Oxidation of defined antigens allows protein unfolding and increases both proteolytic processing and exposes peptide epitopes which are recognized by specific T cells

Implications of Post-Translational Modifications in Autoimmunity with Emphasis on Citrullination, Homocitrullination and Acetylation for the Pathogenesis, Diagnosis and Prognosis of Rheumatoid Arthritis

Post-translational modifications (PTMs) influence cellular processes and consequently, their dysregulation is related to the etiologies of numerous diseases. It is widely known that a variety of autoimmune responses in human diseases depend on PTMs of self-proteins. In this review we summarize the latest findings about the role of PTMs in the generation of autoimmunity and, specifically, we address the most relevant PTMs in rheumatic diseases that occur in synovial tissue. Citrullination, homocitrullination (carbamylation) and acetylation are responsible for the generation of Anti-Modified Protein/Peptide Antibodies (AMPAs family), autoantibodies which have been implicated in the etiopathogenesis, diagnosis and prognosis of rheumatoid arthritis (RA). Synthetic peptides provide complete control over the exact epitopes presented as well as the specific positions in their sequence where post-translationally modified amino acids are located and are key to advancing the detection of serological RA biomarkers that could be useful to stratify RA patients in order to pursue a personalized rheumatology. In this review we specifically address the latest findings regarding synthetic peptides post-translationally modified for the specific detection of autoantibodies in RA patients.

Multi-faced roles of reactive oxygen species in anti-tumor T cell immune responses and combination immunotherapy

T cells play a central role in anti-tumor immunity, and reactive oxygen species (ROS) lie at the crossroad on the anti-tumor T cell responses. To activate efficient T cell immunity, a moderate level of ROS is needed, however, excessive ROS would cause toxicity to the T cells, because the improper level leads to the formation and maintenance of an immunosuppressive tumor microenvironment. Up to date, strategies that modulate ROS, either increasing or decreasing, have been widely investigated. Some of them are utilized in anti-tumor therapies, showing inevitable impacts on the anti-tumor T cell immunity with both obverse and reverse sides. Herein, the impacts of ROS-increasing and ROS-decreasing treatments on the T cell responses in the tumor microenvironment are reviewed and discussed. At the same time, outcomes of combination immunotherapies are introduced to put forward inspirations to unleash the potential of immunotherapies.

Impact of Posttranslational Modification in Pathogenesis of Rheumatoid Arthritis: Focusing on Citrullination, Carbamylation, and Acetylation

Rheumatoid arthritis (RA) is caused by prolonged periodic interactions between genetic, environmental, and immunologic factors. Posttranslational modifications (PTMs) such as citrullination, carbamylation, and acetylation are correlated with the pathogenesis of RA. PTM and cell death mechanisms such as apoptosis, autophagy, NETosis, leukotoxic hypercitrullination (LTH), and necrosis are related to each other and induce autoantigenicity. Certain microbial infections, such as those caused by Porphyromonasgingivalis, Aggregatibacter actinomycetemcomitans, and Prevotella copri, can induce autoantigens in RA. Anti-modified protein antibodies (AMPA) containing anti-citrullinated protein/peptide antibodies (ACPAs), anti-carbamylated protein (anti-CarP) antibodies, and anti-acetylated protein antibodies (AAPAs) play a role in pathogenesis as well as in prediction, diagnosis, and prognosis. Interestingly, smoking is correlated with both PTMs and AMPAs in the development of RA. However, there is lack of evidence that smoking induces the generation of AMPAs.

Deciphering the Mechanisms of Improved Immunogenicity of Hypochlorous Acid-Treated Antigens in Anti-Cancer Dendritic Cell-Based Vaccines

Hypochlorous acid (HOCl)-treated whole tumor cell lysates (Ox-L) have been shown to be more immunogenic when used as an antigen source for therapeutic dendritic cell (DC)-based vaccines, improving downstream immune responses both in vitro and in vivo. However, the mechanisms behind the improved immunogenicity are still elusive. To address this question, we conducted a proteomic and immunopeptidomics analyses to map modifications and alterations introduced by HOCl treatment using a human melanoma cell line as a model system. First, we show that one-hour HOCl incubation readily induces extensive protein oxidation, mitochondrial biogenesis, and increased expression of chaperones and antioxidant proteins, all features indicative of an activation of oxidative stress-response pathways. Characterization of the DC proteome after loading with HOCl treated tumor lysate (Ox-L) showed no significant difference compared to loading with untreated whole tumor lysate (FT-L). On the other hand, detailed immunopeptidomic analyses on monocyte-derived DCs (mo-DCs) revealed a great increase in human leukocyte antigen class II (HLA-II) presentation in mo-DCs loaded with Ox-L compared to the FT-L control. Further, 2026 HLA-II ligands uniquely presented on Ox-L-loaded mo-DCs were identified. In comparison, identities and intensities of HLA class I (HLA-I) ligands were overall comparable. We found that HLA-II ligands uniquely presented by DCs loaded with Ox-L were more solvent exposed in the structures of their source proteins, contrary to what has been hypothesized so far. Analyses from a phase I clinical trial showed that vaccinating patients using autologous Ox-L as an antigen source efficiently induces polyfunctional vaccine-specific CD4+ T cell responses. Hence, these results suggest that the increased immunogenicity of Ox-L is, at least in part, due to qualitative and quantitative changes in the HLA-II ligandome, potentially leading to an increased HLA-II dependent stimulation of the T cell compartment (i.e., CD4+ T cell responses). These results further contribute to the development of more effective and immunogenic DC-based vaccines and to the molecular understanding of the mechanism behind HOCl adjuvant properties.

Neutrophils as Sentinel Cells of the Immune System: A Role of the MPO-halide-system in Innate and Adaptive Immunity

For decades, neutrophils were generally regarded as the cells of innate immunity with proinflammatory and phagocytic properties involved in a dual activity, beneficial (antimicrobial) and detrimental (tissue damage). Importantly, until the discovery of toll-like receptors (TLRs), a role of neutrophils in adaptive immunity was limited to the effector stage of humoral response and phagocytosis of opsonized antigens. Moreover, in common opinion, neutrophils, as well as the entire innate immune system, were not functionally associated with adaptive immunity. At the time we demonstrated protein chlorination by HOCl, the major product of neutrophil MPO-halide system enhances protein immunogenicity. Based on this discovery, we proposed, as the first, a new role for neutrophils as APC-accessory cells involved in the induction stage of adaptive immunity. Thereafter, we developed our theory concerning the role of neutrophils as the cells which link innate and adaptive immunity. We proposed that protein modification by HOCl may act as a neutrophildependent molecular tagging system, by which sentinel dendritic cells can faster recognise pathogen- derived antigens. Contemporaneously, it was demonstrated that taurine, the most abundant free amino acid in neutrophil cytosol and the major scavenger of HOCl, is a part of the oxidantantioxidant network and is responsible for the regulation and termination of acute inflammation. Moreover, it has been described, that taurine chloramine (TauCl), the physiological products of the reaction of HOCl with taurine, show anti-microbial and anti-inflammatory properties. In this review, the role of HOCl, taurine and TauCl in innate and adaptive immunity will be discussed.

The other myeloperoxidase: Emerging functions

Myeloperoxidase (MPO) is a member of the mammalian peroxidase family. It is mainly expressed in neutrophils, monocytes and macrophages. As a catalyzer of reactive oxidative species and radical species formation, it contributes to neutrophil bactericidal activity. Nevertheless MPO invalidation does not seem to have major health consequences in affected individuals. This suggests that MPO might have alternative functions supporting its conservation during evolution. We will review the available data supporting these non-canonical functions in terms of tissue specific expression, function and enzymatic activity. Thus, we discuss its cell type specific expression. We review in between others its roles in angiogenesis, endothelial (dys-) function, immune reaction, and inflammation. We summarize its pathological actions in clinical conditions such as cardiovascular disease and cancer.

Immunotherapy with subcutaneous immunogenic autologous tumor lysate increases murine glioblastoma survival

Immunotherapeutic strategies for glioblastoma, the most frequent malignant primary brain tumor, aim to improve its disastrous consequences. On top of the standard treatment, one strategy uses T cell activation by autologous dendritic cells (DC) ex vivo loaded with tumor lysate to attack remaining cancer cells. Wondering whether 'targeting' in vivo DCs could replace these ex vivo ones, immunogenic autologous tumor lysate was used to treat glioma-inoculated mice in the absence of ex vivo loaded DCs. Potential immune mechanisms were studied in two orthotopic, immunocompetent murine glioma models. Pre-tumoral subcutaneous lysate treatment resulted in a survival benefit comparable to subcutaneous DC therapy. Focussing on the immune response, glioma T cell infiltration was observed in parallel with decreased amounts of regulatory T cells. Moreover, these results were accompanied by the presence of strong tumor-specific immunological memory, shown by complete survival of a second glioblastoma tumor, inoculated 100 days after the first one. Finally, in combination with temozolomide, survival of established glioma in mice could be increased. Our results show the potential of immunogenic autologous tumor lysate used to treat murine glioblastoma, which will be worthwhile to study in clinical trials as it has potential as a cost-efficient adjuvant treatment strategy for gliomas.

Exploiting the Immunogenic Potential of Cancer Cells for Improved Dendritic Cell Vaccines

Cancer immunotherapy is currently the hottest topic in the oncology field, owing predominantly to the discovery of immune checkpoint blockers. These promising antibodies and their attractive combinatorial features have initiated the revival of other effective immunotherapies, such as dendritic cell (DC) vaccinations. Although DC-based immunotherapy can induce objective clinical and immunological responses in several tumor types, the immunogenic potential of this monotherapy is still considered suboptimal. Hence, focus should be directed on potentiating its immunogenicity by making step-by-step protocol innovations to obtain next-generation Th1-driving DC vaccines. We review some of the latest developments in the DC vaccination field, with a special emphasis on strategies that are applied to obtain a highly immunogenic tumor cell cargo to load and to activate the DCs. To this end, we discuss the effects of three immunogenic treatment modalities (ultraviolet light, oxidizing treatments, and heat shock) and five potent inducers of immunogenic cell death [radiotherapy, shikonin, high-hydrostatic pressure, oncolytic viruses, and (hypericin-based) photodynamic therapy] on DC biology and their application in DC-based immunotherapy in preclinical as well as clinical settings.

Irradiation of necrotic cancer cells, employed for pulsing dendritic cells (DCs), potentiates DC vaccine-induced antitumor immunity against high-grade glioma

Dendritic cell (DC)-based immunotherapy has yielded promising results against high-grade glioma (HGG). However, the efficacy of DC vaccines is abated by HGG-induced immunosuppression and lack of attention toward the immunogenicity of the tumor lysate/cells used for pulsing DCs. A literature analysis of DC vaccination clinical trials in HGG patients delineated the following two most predominantly applied methods for tumor lysate preparation: freeze-thaw (FT)-induced necrosis or FT-necrosis followed by X-ray irradiation. However, from the available clinical evidence, it is unclear which of both methodologies has superior immunogenic potential. Using an orthotopic HGG murine model (GL261-C57BL/6), we observed that prophylactic vaccination with DCs pulsed with irradiated FT-necrotic cells (compared to FT-necrotic cells only) prolonged overall survival by increasing tumor rejection in glioma-challenged mice. This was associated, both in prophylactic and curative vaccination setups, with an increase in brain-infiltrating Th1 cells and cytotoxic T lymphocytes (CTL), paralleled by a reduced accumulation of regulatory T cells, tumor-associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC). Further analysis showed that irradiation treatment of FT-necrotic cells considerably increased the levels of carbonylated proteins — a surrogate-marker of oxidation-associated molecular patterns (OAMPs). Through further application of antioxidants and hydrogen peroxide, we found a striking correlation between the amount of lysate-associated protein carbonylation/OAMPs and DC vaccine-mediated tumor rejection capacity thereby suggesting for the first time a role for protein carbonylation/OAMPs in at least partially mediating antitumor immunity. Together, these data strongly advocate the use of protein oxidation-inducing modalities like irradiation for increasing the immunogenicity of tumor lysate/cells used for pulsing DC vaccines.

Personalized approaches to active immunotherapy in cancer

Immunotherapy is emerging as a promising anti-cancer curative modality. However, in contrast to recent advances obtained employing checkpoint blockade agents and T cell therapies, clinical efficacy of therapeutic cancer vaccines is still limited. Most vaccination attempts in the clinic represent "off-the shelf" approaches since they target common "self" tumor antigens, shared among different patients. In contrast, personalized approaches of vaccination are tailor-made for each patient and in spite being laborious, hold great potential. Recent technical advancement enabled the first steps in the clinic of personalized vaccines that target patient-specific mutated neo-antigens. Such vaccines could induce enhanced tumor-specific immune response since neo-antigens are mutation-derived antigens that can be recognized by high affinity T cells, not limited by central tolerance. Alternatively, the use of personalized vaccines based on whole autologous tumor cells, overcome the need for the identification of specific tumor antigens. Whole autologous tumor cells could be administered alone, pulsed on dendritic cells as lysate, DNA, RNA or delivered to dendritic cells in-vivo through encapsulation in nanoparticle vehicles. Such vaccines may provide a source for the full repertoire of the patient-specific tumor antigens, including its private neo-antigens. Furthermore, combining next-generation personalized vaccination with other immunotherapy modalities might be the key for achieving significant therapeutic outcome.

Citrullination and autoimmunity

Autoimmune diseases are characterized by the body's own immune system attack to the self-tissues, a condition enabled, in predisposed subjects, by the reduction of self-tolerance. A central role has been recently recognized to post-translational modifications, since they can promote generation of neo-(auto)antigens and in turn an autoimmune response. During the last years great attention has been paid to citrullination, because of its role in inducing anti-citrullinated proteins/peptide antibodies (ACPA), a class of autoantibodies with diagnostic, predictive and prognostic value for Rheumatoid Arthritis (RA). Nonetheless, citrullination has been reported to be a process present in a wide range of inflammatory tissues. Indeed, citrullinated proteins have been detected also in other inflammatory arthritides and in inflammatory conditions other than arthritides (polymyositis, inflammatory bowel disease and chronic tonsillitis). Moreover, environmental exposure to cigarette smoke and nanomaterials of air pollution may be able to induce citrullination in lung cells prior to any detectable onset of inflammatory responses, suggesting that protein citrullination could be considered as a sign of early cellular damage. Accordingly, citrullination seems to be implicated in all those para-physiological processes, such as cells death pathways, in which intracellular calcium concentration raises to higher levels than in physiologic conditions: hence, peptidylarginine deiminases enzymes are activated during apoptosis, autophagy and NETosis, processes which are well-known to be implicated in autoimmunity. Taken together, these data support the hypothesis that rather than being a disease-dependent process, citrullination is an inflammatory-dependent condition that plays a central role in autoimmune diseases.

Diazoxide attenuates autoimmune encephalomyelitis and modulates lymphocyte proliferation and dendritic cell functionality

Activation of mitochondrial ATP-sensitive potassium (KATP) channels is postulated as an effective mechanism to confer cardio and neuroprotection, especially in situations associated to oxidative stress. Pharmacological activation of these channels inhibits glia-mediated neuroinflammation. In this way, diazoxide, an old-known mitochondrial KATP channel opener, has been proposed as an effective and safe treatment for different neurodegenerative diseases, demonstrating efficacy in different animal models, including the experimental autoimmune encephalomyelitis (EAE), an animal model for Multiple Sclerosis. Although neuroprotection and modulation of glial reactivity could alone explain the positive effects of diazoxide administration in EAE mice, little is known of its effects on the immune system and the autoimmune reaction that triggers the EAE pathology. The aim of the present work was to study the effects of diazoxide in autoimmune key processes related with EAE, such as antigen presentation and lymphocyte activation and proliferation. Results show that, although diazoxide treatment inhibited in vitro and ex-vivo lymphocyte proliferation from whole splenocytes it had no effect in isolated CD4(+) T cells. In any case, treatment had no impact in lymphocyte activation. Diazoxide can also slightly decrease CD83, CD80, CD86 and major histocompatibility complex class II expression in cultured dendritic cells, demonstrating a possible role in modulating antigen presentation. Taken together, our results indicate that diazoxide treatment attenuates autoimmune encephalomyelitis pathology without immunosuppressive effect.

A dendritic cell vaccine pulsed with autologous hypochlorous acid-oxidized ovarian cancer lysate primes effective broad antitumor immunity: from bench to bedside

PURPOSE

Whole tumor lysates are promising antigen sources for dendritic cell (DC) therapy as they contain many relevant immunogenic epitopes to help prevent tumor escape. Two common methods of tumor lysate preparations are freeze-thaw processing and UVB irradiation to induce necrosis and apoptosis, respectively. Hypochlorous acid (HOCl) oxidation is a new method for inducing primary necrosis and enhancing the immunogenicity of tumor cells.

EXPERIMENTAL DESIGN

We compared the ability of DCs to engulf three different tumor lysate preparations, produce T-helper 1 (TH1)-priming cytokines and chemokines, stimulate mixed leukocyte reactions (MLR), and finally elicit T-cell responses capable of controlling tumor growth in vivo.

RESULTS

We showed that DCs engulfed HOCl-oxidized lysate most efficiently stimulated robust MLRs, and elicited strong tumor-specific IFN-γ secretions in autologous T cells. These DCs produced the highest levels of TH1-priming cytokines and chemokines, including interleukin (IL)-12. Mice vaccinated with HOCl-oxidized ID8-ova lysate-pulsed DCs developed T-cell responses that effectively controlled tumor growth. Safety, immunogenicity of autologous DCs pulsed with HOCl-oxidized autologous tumor lysate (OCDC vaccine), clinical efficacy, and progression-free survival (PFS) were evaluated in a pilot study of five subjects with recurrent ovarian cancer. OCDC vaccination produced few grade 1 toxicities and elicited potent T-cell responses against known ovarian tumor antigens. Circulating regulatory T cells and serum IL-10 were also reduced. Two subjects experienced durable PFS of 24 months or more after OCDC.

CONCLUSIONS

This is the first study showing the potential efficacy of a DC vaccine pulsed with HOCl-oxidized tumor lysate, a novel approach in preparing DC vaccine that is potentially applicable to many cancers.

A Phase I vaccine trial using dendritic cells pulsed with autologous oxidized lysate for recurrent ovarian cancer

Purpose

Ovarian cancer, like most solid tumors, is in dire need of effective therapies. The significance of this trial lies in its promise to spearhead the development of combination immunotherapy and to introduce novel approaches to therapeutic immunomodulation, which could enable otherwise ineffective vaccines to achieve clinical efficacy.

Rationale

Tumor-infiltrating T cells have been associated with improved outcome in ovarian cancer, suggesting that activation of antitumor immunity will improve survival. However, molecularly defined vaccines have been generally disappointing. Cancer vaccines elicit a modest frequency of low-to-moderate avidity tumor-specific T-cells, but powerful tumor barriers dampen the engraftment, expansion and function of these effector T-cells in the tumor, thus preventing them from reaching their full therapeutic potential. Our work has identified two important barriers in the tumor microenvironment: the blood-tumor barrier, which prevents homing of effector T cells, and T regulatory cells, which inactivate effector T cells. We hypothesize that cancer vaccine therapy will benefit from combinations that attenuate these two barrier mechanisms.

Design

We propose a three-cohort sequential study to investigate a combinatorial approach of a new dendritic cell (DC) vaccine pulsed with autologous whole tumor oxidized lysate, in combination with antiangiogenesis therapy (bevacizumab) and metronomic cyclophosphamide, which impacts Treg cells.

Innovation

This study uses a novel autologous tumor vaccine developed with 4-day DCs pulsed with oxidized lysate to elicit antitumor response. Furthermore, the combination of bevacizumab with a whole tumor antigen vaccine has not been tested in the clinic. Finally the combination of bevacizumab and metronomic cyclophosphamide in immunotherapy is novel.

HOCl oxidation-modified CT26 cell vaccine inhibits colon tumor growth in a mouse model

Despite progress in elucidating mechanisms associated with colorectal cancer and improvement of treatment methods, it remains a frequent cause of death worldwide. New and more effective therapies are therefore urgently needed. Recent studies have shown that immunogenicity of whole ovarian tumor cells and subsequent T cell response were potentiated by oxidation modification with hypochlorous acid (HOCl) in vitro and ex vivo. These results prompted us to investigate the protective antitumor response with an HOCl treated CT26 colorectal cancer cell vaccine in an in vivo mouse model. Administration of HOCl modified vaccine triggered robust antitumor immunity to autologous tumor cells in mice and prolonged survival period significantly. In addition, increased necrosis and apoptosis were found in tumor tissue from the oxidation group. Interestingly, ELISPOT assays showed that specific T cell responses were not elicited in response to the immunizing cellular antigen, in contrast to raising sera antibody titer and antibody binding activity shown by ELISA assay and flow cytometry. Further evaluation of the mechanisms underlying HOCl modified vaccine mediated humoral immunity highlighted the role of antibody-dependent cell-mediated cytotoxicity. These results combined with previous studies suggest that HOCl oxidation modified whole cell vaccine has wide applicability as a cancer vaccine because it can target both T cell- and B cell-specific responses. It may thus represent a promising approach for the immunotherapy of colorectal cancer.

In vivo relevance of citrullinated proteins and the challenges in their detection

Citrullination is a posttranslational modification of arginine. It plays both a physiological role, for instance during apoptosis and epigenetics, and a pathological role in cancer or diseases of the central nervous system. Most research on citrullination to date focuses on its role in auto-immune diseases such as multiple sclerosis and rheumatoid arthritis. In this context, the exact knowledge of citrullination sites in a protein can provide invaluable information about the etiological importance of these citrullinated proteins. However, few techniques exist that can accurately detect citrullination on the peptide level. This review aims to give an overview of the different methods available to date for the detection of citrullinated proteins and peptides. These include 2D-SDS-PAGE and immunodetection, as well as specific mass spectrometry (MS) approaches, both labeled and unlabeled. These MS approaches have been developed to pinpoint the exact location of citrullination on the peptide level. Improving the currently existing detection strategies while focusing on the role of citrullinated proteins will be invaluable to elucidate the importance of this posttranslational modification in vivo.

Neutrophil myeloperoxidase: soldier and statesman

Myeloperoxidase (MPO) is a major protein constituent of the primary granules of vertebrate neutrophils. It catalyses the hydrogen peroxide-mediated oxidation of halide ions to hypohalous acids, especially HOCl. These reactive oxygen species can participate in a variety of secondary reactions, leading to modifications of amino acids and many types of biological macromolecules. The classic paradigm views MPO as a component of the phagocyte oxygen-dependent intracellular microbicidal system, and thus an important arm of the effector phase of innate immune responses. However, the limited immunodeficiency associated with lack of MPO in mouse and human models has challenged this paradigm. In this review we examine more recent information on the interaction between MPO, its bioreactive reaction products, and targets within the inflammatory microenvironment. We propose that two assumptions of the current model may require revisiting. First, many important targets of MPO modification are extracellular, rather than present only within the phagolysosome, such as various components of neutrophil extracellular traps. Second, we suggest that the pro-inflammatory pathological role of MPO may be a particular feature of chronic inflammation. In the physiological setting of acute neutrophil-mediated inflammation MPO may also form part of a negative feedback loop which down-regulates inflammation, limits tissue damage, and facilitates the switch from innate to adaptive immunity. This different perspective on this well-studied enzyme may usefully inform further research into its function in health and disease.

Adjuvants for enhancing the immunogenicity of whole tumor cell vaccines

Whole tumor cell lysates can serve as excellent multivalent vaccines for priming tumor-specific CD8(+) and CD4(+) T cells. Whole cell vaccines can be prepared with hypochlorous acid oxidation, UVB-irradiation and repeat cycles of freeze and thaw. One major obstacle to successful immunotherapy is breaking self-tolerance to tumor antigens. Clinically approved adjuvants, including Montanide™ ISA-51 and 720, and keyhole-limpet proteins can be used to enhance tumor cell immunogenicity by stimulating both humoral and cellular anti-tumor responses. Other potential adjuvants, such as Toll-like receptor agonists (e.g., CpG, MPLA and PolyI:C), and cytokines (e.g., granulocyte-macrophage colony stimulating factor), have also been investigated.

Impact of product-related factors on immunogenicity of biotherapeutics

All protein therapeutics have the potential to be immunogenic. Several factors, including patient characteristics, disease state, and the therapy itself, influence the generation of an immune response. Product-related factors such as the molecule design, the expression system, post-translational modifications, impurities, contaminants, formulation and excipients, container, closure, as well as degradation products are all implicated. However, a critical examination of the available data shows that clear unequivocal evidence for the impact of these latter factors on clinical immunogenicity is lacking. No report could be found that clearly deconvolutes the clinical impact of the product attributes on patient susceptibility. Aggregation carries the greatest concern as a risk factor for immunogenicity, but the impact of aggregates is likely to depend on their structure as well as on the functionality (e.g., immunostimulatory or immunomodulatory) of the therapeutic. Preclinical studies are not yet capable of assessing the clinically relevant immunogenicity potential of these product-related factors. Simply addressing these risk factors as part of product development will not eliminate immunogenicity. Minimization of immunogenicity has to begin at the molecule design stage by reducing or eliminating antigenic epitopes and building in favorable physical and chemical properties.

Whole tumor antigen vaccines

Although cancer vaccines with defined antigens are commonly used, the use of whole tumor cell preparations in tumor immunotherapy is a very promising approach and can obviate some important limitations in vaccine development. Whole tumor cells are a good source of TAAs and can induce simultaneous CTLs and CD4(+) T helper cell activation. We review current approaches to prepare whole tumor cell vaccines, including traditional methods of freeze-thaw lysates, tumor cells treated with ultraviolet irradiation, and RNA electroporation, along with more recent methods to increase tumor cell immunogenicity with HOCl oxidation or infection with replication-incompetent herpes simplex virus.

Malondialdehyde modification of myelin oligodendrocyte glycoprotein leads to increased immunogenicity and encephalitogenicity

Self proteins may become autoantigenic through structural modification. We studied malondialdehydation of recombinant rat (rr) myelin oligodendrocyte glycoprotein (MOG), an autoantigen in multiple sclerosis. Malondialdehyde (MDA) modification changed protein weight and charge, the location of these adducts being mapped by Fourier transform ion cyclotron resonance. Molecular modelling revealed significant differences in the MDA-rrMOG three-dimensional structure. DBA/1 mice immunised with MDA-rrMOG developed greater proliferative responses and more severe experimental autoimmune encephalomyelitis than mice immunised with unmodified rrMOG. MDA-rrMOG was taken up more effectively by antigen-presenting cells (APC), at least partially through scavenger receptors. Exposure to MDA-rrMOG led to increased expression of IL-23, IL-12 and IL-12R, indicating a role not only for increased antigen uptake but also for activation of APC. We thus provide biochemical, structural, immunological and clinical data that suggest that the post-translationally modified form of this myelin autoantigen is a more relevant form of the molecule.

House dust and forage mite allergens and their role in human and canine atopic dermatitis

This article reviews the literature regarding the role of house dust and forage mite allergens in canine atopic dermatitis. The presence of immunoglobulin E (IgE) to these mites, especially to Dermatophagoides farinae, is common in both normal and atopic dogs. Exposure of dogs to the different mites is described both in the direct environment and in the coat of animals for house dust mites and in the food for forage mites. Allergens causing allergic disease in dogs seem to be different from those in humans. Dogs seem to react to high molecular weight allergens, compared to the low molecular weight group 1 and group 2 proteases that are commonly implicated in humans with atopic diseases. Despite numerous published studies dealing with this subject, a number of questions still need to be addressed to better understand the exact role of these mites in the pathogenesis of canine atopic dermatitis and to improve the quality of the allergens used in practice.

Arthritogenicity of collagen type II is increased by chlorination

During inflammation, activated neutrophils, monocytes and macrophages produce and release myeloperoxidase (MPO). MPO converts hydrogen peroxide to hypochlorous acid, a highly reactive and oxidizing agent. Proteins subjected to hypochlorous acid become chlorinated. We analysed how chlorination of the cartilage antigen collagen type II (CII) affects its immunogenic and arthritogenic properties by studying immune responses to chlorinated CII in comparison to immune responses to CII and by studying the development of arthritis in rats immunized with CII-Cl. CII-Cl immunization of LEW.1AV1 rats caused a 100% incidence of arthritis with a mean maximum score of 9.2 (maximal score possible 16). The same dose of non-chlorinated CII did not induce arthritis at all. Rats immunized with CII-Cl developed high anti-CII-Cl IgG titres and also developed IgG antibodies recognizing the non-chlorinated form of CII. Analysis of cytokine mRNA expression in lymph nodes 10 days after immunzation revealed an increased expression of interferon (IFN)-gamma mRNA and interleukin (IL)-1beta mRNA in CII-Cl-immunized rats compared to CII-immunized rats. Thus, chlorination of CII increased its immunogenicity as well as its arthritogenicity. As neutrophils, monocytes and macrophages are abundant cells in arthritic joints of patients with rheumatoid arthritis, chlorination might be a mechanism by which immunoreactivity to CII is induced and by which chronic joint inflammation is supported.

Immunogenicity of a Yersinia pestis vaccine antigen monomerized by circular permutation

Caf1, a chaperone-usher protein from Yersinia pestis, is a major protective antigen in the development of subunit vaccines against plague. However, recombinant Caf1 forms polymers of indeterminate size. We report the conversion of Caf1 from a polymer to a monomer by circular permutation of the gene. Biophysical evaluation confirmed that the engineered Caf1 was a folded monomer. We compared the immunogenicity of the engineered monomer with polymeric Caf1 in antigen presentation assays to CD4 T-cell hybridomas in vitro, as well as in the induction of antibody responses and protection against subcutaneous challenge with Y. pestis in vivo. In C57BL/6 mice, for which the major H-2(b)-restricted immunodominant CD4 T-cell epitopes were intact in the engineered monomer, immunogenicity and protective efficacy were preserved, although antibody titers were decreased 10-fold. Disruption of an H-2(d)-restricted immunodominant CD4 T-cell epitope during circular permutation resulted in a compromised T-cell response, a low postvaccination antibody titer, and a lack of protection of BALB/c mice. The use of circular permutation in vaccine design has not been reported previously.

Reactive oxygen species are essential mediators in antigen presentation by Kupffer cells

Kupffer cells (KC) act as APC in the liver and play a major role in the clearance of gut-derived antigens and pathogens entering the liver with portal venous blood. Antigen presentation by KC has been implicated in regulation of the local and systemic immune responses. In this study, modulation of KC antigen presentation by antioxidants and the role of reactive oxygen species (ROS) as essential mediators of antigen presentation in KC were investigated. Co-culture of KC with ovalbumin (OVA) antigens resulted in upstream intracellular endogenous ROS generation and increased expression of MHC class II and costimulator molecules, and consequent OVA-specific CD4(+) T-cell proliferation in response to antigen presentation by KC. Scavenging of KC ROS by antioxidants, or blocking of KC ROS generation by specific inhibitors of NADPH oxidase and/or xanthine oxidase, or by specific inhibitors of the mitochondrial electron transport chain, significantly decreased OVA-specific T-cell proliferation in response to antigen presentation by KC. Increased expression of MHC class II and costimulatory molecules in KC pulsed with OVA antigens was blocked by inhibiting ROS generation enzymatically. Intracellular endogenous ROS generation during antigen processing may therefore provide essential secondary signalling for KC antigen presentation.

Major histocompatibility class II molecules prevent destructive processing of exogenous peptides at the cell surface of macrophages for presentation to CD4 T cells

We studied factors affecting major histocompatibility complex class II (MHC-II)-restricted presentation of exogenous peptides at the surface of macrophages. We have previously shown that peptide presentation is modulated by surface-associated proteolytic enzymes, and in this report the role of the binding of MHC-II molecules in preventing proteolysis of exogenous synthetic peptides was addressed. Two peptides containing CD4 T-cell epitopes were incubated with fixed macrophages expressing binding and non-binding MHC-II, and supernatants were analysed by high-performance liquid chromatography and mass spectrometry to monitor peptide degradation. The proportion of full-length peptides that were degraded and the number of peptide fragments increased when non-binding macrophages were used, leading to reduction in peptide presentation. When MHC-II molecules expressed on the surface of fixed macrophages were blocked with monoclonal antibody and incubated with peptides and the supernatants were transferred to fixed macrophages, a significant reduction in peptide presentation was observed. Peptide presentation was up-regulated at pH 5.5 compared to neutral pH, and the latter was found to be the pH optimum of the proteolytic activity of the surface enzymes involved in the degradation of exogenous peptides and proteins. The data suggest that MHC-II alleles that bind peptides protect them from degradation at the antigen-presenting cell surface for presentation to CD4 T cells and we argue that this mechanism could be particularly pronounced at sites of inflammation.

Inhibition of MHC II gene transcription by nitric oxide and antioxidants

MHC class II molecules are expressed on the surface of antigen presenting cells and are loaded with peptides processed from the phagosomal compartment of these cells. Such complexes interact with the CD4 positive T lymphocyte receptor for antigen and a strong interaction is followed by T cell activation and proliferation. As class II expression is critical for antigen specific immunity its expression mostly restricted to a few cell types but can be induced on others in response to interferon gamma. This expansion of antigen presenting ability plays a role in increasing the duration and intensity of the immune response. Nitric oxide and antioxidants attenuate this class II induction through negative effects on the induction of class II transactivator protein expression and on the binding of transcription factor NF-Y to the class II promoter.

Alteration of an Autoantigen by Chlorination, a Process Occurring During Inflammation, Can Overcome Adaptive Immune Tolerance

Autoimmune diseases are characterized by chronic inflammation in target organs and immunoreactivity towards one or multiple autoantigens. Several potential mechanisms of tolerance breaking have been postulated, one being inflammation-associated events. We have investigated whether chlorination of an autoantigen can lead to disruption of self-tolerance. Chlorination of antigens might occur during inflammation via the granulocyte-specific, myeloperoxidase-catalysed conversion of hydrogen peroxide to hypochlorous acid (HOCl). HOCl, being a strong oxidant, reacts with proteins both within cellular phagosomes and in the immediate extracellular environment. By immunizing Lew.1AV1 rats with chlorinated or unmodified rat serum albumin (RSA), we could detect tolerance-breaking effects of chlorination. RSA is a systemic autoantigen in rat not inducing antibody production upon immunization in its unmodified form. Rats immunized with chlorinated RSA (RSA-Cl) developed high titres of immunoglobulin G (IgG) specific for RSA-Cl which cross-reacted with native RSA. T cells reactive with both RSA-Cl and RSA were detected by [(3)H]-thymidine incorporation. We hence speculated that immunological tolerance established for unmodified proteins, during certain circumstances such as inflammation, might be broken by induced protein chlorination. T cells specific for the chlorinated protein can confer help to B cells recognizing both the chlorinated and the native form of the protein, leading to the formation of high-affinity autoreactive antibodies and possibly autoimmune disease.

Differential processing of CD4 T-cell epitopes from the protective antigen of Bacillus anthracis

We have mapped CD4+ T-cell epitopes located in three domains of the recombinant protective antigen of Bacillus anthracis. Mouse T-cell hybridomas specific for these epitopes were generated to study the mechanisms of proteolytic processing of recombinant protective antigen for antigen presentation by bone marrow-derived macrophages. Overall, epitopes differed considerably in their processing requirements. In particular, the kinetics of presentation, ranging from 15 (fast) to 120 min (slow), suggested sequential liberation of epitopes during proteolytic processing of the intact PA molecule. Pretreatment of macrophages with ammonium chloride or inhibitors of the major enzyme families showed that T-cell responses to an epitope presented with fast kinetics were unaffected by raising endosomal pH or inhibiting cysteine or aspartic proteinases, suggesting presentation independent of lysosomal processing. In contrast, responses to epitopes presented with slower kinetics were dependent on low pH and the activity of cysteine or aspartic proteinases indicating a requirement for lysosomal processing. In addition, responses to all epitopes, whether their presentation was dependent on low pH or not, were prevented by treatment of macrophages with broad spectrum serine proteinase inhibitors. Thus, our data are consistent with a model of sequential antigen processing within the endosomal system, beginning with a pre-processing step mediated by serine or metalloproteinases prior to further processing by lysosomal enzymes. Rapidly presented epitopes seemed to require only limited proteolysis at earlier stages of endocytosis, whereas the majority of epitopes required more extensive processing by neutral proteinases followed by lysosomal enzymes.

Diversity in MHC class II antigen presentation

Processing exogenous and endogenous proteins for presentation by major histocompatibility complex (MHC) molecules to T cells is the defining function of antigen-presenting cells (APC) as major regulatory cells in the acquired immune response. MHC class II-restricted antigen presentation to CD4 T cells is achieved by an essentially common pathway that is subject to variation with regard to the location and extent of degradation of protein antigens and the site of peptide binding to MHC class II molecules. These subtle variations reveal a surprising flexibility in the ways a diverse peptide repertoire is displayed on the APC surface. This diversity may have profound consequences for the induction of immunity to infection and tumours, as well as autoimmunity and tolerance.

Characterisation of major and minor Dermatophagoides allergens in canine atopic dermatitis

Atopic dermatitis is a well-recognised chronic inflammatory skin disease of humans and dogs. Most atopic dogs are sensitised to Dermatophagoides mites. The aim of this study was to characterise allergens in different Dermatophagoides species using polyclonal and monoclonal antibodies to canine IgE. Western blots were prepared from crude extracts of D farinae, D pteronyssinus and D microceras, and purified group 1 and 2 allergens under reducing and non-reducing conditions. They were probed with sera from atopic (n = 33) and healthy (n = 27) dogs. There was no significant difference in the sensitivity or specificity between the polyclonal and monoclonal sera in detecting Dermatophagoides -specific IgE. Major allergens common to both D farinae and D pteronyssinus were detected at 97-98 kDa, 103-104 kDa and 134-139 kDa on both reducing and non-reducing blots. Major allergens at 84-85 kDa, 65-69 kDa and 44-45 kDa were only recognised on reducing blots, suggesting that these are fragments of the larger allergens. Only a few sera recognised group 1 or 2 allergens on blots of crude extracts or purified allergens. These results confirm that, in atopic dogs, high molecular weight allergens are the most important Dermatophagoides allergens, rather than the low molecular weight group 1 and 2 proteins.

The contribution of both oxygen and nitrogen intermediates to the intracellular killing mechanisms of C1q-opsonized Listeria monocytogenes by the macrophage-like IC-21 cell line

Listeria monocytogenes is a facultative intracellular pathogen which is internalized by host mammalian cells upon binding to their surface. Further listerial growth occurs in the cytosol after escape from the phagosomal-endosomal compartment. We have previously reported that C1q is able to potentiate L. monocytogenes phagocytosis upon bacterial opsonization by ingestion through C1q-binding structures. In this report, we analysed the post-phagocytic events upon internalization of C1q-opsonized L. monocytogenes and found an induction of macrophage (Mphi)-like IC-21 cell bactericidal mechanisms displayed by the production of oxygen and nitrogen metabolites. Both types of molecules are effective in L. monocytogenes killing. Further analysis of the cellular responses promoted by interaction of C1q with its surface binding structures, leads us to consider C1q as a collaborative molecule involved in Mphi activation. Upon interaction with surface binding structures, C1q was able to trigger and/or amplify the production of reactive oxygen and nitrogen intermediates induced by stimuli such as interferon-gamma and L. monocytogenes phagocytosis.

Accessory molecules for MHC class II peptide loading

Accessory molecules, such as HLA-DM and invariant chain, modulate the ligands bound to MHC class II molecules in antigen-presenting cells. Recent investigations, including gene targeting experiments, have shed light on the functions of these molecules, their mechanisms of action, interactions with class II molecules, and the relationships with associated molecules such as tetraspanins and HLA-DO.

Reactive Oxygen Intermediates During Programmed Cell Death Induced in the Thymus of the Ts(1716)65Dn Mouse, a Murine Model for Human Down’s Syndrome

Down’s syndrome (DS) is one of the most frequent genetic disorders in humans. It has been suggested that overexpression of copper-zinc superoxide dismutase (SOD-1) in DS may be involved in some of the abnormalities observed, mainly neurodegenerative and immunopathological processes. One of the consequences is early thymic involution. Recently, Ts(1716)65Dn mice (Ts65Dn mice), made segmentally trisomic for a chromosome 16 segment, fulfill the criteria for a DS model. To study the possible role of SOD-1 overexpression in thymocyte biology, we analyzed the role of reactive oxygen intermediates during in vivo and in vitro programmed cell death (PCD) induced in the thymus of Ts65Dn mice. Our main findings can be summarized as follows. Ts65Dn thymuses exhibit greater PCD activity than controls, as ascertained by a combination of morphological, histochemical, and ultrastructural procedures. Ts65Dn thymocytes were highly susceptible to PCD induced by both LPS (in vivo) and dexamethasone, a synthetic glucocorticoid agonist (both in vivo and in vitro). Thymus abnormalities were probably caused by SOD-1 hyperexpression in Ts65Dn cells, in that reactive oxygen intermediate generation (specifically H2O2 production) is enhanced in thymocytes and clearly correlates with apoptosis. Similarly, oxidative injury correlated with the formation of lipid peroxidation by-products and antioxidants which partly inhibit PCD in thymocytes.