Mast cells drive IgE-mediated disease but might be bystanders in many other inflammatory and neoplastic conditions.

Mast cells (MCs) are capable of executing powerful inflammatory response programs triggered by surface IgE cross-linking or through pattern recognition receptors. The question of how MCs contribute to human disease has been intensely investigated and stimulated much controversy. Correlative evidence comes from human studies, pointing to pathogenetic or protective MC functions in patients with atopic conditions, autoimmune disorders, type 2 diabetes, chronic urticaria, mastocytosis, and cancer. Experiments in MC-deficient mice underpinned key roles for MCs in patients with IgE-mediated allergic conditions. Important pathogenetic MC contributions to other inflammatory and neoplastic conditions were suggested by studies in traditional KIT mutant MC-deficient mouse strains. However, many of these findings were not reproduced in more recently developed improved mouse models of MC deficiency, largely ruling out roles for MCs in mouse models for autoimmune disease, diabetes, and cancer. We discuss limitations of studies in mice and human subjects and provide suggestions for how they can be overcome, such as through the development of specific and selective MC-targeted treatments.

Mast cells are critical for the limitation of thrombin-induced skin inflammation.

Thrombin, a key player in coagulation, is widely held to induce and promote inflammation. As of now, the features, kinetics and control of thrombin's proinflammatory effects on the skin remain to be characterized in detail. We, therefore, injected thrombin into the ear skin of mice and observed strong, dose-dependent and transient ear swelling responses as well as mast cell (MC) degranulation. Unexpectedly, thrombin induced even stronger, not reduced, ear swelling in MC-deficient KitW-sh/W-sh mice. Prior local reconstitution of KitW-sh/W-sh mice with MCs inhibited this effect, indicating that MCs may contribute to the control of thrombin-induced skin inflammation. In line with previous studies, we found that MCs express the thrombin receptors PAR1, PAR3 and PAR4, thrombin induces direct and dose-dependent MC degranulation, and that degranulated MCs inactivate thrombin. Further findings suggested that MC-mediated protection from thrombin-induced inflammation is likely to rely on the effects of MC proteases. We show for the first time that MC-deficient mice and MC protease 4-deficient mice with normal numbers of MCs show markedly increased ear swelling in response to thrombin as compared to wild-type mice. Taken together, these results suggest that thrombin-induced skin inflammation is controlled, in part, by MC protease 4 released from activated MCs. For MC-driven diseases such as chronic spontaneous urticaria, which has been linked to increased thrombin generation, this might mean that MCs may contribute to the resolution of skin inflammatory responses.

Membrane-bound stem cell factor is the major but not only driver of fibroblast-induced murine skin mast cell differentiation.

The maintenance and modulation of cutaneous mast cell (MC) numbers is held to be important for skin immune responses to allergens and pathogens. The increase in MC numbers in the skin is achieved by proliferation and the differentiation of precursor to mature MCs. Fibroblast-derived SCF is thought to be the major skin MC growth factor and it potently induces MC proliferation. The mechanisms of fibroblast-induced skin MC differentiation, including the role of SCF, however, remain insufficiently characterized and understood. Using cocultures of immature murine MCs and fibroblasts, we found that the adhesion of immature MCs to fibroblasts via VCAM-1 and α4 ß7 integrin is very important for subsequent differentiation, which is driven by fibroblast membrane-bound SCF and additional fibroblast-derived membrane-bound signals. Thus, our results show that fibroblast-induced MC differentiation is induced by direct cell-cell contact and involves both Kit-dependent and Kit-independent pathways. Our findings add to the understanding of how immature mast cells mature in murine skin and encourage further analyses of the underlying mechanisms, which may result in novel targets for the modulation of skin mast cell driven diseases.

Therapeutic vaccination for cancer immunotherapy: antigen selection and clinical responses.

BACKGROUND: Because of its high specificity and low toxicity therapeutic vaccination is considered a desirable treatment for cancer. So far, however, the results of cancer vaccination trials have been disappointing, which is often attributed to the problem identifying appropriate vaccine antigens. Tumorassociated antigens are mostly autoantigens and therefore expected to be subject to immunosuppressive mechanisms. Cancer-testis antigens are the most prominent exception as, still being self, they are physiologically only expressed in immunopriviledged tissues and should therefore not induce autotolerance. This leads to the widely accepted hypothesis that cancer-testis antigens should be more efficient inducers of anti-tumor cellular immune responses than differentiation antigens. Aim of the study was to test this hypothesis by evaluating the published reports on clinical therapeutic vaccination trials for the objective clinical response rates to vaccination with cancer testis antigen vs. differentiation antigens. APPROACH: The results of vaccination clinical trials with cancer testis and/or differentiation antigens published in literature and databanks were analyzed for clinical outcome versus vaccine antigens. 21 publications on cancer testis antigen-based trials in which clinical outcome was reported according to WHO or RECIST were identified and analyzed. RESULTS: The rate of objective responses to cancer testis antigen vaccines in 239 patients was 3.8% and for the 235 patients vaccinated with cancer testis plus 3 differentiation antigens 4.3% compared to 2.6% for the 496 patients vaccinated with differentiation antigens alone. CONCLUSIONS: Cancer testis antigen-based vaccines seem slightly superior over vaccines based on differentiation antigens providing support for the hypothesis.

High yields of stable and highly pure nucleocapsid proteins of different hantaviruses can be generated in the yeast Saccharomyces cerevisiae.

Recently, the high-level expression of authentic and hexahistidine (His)-tagged Puumala (strain Vranica/Hällnäs) hantavirus nucleocapsid protein derivatives in the yeast Saccharomyces cerevisiae has been reported [Dargeviciute et al., Vaccine, 20 (2002) 3523-3531]. Here we describe the expression of His-tagged nucleocapsid proteins of other Puumala virus strains (Sotkamo, Kazan) as well as Dobrava (strains Slovenia and Slovakia) and Hantaan (strain Fojnica) hantaviruses using the same system. All nucleocapsid proteins were expressed in the yeast S. cerevisiae at high levels. The nucleocapsid proteins can be easily purified by nickel chelate chromatography; the yield for all nucleocapsid proteins ranged from 0.5 to 1.5 mg per g wet weight of yeast cells. In general, long-term storage of all nucleocapsid proteins without degradation can be obtained by storage in PBS at -20 degrees C or lyophilization. The nucleocapsid protein of Puumala virus (strain Vranica/Hällnäs) was demonstrated to contain only traces of less than 10 pg nucleic acid contamination per 100 microg of protein. The yeast-expressed nucleocapsid proteins of Hantaan, Puumala and Dobrava viruses described here represent useful tools for serological hantavirus diagnostics and for vaccine development.

Immunosuppressive mechanisms in cancer: consequences for the development of therapeutic vaccines.

Recent investigations revealed strong immunosuppressive mechanisms in tumors that may block anti-tumor T cells and be responsible for failures of immunotherapies. Current attempts to overcome this immunosuppression include blockade of co-inhibitory factors on T cells. Reports from the respective trials indicate that the strategy can improve efficacy of therapeutic vaccination, but at the cost of severe inflammatory and autoimmune reactions. We tried to circumvent tumor-associated immunosuppression by mimotope vaccination to broaden reactive anti-tumor T cell repertoires to include T cells that have not been rendered anergic by the tumor. Initial clinical observations suggest that this strategy bears considerable promise.

A hantavirus nucleocapsid protein segment exposed on hepatitis B virus core particles is highly immunogenic in mice when applied without adjuvants or in the presence of pre-existing anti-core antibodies.

Hepatitis B virus (HBV) core particles carrying the amino-terminal 120 amino acids (aa) of the nucleocapsid (N) protein of the hantaviruses Dobrava, Hantaan or Puumala have been demonstrated to be highly immunogenic in mice when complexed with adjuvants. Here we demonstrate that even without adjuvant, these chimeric particles induced high-titered, and strongly cross-reactive N-specific antibody responses in BALB/c and C57BL/6 mice. The induced N-specific antibodies represented all IgG subclasses. Pre-existing core-specific antibodies did not abrogate the induction of an N-specific immune response by a hantavirus N insert presented on core particles. Therefore, chimeric core particles should represent promising vaccine candidates even for anti-core positive humans.

An amino-terminal segment of hantavirus nucleocapsid protein presented on hepatitis B virus core particles induces a strong and highly cross-reactive antibody response in mice.

Previously, we have demonstrated that hepatitis B virus (HBV) core particles tolerate the insertion of the amino-terminal 120 amino acids (aa) of the Puumala hantavirus nucleocapsid (N) protein. Here, we demonstrate that the insertion of 120 amino-terminal aa of N proteins from highly virulent Dobrava and Hantaan hantaviruses allows the formation of chimeric core particles. These particles expose the inserted foreign protein segments, at least in part, on their surface. Analysis by electron cryomicroscopy of chimeric particles harbouring the Puumala virus (PUUV) N segment revealed 90% T = 3 and 10% T = 4 shells. A map computed from T = 3 shells shows additional density splaying out from the tips of the spikes producing the effect of an extra shell of density at an outer radius compared with wild-type shells. The inserted Puumala virus N protein segment is flexibly linked to the core spikes and only partially icosahedrally ordered. Immunisation of mice of two different haplotypes (BALB/c and C57BL/6) with chimeric core particles induces a high-titered and highly cross-reactive N-specific antibody response in both mice strains.