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S Grabbe

Publications and source records attributed to S Grabbe.

At least 55 records · Page 3Linked to original sources
PubMed2001

Dendritic cells and tumor immunity.

Researchers and clinicians have tried for decades to use the mechanisms of immunity for the fight against cancer. Early attempts aimed at the instrumentation of soluble immune mediators such as antibodies or cytotoxic proteins for the therapy of malignancies. Major improvements in understanding the induction and regulation of cellular immunity have now made it possible to generate effector cells in cancer patients which are specific for the neoplastic disease. At the beginning of every cellular immune reaction against cancers tumor antigens have to be presented to T cells in order to activate them and drive them into clonal expansion. This is done by antigen presenting cells, the most powerful of which is the dendritic cell (DC). While DC were hard to isolate initially, they can be generated in large numbers in vitro today and manipulated in multiple ways before given back to a patient to induce tumor immunity. Thus, a great amount of hope lies in the use of DC as inducers of tumor immunity. However, the first clinical studies, which have now been completed with only limited success make clear, that still a lot of open questions remain to be answered. This review tries to give an overview of this rapidly developing field, mentioning the major conceptual approaches and techniques, but also discussing important caveats. The next years will show whether we can improve our understanding of DC biology and the mechanisms of immune induction strongly enough to effectively employ DC for immunotherapy of cancer.

Animals↗
PubMed2001

Dendritic cells in cancer immunotherapy.

Antigen presentation is a critical regulatory element for the induction of cellular immune responses. Thus, one of the principal current goals of tumor immunotherapy is to control and enhance tumor antigen presentation. In this respect, dendritic cells (DC) are now being widely investigated as immunotherapeutic agents for the treatment of disseminated malignancies. At present, numerous ways to employ DCs for tumor immunotherapy are being tested, ranging from direct in situ expansion and activation of DCs to adoptive transfer of ex vivo generated DCs, and numerous techniques have been designed to optimize DC activation, tumor antigen delivery to DCs, and induction of tumor-specific, as well as helper immune responses, in vivo. However, the results of recent preclinical studies and the diversity of the clinical phase I trials that are currently underway indicate that little is still known about the exact mechanisms by which DCs modulate tumor immunity and pose the concern that premature clinical trials might not yield the desired results and might be harmful to, rather than promote, the concept of DC-based tumor immunotherapy. This review summarizes some of the current approaches to induce tumor immunity by DC-based vaccination and discusses their advantages and concerns.

Animals↗
PubMed2000

Mycophenolate mofetil impairs the maturation and function of murine dendritic cells.

The immunosuppressive drug, mycophenolate mofetil (MMF), has been successfully introduced in allogeneic transplantation medicine and, more recently, in the treatment of autoimmune skin disorders. MMF inhibits lymphocyte proliferation via a blockade of the enzyme inosine 5'-monophosphate dehydrogenase, an enzyme on which lymphocytes solely depend to generate the purines necessary for DNA/RNA synthesis. To investigate the effects of MMF on cutaneous immune responses, a murine model of contact hypersensitivity (CHS) was used, with oxazolone or trinitrochlorobenzene as a contact allergen. Compared with the respective vehicle, i.p. applied MMF significantly inhibited the elicitation and, surprisingly, the induction of CHS responses. This prompted further studies into the effects of MMF on Ag presentation. Bone marrow-derived dendritic cells (DC) were cultured with GM-CSF and IL-4 in the presence of MMF and were tested for their Ag-presenting capacity. Sensitization and elicitation of CHS and delayed-type hypersensitivity responses by s. c. injected haptenated DC were reduced upon preincubation of DC with MMF. CHS responses were not impaired upon resensitization, indicating that MMF does not induce hapten-specific immunotolerance. In addition, MMF decreased the ability of DC to stimulate allogeneic T cells in MLR assays. Accordingly, flow cytometric analyses revealed a dose-dependent reduction of the expression of CD40, CD80, CD86, I-A, and ICAM-1 on DC with a concurrent reduction of IL-12 production. These data suggest that MMF, in addition to affecting T lymphocytes, directly affects APC, resulting in an impairment of immune responses. They furthermore point to a possible role of inosine 5'-monophosphate dehydrogenase in the maturation of DC.

Animals↗
PubMed2000

Evidence for functional relevance of CTLA-4 in ultraviolet-radiation-induced tolerance.

Hapten sensitization through UV-exposed skin induces hapten-specific tolerance that can be adoptively transferred by injecting T lymphocytes into naive recipients. The exact phenotype of T cells responsible for inhibiting the immune response and their mode of action remain unclear. Evidence exists that CTLA-4 negatively regulates T cell activation. We addressed whether CTLA-4 is involved in the transfer of UV-induced tolerance. Injection of lymph node cells from mice that were sensitized with dinitrofluorobenzene (DNFB) through UV-irradiated skin inhibited induction of contact hypersensitivity against DNFB in the recipient animals. When CTLA-4+ cells were depleted, transfer of suppression was lost. Likewise, significantly fewer lymphocytes enriched for CTLA-4+ cells were necessary to transfer suppression than unfractionated cells. Expression of CTLA-4 appears to be functionally relevant, since in vivo injection of a blocking anti-CTLA-4 Ab was able to break UV-induced tolerance and inhibited transfer of suppression. Upon stimulation with dendritic cells in the presence of the water-soluble DNFB analogue, DNBS, CTLA-4+ T cells from DNFB-tolerized mice secreted high levels of IL-10, TGF-beta, and IFN-gamma; low levels of IL-2; and no IL-4, resembling the cytokine pattern of T regulatory 1 cells. Ab blocking of CTLA-4 resulted in inhibition of IL-10 release. Accordingly, transfer of tolerance was not observed when recipients were treated with an anti-IL-10 Ab. Hence we propose that T cells, possibly of the T regulatory 1 type, transfer UV-mediated suppression through the release of IL-10. Activation of CTLA-4 appears to be important in this process.

Abatacept↗
PubMed2000

In experimental leishmaniasis deficiency of CD18 results in parasite dissemination associated with altered macrophage functions and incomplete Th1 cell response.

We investigated experimental leishmaniasis in CD18-deficient mice. Whereas wild-type (WT) CD18-/- mice (129SV/C57BL/6) were resistant to infection, CD18-/- mice revealed increasing visceral dissemination of parasites. Unlike in other susceptible strains, infected footpads of CD18-/- mice did not ulcerate, due to an abolished recruitment of granulocytes. In vitro, CD18-/- macrophages were able to phagocytose opsonized Leishmania major despite absence of CR3, albeit phagocytosis rate was 50% lower than in WT macrophages. We found that uptake was partially mediated by scavenger receptors. As infected CD18-/- macrophages showed impaired ability to produce NO and to eliminate parasites, CD18 is one mediator of NO production. CD18 is also involved in reduction of IL-12 release by L. major-infected macrophages, as uptake of opsonized parasites (via CR3) decreased IL-12 release only in WT, but not in CD18-/- macrophages. When T cells from infected CD18-/- mice were restimulated with antigen-presenting cells (APC), they released no IL-2 or IL-4, but a little IFN-gamma, associated with lack of proliferation. This deficiency was linked to absence of CD18 on T cells, but not on APC. Substitution with IL-2 specifically restored a Th1-like response with proliferation and release of IFN-gamma. Thus, while impaired phagocytosis, NO production, and recruitment of granulocytes in CD18-/- mice may not reverse resistance, and while unrestricted IL-12 release supports development of Th1 cells, the failure of T cells to release IL-2 and to proliferate causes susceptibility.

Animals↗
PubMed2000

Antigen presentation in extracellular matrix: interactions of T cells with dendritic cells are dynamic, short lived, and sequential.

Cognate interactions of naive T cells with antigen-presenting dendritic cells require physical cell-cell contacts leading to signal induction and T cell activation. Using a three-dimensional collagen matrix videomicroscopy model for ovalbumin peptide-specific activation of murine and oxidative mitogenesis of human T cells, we show that T cells maintain vigorous migration upon cognate interactions to DC (dendritic cell), continuously crawl across the DC surface, and rapidly detach (median within 6-12 min). These dynamic and short-lived encounters favor sequential contacts with the same or other DC and trigger calcium influx, upregulation of activation markers, T blast formation, and proliferation. We conclude that a tissue environment supports the accumulation of sequential signals, implicating a numeric or "digital" control mechanism for an ongoing primary immune response.

Animals↗
PubMed1999

Reduced ultraviolet-induced carcinogenesis in mice with a functional disruption in B7-mediated costimulation.

Immunosuppression by UV light contributes significantly to the induction of skin cancer by suppressing the cell-mediated immune responses which control the development of carcinogenesis. The B7/CD28-CTLA-4 signaling pathway provides costimulatory signals essential for Ag-specific T cell activation. To investigate the role of this pathway in photocarcinogenesis, we utilized transgenic (Tg) mice which constitutively express CTLA-4Ig, a high-affinity CD28/CTLA-4 antagonist that binds to both B7-1 and B7-2. The transgene is driven by a skin-specific promoter yielding high levels of CTLA-4Ig in the skin and serum. Chronic UV exposure of CTLA-4Ig Tg mice resulted in significantly reduced numbers of skin tumors, when compared to control mice. In addition, Tg mice were resistant to UV-induced suppression of delayed-type hypersensitivity responses to alloantigens. Most importantly, upon stimulation with mitogens and alloantigens, T cells isolated from CTLA-4Ig Tg mice produced significantly less IL-4 but more IFN-gamma compared to control T cells, suggesting an impaired Th2 response and a relative increase of Th1-type immunity. Together, these data show that overall B7 engagement directs immune responses toward the Th2 pathway. Moreover, they point out the crucial role of Th1 immune reactions in the protection against photocarcinogenesis.

Abatacept↗
PubMed1999

Human peripheral blood-derived dendritic cells express functional melanocortin receptor MC-1R.

The neuropeptide, alpha-melanocyte-stimulating hormone (alpha-MSH) is well known for its immunomodulating capabilities. alpha-MSH antagonizes the activity of numerous proinflammatory mediators; for example, Interleukin-1 (IL-1), IL-6, tumor necrosis factor alpha (TNF alpha), and bacterial endotoxin. In vivo alpha-MSH has been shown to suppress a contact hypersensitivity reaction in mice, and to induce hapten-specific tolerance. Since antigen presenting cells (APC) represent key elements for tolerance induction, the effect of alpha-MSH, and the expression of its receptor-melanocortin receptor-1 (MC-1R), on human peripheral blood-derived monocytes and dendritic cells (DC), was investigated. Semiquantitative RT-PCR demonstrated that monocytes and DC express MC-1R, but none of the other members of the MC-receptor family. Moreover, the extent of MC-1R expression correlated with the state of activation of these cells. Since the major ligand of MC-1R is alpha-MSH the question of whether alpha-MSH affects the function of monocyte derived DC was further investigated. We found that the expression of the costimulatory molecules CD 86 and CD 40 was downregulated on DC in the presence of alpha-MSH. Thus, alpha-MSH may exert its immunosuppressive effects by altering the function of APC.

Animals↗
PubMed1999

Transfection of immature murine bone marrow-derived dendritic cells with the granulocyte-macrophage colony-stimulating factor gene potently enhances their in vivo antigen-presenting capacity.

Ag presentation by dendritic cells (DC) is crucial for induction of primary T cell-mediated immune responses in vivo. Because DC culture from blood or bone marrow-derived progenitors is now clinically applicable, this study investigated the effectiveness of in vitro-generated murine bone marrow-derived DC (Bm-DC) for in vivo immunization protocols. Previous studies demonstrated that GM-CSF is an essential growth and differentiation factor for DC in culture and that in vivo administration of GM-CSF augments primary immune responses, which renders GM-CSF an attractive candidate to further enhance the effectiveness of DC-based immunotherapy protocols. Therefore, immature Bm-DC were transiently transfected with the GM-CSF gene and tested for differentiation, migration, and Ag-presenting capacity in vitro and in vivo. In vitro, GM-CSF gene-transfected Bm-DC were largely unaltered with regard to MHC and costimulatory molecule expression as well as alloantigen or peptide Ag-presenting capacity. When used for in vivo immunizations, however, the Ag-presenting capacity of GM-CSF gene-transfected Bm-DC was greatly enhanced compared with mock-transfected or untransfected cells, as determined by their effectiveness to induce primary immune reactions against hapten, protein Ag, and tumor Ag, respectively. Increased effectiveness in vivo correlated with the better migratory capacity of GM-CSF gene-transfected Bm-DC. These results show that GM-CSF gene transfection significantly enhances the capacity of DC to induce primary immune responses in vivo, which might also improve DC-based vaccines currently under clinical investigation.

Adjuvants, Immunologic↗
PubMed1999

Interaction of dendritic cells with skin endothelium: A new perspective on immunosurveillance.

The goal of this study was to determine the mechanisms by which dendritic cells (DCs) in blood could interact with endothelium, a prerequisite to extravasation into tissues. Our results indicate that DCs express both HECA-452-reactive and nonreactive isoforms of P-selectin glycoprotein ligand 1 (PSGL-1) and can tether and roll efficiently on E- and P-selectin under flow conditions in vitro. Freshly isolated blood DCs were further observed to roll continuously along noninflamed murine dermal endothelium in vivo. This interaction is strictly dependent on endothelial selectins, as shown by experiments with blocking antibodies and with E- and P-selectin-deficient mice. We hypothesize that DCs in blood are constitutively poised at the interface of blood and skin, ready to extravasate upon induction of inflammation, and we showed that cutaneous inflammation results in a rapid recruitment of DCs from the blood to tissues. We propose that this is an important and previously unappreciated element of immunosurveillance.

Animals↗
PubMed1999

Generation of tumor immunity by bone marrow-derived dendritic cells correlates with dendritic cell maturation stage.

Bone marrow-derived dendritic cells (BmDC) are potent APC and can promote antitumor immunity in mice when pulsed with tumor Ag. This study aimed to define the culture conditions and maturation stages of BmDC that enable them to optimally function as APC in vivo. BmDC cultured under various conditions (granulocyte-macrophage CSF (GM-CSF) or GM-CSF plus IL-4 alone or in combination with Flt3 ligand, TNF-alpha, LPS, or CD40 ligand (CD40L)) were analyzed morphologically, phenotypically, and functionally and were tested for their ability to promote prophylactic and/or therapeutic antitumor immunity. Each of the culture conditions generated typical BmDC. Whereas cells cultured in GM-CSF alone were functionally immature, cells incubated with CD40L or LPS were mature BmDC, as evident by morphology, capacity to internalize Ag, migration into regional lymph nodes, IL-12 secretion, and alloantigen or peptide Ag presentation in vitro. The remaining cultures exhibited intermediate dendritic cell maturation. The in vivo Ag-presenting capacity of BmDC was compared with respect to induction of both protective tumor immunity and immunotherapy of established tumors, using the poorly immunogenic squamous cell carcinoma, KLN205. In correspondence to their maturation stage, BmDC cultured in the presence of CD40L exhibited the most potent immunostimulatory effects. In general, although not entirely, the capacity of BmDC to induce an antitumor immune response in vivo correlated to their degree of maturation. The present data support the clinical use of mature, rather than immature, tumor Ag-pulsed dendritic cells as cancer vaccines and identifies CD40L as a potent stimulus to enhance their in vivo Ag-presenting capacity.

Animals↗
PubMed1999

Analysis of mouse dendritic cell migration in vivo upon subcutaneous and intravenous injection.

Dendritic cells (DC) have an increasingly important role in vaccination therapy; therefore, this study sought to determine the migratory capacity and immunogenic function of murine bone-marrow (BM)-derived DC following subcutaneous (s.c.) and intravenous (i.v.) injection in vivo. DC were enriched from BM cultures using metrizamide. Following centrifugation, the low-buoyant density cells, referred to throughout as DC, were CD11c(high), Iab(high), B7-1(high) and B7-2(high) and potently activated alloreactive T cells in mixed lymphocyte reactions (MLR). In contrast, the high-density cells expressed low levels of the above markers, comprised mostly of granulocytes based on GR1 expression, and were poor stimulators in MLR. Following s.c. injection of fluorescently labelled cells into syngeneic recipient mice, DC but not granulocytes migrated to the T-dependent areas of draining lymph nodes (LN). DC numbers in LN were quantified by flow-cytometric analysis, on 1, 2, 3, 5 and 7 days following DC transfer. Peak numbers of around 90 DC per draining LN were found at 2 days. There was very little migration of DC to non-draining LN, thymus or spleen at any of the time-points studied. In contrast, following i.v. injection, DC accumulated mainly in the spleen, liver and lungs of recipient mice but were largely absent from peripheral LN and thymus. The ability of DC to induce T-cell-mediated immune responses was examined using trinitrobenzenesulphate (TNBS)-derivatized DC (TNBS-DC) to sensitize for contact hypersensitivity responses (CHS) in naive syngeneic recipients. Following s.c. injection, as few as 105 TNBS-DC, but not TNBS-granulocytes, sensitized for CHS responses. However, the same number of TNBS-DC failed to induce CHS following i.v. injection. In summary, this study provides new and quantitative data on the organ specific migration of murine BM-derived DC following s.c. and i.v. injection. The demonstration that the route of DC administration determines the potency of CHS induction, strongly suggests that the route of immunization should be considered in the design of vaccine protocols using DC.

Adoptive Transfer↗
PubMed1998

Impaired cutaneous immune responses in Thy-1-deficient mice.

Thy-1 is a cell surface glycoprotein expressed mainly on brain and lymphoid tissue. Although the functions of Thy-1 are incompletely understood, evidence exists that Thy-1 participates in T cell activation. To examine the functional role of Thy-1 in cutaneous immune responses in vivo, Thy-1 gene-targeted mice (Thy-1-/-) and wild-type mice (Thy-1+/+) were immunized with the hapten oxazolone. After challenge with oxazolone, contact hypersensitivity responses in Thy-1-/- mice were reduced by 25% compared with Thy-1+/+ mice. Likewise, irritant dermatitis induced by croton oil was also decreased. In addition, Thy-1-/- mice showed a significantly reduced delayed-type hypersensitivity response after injection of allogeneic spleen cells into the hind footpads of allosensitized animals when compared with Thy-1+/+ mice. Moreover, proliferative responses to immobilized anti-CD3 were decreased in peripheral Thy-1-/- lymphocytes; this decrease was associated with a significantly reduced intracellular Ca2+ influx and protein tyrosine phosphorylation, indicating impairment of early lymphocyte activation. In contrast, the T cell proliferation induced by mitogens was normal, suggesting that Thy-1 expression weakly contributes to TCR-mediated T cell activation. Epidermal Langerhans cells and bone marrow-derived dendritic cells from Thy-1-/- mice exhibited a normal expression of costimulatory surface molecules as well as an unaltered ability to stimulate allogeneic T cells. Taken together, these findings demonstrate that a lack of Thy-1 expression does not generally compromise the immune system; however, Thy-1 expression may be involved in the fine-tuning of T cell-mediated immune responses.

Animals↗
PubMed1998

Spontaneous skin ulceration and defective T cell function in CD18 null mice.

A null mutation was prepared in the mouse for CD18, the beta2 subunit of leukocyte integrins. Homozygous CD18 null mice develop chronic dermatitis with extensive facial and submandibular erosions. The phenotype includes elevated neutrophil counts, increased immunoglobulin levels, lymphadenopathy, splenomegaly, and abundant plasma cells in skin, lymph nodes, gut, and kidney. Very few neutrophils were found in spontaneously occurring skin lesions or with an induced toxic dermatitis. Intravital microscopy in CD18 null mice revealed a lack of firm neutrophil attachment to venules in the cremaster muscle in response to N-formyl- methionyl-leucyl-phenylalanine. A severe defect in T cell proliferation was found in the CD18 null mice when T cell receptors were stimulated either by staphylococcal enterotoxin A or by major histocompatibility complex alloantigens demonstrating a greater role of CD11/CD18 integrins in T cell responses than previously documented. The null mice are useful for delineating the functions of CD18 in vivo.

Animals↗