. It has 234 amino acids consisting of a central RGS box and short divergent NH(2) and COOH termini. The calculated molecular weight of RGS18 is 27,610 and the isoelectric point is 8.63. Mouse RGS18 is expressed from a single gene and shows tissue specific distribution. It is most highly expressed in bone marrow followed by fetal liver, spleen, and then lung. In bone marrow, RGS18 level is highest in long-term and short-term hematopoietic stem cells, and is decreased as they differentiate into more committed multiple progenitors. The human RGS18 ortholog has a tissue-specific expression pattern similar to that of mouse RGS18. Purified RGS18 interacts with the alpha subunit of both G(i) and G(q) subfamilies. The results of in vitro GTPase single-turnover assays using Galpha(i) indicated that RGS18 accelerates the intrinsic GTPase activity of Galpha(i). Transient overexpression of RGS18 attenuated inositol phosphates production via angiotensin receptor and transcriptional activation through cAMP-responsive element via M1 muscarinic receptor. This suggests RGS18 can act on G(q)-mediated signaling pathways in vivo.

Amino Acid Sequence↗
PubMed2001

A genetic analysis of neural progenitor differentiation.

Genetic mechanisms regulating CNS progenitor function and differentiation are not well understood. We have used microarrays derived from a representational difference analysis (RDA) subtraction in a heterogeneous stem cell culture system to systematically study the gene expression patterns of CNS progenitors. This analysis identified both known and novel genes enriched in progenitor cultures. In situ hybridization in a subset of clones demonstrated that many of these genes were expressed preferentially in germinal zones, some showing distinct ventricular or subventricular zone labeling. Several genes were also enriched in hematopoietic stem cells, suggesting an overlap of gene expression in neural and hematopoietic progenitors. This combination of methods demonstrates the power of using custom microarrays derived from RDA-subtracted libraries for both gene discovery and gene expression analysis in the central nervous system.

Animals↗
PubMed2001

Immunity to infections following hematopoietic cell transplantation.

Hematopoietic cell transplantation has progressed from the use of unpurified bone marrow cells or mobilized peripheral blood cells to the use of purified stem cells and progenitor cells. These kinds of transplants can be designed to provide not only hematopoietic rescue but also augmented innate and acquired immunity.

Animals↗
PubMed2001

Lymphocyte development from hematopoietic stem cells.

The recent application of new techniques, such as multi-color cell sorting and the production of transgenic and gene-knockout mice, has contributed to a better understanding of lymphocyte development from hematopoietic stem cells. Now that we can purify progenitors at different maturational stages during lymphocyte development, the challenge is to understand the processes that govern each developmental stage transition.

Animals↗
PubMed2001

Dendritic cell development from common myeloid progenitors.

Dendritic cells (DCs) are professional antigen-presenting cells which both initiate adaptive immune responses and control tolerance to self-antigens. It has been suggested that these different effects on responder cells depend on subsets of DCs arising from either myeloid or lymphoid hematopoietic origins. In this model, CD8 alpha+ Mac-1- DCs are supposed to be of lymphoid while CD8 alpha- Mac-1+ DCs are supposed to be of myeloid origin. Here we summarize our findings that both CD8 alpha+ and CD8 alpha- DCs can arise from clonogenic common myeloid progenitors (CMPs) in both thymus and spleen. Therefore CD8 alpha expression DCs does not indicate a lymphoid origin and differences among CD8 alpha+ and CD8 alpha- DCs might rather reflect maturation status than ontogeny. On the basis of transplantation studies, it seems likely that most of the DCs in secondary lymphoid organs and a substantial fraction of thymic DCs are myeloid-derived.

Animals↗
PubMed2001

Stem and progenitor cells: origins, phenotypes, lineage commitments, and transdifferentiations.

Multipotent stem cells are clonal cells that self-renew as well as differentiate to regenerate adult tissues. Whereas stem cells and their fates are known by unique genetic marker studies, the fate and function of these cells are best studied by their prospective isolation. This review is about the properties of various highly purified tissue-specific multipotent stem cells and purified oligolineage progenitors. We contend that unless the stem or progenitor cells in question have been purified to near homogeneity, one cannot know whether their generation of expected (or unexpected) progeny is a property of a known cell type. It is interesting that in the hematopoietic system the only long-term self-renewing cells in the stem and progenitors pool are the hematopoietic stem cells. This fact is discussed in the context of normal and leukemic hematopoiesis.

Animals↗
PubMed2000

Direct isolation of human central nervous system stem cells.

Stem cells, which are clonogenic cells with self-renewal and multilineage differentiation properties, have the potential to replace or repair damaged tissue. We have directly isolated clonogenic human central nervous system stem cells (hCNS-SC) from fresh human fetal brain tissue, using antibodies to cell surface markers and fluorescence-activated cell sorting. These hCNS-SC are phenotypically 5F3 (CD133)(+), 5E12(+), CD34(-), CD45(-), and CD24(-/lo). Single CD133(+) CD34(-) CD45(-) sorted cells initiated neurosphere cultures, and the progeny of clonogenic cells could differentiate into both neurons and glial cells. Single cells from neurosphere cultures initiated from CD133(+) CD34(-) CD45(-) cells were again replated as single cells and were able to reestablish neurosphere cultures, demonstrating the self-renewal potential of this highly enriched population. Upon transplantation into brains of immunodeficient neonatal mice, the sorted/expanded hCNS-SC showed potent engraftment, proliferation, migration, and neural differentiation.

Animals↗
PubMed2000

Hematopoietic stem cells need two signals to prevent apoptosis; BCL-2 can provide one of these, Kitl/c-Kit signaling the other.

Growth factors can cause cells to proliferate, differentiate, survive, or die. Distinguishing between these responses is difficult in multicellular, multiparameter systems. Yet this is essential to understand the impact on cells like hematopoietic stem cells (HSCs), which have strict and still poorly understood growth factor requirements. Single cell plating in serum-free medium allows direct assessment of growth factor responses. The range of tested factors can be expanded if the cells are protected from growth factor deprivation-induced apoptosis. BCL-2 is overexpressed in HSCs of H2K-BCL-2 transgenic mice, protecting them from many apoptotic stimuli. The response of single wild-type and transgenic HSCs to stimulations with individual factors was tested. Surprisingly, we find that high level BCL-2 expression does not prevent rapid death under serum-free conditions, even though it does in the presence of serum. We also find that transgenic, but not wild-type cells, survive and proliferate rapidly in response to steel factor (Kit ligand). These studies show that two separate signals are necessary to prevent apoptosis in HSCs, and that Kit ligand by itself provides a strong proliferative stimulus to HSCs. However, the proliferative response does not result in self-renewal, but in differentiation to all known hematopoietic oligolineage progenitors.

Animals↗
PubMed2000

Development of CD8alpha-positive dendritic cells from a common myeloid progenitor.

Dendritic cells (DCs) are critical in both initiating adaptive immune responses and maintaining tolerance to self antigens. These apparently contradictory roles have been suggested to depend on different subsets of DCs that arise from either myeloid or lymphoid hematopoietic origins, respectively. Although DC expression of CD8alpha is attributed to a lymphoid origin, here we show that both CD8alpha+ and CD8alpha- DCs can arise from clonogenic common myeloid progenitors in both thymus and spleen. Thus, expression of CD8alpha is not indicative of a lymphoid origin, and phenotypic and functional differences among DC subsets are likely to reflect maturation status rather than ontogeny.

Animals↗
PubMed2000

Cell-fate conversion of lymphoid-committed progenitors by instructive actions of cytokines.

The primary role of cytokines in haemato-lymphopoiesis is thought to be the regulation of cell growth and survival. But the instructive action of cytokines in haematopoiesis has not been well addressed. Here we show that a clonogenic common lymphoid progenitor, a bone marrow-resident cell that gives rise exclusively to lymphocytes (T, B and natural killer cells), can be redirected to the myeloid lineage by stimulation through exogenously expressed interleukin (IL)-2 and GM-CSF (granulocyte/macrophage colony-stimulating factor) receptors. Analysis of mutants of the beta-chain of the IL-2 receptor revealed that the granulocyte- and monocyte-differentiation signals are triggered by different cytoplasmic domains, showing that the signalling pathway(s) responsible for these unique developmental outcomes are separable. Finally, we show that the endogenous myelomonocytic cytokine receptors for GM-CSF and macrophage colony-stimulating factor (M-CSF) are expressed at low to moderate levels on the more primitive haematopoietic stem cells, are absent on common lymphoid progenitors, and are upregulated after myeloid lineage induction by IL-2. We conclude that cytokine signalling can regulate cell-fate decisions and propose that a critical step in lymphoid commitment is downregulation of cytokine receptors that drive myeloid cell development.

Animals↗
PubMed2000

Purified hematopoietic stem cell grafts induce tolerance to alloantigens and can mediate positive and negative T cell selection.

Engraftment of allogeneic bone marrow (BM) has been shown to induce tolerance to organs genotypically matched with the BM donor. Immune reconstitution after BM transplantation therefore involves re-establishment of a T cell pool tolerant to antigens present on both donor and host tissues. However, how hematopoietic grafts exert their influence over the regenerating immune system is not completely understood. Prior studies suggest that education of the newly arising T cell pool involves distinct contributions from donor and host stromal elements. Specifically, negative selection is thought to be mediated primarily by donor BM-derived antigen-presenting cells, whereas positive selection is dictated by radio-resistant host-derived thymic stromal cells. In this report we studied the effect of highly purified allogeneic hematopoietic stem cells (HSCs) on organ transplantation tolerance induction and immune reconstitution. In contrast to engraftment of BM that results in near-complete donor T cell chimerism, HSC engraftment results in mixed T cell chimerism. Nonetheless we observed that HSC grafts induce tolerance to donor-matched neonatal heart grafts, and one way the HSC grafts alter host immune responses is via deletion of newly arising donor as well as radiation-resistant host T cells. Furthermore, using an in vivo assay of graft rejection to study positive selection we made the unexpected observation that T cells in chimeric mice rejected grafts only in the context of the donor MHC type. These latter findings conflict with the conventionally held view that radio-resistant host elements primarily dictate positive selection.

Animals↗
PubMed2000

Inactivation of a GFP retrovirus occurs at multiple levels in long-term repopulating stem cells and their differentiated progeny.

Hematopoietic stem cell gene therapy holds promise for the treatment of many hematologic disorders. One major variable that has limited the overall success of gene therapy to date is the lack of sustained gene expression from viral vectors in transduced stem cell populations. To understand the basis for reduced gene expression at a single-cell level, we have used a murine retroviral vector, MFG, that expresses the green fluorescent protein (GFP) to transduce purified populations of long-term self-renewing hematopoietic stem cells (LT-HSC) isolated using the fluorescence-activated cell sorter. Limiting dilution reconstitution of lethally irradiated recipient mice with 100% transduced, GFP(+) LT-HSC showed that silencing of gene expression occurred rapidly in most integration events at the LT-HSC level, irrespective of the initial levels of GFP expression. When inactivation occurred at the LT-HSC level, there was no GFP expression in any hematopoietic lineage clonally derived from silenced LT-HSC. Inactivation downstream of LT-HSC that stably expressed GFP( )in long-term reconstituted animals was restricted primarily to lymphoid cells. These observations suggest at least 2 distinct mechanisms of silencing retrovirally expressed genes in hematopoietic cells.

Animals↗
PubMed2000

AML1/ETO-expressing nonleukemic stem cells in acute myelogenous leukemia with 8;21 chromosomal translocation.

Leukemia-specific AML1/ETO transcripts are detectable in most patients with t(8;21) acute myelogenous leukemia (AML) in long-term remission. To understand the inconsistency between the clinical cure and the presence of "residual disease" at a molecular level, we separated and identified the cells expressing AML1/ETO by phenotype and function. Here we demonstrate that AML1/ETO transcripts are present in a fraction of stem cells, monocytes, and B cells in remission marrow, and in a fraction of B cells in leukemic marrow, but not in T cells. AML1/ETO transcripts also were demonstrated in a fraction of colony-forming cells of erythroid, granulocyte-macrophage, and/or megakaryocyte lineages in both leukemic and remission marrow. These data strongly suggest that the acquisition of the t(8;21) occurs at the level of stem cells capable of differentiating into B cells as well as all myeloid lineages, and that a fraction of the AML1/ETO-expressing stem cells undergo additional oncogenic event(s) that ultimately leads to transformation into AML.

Adult↗
PubMed2000

B lymphopoiesis in the thymus.

The thymus has been regarded as the major site of T cell differentiation. We find that in addition to alphabeta and gammadelta T cells, a significant number (approximately 3 x 104 per day) of B220+IgM+ mature B cells are exported from the thymus of C57BL/6 mice. Of these emigrating B cells, we estimate that at least approximately 2 x 104 per day are cells which developed intrathymically, whereas a maximum of approximately 0.8 x 104 per day are cells which circulated through the thymus from the periphery. The thymus possesses a significant number of pro-B and pre-B cells that express CD19, VpreB, lambda5, and pax-5. These B cell progenitors were found in the thymic cortex, whereas increasingly mature B cells were found in the corticomedullar and medullary regions. Other lymphoid cells, including NK cells and lymphoid dendritic cells, are not exported from the thymus at detectable levels. Thus, the thymus contributes to the formation of peripheral pools of B cells as well as of alphabeta and gammadelta T cells.

Animals↗