Enhancement of dendritic cell antigen cross-presentation by CpG DNA involves type I IFN and stabilization of class I MHC mRNA

An innate immune response to adeno-associated virus genomes decreases cortical dendritic complexity and disrupts synaptic transmission

Recombinant adeno-associated viruses (AAVs) allow rapid and efficient gene delivery to the nervous system, are widely used in neuroscience research, and are the basis of FDA-approved neuron-targeting gene therapies. Here we find that an innate immune response to the AAV genome reduces dendritic length and complexity and disrupts synaptic transmission in mouse somatosensory cortex. Dendritic loss is apparent 3 weeks after injection of experimentally relevant viral titers, is not restricted to a particular capsid serotype, transgene, promoter, or production facility, and cannot be explained by responses to surgery or transgene expression. AAV-associated dendritic loss is accompanied by a decrease in the frequency and amplitude of miniature excitatory postsynaptic currents and an increase in the proportion of GluA2-lacking, calcium-permeable AMPA receptors. The AAV genome is rich in unmethylated CpG DNA, which is recognized by the innate immunoreceptor Toll-like receptor 9 (TLR9), and acutely blocking TLR9 preserves dendritic complexity and AMPA receptor subunit composition in AAV-injected mice. These results reveal unexpected impacts of an immune response to the AAV genome on neuronal structure and function and identify approaches to improve the safety and efficacy of AAV-mediated gene delivery in the nervous system.

The role of gut microbiota and probiotics in preventing, treating, and boosting the immune system in colorectal cancer

The gut microbiome plays a significant role in developing colorectal cancer (CRC). The gut microbiome usually acts as a protective barrier against harmful pathogens and infections in the intestine, while also regulating inflammation by affecting the human immune system. The gut microbiota and probiotics play a role not only in intestinal inflammation associated with tumor formation but also in regulating anti-cancer immune response. As a result, they associated with tumor progression and the effectiveness of anti-cancer therapies. Research indicates that gut microbiota and probiotics can be used as biomarkers to predict the impact of immunotherapy and enhance its efficacy in treating CRC by regulating it. This review examines the importance of gut microbiota and probiotics in the development and progression of CRC, as well as their synergistic impact on anti-cancer treatments.

A new strategy for treating colorectal cancer: Regulating the influence of intestinal flora and oncolytic virus on interferon

Colorectal cancer (CRC) has the third highest incidence and the second highest mortality in the world, which seriously affects human health, while current treatments methods for CRC, including systemic therapy, preoperative radiotherapy, and surgical local excision, still have poor survival rates for patients with metastatic disease, making it critical to develop new strategies for treating CRC. In this article, we found that the gut microbiota can modulate the signaling pathways of cancer cells through direct contact with tumor cells, generate inflammatory responses and oxidative stress through interactions between the innate and adaptive immune systems, and produce diverse metabolic combinations to trigger specific immune responses and promote the initiation of systemic type I interferon (IFN-I) and anti-viral immunity. In addition, oncolytic virus-mediated immunotherapy for regulating oncolytic virus can directly lyse tumor cells, induce the immune activity of the body, interact with interferon, inhibit the anti-viral effect of IFN-I, and enhance the anti-tumor effect of IFN-II. Interferon plays an important role in the anti-tumor process. We put forward that exploring the effects of intestinal flora and oncolytic virus on interferon to treat CRC is a promising therapeutic option.

Deciphering the role of cDC2s in Sjögren's syndrome: transcriptomic profile links altered antigen processes with IFN signature and autoimmunity

OBJECTIVE

Type 2 conventional dendritic cells (cDC2s) are key orchestrators of inflammatory responses, linking innate and adaptative immunity. Here we explored the regulation of immunological pathways in cDC2s from patients with primary Sjögren's syndrome (pSS).

METHODS

RNA sequencing of circulating cDC2s from patients with pSS, patients with non-Sjögren's sicca and healthy controls (HCs) was exploited to establish transcriptional signatures. Phenotypical and functional validation was performed in independent cohorts.

RESULTS

Transcriptome of cDC2s from patients with pSS revealed alterations in type I interferon (IFN), toll-like receptor (TLR), antigen processing and presentation pathways. Phenotypical validation showed increased CX3CR1 expression and decreased integrin beta-2 and plexin-B2 on pSS cDC2s. Functional validation confirmed impaired capacity of pSS cDC2s to degrade antigens and increased antigen uptake, including self-antigens derived from salivary gland epithelial cells. These changes in antigen uptake and degradation were linked to anti-SSA/Ro (SSA) autoantibodies and the presence of type I IFNs. In line with this, in vitro IFN-α priming enhanced the uptake of antigens by HC cDC2s, reflecting the pSS cDC2 profile. Finally, pSS cDC2s compared with HC cDC2s increased the proliferation and the expression of CXCR3 and CXCR5 on proliferating CD4⁺ T cells.

CONCLUSIONS

pSS cDC2s are transcriptionally altered, and the aberrant antigen uptake and processing, including (auto-)antigens, together with increased proliferation of tissue-homing CD4⁺ T cells, suggest altered antigen presentation by pSS cDC2s. These functional alterations were strongly linked to anti-SSA positivity and the presence of type I IFNs. Thus, we demonstrate novel molecular and functional pieces of evidence for the role of cDC2s in orchestrating immune response in pSS, which may yield novel avenues for treatment.

The paradox of radiation and T cells in tumors

In this review we consider what appears to be a paradox in immunotherapies based around radiation therapy. The paradox is based on three main points. 1. That T cells are needed for radiation's efficacy; 2. That tumor-specific T cells are enriched in the field of treatment; and 3. That radiation kills T cells in the treatment field. We discuss evidence of the effect of radiation on T cells in the field given their ongoing movement in and out of tissues and the tumor, and how the movement of T cells impacts the treated primary tumor and untreated distant metastases. Given this evidence, we revisit the paradox to understand how the extraordinary efficacy of radiation and immunity in preclinical models is dependent on this radiation sensitive cell.

The Dynamic Entropy of Tumor Immune Infiltrates: The Impact of Recirculation, Antigen-Specific Interactions, and Retention on T Cells in Tumors

Analysis of tumor infiltration using conventional methods reveals a snapshot view of lymphocyte interactions with the tumor environment. However, lymphocytes have the unique capacity for continued recirculation, exploring varied tissues for the presence of cognate antigens according to inflammatory triggers and chemokine gradients. We discuss the role of the inflammatory and cellular makeup of the tumor environment, as well as antigen expressed by cancer cells or cross-presented by stromal antigen presenting cells, on recirculation kinetics of T cells. We aim to discuss how current cancer therapies may manipulate lymphocyte recirculation versus retention to impact lymphocyte exclusion in the tumor.

Intestinal microbiota: A potential target for enhancing the antitumor efficacy and reducing the toxicity of immune checkpoint inhibitors

Accumulating evidence suggests that the intestinal microbiota is associated with the antitumor efficacy of immune checkpoint inhibitors (ICIs) and the occurrence of immune-related adverse events (irAEs) following ICI treatment. However, the mechanisms underlying these interactions remain unclear. Recent technological advances have allowed more extensive investigation into the interplay between the intestinal microbiota and the tumor immune microenvironment. Breakthroughs by two research groups revealed that Bifidobacterium enhanced the efficacy of ICIs via the stimulator of interferon genes (STING) and adenosine 2A receptor (A_2AR) signaling pathways, highlighting the molecular mechanisms through which the intestinal microbiota modulates immunotherapy. In this review, we summarize recent findings related to the potential role and mechanisms of the gut microbiota in ICI therapy, available microbiota-targeting strategies, and ongoing clinical trials. Further we discuss the associated challenges that remain in this field of research. The current review aims to evaluate the potential of the intestinal microbiota in maximizing the antitumor efficacy of ICIs while minimizing their toxic effects and guiding the development of more specific treatment regimens.

Intratumoral accumulation of gut microbiota facilitates CD47-based immunotherapy via STING signaling

Most studies focus on how intestinal microbiota influence cancer immunotherapy through activating gut immunity. However, immunotherapies related to innate responses such as CD47 blockade rely on the rapid immune responses within the tumor microenvironment. Using one defined anaerobic gut microbiota to track whether microbiota interact with host immunity, we observed that Bifidobacterium facilitates local anti-CD47 immunotherapy on tumor tissues through the capacity to accumulate within the tumor microenvironment. Systemic administration of Bifidobacterium leads to its accumulation within the tumor and converts the nonresponder mice into responders to anti-CD47 immunotherapy in a stimulator of interferon genes (STING)– and interferon-dependent fashion. Local delivery of Bifidobacterium potently stimulates STING signaling and increases cross-priming of dendritic cells after anti-CD47 treatment. Our study identifies the mechanism by which gut microbiota preferentially colonize in tumor sites and facilitate immunotherapy via STING signaling.

Characterization of Bacillus anthracis Spore Proteins Using a Nanoscaffold Vaccine Platform

Subunit vaccines are theoretically safe and easy to manufacture but require effective adjuvants and delivery systems to yield protective immunity, particularly at critical mucosal sites such as the lung. We investigated nanolipoprotein particles (NLPs) containing the Toll-like receptor 4 agonist monophosphoryl lipid A (MPLA) as a platform for intranasal vaccination against Bacillus anthracis. Modified lipids enabled attachment of disparate spore and toxin protein antigens. Intranasal vaccination of mice with B. anthracis antigen-MPLA-NLP constructs induced robust IgG and IgA responses in serum and in bronchoalveolar and nasal lavage. Typically, a single dose sufficed to induce sustained antibody titers over time. When multiple immunizations were required for sustained titers, specific antibodies were detected earlier in the boost schedule with MPLA-NLP-mediated delivery than with free MPLA. Administering combinations of constructs induced responses to multiple antigens, indicating potential for a multivalent vaccine preparation. No off-target responses to the NLP scaffold protein were detected. In summary, the NLP platform enhances humoral and mucosal responses to intranasal immunization, indicating promise for NLPs as a flexible, robust vaccine platform against B. anthracis and potentially other inhalational pathogens.

Liposomal TLR9 Agonist Combined with TLR2 Agonist-Fused Antigen Can Modulate Tumor Microenvironment through Dendritic Cells

Dendritic cells (DCs) are antigen-presenting cells involved in T cell activation and differentiation to regulate immune responses. Lipoimmunogens can be developed as pharmaceutical lipoproteins for cancer immunotherapy to target DCs via toll-like receptor 2 (TLR2) signaling. Previously, we constructed a lipoimmunogen, a lipidated human papillomavirus (HPV) E7 inactive mutant (rlipoE7m), to inhibit the growth of HPV16 E7-expressing tumor cells in a murine model. Moreover, this antitumor effect could be enhanced by a combinatory treatment with CpG oligodeoxynucleotides (ODN). To improve safety, we developed a rlipoE7m plus DOTAP liposome-encapsulated native phosphodiester CpG (POCpG/DOTAP) treatment to target DCs to enhance antitumor immunity. We optimized the formulation of rlipoE7m and POCpG/DOTAP liposomes to promote conventional DC and plasmacytoid DC maturation in vitro and in vivo. Combination of rlipoE7m plus POCpG/DOTAP could activate conventional DCs and plasmacytoid DCs to augment IL-12 production to promote antitumor responses by intravenous injection. In addition, the combination of rlipoE7m plus POCpG/DOTAP could elicit robust cytotoxic T lymphocytes (CTLs) by intravenous immunization. Interestingly, the combination of rlipoE7m plus POCpG/DOTAP could efficiently inhibit tumor growth via intravenous immunization. Moreover, rlipoE7m plus POCpG/DOTAP combined reduced the number of tumor-infiltrating regulatory T cells dramatically due to downregulation of IL-10 production by DCs. These results showed that the combination of rlipoE7m plus POCpG/DOTAP could target DCs via intravenous delivery to enhance antitumor immunity and reduce the number of immunosuppressive cells in the tumor microenvironment.

The Content of CpG-DNA in Antigen-CpG Conjugate Vaccines Determines Their Cross-Presentation Activity

Cross-presentation, the process that facilitates display of exogenous antigens on MHC-I molecules, is a crucial step in the cascade of CD8 T cell activation. Potentiation of cross-presentation therefore represents an essential design criterion for development of subunit vaccines that target the induction of CD8 T cell immunity. Covalent conjugation of CpG-DNA to antigenic proteins has shown the potential to promote cross-presentation and has attracted great interest as a promising approach for vaccine development. However, heterogeneous product mixtures that result from typical conjugation schemes precluded identification of active conjugate species and impeded optimization of cross-presentation activity. In this report, we explore the effect of molecular composition of antigen-CpG conjugates on their cross-presentation activity using model Ovalbumin (OVA)-CpG conjugates. We developed a method to generate antigen-CpG conjugates with defined molecular compositions and leveraged this method to produce a series of OVA-CpG conjugates with one, two, and three CpG molecules linked to OVA. We observed that conjugates containing one CpG per OVA enhanced cross-presentation by 4-fold compared to native OVA, while conjugates with higher contents of CpG provided no cross-presentation enhancement. These differences are likely due to enhanced aggregation propensity observed for conjugates that carry more than one CpG per OVA. Our findings suggest that tuning molecular composition of antigen-CpG conjugates to maintain physical stability may be essential for achieving potent cross-presentation activity. Our method to generate defined conjugates could facilitate such molecular tuning and may be useful for continued development of antigen-CpG vaccines.

Class-B CpG-ODN Formulated With a Nanostructure Induces Type I Interferons-Dependent and CD4+ T Cell-Independent CD8+ T-Cell Response Against Unconjugated Protein Antigen

There is a need for new vaccine adjuvant strategies that offer both vigorous antibody and T-cell mediated protection to combat difficult intracellular pathogens and cancer. To this aim, we formulated class-B synthetic oligodeoxynucleotide containing unmethylated cytosine-guanine motifs (CpG-ODN) with a nanostructure (Coa-ASC16 or coagel) formed by self-assembly of 6-0-ascorbyl palmitate ester. Our previous results demonstrated that mice immunized with ovalbumin (OVA) and CpG-ODN formulated with Coa-ASC16 (OVA/CpG-ODN/Coa-ASC16) elicited strong antibodies (IgG1 and IgG2a) and Th1/Th17 cellular responses without toxic systemic effects. These responses were superior to those induced by a solution of OVA with CpG-ODN or OVA/CpG-ODN formulated with aluminum salts. In this study, we investigated the capacity of this adjuvant strategy (CpG-ODN/Coa-ASC16) to elicit CD8+ T-cell response and some of the underlying cellular and molecular mechanisms involved in adaptive response. We also analyzed whether this adjuvant strategy allows a switch from an immunization scheme of three-doses to one of single-dose. Our results demonstrated that vaccination with OVA/CpG-ODN/Coa-ASC16 elicited an antigen-specific long-lasting humoral response and importantly-high quality CD8+ T-cell immunity with a single-dose immunization. Moreover, Coa-ASC16 promoted co-uptake of OVA and CpG-ODN by dendritic cells. The CD8+ T-cell response induced by OVA/CpG-ODN/Coa-ASC16 was dependent of type I interferons and independent of CD4+ T-cells, and showed polyfunctionality and efficiency against an intracellular pathogen. Furthermore, the cellular and humoral responses elicited by the nanostructured formulation were IL-6-independent. This system provides a simple and inexpensive adjuvant strategy with great potential for future rationally designed vaccines.

Induction of Cytotoxic T-Lymphocyte Responses Upon Subcutaneous Administration of a Subunit Vaccine Adjuvanted With an Emulsion Containing the Toll-Like Receptor 3 Ligand Poly(I:C)

There is an unmet medical need for new subunit vaccines that induce cytotoxic T-lymphocyte (CTL) responses to prevent infection with a number of pathogens. However, stimulation of CTL responses via clinically acceptable subcutaneous (s.c.) and intramuscular (i.m.) injection is challenging. Recently, we designed a liposomal adjuvant [cationic adjuvant formulation (CAF)09] composed of the cationic lipid dimethyldioctadecylammonium (DDA) bromide, a synthetic monomycoloyl glycerol analog and polyinosinic:polycytidylic acid, which induce strong CTL responses to peptide and protein antigens after intraperitoneal administration. By contrast, CAF09 does not stimulate CTL responses upon s.c. or i.m. injection because the vaccine forms a depot that remains at the injection site. Hence, we engineered a series of nanoemulsions (CAF24a-c) based on the active components of CAF09. The oil phase consisted of biodegradable squalane, and the surface charge was varied systematically by replacing DDA with zwitterionic distearoylphosphoethanolamine. We hypothesized that the nanoemulsions drain to the lymph nodes to a larger extent than CAF09, upon s.c. co-administration with the model antigen chicken egg ovalbumin (OVA). This results in an increased dose fraction that reaches the draining lymph nodes (dLNs) and subsequently activates cross-presenting dendritic cells (DCs), which can prime CTL responses. Indeed, the nanoemulsions induced antigen-specific CD8⁺ T-cell responses, which were significantly higher than those stimulated by OVA adjuvanted with CAF09. We explain this by the observed rapid localization of CAF24a in the dLNs and the subsequent association with conventional DCs, which promotes induction of CTL responses. Uptake of CAF24a was not specific for DCs, because CAF24a was also detected with B cells and macrophages. No measurable dose fraction of CAF09 was detected in the dLNs within the study period, and CAF09 formed a depot at the site of injection. Importantly, s.c. vaccination with OVA adjuvanted with CAF24a induced significant levels of specific lysis of antigen-pulsed splenocytes were induced after, which was not observed for OVA adjuvanted with CAF09. Thus, CAF24a is a promising adjuvant for induction of CTL responses upon s.c. and i.m. immunization, and it offers interesting perspectives for the design of vaccines against pathogens for which CTL responses are required to prevent infection.

Pattern recognition receptors and coordinated cellular pathways involved in tuberculosis immunopathogenesis: Emerging concepts and perspectives

Pattern Recognition Receptors (PRRs) play a central role in the recognition of numerous pathogens, including Mycobacterium tuberculosis, resulting in activation of innate and adaptive immune responses. Besides Toll Like Receptors, C-type Lectin Receptors and Nod Like Receptors are now being recognized for their involvement in inducing immune response against M. tuberculosis infection. Although, a functional redundancy of the PRRs has also been reported in many studies, emerging evidences support the notion that a cooperative and coordinated response generated by these receptors is critical to sustain the full immune control of M. tuberculosis infection. Many of the PRRs are now found to be involved in various cellular host defenses, such as inflammasome activation, phagosome biogenesis, endosomal trafficking, and antigen processing pathways that are all very critical for an effective immune response against M. tuberculosis. In support, polymorphism in several of these receptors has also been found associated with increased susceptibility to tuberculosis in humans. Nonetheless, increasing evidences also show that in order to enhance its intracellular survival, M. tuberculosis has also evolved multiple strategies to subvert and reprogram PPR-mediated immune responses. In light of these findings, this review analyzes the interaction of bacterial and host factors at the intersections of PRR signaling pathways that could provide integrative insights for the development of better vaccines and therapeutics for tuberculosis.

Enhancement of antigen-specific CD4+ and CD8+ T cell responses using a self-assembled biologic nanolipoprotein particle vaccine

To address the need for vaccine platforms that induce robust cell-mediated immunity, we investigated the potential of utilizing self-assembling biologic nanolipoprotein particles (NLPs) as an antigen and adjuvant delivery system to induce antigen-specific murine T cell responses. We utilized OT-I and OT-II TCR-transgenic mice to investigate the effects of NLP-mediated delivery of the model antigen ovalbumin (OVA) on T cell activation. Delivery of OVA with the TLR4 agonist monophosphoryl lipid A (MPLA) in the context of NLPs significantly enhanced the activation of both CD4⁺ and CD8⁺ T cells in vitro compared to co-administration of free OVA and MPLA. Upon intranasal immunization of mice harboring TCR-transgenic cells, NLPs enhanced the adjuvant effects of MPLA and the in vivo delivery of OVA, leading to significantly increased expansion of CD4⁺ and CD8⁺ T cells in lung-draining lymph nodes. Therefore, NLPs are a promising vaccine platform for inducing T cell responses following intranasal administration.

A bacterial cyclic dinucleotide activates the cytosolic surveillance pathway and mediates innate resistance to tuberculosis

Detection of cyclic-di-adenosine monophosphate (c-di-AMP), a bacterial second messenger, by the host cytoplasmic surveillance pathway (CSP) is known to elicit Type I interferon responses critical for antimicrobial defense^1–3. However, the mechanisms and role of c-di-AMP signaling in Mycobacterium tuberculosis virulence remain unclear. Here we show that resistance to tuberculosis (TB) requires CSP-mediated detection of c-di-AMP produced by M. tuberculosis and that levels of c-di-AMP modulate the fate of infection. We found that a di-adenylate cyclase (disA or dacA)⁴ over-expressing M. tuberculosis strain that secretes excess c-di-AMP activates the interferon regulatory factor (IRF) pathway with enhanced levels of IFN-β, elicits increased macrophage autophagy, and exhibits significant attenuation in mice. We show that c-di-AMP-mediated IFN-β induction during M. tuberculosis infection requires stimulator of interferon genes (STING)⁵-signaling. We observed that c-di-AMP induction of IFN-β is independent of the cytosolic nucleic acid receptor cyclic-GMP-AMP (cGAMP) synthase (cGAS)^6–7, but cGAS nevertheless contributes substantially to the overall IFN-β response to M. tuberculosis infection. In sum, our results reveal c-di-AMP to be a key mycobacterial pathogen associated molecular pattern (PAMP) driving host Type I IFN responses and autophagy. These findings suggest that modulating the levels of this small molecule may lead to novel immunotherapeutic strategies against TB.

Cancer immunotherapy employing an innovative strategy to enhance CD4+ T cell help in the tumor microenvironment

Chemotherapy and/or radiation therapy are widely used as cancer treatments, but the antitumor effects they produce can be enhanced when combined with immunotherapies. Chemotherapy kills tumor cells, but it also releases tumor antigen and allows the cross-presentation of the tumor antigen to trigger antigen-specific cell-mediated immune responses. Promoting CD4+ T helper cell immune responses can be used to enhance the cross-presentation of the tumor antigen following chemotherapy. The pan HLA-DR binding epitope (PADRE peptide) is capable of generating antigen-specific CD4+ T cells that bind various MHC class II molecules with high affinity and has been widely used in conjunction with vaccines to improve their potency by enhancing CD4+ T cell responses. Here, we investigated whether intratumoral injection of PADRE and the adjuvant CpG into HPV16 E7-expressing TC-1 tumors following cisplatin chemotherapy could lead to potent antitumor effects and antigen-specific cell-mediated immune responses. We observed that treatment with all three agents produced the most potent antitumor effects compared to pairwise combinations. Moreover, treatment with cisplatin, CpG and PADRE was able to control tumors at a distant site, indicating that our approach is able to induce cross-presentation of the tumor antigen. Treatment with cisplatin, CpG and PADRE also enhanced the generation of PADRE-specific CD4+ T cells and E7-specific CD8+ T cells and decreased the number of MDSCs in tumor loci. The treatment regimen presented here represents a universal approach to cancer control.

Crosstalk between Mycobacterium tuberculosis and the host cell

The successful establishment and maintenance of a bacterial infection depend on the pathogen's ability to subvert the host cell's defense response and successfully survive, proliferate, or persist within the infected cell. To circumvent host defense systems, bacterial pathogens produce a variety of virulence factors that potentiate bacterial adherence and invasion and usurp host cell signaling cascades that regulate intracellular microbial survival and trafficking. Mycobacterium tuberculosis, probably one of the most successful pathogens on earth, has coexisted with humanity for centuries, and this intimate and persistent connection between these two organisms suggests that the pathogen has evolved extensive mechanisms to evade the human immune system at multiple levels. While some of these mechanisms are mediated by factors released by M. tuberculosis, others rely on host components that are hijacked to prevent the generation of an effective immune response thus benefiting the survival of M. tuberculosis within the host cell. Here, we describe several of these mechanisms, with an emphasis on the cyclic nucleotide signaling and subversion of host responses that occur at the intracellular level when tubercle bacilli encounter macrophages, a cell that becomes a safe-house for M. tuberculosis although it is specialized to kill most microbes.

Type I interferons as regulators of human antigen presenting cell functions

Type I interferons (IFNs) are pleiotropic cytokines, initially described for their antiviral activity. These cytokines exhibit a long record of clinical use in patients with some types of cancer, viral infections and chronic inflammatory diseases. It is now well established that IFN action mostly relies on their ability to modulate host innate and adaptive immune responses. Work in recent years has begun to elucidate the mechanisms by which type I IFNs modify the immune response, and this is now recognized to be due to effects on multiple cell types, including monocytes, dendritic cells (DCs), NK cells, T and B lymphocytes. An ensemble of results from both animal models and in vitro studies emphasized the key role of type I IFNs in the development and function of DCs, suggesting the existence of a natural alliance between these cytokines and DCs in linking innate to adaptive immunity. The identification of IFN signatures in DCs and their dysregulation under pathological conditions will therefore be pivotal to decipher the complexity of this DC-IFN interaction and to better exploit the therapeutic potential of these cells.

Coadministration of polyinosinic:polycytidylic acid and immunostimulatory complexes modifies antigen processing in dendritic cell subsets and enhances HIV gag-specific T cell immunity

Currently approved adjuvants induce protective Ab responses but are more limited for generating cellular immunity. In this study, we assessed the effect of combining two adjuvants with distinct mechanisms of action on their ability to prime T cells: the TLR3 ligand, polyinosinic:polycytidylic acid (poly I:C), and immunostimulatory complexes (ISCOMs). Each adjuvant was administered alone or together with HIV Gag protein (Gag), and the magnitude, quality, and phenotype of Gag-specific T cell responses were assessed. For CD8 T cells, all adjuvants induced a comparable response magnitude, but combining poly I:C with ISCOMs induced a high frequency of CD127(+), IL-2-producing cells with decreased expression of Tbet compared with either adjuvant alone. For CD4 T cells, combining poly I:C and ISCOMs increased the frequency of multifunctional cells, producing IFN-γ, IL-2, and TNF, and the total magnitude of the response compared with either adjuvant alone. CD8 or CD4 T cell responses induced by both adjuvants mediated protection against Gag-expressing Listeria monocytogenes or vaccinia viral infections. Poly I:C and ISCOMs can alter Ag uptake and/or processing, and we therefore used fluorescently labeled HIV Gag and DQ-OVA to assess these mechanisms, respectively, in multiple dendritic cell subsets. Poly I:C promoted uptake and retention of Ag, whereas ISCOMs enhanced Ag degradation. Combining poly I:C and ISCOMs caused substantial death of dendritic cells but persistence of degraded Ag. These data illustrate how combining adjuvants, such as poly I:C and ISCOMs, that modulate Ag processing and have potent innate activity, can enhance the magnitude, quality, and phenotype of T cell immunity.

TLR7 triggering with polyuridylic acid promotes cross-presentation in CD8α+ conventional dendritic cells by enhancing antigen preservation and MHC class I antigen permanence on the dendritic cell surface

ssRNA can interact with dendritic cells (DCs) through binding to TLR7, inducing secretion of proinflammatory cytokines and type I IFN. Triggering TLR7 enhances cross-priming of CD8(+) T cells, which requires cross-presentation of exogenous Ag to DCs. However, how TLR triggering can affect Ag cross-presentation is still not clear. Using OVA as an Ag model, we observed that stimulation of TLR7 in DCs by polyuridylic acid (polyU), a synthetic ssRNA analog, generates a strong specific cytotoxic response in C57BL/6 mice. PolyU stimulate CD8α(+) DCs to cross-prime naive CD8(+) T cells in a type I IFN-dependent fashion. This enhanced cross-priming is accompanied by a higher density of OVA(256-264)/H-2K(b) complexes on CD8α(+) DCs treated with polyU, as well as by upregulation of costimulatory molecules and increased secretion of proinflammatory cytokines by DCs. Cross-priming of CD8(+) T cells by DCs treated with polyU requires proteasome and Ag translocation to cytosol through the Sec61 channel in DCs. The observed enhancement in OVA cross-presentation with polyU in DCs could be mediated by a limited Ag degradation in endophagosomal compartments and a higher permanence of OVA peptide/MHC class I complexes on DCs. These observations clearly reveal that key steps of Ag processing for cross-presentation can be modulated by TLR ligands, opening new avenues for understanding their mechanisms as adjuvants of the immune response.

A novel post-transcriptional role for ubiquitin in the differential regulation of MHC class I allotypes

By providing ligands for Cytotoxic T-Lymphocytes (CTL) as well as Natural Killer (NK) cells, the HLA-A/B/C MHC class I molecules (MHC-I) play a central role in both innate and adaptive immunity. In addition to CTL-mediated recognition of MHC-peptide complexes, cell surface expression of MHC-I is closely monitored by NK cells, whose killer-cell immunoglobulin-like receptors encode activatory and inhibitory receptors with specificity for MHC-I. How the cell surface expression of MHC-I is tightly controlled is not well understood. In a functional siRNA ubiquitome screen to identify E3 ligases involved in MHC-I regulation we recently found that MEX-3C, a novel RNA-binding ubiquitin E3 ligase, is responsible for the post-transcriptional, HLA-A allotype-specific regulation of MHC-I. MEX-3C expression is increased upon NK cell activation and modulates the threshold of killing by these cells. We find that MEX-3C binds the 3′-untranslated region of HLA-A2 mRNA, inducing its RING-dependent degradation. The RING domain of MEX-3C is not required for HLA-A2 cell surface downregulation, but regulates the degradation of HLA-A2 mRNA. We have therefore uncovered a novel post-transcriptional pathway for regulation of HLA-A allotypes and provide a direct link between ubiquitination and mRNA decay.

Type I IFN drives a distinctive dendritic cell maturation phenotype that allows continued class II MHC synthesis and antigen processing

Microbial molecules or cytokines can stimulate dendritic cell (DC) maturation, which involves DC migration to lymph nodes and enhanced presentation of Ag to launch T cell responses. Microbial TLR agonists are the most studied inducers of DC maturation, but type I IFN (IFN-I) also promotes DC maturation. In response to TLR stimulation, DC maturation involves a burst of Ag processing with enhanced expression of peptide-class II MHC complexes and costimulator molecules. Subsequently, class II MHC (MHC-II) synthesis and expression in intracellular vacuolar compartments is inhibited, decreasing Ag processing function. This limits presentation to a cohort of Ags kinetically associated with the maturation stimulus and excludes presentation of Ags subsequently experienced by the DC. In contrast, our studies show that IFN-I enhances DC expression of MHC-II and costimulatory molecules without a concomitant inhibition of subsequent MHC-II synthesis and Ag processing. Expression of mRNA for MHC-II and the transcription factor CIITA is inhibited in DCs treated with TLR agonists but maintained in cells treated with IFN-I. After stimulation with IFN-I, MHC-II expression is increased on the plasma membrane but is also maintained in intracellular vacuolar compartments, consistent with sustained Ag processing function. These findings suggest that IFN-I drives a distinctive DC maturation program that enhances Ag presentation to T cells without a shutdown of Ag processing, allowing continued sampling of Ags for presentation.

Effects of CpG-ODNs on phenotype and function of monocyte-derived dendritic cells in chronic hepatitis B

AIM: To study the effects of synthetic nonmethylated CpG-containing oligodeoxynucleotides (CpG-ODNs), either alone or combined with recombinant Hepatitis B surface antigen (HBsAg) polypeptide, on the phenotype, function, and intracellular signaling pathways of monocyte-derived dendritic cells (DCs) in patients with chronic hepatitis B (CHB).

METHODS: Peripheral blood monocytes isolated from CHB patients and healthy volunteers were induced to be dendritic cells by recombinant human granulocyte-monocyte colony stimulating factor and interleukin-4. The DCs were then treated with CpG-ODNs, CpG-ODNs/HBsAg, or tumor necrosis factor (TNF)-α for 18 h. The expression of surface molecules including HLA-DR, CD86, and CD1a in DCs were detected by flow cytometry, and the expression of signal transducers and activators of transcription (STAT1, 3, 4, 5, 6) and suppressors of cell signaling (SOCS1, 3) were determined by Western blotting assay. In addition, the capacity of DCs to stimulate allogeneic T lymphocytes and the amount of IL-12p70 released from DCs were measured.

RESULTS: In the DCs derived from patients with CHB, treatment with TNF-α, CpG-ODNs, or CpG-ODNs/HBsAg, as compared to the vector control, significantly increased the expression of HLA-DR, stimulated the release of IL-12p70, and enhanced the capacity of DCs to stimulate allogenic T lymphocytes. The expressions of STAT1/4/6 and SOCS1/3, but not STAT3/5, were upregulated by TNF-α, CpG-ODNs, and CpG-ODNs/HBsAg. In addition, the expression of CD1a was upregulated only in the presence of both CpG-ODNs and HBsAg.

CONCLUSION: The treatment with CpG-ODNs, either alone or combined with HBsAg, has a remarkable stimulatory effect on the impaired phenotype and function of DCs in CHB, possibly by regulating the expression of STAT1, 4, 6 and SOCS1, 3.

Mechanisms of antigen presentation to T cells in murine graft-versus-host disease: cross-presentation and the appearance of cross-presentation

Recipient antigen-presenting cells (APCs) initiate GVHD by directly presenting host minor histocompatibility antigens (miHAs) to donor CD8 cells. However, later after transplantation, host APCs are replaced by donor APCs, and if pathogenic CD8 cells continue to require APC stimulation, then donor APCs must cross-present host miHAs. Consistent with this, CD8-mediated GVHD is reduced when donor APCs are MHC class I(-). To study cross-presentation, we used hosts that express defined MHC class I K(b)-restricted miHAs, crossed to K(b)-deficient backgrounds, such that these antigens cannot be directly presented. Cross-priming was surprisingly efficient, whether antigen was restricted to the hematopoietic or nonhematopoietic compartments. Cross-primed CD8 cells were cytolytic and produced IFN-γ. CD8 cells were exclusively primed by donor CD11c(+) cells, and optimal cross-priming required that they are stimulated by both type I IFNs and CD40L. In studying which donor APCs acquire host miHAs, we made the surprising discovery that there was a large-scale transfer of transmembrane proteins from irradiated hosts, including MHC class I-peptide complexes, to donor cells, including dendritic cells. Donor dendritic cells that acquired host MHC class I-peptide complexes were potent stimulators of peptide-specific T cells. These studies identify new therapeutic targets for GVHD treatment and a novel mechanism whereby donor APCs prime host-reactive T cells.

Presentation of type B peptide-MHC complexes from hen egg white lysozyme by TLR ligands and type I IFNs independent of H2-DM regulation

In APCs, presentation by MHC II molecules of the chemically dominant peptide from the protein hen egg white lysozyme (HEL) generates different conformational isomers of the peptide-MHC II complexes (pMHC). Type B pMHCs are formed in early endosomes from exogenous peptides in the absence of H2-DM, whereas in contrast, type A pMHC complexes are formed from HEL protein in late vesicles after editing by H2-DM. Thus, H2-DM edits off the more unstable pMHC complexes, which are not presented from HEL. In this study, we show that type B pMHC complexes were presented from HEL protein only after stimulation of dendritic cells (DC) with TLR ligands or type I IFN. Type I IFN contributed to most TLR ligand-induced type B pMHC generation, as presentation decreased in DC lacking the receptor for type I IFNs (IFNAR1(-/-)). In contrast, presentation of type A pMHC from HEL and from peptide was minimally affected by TLR ligands. The relative effectiveness of CD8α(+) DC or CD8α(-) DC in presenting type B pMHC complexes varied depending on the TLR ligand used. The mechanisms of generation of type B pMHC from HEL protein with TLR stimulation did not involve H2-DM or release of peptides. DC from H2-DM-deficient mice in the presence of TLR ligands presented type B pMHC. Such DC showed a slight enhancement of HEL catabolism, but peptide release was not evident. Thus, TLR ligands and type I IFN alter the pathways of presentation by MHC II molecules of DC such that type B pMHCs are generated from protein Ag.

IFN-α boosts epitope cross-presentation by dendritic cells via modulation of proteasome activity

We have investigated the molecular mechanisms underlying the peculiar cross-presentation efficiency of human dendritic cells (DCs) differentiated from monocytes in the presence of Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) and Interferon (IFN)-α (IFN-DCs). To this end, we evaluated the capability of IFN-DCs to present and cross-present epitopes derived from Epstein-Barr Virus (EBV) or human melanoma-associated antigens after exposure to cell lysates or apoptotic cells. In an autologous setting, IFN-DCs loaded with Lymphoblastoid Cell Lines (LCL) lysates or apoptotic LCL were highly efficient in expanding, respectively, EBV-specific class II- or class I-restricted memory T cell responses. Of note, IFN-DCs loaded with apoptotic LCL were more potent than fully mature DCs in triggering the cytotoxicity of CD8(+) T lymphocytes recognizing a subdominant HLA-A*0201-restricted epitope derived from EBV latent membrane protein 2 (LMP2). In addition, IFN-DCs loaded with apoptotic human melanoma cells were highly efficient in cross-presenting the MART-1(27-35) epitope to a specific CD8(+) cytotoxic T cell clone, and this functional activity was proteasome-dependent. These IFN-DC properties were associated with an enhanced expression of all the immunoproteasome subunits as well as of TAP-1, TAP-2 and tapasin, and, interestingly, to a higher proteasome proteolytic activity as compared to immature or mature DCs. Altogether, these results highlight new mechanisms by which IFN-α influences antigen processing and cross-presentation ability of monocyte-derived DCs, with potentially important implications for the development of DC-based therapeutic vaccines.

Mycobacterium tuberculosis and TLR2 agonists inhibit induction of type I IFN and class I MHC antigen cross processing by TLR9

Dendritic cells (DCs) cross process exogenous Ags and present them by class I MHC (MHC-I) molecules to CD8(+) T cells specific for Ags from viruses and bacteria such as Mycobacterium tuberculosis. Unmethylated CpG DNA signals through TLR9 to induce type I IFN (IFN-alpha/beta), which enhances MHC-I Ag cross processing, but lipoproteins that signal through TLR2 do not induce IFN-alpha/beta. In these studies we observed that M. tuberculosis, which expresses agonists of both TLR9 and TLR2, did not induce production of IFN-alpha/beta or cross processing by murine DCs. Furthermore, M. tuberculosis and TLR2 agonists inhibited induction of IFN-alpha/beta and DC cross processing by CpG DNA. Exogenous IFN-alpha/beta effectively enhanced cross processing of M. bovis bacillus Calmette-Guérin expressing OVA, bypassing the inhibition of induction of endogenous IFN-alpha/beta. In addition, inhibition of TLR9-induced cross processing of M. bovis bacillus Calmette-Guérin expressing OVA could be circumvented by pretreating cells with CpG DNA to induce IFN-alpha/beta and MHC-I cross processing before inhibitory mycobacterial TLR2 agonists were present. Inhibition of the response to one TLR by another may affect the ultimate response to pathogens like M. tuberculosis that express agonists of multiple TLRs, including TLR2 and TLR9. This mechanism may contribute to immune evasion and explain why IFN-alpha/beta provides little contribution to host immunity to M. tuberculosis. However, downregulation of certain TLR responses may benefit the host by preventing detrimental excessive inflammation that may occur in the presence of persistent infection.

CpG-B oligodeoxynucleotides inhibit TLR-dependent and -independent induction of type I IFN in dendritic cells

CpG oligodeoxynucleotides (ODNs) signal through TLR9 to induce type I IFN (IFN-alphabeta) in dendritic cells (DCs). CpG-A ODNs are more efficacious than CpG-B ODNs for induction of IFN-alphabeta. Because IFN-alphabeta may contribute to autoimmunity, it is important to identify mechanisms to inhibit induction of IFN-alphabeta. In our studies, CpG-B ODN inhibited induction of IFN-alphabeta by CpG-A ODN, whereas induction of TNF-alpha and IL-12p40 by CpG-A ODN was not affected. CpG-B inhibition of IFN-alphabeta was observed in FLT3 ligand-induced murine DCs, purified murine myeloid DCs, plasmacytoid DCs, and human PBMCs. CpG-B ODN inhibited induction of IFN-alphabeta by agonists of multiple receptors, including MyD88-dependent TLRs (CpG-A ODN signaling via TLR9, or R837 or Sendai virus signaling via TLR7) and MyD88-independent receptors (polyinosinic:polycytidylic acid signaling via TLR3 or ds break-DNA signaling via a cytosolic pathway). CpG-B ODN did not inhibit the IFN-alphabeta positive feedback loop second-wave IFN-alphabeta, because IFN-alphabeta-induced expression of IFN-alphabeta was unaffected, and CpG-B inhibition of IFN-alphabeta was manifested in IFN-alphabetaR(-/-) DCs, which lack the positive feedback mechanism. Rather, CpG-B ODN inhibited early TLR-induced first wave IFN-alpha4 and IFN-beta. Chromatin immunoprecipitation revealed that association of IFN regulatory factor 1 with the IFN-alpha4 and IFN-beta promoters was induced by CpG-A ODN but not CpG-B ODN. Moreover, CpG-A-induced association of IFN regulatory factor 1 with these promoters was inhibited by CpG-B ODN. Our studies demonstrate a novel mechanism of transcriptional regulation of first-wave IFN-alphabeta that selectively inhibits induction of IFN-alphabeta downstream of multiple receptors and may provide targets for future therapeutic inhibition of IFN-alphabeta expression in vivo.

NCI First International Workshop on The Biology, Prevention, and Treatment of Relapse After Allogeneic Hematopoietic Stem Cell Transplantation: Report from the Committee on the Biology Underlying Recurrence of Malignant Disease following Allogeneic HSCT: Graft-versus-Tumor/Leukemia Reaction

The success of allogeneic hematopoietic stem cell transplantation (HSCT) depends on the infusion of benign stem cells as well as lymphocytes capable of participating in a graft-versus-tumor/leukemia (GVL) reaction. Clinical proof of concept is derived from studies showing increased relapse after the infusion of lymphocyte depleted hematopoietic grafts as well as the therapeutic efficacy of donor lymphocyte infusions without chemotherapy to treat relapse in some diseases. Despite this knowledge, relapse after allogeneic HSCT is common with rates approaching 40% in those with high-risk disease. In this review, we cover the basic biology and potential application to exploit adaptive T cell responses, minor histocompatibility antigens, contraction and suppression mechanisms that hinder immune responses, adaptive B cell responses and innate NK cell responses, all orchestrated in a GVL reaction. Optimal strategies to precisely balance immune responses to favor GVL without harmful graft-versus-host disease (GVHD) are needed to protect against relapse, treat persistent disease and improve disease-free survival after HSCT.

Topical resiquimod promotes priming of CTL to parenteral antigens

We explored the topical use of resiquimod (R-848), a Toll-like receptor (TLR) 7/8 agonist, in gel formulation, to enhance cross-priming to subcutaneously administered protein antigen in a murine model. Resiquimod application at the time of subcutaneous administration of ovalbumin generated robust antigen-specific CTL as detected by tetramers, IFN-gamma ELISPOT assays and standard cytotoxicity assays. Induced CTL were capable of mediating antigen-specific killing in vivo as measured by in vivo cytotoxicity assays and an ability to protect against B16-OVA tumor challenge. Multiple serial applications of topical resiquimod increased the frequency of antigen-specific CTL when compared to single application. This enhanced frequency was noted despite a marked inhibition of adjuvant mediated pro-inflammatory cytokine release following repeated administration. Topical resiquimod is a potent adjuvant for locally administered subcutaneous vaccines, inducing clinically relevant CTL responses following single application at the time of subcutaneous vaccination.

CTL induction by cross-priming is restricted to immunodominant epitopes

CTL are induced by two pathways, i.e. direct priming, where tumor cells present tumor antigens to naïve specific CTL, and cross-priming, where professional APC cross-present captured tumor antigens to CTL. Here, we examined direct priming versus cross-priming after immunizing (H-2(b) x H-2(d)) F1 mice with either H-2(b) or H-2(d) positive tumor cells transfected with the GP or nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV). Cross-priming was observed for the immunodominant epitopes LCMV-gp33 and -np118, although direct induction resulted in higher CTL frequencies. In contrast, CTL specific for the subdominant epitopes LCMV-gp283 or -np396 were induced only if epitopes were presented directly on MHC class I molecules of the immunizing cell. The broader repertoire and the higher CTL frequencies induced after vaccination with haplotype-matched tumor cells resulted in more efficient anti-tumor and antiviral protection. Firstly, our results indicate that certain virus and tumor antigens may not be detected by CD8(+) T cells because of impaired cross-priming. Secondly, efficient cross-priming contributes to the immunodominant nature of a tumor-specific CTL epitope. Thirdly, vaccine strategies using autologous or syngenic antigen-expressing cells induce a broader repertoire of tumor-specific CTL and higher CTL frequencies.

Therapeutic injection of C-class CpG ODN in draining lymph node area induces potent activation of immune cells and rejection of established breast cancer in mice

In order to develop novel CpG ODNs for the treatment of breast cancer, we have designed a series of CpG ODNs and evaluated their anti-tumor activity in a breast cancer mouse model. Interestingly, a C-class CpG ODN, designated as YW002, showed a vigorous activity on the inhibition of tumor growth in mice and completely cured some of the tumor-bearing mice through injection at tumor draining lymph node (TDLN) area. The expansion of immune cells in the TDLN and tumor and the generation of tumor specific immune memory were found associated with YW002-induced anti-tumor activity in mice. These results indicate that C-class CpG ODN could be developed into a medicament in a monotherapeutic regimen for the treatment of breast cancer through injection at TDLN area in clinic.

Circumvention of regulatory CD4(+) T cell activity during cross-priming strongly enhances T cell-mediated immunity

Immunization with purified antigens is a safe and practical vaccination strategy but is generally unable to induce sustained CD8(+) T cell-mediated protection against intracellular pathogens. Most efforts to improve the CD8(+) T cell immunogenicity of these vaccines have focused on co-administration of adjuvant to support cross-presentation and dendritic cell maturation. In addition, it has been shown that CD4(+) T cell help during the priming phase contributes to the generation of protective CD8(+) memory T cells. In this report we demonstrate that the depletion of CD4(+) T cells paradoxically enhances long-lasting CD8-mediated protective immunity upon protein vaccination. Functional and genetic in vivo inactivation experiments attribute this enhancement primarily to MHC class II-restricted CD4(+) regulatory T cells (Treg), which appear to physiologically suppress the differentiation process towards long-living effector memory T cells. Since, in functional terms, this suppression by Treg largely exceeds the positive effects of conventional CD4(+) T cell help, even the absence of all CD4(+) T cells or lack of MHC class II-mediated interactions on priming dendritic cells result in enhanced CD8(+) T cell immunogenicity. These findings have important implications for the improvement of vaccines against intracellular pathogens or tumors, especially in patients with highly active Treg.

Identification of TTP mRNA targets in human dendritic cells reveals TTP as a critical regulator of dendritic cell maturation

Dendritic cells provide a critical link between innate and adaptive immunity and are essential to prime a naive T-cell response. The transition from immature dendritic cells to mature dendritic cells involves numerous changes in gene expression; however, the role of post-transcriptional changes in this process has been largely ignored. Tristetraprolin is an AU-rich element mRNA-binding protein that has been shown to regulate the stability of a number of cytokines and chemokines of mRNAs. Using TTP immunoprecipitations and Affymetrix GeneChips, we identified 393 messages as putative TTP mRNA targets in human dendritic cells. Gene ontology analysis revealed that approximately 25% of the identified mRNAs are associated with protein synthesis. We also identified six MHC Class I alleles, five MHC Class II alleles, seven chemokine and chemokine receptor genes, indoleamine 2,3 dioxygenase, and CD86 as putative TTP ligands. Real-time PCR was used to validate the GeneChip data for 15 putative target genes and functional studies performed for six target genes. These data establish that TTP regulates the expression of DUSP1, IDO, SOD2, CD86, and MHC Class I-B and F via the 3'-untranslated region of each gene. A novel finding is the demonstration that TTP can interact with and regulate the expression of non-AU-rich element-containing messages. The data implicate TTP as having a broader role in regulating and limiting the immune response than previously suspected.

Direct proteasome-independent cross-presentation of viral antigen by plasmacytoid dendritic cells on major histocompatibility complex class I

Although plasmacytoid dendritic cells (pDCs) respond to virus replication in a nonspecific way by producing large amounts of type I interferon, a rapid, direct function for pDCs in activating antiviral lymphocytes is less apparent. Here we show that pDCs were able to rapidly initiate antigen-specific antiviral CD8+ T cell responses. After being exposed to virus, pDCs efficiently and rapidly internalized exogenous viral antigens and then presented those antigens on major histocompatibility complex (MHC) class I to CD8+ T cells. Processing of exogenous antigen occurred in endocytic organelles and did not require transit of antigen to the cytosol. Intracellular stores of MHC class I partially localized together with the transferrin receptor and internalized transferrin in endosomes, which suggested that such recycling endosomes are sites for loading peptide onto MHC class I or for peptide transit. Our data demonstrate that pDCs use 'ready-made' stores of MHC class I to rapidly present exogenous antigen to CD8+ T cells.

Targeting DCIR on human plasmacytoid dendritic cells results in antigen presentation and inhibits IFN-alpha production

C-type lectin receptors (CLRs) fulfill multiple functions within the immune system by recognition of carbohydrate moieties on foreign or (altered) self-structures. CLRs on myeloid dendritic cells (DCs) have been well characterized as pattern-recognition receptors (PRRs) combining ligand internalization with complex signaling events. Much less is known about CLR expression and function in human plasmacytoid DCs (pDCs), the major type I interferon (IFN) producers. In this study, we demonstrate that, next to the CLR BDCA-2, human pDCs express DC immunoreceptor (DCIR), a CLR with putative immune-inhibitory function, but not dectin-1, mannose receptor, or DC-specific ICAM-3-grabbing nonintegrin. DCIR surface levels are reduced on pDC maturation after TLR9 triggering. Interestingly, DCIR triggering inhibits TLR9-induced IFN-alpha production while leaving up-regulation of costimulatory molecule expression unaffected. Furthermore, DCIR is readily internalized into pDCs after receptor triggering. We show that DCIR internalization is clathrin-dependent because it can be inhibited by hypertonic shock and dominant-negative dynamin. Importantly, antigens targeted to pDCs via DCIR are presented to T cells. These findings indicate that targeting DCIR on pDCs not only results in efficient antigen presentation but also affects TLR9-induced IFN-alpha production. Collectively, the data show that targeting of DCIR can modulate human pDC function and may be applied in disease prevention and treatment.

Human Toll-like receptor-dependent induction of interferons in protective immunity to viruses

Five of the 10 human Toll-like receptors (TLRs) (TLR3, TLR4, TLR7, TLR8, and TLR9), and four of the 12 mouse TLRs (TLR3, TLR4, TLR7, TLR9) can trigger interferon (IFN)-alpha, IFN-beta, and IFN-lambda, which are critical for antiviral immunity. Moreover, TLR3, TLR7, TLR8, and TLR9 differ from TLR4 in two particularly important ways for antiviral immunity: they can be activated by nucleic acid agonists mimicking compounds produced during the viral cycle, and they are typically present within the cell, along the endocytic pathway, where they sense viral products in the intraluminal space. Investigations in mice have demonstrated that the TLR7/9-IFN and TLR3-IFN pathways are different and critical for protective immunity to various experimental viral infections. Investigations in humans with interleukin-1 receptor-associated kinase-4 (IRAK-4) deficiency (unresponsive to TLR7, TLR8, and TLR9), UNC-93B deficiency (unresponsive to TLR3, TLR7, TLR8, and TLR9), and TLR3 deficiency have recently shed light on the role of these two pathways in antiviral immunity in natural conditions. UNC-93B- and TLR3-deficient patients appear to be specifically prone to herpes simplex virus 1 (HSV-1) encephalitis, although clinical penetrance is incomplete, whereas IRAK-4-deficient patients appear to be normally resistant to most viruses, including HSV-1. These experiments of nature suggest that the TLR7-, TLR8-, and TLR9-dependent induction of IFN-alpha, IFN-beta, and IFN-lambda is largely redundant in human antiviral immunity, whereas the TLR3-dependent induction of IFN-alpha, IFN-beta, and IFN-lambda is critical for primary immunity to HSV-1 in the central nervous system in children but redundant for immunity to most other viral infections.

Topical TLR9 agonists induce more efficient cross-presentation of injected protein antigen than parenteral TLR9 agonists do

Topical application of adjuvant to the skin promotes the generation of immune responses to co-administered peptide or protein antigen. We demonstrate that topical administration of CpG adjuvant (a TLR9 agonist) induces the cross-presentation of, and antigen-specific CTL induction to, locally injected soluble protein antigen. C57BL/6 mice were immunized by subcutaneous or intramuscular injection with ovalbumin (OVA) protein as model antigen. Application of CpG to the local skin induced more efficient cross-presentation of the injected antigen than co-injected adjuvant. Robust antigen-specific CTL responses were generated, as determined by antigen-specific CTL enumeration using tetramers, IFN-gamma ELISPOT analysis and cytotoxicity assays. Long-term memory CTL responses were induced. Topical administration of adjuvant induced Langerhans cell migration, local type 1 IFN-dependent myxovirus-resistance protein A expression and bystander dendritic cell (DC) activation. Soluble antigen-bearing DC within the skin draining lymph nodes were mainly CD11chiCD11bhilangerinloDEC205lo. Topical administration did not result in the splenomegaly or systemic cytokine induction (including TNF-alpha, IL-12, IFN-gamma and MCP-1) noted with parenteral administration. Topical TLR9 family agonists may be used to modulate the immune response to soluble protein vaccines administered by standard percutaneous route. Topical adjuvant administration increases efficacy of CTL induction and reduces toxicity when compared to parenteral adjuvant administration.

Induction of MHC class I molecule cell surface expression and epigenetic activation of antigen-processing machinery components in a murine model for human papilloma virus 16-associated tumours

Epigenetic events play an important role in tumour progression and also contribute to escape of the tumour from immune surveillance. In this study, we investigated the up-regulation of major histocompatibility complex (MHC) class I surface expression on tumour cells by epigenetic mechanisms using a murine tumour cell line expressing human E6 and E7 human papilloma virus 16 (HPV16) oncogenes and deficient in MHC class I expression, as a result of impaired antigen-presenting machinery (APM). Treatment of the cells with the histone deacetylase inhibitor Trichostatin A, either alone or in combination with the DNA demethylating agent 5-azacytidine, induced surface re-expression of MHC class I molecules. Consequently, the treated cells became susceptible to lysis by specific cytotoxic T lymphocytes. Further analysis revealed that epigenetic induction of MHC class I surface expression was associated with the up-regulation of APM genes [transporter associated with antigen processing 1 (TAP-1), TAP-2, low-molecular-mass protein 2 (LMP-2) and LMP-7]. The results demonstrate that expression of the genes involved in APM are modulated by epigenetic mechanisms and suggest that agents modifying DNA methylation and/or histone acetylation have the potential to change the effectiveness of antitumour immune responses and therapeutically may have an impact on immunological output.

Cross-priming of long lived protective CD8+ T cells against Trypanosoma cruzi infection: importance of a TLR9 agonist and CD4+ T cells

We recently described that vaccination of mice with a glutathione S transferase fusion protein representing amino acids 261-500 of the Amastigote Surface Protein-2 efficiently cross-primed protective CD8+ T cells against a lethal challenge with the human protozoan parasite Trypanosoma cruzi. In this study, we initially established that this protective immunity was long lived. Subsequently, we studied the importance of TLR9 agonist CpG ODN 1826, TLR4 and CD4+ T cells for the generation of these protective CD8+ T cells. We found that: (i) the TLR9 agonist CpG ODN 1826 improved the efficiency of protective immunity; (ii) TLR4 is not relevant for priming of specific CD8+ T cells; (iii) CD4+ T cells are critical for priming of memory/protective CD8+ T cells.

Rapid transit in the immune cells: the role of mRNA turnover regulation

There have been recent, significant advances about the role of mRNA turnover in controlling gene expression in immune cells. Post‐transcriptional regulation of gene expression contributes to the characteristics of many of the processes underlying the immune response by ensuring early, rapid, and transient action. The emphasis of this review is on current work that deals with the regulation of mRNA decay during innate immunity against microbes and T cell activation as a model of the adaptive response.

Post-transcriptional control of the interferon system

The interferon (IFN) system is a well-controlled network of signaling, transcriptional, and post-transcriptional processes that orchestrate host defense against microbes. The IFN response comprises a multi-array of IFN-stimulated gene products that mediate a variety of biological processes designed to control infection and regulate specific immune responses. In this review, we focus on post-transcriptional mechanisms of gene regulation that occur during the course of IFN induction and during the response of cells to IFN. Post-transcriptional mechanisms involve different levels of regulation such as mRNA stability, alternative splicing, and translation. Such controls offer a fine tuning mechanism for efficient and rapid response and as a negative feedback control in IFN biosynthesis and response.

Murine liver plasmacytoid dendritic cells become potent immunostimulatory cells after Flt-3 ligand expansion

The liver has unique immunological properties. Although dendritic cells (DCs) are central mediators of immune regulation, little is known about liver DCs. Plasmacytoid DCs (pDCs) are a recently identified subtype of murine liver DC. We sought to define the function of freshly isolated murine liver pDCs. We found that normal liver pDCs were weak in stimulating T cells, yet they possessed a proinflammatory cytokine profile with high tumor necrosis factor-alpha and low IL-10 secretion. To facilitate the investigation of murine liver pDCs, we expanded them in vivo with fms-like tyrosine kinase 3 ligand (Flt3L). After Toll-like receptor-9 ligation, expanded liver pDCs secreted high levels of IFN-alpha and were able to stimulate NK cells, NKT cells, and antigen-specific CD8+ T cells in vitro. In addition, Flt3L expansion alone generated pDCs capable of activating antigen-specific CD8+ T cells in vivo.

CONCLUSION

Unstimulated liver pDCs exist in a latent state with the potential to become potent activators of the innate and adaptive immune systems through their interactions with other immune effectors. Our findings have implications for understanding the role of the liver in tolerance and immunity.

CpG-B ODNs potently induce low levels of IFN-alphabeta and induce IFN-alphabeta-dependent MHC-I cross-presentation in DCs as effectively as CpG-A and CpG-C ODNs

Deoxycytidyl-deoxyguanosine [(CpG)3] oligodeoxynucleotides (ODNs) signal through TLR9 to induce type-I IFN (IFN-alphabeta) and IFN-alphabeta-dependent MHC-I cross-presentation of exogenous antigens by dendritic cells (DCs). A puzzle was presented by our observation that three ODN classes, CpG-A, CpG-B, and CpG-C, had similar efficacy for induction of IFN-alphabeta-dependent MHC-I antigen cross-presentation by myeloid DCs despite greatly differing for induction of IFN-alphabeta (CpG-A>CpG-C>>CpG-B). All ODN classes similarly enhanced plasmacytoid DC (pDC) presentation of exogenous MHC-I-restricted peptide, although pDCs did not cross-process protein antigen. MHC-I and the transporter for antigen presentation were induced by all ODN classes or IFN-alpha. CpG-B ODNs were slightly more potent than CpG-A or CpG-C ODNs for induction of low levels of IFN-alphabeta but less efficacious at high concentrations than CpG-A or CpG-C ODNs. Low levels of IFN-alphabeta induced by CpG-B ODNs sufficed for full induction of MHC-I cross-presentation. Thus, CpG-B ODNs are slightly more potent but less efficacious than CpG-A and CpG-C ODNs for induction of IFN-alphabeta. High sensitivity to IFN-alphabeta allows CpG-B ODNs to be equally efficacious for induction of MHC-I cross-presentation. CpG-B ODNs may be effective for inducing therapeutic responses that require low levels of IFN-alphabeta and may avoid unnecessarily high induction of IFN-alphabeta.

Cyclooxygenase-2 inhibition promotes enhancement of antitumor responses by transcutaneous vaccination with cytosine-phosphate-guanosine-oligodeoxynucleotides and model tumor antigen

One of the principal goals in tumor immune prophylaxis and tumor therapy is the induction of antitumor responses by generating sufficient numbers of tumor antigen-specific helper T (Th)1 cells and cytotoxic T lymphocytes (CTLs). We have demonstrated that the administration of cytosine-phosphate-guanosine-oligodeoxynucleotide (CpG-ODN) through tape-stripped skin induced a Th1-type immune response and suggested that the skin is a potential site for vaccination. CpG-ODN induces the expression of cyclooxygenase (COX)-2, and its product prostaglandin (PG) E2 underlies an immunosuppressive network, therefore it is a simple strategy to use a COX-2 inhibitor for tumor vaccination with CpG-ODN. In this study, we examined whether a COX-2 inhibitor enhances the antitumor immune response induced by CpG-ODN with model tumor antigen, ovalbumin (OVA), applied to tape-stripped skin in mice. The COX-2 inhibitor remarkably enhanced antigen-specific Th1-type immune responses and generation of CTLs induced by transcutaneous vaccination with CpG-ODN and OVA. PGE2 and IL-10 levels in the skin were significantly decreased and production of IL-12 was enhanced. This vaccination also induces an effective antitumor immunity in tumor-challenged mice. These results suggested that transcutaneous vaccination with a COX-2 inhibitor, CpG-ODN, and tumor antigen is a very simple and cost-effective strategy for tumor vaccine and may be readily achievable.

Targeting dendritic cells in allergen immunotherapy

Allergen immunotherapy is a well-established strategy for treating allergic diseases with the goal of inducing allergen-specific tolerance. Identified mechanisms contributing to the therapeutic effect of immunotherapy include a shift of T helper 2 (Th2)-type immune responses to a modified Th2 immune response, a change of the balance of IgE-producing B cells to the production of IgG subtypes, in addition to increased IL-10 and TGF-beta secretion and activation of the suppressive functions of regulatory T-cells. Dendritic cells (DCs), which as outposts of the immune system are capable of T-cell priming through efficient allergen uptake by IgE receptors expressed on their cell surface. Most of the hypotheses concerning the function of DCs as facilitators of allergen-specific tolerance in allergen immunotherapy remain speculative. Therefore, studies must focus on the functional changes of DCs under immunotherapy to close the gap of knowledge about their exact role. These experimental data should help confirm the hypothesis of DCs as efficient silencers and potential target cells and take advantage of the bivalent character and tolerogenic properties of DCs.

CpG DNA modulates interleukin 1beta-induced interleukin-8 expression in human bronchial epithelial (16HBE14o-) cells

Background

Recognition of repeat unmethylated CpG motifs from bacterial DNA through Toll-like receptor (TLR-9) has been shown to induce interleukin (IL)-8 expression in immune cells. We sought to investigate the role of CpG oligodeoxynucleotides (ODN) on a human bronchial epithelial cells.

Methods

RT-PCR and Western blot analysis were used to determine expression of TLR-9 in human bronchial epithelial cells (16HBE14o-). Cells were treated with CpG ODN in the presence or absence of IL-1β and IL-8 protein was determined using ELISA. In some cases cells were pretreated with chloroquine, an inhibitor of TLR-9 signaling, or SB202190, an inhibitor of the mitogen activated protein kinase p38, prior to treatment with IL-1β and CpG. TLR9 siRNA was used to silence TLR9 prior to treatment with IL-1β and CpG. IκBα and p38 were assessed by Western blot, and EMSA's were performed to determine NF-κB activation. To investigate IL-8 mRNA stability, cells were treated with IL-1β in the absence or presence of CpG for 2 h and actinomycin D was added to induce transcriptional arrest. Cells were harvested at 15 min intervals and Northern blot analysis was performed.

Results

TLR-9 is expressed in 16HBE14o- cells. CpG synergistically increased IL-1β-induced IL-8 protein abundance, however treatment with CpG alone had no effect. CpC (a control ODN) had no effect on IL-1β-induced IL-8 levels. In addition, CpG synergistically upregulated TNFα-induced IL-8 expression. Silencing TLR9 using siRNA or pretreatment of cells with chloroquine had little effect on IL-1β-induced IL-8 levels, but abolished CpG-induced synergy. CpG ODN had no effect on NF-κB translocation or DNA binding in 16HBE14o- cells. Treatment with CpG increased phosphorylation of p38 and pretreatment with the p38 inhibitor SB202190 attenuated the synergistic increase in IL-8 protein levels. Analysis of the half-life of IL-8 mRNA revealed that IL-8 mRNA had a longer half-life following the co-treatment of CpG and IL-1β compared to treatment with IL-1β alone.

Conclusion

Together, these data demonstrate that CpG modulates IL-8 synthesis in the presence of a pro-inflammatory mediator utilizing TLR9 and post-transcriptional mechanisms involving the activation of p38 and stabilization of IL-8 mRNA.