Enhancement of immunogenic properties of ovalbumin as a result of its chlorination

Activation of Cellular Players in Adaptive Immunity via Exogenous Delivery of Tumor Cell Lysates

Tumor cell lysates (TCLs) are a good immunogenic source of tumor-associated antigens. Since whole necrotic TCLs can enhance the maturation and antigen-presenting ability of dendritic cells (DCs), multiple strategies for the exogenous delivery of TCLs have been investigated as novel cancer immunotherapeutic solutions. The TCL-mediated induction of DC maturation and the subsequent immunological response could be improved by utilizing various material-based carriers. Enhanced antitumor immunity and cancer vaccination efficacy could be eventually achieved through the in vivo administration of TCLs. Therefore, (1) important engineering methodologies to prepare antigen-containing TCLs, (2) current therapeutic approaches using TCL-mediated DC activation, and (3) the significant sequential mechanism of DC-based signaling and stimulation in adaptive immunity are summarized in this review. More importantly, the recently reported developments in biomaterial-based exogenous TCL delivery platforms and co-delivery strategies with adjuvants for effective cancer vaccination and antitumor effects are emphasized.

Rational Vaccinology: Harnessing Nanoscale Chemical Design for Cancer Immunotherapy

Cancer immunotherapy is a powerful treatment strategy that mobilizes the immune system to fight disease. Cancer vaccination is one form of cancer immunotherapy, where spatiotemporal control of the delivery of tumor-specific antigens, adjuvants, and/or cytokines has been key to successfully activating the immune system. Nanoscale materials that take advantage of chemistry to control the nanoscale structural arrangement, composition, and release of immunostimulatory components have shown significant promise in this regard. In this Outlook, we examine how the nanoscale structure, chemistry, and composition of immunostimulatory compounds can be modulated to maximize immune response and mitigate off-target effects, focusing on spherical nucleic acids as a model system. Furthermore, we emphasize how chemistry and materials science are driving the rational design and development of next-generation cancer vaccines. Finally, we identify gaps in the field that should be addressed moving forward and outline future directions to galvanize researchers from multiple disciplines to help realize the full potential of this form of cancer immunotherapy through chemistry and rational vaccinology.

Spherical Nucleic Acids as Precision Therapeutics for the Treatment of Cancer-From Bench to Bedside

Spherical Nucleic Acids (SNAs) emerged as a new class of nanotherapeutics consisting of a nanoparticle core densely functionalized with a shell of radially oriented synthetic oligonucleotides. The unique three-dimensional architecture of SNAs protects the oligonucleotides from nuclease-mediated degradation, increases oligonucleotide bioavailability, and in the absence of auxiliary transfection agents, enables robust uptake into tumor and immune cells through polyvalent association with cell surface pattern recognition receptors. When composed of gene-regulatory small interfering (si)RNA or immunostimulatory DNA or RNA oligonucleotides, SNAs silence gene expression and induce immune responses superior to those raised by the oligonucleotides in their "free" form. Early phase clinical trials of gene-regulatory siRNA-based SNAs in glioblastoma (NCT03020017) and immunostimulatory Toll-like receptor 9 (TLR9)-agonistic SNAs carrying unmethylated CpG-rich oligonucleotides in solid tumors (NCT03086278) have shown that SNAs represent a safe, brain-penetrant therapy for inhibiting oncogene expression and stimulating immune responses against tumors. This review focuses on the application of SNAs as precision cancer therapeutics, summarizes the findings from first-in-human clinical trials of SNAs in solid tumors, describes the most recent preclinical efforts to rationally design next-generation multimodal SNA architectures, and provides an outlook on future efforts to maximize the anti-neoplastic activity of the SNA platform.

Secretions from hypochlorous acid-treated tumor cells delivered in a melittin hydrogel potentiate cancer immunotherapy

Autologous tumor cells and cell-derived secretions (CDS) can induce antitumor immune responses. The conditions in which cells are cultured and treated impact CDS, and cellular insults alter their composition and function. In this study, we generated CDS from tumor cells exposed to normal culture conditions, hypoxia, cisplatin, radiotherapy, photodynamic therapy, or hypochlorous acid (HOCl). In vitro HOCl-CDS showed the strongest stimulatory effects on dendritic cells and macrophages compared to CDS generated by hypoxia, cisplatin, radiotherapy or photodynamic therapy. To improve HOCl-CDS activity at the tumor site, we loaded HOCl-CDS into a melittin-encapsulated hydrogel scaffold. When injected intratumorally, the HOCl-CDS hydrogel promoted tumor cell death, cytotoxic T lymphocyte infiltration, and tumor-associated macrophage reprogramming towards an M1 phenotype. The hydrogel inhibited tumor growth and prolonged the survival of mice bearing B16–F10 melanoma. Furthermore, hydrogel-delivered HOCl-CDS augmented the antitumor effects of immune checkpoint blockade. These results underscore the importance of the CDS generation method and delivery approach for improving cancer immunotherapy.

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HOCl-treated tumor cell-derived secretions (HOCl-CDS) is a robust immune-stimulator on dendritic cells and macrophages.

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A multifunctional HOCl-CDS hydrogel was developed by loading HOCl-CDS into a melittin-encapsulated hydrogel scaffold.

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HOCl-CDS hydrogel promoted tumor cell death, cytotoxic T lymphocyte infiltration and M1-TAM polarization in mice.

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HOCl-CDS hydrogel synergistically augmented the therapeutic effect of anti-PD-1 and further potentiated cancer immunotherapy.

Polymer Nanoparticle-Mediated Delivery of Oxidized Tumor Lysate-Based Cancer Vaccines

Cancer vaccination is a powerful strategy to combat cancer. A very attractive approach to prime the immune system against cancer cells involves the use of tumor lysate as antigen source. The immunogenicity of tumor lysate can be further enhanced by treatment with hypochlorous acid. This study explores poly(lactic-co-glycolic acid) (PLGA) nanoparticles to enhance the delivery of oxidized tumor lysate to dendritic cells. Using human donor-derived dendritic cells, it is found that the use of PLGA nanoparticles enhances antigen uptake and dendritic cell maturation, as compared to the use of the free tumor lysate. The ability of the activated dendritic cells to stimulate autologous peripheral blood mononuclear cells (PBMCs) is assessed in vitro by coculturing PBMCs with A375 melanoma cells. Live cell imaging analysis of this experiment highlights the potential of nanoparticle-mediated dendritic-cell-based vaccination approaches. Finally, the efficacy of the PLGA nanoparticle formulation is evaluated in vivo in a therapeutic vaccination study using B16F10 tumor-bearing C57BL/6J mice. Animals that are challenged with the polymer nanoparticle-based oxidized tumor lysate formulation survive for up to 50 days, in contrast to a maximum of 41 days for the group that receives the corresponding free oxidized tumor lysate-based vaccine.

Integrating Cancer Vaccines in the Standard-of-Care of Ovarian Cancer: Translating Preclinical Models to Human

Simple Summary

The overall survival of ovarian cancer (OC) remains poor for most patients. Despite incorporation of novel therapeutic agents such as bevacizumab and PARP inhibitors to OC standard-of-care, efficacy is only observed in a subset of patients. Cancer vaccination has demonstrated effectiveness in OC patients and could be considered for potential incorporation into OC standard-of-care. This review provides an overview of the different types of cancer vaccination strategies and discusses the use of murine OC tumor models to evaluate combinatorial regimens comprising cancer vaccines and OC standard-of-care.

Abstract

As the majority of ovarian cancer (OC) patients are diagnosed with metastatic disease, less than 40% will survive past 5 years after diagnosis. OC is characterized by a succession of remissions and recurrences. The most promising time point for immunotherapeutic interventions in OC is following debulking surgery. Accumulating evidence shows that T cells are important in OC; thus, cancer vaccines capable of eliciting antitumor T cells will be effective in OC treatment. In this review, we discuss different cancer vaccines and propose strategies for their incorporation into the OC standard-of-care regimens. Using the murine ID8 ovarian tumor model, we provide evidence that a cancer vaccine can be effectively combined with OC standard-of-care to achieve greater overall efficacy. We demonstrate several important similarities between the ID8 model and OC patients, in terms of response to immunotherapies, and the ID8 model can be an important tool for evaluating combinatorial regimens and clinical trial designs in OC. Other emerging models, including patient-derived xenograft and genetically engineered mouse models, are continuing to improve and can be useful for evaluating cancer vaccination therapies in the near future. Here, we provide a comprehensive review of the completed and current clinical trials evaluating cancer vaccines in OC.

Myeloid cell-derived HOCl is a paracrine effector that trans-inhibits IKK/NF-κB in melanoma cells and limits early tumor progression

The myeloperoxidase (MPO) system of myeloid-derived cells (MDCs) is central to cellular innate immunity. Upon MDC activation, MPO is secreted into phagosomes where it catalyzes the production of hypochlorous acid (HOCl), a potent chlorinating oxidant. Here, we demonstrated that the myeloid lineage-restricted MPO-HOCl system had antitumor effects in early melanoma growth in aged mice. Orthotopic melanomas grew more slowly in immunocompetent MPO^+/+ host mice compared to age-matched syngeneic MPO^-/- mice. Real-time intravital tumor imaging in vivo and in cell cocultures revealed a cell-cell proximity-dependent association between MDC-derived MPO enzyme activity and blockade of ligand-induced IκBα degradation in tumor cells. HOCl directly trans-inhibited IκB kinase (IKK) activity in tumor cells, thereby decreasing nuclear factor κB (NF-κB) transcriptional activation and inducing changes in the expression of genes involved in metabolic pathways, cell cycle progression, and DNA replication. By contrast, HOCl induced transcriptional changes in CD8⁺ T cells related to ion transport and the MAPK and PI3K-AKT signaling pathways that are associated with T cell activation. MPO increased the circulating concentrations of the myeloid cell-attracting cytokines CXCL1 and CXCL5, enhanced local infiltration by CD8⁺ cytotoxic T cells, and decreased tumor growth. Overall, these data reveal a role for MDC-derived HOCl as a small-molecule paracrine signaling factor that trans-inhibits IKK in melanoma tumor cells, mediating antitumor responses during early tumor progression.

Oxidatively Modified Proteins: Cause and Control of Diseases

Proteins succumb to numerous post-translational modifications (PTMs). These relate to enzymatic or non-enzymatic reactions taking place in either the intracellular or extracellular compartment. While intracellular oxidative changes are mainly due to redox stress, extracellular PTMs may be induced in an inflammatory micro milieu that is rich in reactive species. The increasing recognition of oxidative modifications as a causing agent or side-effect of pathophysiological states and diseases puts oxidative PTMS (oxPTMs) into the spotlight of inflammation research. Pathological hyper-modification of proteins can lead to accumulation, aggregation, cell stress, altered antigenic peptides, and damage-associated molecular pattern (DAMP)-like recognition by host immunity. Such processes are linked to cardiovascular disease and autoinflammation. At the same time, a detailed understanding of the mechanisms governing inflammatory responses to oxPTMs may capitalize on new therapeutic routes for enhancing adaptive immune responses as needed, for instance, in oncology. We here summarize some of the latest developments of oxPTMs in disease diagnosis and therapy. Potential target proteins and upcoming technologies, such as gas plasmas, are outlined for future research that may aid in identifying the molecular basis of immunogenic vs. tolerogenic oxPTMs.

Rapid tumor vaccine using Toll-like receptor-activated ovarian cancer ascites monocytes

Background

Novel therapeutic strategies in ovarian cancer (OC) are needed as the survival rate remains dismally low. Although dendritic cell-based cancer vaccines are effective in eliciting therapeutic responses, their complex and costly manufacturing process hampers their full clinical utility outside specialized clinics. Here, we describe a novel approach of generating a rapid and effective cancer vaccine using ascites-derived monocytes for treating OC.

Methods

Using the ID8 mouse ovarian tumor model and OC patient samples, we isolated ascites monocytes and evaluated them with flow cytometry, Luminex cytokine and chemokine array analysis, ex vivo cocultures with T cells, in vivo tumor challenge and T cell transfer experiments, RNA-sequencing and mass spectrometry.

Results

We demonstrated the feasibility of isolating ascites monocytes and restoring their ability to function as bona fide antigen-presenting cells (APCs) with Toll-like receptor (TLR) 4 lipopolysaccharide and TLR9 CpG-oligonucleotides, and a blocking antibody to interleukin-10 receptor (IL-10R Ab) in the ID8 model. The ascites monocytes were laden with tumor antigens at a steady state in vivo. After a short 48 hours activation, they upregulated maturation markers (CD80, CD86 and MHC class I) and demonstrated strong ex vivo T cell stimulatory potential and effectively suppressed tumor and malignant ascites in vivo. They also induced protective long-term T cell memory responses. To evaluate the translational potential of this approach, we isolated ascites monocytes from stage III/IV chemotherapy-naïve OC patients. Similarly, the human ascites monocytes presented tumor-associated antigens (TAAs), including MUC1, ERBB2, mesothelin, MAGE, PRAME, GPC3, PMEL and TP53 at a steady state. After a 48-hour treatment with TLR4 and IL-10R Ab, they efficiently stimulated oligoclonal tumor-associated lymphocytes (TALs) with strong reactivity against TAAs. Importantly, the activated ascites monocytes retained their ability to activate TALs in the presence of ascitic fluid.

Conclusions

Ascites monocytes are naturally loaded with tumor antigen and can perform as potent APCs following short ex vivo activation. This novel ascites APC vaccine can be rapidly prepared in 48 hours with a straightforward and affordable manufacturing process, and would be an attractive therapeutic vaccine for OC.

Tumor cell lysate-loaded immunostimulatory spherical nucleic acids as therapeutics for triple-negative breast cancer

Highly heterogenous cancers, such as triple-negative breast cancer (TNBC), remain challenging immunotherapeutic targets. Herein, we describe the synthesis and evaluation of immunotherapeutic liposomal spherical nucleic acids (SNAs) for TNBC therapy. The SNAs comprise immunostimulatory oligonucleotides (CpG-1826) as adjuvants and encapsulate lysates derived from TNBC cell lines as antigens. The resulting nanostructures (Lys-SNAs) enhance the codelivery of adjuvant and antigen to immune cells when compared to simple mixtures of lysates with linear oligonucleotides both in vitro and in vivo, and reduce tumor growth relative to simple mixtures of lysate and CpG-1826 (Lys-Mix) in both Py230 and Py8119 orthotopic syngeneic mouse models of TNBC. Furthermore, oxidizing TNBC cells prior to lysis and incorporation into SNAs (OxLys-SNAs) significantly increases the activation of dendritic cells relative to their nonoxidized counterparts. When administered peritumorally in vivo in the EMT6 mouse mammary carcinoma model, OxLys-SNAs significantly increase the population of cytotoxic CD8+ T cells and simultaneously decrease the population of myeloid derived suppressor cells (MDSCs) within the tumor microenvironment, when compared with Lys-SNAs and simple mixtures of oxidized lysates with CpG-1826. Importantly, animals administered OxLys-SNAs exhibit significant antitumor activity and prolonged survival relative to all other treatment groups, and resist tumor rechallenge. Together, these results show that the way lysates are processed and packaged has a profound impact on their immunogenicity and therapeutic efficacy. Moreover, this work points toward the potential of oxidized tumor cell lysate-loaded SNAs as a potent class of immunotherapeutics for cancers lacking common therapeutic targets.

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.

Personalized Dendritic Cell Vaccines-Recent Breakthroughs and Encouraging Clinical Results

With the advent of combined immunotherapies, personalized dendritic cell (DC)-based vaccination could integrate the current standard of care for the treatment of a large variety of tumors. Due to their proficiency at antigen presentation, DC are key coordinators of the innate and adaptive immune system, and have critical roles in the induction of antitumor immunity. However, despite proven immunogenicity and favorable safety profiles, DC-based immunotherapies have not succeeded at inducing significant objective clinical responses. Emerging data suggest that the combination of DC-based vaccination with other cancer therapies may fully unleash the potential of DC-based cancer vaccines and improve patient survival. In this review, we discuss the recent efforts to develop innovative personalized DC-based vaccines and their use in combined therapies, with a particular focus on ovarian cancer and the promising results of mutanome-based personalized immunotherapies.

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.

Chlorinative stress in age-related diseases: a literature review

Aging is an agglomerate of biological long-lasting processes that result being inevitable. Main actors in this scenario are both long-term inflammation and oxidative stress. It has been proved that oxidative stress induce alteration in proteins and this fact itself is critically important in the pathophysiological mechanisms leading to diseases typical of aging. Among reactive species, chlorine ones such as hypochlorous acid (HOCl) are cytotoxic oxidants produced by activated neutrophils during chronic inflammation processes. HOCl can also cause damages by reacting with biological molecules. HOCl is generated by myeloperoxidase (MPO) and augmented serum levels of MPO have been described in acute and chronic inflammatory conditions in cardiovascular patients and has been implicated in many inflammatory diseases such as atherosclerosis, neurodegenerative conditions, and some cancers. Due to these data, we decided to conduct an up-to-date review evaluating chlorinative stress effects on every age-related disease linked; potential anti-oxidant countermeasures were also assessed. Results obtained associated HOCl generation to the aging processes and confirmed its connection with diseases like neurodegenerative and cardiovascular pathologies, atherosclerosis and cancer; chlorination was mainly linked to diseases where molecular (protein) alteration constitute the major suspected cause: i.e. inflammation, tissue lesions, DNA damages, apoptosis and oxidative stress itself. According data collected, a healthy lifestyle together with some dietary suggestion and/or the administration of nutracetical antioxidant integrators could balance the effects of chlorinative stress and, in some cases, slow down or prevent the onset of age-releated diseases.

Oxidation by neutrophils-derived HOCl increases immunogenicity of proteins by converting them into ligands of several endocytic receptors involved in antigen uptake by dendritic cells and macrophages

The initiation of adaptive immune responses to protein antigens has to be preceded by their uptake by antigen presenting cells and intracellular proteolytic processing. Paradoxically, endocytic receptors involved in antigen uptake do not bind the majority of proteins, which may be the main reason why purified proteins stimulate at most weak immune responses. A shared feature of different types of adjuvants, capable of boosting immunogenicity of protein vaccines, is their ability to induce acute inflammation, characterized by early influx of activated neutrophils. Neutrophils are also rapidly recruited to sites of tissue injury or infection. These cells are the source of potent oxidants, including hypochlorous acid (HOCl), causing oxidation of proteins present in inflammatory foci. We demonstrate that oxidation of proteins by endogenous, neutrophils-derived HOCl increases their immunogenicity. Upon oxidation, different, randomly chosen simple proteins (yeast alcohol dehydrogenase, human and bovine serum albumin) and glycoproteins (human apo-transferrin, ovalbumin) gain the ability to bind with high affinity to several endocytic receptors on antigen presenting cells, which seems to be the major mechanism of their increased immunogenicity. The mannose receptor (CD206), scavenger receptors A (CD204) and CD36 were responsible for the uptake and presentation of HOCl-modified proteins by murine dendritic cells and macrophages. Other scavenger receptors, SREC-I and LOX-1, as well as RAGE were also able to bind HOCl-modified proteins, but they did not contribute significantly to these ligands uptake by dendritic cells because they were either not expressed or exhibited preference for more heavily oxidised proteins. Our results indicate that oxidation by neutrophils-derived HOCl may be a physiological mechanism of conferring immunogenicity on proteins which in their native forms do not bind to endocytic receptors. This mechanism might enable the immune system to detect infections caused by pathogens not recognized by pattern recognition receptors.

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.

Atomic force microscopy-based molecular studies on the recognition of immunogenic chlorinated ovalbumin by macrophage receptors

This report presents simple and reliable approach developed to study the specific recognition events between chlorinated ovalbumin (OVA) and macrophages using atomic force microscopy (AFM). Thanks to the elimination of nonspecific adhesion, the interactions of the native and chlorinated OVA with a membrane of macrophages could be quantified using exclusively the so-called adhesion frequency (AF). The proposed system not only enabled the application of AFM-based force measurements for such poorly defined ligand-receptor pairs but also significantly improved both the acquisition and the processing of the data. The proteins were immobilized on the gold-coated AFM tips from the aqueous solutions containing charged thiol adsorbates. Such surface dilution of the proteins ensured the presence of single or just a few macromolecules at the tip-surface contact. The formation of negatively charged monolayer on the tip dramatically limited its nonspecific interactions with the macrophage surface. In such systems, AF was used as a measure of the recognition events even if the interaction forces varied significantly for sets of measurements. The system with the native OVA, a weak immunogen, showed only negligible AF compared with 85% measured for the immunogenic chlorinated OVA. The AF values varied with the tip-macrophage contact time and loading velocity. Blocking of the receptors by the chlorinated OVA was also confirmed. The developed approach can be also used to study other ligand-receptor interactions in poorly defined biological systems with intrinsically broad distribution of the rupture forces, thus opening new fields for AFM-based recognition on molecular level.

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.

Airway exposure to hypochlorite prior to ovalbumin induces airway hyperreactivity without evidence for allergic sensitization

BACKGROUND

Some epidemiologic studies have indicated that attendance to chlorinated swimming pools is associated with airway hyperreactivity (AHR), allergies and asthma.

AIM

To investigate the effects of sodium hypochlorite (NaClO), the main pool disinfectant, on allergic sensitization and airway inflammation in mice.

METHODS

In a first series of experiments, mice were sensitized to ovalbumin (OVA), followed by OVA aerosols with or without prior nasal instillation of NaClO (3ppm active chlorine). In a second series, naïve mice received 1-7 nasal instillations of OVA, 10min after instillations of NaClO or water. After 1, 3, 5 and 7 exposures airway reactivity to methacholine, cellular inflammation in bronchoalveolar lavage (BAL), serum OVA-specific IgEs and lung Th2 cytokines were measured.

RESULTS

In the first mouse model, airway allergy parameters were not significantly altered upon NaClO administration. However in the second model, NaClO exposure prior to OVA did induce AHR, already after 1 combined application. Combined NaClO+OVA exposure did not lead to an influx of inflammatory cells in BAL fluid or production of anti-OVA IgEs. No AHR developed when OVA was heat-denatured, pre-chlorinated, or replaced by bovine serum albumin or lipopolysaccharide.

CONCLUSION

Nasal instillation of NaClO prior to OVA induces AHR without allergic sensitization. This response is OVA-specific.

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.

Hypochlorous acid: a natural adjuvant that facilitates antigen processing, cross-priming, and the induction of adaptive immunity

The production of hypochlorous acid (HOCl) is a characteristic of granulocyte activation, a hallmark of the early phase of innate immune responses. In this study, we show that, in addition to its well-established role as a microbicide, HOCl can act as a natural adjuvant of adaptive immunity. HOCl enhances the T cell responses to the model Ag OVA, facilitating the processing and presentation of this protein via the class II MHC pathway. HOCl modification also enhances cross-presentation of the tumor Ag tyrosinase-related protein 2 via class I MHC. The adjuvant effects of HOCl are independent of TLR signaling. The enhanced presentation of HOCl-modified OVA is mediated via modification of the N-linked carbohydrate side chain rather than formation of protein aldehydes or chloramines. HOCl-modified OVA is taken up more efficiently by APCs and is degraded more efficiently by proteinases. Atomic force microscopy demonstrated that enhanced uptake is mediated via specific receptor binding, one candidate for which is the scavenger receptor lectin-like oxidized low-density lipoprotein receptor, which shows enhanced binding to chlorinated OVA. A function of HOCl is therefore to target glycoprotein Ags to scavenger receptors on the APC surface. This additional mechanism linking innate and adaptive immunity suggests novel strategies to enhance immunity to vaccines.

Oxidation of ovarian epithelial cancer cells by hypochlorous acid enhances immunogenicity and stimulates T cells that recognize autologous primary tumor

PURPOSE

Hypochlorous acid, a product of neutrophil myeloperoxidase, is a powerful enhancer of antigen processing and presentation. In this study, we examine whether ovarian epithelial cells (SK-OV-3) exposed to hypochlorous acid can stimulate T cells from patients with ovarian epithelial cancer that recognize common tumor antigens as well as autologous tumor.

EXPERIMENTAL DESIGN

T cells from human leukocyte antigen (HLA)-A2(+) and HLA-A2(-) patients or healthy controls were stimulated with autologous dendritic cells cocultured with the generic ovarian tumor line SK-OV-3, previously exposed to hypochlorous acid.

RESULTS

Hypochlorous acid-treated SK-OV-3 cells drove expansion of CD8(+) T cells from HLA-A2(+) individuals, which recognized the HLA-A2-restricted tumor antigen epitopes of HER-2/neu (E75 and GP2) and MUC1 (M1.1 and M1.2). Up to 4.1% of the T cells were positive for the HER-2/neu KIFGSLAFL epitope using pentamer staining. Dendritic cells loaded with oxidized SK-OV-3 cells and further matured with CD40 agonistic antibody or monophosphoryl lipid A additionally induced CD4(+) class II-restricted responses. Critically, T cells stimulated with mature oxidized SK-OV-3 (but not a control oxidized melanoma cell line) directly recognized autologous tumor cells isolated from patient ascites.

CONCLUSIONS

Immunization with mature dendritic cells loaded with a generic oxidized tumor cell line stimulates a polyclonal antitumor response that recognizes autologous tumor. These findings suggest a new immunotherapeutic strategy to extend remission in ovarian cancer.

Hypochlorous acid enhances immunogenicity and uptake of allogeneic ovarian tumor cells by dendritic cells to cross-prime tumor-specific T cells

BACKGROUND

Ovarian cancer commonly relapses after remission and new strategies to target microscopic residual diseases are required. One approach is to activate tumor-specific cytotoxic T cells with dendritic cells loaded with tumor cells. In order to enhance their immunogenicity, ovarian tumor cells (SK-OV-3, which express two well-characterized antigens HER-2/neu and MUC-1) were killed by oxidation with hypochlorous acid (HOCl).

RESULTS

Treatment for 1 h with 60 microM HOCl was found to induce necrosis in all SK-OV-3 cells. Oxidized, but not live, SK-OV-3 was rapidly taken up by monocyte-derived dendritic cells, and induced partial dendritic cell maturation. Dendritic cells cultured from HLA-A2 healthy volunteers were loaded with oxidized SK-OV-3 (HLA-A2-) and co-cultured with autologous T cells. Responding T cells were tested for specificity after a further round of antigen stimulation. In ELISPOT assays, T cells produced interferon-gamma (IFN-gamma) in response to the immunizing cellular antigen, and also to peptides coding for MUC-1 and HER-2/neu HLA-A2 restricted epitopes, demonstrating efficient cross-presentation of cell-associated antigens. In contrast, no responses were seen after priming with heat-killed or HCl-killed SK-OV-3, indicating that HOCl oxidation and not cell death/necrosis per se enhanced the immunogenicity of SK-OV-3. Finally, T cells stimulated with oxidized SK-OV-3 showed no cross-reaction to oxidized melanoma cells, nor vice versa, demonstrating that the response was tumor-type specific.

CONCLUSIONS

Immunization with oxidized ovarian tumor cell lines may represent an improved therapeutic strategy to stimulate a polyclonal anti-tumor cellular immune response and hence extend remission in ovarian cancer.

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.

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.

Current issues in antigen presentation—focus on the dendritic cell

A personal view of some of the major current issues in antigen presentation, which focuses on the biology of the dendritic cell. The question of dendritic cell heterogeneity is discussed and the inclusion of the "plasmacytoid" dendritic cell in this family is questioned. Defining the molecules involved in dendrite formation may ultimately provide the only reliable signature of the dendritic cell. The role of the dendritic cell as a key link between innate and adaptive immunity is here revisited, and the direct and indirect interactions between dendritic cells and microorganisms are discussed. Reactive oxygen species may be key modulators of dendritic cell function, although it remains unclear whether direct or indirect mechanisms are more important. Study of the cell biology of antigen processing reveals a tightly regulated complex system involving multiple proteinases, adapted to the most efficient presentation of invading microorganisms and playing a key role in shaping the T cell repertoire.

Myeloperoxidase-mediated protein oxidation: its possible biological functions

Oxidation of proteins occurs both as a side-effect of aerobic energy metabolism and as an effect of specific metabolism of phagocytic polymorphonuclear granulocytes producing O2- and H2O2. In contrast to other cells, which control their H2O2 level by degrading it to O2 and H2O, polymorphonuclear neutrophilic leukocytes (PMN) use H2O2 as a substrate for oxidizing chloride ions to HOCl which rapidly react with all neighboring thiol, disulfide and amino residues. Chloramines, which are the most abundant HOCl reaction products, react with proteins, modifying only certain exposed methionine and cysteine residues. This may account for selective inactivation of a number of enzymes, carrier proteins and peptide mediators, including the alpha1-proteinase inhibitor, alpha2-macroglobulin and plasminogen activator inhibitor. Inactivaton of plasma proteinase inhibitors protects PMN elastase, collagenase, cathepsin G and other serine proteases in the inflammatory foci. This promotes proteolytic degradation of damaged tissue, removal of bacterial debris and wound healing, as well as tissue remodeling related to the inflammatory processes. Oxidative control of protease-anti-protease balance affects the development of the inflammatory processes. Moreover, inactivation of plasma proteinase inhibitors facilitates primary antigen processing, upregulates lymphocyte proliferative response and activates the local immune response. Oxidation produces a specific protein tagging which attracts and stimulates immune active cells. Therefore, humoral response against oxidatively modified proteins occurs more effectively than that of the native proteins. The effect is dose-dependent with respect to the amount of oxidant employed. Glycol aldehyde, which is the serine chloramine spontaneous decay product, in mice immunized with glycol aldehyde-modified egg-white albumin, yields specific IgG production manifold higher than that in mice immunized with native albumin. Immunopotentiation is produced by proliferation expansion of the same immunocompetent clones. Oxidative tagging of proteins may also affect the autoimmune-type reaction. Thus, a growing body of data suggest that the specific role of protein oxidation by activated PMN is oxidative protein tagging facilitating further development of the immune reaction.

Correlation between intima-to-media ratio, apolipoprotein B-100, myeloperoxidase, and hypochlorite-oxidized proteins in human atherosclerosis

The oxidative modification of low-density lipoprotein (LDL) is thought to contribute to atherogenesis, and there is evidence that oxidants derived from myeloperoxidase (MPO) contribute to such oxidative damage. Using human iliac arteries we investigated the relationship between lesion stage indicated by the intima-to-media (I/M) ratio and the presence of apolipoprotein B-100 (apoB, a marker for LDL), MPO, and hypochlorite (HOCl)-oxidized proteins identified by immunohistochemistry in the intima, media, and adventitia. More staining for apoB, MPO, and HOCl-oxidized proteins was observed in diseased than healthy vessels. Diseased segments also stained more for the three parameters than healthy segments in the same diseased vessel, highlighting the variability that can occur within a single cross-section of a vessel. However, significant positive correlation between I/M ratio and positive staining for apoB, MPO, and HOCl-oxidized proteins in different segments of individual arteries were apparent in segments with an I/M ratio of > 1.8. Also, the overall extent of intimal staining for apoB, MPO, and HOCl-oxidized proteins increased with increasing I/M ratio. In addition, the extent of apoB staining was greater and appeared at comparatively lower I/M ratios than that of MPO and HOCl-oxidized proteins. Our results support a contribution to atherogenesis of all three parameters assessed, although MPO and HOCl-oxidized proteins appear to participate in the disease process at a later stage than apoB.

Regulation of murine dendritic cell functions in vitro by taurine chloramine, a major product of the neutrophil myeloperoxidase-halide system

Taurine chloramine (TauCl) is a major chloramine generated in activated neutrophils as a result of the reaction of highly toxic hypochlorous acid and taurine, the most abundant free amino acid in cytosol. In this study we have tested the influence of TauCl on the properties of murine dendritic cells (DC), the major cell population involved in the initiation of an adaptive immune response against pathogenic organisms. N418+, MHC II+, B7-2+ dendritic cells, generated from the mouse bone marrow cells cultured in the presence of granulocyte-macrophage colony-stimulating factor, were stimulated by interferon-gamma and lipopolysaccharide to produce nitric oxide, reactive oxygen species, interleukin-6 (IL-6), tumour necrosis factor-alpha, and IL-12, in the presence of different doses of TauCl. TauCl differently inhibited the generation of these inflammatory mediators in a dose-dependent manner. Furthermore, TauCl selectively modulated the ability of DC to induce the release IL-2 and IL-10 from T cells. These results suggest that neutrophil-derived mediators, such as TauCl, at a site of inflammation, may affect the functions of sentinel DC and macrophages, and play a role in maintaining the balance between the inflammatory response and the induction of an antigen-specific immune response.

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

The participation of oxidative mechanisms in major histocompatibility complex (MHC) class II-restricted antigen presentation was studied in vitro. In general, antigen processing is inhibited when peritoneal macrophages (MO) are incubated with scavengers of reactive oxygen intermediates (ROI): mannitol (an.OH scavenger), dimethylurea (DMTU, which reacts with H2O2 and HOCl) and NCO-700 (an epoxysuccinic acid derivative which inhibits oxidant production by activated phagocytes and can scavenge reactive oxygen species in both NaOCl and hypoxanthine (XOD) systems). However, neither rotenone and antimycins (inhibitors of O-2 production at the NADH dehydrogenase and ubiquinone-cytochrome b regions, respectively) nor aminoguanidine (an inducible nitric oxide synthase inhibitor) impaired antigen presentation, thus indirectly discarding the participation of mitochondrial oxidation and reactive nitrogen intermediates (RNI) in antigen processing. ROI scavengers do not inhibit the MHC class II-restricted presentation of antigens that need processing but have their disulphide bonds reduced. It can be shown that oxidation of protein antigens (either by chlorination or performic acid treatment) allow protein unfolding and enhance both processing and exposure of immunogenic epitopes to specific T cells.

Taurine chloramine down-regulates the generation of murine neutrophil inflammatory mediators

We previously reported that taurine chloramine (TauCl), a product of activated neutrophils, inhibits the generation of macrophage inflammatory mediators such as nitric oxide (NO), TNF-alpha, and PGE2. Taurine, the most abundant free amino acid in the cytosol of neutrophils, is chlorinated to form TauCl by the halide-dependent myeloperoxidase (MPO) system. Under physiological conditions, TauCl reduces HOCl toxicity. In this study, we investigated the influence of TauCl on generation of oxygen free radicals, cytokines and eicosanoids by activated murine peritoneal neutrophils. We found that TauCl, but not taurine alone, inhibited the production of NO, prostaglandin E2, interleukin-6 and tumor necrosis factor-alpha, in a dose-dependent manner. In contrast, the products of the respiratory burst, as measured by luminol-dependent chemiluminescence (LCL), were reduced by both taurine and TauCl. However, taurine affected LCL at higher concentrations and to a lesser extent than TauCl. The results of these studies suggest that TauCl decreases production of tissue-damaging inflammatory mediators and may regulate the balance between protective, microbicidal and toxic effect of neutrophils.

Modulation of antigen-specific T-cell activation in vitro by taurine chloramine

Taurine chloramine (TauCl) is produced during inflammation by reaction of hypochlorous acid (HOCl) with taurine, the most abundant free amino acid in neutrophils. We previously reported that TauCl inhibits the generation of macrophage inflammatory mediators such as nitric oxide, prostaglandin E2 (PGE2), tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). In this study, the activity of TauCl in modulating T-cell activation was investigated. Treatment of T cells with TauCl (0.1-0.3 mM), prior to activation, was found to inhibit interleukin-2 (IL-2) release in response to both mitogen and antigen stimulation. Similarly, pretreatment of A-20 antigen presenting cells (APCs), at low cell numbers, was found to inhibit their ability to process and present ovalbumin (OVA) to a specific T-cell hybridoma. In contrast, pretreatment of higher numbers of A-20 cells with TauCl in the presence of OVA enhanced subsequent presentation of OVA. Finally, OVA modified with TauCl was processed and presented more efficiently than native OVA. Thus, TauCl is able to modulate induction of a specific adaptive immune response at several independent points of the overall antigen-presenting pathway.

Neutrophil chloramines: missing links between innate and acquired immunity

Neutrophils are the major cellular component of the acute inflammatory response. By contrast, macrophages are the major cellular component in most chronic immunological responses, and act as key regulators of the specific acquired response. Here, Janusz Marcinkiewicz examines recent data indicating that chloramines, the neutrophil-specific products of the myeloperoxidase--hydrogen-peroxide--halide system, may provide a bridge between the afferent branches of the innate and acquired immune response.

Participation of intracellular oxidative pathways in antigen processing by dendritic cells, B cells and macrophages

The antigen presentation abilities of antigen presenting cells (APC) from different lineages [mainly macrophages (M phi), B cells and dendritic cells (DC)] were compared. In this review we focus on the participation of intracellular oxidative mechanisms in intracellular degradation of protein antigens: an aspect that is often neglected when the issue of antigen processing is considered. Special emphasis is given to recent findings from our laboratory indicating that in addition to a lysosomal proteolytic step being present in all APC, a previous or simultaneous oxidative step is operative in some APC (M phi) but absent or less important in others (B cells, DC).