Biomedical subjects

Hergen Spits

Publications and source records attributed to Hergen Spits.

25 records · Page 2Linked to original sources

PubMed2003

Ectopic hTERT expression extends the life span of human CD4+ helper and regulatory T-cell clones and confers resistance to oxidative stress-induced apoptosis.

Human somatic cells have a limited life span in vitro. Upon aging and with each cell division, shortening of telomeres occurs, which eventually will lead to cell cycle arrest. Ectopic hTERT expression has been shown to extend the life span of human T cells by preventing this telomere erosion. In the present study, we have shown that ectopic hTERT expression extends the life span of CD4+ T helper type 1 or 2 and regulatory T-cell clones and affected neither the in vitro cytokine production profile nor their specificity for antigen. In mixed cell cultures, ectopic hTERT-expressing clones were found to expand in greater numbers than untransduced cells of the same replicative age. This ectopic hTERT-induced growth advantage was not due to an enhanced cell division rate or number of divisions following T-cell receptor-mediated activation, as determined in carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeling experiments. Moreover, the susceptibility to activation-induced cell death of both cell types was similar. However, cultures of resting hTERT-transduced T cells contained higher frequencies of Bcl-2-expressing cells and lower active caspase-3-expressing cells, compared with wild-type cells. Furthermore, hTERT-transduced cells were more resistant to oxidative stress, which causes preferential DNA damage in telomeres. Taken together, these results show that ectopic hTERT expression not only protects proliferating T cells from replicative senescence but also confers resistance to apoptosis induced by oxidative stress.

Apoptosis↗

PubMed2002

The transcription factor Spi-B is expressed in plasmacytoid DC precursors and inhibits T-, B-, and NK-cell development.

Human plasmacytoid dendritic cells (pDCs), also called type 2 dendritic cell precursors or natural interferon (IFN)-producing cells, represent a cell type with distinctive phenotypic and functional features. They are present in the thymus and probably share a common precursor with T and natural killer (NK) cells. In an effort to identify genes that control pDC development we searched for genes of which the expression is restricted to human pDC using a cDNA subtraction technique with activated monocyte-derived DCs (Mo-DCs) as competitor. We identified the transcription factor Spi-B to be expressed in pDCs but not in Mo-DCs. Spi-B expression in pDCs was maintained on in vitro maturation of pDCs. Spi-B was expressed in early CD34(+)CD38(-) hematopoietic progenitors and in CD34(+)CD1a(-) thymic precursors. Spi-B expression is down-regulated when uncommitted CD34(+)CD1a(-) thymic precursors differentiate into committed CD34(+)CD1a(+) pre-T cells. Overexpression of Spi-B in hematopoietic progenitor cells resulted in inhibition of development of T cells both in vitro and in vivo. In addition, development of progenitor cells into B and NK cells in vitro was also inhibited by Spi-B overexpression. Our results indicate that Spi-B is involved in the control of pDC development by limiting the capacity of progenitor cells to develop into other lymphoid lineages.

Apoptosis↗

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

A senescence rescue screen identifies BCL6 as an inhibitor of anti-proliferative p19(ARF)-p53 signaling.

Senescence limits the proliferative capacity of primary cells in culture. We describe here a genetic screen to identify genes that allow bypass of this checkpoint. Using retroviral cDNA expression libraries, we identify BCL6 as a potent inhibitor of senescence. BCL6 is frequently activated in non-Hodgkin's lymphoma, but its mechanism of action has remained unclear. BCL6 efficiently immortalizes primary mouse embryonic fibroblasts and cooperates with RAS in oncogenic transformation. BCL6 overrides the senescence response downstream of p53 through a process that requires induction of cyclin D1 expression, as cyclin D1 knockout fibroblasts are specifically resistant to BCL6 immortalization. We show that BCL6 expression also dramatically extends the replicative lifespan of primary human B cells in culture and induces cyclin D1 expression, indicating that BCL6 has a similar activity in lymphoid cells. Our results suggest that BCL6 contributes to oncogenesis by rendering cells unresponsive to antiproliferative signals from the p19(ARF)-p53 pathway.

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↗

PubMed2002

Development of alphabeta T cells in the human thymus.

The thymus is the main producer of alphabeta T cells and is, therefore, crucial for a normal immune system. The intrathymic developmental pathway of human alphabeta T cells has now been delineated. The production of new T cells by the thymus decreases with age, and the thymus was thought to be redundant in adults once the peripheral T-cell pool has been formed early in life. However, recent work has shown that the thymus can function even at an advanced age. Research into the production of T cells in clinical settings that are associated with loss of T cells in the periphery has sparked renewed interest in the function of the human thymus.

Aging↗

PubMed2002

Generation of regulatory gut-homing human T lymphocytes using ex vivo interleukin 10 gene transfer.

BACKGROUND & AIMS: Systemic treatment of Crohn's disease patients using recombinant interleukin (rIL)-10 has not resulted in significant therapeutic benefit presumably because of limited bioavailability and unexpected proinflammatory effects of high-dose rIL-10. Ex vivo gene transfer of the interleukin (IL)-10 gene to gut-homing CD4(+) cells may lead to improved long-term management. METHODS: Peripheral blood mononuclear cells (PBMCs) were transduced with a retroviral vector containing the IL-10 and green fluorescent protein (GFP) gene or a control vector containing GFP only. Transduced CD4(+) cells were sorted and maintained in culture for phenotypic and functional analysis. RESULTS: Stimulated IL-10-GFP CD4(+) cells produced significantly higher levels of IL-10 than control cells for at least 4 months. The IL-10 transgene was biologically active and decreased proliferation of IL-10-GFP CD4(+) cells as well as expression of major histocompatibility class (MHC) class II, proliferation of autologous responder cells, and IL-12 production by dendritic cells (DCs). The majority of transduced CD4(+) cells had a gut-homing potential because they expressed the mucosal integrin alpha4beta7, and displayed efficient binding to MAdCAM-1-expressing cells in vitro. CONCLUSIONS: Transduction of peripheral blood CD4(+) lymphocytes with IL-10 results in a regulatory phenotype. The use of regulatory gut-homing human CD4(+) cells may provide a novel approach to local delivery of immunomodulatory signals to the intestine in Crohn's disease.

Cell Adhesion↗