Influenza A infection enhances cross-priming of CD8+ T cells to cell-associated antigens in a TLR7- and type I IFN-dependent fashion

Innate immune inflammatory cell death: PANoptosis and PANoptosomes in host defense and disease

Regulated cell death (RCD) triggered by innate immune activation is an important strategy for host survival during pathogen invasion and perturbations of cellular homeostasis. There are two main categories of RCD, including nonlytic and lytic pathways. Apoptosis is the most well-characterized nonlytic RCD, and the inflammatory pyroptosis and necroptosis pathways are among the best known lytic forms. While these were historically viewed as independent RCD pathways, extensive evidence of cross-talk among their molecular components created a knowledge gap in our mechanistic understanding of RCD and innate immune pathway components, which led to the identification of PANoptosis. PANoptosis is a unique innate immune inflammatory RCD pathway that is regulated by PANoptosome complexes upon sensing pathogens, pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs) or the cytokines produced downstream. Cytosolic innate immune sensors and regulators, such as ZBP1, AIM2 and RIPK1, promote the assembly of PANoptosomes to drive PANoptosis. In this review, we discuss the molecular components of the known PANoptosomes and highlight the mechanisms of PANoptosome assembly, activation and regulation identified to date. We also discuss how PANoptosomes and mutations in PANoptosome components are linked to diseases. Given the impact of RCD, and PANoptosis specifically, across the disease spectrum, improved understanding of PANoptosomes and their regulation will be critical for identifying new therapeutic targets and strategies.

STING Agonist Mitigates Experimental Autoimmune Encephalomyelitis by Stimulating Type I IFN-Dependent and -Independent Immune-Regulatory Pathways

The cGAS-cyclic GMP-AMP (cGAMP)-stimulator of IFN genes (STING) pathway induces a powerful type I IFN (IFN-I) response and is a prime candidate for augmenting immunity in cancer immunotherapy and vaccines. IFN-I also has immune-regulatory functions manifested in several autoimmune diseases and is a first-line therapy for relapsing-remitting multiple sclerosis. However, it is only moderately effective and can induce adverse effects and neutralizing Abs in recipients. Targeting cGAMP in autoimmunity is unexplored and represents a challenge because of the intracellular location of its receptor, STING. We used microparticle (MP)-encapsulated cGAMP to increase cellular delivery, achieve dose sparing, and reduce potential toxicity. In the C57BL/6 experimental allergic encephalomyelitis (EAE) model, cGAMP encapsulated in MPs (cGAMP MPs) administered therapeutically protected mice from EAE in a STING-dependent fashion, whereas soluble cGAMP was ineffective. Protection was also observed in a relapsing-remitting model. Importantly, cGAMP MPs protected against EAE at the peak of disease and were more effective than rIFN-β. Mechanistically, cGAMP MPs showed both IFN-I-dependent and -independent immunosuppressive effects. Furthermore, it induced the immunosuppressive cytokine IL-27 without requiring IFN-I. This augmented IL-10 expression through activated ERK and CREB. IL-27 and subsequent IL-10 were the most important cytokines to mitigate autoreactivity. Critically, cGAMP MPs promoted IFN-I as well as the immunoregulatory cytokines IL-27 and IL-10 in PBMCs from relapsing-remitting multiple sclerosis patients. Collectively, this study reveals a previously unappreciated immune-regulatory effect of cGAMP that can be harnessed to restrain T cell autoreactivity.

Escape from X chromosome inactivation and female bias of autoimmune diseases

Generally, autoimmune diseases are more prevalent in females than males. Various predisposing factors, including female sex hormones, X chromosome genes, and the microbiome have been implicated in the female bias of autoimmune diseases. During embryogenesis, one of the X chromosomes in the females is transcriptionally inactivated, in a process called X chromosome inactivation (XCI). This equalizes the impact of two X chromosomes in the females. However, some genes escape from XCI, providing a basis for the dual expression dosage of the given gene in the females. In the present review, the contribution of the escape genes to the female bias of autoimmune diseases will be discussed.

Host CD8α+ and CD103+ dendritic cells prime transplant antigen-specific CD8+ T cells via cross-dressing

The participation of dendritic cells (DCs) in CD8⁺ T-cell-mediated allograft rejection is a long-standing question of great clinical relevance for tissue transplantation. Here, we show that Batf3^-/- mice demonstrate delayed allo-skin graft rejection and are deficient in priming allo-specific CD8⁺ T cells. Batf3^-/- mouse priming is restored by transferring either purified CD8α⁺ or CD103⁺ DCs, demonstrating the critical role of these cells in alloreactivity. Using D^b -restricted antiviral F5 transgenic T-cell receptor T cells, which we demonstrate are alloreactive with H-2K^d , we show that cross-dressing of CD8α⁺ and CD103⁺ primes CD8⁺ T-cell or allo-specific responses in vitro and in vivo. These findings suggest novel strategies for moderating tissue rejection based on interfering with DC cross-dressing or subsequent interaction with T cells.

Granzyme A Stimulates pDCs to Promote Adaptive Immunity via Induction of Type I IFN

Granzyme A (GzmA), together with perforin, are well-known for their cytotoxic activity against tumor or virus-infected cells. In addition to this cytotoxic function, GzmA stimulates several immune cell types and induces inflammation in the absence of perforin, however, its effect on the dendritic cell (DC) is unknown. In the current study, we showed that recombinant GzmA induced the phenotypic maturation of plasmacytoid DCs (pDCs) and conventional DCs (cDCs), but not their apoptosis. Particularly, GzmA made pDCs more functional, thus leading to production of type I interferon (IFN) via the TLR9-MyD88 pathway. We also demonstrated that GzmA binds TLR9 and co-localizes with it in endosomes. When co-administered with antigen, GzmA acted as a powerful adjuvant for eliciting antigen-specific cytotoxic CD8⁺ T lymphocytes (CTLs) that protected mice from tumor challenge. The induction of CTL was completely abolished in XCR1⁺ DC-depleted mice, whereas it was reduced to less than half in pDC-depleted or IFN-α/β receptor knockout mice. Thus, CTL cross-priming was dependent on XCR1⁺cDC and also type I IFN, which was produced by GzmA-activated pDCs. These results indicate that GzmA -stimulated pDCs enhance the cross-priming activity of cDCs in situ. We also showed that the adjuvant effect of GzmA is superior to CpG-ODN and LPS. Our findings highlight the ability of GzmA to bridge innate and adaptive immune responses via pDC help and suggest that GzmA may be useful as a vaccine adjuvant.

Activation of Toll-like receptor 7 signaling in labial salivary glands of primary Sjögren's syndrome patients

The aim of this study was to determine the expressions of Toll-like receptors (TLRs) 7-9 and type I interferon (IFN) signal in labial salivary glands (LSGs) and cultured salivary gland epithelial cells (SGECs) from primary Sjögren's syndrome (pSS) patients. We performed an immunohistochemistry analysis of LSGs from 11 patients with pSS as defined by American-European Consensus Group classification criteria and five healthy subjects. The pSS patients' SGECs were analyzed by immunofluorescence and western blotting. IFN-α expression was examined by immunosorbent assay and flow cytometry. Mononuclear cells (MNCs) from pSS patients' LSGs showed TLR-7-dominant expression. B cells, plasma cells and plasmacytoid dendritic cells (pDCs) co-expressed with TLR-7. Myeloid differentiation primary response gene 88 (MyD88), tumor necrosis factor receptor-associated factor 6 (TRAF6) and interferon regulatory factor 7 (IRF7) co-expressed with the pDC marker CD303 in LSGs. Ducts from pSS patients dominantly expressed TLR-7, and TLR-7 in the ducts co-expressed with MyD88, TRAF6 and IRF7. Type I IFNs including IFN-α and IFN-β were detected in MNCs and ducts in pSS patients' LSGs. Increased TRAF6 expression and the nuclear translocation of IRF7 in SGECs were detected by immunofluorescence following loxoribine (a TLR-7 ligand) stimulation despite IFN-β pretreatment. Western blotting showed increased TRAF6 expression in SGECs following IFN-β and loxoribine stimulation. Although no increase in IFN-α was detected in supernatant from stimulated SGECs, the IFN-α in supernatant from stimulated peripheral blood pDCs from pSS patients was significantly increased. Our findings suggest that TLR-7 is dominantly expressed in both MNCs and ducts with downstream signals for type I IFNs, indicating that TLR7-dominant innate immunity is related to the development of sialadenitis in pSS.

CD169+ Macrophages Capture and Dendritic Cells Instruct: The Interplay of the Gatekeeper and the General of the Immune System

Since the seminal discovery of dendritic cells (DCs) by Steinman and Cohn in 1973, there has been an ongoing debate to what extent macrophages and DCs are related and perform different functions. The current view is that macrophages and DCs originate from different lineages and that only DCs have the capacity to initiate adaptive immunity. Nevertheless, as we will discuss in this review, lymphoid tissue resident CD169⁺ macrophages have been shown to act in concert with DCs to promote or suppress adaptive immune responses for pathogens and self-antigens, respectively. Accordingly, we propose a functional alliance between CD169⁺ macrophages and DCs in which a division of tasks is established. CD169⁺ macrophages are responsible for the capture of pathogens and are frequently the first cell type infected and thereby provide a confined source of antigen. Subsequently, cross-presenting DCs interact with these antigen-containing CD169⁺ macrophages, pick up antigens and activate T cells. The cross-priming of T cells by DCs is enhanced by the localized production of type I interferons (IFN-I) derived from CD169⁺ macrophages and plasmacytoid DCs (pDCs) that induces DC maturation. The interaction between CD169⁺ macrophages and DCs appears not only to be essential for immune responses against pathogens, but also plays a role in the induction of self-tolerance and immune responses against cancer. In this review we will discuss the studies that demonstrate the collaboration between CD169⁺ macrophages and DCs in adaptive immunity.

The Use of CRISPR/Cas9 Gene Editing to Confirm Congenic Contaminations in Host-Pathogen Interaction Studies

Murine models of Salmonella enterica serovar Typhimurium infection are one of the commonest tools to study host-pathogen interactions during bacterial infections. Critically, the outcome of S. Typhimurium infection is impacted by the genetic background of the mouse strain used, with macrophages from C57BL/6 and BALB/c mice lacking the capacity to control intracellular bacterial replication. For this reason, the use of congenic strains, which mix the genetic backgrounds of naturally protected mouse strains with those of susceptible strains, has the capacity to significantly alter results and interpretation of S. Typhimurium infection studies. Here, we describe how macrophage knockout cell lines generated by CRISPR/Cas9 gene editing can help determine the contribution of background contaminations in the phenotypes of primary macrophages from congenic mice, on the outcome of S. Typhimurium infection studies. Our own experience illustrates how the CRISPR/Cas9 technology can be used to complement pre-existing knockout models, and shows that there is great merit in performing concurrent studies with both genetic models, to exclude unanticipated side-effects on host-pathogen interactions.

Capitalizing on Cancer Specific Replication: Oncolytic Viruses as a Versatile Platform for the Enhancement of Cancer Immunotherapy Strategies

The past decade has seen considerable excitement in the use of biological therapies in treating neoplastic disease. In particular, cancer immunotherapy and oncolytic virotherapy have emerged as two frontrunners in this regard with the first FDA approvals for agents in both categories being obtained in the last 5 years. It is becoming increasingly apparent that these two approaches are not mutually exclusive and that much of the therapeutic benefit obtained from the use of oncolytic viruses (OVs) is in fact the result of their immunotherapeutic function. Indeed, OVs have been shown to recruit and activate an antitumor immune response and much of the current work in this field centers around increasing this activity through strategies such as engineering genes for immunomodulators into OV backbones. Because of their broad immunostimulatory functions, OVs can also be rationally combined with a variety of other immunotherapeutic approaches including cancer vaccination strategies, adoptive cell transfer and checkpoint blockade. Therefore, while they are important therapeutics in their own right, the true power of OVs may lie in their ability to enhance the effectiveness of a wide range of immunotherapies.

Mosla scabra flavonoids ameliorate the influenza A virus-induced lung injury and water transport abnormality via the inhibition of PRR and AQP signaling pathways in mice

ETHNOPHARMACROLOGICAL RELEVANCE

Mosla scabra (Thunb.) C.Y. Wu and H.W. Li has been used as a traditional medicinal herb for centuries in East Asian countries. It has antibacterial, antiviral, antioxidant, anti-inflammatory and immunomodulatory effects. In folk medicine, it is used as a remedy for the treatment of pulmonary diseases, such as fever, cold, cough, pulmonary edema and emphysema.

AIM OF THE STUDY

This study was to investigate the protective mechanism of total flavonoids from M. scabra (MF) in influenza A virus (IAV)-infected mice.

MATERIALS AND METHODS

The mice were infected with IAV and then were treated daily with MF for five days. At the end of the experiment, the levels of inflammatory-related cytokines (IFN-α, IL-6, TNF-α and IL-1β) were determined by ELISA. Pathological changes of lung tissue were examined by H&E staining. The protein expressions of AQP5, p-p38, caspase-3 and NF-κB p65 were detected by western blot analysis while the gene expressions of key effectors in AQP5 and PRRs signaling pathways were detected by real-time Fluorescence Quantitative Polymerase Chain Reaction (RFQ-PCR) analysis.

RESULTS

The results showed that treatment with MF at doses of 120-360mg/kg for five days to IAV-infected mice significantly attenuated IAV-induced pulmonary injury and decreased the serum levels of IL-6, TNF-α and IL-1β, but increased IFN-α levels. MF treatment could up-regulate the mRNA expressions of TLR-7, RIG-1, TRAF6, Bcl-2, Bax, VIPR1, PKCα and AQP5 and down-regulate caspase-3 and NF-κB p65 protein expression.

CONCLUSION

Treatment with MF could significantly alleviate IAV-induced pulmonary inflammation, apoptosis and water transport abnormality, which was probably through the regulation of TLR7, RIG-1 and AQP5 signaling pathway.

Functional Specialty of CD40 and Dendritic Cell Surface Lectins for Exogenous Antigen Presentation to CD8(+) and CD4(+) T Cells

Dendritic cells (DCs) are major antigen-presenting cells that can efficiently prime and cross-prime antigen-specific T cells. Delivering antigen to DCs via surface receptors is thus an appealing strategy to evoke cellular immunity. Nonetheless, which DC surface receptor to target to yield the optimal CD8⁺ and CD4⁺ T cell responses remains elusive. Herein, we report the superiority of CD40 over 9 different lectins and scavenger receptors at evoking antigen-specific CD8⁺ T cell responses. However, lectins (e.g., LOX-1 and Dectin-1) were more efficient than CD40 at eliciting CD4⁺ T cell responses. Common and distinct patterns of subcellular and intracellular localization of receptor-bound αCD40, αLOX-1 and αDectin-1 further support their functional specialization at enhancing antigen presentation to either CD8⁺ or CD4⁺ T cells. Lastly, we demonstrate that antigen targeting to CD40 can evoke potent antigen-specific CD8⁺ T cell responses in human CD40 transgenic mice. This study provides fundamental information for the rational design of vaccines against cancers and viral infections.

•

Antigen delivery to DCs via CD40 is more efficient than through nine other receptors at eliciting CD8 T⁺ cell response.

•

Antigen delivery via lectins (e.g., LOX-1 and Dectin-1) is more efficient than CD40 at eliciting CD4⁺ T cell responses.

The success of an immunotherapeutic vaccine for cancer is largely dependent on its ability to evoke potent cellular immunity. Although targeting antigens to dendritic cells (DCs) has been known to be an efficient strategy to evoke cellular immunity, which targeted receptors yield the optimal cellular immunity remained elusive. We report that targeting CD40, compared to 9 other DC receptors, results in the greatest levels of CD8⁺ cytotoxic T cell responses, while targeting lectins results in enhanced CD4⁺ helper T cell responses. The findings of this study will assist us in the rational design of immunotherapeutic vaccines against cancers.

Transcription factor Batf3 is important for development of CD8+ T-cell response against a phagosomal bacterium regardless of the location of antigen

Salmonella enterica serovar Typhimurium (ST) is a virulent intracellular bacterium that conceals itself in the phagosomes of infected cells. Although CD8(+) T cells promote protection against various intracellular pathogens, the role of CD8(+) T cells against virulent ST has been unclear due to early fatality of susceptible (B6) mice. Herein, we generated MHC I-deficient mice on the resistant (129SvJ) and susceptible (Nramp1 transgenic B6) background to evaluate the role of CD8(+) T cells against virulent ST. Our results indicate that CD8(+) T cells have a critical protective role in host survival during infection with virulent ST. As antigen presentation and CD8(+) T-cell activation against phagosomal antigens are considered to operate through the cross-presentation pathway, we have evaluated CD8(+) T-cell response against ST in Batf3-deficient mice that lack CD8α dendritic cells (DCs). Using a recombinant of ST that expresses antigen (ST-OVA) mainly in the phagosomes of infected cells, we show that CD8(+) T-cell response is compromised throughout the duration of infection in Batf3-deficient mice. In contrast, when ST delivers antigen to the cytosol of infected cells (ST-OVA-C), CD8(+) T-cell response against the cytosolic antigen was compromised only in the short term in the absence of CD8α DCs, with wild-type and Batf3-deficient mice generating similar CD8(+) T-cell response in the long term. Thus, Batf3 has an important role in CD8(+) T-cell priming regardless of antigenic location; however, its role is redundant at later time intervals against cytosolic antigen.

Oncolytic Immunotherapy: Dying the Right Way is a Key to Eliciting Potent Antitumor Immunity

Oncolytic viruses (OVs) are novel immunotherapeutic agents whose anticancer effects come from both oncolysis and elicited antitumor immunity. OVs induce mostly immunogenic cancer cell death (ICD), including immunogenic apoptosis, necrosis/necroptosis, pyroptosis, and autophagic cell death, leading to exposure of calreticulin and heat-shock proteins to the cell surface, and/or released ATP, high-mobility group box 1, uric acid, and other damage-associated molecular patterns as well as pathogen-associated molecular patterns as danger signals, along with tumor-associated antigens, to activate dendritic cells and elicit adaptive antitumor immunity. Dying the right way may greatly potentiate adaptive antitumor immunity. The mode of cancer cell death may be modulated by individual OVs and cancer cells as they often encode and express genes that inhibit/promote apoptosis, necroptosis, or autophagic cell death. We can genetically engineer OVs with death-pathway-modulating genes and thus skew the infected cancer cells toward certain death pathways for the enhanced immunogenicity. Strategies combining with some standard therapeutic regimens may also change the immunological consequence of cancer cell death. In this review, we discuss recent advances in our understanding of danger signals, modes of cancer cell death induced by OVs, the induced danger signals and functions in eliciting subsequent antitumor immunity. We also discuss potential combination strategies to target cells into specific modes of ICD and enhance cancer immunogenicity, including blockade of immune checkpoints, in order to break immune tolerance, improve antitumor immunity, and thus the overall therapeutic efficacy.

Rotavirus activates lymphocytes from non-obese diabetic mice by triggering toll-like receptor 7 signaling and interferon production in plasmacytoid dendritic cells

It has been proposed that rotavirus infection promotes the progression of genetically-predisposed children to type 1 diabetes, a chronic autoimmune disease marked by infiltration of activated lymphocytes into pancreatic islets. Non-obese diabetic (NOD) mice provide a model for the human disease. Infection of adult NOD mice with rhesus monkey rotavirus (RRV) accelerates diabetes onset, without evidence of pancreatic infection. Rather, RRV spreads to the pancreatic and mesenteric lymph nodes where its association with antigen-presenting cells, including dendritic cells, induces cellular maturation. RRV infection increases levels of the class I major histocompatibility complex on B cells and proinflammatory cytokine expression by T cells at these sites. In autoimmunity-resistant mice and human mononuclear cells from blood, rotavirus-exposed plasmacytoid dendritic cells contribute to bystander polyclonal B cell activation through type I interferon expression. Here we tested the hypothesis that rotavirus induces bystander activation of lymphocytes from NOD mice by provoking dendritic cell activation and proinflammatory cytokine secretion. NOD mouse splenocytes were stimulated with rotavirus and assessed for activation by flow cytometry. This stimulation activated antigen-presenting cells and B cells independently of virus strain and replicative ability. Instead, activation depended on virus dose and was prevented by blockade of virus decapsidation, inhibition of endosomal acidification and interference with signaling through Toll-like receptor 7 and the type I interferon receptor. Plasmacytoid dendritic cells were more efficiently activated than conventional dendritic cells by RRV, and contributed to the activation of B and T cells, including islet-autoreactive CD8+ T cells. Thus, a double-stranded RNA virus can induce Toll-like receptor 7 signaling, resulting in lymphocyte activation. Our findings suggest that bystander activation mediated by type I interferon contributes to the lymphocyte activation observed following RRV infection of NOD mice, and may play a role in diabetes acceleration by rotavirus.

Systems biology unravels interferon responses to respiratory virus infections

Interferon production is an important defence against viral replication and its activation is an attractive therapeutic target. However, it has long been known that viruses perpetually evolve a multitude of strategies to evade these host immune responses. In recent years there has been an explosion of information on virus-induced alterations of the host immune response that have resulted from data-rich omics technologies. Unravelling how these systems interact and determining the overall outcome of the host response to viral infection will play an important role in future treatment and vaccine development. In this review we focus primarily on the interferon pathway and its regulation as well as mechanisms by which respiratory RNA viruses interfere with its signalling capacity.

Type I Interferons as Stimulators of DC-Mediated Cross-Priming: Impact on Anti-Tumor Response

Induction of potent tumor-specific cytotoxic T-cell responses is a fundamental objective in anticancer therapeutic strategies. This event requires that antigen-presenting cells present tumor-associated antigens (Ag) on their MHC class-I molecule, in a process termed cross-presentation. Dendritic cells (DC) are particularly keen on this task and can induce the cross-priming of CD8⁺ T cells, when exposed to danger or inflammatory signals that stimulate their activation. Type I interferons (IFN-I), a family of long-known immunostimulatory cytokines, have been proven to produce optimal activation signal for DC-induced cross-priming. Recent in vitro and in vivo evidences have suggested that IFN-I-stimulated cross-priming by DC against tumor-associated Ag is a key mechanism for cancer immunosurveillance and may be usefully exploited to boost anti-tumor CD8⁺ T-cell responses. Here, we will review the cross-presentation properties of different DC subsets, with special focus on cell-associated and tumor Ag, and discuss how IFN-I can modify this function, with the aim of identifying more specific and effective strategies for improving anticancer responses.

Oncolytic viruses as therapeutic cancer vaccines

Oncolytic viruses (OVs) are tumor-selective, multi-mechanistic antitumor agents. They kill infected cancer and associated endothelial cells via direct oncolysis, and uninfected cells via tumor vasculature targeting and bystander effect. Multimodal immunogenic cell death (ICD) together with autophagy often induced by OVs not only presents potent danger signals to dendritic cells but also efficiently cross-present tumor-associated antigens from cancer cells to dendritic cells to T cells to induce adaptive antitumor immunity. With this favorable immune backdrop, genetic engineering of OVs and rational combinations further potentiate OVs as cancer vaccines. OVs armed with GM-CSF (such as T-VEC and Pexa-Vec) or other immunostimulatory genes, induce potent anti-tumor immunity in both animal models and human patients. Combination with other immunotherapy regimens improve overall therapeutic efficacy. Coadministration with a HDAC inhibitor inhibits innate immunity transiently to promote infection and spread of OVs, and significantly enhances anti-tumor immunity and improves the therapeutic index. Local administration or OV mediated-expression of ligands for Toll-like receptors can rescue the function of tumor-infiltrating CD8⁺ T cells inhibited by the immunosuppressive tumor microenvironment and thus enhances the antitumor effect. Combination with cyclophosphamide further induces ICD, depletes Treg, and thus potentiates antitumor immunity. In summary, OVs properly armed or in rational combinations are potent therapeutic cancer vaccines.

Optimal conditions required for influenza A infection-enhanced cross-priming of CD8⁺ T cells specific to cell-associated antigens

Dendritic cells can take up exogenous tumor antigens and present their antigenic epitopes to CD8⁺ T cells (T(CD8⁺)), a process called cross-presentation. Cross-presentation is especially important in antitumor immunity because tumor cells, although carrying tumor antigens, do not activate naive T cells efficiently because of a lack of co-stimulatory molecules. Our group has recently shown that influenza A virus (IAV) infection of allogeneic cells lead to enhanced cross-priming of T(CD8⁺) specific to cellular antigens. To develop this into a potential vaccine strategy, in this study, we have systematically investigated the numbers of allogeneic cells infected by IAV, IAV doses and their infectious activity, the length of in vitro infection and other associated factors. We have defined the optimal immune-enhancing conditions and we have also shown in vivo that such enhanced cross-priming did lead to enhanced tumor protection. The knowledge should be useful for developing more robust cancer vaccine.

Invariant NKT cells induce plasmacytoid dendritic cell (DC) cross-talk with conventional DCs for efficient memory CD8+ T cell induction

A key goal of vaccine immunotherapy is the generation of long-term memory CD8(+) T cells capable of mediating immune surveillance. We discovered a novel intercellular pathway governing the development of potent memory CD8(+) T cell responses against cell-associated Ags that is mediated through cross-presentation by XCR1(+) dendritic cells (DCs). Generation of CD8(+) memory T cells against tumor cells pulsed with an invariant NKT cell ligand depended on cross-talk between XCR1(+) and plasmacytoid DCs that was regulated by IFN-α/IFN-αR signals. IFN-α production by plasmacytoid DCs was stimulated by an OX40 signal from the invariant NKT cells, as well as an HMGB1 signal from the dying tumor cells. These findings reveal a previously unknown pathway of intercellular collaboration for the generation of tumor-specific CD8(+) memory T cells that can be exploited for strategic vaccination in the setting of tumor immunotherapy.

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.

Asparagine endopeptidase controls anti-influenza virus immune responses through TLR7 activation

Intracellular Toll-like receptors (TLRs) expressed by dendritic cells recognize nucleic acids derived from pathogens and play an important role in the immune responses against the influenza virus (IAV), a single-stranded RNA sensed by different receptors including TLR7. However, the importance of TLR7 processing in the development of anti-viral immune responses is not known. Here we report that asparagine endopeptidase (AEP) deficient mice are unable to generate a strong anti-IAV response, as demonstrated by reduced inflammation, cross presentation of cell-associated antigens and priming of CD8⁺ T cells following TLR7-dependent pulmonary infection induced by IAV. Moreover, AEP deficient lung epithelial- or myeloid-cells exhibit impaired TLR7 signaling due to defective processing of this receptor. Indeed, TLR7 requires a proteolytic cleavage by AEP to generate a C-terminal fragment competent for signaling. Thus, AEP activity is critical for TLR7 processing, opening new possibilities for the treatment of influenza and TLR7-dependent inflammatory diseases.

Influenza A virus, a negative stranded RNA, can cause severe illness in humans and animals and stimulates many receptors including Toll like receptors 7 (TLR7). TLR signaling induces maturation of dendritic cells and the production of a variety of inflammatory cytokines that are crucial for both innate and adaptive immunity. TLR7 is an intracellular receptor, which resides in endosomes and senses viruses to trigger host defence. Previous data have shown that TLR9 requires proteolysis to be functional but it is unclear whether other intracellular TLRs (TLR3 and TLR7) are also subject to degradation. Here, we used a protease deficient mouse model to show the in vivo importance of TLR7 processing in influenza infection. Inflammation monitored by cytokine release and adaptive immunity measured by cross priming of CD8⁺ T cells was significantly reduced in infected protease-deficient animals in comparison to control animals. We showed that TLR7 requires a proteolytic cleavage by a cysteine endopeptidase in order to be functional. Our findings indicate that TLR7 processing mediated by a protease, asparagynil endopeptidase, is critical for inducing robust anti-influenza immune responses. Given our results, targeting TLR7 response in the lungs through proteases may offer new therapeutic potential in pulmonary infection.

Antigen Cross-Priming of Cell-Associated Proteins is Enhanced by Macroautophagy within the Antigen Donor Cell

Phagocytosis of dying cells constitutes an important mechanism of antigen capture for the cross-priming of CD8⁺ T cells. This process has been shown to be critical for achieving tumor and viral immunity. While most studies have focused on the mechanisms inherent in the dendritic cell that account for exogenous antigen accessing MHC I, several recent reports have highlighted the important contribution made by the antigen donor cell. Specifically, the cell stress and cell death pathways that precede antigen transfer are now known to impact cross-presentation and cross-priming. Herein, we review the current literature regarding a role for macroautophagy within the antigen donor cell. Further examination of this point of immune regulation is warranted and may contribute to a better understanding of how to optimize immunotherapy for treatment of cancer and chronic infectious disease.

A temporal role of type I interferon signaling in CD8+ T cell maturation during acute West Nile virus infection

A genetic absence of the common IFN-α/β signaling receptor (IFNAR) in mice is associated with enhanced viral replication and altered adaptive immune responses. However, analysis of IFNAR(-/-) mice is limited for studying the functions of type I IFN at discrete stages of viral infection. To define the temporal functions of type I IFN signaling in the context of infection by West Nile virus (WNV), we treated mice with MAR1-5A3, a neutralizing, non cell-depleting anti-IFNAR antibody. Inhibition of type I IFN signaling at or before day 2 after infection was associated with markedly enhanced viral burden, whereas treatment at day 4 had substantially less effect on WNV dissemination. While antibody treatment prior to infection resulted in massive expansion of virus-specific CD8(+) T cells, blockade of type I IFN signaling starting at day 4 induced dysfunctional CD8(+) T cells with depressed cytokine responses and expression of phenotypic markers suggesting exhaustion. Thus, only the later maturation phase of anti-WNV CD8(+) T cell development requires type I IFN signaling. WNV infection experiments in BATF3(-/-) mice, which lack CD8-α dendritic cells and have impaired priming due to inefficient antigen cross-presentation, revealed a similar effect of blocking IFN signaling on CD8(+) T cell maturation. Collectively, our results suggest that cell non-autonomous type I IFN signaling shapes maturation of antiviral CD8(+) T cell response at a stage distinct from the initial priming event.

Osteopontin modulates the generation of memory CD8+ T cells during influenza virus infection

The adaptive immune system generates memory cells, which induce a rapid and robust immune response following secondary Ag encounter. Memory CD8(+) T cells are a critical component of protective immunity against infections and cancers. Therefore, understanding the mechanism whereby memory CD8(+) T cells are generated and maintained is important for inducing effective memory CD8(+) T cell response. Recent studies have demonstrated that the inflammatory cytokine IL-12 favors the generation of terminal effector CD8(+) T cells rather than memory precursor effector CD8(+) T cells by regulating the expression of the transcription factor T-bet. In this study, we report that the inflammatory cytokine osteopontin (Opn) modulates memory CD8(+) T cell generation during influenza virus infection. Although Opn wild-type and Opn knockout (KO) mice had similar numbers of virus-specific effector CD8(+) T cells, virus-specific effector CD8(+) T cells generated in Opn KO mice showed low levels of T-bet expression and an increased memory precursor cell population compared with cells generated in Opn wild-type mice. This resulted in the persistently increased number of memory CD8(+) T cells in Opn KO mice. Studies with bone marrow-derived dendritic cells demonstrated that Opn deficiency in bone marrow-derived dendritic cells results in low levels of IL-12 production in response to the stimulation with influenza virus. Thus, we hypothesize that Opn modulates the generation of memory precursor effector CD8(+) T cells by regulating cytokine milieu during the acute phase of virus infection. This finding may provide new insight into the role of Opn in adaptive immune response.

Toll like receptors in diseases of the lung

The lung is in continuous contact with a diverse array of infectious agents, foreign antigens, and host-derived danger signals. To sample this expansive internal and external milieu, both resident myeloid and stromal/structure cells of the lung express a full complement of toll like receptors (TLRs) which recognize pathogen-associated molecular patterns (PAMPs) and endogenous danger-associated molecular patterns (DAMPs). TLRs play a vital role in immune host defense against bacterial, mycobacterial, fungal, and viral pathogens of the lung. Additionally, TLRs contribute to disease pathogenesis in non-infectious pulmonary disorders, including airway disease, acute lung injury, and interstitial lung disease. In this review, TLR biology in the context of experimental infectious and non-infectious lung disease is discussed, and correlates to human lung disease, including therapeutic implications of these findings, are defined.

Baculovirus capsid display potentiates OVA cytotoxic and innate immune responses

Baculoviruses (BV) are DNA viruses that are pathogenic for insects. Although BV infect a range of mammalian cell types, they do not replicate in these cells. Indeed, the potential effects of these insect viruses on the immune responses of mammals are only just beginning to be studied. We show in this paper that a recombinant Autographa californica multiple nuclear polyhedrosis virus carrying a fragment of ovalbumin (OVA) on the VP39 capsid protein (BV-OVA) has the capacity to act as an adjuvant and vector of antigens in mice, thereby promoting specific CD4 and cytotoxic T cell responses against OVA. BV also induced in vivo maturation of dendritic cells and the production of inflammatory cytokines, thus promoting innate and adaptive immune responses. The OVA-specific response induced by BV-OVA was strong enough to reject a challenge with OVA-expressing melanoma cells (MO5 cells) and effectively prolonged survival of MO5 bearing mice. All these findings, together with the absence of pre-existing immunity to BV in humans and the lack of viral gene expression in mammalian cells, make BV a candidate for vaccination.