Biomedical subjects

Bianca Blom

Publications and source records attributed to Bianca Blom.

12 recordsLinked to original sources

PubMed2006

Stimulated plasmacytoid dendritic cells impair human T-cell development.

Thymic plasmacytoid dendritic cells (pDCs) are located predominantly in the medulla and at the corticomedullary junction, the entry site of bone marrow-derived multipotential precursor cells into the thymus, allowing for interactions between thymic pDCs and precursor cells. We demonstrate that in vitro-generated pDCs stimulated with CpG or virus impaired the development of human autologous CD34(+)CD1a(-) thymic progenitor cells into the T-cell lineage. Rescue by addition of neutralizing type I interferon (IFN) antibodies strongly implies that endogenously produced IFN-alpha/beta is responsible for this inhibitory effect. Consistent with this notion, we show that exogenously added IFN-alpha had a similar impact on IL-7- and Notch ligand-induced development of thymic CD34(+)CD1a(-) progenitor cells into T cells, because induction of CD1a, CD4, CD8, and TCR/CD3 surface expression and rearrangements of TCRbeta V-DJ gene segments were severely impaired. In addition, IL-7-induced proliferation but not survival of the developing thymic progenitor cells was strongly inhibited by IFN-alpha. It is evident from our data that IFN-alpha inhibits the IL-7R signal transduction pathway, although this could not be attributed to interference with either IL-7R proximal (STAT5, Akt/PKB, Erk1/2) or distal (p27(kip1), pRb) events.

Animals↗

PubMed2006

Immunological and antitumor effects of IL-23 as a cancer vaccine adjuvant.

The promising, but modest, clinical results of many human cancer vaccines indicate a need for vaccine adjuvants that can increase both the quantity and the quality of vaccine-induced, tumor-specific T cells. In this study we tested the immunological and antitumor effects of the proinflammatory cytokine, IL-23, in gp100 peptide vaccine therapy of established murine melanoma. Neither systemic nor local IL-23 alone had any impact on tumor growth or tumor-specific T cell numbers. Upon specific vaccination, however, systemic IL-23 greatly increased the relative and absolute numbers of vaccine-induced CD8(+) T cells and enhanced their effector function at the tumor site. Although IL-23 specifically increased IFN-gamma production by tumor-specific T cells, IFN-gamma itself was not a primary mediator of the vaccine adjuvant effect. The IL-23-induced antitumor effect and accompanying reversible weight loss were both partially mediated by TNF-alpha. In contrast, local expression of IL-23 at the tumor site maintained antitumor activity in the absence of weight loss. Under these conditions, it was also clear that enhanced effector function of vaccine-induced CD8(+) T cells, rather than increased T cell number, is a primary mechanism underlying the antitumor effect of IL-23. Collectively, these results suggest that IL-23 is a potent vaccine adjuvant for the induction of therapeutic, tumor-specific CD8(+) T cell responses.

Adjuvants, Immunologic↗

PubMed2006

Development of human lymphoid cells.

The lymphocytes, T, B, and NK cells, and a proportion of dendritic cells (DCs) have a common developmental origin. Lymphocytes develop from hematopoietic stem cells via common lymphocyte and various lineage-restricted precursors. This review discusses the current knowledge of human lymphocyte development and the phenotypes and functions of the rare intermediate populations that together form the pathways of development into T, B, and NK cells and DCs. Clearly, development of hematopoietic cells is supported by cytokines. The studies of patients with genetic deficiencies in cytokine receptors that are discussed here have illuminated the importance of cytokines in lymphoid development. Lineage decisions are under control of transcription factors, and studies performed in the past decade have provided insight into transcriptional control of human lymphoid development, the results of which are summarized and discussed in this review.

B-Lymphocytes↗

PubMed2005

Delta-like1-induced Notch1 signaling regulates the human plasmacytoid dendritic cell versus T-cell lineage decision through control of GATA-3 and Spi-B.

Human early thymic precursors have the potential to differentiate into multiple cell lineages, including T cells and plasmacytoid dendritic cells (pDCs). This decision is guided by the induction or silencing of lineage-specific transcription factors. The ETS family member Spi-B is a key regulator of pDC development, whereas T-cell development is critically dependent on GATA-3. Here we show that triggering of the Notch1 signaling pathway by Delta-like1 controls the T/pDC lineage decision by regulating the balance between these factors. CD34+ CD1a- thymic progenitor cells express Notch1, but down-regulate this receptor when differentiating into pDCs. On coculture with stromal cell lines expressing either human Delta-like1 (DL1) or Jagged1 (Jag1) Notch ligands, thymic precursors express GATA-3 and develop into CD4+ CD8+ TCRalphabeta+ T cells. On the other hand, DL1, but not Jag1, down-regulates Spi-B expression, resulting in impaired development of pDCs. The Notch1-induced block in pDC development can be relieved through the ectopic expression of Spi-B. These data indicate that DL1-induced activation of the Notch1 pathway controls the lineage commitment of early thymic precursors by altering the levels between Spi-B and GATA-3.

Antigens, CD34↗

PubMed2005

STAT5 regulates the self-renewal capacity and differentiation of human memory B cells and controls Bcl-6 expression.

It is unknown how B cells that mature during a germinal center reaction 'decide' between plasma or memory cell fate. Here we describe a previously unknown subpopulation of B cells in the human germinal center that is characterized by tyrosine phosphorylated transcriptional activator STAT5. These cells had an activated centrocyte phenotype and had abundant expression of BCL6 but low expression of PRDM1, both encoding transcriptional repression proteins. Using RNA interference and ectopic expression of constitutively activated forms of STAT5, we demonstrate here a function for STAT5 in the self-renewal of B cells in vitro. STAT5b isoform seemed to directly upregulate Bcl-6, and ectopic expression of Bcl-6 in B cells resulted in self-renewal and inhibition of plasma cell differentiation. These data indicate that activation of STAT5 is involved in regulation of memory B cell differentiation.

B-Lymphocytes↗

PubMed2005

Development and activation of regulatory T cells in the human fetus.

There is an increasing amount of knowledge on the functional properties of regulatory T cells (Treg) in the adult immune system, but data on the generation and function of these cells during human embryonic development are scarce. In this study, we show that in the fetal thymus, double-positive cells initiate expression of CD25, GITR, CTLA4 and CD122 during their transition from the CD27- to the CD27+ stage. Moreover, CD4+CD25+ fetal thymocytes already have the potential to suppress proliferation of CD25- cells. After leaving the thymus, FoxP3+CD4+CD25+ Treg enter the fetal lymph nodes and spleen, where they acquire a primed/memory phenotype. A model is proposed for the development of human fetal Treg that encompasses two sequential maturation steps: initiation of a regulatory phenotype and suppressive activity in the thymus; and subsequent activation within the peripheral lymphoid organs. Upon activation, FoxP3+CD4+CD25+ Treg suppress potentially deleterious responses by autoreactive lymphocytes and maintain homeostasis within the developing fetus.

CD4-Positive T-Lymphocytes↗

PubMed2004

Endogenous IFN-alpha production by plasmacytoid dendritic cells exerts an antiviral effect on thymic HIV-1 infection.

Plasmacytoid dendritic cells (pDC) are the principal producers of IFN-alpha in response to viral infection. Because pDC are present in the thymus, we investigated the consequences of HIV-1-induced IFN-alpha production by thymic pDC. We observed that thymic pDC as well as thymocytes express intracellular IFN-alpha upon infection with HIV-1. However, only the pDC could suppress HIV-1 replication, because depletion of pDC resulted in enhancement of HIV-1 replication in thymocytes. Thymic pDC could also produce IFN-alpha in response to CpG oligonucleotides, consistent with the observations of others that peripheral pDC produce IFN-alpha upon engagement of TLR-9. Importantly, CpG considerably increased IFN-alpha production induced by HIV-1, and addition of CpG during HIV-1 infection enhanced expression of the IFN response protein MxA in thymocytes and strongly reduced HIV-replication. Our data indicate that thymic pDC modulate HIV-1 replication through secretion of IFN-alpha. The degree of inhibition depends on the level of IFN-alpha produced by the thymic pDC.

Animals↗

PubMed2004

The ETS transcription factor Spi-B is required for human plasmacytoid dendritic cell development.

A number of transcription factors that act as molecular switches for hematopoietic lineage decisions have been identified. We recently described the ETS transcription factor Spi-B to be exclusively expressed in plasmacytoid dendritic cells (pDCs), but not in myeloid DCs. To assess whether Spi-B is required for pDC development we used an RNA interference knock down approach to specifically silence Spi-B protein synthesis in CD34(+) precursor cells. We observed that a knock down of Spi-B mRNA strongly inhibited the ability of CD34(+) precursor cells to develop into pDCs in both in vitro assays as well as in vivo upon injection into recombination activating gene 2(-/-) gamma common(-/-) mice. The observed effects were restricted to the pDC lineage as the differentiation of pro-B cells and CD14(+) myeloid cells was not inhibited but slightly elevated by Spi-B knock down. Knock down of the related ETS factor PU.1 also inhibited in vitro development of CD34(+) cells into pDCs. However, in contrast to Spi-B, PU.1 knock down inhibited B cell and myeloid cell development as well. These results identify Spi-B as a key regulator of human pDC development.

Antigens, CD34↗

PubMed2004

Monitoring the effect of gene silencing by RNA interference in human CD34+ cells injected into newborn RAG2-/- gammac-/- mice: functional inactivation of p53 in developing T cells.

Tumor suppressor p53 plays an important role in regulating cell cycle progression and apoptosis. Here we applied RNA interference to study the role of p53 in human hematopoietic development in vivo. An siRNA construct specifically targeting the human tumor-suppressor gene p53 was introduced into human CD34(+) progenitor cells by lentivirus-mediated gene transfer, which resulted in more than 95% knockdown of p53. We adapted the human-SCID mouse model to optimize the development of hematopoietic cells, particularly of T cells. This was achieved by the intraperitoneal injection of CD34(+) precursor cells into newborn Rag2(-/-) gammac(-/-) mice that lack T, B, and NK cells. Robust development of T cells was observed in these mice, with peripheral T-cell repopulation 8 weeks after injection of the precursor cells. Other lymphocyte and myeloid subsets also developed in these mice. Injecting p53 siRNA-transduced CD34(+) cells resulted in stable expression and down-modulation of p53 in the mature T-cell offspring. Inactivating p53 did not affect the development of CD34(+) cells into various mature leukocyte subsets, including T cells, but it conferred resistance to gamma-irradiation and other p53-dependent apoptotic stimuli to the T cells.

Animals↗

PubMed2003

Thrombopoietin cooperates with FLT3-ligand in the generation of plasmacytoid dendritic cell precursors from human hematopoietic progenitors.

Type 1 interferon-producing cells (IPCs), also known as plasmacytoid dendritic cell (DC) precursors, represent the key effectors in antiviral innate immunity and triggers for adaptive immune responses. IPCs play important roles in the pathogenesis of systemic lupus erythematosus (SLE) and in modulating immune responses after hematopoietic stem cell transplantation. Understanding IPC development from hematopoietic progenitor cells (HPCs) may provide critical information in controlling viral infection, autoimmune SLE, and graft-versus-host disease. FLT3-ligand (FLT3-L) represents a key IPC differentiation factor from HPCs. Although hematopoietic cytokines such as interleukin-3 (IL-3), IL-7, stem cell factor (SCF), macrophage-colony-stimulating factor (M-CSF), and granulocyte M-CSF (GM-CSF) promote the expansion of CD34+ HPCs in FLT3-L culture, they strongly inhibit HPC differentiation into IPCs. Here we show that thrombopoietin (TPO) cooperates with FLT3-L, inducing CD34+ HPCs to undergo a 400-fold expansion in cell numbers and to generate more than 6 x 10(6) IPCs per 10(6) CD34+ HPCs within 30 days in culture. IPCs derived from HPCs in FLT3-L/TPO cultures display blood IPC phenotype and have the capacity to produce large amounts of interferon-alpha (IFN-alpha) and to differentiate into mature DCs. This culture system, combined with the use of adult peripheral blood CD34+ HPCs purified from G-CSF-mobilized donors, permits the generation of more than 10(9) IPCs from a single blood donor.

Antigens, CD↗

PubMed2002

Intrathymic and extrathymic development of human plasmacytoid dendritic cell precursors in vivo.

The development of plasmacytoid dendritic cells (pDC2) from human CD34(+) stem cells in vivo was studied in RAG-2(-/-) interleukin (IL)-2Rgamma(-/-) mice that lack functional T and B cells and natural killer cells. CD34(+) cells isolated from fetal liver or thymus were labeled with 5- and 6-carboxyfluorescein diacetate succinimidyl ester (CFSE) and were injected into a human thymus grafted subcutaneously in the RAG-2(-/-) IL-2Rgamma(-/-) mice. One to 4 weeks later the CFSE label was found not only in T cells but also in CD123(+/high) CD4(+)CD45RA(+) pDC2, indicating that the CD34(+) cells can develop into pDC2 within a thymus. In addition to pDC2, CFSE-labeled dendritic cells with a mature phenotype, determined by the cell surface markers CD11c, CD83, and CD80, were found in the injected human thymus graft. pDC2 was not found in the periphery of mice carrying a human thymic graft, indicating that the intrathymic pDC2 failed to emigrate from the thymus. We also demonstrate that pDC2 can develop outside the thymus because relatively high percentages of pDC2 were found in the periphery after the intravenous injection of CD34(+)CD38(-) fetal liver cells in RAG-2(-/-) IL-2Rgamma(-/-) mice without a human thymus graft. These data indicate that the thymus and the peripheral pDC2 develop independently of each other.

Animals↗

PubMed2002

Developmental origin of pre-DC2.

It is generally accepted that dendritic cells can be generated from either myeloid or lymphoid derived progenitors. Ample information has been collected on the development and nature of myeloid DC type 1 (DC1). In contrast, our current understanding on the origin and function of the lymphoid derived DC type 2 (DC2) is still limited but is increasing rapidly. Here we will summarize recent findings on the developmental origin of the precursor of DC2 (pre-DC2). The presence of pre-DC2 has been revealed in bone marrow, fetal liver, and cord blood, where they develop from hematopoietic stem cells (HSC) most likely via an intermediate pro-DC2 stage. Both in human and mouse, development of pre-DC2 depends on the cytokine FLT3-ligand (FLT3-L). In addition, transcription factors such as Spi-B and members of the basic helix-loop helix (bHLH) family have been shown to be involved in the proper differentiation of HSC into pre-DC2. The human thymus contains a population of cells that closely resembles the peripheral pre-DC2, including interferon (INF)-a production after viral stimulation. Some phenotypic differences have been observed however. Furthermore, we have shown that the thymic microenvironment is able to support development of pre-DC2 from HSC in vivo. A thymus independent pathway of pre-DC2 development exists as well, although at present it is not clear where these extrathymic pre-DC2 are generated. In regard of the absence of a phenotypic defined pro-DC2 population in the thymus, we speculate that development of thymic pre-DC2 may differ from peripheral pre-DC2. The challenge of the near future will be to determine the role of pre-DC2 during thymic T cell development.

Animals↗