Inactivated influenza virus, when presented on dendritic cells, elicits human CD8+ cytolytic T cell responses

Pathways of MHC I cross-presentation of exogenous antigens

Phagocytes, particularly dendritic cells (DCs), generate peptide-major histocompatibility complex (MHC) I complexes from antigens they have collected from cells in tissues and report this information to CD8 T cells in a process called cross-presentation. This process allows CD8 T cells to detect, respond and eliminate abnormal cells, such as cancers or cells infected with viruses or intracellular microbes. In some settings, cross-presentation can help tolerize CD8 T cells to self-antigens. One of the principal ways that DCs acquire tissue antigens is by ingesting this material through phagocytosis. The resulting phagosomes are key hubs in the cross-presentation (XPT) process and in fact experimentally conferring the ability to phagocytize antigens can be sufficient to allow non-professional antigen presenting cells (APCs) to cross-present. Once in phagosomes, exogenous antigens can be cross-presented (XPTed) through three distinct pathways. There is a vacuolar pathway in which peptides are generated and then bind to MHC I molecules within the confines of the vacuole. Ingested exogenous antigens can also be exported from phagosomes to the cytosol upon vesicular rupture and/or possibly transport. Once in the cytosol, the antigen is degraded by the proteasome and the resulting oligopeptides can be transported to MHC I molecule in the endoplasmic reticulum (ER) (a phagosome-to-cytosol (P2C) pathway) or in phagosomes (a phagosome-to-cytosol-to-phagosome (P2C2P) pathway). Here we review how phagosomes acquire the necessary molecular components that support these three mechanisms and the contribution of these pathways. We describe what is known as well as the gaps in our understanding of these processes.

HIV-1 trans-Infection Mediated by DCs: The Tip of the Iceberg of Cell-to-Cell Viral Transmission

HIV-1 cell-to-cell transmission is key for an effective viral replication that evades immunity. This highly infectious mechanism is orchestrated by different cellular targets that utilize a wide variety of processes to efficiently transfer HIV-1 particles. Dendritic cells (DCs) are the most potent antigen presenting cells that initiate antiviral immune responses, but are also the cells with highest capacity to transfer HIV-1. This mechanism, known as trans-infection, relies on the capacity of DCs to capture HIV-1 particles via lectin receptors such as the sialic acid-binding I-type lectin Siglec-1/CD169. The discovery of the molecular interaction of Siglec-1 with sialylated lipids exposed on HIV-1 membranes has enlightened how this receptor can bind to several enveloped viruses. The outcome of these interactions can either mount effective immune responses, boost the productive infection of DCs and favour innate sensing, or fuel viral transmission via trans-infection. Here we review these scenarios focusing on HIV-1 and other enveloped viruses such as Ebola virus or SARS-CoV-2.

Recent advancements in the measurement of pathogenic airborne viruses

Air-transmissible pathogenic viruses, such as influenza viruses and coronaviruses, are some of the most fatal strains and spread rapidly by air, necessitating quick and stable measurements from sample air volumes to prevent further spread of diseases and to take appropriate steps rapidly. Measurements of airborne viruses generally require their collection into liquids or onto solid surfaces, with subsequent hydrosolization and then analysis using the growth method, nucleic-acid-based techniques, or immunoassays. Measurements can also be performed in real time without sampling, where species-specific determination is generally disabled. In this review, we introduce some recent advancements in the measurement of pathogenic airborne viruses. Air sampling and measurement technologies for viral aerosols are reviewed, with special focus on the effects of air sampling on damage to the sampled viruses and their measurements. Measurement of pathogenic airborne viruses is an interdisciplinary research area that requires understanding of both aerosol technology and biotechnology to effectively address the issues. Hence, this review is expected to provide some useful guidelines regarding appropriate air sampling and virus detection methods for particular applications.

Protein Tyrosine Phosphatase SHP2 Suppresses Host Innate Immunity against Influenza A Virus by Regulating EGFR-Mediated Signaling

Influenza A virus (IAV) is a highly contagious pathogen, causing acute respiratory illnesses in human beings and animals and frequently giving rise to epidemic outbreaks. Evasion by IAV of host immunity facilitates viral replication and spread, which can be initiated through various mechanisms, including epidermal growth factor receptor (EGFR) activation. However, how EGFR mediates the suppression of antiviral systems remains unclear. Here, we examined host innate immune responses and their relevant signaling to EGFR upon IAV infection. IAV was found to induce the phosphorylation of EGFR and extracellular signal-regulated kinase (ERK) at an early stage of infection. Inhibition of EGFR or ERK suppressed the viral replication but increased the expression of type I and type III interferons (IFNs) and interferon-stimulated genes (ISGs), supporting the idea that IAV escapes from antiviral innate immunity by activating EGFR/ERK signaling. Meanwhile, IAV infection also induced the activation of Src homology region 2-containing protein tyrosine phosphatase 2 (SHP2). Pharmacological inhibition or small interfering RNA (siRNA)-based silencing of SHP2 enhanced the IFN-dependent antiviral activity and reduced virion production. Furthermore, knockdown of SHP2 attenuated the EGFR-mediated ERK phosphorylation triggered by viral infection or EGF stimulation. Conversely, ectopic expression of constitutively active SHP2 noticeably promoted ERK activation and viral replication, concomitant with diminished immune function. Altogether, the results indicate that SHP2 is crucial for IAV-induced activation of the EGFR/ERK pathway to suppress host antiviral responses.IMPORTANCE Viral immune evasion is the most important strategy whereby viruses evolve for their survival. This work shows that influenza A virus (IAV) suppressed the antiviral innate immunity through downregulation of IFNs and ISGs by activating EGFR/ERK signaling. Meanwhile, IAV also induced the activation of protein tyrosine phosphatase SHP2, which was found to be responsible for modulating the EGFR-mediated ERK activity and subsequent antiviral effectiveness both in vitro and in vivo The results suggest that SHP2 is a key signal transducer between EGFR and ERK and plays a crucial role in suppressing host innate immunity during IAV infection. The finding enhances our understanding of influenza immune evasion and provides a new therapeutic approach to viral infection.

Surprisingly Effective Priming of CD8+ T Cells by Heat-Inactivated Vaccinia Virus Virions

Robust priming of CD8+ T cells by viruses is considered to require infection and de novo expression of viral antigens. A corollary of this is that inactivated viruses are thought of as being inevitably poor vaccines for eliciting these responses. In contrast to this dogma, we found that some antigens present in vaccinia virus (VACV) virions prime strong CD8+ T cell responses when the virus was rendered noninfectious by heat. More surprisingly, in some cases these responses were similar in magnitude to those primed by infectious virus administered at an equivalent dose. Next, we tested whether this was a special property of particular antigens and their epitopes and found that foreign epitopes tagged onto three different VACV virion proteins were able to elicit CD8+ T cell responses irrespective of whether the virus was viable or heat killed. Further, the polyfunctionality and cytotoxic ability of the CD8+ T cells primed by these VACVs was equivalent irrespective of whether they were administered to mice as inactivated or live viruses. Finally, we used these VACVs in prime-boost combinations of inactivated and live virus and found that priming with dead virus before a live booster was the most immunogenic regime. We conclude that VACV virions can be efficient vectors for targeting antigens to dendritic cells for effective priming of CD8+ T cells, even when rendered noninfectious and speculate that this might also be the case for other viruses.IMPORTANCE The design of viral vectored vaccines is often considered to require a trade-off between efficacy and safety. This is especially the case for vaccines that aim to induce killer (CD8+) T cells, where there is a well-established dogma that links infection in vaccinated individuals with effective induction of immunity. However, we found that some proteins of vaccinia virus generate strong CD8+ T cell responses even when the virus preparation was inactivated by heat prior to administration as a vaccine. We took advantage of this finding by engineering a new vaccine vector virus that could be used as an inactivated vaccine. These results suggest that vaccinia virus may be a more versatile vaccine vector than previously appreciated and that in some instances safety can be prioritized by the complete elimination of viral replication without a proportional loss of immunogenicity.

Rapid Airborne Influenza Virus Quantification Using an Antibody-Based Electrochemical Paper Sensor and Electrostatic Particle Concentrator

Airborne influenza viruses are responsible for serious respiratory diseases, and most detection methods for airborne viruses are based on extraction of nucleic acids. Herein, vertical-flow-assay-based electrochemical paper immunosensors were fabricated to rapidly quantify the influenza H1N1 viruses in air after sampling with a portable electrostatic particle concentrator (EPC). The effects of antibodies, anti-influenza nucleoprotein antibodies (NP-Abs) and anti-influenza hemagglutinin antibodies (HA-Abs), on the paper sensors as well as nonpulsed high electrostatic fields with and without corona charging on the virus measurement were investigated. The antigenicity losses of the surface (HA) proteins were caused by H₂O₂ via lipid oxidation-derived radicals and ¹O₂ via direct protein peroxidation upon exposure of a high electrostatic field. However, minimal losses in antigenicity of NP of the influenza viruses were observed, and the concentration of the H1N1 viruses was more than 160 times higher in the EPC than the BioSampler upon using NP-Ab based paper sensors after 60 min collection. This NP-Ab-based paper sensors with the EPC provided measurements comparable to quantitative polymerase chain reaction (qPCR) but much quicker, specific to the influenza H1N1 viruses in the presence of other airborne microorganisms and beads, and more cost-effective than enzyme-linked immunosorbent assay and qPCR.

The HIV-1 integrase-LEDGF allosteric inhibitor MUT-A: resistance profile, impairment of virus maturation and infectivity but without influence on RNA packaging or virus immunoreactivity

Background

HIV-1 Integrase (IN) interacts with the cellular co-factor LEDGF/p75 and tethers the HIV preintegration complex to the host genome enabling integration. Recently a new class of IN inhibitors was described, the IN-LEDGF allosteric inhibitors (INLAIs). Designed to interfere with the IN-LEDGF interaction during integration, the major impact of these inhibitors was surprisingly found on virus maturation, causing a reverse transcription defect in target cells.

Results

Here we describe the MUT-A compound as a genuine INLAI with an original chemical structure based on a new type of scaffold, a thiophene ring. MUT-A has all characteristics of INLAI compounds such as inhibition of IN-LEDGF/p75 interaction, IN multimerization, dual antiretroviral (ARV) activities, normal packaging of genomic viral RNA and complete Gag protein maturation. MUT-A has more potent ARV activity compared to other INLAIs previously reported, but similar profile of resistance mutations and absence of ARV activity on SIV. HIV-1 virions produced in the presence of MUT-A were non-infectious with the formation of eccentric condensates outside of the core. In studying the immunoreactivity of these non-infectious virions, we found that inactivated HIV-1 particles were captured by anti-HIV-specific neutralizing and non-neutralizing antibodies (b12, 2G12, PGT121, 4D4, 10-1074, 10E8, VRC01) with efficiencies comparable to non-treated virus. Autologous CD4⁺ T lymphocyte proliferation and cytokine induction by monocyte-derived dendritic cells (MDDC) pulsed either with MUT-A-inactivated HIV or non-treated HIV were also comparable.

Conclusions

Although strongly defective in infectivity, HIV-1 virions produced in the presence of the MUT-A INLAI have a normal protein and genomic RNA content as well as B and T cell immunoreactivities comparable to non-treated HIV-1. These inactivated viruses might form an attractive new approach in vaccine research in an attempt to study if this new type of immunogen could elicit an immune response against HIV-1 in animal models.

Electronic supplementary material

The online version of this article (10.1186/s12977-017-0373-2) contains supplementary material, which is available to authorized users.

Dying cells actively regulate adaptive immune responses

Dying cells have an important role in the initiation of CD8⁺ T cell-mediated immunity. The cross-presentation of antigens derived from dying cells enables dendritic cells to present exogenous tissue-restricted or tumour-restricted proteins on MHC class I molecules. Importantly, this pathway has been implicated in multiple autoimmune diseases and accounts for the priming of tumour antigen-specific T cells. Recent data have revealed that in addition to antigen, dying cells provide inflammatory and immunogenic signals that determine the efficiency of CD8⁺ T cell cross-priming. The complexity of these signals has been evidenced by the multiple molecular pathways that result in cell death and that have now been shown to differentially influence antigen transfer and immunity. In this Review, we provide a detailed summary of both the passive and active signals that are generated by dying cells during their initiation of CD8⁺ T cell-mediated immunity. We propose that molecules generated alongside cell death pathways - inducible damage-associated molecular patterns (iDAMPs) - are upstream immunological cues that actively regulate adaptive immunity.

Nanoparticles and antigen-specific T-cell therapeutics: a comprehensive study on uptake and release

AIM

T lymphocytes are used as cellular therapeutics in many disease entities including cancer. We investigated the uptake and retention of nanoparticles (NPs) by these nonphagocytic cells.

MATERIALS & METHODS

Uptake, release and toxicity of various polymeric NP preparations were analyzed by flow cytometry, confocal laser scanning microscopy and transmission electron microscopy. T-cell effector functions were measured using IFN-γ-ELISPOT and (51)Chromium-release assays.

RESULTS

Amino-functionalized NPs were efficiently ingested by antigen-specific T cells without adversely influencing effector functions. NPs were stored in membrane-surrounded vesicles, with major proportions released extracellularly during 24 h.

CONCLUSION

Amino-functionalized polymeric NPs are efficiently taken up by human T cells and could be used to design nanocarriers for direct access and manipulation of antigen-specific T cells in vivo.

Ion efflux and influenza infection trigger NLRP3 inflammasome signaling in human dendritic cells

The nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome, a multiprotein complex, is an essential intracellular mediator of antiviral immunity. In murine dendritic cells, this complex responds to a wide array of signals, including ion efflux and influenza A virus infection, to activate caspase-1-mediated proteolysis of IL-1β and IL-18 into biologically active cytokines. However, the presence and function of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome in human dendritic cells, in response to various triggers, including viral infection, has not been defined clearly. Here, we delineate the contribution of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome to the secretion of IL-1β, IL-18, and IL-1α by human dendritic cells (monocyte-derived and primary conventional dendritic cells). Activation of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome in human dendritic cells by various synthetic activators resulted in the secretion of bioactive IL-1β, IL-18, and IL-1α and induction of pyroptotic cell death. Cellular IL-1β release depended on potassium efflux and the activity of proteins nucleotide-binding oligomerization domain-like receptor protein 3 and caspase-1. Likewise, influenza A virus infection of dendritic cells resulted in priming and activation of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome and secretion of IL-1β and IL-18 in an M2- and nucleotide-binding oligomerization domain-like receptor protein 3-dependent manner. The magnitude of priming by influenza A virus varied among different strains and inversely corresponded to type I IFN production. To our knowledge, this is the first report describing the existence and function of the nucleotide-binding oligomerization domain-like receptor protein 3 inflammasome in human dendritic cells and the ability of influenza A virus to prime and activate this pathway in human dendritic cells, with important implications for antiviral immunity and pathogenesis.

The Role of Dendritic Cells in Fibrosis Progression in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most frequent cause of chronic liver disease. NAFLD encompasses a wide range of pathologies, from simple steatosis to steatosis with inflammation to fibrosis. The pathogenesis of NAFLD progression has not been completely elucidated, and different liver cells could be implicated. This review focuses on the current evidence of the role of liver dendritic cells (DCs) in the progression from NAFLD to fibrosis. Liver DCs are a heterogeneous population of hepatic antigen-presenting cells; their main function is to induce T-cell mediated immunity by antigen processing and presentation to T cells. During the steady state liver DCs are immature and tolerogenic. However, in an environment of chronic inflammation, DCs are transformed to potent inducers of immune responses. There is evidence about the role of DC in liver fibrosis, but it is not clearly understood. Interestingly, there might be a link between lipid metabolism and DC function, suggesting that immunogenic DCs are associated with liver lipid storage, representing a possible pathophysiological mechanism in NAFLD development. A better understanding of the interaction between inflammatory pathways and the different cell types and the effect on the progression of NAFLD is of great relevance.

Activation of the aryl hydrocarbon receptor during development enhances the pulmonary CD4+ T-cell response to viral infection

Respiratory infections are a threat to health and economies worldwide, yet the basis for striking variation in the severity of infection is not completely understood. Environmental exposures during development are associated with increased severity and incidence of respiratory infection later in life. Many of these exposures include ligands of the aryl hydrocarbon receptor (AHR), a transcription factor expressed by immune and nonimmune cells. In adult animals, AHR activation alters CD4(+) T cells and changes immunopathology. Developmental AHR activation impacts CD4(+) T-cell responses in lymphoid tissues, but whether skewed responses are also present in the infected lung is unknown. To determine whether pulmonary CD4(+) T-cell responses are modified by developmental AHR activation, mice were exposed to the prototypical AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin during development and infected with influenza virus as adults. Lungs of exposed offspring had greater bronchopulmonary inflammation compared with controls, and activated, virus-specific CD4(+) T cells contributed to the infiltrating leukocytes. These effects were CD4(+) T cell subset specific, with increases in T helper type 1 and regulatory T cells, but no change in the frequency of T helper type 17 cells in the infected lung. This is in direct contrast to prior reports of suppressed conventional CD4(+) T-cell responses in the lymph node. Using adoptive transfers and manipulating the pathogen properties, we determined that developmental exposure influenced factors intrinsic and extrinsic to CD4(+) T cells and may involve developmentally induced changes in signals from infected lung epithelial cells. Thus developmental exposures lead to context-dependent changes in pulmonary CD4(+) T-cell subsets, which may contribute to differential responses to respiratory infection.

Superior in vitro stimulation of human CD8+ T-cells by whole virus versus split virus influenza vaccines

Pandemic and seasonal influenza viruses cause considerable morbidity and mortality in the general human population. Protection from severe disease may result from vaccines that activate antigen-presenting DC for effective stimulation of influenza-specific memory T cells. Special attention is paid to vaccine-induced CD8+ T-cell responses, because they are mainly directed against conserved internal influenza proteins thereby presumably mediating cross-protection against circulating seasonal as well as emerging pandemic virus strains. Our study showed that influenza whole virus vaccines of major seasonal A and B strains activated DC more efficiently than those of pandemic swine-origin H1N1 and pandemic-like avian H5N1 strains. In contrast, influenza split virus vaccines had a low ability to activate DC, regardless which strain was investigated. We also observed that whole virus vaccines stimulated virus-specific CD8+ memory T cells much stronger compared to split virus counterparts, whereas both vaccine formats activated CD4+ Th cell responses similarly. Moreover, our data showed that whole virus vaccine material is delivered into the cytosolic pathway of DC for effective activation of virus-specific CD8+ T cells. We conclude that vaccines against seasonal and pandemic (-like) influenza strains that aim to stimulate cross-reacting CD8+ T cells should include whole virus rather than split virus formulations.

Immunization with baculovirus displayed H6 hemagglutinin vaccine protects mice against lethal H6 influenza virus challenge

Low pathogenic influenza viruses of H6 hemagglutinin (HA) subtype have a high prevalence among aquatic and domestic birds and have caused outbreaks in poultry worldwide. The first human infection with wild avian influenza H6N1 virus was reported in Taiwan and these subtype viruses may continue to evolve and accumulate changes which increasing the potential risk of human-to-human transmission. To develop a vaccine against influenza viruses of the H6 subtype, we displayed the HA gene on the baculovirus surface (Bac-HA), and studied its vaccine efficacy against a lethal challenge with mouse-adapted RG-H6(Shorebird) virus carrying the H6 HA gene from A/shorebird/DE/12/2004 (H6N8) virus and 7 genes from A/Puerto Rico/8/1934 (H1N1) virus. Immunization with 256 HA units of Bac-HA via the intranasal route triggered HA-specific serum and mucosal antibodies in mice besides increased HA inhibition titers compared to mice immunized subcutaneously. Moreover, we observed an increase in cellular immune response (IL-4) and improved in vitro neutralization activity in the mice immunized intranasally with live Bac-HA compared to mice immunized with inactivated influenza virus (IV). Interestingly, Bac-HA intranasal immunized mice showed one fold higher neutralization titer against heterologous H6 influenza virus compared to inactivated IV immunized mice. In addition, the live Bac-HA, administered through either immunization route, as well as the adjuvanted inactivated Bac-HA, administered subcutaneously, conferred 100% protection to mice challenged with homologous mouse-adapted RG-H6(Shorebird) virus. The reduction in viral titers and extend of histopathological changes of Bac-HA immunized mice lungs further demonstrated the protective efficacy of Bac-HA. Hence, the recombinant baculovirus subunit vaccine is an alternative candidate against H6 subtypes that could be propagated and administered with minimal biosafety concerns.

Understanding MHC class I presentation of viral antigens by human dendritic cells as a basis for rational design of therapeutic vaccines

Effective viral clearance requires the induction of virus-specific CD8⁺ cytotoxic T lymphocytes (CTL). Since dendritic cells (DC) have a central role in initiating and shaping virus-specific CTL responses, it is important to understand how DC initiate virus-specific CTL responses. Some viruses can directly infect DC, which theoretically allow direct presentation of viral antigens to CTL, but many viruses target other cells than DC and thus the host depends on the cross-presentation of viral antigens by DC to activate virus-specific CTL.

Research in mouse models has highly enhanced our understanding of the mechanisms underlying cross-presentation and the dendritic cells (DC) subsets involved, however, these results cannot be readily translated toward the role of human DC in MHC class I-antigen presentation of human viruses. Here, we summarize the insights gained in the past 20 years on MHC class I presentation of viral antigen by human DC and add to the current debate on the capacities of different human DC subsets herein. Furthermore, possible sources of viral antigens and essential DC characteristics for effective induction of virus-specific CTL are evaluated.

We conclude that cross-presentation is not only an efficient mechanism exploited by DC to initiate immunity to viruses that do not infect DC but also to viruses that do infect DC, because cross-presentation has many conceptual advantages and bypasses direct immune modulatory effects of the virus on its infected target cells.

Since knowledge on the mechanism of viral antigen presentation and the preferred DC subsets is crucial for rational vaccine design, the obtained insights are very instrumental for the development of effective anti-viral immunotherapy.

Suppression of interferon lambda signaling by SOCS-1 results in their excessive production during influenza virus infection

Innate cytokine response provides the first line of defense against influenza virus infection. However, excessive production of cytokines appears to be critical in the pathogenesis of influenza virus. Interferon lambdas (IFN-λ) have been shown to be overproduced during influenza virus infection, but the precise pathogenic processes of IFN-λ production have yet to be characterized. In this report, we observed that influenza virus induced robust expression of IFN-λ in alveolar epithelial cells (A549) mainly through a RIG-I-dependent pathway, but IFN-λ-induced phosphorylation of the signal transducer and activator of transcription protein 1 (STAT1) was dramatically inhibited in the infected cells. Remarkably, influenza virus infection induced robust expression of suppressor of cytokine signaling-1 (SOCS-1), leading to inhibition of STAT1 activation. Interestingly, the virus-induced SOCS-1 expression was cytokine-independent at early stage of infection both in vitro and in vivo. Using transgenic mouse model and distinct approaches altering the expression of SOCS-1 or activation of STAT signaling, we demonstrated that disruption of the SOCS-1 expression or expression of constitutively active STAT1 significantly reduced the production of IFN-λ during influenza virus infection. Furthermore, we revealed that disruption of IFN-λ signaling pathway by increased SOCS-1 protein resulted in the activation of NF-κB and thereby enhanced the IFN-λ expression. Together, these data imply that suppression of IFN-λ signaling by virus-induced SOCS-1 causes an adaptive increase in IFN-λ expression by host to protect cells against the viral infection, as a consequence, leading to excessive production of IFN-λ with impaired antiviral response.

Influenza virus infection triggers innate immune responses. However, aberrant host immune responses such as excessive production of cytokines contribute to the pathogenesis of influenza virus. Type III interferons (IFN-λ) constitute the major innate immune response to influenza virus infection, but the precise pathogenic processes of IFN-λ production and mechanistic underpinnings are not well understood. In this study, we report that influenza virus induces robust IFN-λ expression mainly through a RIG-I-dependent pathway, but signaling activated by IFN-λ was dramatically inhibited by virus-induced SOCS-1. Importantly, we found that disruption of the SOCS-1 expression or forced activation of STAT1 significantly reduced the expression of IFN-λ in vitro and in vivo, suggesting that suppression of IFN-λ signaling by SOCS-1 results in their excessive production during influenza virus infection. Furthermore, our experiments revealed that disruption of IFN-λ signaling pathway resulted in the activation of NF-κB that governs the IFN-λ expression. Together these findings, we propose that impaired antiviral response of IFN-λ due to the inhibitory effect of SOCS-1 causes an adaptive increase in IFN-λ expression by host to protect cells against the viral infection. This is a novel mechanism that may be critical in the pathogenesis of the influenza virus strains that induce hypercytokinemia.

Use of RT-defective HIV virions: new tool to evaluate specific response in chronic asymptomatic HIV-infected individuals

Background

Generation of new reagents that can be used to screen or monitor HIV-1-specific responses constituted an interesting field in the development of HIV vaccines to improve their efficacy.

Methods

We have evaluated the specific T cell response against different types of NL4-3 virions (including NL4-3 aldrithiol-2 treated, NL4-3/ΔRT and R5 envelopes: NL4-3/ΔRT/ΔEnv[AC10] and NL4-3/ΔRT/ΔEnv[Bal]) and against pools of overlapping peptides (15 mer) encompassing the HIV-1 Gag and Nef regions. Cryopreserved PBMC from a subset of 69 chronic asymptomatic HIV positive individuals have been employed using different techniques including IFN-γ ELISPOT assay, surface activation markers and intracellular cytokine staining (ICS) by flow cytometry.

Results

The differential response obtained against NL4-3 aldrithiol-2 treated and NL4-3/ΔRT virions (25% vs 55%, respectively) allow us to divide the population in three groups: “full-responders” (positive response against both viral particles), “partial-responders” (positive response only against NL4-3/ΔRT virions) and “non-responders” (negative responses). There was no difference between X4 and R5 envelopes. The magnitude of the total responses was higher against NL4-3/ΔRT and was positively correlated with gender and inverse correlated with viral load. On the contrary CD4+ T cell count was not associated with this response. In any case responses to the viruses tended to be lower in magnitude than those detected by the overlapping peptides tested. Finally we have found an increased frequency of HLA-B27 allele (23% vs 9%) and a significant reduction in some activation markers (CD69 and CD38) on T cells surface in responders vs non-responders individuals.

Conclusions

In summary these virions could be considered as alternative and useful reagents for screening HIV-1-specific T cell responses in HIV exposed uninfected people, HIV infected patients and to assess immunogenicity of new prototypes both in vitro and in vaccine trials, by a feasible, simply, effective and low cost assay.

Abortive replication of influenza virus in mouse dendritic cells

The interaction between influenza virus and dendritic cells (DCs) remains poorly defined and controversial. Here we show that influenza virus replication in mouse bone marrow-derived DCs is abortive, despite viral genome transcription and replication occurring for each gene segment and viral hemagglutinin and nucleoprotein, at least, being produced. Electron microscopy reveals that virus assembly, rather than release of virus from the cell surface, is defective.

Influenza A virus infection of human primary dendritic cells impairs their ability to cross-present antigen to CD8 T cells

Influenza A virus (IAV) infection is normally controlled by adaptive immune responses initiated by dendritic cells (DCs). We investigated the consequences of IAV infection of human primary DCs on their ability to function as antigen-presenting cells. IAV was internalized by both myeloid DCs (mDCs) and plasmacytoid DCs but only mDCs supported viral replication. Although infected mDCs efficiently presented endogenous IAV antigens on MHC class II, this was not the case for presentation on MHC class I. Indeed, cross-presentation by uninfected cells of minute amounts of endocytosed, exogenous IAV was -300-fold more efficient than presentation of IAV antigens synthesized by infected cells and resulted in a statistically significant increase in expansion of IAV-specific CD8 T cells. Furthermore, IAV infection also impaired cross-presentation of other exogenous antigens, indicating that IAV infection broadly attenuates presentation on MHC class I molecules. Our results suggest that cross-presentation by uninfected mDCs is a preferred mechanism of antigen-presentation for the activation and expansion of CD8 T cells during IAV infection.

Induction of heterosubtypic cross-protection against influenza by a whole inactivated virus vaccine: the role of viral membrane fusion activity

BACKGROUND

The inability of seasonal influenza vaccines to effectively protect against infection with antigenically drifted viruses or newly emerging pandemic viruses underlines the need for development of cross-reactive influenza vaccines that induce immunity against a variety of virus subtypes. Therefore, potential cross-protective vaccines, e.g., whole inactivated virus (WIV) vaccine, that can target conserved internal antigens such as the nucleoprotein (NP) and/or matrix protein (M1) need to be explored.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study we show that a WIV vaccine, through induction of cross-protective cytotoxic T lymphocytes (CTLs), protects mice from heterosubtypic infection. This protection was abrogated after depletion of CD8+ cells in vaccinated mice, indicating that CTLs were the primary mediators of protection. Previously, we have shown that different procedures used for virus inactivation influence optimal activation of CTLs by WIV, most likely by affecting the membrane fusion properties of the virus. Specifically, inactivation with formalin (FA) severely compromises fusion activity of the virus, while inactivation with β-propiolactone (BPL) preserves fusion activity. Here, we demonstrate that vaccination of mice with BPL-inactivated H5N1 WIV vaccine induces solid protection from lethal heterosubtypic H1N1 challenge. By contrast, vaccination with FA-inactivated WIV, while preventing death after lethal challenge, failed to protect against development of disease and severe body weight loss. Vaccination with BPL-inactivated WIV, compared to FA-inactivated WIV, induced higher levels of specific CD8+ T cells in blood, spleen and lungs, and a higher production of granzyme B in the lungs upon H1N1 virus challenge.

CONCLUSION/SIGNIFICANCE

The results underline the potential use of WIV as a cross-protective influenza vaccine candidate. However, careful choice of the virus inactivation procedure is important to retain membrane fusion activity and full immunogenicity of the vaccine.

Immunogenicity of a recombinant influenza virus bearing both the CD4+ and CD8+ T cell epitopes of ovalbumin

Recombinant influenza viruses that bear the single immunodominant CD8+ T cell epitope OVA_257−264 or the CD4+ T cell epitope OVA_323−339 of the model antigen ovalbumin (OVA) have been useful tools in immunology. Here, we generated a recombinant influenza virus, WSN-OVA_I/II, that bears both OVA-specific CD8+ and CD4+ epitopes on its hemagglutinin molecule. Live and heat-inactivated WSN-OVA_I/II viruses were efficiently presented by dendritic cells in vitro to OT-I TCR transgenic CD8+ T cells and OT-II TCR transgenic CD4+ T cells. In vivo, WSN-OVA_I/II virus was attenuated in virulence, highly immunogenic, and protected mice from B16-OVA tumor challenge in a prophylactic model of vaccination. Thus, WSN-OVA_I/II virus represents an additional tool, along with OVA TCR transgenic mice, for further studies on T cell responses and may be of value in vaccine design.

Innate immune sensing of retroviral infection via Toll-like receptor 7 occurs upon viral entry

Innate immune sensors are required for induction of pathogen-specific immune responses. Retroviruses are notorious for their ability to evade immune defenses and establish long-term persistence in susceptible hosts. However, some infected animals are able to develop efficient virus-specific immune responses, and thus can be employed for identification of critical innate virus-sensing mechanisms. With mice from two inbred strains that control retroviruses via adaptive immune mechanisms, we found that of all steps in viral replication, the ability to enter the host cell was sufficient to induce antivirus humoral immune responses. Virus sensing occurred in endosomes via a MyD88-Toll-like receptor 7-dependent mechanism and stimulated virus-neutralizing immunity independently of type I interferons. Thus, efficient adaptive immunity to retroviruses is induced in vivo by innate sensing of the early stages of retroviral infection.

Enhanced local dendritic cell activity and tumor-specific immunoresponse in combined radiofrequency ablation and interleukin-2 for the treatment of human head and neck cancer in a murine orthotopic model

BACKGROUND

Radiofrequency ablation (RFA) is a minimally invasive tumor destruction technique and can provide the antigen source initiating tumor immunity. However, induced immune response is weak and requires additional immunotherapy for optimized RFA treatment against cancer.

METHODS

A murine orthotopic model of head and neck squamous cell carcinoma (HNSCC) was established to investigate the efficacy and mechanism of an RFA + interleukin-2 (IL-2) combination adenoviral gene therapy among 6 groups. Tumor volume change, apoptosis, in situ macrophage recruitment, cytotoxic T lymphocyte (CTL) activity, migration of dendritic cells into the regional lymph nodes, and systemic antitumor immunity were examined.

RESULTS

RFA + IL-2 therapy induced the highest levels of macrophage recruitment and dendritic cell migration resulting in enhanced CTL activity, increased tumor apoptosis, enhanced systemic antitumor immunity, and the best inhibition of tumor growth among all groups.

CONCLUSION

RFA + IL-2 combination therapy generates potent tumor immunity to suppress tumor growth in HNSCC.

Dendritic cells in viral bronchiolitis

Dendritic cells (DCs) are major antigen-presenting cells that constitute a link between innate and adaptive immune responses, and are critical in the processes of control and elimination of viral infections. On the other hand, there is a large body of data strongly implicating respiratory viruses in morbidity during infancy through the induction of lower respiratory tract infections, such as bronchiolitis, and later on in childhood and adult life, mainly due to their association with asthma exacerbations. Little is known, however, about the precise role of DCs in human respiratory tract infections. This review focuses on current data, both from in vivo and in vitro studies, that highlight the interplay between DCs and the viral causes of bronchiolitis.

Prolonged antigen survival and cytosolic export in cross-presenting human gammadelta T cells

Human blood Vgamma9Vdelta2 T cells respond to signals from microbes and tumors and subsequently differentiate into professional antigen-presenting cells (gammadelta T-APCs) for induction of CD4(+) and CD8(+) T cell responses. gammadelta T-APCs readily take up and degrade exogenous soluble protein for peptide loading on MHC I, in a process termed antigen cross-presentation. The mechanisms underlying antigen cross-presentation are ill-defined, most notably in human dendritic cells (DCs), and no study has addressed this process in gammadelta T-APCs. Here we show that intracellular protein degradation and endosomal acidification were significantly delayed in gammadelta T-APCs compared with human monocyte-derived DCs (moDCs). Such conditions are known to favor antigen cross-presentation. In both gammadelta T-APCs and moDCs, internalized antigen was transported across insulin-regulated aminopeptidase (IRAP)-positive early and late endosomes; however, and in contrast to various human DC subsets, gammadelta T-APCs efficiently translocated soluble antigen into the cytosol for processing via the cytosolic proteasome-dependent cross-presentation pathway. Of note, gammadelta T-APCs cross-presented influenza antigen derived from virus-infected cells and from free virus particles. The robust cross-presentation capability appears to be a hallmark of gammadelta T-APCs and underscores their potential application in cellular immunotherapy.

Dendritic Cells in Innate and Adaptive Immune Responses against Influenza Virus

Dendritic cells (DC) are major players in both innate and adaptive immune responses against influenza virus. These immune responses, as well as the important interface between the innate and adaptive systems, are orchestrated by specialized subsets of DC, including conventional steady-state DC, migratory DC and plasmacytoid DC. The characteristics and efficacy of the responses are dependent on the relative activity of these DC subsets, rendering DC crucial for the development of both naïve and memory immune responses. However, due to their critical role, DC also contribute to the immunopathological processes observed during acute influenza, such as that caused by the pathogenic H5N1 viruses. Therein, the role of different DC subsets in the induction of interferon type I, pro-inflammatory cytokine and chemokine responses is important for the outcome of interaction between the virus and host immune defences. The present review will present current knowledge on this area, relating to the importance of DC activity for the induction of efficacious humoral and cell-mediated immune responses. This will include the main viral elements associated with the triggering or inhibition of DC activation. Finally, the current knowledge on understanding how differences in various vaccines influence the manner of immune defence induction will be presented.

A multisystem approach for development and evaluation of inactivated vaccines for Venezuelan equine encephalitis virus (VEEV)

A multisystem approach was used to assess the efficiency of several methods for inactivation of Venezuelan equine encephalitis virus (VEEV) vaccine candidates. A combination of diverse assays (plaque, in vitro cytopathology and mouse neurovirulence) was used to verify virus inactivation, along with the use of a specific ELISA to measure retention of VEEV envelope glycoprotein epitopes in the development of several inactivated VEEV candidate vaccines derived from an attenuated strain of VEEV (V3526). Incubation of V3526 aliquots at temperatures in excess of 64 degrees C for periods >30 min inactivated the virus, but substantially reduced VEEV specific monoclonal antibody binding of the inactivated material. In contrast, V3526 treated either with formalin at concentrations of 0.1% or 0.5% (v/v) for 4 or 24 h, or irradiated with 50 kGy gamma radiation rendered the virus non-infectious while retaining significant levels of monoclonal antibody binding. Loss of infectivity of both the formalin inactivated (fV3526) and gamma irradiated (gV3526) preparations was confirmed via five successive blind passages on BHK-21 cells. Similarly, loss of neurovirulence for fV3526 and gV3526 was demonstrated via intracerebral inoculation of suckling BALB/c mice. Excellent protection against subcutaneous challenge with VEEV IA/B Trinidad donkey strain was demonstrated using a two dose immunization regimen with either fV3526 or gV3526. The combination of in vitro and in vivo assays provides a practical approach to optimize manufacturing process parameters for development of other inactivated viral vaccines.

Presentation of human T cell leukemia virus type 1 (HTLV-1) Tax protein by dendritic cells: the underlying mechanism of HTLV-1-associated neuroinflammatory disease

HTLV-1 is the etiologic agent of a debilitating neurologic disorder, HAM/TSP. This disease features a robust immune response including the oligoclonal expansion of CD8+ CTLs specific for the viral oncoprotein Tax. The key pathogenic process resulting in the proliferation of CTLs and the presentation of Tax peptide remains uncharacterized. We have investigated the role of APCs, particularly DCs, in priming of the anti-Tax CTL response under in vitro and in vivo conditions. We investigated two routes (direct vs. indirect) of Tax presentation using live virus, infected primary CD4+/CD25+ T cells, and the CD4+ T cell line (C8166, a HTLV-1-mutated line that only expresses Tax). Our results indicated that DCs are capable of priming a pronounced Tax-specific CTL response in cell cultures consisting of naïve PBLs as well as in HLA-A*0201 transgenic mice (line HHD II). DCs were able to direct the presentation of Tax successfully through infected T cells, live virus, and cell-free Tax. These observations were comparable with those made with a known stimulant of DC maturation, a combination of CD40L and IFN-gamma. Our studies clearly establish a role for this important immune cell component in HTLV-1 immuno/neuropathogenesis and suggest that modulation of DC functions could be an important tool for therapeutic interventions.

Chronic antigen stimulation alone is sufficient to drive CD8+ T cell exhaustion

The failure of CD8(+) T cells to respond to chronic infection has been termed "exhaustion" and describes the condition in which CD8(+) T cells exhibit reduced differentiation, proliferation, and effector function. CD8(+) T cell exhaustion has been extensively studied in the murine model of chronic infection, lymphocytic choriomeningitis virus (LCMV). Although LCMV-based studies have yielded many interesting findings, they have not allowed for discrimination between the roles of cytokine- and Ag-driven exhaustion. We have created a system of chronic Ag stimulation using murine influenza A virus that leads to exhaustion and functional disability of virus-specific CD8(+) T cells, in the absence of high viral titers, sustained proinflammatory cytokine production and lymphocyte infection. Our findings show that Ag alone is sufficient to drive CD8(+) T cell impairment, that Ag-driven loss of virus-specific CD8(+) T cells is TRAIL mediated, and that removal of Ag reverses exhaustion. Although programmed death 1 was up-regulated on chronic Ag-stimulated CD8(+) T cells, it played no role in the exhaustion. These findings provide a novel insight into the mechanisms that control functional exhaustion of CD8(+) T cells in chronic infection.

Prospects for an influenza vaccine that induces cross-protective cytotoxic T lymphocytes

Our approach to vaccination against influenza is unique. For no other pathogen do we construct and produce a new vaccine every year in the face of uncertainty about the strains that will be circulating when it is used. The huge global cooperative effort that underpins this process reflects our awareness of the need to control this major pathogen. Moreover, the threat of devastation by a pandemic due to a newly emerging viral subtype has triggered an intense effort to improve and accelerate the production of vaccines for use if a pandemic arises. However, type A influenza viruses responsible for seasonal epidemics and those with the potential to cause a pandemic share amino acid sequences that form the targets of cytotoxic T lymphocytes (CTL). CTL activated by currently circulating viruses, therefore, offer a possible means to limit the impact of infection with future variant seasonal strains and even new subtypes. This review examines how cross-protective CTL can be exploited to improve influenza vaccination and issues that need to be considered when attempting to induce this type of immunity. We discuss the role of CTL responses in viral control and review the current knowledge relating to specificity and longevity of memory CD8(+) T cells, how vaccine antigen can be loaded into antigen-presenting cells to prime these responses and factors influencing the class of response induced. Application of these principles to the next generation of influenza vaccines should lead to much greater control of infection.

Clearance of influenza virus from the lung depends on migratory langerin+CD11b- but not plasmacytoid dendritic cells

Although dendritic cells (DCs) play an important role in mediating protection against influenza virus, the precise role of lung DC subsets, such as CD11b- and CD11b+ conventional DCs or plasmacytoid DCs (pDCs), in different lung compartments is currently unknown. Early after intranasal infection, tracheal CD11b-CD11chi DCs migrated to the mediastinal lymph nodes (MLNs), acquiring co-stimulatory molecules in the process. This emigration from the lung was followed by an accumulation of CD11b+CD11chi DCs in the trachea and lung interstitium. In the MLNs, the CD11b+ DCs contained abundant viral nucleoprotein (NP), but these cells failed to present antigen to CD4 or CD8 T cells, whereas resident CD11b-CD8+ DCs presented to CD8 cells, and migratory CD11b-CD8- DCs presented to CD4 and CD8 T cells. When lung CD11chi DCs and macrophages or langerin+CD11b-CD11chi DCs were depleted using either CD11c-diphtheria toxin receptor (DTR) or langerin-DTR mice, the development of virus-specific CD8+ T cells was severely delayed, which correlated with increased clinical severity and a delayed viral clearance. 120G8+ CD11cint pDCs also accumulated in the lung and LNs carrying viral NP, but in their absence, there was no effect on viral clearance or clinical severity. Rather, in pDC-depleted mice, there was a reduction in antiviral antibody production after lung clearance of the virus. This suggests that multiple DCs are endowed with different tasks in mediating protection against influenza virus.

New assays to measure equine influenza virus-specific Type 1 immunity in horses

Equine influenza virus (EIV) is a leading cause of respiratory disease in horses. Equine influenza infection induces a long-term immunity to re-infection. Recent strategies of vaccination aim to mimic this immunity by stimulating both antibody and cellular immune responses. Cell-mediated immunity (CMI) to influenza is well defined in man, but little has been done to characterise the responses in the horse. Additionally, the development of reliable assays for the measurement of equine CMI has lagged behind serological methods and vaccine development. In this study, two methods of measuring EIV-specific T lymphocyte responses have been developed. An EIV 'bulk' cytotoxic T lymphocytes (CTL) assay using equine dermal fibroblasts as target cells has been adapted from a method used in the 1980s. This method was also complemented with a new EIV-specific IFNgamma synthesis assay. When compared with the measurement of EIV-specific IFNgamma synthesis previously described, this method required the amplification of EIV-specific lymphocytes by culture and was sensitive enough to detect stimulation of EIV-specific T lymphocytes induced by experimental infection with EIV or vaccination with recombinant canarypox viruses coding for EIV-HA molecules. This study provides the tools to characterise the stimulation of CMI by the new generation of vaccines against equine influenza.

Pathways utilized by dendritic cells for binding, uptake, processing and presentation of antigens derived from HIV-1

The outcome following HIV infection depends on the nature and durability of the HIV-specific T cell response induced initially. The activation of protective T cell responses depends upon dendritic cells (DC), antigen-presenting cells which have the capacity to process and present viral antigens. DC pulsed with aldrithiol-2-inactivated HIV and delivered in vivo were reported to induce immune responses and promote virologic control in chronically HIV-1-infected subjects. To gain an understanding of this phenomenon, we characterized the steps involved in the presentation of antigens derived from aldrithiol-2-treated vs. infectious HIV-1 by DC. Antigen presentation, on both MHC class I and II, was independent of DC-specific ICAM-3-grabbing integrin, DEC-205 and macrophage mannose receptor, C-type lectins expressed by the DC. Inhibitor studies showed that presentation on MHC class I was dependent on viral fusion in a CD4/coreceptor-dependent manner, both at the cell surface and within endosomes, and access to the classical endosomal processing pathway. MHC class II presentation of HIV-associated antigens was dependent on active endocytosis, probably receptor-mediated, and subsequent degradation of virions in acidified endosomes in the DC. Our study brings forth new facts regarding the binding, uptake, and processing of chemically inactivated virions leading to efficient antigen presentation and should aid in the design of more effective HIV vaccines.

Intestinal and pulmonary mucosal T cells: local heroes fight to maintain the status quo

Mucosal immunity in the lung and intestine is controlled by complex multifaceted systems. While mucosal T cells are essential for protection against invading pathogens owing to their proximity to the outside world, powerful systems must also be in place to harness ongoing inflammatory processes. In each site, distinct anatomical structures play key roles in mounting and executing both protective and deleterious mucosal T cell responses. Although analogies can be drawn regarding the immune systems of these two organs, there are substantial dissimilarities necessitated by unique physiologic constraints. Here, we discuss how T cell activation and effector function are generated in the mucosae.

Human dendritic cell interactions with whole recombinant yeast: implications for HIV-1 vaccine development

Defects in number and function of dendritic cells (DCs) have been observed during HIV-1 infection, so therapeutic HIV-1 vaccine approaches that target or activate DCs may improve vaccine immunogenicity. To determine the potential of recombinant Saccharomyces cerevisiae yeast as an HIV-1 vaccine, we investigated interactions between yeast and human DCs. Yeast induced direct phenotypic maturation of monocyte-derived DCs (MDDCs) and enriched blood myeloid DCs (mDCs), but only indirectly matured blood plasmacytoid DCs (pDCs). Yeast-pulsed MDDCs and blood mDCs produced inflammatory cytokines and stimulated strong allo-reactive T cell proliferation. Both blood DC subsets internalized yeast, and when pulsed with yeast recombinant for HIV-1 Gag protein, both stimulated in vitro expansion of Gag-specific CD8+ memory T cells. These results suggest that S. cerevisiae yeast have potent adjuvant effects on human DCs. Furthermore, recombinant yeast-derived antigens are processed by human blood DCs for MHC class-I cross-presentation. These DC-targeting characteristics of yeast suggest that it may be an effective vaccine vector for induction of HIV-1-specific cellular immune responses.

Decreased in vitro type 1 immune response against coxsackie virus B4 in children with type 1 diabetes

Enteroviruses, particularly Coxsackie virus B4 (CVB4), are considered to be involved in the pathogenesis of type 1 diabetes. We wanted to compare the characteristics of T-cell immune response to CVB4 in children with type 1 diabetes and healthy children with and without HLA risk-associated haplotypes (HLA-DR3-DQ2 or HLA-DR4-DQ8) for type 1 diabetes. Peripheral blood mononuclear cells (PBMCs) were isolated and cultured with CVB4 and analyzed for cytokine and chemokine receptors by flow cytometry and for expression of transcription factors Tbet and GATA-3 by RT-PCR and Western blot. Culture supernatants were analyzed for secretion of gamma-interferon (IFN-gamma). In children with type 1 diabetes, a decreased percentage of T-cells expressed CCR2, CXCR6, interleukin (IL)-18R, and IL-12Rbeta2-chain after in vitro stimulation with CVB4 in comparison with healthy children with or without HLA risk genotype. Moreover, we found that children with type 1 diabetes had decreased IFN-gamma secretion and expression of Tbet, both on mRNA and protein level, in CVB4-stimulated PBMCs. Accordingly, children with type 1 diabetes show an impaired type 1 immune response against CVB4 compared with healthy children. This may lead to a delayed clearance of the virus and, at least partly, explain why children with type 1 diabetes may be more prone to CVB4 infections and related complications, such as beta-cell damage.

Is hepatitis C virus infection of dendritic cells a mechanism facilitating viral persistence?

More than 170 million people worldwide are chronically infected with hepatitis C virus (HCV), which is a major cause of chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Impaired T-cell reactivity to HCV, a hallmark of inefficient adaptive immunity, is believed to be responsible for the high propensity of HCV to cause chronic infection. Dendritic cells are the most potent antigen-presenting cells and many viruses affect various dendritic cell functions. Data suggest that such changes induced by HCV may have an important role in viral persistence. HCV has been shown to bind to dendritic cells, although viral replication within these cells occurs at a very low level. Dendritic cells from people with chronic HCV infection are impaired in their capacity to stimulate T cells. This impairment may be a consequence of changes in the expression of major histocompatibility complex and costimulatory molecules on its surface, as well as in the production of cytokines such as interleukin 12. In addition, hepatic dendritic cells may be affected by the tolerogenic microenvironment of the liver, possibly generating dendritic cells that promote regulatory T cells, which suppress the cellular immune response mounted against HCV.

Generation of Aspergillus- and CMV- specific T-cell responses using autologous fast DC

BACKGROUND

Recent reports have described a new strategy for differentiation and maturation of monocyte (Mo)-derived DCs within only 48 h of in vitro culture (fast-DC). Here we assess the efficacy of the fast-DC to process and present different Aspergillus fumigatus and CMV Ag preparations to autologous T cells, compared with DCs generated in standard 7-day cultures (standard-DC).

METHODS

Adherent blood Mo were treated with GM-CSF and IL-4 (1 day for fast-DC, 5 days in the standard-DC) to generate immature DCs, and then were matured for either 1-2 days (fast-DC) or 2 days (standard-DC) with inflammatory cytokines. DCs were pulsed with A. fumigatus or CMV Ag preparation immediately prior to maturation, or infected after maturation with adeno-pp65. Mature DCs were then used to prime Ag-specific proliferative and cytotoxic T lymphocytes (CTL) responses.

RESULTS

Fast-DC were CD14- and expressed mature DC surface markers to the same degree as standard-DC, and maintained this phenotype after withdrawing cytokine from the cultures. Fast-DC and standard-DC were equally capable of inducing A. fumigatus and CMV-specific T-cell proliferation, as well as priming Ag-specific CTL activity. The Aspergillus- and CMV-specific CTL were of mixed CD3+/CD4+ and CD3+/CD8+ phenotype, and specifically killed autologous DC pulsed with A. fumigatus Ag and autologous CMV infected fibroblasts, respectively.

DISCUSSION

Fast-DC are as effective as standard-DC in the generation of Ag-specific T-cell responses. Moreover, use of fast-DC not only reduces labor and supply cost, as well as workload and time, but also increases the number of DCs derived from adherent Mo, which may facilitate the use of DCs in clinical trials of cellular immunotherapy.

Virosome-mediated delivery of protein antigens in vivo: efficient induction of class I MHC-restricted cytotoxic T lymphocyte activity

Induction of CTL responses against protein antigens is an important aim in vaccine development. In this paper we present fusion-active virosomes as a vaccine delivery system capable of efficient induction of CTL responses in vivo. Virosomes are reconstituted viral membranes, which do not contain the genetic material of the virus they are derived from. Foreign macromolecules, including protein antigens, can be encapsulated in virosomes during the reconstitution process. Functionally reconstituted virosomes retain the cell binding and fusion characteristics of the native virus. Thus, upon uptake by cells through receptor-mediated endocytosis, virosomes will deliver their content to the cell cytosol. In a previous study, we demonstrated that protein antigens delivered in this manner to dendritic cells are efficiently processed for both MHC class I and class II presentation. Here, we studied in vivo induction of cellular immune responses against virosome-encapsulated ovalbumin (OVA) in mice. As little as 0.75 microg OVA delivered by fusion-active virosomes was sufficient to induce a powerful class I MHC-restricted CTL response. All immunization routes that were used (i.m., i.p. and s.c.) resulted in efficient induction of CTL activity. The CTLs induced were cytotoxic in a standard 51Cr-release assay and produced IFNgamma in response to OVA peptide. Thus, virosomes represent an ideal antigen delivery system for induction of cellular immunity against encapsulated protein antigens.

HIV-1 and the hijacking of dendritic cells: a tug of war

Dendritic cells are critical for host immunity and are involved both in the innate and adaptive immune responses. They are among the first cells targeted by HIV-1 in vivo at mucosal sites. Dendritic cells can sequester HIV-1 in endosomal compartments for several days and transmit infectious HIV-1 to interacting T cells in the lymph node, which is the most important site for viral replication and spread. Initially, the cellular immune response developed against HIV-1 is strong, but eventually it fails to control and resolve the infection. The most dramatic effect seen on the immune system during untreated HIV-1 infection is the destruction of helper CD4(+) T cells, which leads to subsequent immune deficiency. However, the immunomodulatory effects of HIV-1 on different dendritic cell subpopulations may also play an important role in the pathogenesis of HIV-1. This review discusses the effects HIV-1 exerts on dendritic cells in vivo and in vitro, including the binding and uptake of HIV by dendritic cells, the formation of infectious synapses, infection, and the role of dendritic cells in HIV-1 pathogenesis.

Immunomodulating effect of influenza vaccination in the elderly differing in health status

The aim of this study was to analyse whether split influenza vaccine may elicit NK cytotoxic response in the vaccinated elderly people and whether this effect may be maintained over few weeks after vaccination. It was also worth investigating the relation between NK activity in the vaccinated and specific immune protection against influenza and non-specific against other infections. Two groups of volunteers were vaccinated with trivalent split viron influenza vaccine in two consecutive seasons (1999/2000; 2000/2001). The elderly group consisted of 142 people (65-92 years old) in the first season and 110 in the second; while the young (16-44 years old) of 98 and 67 people, respectively. An analysis of NK cytotoxic activity had been done before vaccination, two days, one month and fifth months thereafter. The results revealed that vaccination with the influenza vaccine had an augmenting effect on NK activity, in all groups examined, in both epidemic seasons, visible at two days and 1 month after the vaccination. In the elderly high pre- and post-vaccination NK activity was related to higher titers of anti-hemagglutinin, better health status and lower incidence of all cause respiratory tract infections. At the second vaccination, most of the elderly with chronic medical conditions and high NK activity, who did not attain the protective level of anti-hemagglutinins in the first season, converted into the protected. High pre- and post-vaccination NK activity predisposes elderly people to the protective humoral anti-hemagglutinin response and gives better protection from respiratory tract infections.

Intranasal immunization with inactivated influenza virus enhances immune responses to coadministered simian-human immunodeficiency virus-like particle antigens

Intranasal immunization with inactivated influenza virus vaccine can provide protective immunity, whereas many other antigens are less effective when used for mucosal immunization. To determine whether influenza virus could enhance immune responses to an antigen coadministered to a mucosal surface, we studied the intranasal immunization of mice with a mixture of simian-human immunodeficiency virus (SHIV) virus-like particles (VLPs) and inactivated influenza virus. Compared to mice immunized with SHIV VLPs alone, mice coimmunized with SHIV VLPs and inactivated influenza virus showed significant increases in serum immunoglobulin G (IgG) and mucosal IgA antibodies specific to the human immunodeficiency virus envelope protein, neutralizing activities, numbers of gamma interferon- and interleukin 4-secreting lymphocytes, and cytotoxic-T-lymphocyte activities. The levels of enhancement of immune response by coimmunization with inactivated influenza virus were equivalent to those induced by inclusion of immunostimulatory CpG oligodeoxynucleotides (CpG DNA). We also observed that SHIV VLPs bind to influenza virus virions, forming mixed aggregates. These results indicate that inactivated influenza virus can play a role as a mucosal adjuvant to coadministered antigens.

Innate antiviral responses by means of TLR7-mediated recognition of single-stranded RNA

Interferons (IFNs) are critical for protection from viral infection, but the pathways linking virus recognition to IFN induction remain poorly understood. Plasmacytoid dendritic cells produce vast amounts of IFN-alpha in response to the wild-type influenza virus. Here, we show that this requires endosomal recognition of influenza genomic RNA and signaling by means of Toll-like receptor 7 (TLR7) and MyD88. Single-stranded RNA (ssRNA) molecules of nonviral origin also induce TLR7-dependent production of inflammatory cytokines. These results identify ssRNA as a ligand for TLR7 and suggest that cells of the innate immune system sense endosomal ssRNA to detect infection by RNA viruses.

Regulation of Mite Allergen-pulsed Murine Dendritic Cells by Respiratory Syncytial Virus

Dendritic cells (DCs) are the only antigen-presenting cells that determine T-cell differentiation and play an important role in both allergy and viral infection. Respiratory syncytial virus (RSV) can infect DCs and affect their functions. The aim of this study was to determine the interaction between RSV infection and Dermatophagoides farinae allergen (D. farinae) sensitization on the development of allergy at the DC level. Murine bone marrow-derived DCs were prepared and treated as: control; D. farinae-pulsed DCs (D. farinae-DCs); ultraviolet-inactivated RSV challenged; RSV-infected, D. farinae-pulsed plus ultraviolet-inactivated RSV-challenged; and D. farinae-pulsed plus RSV-infected. In in vitro experiments, we compared the expression of costimulatory molecules and cytokine production between the six groups of DCs. Another group of naive mice were then intranasally inoculated with these DCs, after which intranasal challenge with D. farinae was performed to develop allergic airway inflammation in vivo. In comparison with D. farinae-DCs, D. farinae-pulsed plus RSV-infected DCs showed helper T cell (Th) 1-favored expression of costimulatory molecules and cytokine production. Allergic airway inflammation induced by intranasal instillation of D. farinae-DCs was abrogated when infected with RSV, which was associated with a concomitant suppression of Th2 response in the lung. Our results indicated that RSV suppresses D. farinae-DCs to induce Th2 response both in vitro and in vivo through regulation of expression of surface markers and production of immunoregulatory cytokines.

Characterization of the MHC class I cross-presentation pathway for cell-associated antigens by human dendritic cells

Major histocompatibility complex (MHC) class I presentation of exogenous antigens is the mechanism enabling professional antigen-presenting cells (APCs) to induce CD8+ T-cell responses against viruses and tumors that do not have access to the classical MHC class I pathway. We have characterized the uptake, processing, and MHC class I cross-presentation by human dendritic cells (DCs) of cell-associated antigens derived from physiologically relevant sources, namely, vaccinia virus-infected apoptotic and necrotic cells. We show that cross-presentation is a rapid process, detectable within 2 to 4 hours after uptake of dead cells, and that proteolysis by cathepsin D in an acidic endosomal compartment is essential for cross-presentation. The presentation is abolished when the phagocytic or macropinocytic functions of the cells are inhibited and is dependent on transporter associated with antigen processing, sensitive to brefeldin A, and requires functional proteasomes. Altogether, these data suggest that antigens derived from apoptotic and necrotic cells require access to the cytosol to intersect with the conventional MHC class I pathway for presentation of cytosolic proteins.

Viral vectors for dendritic cell-based immunotherapy

Dendritic cells (DCs) constitute a specialised system of antigen-presenting cells with a high capacity to induce and to modulate the immune response against microbial, tumour and self-antigens. New techniques to generate large amounts of DCs together with the molecular identification of human tumour-associated antigens (TAA) have opened new ways for antigen-specific cancer immunotherapies. DCs loaded either with TAA-derived MHC class I-specific synthetic peptides or with whole tumour cell preparations have been used in numerous clinical trials evaluating the efficacy of DCs in patients with cancer. However, the disadvantages of DCs pulsed with synthetic peptides from TAA include the uncertainty regarding the longevity of antigen presentation, the restriction by the patient's haplotype and the relatively low number of known MHC class I and in particular of MHC class II helper cell-related epitopes. Whole tumour cell preparations are difficult to standardise, and they depend on the availability of tumour cells. Thus the utilisation of viral vectors genetically modified to express TAA for the ex vivo transduction of DCs is an attractive alternative to achieve a MHC I- and MHC II-restricted presentation of tumoural antigens. To induce protective anti-tumoural immune response an increasing number of modified viral vectors have been used to transduce DCs. Although high transduction efficacies were reported for several viruses, analysis of the interaction of viral vectors with DCs has revealed several viral mechanisms that interfere with main functions of DCs, dampening somewhat the initial optimism in the field of DC transduction. However, promising results with different vectors have been achieved. In this review we summarise available data and discuss advantages and drawbacks of currently available vectors.

Activation of influenza virus-specific CD4+ and CD8+ T cells: a new role for plasmacytoid dendritic cells in adaptive immunity

Plasmacytoid dendritic cells (pDCs) contribute to innate antiviral immune responses by producing type I interferons (IFNs) upon exposure to enveloped viruses. However, their role in adaptive immune responses, such as the initiation of antiviral T-cell responses, is not known. In this study, we examined interactions between blood pDCs and influenza virus with special attention to the capacity of pDCs to activate influenza-specific T cells. pDCs were compared with CD11c(+) DCs, the most potent antigen-presenting cells (APCs), for their capacity to activate T-cell responses. We found that like CD11c(+) DCs, pDCs mature following exposure to influenza virus, express CCR7, and produce proinflammatory chemokines, but differ in that they produce type I IFN and are resistant to the cytopathic effect of the infection. After influenza virus exposure, both DC types exhibited an equivalent efficiency to expand anti-influenza virus cytotoxic T lymphocytes (CTLs) and T helper 1 (TH1) CD4(+) T cells. Our results pinpoint a new role of pDCs in the induction of antiviral T-cell responses and suggest that these DCs play a prominent role in the adaptive immune response against viruses.

NKT cells provide help for dendritic cell-dependent priming of MHC class I-restricted CD8+ T cells in vivo

Dendritic cells (DC) are potent APCs for naive T cells in vivo. This is evident by inducing T cell responses through adoptive DC transfer. Priming specific CTL responses in vivo often requires "help". We study alternative sources of help in DC-dependent priming of MHC class I-restricted CTL. Priming an anti-viral CTL response in naive B6 mice by adoptive transfer of antigenic peptide-pulsed DC required CD4(+) T cell help. CTL priming was facilitated by providing MHC class II-dependent specific help. Furthermore, transfers of MHC class II-deficient pulsed DC into naive, normal hosts, or DC transfers into naive, CD4(+) T cell-depleted hosts primed CTL inefficiently. Pretreatment of DC with immune-stimulating oligodeoxynucleotides rendered them more efficient for CD4(+) T cell-independent priming of CTL. DC copresenting a K(b)-binding antigenic peptide and the CD1d-binding glycolipid alpha-galactosyl-ceramide efficiently primed CTL in a class II-independent way. To obtain NKT cell-dependent help in CTL priming, the same DC had to present both the peptide and the glycolipid. CTL priming by adoptive DC transfer was largely NK cell-dependent. The requirement for NK cells was only partially overcome by recruiting NKT cell help into DC-dependent CTL priming. NKT cells thus are potent helper cells for DC-dependent CTL priming.

Genetically modified dendritic cells--a new, promising cancer treatment strategy?

Dendritic cells (DCs), the most potent antigen-presenting cells (APCs), were discovered almost 30 years ago. Due to the priming of antigen-specific immune responses mediated by CD4+ and CD8+ lymphocytes, DCs are crucial for the induction of adaptive immunity against cancer. Therefore, vaccination of cancer patients with DCs presenting tumour-associated antigens (TAAs) have been believed to be a promising anticancer strategy. Multiple clinical trials have been carried out in order to evaluate the safety and efficacy of cancer vaccines based on antigen-pulsed DCs. However, pulsing of DCs with particular peptides has several disadvantages: i) short-time duration of antigen-major histocompatability complex (MHC) complexes, ii) a requirement for matching defined peptides with MHC complexes and iii) exclusive presentation of single antigen epitopes. Application of gene transfer technologies in the field of DC-based vaccines made possible the development of novel, anticancer immunisation strategies. In several animal models, DCs modified with genes encoding TAA or immunostimulatory proteins have been shown to be effective in the induction of antitumour immune responses. Based on these encouraging results, a first clinical trial of prostate cancer patients vaccinated with gene modified DCs has recently been initiated. In this article, methods used for genetic modification of DCs and anticancer vaccination strategies based on genetically modified DCs are reviewed.