Silke Appel

The complexity of Sjögren's syndrome: Novel aspects on pathogenesis

In Sjögrens syndrome, like in most other autoimmune diseases, the enigma leading to a pathogenic attack against self has not yet been solved. By definition, the disease must be mediated by specific immune reactions against endogenous tissues to qualify as an autoimmune disease. In Sjögrens syndrome the autoimmune response is directed against the exocrine glands, which, as histopathological hallmark of the disease, display persistent and progressive focal mononuclear cell infiltrates. Clinically, the disease in most patients is manifested by two severe symptoms: dryness of the mouth (xerostomia) and the eyes (keratoconjunctivitis sicca). A number of systemic features have also been described and the presence of autoantibodies against the ubiquitously expressed ribonucleoprotein particles Ro (Sjögrens-syndrome-related antigen A - SSA) and La (SSB) further underline the systemic nature of Sjögrens syndrome. The original explanatory concept for the pathogenesis of Sjögrens syndrome proposed a specific, self-perpetuating, immune mediated loss of acinar and ductal cells as the principal cause of salivary gland hypofunction. Although straightforward and plausible, the hypothesis, however, falls short of accommodating several Sjögrens syndrome-related phenomena and experimental findings. Consequently, researchers considered immune-mediated salivary gland dysfunction prior to glandular destruction and atrophy as potential molecular mechanisms underlying the symptoms of dryness in Sjögrens syndrome. Accordingly, apoptosis, fibrosis and atrophy of the salivary glands would represent consequences of salivary gland hypofunction. The emergence of advanced bio-analytical platforms further enabled the identification of potential biomarkers with the intent to improve Sjögrens syndrome diagnosis, promote the development of prognostic tools for Sjögrens syndrome and the long-term goal to identify possible processes for therapeutic treatment interventions. In addition, such approaches allowed us to glimpse at the apparent complexity of Sjögrens syndrome.

Association of EBF1 , FAM167A(C8orf13)-BLK and TNFSF4 gene variants with primary Sjögren's syndrome

We performed a candidate gene association study in 540 patients with primary Sjögrens Syndrome (SS) from Sweden (n=344) and Norway (n=196) and 532 controls (n=319 Swedish, n=213 Norwegian). A total of 1139 single-nucleotide polymorphisms (SNPs) in 84 genes were analyzed. In the meta-analysis of the Swedish and Norwegian cohorts, we found high signals for association between primary SS and SNPs in three gene loci, not previously associated with primary SS. These are the early B-cell factor 1 (EBF1) gene, P=9.9 × 10−5, OR 1.68, the family with sequence similarity 167 member A–B-lymphoid tyrosine kinase (FAM167A–BLK) locus, P=4.7 × 10−4, OR 1.37 and the tumor necrosis factor superfamily (TNFSF4=Ox40L) gene, P=7.4 × 10−4, OR 1.34. We also confirmed the association between primary SS and the IRF5/TNPO3 locus and the STAT4 gene. We found no association between the SNPs in these five genes and the presence of anti-SSA/anti-SSB antibodies. EBF1, BLK and TNFSF4 are all involved in B-cell differentiation and activation, and we conclude that polymorphisms in several susceptibility genes in the immune system contribute to the pathogenesis of primary SS.

Effects of Imatinib on Monocyte-Derived Dendritic Cells Are Mediated by Inhibition of Nuclear Factor-κB and Akt Signaling Pathways

Dendritic cells are the most powerful antigen-presenting cells playing a decisive role for the initiation and maintenance of primary immune responses. However, signaling pathways involved in the differentiation of these cells have not been fully determined. Imatinib is a novel tyrosine kinase inhibitor effective against Abl kinases, c-Kit, and platelet-derived growth factor receptor. Using this compound, we show that human monocyte-derived dendritic cells generated in the presence of therapeutic concentrations of imatinib show a reduced expression of CD1a, MHC class I and II, and costimulatory molecules as well as decreased secretion of chemokines and cytokines resulting in an impaired capacity of dendritic cells to elicit primary T-cell responses. Using Western blot analyses, we found that these effects are mediated by inhibition of phosphatidylinositol 3-kinase/Akt pathways and a pronounced down-regulation of nuclear localized protein levels of nuclear factor-κB family members. Importantly, using blocking antibodies and tyrosine kinase inhibitors, we show that the inhibitory effects of imatinib on dendritic cell differentiation are not mediated via platelet-derived growth factor receptor and c-Kit. Taken together, our study reveals that imatinib inhibits dendritic cell differentiation and function via Akt and nuclear factor-κB signal transduction. Importantly, we show that imatinib can inhibit the function of normal, nonmalignant cells that may result in immunosuppression of these patients.

Effects of Imatinib on Normal Hematopoiesis and Immune Activation

The selective tyrosine kinase inhibitor imatinib (Glivec; Novartis International, Basel, Switzerland, http://www.glivec.com/content/home.jsp) is increasingly used for the treatment of Philadelphia chromosome–positive leukemias and other malignancies. In principle, the drug is well tolerated and clinical side effects are mostly moderate. However, it was shown that imatinib can affect the function of normal, nonmalignant cells, resulting in myelosuppression in treated patients. Recently, it has been demonstrated that imatinib might affect mobilization, proliferation, and differentiation of hematopoietic progenitor cells while leaving hematopoietic stem cells unaffected. Furthermore, in several in vitro studies and animal models, it was demonstrated that imatinib can affect the function and differentiation of antigen‐presenting cells and inhibit the effector functions of T lymphocytes. Moreover, the induction of specific cytotoxic T cells seems to be impaired in chronic myeloid leukemia (CML) patients treated with imatinib compared with patients receiving interferon‐α. This is of importance because some of the therapeutic effects in the treatment of patients with CML are mediated by the induction of leukemia‐specific T‐cell responses. Further studies investigating the effects of imatinib on normal hematopoiesis are of interest as they might lead to a better understanding of the clinically observed side effects and also might help identify new therapeutic applications of the drug, possibly in Bcr‐Abl–negative myeloproliferative disorders and potentially as an immunomodulatory agent.

New Concepts in the Pathogenesis of Sjögren's Syndrome

Sjögrens syndrome (SS) is a rheumatic disease in which the salivary and lacrimal glands are the principal targets of a pathologic autoimmune reaction. SS is manifested by xerostemia and keratoconjunctivitis sicca and marked by persistent focal mononuclear cell infiltration within the salivary glands, often accompanied by glandular atrophy and fibrosis. A challenge is to clarify the roles of genetic backgrounds and environmental trigger. Advanced bioanalytic platforms have enabled identification of potential biomarkers with the intent to improve diagnosis, promote development of prognostic tools, and identify processes for therapeutic treatment. Such approaches allow a glimpse at the apparent complexity of SS.

Type 1 Regulatory T Cells and Regulatory B Cells Induced by Tolerogenic Dendritic Cells

Dendritic cells (DC) are professional antigen‐presenting cells that are capable of both activating immune responses and inducing tolerance. Several studies have revealed efficiency of therapeutic vaccination with tolerogenic DC (tolDC) in inhibition of experimental autoimmunity. The purpose of this study was to compare four different protocols for generation of tolDC – the antidiabetic drug troglitazone (TGZ DC), NF‐κB inhibitor BAY 11‐7082 (BAY DC), prostaglandin D2 metabolite 15d‐PGJ2 (PGJ DC) and a combination of dexamethasone and 1α,25‐dihydroxyvitamin D3 (DexVD3 DC) regarding phenotype, cytokine production and T cell stimulatory capacity. TGZ DC and BAY DC had a phenotype comparable to immature DC, while DexVD3 DC were more macrophage like. Analysis of cytokine production using cell culture supernatants from all DC populations revealed that DexVD3 DC were efficient producers of IL‐10 and produced less pro‐inflammatory cytokines. T cells primed with DexVD3 DC showed reduced proliferation, and further analyses of these T cells revealed that functionally effective type 1 regulatory T cells (Tr1) but not FoxP3+ Treg were induced. Furthermore, DexVD3 DC promoted the induction of regulatory B cells (Breg). Together, these results indicate that DexVD3 DC have the best potential to be used in a tolerogenic antigen‐presenting cell‐based immunotherapy setting.

Identification of a Lysosomal Peptide Transport System Induced during Dendritic Cell Development

The delivery of protein fragments to major histocompatibility complex (MHC)-loading compartments of professional antigen-presenting cells is essential in the adaptive immune response against pathogens. Apart from the crucial role of the transporter associated with antigen processing (TAP) for peptide loading of MHC class I molecules in the endoplasmic reticulum, TAP-independent translocation pathways have been proposed but not identified so far. Based on its overlapping substrate specificity with TAP, we herein investigated the ABC transporter ABCB9, also named TAP-like (TAPL). Remarkably, TAPL expression is strongly induced during differentiation of monocytes to dendritic cells and to macrophages. TAPL does not, however, restore MHC class I surface expression in TAP-deficient cells, demonstrating that TAPL alone or in combination with single TAP subunits does not form a functional transport complex required for peptide loading of MHC I in the endoplasmic reticulum. In fact, by using quantitative immunofluorescence and subcellular fractionation, TAPL was detected in the lysosomal compartment co-localizing with the lysosome-associated membrane protein LAMP-2. By in vitro assays, we demonstrate a TAPL-specific translocation of peptides into isolated lysosomes, which strictly requires ATP hydrolysis. These results suggest a mechanism by which antigenic peptides have access to the lysosomal compartment in professional antigen-presenting cells.

Identification of C-Met Oncogene as a Broadly Expressed Tumor-Associated Antigen Recognized by Cytotoxic T-Lymphocytes

Purpose: C-Met proto-oncogene is a receptor tyrosine kinase that mediates the oncogenic activities of the hepatocyte growth factor. Using a DNA chip analysis of tumor samples from patients with renal cell carcinoma and sequencing of peptides bound to the HLA-A*0201 molecules on tumor cells a peptide derived from the c-Met protein was identified recently. Experimental Design: We used this novel HLA-A*0201 peptide for the induction of specific CTLs to analyze the presentation of this epitope by malignant cells. Results: The induced CTL efficiently lysed target cells pulsed with the cognate peptide, as well as HLA-A*0201-matched tumor cell lines in an antigen-specific and HLA-restricted manner. Furthermore, the induced c-Met-specific CTLs recognized autologous dendritic cells (DCs) pulsed with the peptide or transfected with whole-tumor mRNA purified from c-Met-expressing cell lines. We next induced c-Met-specific CTLs using peripheral blood mononuclear cells and DC from an HLA-A*0201-positive patient with plasma cell leukemia to determine the recognition of primary autologous malignant cells. These CTLs lysed malignant plasma cells while sparing nonmalignant B- and T-lymphocytes, monocytes, and DCs. Conclusion: Our results demonstrate that c-Met oncogene is a novel tumor rejection antigen recognized by CTL and expressed on a broad variety of epithelial and hematopoietic malignant cells.

Current Status and Future Perspectives of Dendritic Cell–Based Cancer Immunotherapy

Dendritic cells (DCs) are considered to be the most potent antigen‐presenting cells. Ever since the development of protocols for the in vitro generation of DCs, their application in immunotherapy against various malignancies has been explored. Even though the approach of using tumour antigen–presenting DCs in therapeutic vaccination strategies has been shown to work effectively in mice and look promising in in vitro studies, the actual clinical benefit for patients with cancer has been marginal. There clearly is still room for improvement. In this review, we will summarize recent clinical trials and findings and try to shed some light on the current status and the future of DC‐based cancer immunotherapy.

Levels of plasmacytoid dendritic cells and type-2 myeloid dendritic cells are reduced in peripheral blood of patients with primary Sjögren's syndrome

Objective Sjögrens syndrome (SS) is a lymphoproliferative autoimmune disease, characterised by dryness of the mouth and eyes. Dendritic cells (DC) are potent antigen-presenting cells crucial for initiating and maintaining primary immune responses. This study quantified interferon-producing plasmacytoid DC (pDC) and two myeloid DC subsets (mDC1 and mDC2) in peripheral blood (PB) from primary SS (pSS) patients and healthy controls. Methods Blood samples from 31 pSS patients and 28 gender and age-matched healthy controls were analysed by flow cytometry using the Miltenyi Blood DC enumeration kit. The presence of pDC in salivary glands (SG) from pSS patients was analysed by immunohistochemistry. Results Patients with pSS had significantly less pDC and mDC2 in PB compared with healthy controls. Moreover, pDC are present in SG from patients with pSS. Conclusion Patients with pSS have alterations among DC populations in PB, and pDC are present in the SG, suggesting a potential role of these cells in SS.