Priming Th1 immunity to viral core particles is facilitated by trace amounts of RNA bound to its arginine-rich domain

Early application of IFNγ mediated the persistence of HBV in an HBV mouse model

The antiviral activity of interferon gamma (IFNγ) against hepatitis B virus (HBV) was demonstrated both in vivo and in vitro in a previous study. IFNγ can suppress HBV replication by accelerating the decay of replication-competent nucleocapsids of HBV. However, in this study, we found that the direct application of the mouse IFNγ (mIFNγ) expression plasmid to the liver of an HBV hydrodynamic injection (HI) mouse model led to the persistence of HBV, as indicated by sustained HBsAg and HBeAg levels in the serum as well as an increased percentage of the HBsAg positive mice, whereas the level of HBV DNA in the serum and the expression of HBcAg in the liver were inhibited at the early stage after HI. Meanwhile, we found that the productions of both HBcAb and HBsAb were suppressed after the application of mIFNγ. In addition, we found that HBV could be effectively inhibited in mice immunized with HBsAg expression plasmid before the application of mIFNγ. Furthermore, mIFNγ showed antiviral effect and promoted the production of HBsAb when the mice subjected to the core-null HBV plasmid. These results indicate that the application of mIFNγ in the HBV HI mouse model, the mice showed defective HBcAg-specific immunity that impeded the production of HBcAb and HBsAb, finally allowing the persistence of the virus. Moreover, IFNγ-induced negative immune regulatory factors also play an important role in virus persistence.

Introducing adjuvant-loaded particulate hepatitis B core antigen as an alternative therapeutic hepatitis B vaccine component

Background & Aims

Particulate hepatitis B core antigen (HBcoreAg) is a potent immunogen used as a vaccine carrier platform. HBcoreAg produced in E. coli encapsidates random bacterial RNA (bRNA). Using the heterologous protein-prime, viral-vector-boost therapeutic hepatitis B vaccine TherVacB, we compared the properties of different HBcoreAg forms. We explored how the content of HBcoreAg modulates antigen stability, immunogenicity, and antiviral efficacy.

Methods

bRNA was removed from HBcoreAg by capsid disassembly, followed by reassembly in the absence or presence of specific nucleic acid-based adjuvants poly I:C or CpG. The morphology and structure of empty, bRNA-containing and adjuvant-loaded HBcoreAg were monitored by electron microscopy and nuclear magnetic resonance spectroscopy. Empty, bRNA-containing or adjuvant-loaded HBcoreAg were applied together with HBsAg and with or without nucleic acid-based external adjuvants within the TherVacB regimen in both wild-type and HBV-carrier mice.

Results

While HBcoreAg retained its structure upon bRNA removal, its stability and immunogenicity decreased significantly. Loading HBcoreAg with nucleic acid-based adjuvants re-established stability of the capsid-like antigen. Immunization with poly I:C- or CpG-loaded HBcoreAg induced high antibody titers against co-administered HBsAg. When applied within the TherVacB regimen, they activated vigorous HBcoreAg- and HBsAg-specific T-cell responses in wild-type and HBV-carrier mice, requiring a significantly lower dose of adjuvant compared to externally added adjuvant. Finally, immunization with adjuvant-loaded HBcoreAg mixed with HBsAg led to long-term control of persistent HBV replication in the HBV-carrier mice.

Conclusion

Adjuvant-loaded HBcoreAg retained capsid integrity and stability, was as immunogenic in vivo as externally adjuvanted HBcoreAg, requiring lower adjuvant levels, and supported immunity against co-administered, non-adjuvanted HBsAg. Thus, adjuvant-loaded HBcoreAg represents a promising novel platform for vaccine development.

Impact and implications

Hepatitis B core antigen (HBcoreAg) recapitulates the capsid of the HBV that hosts the viral genome. Produced recombinantly, it is not infectious but emerges as a potent immunogen in vaccine development. In this preclinical study, we show that loading HBcoreAg with defined nucleic-acid-based adjuvants on the one hand stabilizes the HBcoreAg with standardized capsid content and, on the other hand, efficiently promotes the immunity of HBcoreAg and a co-administered antigen, allowing for reduced adjuvant doses. Therefore, adjuvant-loaded HBcoreAg not only serves as an encouraging option for therapeutic hepatitis B vaccines, but could also act as an efficient adjuvant delivery system for other types of vaccine.

Preparing for the Next Pandemic: Increased Expression of Interferon-Stimulated Genes After Local Administration of Nasalferon or HeberNasvac

HeberNasvac, a therapeutic vaccine for chronic hepatitis B, is able to safely stimulate multiple Toll-like receptors, increasing antigen presentation in vitro and in a phase II clinical trial (Profira) in elderly volunteers who were household contacts of respiratory infection patients. Thus, a new indication as a postexposure prophylaxis or early therapy for respiratory infections has been proposed. In this study, we evaluated the expression of several interferon-stimulated genes (ISGs) after mucosal administration of HeberNasvac and compared this effect with the nasal delivery of interferon alpha 2b (Nasalferon). Molecular studies of blood samples of 50 subjects from the Profira clinical trial who were locally treated with HeberNasvac or Nasalferon and concurrent untreated individuals were compared based on their relative mRNA expression of OAS1, ISG15, ISG20, STAT1, STAT3, and DRB1-HLA II genes. In most cases, the gene expression induced by HeberNasvac was similar in profile and intensity to the expression induced by Nasalferon and significantly superior to that observed in untreated controls. The immune stimulatory effect of HeberNasvac on ISGs paved the way for its future use as an innate immunity stimulator in elderly persons and immunocompromised subjects or as part of Mambisa, a nasal vaccine to prevent severe acute respiratory syndrome coronavirus 2 infection.

PreS1 Containing HBc VLPs for the Development of a Combined Therapeutic/Prophylactic Hepatitis B Vaccine

The available HBV vaccines based on the HBV surface protein are manufactured in yeasts and demonstrate excellent prophylactic but no therapeutic activity and are thus ineffective against chronic HBV infection. Five different HBV core proteins (HBc)-full length and C-terminally truncated-were used for the insertion of the short, preS1,aa 20-47 and long, preS1phil, aa 12-60 + 89-119 fragments. Modified virus-like particles (VLPs) were compared for their biotechnological and immunological properties. The expression level of HBc-preS1 proteins was high for all investigated proteins, allowing us to obtain 10-20 mg of purified VLPs from a gram of biomass with the combination of gel filtration and ion-exchange chromatography to reach approximately 90% purity of target proteins. The immunogenicity of chimeric VLPs was tested in BALB/c mice, showing a high anti-preS1 response and substantial T-cell proliferation after stimulation with HBc protein. Targeted incorporation of oligonucleotide ODN 1668 in modified HBc-preS1 VLPs was demonstrated.

Activation of CD4 T cells during prime immunization determines the success of a therapeutic hepatitis B vaccine in HBV-carrier mouse models

BACKGROUND & AIMS

We recently developed a heterologous therapeutic vaccination scheme (TherVacB) comprising a particulate protein prime followed by a modified vaccinia-virus Ankara (MVA)-vector boost for the treatment of HBV. However, the key determinants required to overcome HBV-specific immune tolerance remain unclear. Herein, we aimed to study new combination adjuvants and unravel factors that are essential for the antiviral efficacy of TherVacB.

METHODS

Recombinant hepatitis B surface and core antigen (HBsAg and HBcAg) particles were formulated with different liposome- or oil-in-water emulsion-based combination adjuvants containing saponin QS21 and monophosphoryl lipid A; these formulations were compared to STING-agonist c-di-AMP and conventional aluminium hydroxide formulations. Immunogenicity and the antiviral effects of protein antigen formulations and the MVA-vector boost within TherVacB were evaluated in adeno-associated virus-HBV-infected and HBV-transgenic mice.

RESULTS

Combination adjuvant formulations preserved HBsAg and HBcAg integrity for ≥12 weeks, promoted human and mouse dendritic cell activation and, within TherVacB, elicited robust HBV-specific antibody and T-cell responses in wild-type and HBV-carrier mice. Combination adjuvants that prime a balanced HBV-specific type 1 and 2 T helper response induced high-titer anti-HBs antibodies, cytotoxic T-cell responses and long-term control of HBV. In the absence of an MVA-vector boost or following selective CD8 T-cell depletion, HBsAg still declined (mediated mainly by anti-HBs antibodies) but HBV replication was not controlled. Selective CD4 T-cell depletion during the priming phase of TherVacB resulted in a complete loss of vaccine-induced immune responses and its therapeutic antiviral effect in mice.

CONCLUSIONS

Our results identify CD4 T-cell activation during the priming phase of TherVacB as a key determinant of HBV-specific antibody and CD8 T-cell responses.

IMPACT AND IMPLICATIONS

Therapeutic vaccination is a potentially curative treatment option for chronic hepatitis B. However, it remains unclear which factors are essential for breaking immune tolerance in HBV carriers and determining successful outcomes. Our study provides the first direct evidence that efficient priming of HBV-specific CD4 T cells determines the success of therapeutic hepatitis B vaccination in two preclinical HBV-carrier mouse models. Applying an optimal formulation of HBV antigens that activates CD4 and CD8 T cells during prime immunization provided the foundation for an antiviral effect of therapeutic vaccination, while depletion of CD4 T cells led to a complete loss of vaccine-induced antiviral efficacy. Boosting CD8 T cells was important to finally control HBV in these mouse models. Our findings provide important insights into the rational design of therapeutic vaccines for the cure of chronic hepatitis B.

Photodynamic Therapy in Combination with the Hepatitis B Core Virus-like Particles (HBc VLPs) to Prime Anticancer Immunity for Colorectal Cancer Treatment

Simple Summary

Photodynamic therapy (PDT) by means of a photosensitizer is a clinically used therapeutic treatment in a variety of cancers. To further improve the anti-cancer efficiency of PDT, combination therapy with immune agents is a promising option. In this study, we used a viral vaccine as the immune therapeutic partner for PDT. We studied the biological properties of single and combined modalities. Our research suggests that combination therapy enhances innate and humoral immunity, improved survival, and generated a long-term memory capacity in the MC-38 murine colorectal tumor model to prevent a recurrence.

Abstract

Photodynamic therapy (PDT), which combines light and oxygen with a photosensitizer to induce reactive oxygen species (ROS)-mediated killing of primary tumor cells, benefits from non-invasive properties and its negligible toxicity to surrounding healthy tissues. In this study, we have shown that the second-generation photosensitizer FOSCAN can be internalized by tumor cells and effectively induce tumor cell death when exposed to laser irradiation in vitro. In addition, these dying tumor cells can be phagocytosed by dendritic cells and lead to their activation and maturation as assessed by in vitro co-culture models. While PDT induces immunogenic tumor cell apoptosis, its application for the treatment of tumors located in deep tissues and advanced malignancies has been limited. In this study, we demonstrate that hepatitis B core virus-like particles (HBc VLPs) can serve as a vaccine to enhance PDT-induced anti-cancer immunity by priming humoral immune responses and inducing CD8⁺ T cell responses. The combination of PDT and HBc VLPs increased the survival rate of MC-38 tumor-bearing mice to 55%, compared to 33% in PDT alone and no tumor-free mice in vaccine alone. Moreover, the combination effectively prevented tumor recurrence in vivo through enhanced immune memory T cells after therapy. Therefore, as both are clinically approved techniques, this combination provides a promising strategy for cancer therapy.

A recombinant SARS-CoV-2 receptor-binding domain expressed in an engineered fungal strain of Thermothelomyces heterothallica induces a functional immune response in mice

Since the beginning of the COVID-19 pandemic, the development of effective vaccines against this pathogen has been a priority for the scientific community. Several strategies have been developed including vaccines based on recombinant viral protein fragments. The receptor-binding domain (RBD) in the S1 subunit of S protein has been considered one of the main targets of neutralizing antibodies. In this study we assess the potential of a vaccine formulation based on the recombinant RBD domain of SARS-CoV-2 expressed in the thermophilic filamentous fungal strain Thermothelomyces heterothallica and the hepatitis B virus (HBV) core protein. Functional humoral and cellular immune responses were detected in mice. To our knowledge, this is the first report on the immune evaluation of a biomedical product obtained in the fungal strain T. heterothallica. These results together with the intrinsic advantages of this expression platform support its use for the development of biotechnology products for medical purpose.

Hepatitis B core-based virus-like particles: A platform for vaccine development in plants

Virus-like particles (VLPs) are a class of structures formed by the self-assembly of viral capsid protein subunits and contain no infective viral genetic material. The Hepatitis B core (HBc) antigen is capable of assembling into VLPs that can elicit strong immune responses and has been licensed as a commercial vaccine against Hepatitis B. The HBc VLPs have also been employed as a platform for the presentation of foreign epitopes to the immune system and have been used to develop vaccines against, for example, influenza A and Foot-and-mouth disease. Plant expression systems are rapid, scalable and safe, and are capable of providing correct post-translational modifications and reducing upstream production costs. The production of HBc-based virus-like particles in plants would thus greatly increase the efficiency of vaccine production. This review investigates the application of plant-based HBc VLP as a platform for vaccine production.

Efficient Production of Chimeric Hepatitis B Virus-Like Particles Bearing an Epitope of Hepatitis E Virus Capsid by Transient Expression in Nicotiana benthamiana

The core antigen of hepatitis B virus (HBcAg) is capable of self-assembly into virus-like particles (VLPs) when expressed in a number of heterologous systems. Such VLPs are potential carriers of foreign antigenic sequences for vaccine design. In this study, we evaluated the production of chimeric HBcAg VLPs presenting a foreign epitope on their surface, the 551–607 amino acids (aa) immunological epitope of the ORF2 capsid protein of hepatitis E virus. A chimeric construct was made by the insertion of 56 aa into the immunodominant loop of the HBcAg. The sequences encoding the chimera were inserted into the pEAQ-HT vector and infiltrated into Nicotiana benthamiana leaves. The plant-expressed chimeric HBcHEV ORF2 551–607 protein was recognized by an anti-HBcAg mAb and anti-HEV IgG positive swine serum. Electron microscopy showed that plant-produced chimeric protein spontaneously assembled into “knobbly” ~34 nm diameter VLPs. This study shows that HBcAg is a promising carrier platform for the neutralizing epitopes of hepatitis E virus (HEV) and the chimeric HBcAg/HEV VLPs could be a candidate for a bivalent vaccine.

Aiming at the heart: the capsid protein of dengue virus as a vaccine candidate

INTRODUCTION

Dengue fever remains as a health problem worldwide. Although Dengvaxia®, was registered in several countries, the results after the immunization of people suggest an increase of risk in non-immune persons and children younger than 9 years old. No other vaccine is registered so far, thus the development of a safe and effective vaccine continues to be a priority for the WHO and the scientific community.

AREAS COVERED

This work reviews the structural and antigenic properties of the capsid protein of Dengue virus, along with results of studies performed to assess the immunogenicity and protective capacity in animals of vaccine candidates based on this protein.

EXPERT OPINION

The generation of a memory cellular immune response alone, after vaccination against Dengue virus, could be advantageous, as there would not be risk of increasing viral infectivity through sub-neutralizing antibodies. However, it is improbable to achieving sterilizing immunity. In this scenario, an infection could stablished but without the appearance of the severe disease. The cell-mediated immunity should keep the virus at bay. The capsid protein induces a protective immune response in animals without the induction of virus-binding antibodies. Vaccine candidates based on this protein could be an attractive strategy to induce protection against the severe Dengue disease.

Endogenously Expressed Antigens Bind Mammalian RNA via Cationic Domains that Enhance Priming of Effector CD8 T Cells by DNA Vaccination

Hepatitis B virus (HBV) core (HBV-C) antigens with homologous or heterologous HIV-tat48-57-like (HBV-C149tat) cationic domains non-specifically bind cellular RNA in vector-transfected cells. Here, we investigated whether RNA-binding to cationic domains influences the immunogenicity of endogenously expressed antigens delivered by DNA vaccination. We initially evaluated induction of HBV-C (K^b/C93)-specific CD8⁺ T cell responses in C57BL/6J (B6) and 1.4HBV-S^mut transgenic (tg) mice that harbor a replicating HBV genome in hepatocytes by DNA immunization. RNA-binding HBV-C and HBV-C149tat antigens moderately enhanced K^b/C93-specific CD8⁺ T cells in B6 mice as compared with RNA-free HBV-C149 antigen (lacking cationic domains). However, only the RNA-binding antigens elicited K^b/C93-specific CD8⁺ T cells that inhibited HBV replication in 1.4HBV-S^mut tg mice. Moreover, RNA-binding to designer antigens, which express a K^b/p15E epitope from an endogenous murine leukemia virus-derived tumor-specific gp70 protein, was crucial to prime tumor-rejecting effector CD8⁺ T cells in B6 mice. Antigen-bound endogenous RNAs function as a Toll-like receptor 7 (TLR-7) ligand and stimulated priming of K^b/p15E-specific CD8⁺ T cells in B6, but not TLR-7^−/−, mice. Antigen-bound cellular RNAs thus function as an endogenous natural adjuvant in in vivo vector-transfected cells, and thus are an attractive tool to induce and/or enhance effector CD8⁺ T cell responses directed against chronic viral infections or tumor self-antigens by DNA vaccination.

Cationic domains in particle-forming and assembly-deficient HBV core antigens capture mammalian RNA that stimulates Th1-biased antibody responses by DNA vaccination

The HBV core protein self-assembles into particles and encapsidates immune-stimulatory bacterial RNA through a cationic COOH-terminal (C150-183) domain. To investigate if different cationic domains have an impact on the endogenous RNA-binding of HBV-C antigens in mammalian cells, we developed a strep-tag (st) based expression/purification system for HBV-C/RNA antigens in vector-transfected HEK-293 cells. We showed that HBV-stC but not HBV-stC149 particles (lacking the cationic domain) capture low amounts of mammalian RNA. Prevention of specific phosphorylation in cationic domains, either by exchanging the serine residues S155, S162 and S170 with alanines (HBV-stCAAA) or by exchanging the entire cationic domain with a HIV-tat_48-57-like sequence (HBV-stC149tat) enhanced the encapsidation of RNA into mutant core particles. Particle-bound mammalian RNA functioned as TLR-7 ligand and induced a Th1-biased humoral immunity in B6 but not in TLR-7^-/- mice by exogenous (protein) and endogenous (DNA) vaccines. Compared to core particles, binding of mammalian RNA to freely exposed cationic domains in assembly-deficient antigens was enhanced. However, RNA bound to non-particulate antigens unleash its Th1-stimulating adjuvant activity by DNA- but not protein-based vaccination. Mammalian RNAs targeted by an endogenously expressed antigen thus function as a natural adjuvant in the host that facilitates priming of Th1-biased immune responses by DNA-based immunization.

CONSTRUCTION OF MOSAIC HBC PARTICLES PRESENTING CONSERVATIVE FRAGMENTS OF M2 PROTEIN AND HEMAGGLUTININ OF INFLUENZA A VIRUS

Virus-like HBc particles formed as a result of the self-assembly of the nuclear antigen of the hepatitis B virus can be used as a highly immunogenic carrier for the presentation of foreign epitopes when creating recombinant vaccines. We use this vehicle to create influenza vaccines based on the conservative antigens of the influenza virus, the extracellular domain of the transmembrane protein M2 (M2e) and the fragment of the second subunit of hemagglutinin (HA2). Presentation on the surface of HBc particles should improve the immunogenicity of these peptides. Using genetic engineering techniques, we obtained a fusion protein in which the HA2 sequence is attached to the N-terminus of the HBc antigen, and the M2e peptide is included in the immunodominant loop region exposed on the surface of HBc particle. The hybrid protein expressed in Escherichia coli and purified under denaturing conditions formed virus-like HBc particles after refolding in vitro. Refolding of this protein in the presence of a previously denatured HBc antigen carrying no inserts resulted in formation of mosaic virus-like particles. The developed method will allow construction of mosaic HBc particles carrying different target epitopes of the influenza virus by combining the corresponding modified HBc proteins, which opens the possibility of creating vaccines with a wider spectrum of protection.

Whole-Chain Tick Saliva Proteins Presented on Hepatitis B Virus Capsid-Like Particles Induce High-Titered Antibodies with Neutralizing Potential

Ticks are vectors for various, including pathogenic, microbes. Tick saliva contains multiple anti-host defense factors that enable ticks their bloodmeals yet also facilitate microbe transmission. Lyme disease-causing borreliae profit specifically from the broadly conserved tick histamine release factor (tHRF), and from cysteine-rich glycoproteins represented by Salp15 from Ixodes scapularis and Iric-1 from Ixodes ricinus ticks which they recruit to their outer surface protein C (OspC). Hence these tick proteins are attractive targets for anti-tick vaccines that simultaneously impair borrelia transmission. Main obstacles are the tick proteins´ immunosuppressive activities, and for Salp15 orthologs, the lack of efficient recombinant expression systems. Here, we exploited the immune-enhancing properties of hepatitis B virus core protein (HBc) derived capsid-like particles (CLPs) to generate, in E. coli, nanoparticulate vaccines presenting tHRF and, as surrogates for the barely soluble wild-type proteins, cysteine-free Salp15 and Iric-1 variants. The latter CLPs were exclusively accessible in the less sterically constrained SplitCore system. Mice immunized with tHRF CLPs mounted a strong anti-tHRF antibody response. CLPs presenting cysteine-free Salp15 and Iric-1 induced antibodies to wild-type, including glycosylated, Salp15 and Iric-1. The broadly distributed epitopes included the OspC interaction sites. In vitro, the anti-Salp15 antibodies interfered with OspC binding and enhanced human complement-mediated killing of Salp15 decorated borreliae. A mixture of all three CLPs induced high titered antibodies against all three targets, suggesting the feasibility of combination vaccines. These data warrant in vivo validation of the new candidate vaccines´ protective potential against tick infestation and Borrelia transmission.

Development of a candidate influenza vaccine based on virus-like particles displaying influenza M2e peptide into the immunodominant loop region of hepatitis B core antigen: Insertion of multiple copies of M2e increases immunogenicity and protective efficiency

The extracellular domain of the transmembrane protein M2 (M2e) of influenza A virus is a promising target for the development of "universal" vaccines against influenza. M2e is a poor immunogen by itself; however, when M2e is linked to an appropriate carrier, such as hepatitis B virus core (HBc) particles, it becomes highly immunogenic. Insertions of target peptides into the surface-exposed major immunodominant loop region (MIR) of the HBc antigen are especially immunogenic, but such insertions often affect the protein folding and formation of recombinant virus-like particles. To facilitate an appropriate conformation of the M2e insert, we introduced flexible linkers at the junction points between the insert and flanking HBc sequences. This approach allowed the construction of recombinant HBc particles carrying 1, 2 and 4 copies of M2e in the MIR region. These particles were produced in Escherichia coli and purified to homogeneity. The immune response and protective activity of hybrid HBc particles in mice correlated with the number of inserted M2e peptides: the highest immunogenicity and complete protection of mice against the lethal challenge by influenza virus was observed with particles carrying four copies of M2e. The possibility of the simultaneous presentation of M2e peptides from several important influenza strains on a single HBc particle could also facilitate the development of a broad-specificity vaccine efficient not only against influenza A strains of human origin but also for newly emerging strains of animal origin, such as the avian influenza.

Tandem fusion of hepatitis B core antigen allows assembly of virus-like particles in bacteria and plants with enhanced capacity to accommodate foreign proteins

The core protein of the hepatitis B virus, HBcAg, assembles into highly immunogenic virus-like particles (HBc VLPs) when expressed in a variety of heterologous systems. Specifically, the major insertion region (MIR) on the HBcAg protein allows the insertion of foreign sequences, which are then exposed on the tips of surface spike structures on the outside of the assembled particle. Here, we present a novel strategy which aids the display of whole proteins on the surface of HBc particles. This strategy, named tandem core, is based on the production of the HBcAg dimer as a single polypeptide chain by tandem fusion of two HBcAg open reading frames. This allows the insertion of large heterologous sequences in only one of the two MIRs in each spike, without compromising VLP formation. We present the use of tandem core technology in both plant and bacterial expression systems. The results show that tandem core particles can be produced with unmodified MIRs, or with one MIR in each tandem dimer modified to contain the entire sequence of GFP or of a camelid nanobody. Both inserted proteins are correctly folded and the nanobody fused to the surface of the tandem core particle (which we name tandibody) retains the ability to bind to its cognate antigen. This technology paves the way for the display of natively folded proteins on the surface of HBc particles either through direct fusion or through non-covalent attachment via a nanobody.

Silica nanoparticles as the adjuvant for the immunisation of mice using hepatitis B core virus-like particles

Advances in nanotechnology and nanomaterials have facilitated the development of silicon dioxide, or Silica, particles as a promising immunological adjuvant for the generation of novel prophylactic and therapeutic vaccines. In the present study, we have compared the adjuvanting potential of commercially available Silica nanoparticles (initial particles size of 10–20 nm) with that of aluminium hydroxide, or Alum, as well as that of complete and incomplete Freund's adjuvants for the immunisation of BALB/c mice with virus-like particles (VLPs) formed by recombinant full-length Hepatitis B virus core (HBc) protein. The induction of B-cell and T-cell responses was studied after immunisation. Silica nanoparticles were able to adsorb maximally 40% of the added HBc, whereas the adsorption capacity of Alum exceeded 90% at the same VLPs/adjuvant ratio. Both Silica and Alum formed large complexes with HBc VLPs that sedimented rapidly after formulation, as detected by dynamic light scattering, spectrophotometry, and electron microscopy. Both Silica and Alum augmented the humoral response against HBc VLPs to the high anti-HBc level in the case of intraperitoneal immunisation, whereas in subcutaneous immunisation, the Silica-adjuvanted anti-HBc level even exceeded the level adjuvanted by Alum. The adjuvanting of HBc VLPs by Silica resulted in the same typical IgG2a/IgG1 ratios as in the case of the adjuvanting by Alum. The combination of Silica with monophosphoryl lipid A (MPL) led to the same enhancement of the HBc-specific T-cell induction as in the case of the Alum and MPL combination. These findings demonstrate that Silica is not a weaker putative adjuvant than Alum for induction of B-cell and T-cell responses against recombinant HBc VLPs. This finding may have an essential impact on the development of the set of Silica-adjuvanted vaccines based on a long list of HBc-derived virus-like particles as the biological component.

Mosaic RNA phage VLPs carrying domain III of the West Nile virus E protein

The virus-neutralising domain III (DIII) of the West Nile virus glycoprotein E was exposed on the surface of RNA phage AP205 virus-like particles (VLPs) in mosaic form. For this purpose, a 111 amino acid sequence of DIII was added via amber or opal termination codons to the C-terminus of the AP205 coat protein, and mosaic AP205-DIII VLPs were generated by cultivation in amber- or opal-suppressing Escherichia coli strains. After extensive purification to 95 % homogeneity, mosaic AP205-DIII VLPs retained up to 11-16 % monomers carrying DIII domains. The DIII domains appeared on the VLP surface because they were fully accessible to anti-DIII antibodies. Immunisation of BALB/c mice with AP205-DIII VLPs resulted in the induction of specific anti-DIII antibodies, of which the level was comparable to that of the anti-AP205 antibodies generated against the VLP carrier. The AP205-DIII-induced anti-DIII response was represented by a significant fraction of IgG2 isotype antibodies, in contrast to parallel immunisation with the DIII oligopeptide, which failed to induce IgG2 isotype antibodies. Formulation of AP-205-DIII VLPs in alum adjuvant stimulated the level of the anti-DIII response, but did not alter the fraction of IgG2 isotype antibodies. Mosaic AP205-DIII VLPs could be regarded as a promising prototype of a putative West Nile vaccine.

In vitro stimulation with HBV therapeutic vaccine candidate Nasvac activates B and T cells from chronic hepatitis B patients and healthy donors

Hepatitis B virus (HBV) chronic infections remain a considerable health problem worldwide. The standard therapies have demonstrated limited efficacy, side effects or need life-long treatments. Nowadays therapeutic vaccination is a promising option. Recently, we developed a new vaccine formulation called Nasvac, based on the combination of surface and core antigens from HBV. Clinical trials already performed showed good efficacy in virus control. However, the exact mode of action of Nasvac formulation remains unclear. So far the functional impairment of DCs during persistent HBV infection is a controversial issue. On the other hand, it is known that B cells may function as antigen presenting cells (APC) activating T cells. The hepatitis B core antigen contained in Nasvac vaccine is able to bind and activate a high frequency of naive human B cells. In the present study the surface expression of activation and exhaustion markers on B cells and the subsequent activation of T cells after in vitro stimulation with Nasvac antigens were evaluated in chronic HBV patients and healthy donors. B- and T-cell phenotype and proliferation were assessed by flow cytometry. Our results indicate that in contrast to exhaustions markers B cell activation markers were increased on both study groups after Nasvac stimulation. A shift toward an activation phenotype was observed for both B and T cells. The present work suggests that B cells could act as efficient APCs for Nasvac antigens in humans, which might suggest the use of activated B cells as immunotherapeutic strategy for chronic hepatitis B.

A VLP library of C-terminally truncated Hepatitis B core proteins: correlation of RNA encapsidation with a Th1/Th2 switch in the immune responses of mice

An efficient pBR327- and Ptrp-based E. coli expression system was used to generate a large-scale library of virus like particles (VLP) formed by recombinant hepatitis B virus (HBV) core (HBc) protein derivatives. To construct the library, the gene of HBc protein of the genotype D/subtype ayw2 virus was gradually truncated from the 3`-end and twenty-two HBc variants (with truncation up to 139 aa) were expressed at high levels. The proteins were purified by salt precipitation and gel filtration. Background RNA binding was observed for VLPs formed by HBc1-149, which lacked all C-terminal Arg blocks, and the addition of three Arg residues (HBc1-152) only slightly increased RNA binding. The presence of two Arg blocks (proteins HBc1-162 and HBc1-163) resulted in approximately half of the typical level of RNA binding, and the presence of three blocks (protein HBc1-171) led to approximately 85% of the typical level of binding. Only a small increase in the level of RNA binding was found for the HBc1-175 VLPs, which contained all four Arg blocks but lacked the last 8 aa of the full-length HBc protein. VLPs containing high levels of RNA had higher antigenicity according to an ELISA with anti-HBc mAbs than the VLPs formed by HBc variants without C-terminal Arg blocks and lacking RNA. The results indicate that the VLPs were stabilised by nucleic acids. The immunogenicity in BALB/c mice was comparable for VLPs formed by different HBc proteins, but a clear switch from a Th1 response to a Th2 response occurred after the loss of encapsidated RNA. We did not observe significant differences in lymphocyte proliferation in vitro for the tested VLP variants; however, the loss of RNA encapsidation correlated with a decreased level of IFN-γ induction, which is a measure of the potential CTL activity of immunogens.

Hepatitis B core-based virus-like particles to present heterologous epitopes

Since the first effort to recombinantly express the hepatitis B core protein (HBc) in bacteria, the remarkable virion-like structure has fuelled interest in unraveling the structural and antigenic properties of this protein. Initial studies proved HBc virus-like particles to possess strong immunogenic properties, which can be conveyed to linked antigens. More than 35 years later, numerous studies have been performed using HBc as a carrier protein for antigens derived from over a dozen different pathogens and diseases. In this review, the authors highlight the intriguing features of HBc as carrier and antigen, illustrated by some examples and experimental results that underscore the value of HBc as an antigen-presenting platform. Two of these HBc fusions, targeting influenza A and malaria, have even progressed into clinical testing. In the future, the HBc-based virus-like particles platform will probably continue to be used for the display of poorly immunogenic antigens, mainly because virus-like particle formation by HBc capsomers is compatible with nearly any available recombinant gene expression system.

Anti-Aβ antibodies induced by Aβ-HBc virus-like particles prevent Aβ aggregation and protect PC12 cells against toxicity of Aβ1-40

β-Amyloid peptide (Aβ) immunization is regarded as the most promising therapy to Alzheimer' s disease. The full length Aβ as antigen might induce meningoencepholontis adverse effect since the middle and C-terminal fragments of Aβ contain T cell epitopes. While N-terminal fragment of Aβ, containing B cell epitope, has weak or no immunogenicity. To improve the immunogenicity, we used HBV core antigen as carrier to make fusion protein containing 2 Aβ1-15. The fusion protein was expressed in Escherichia coli harboring the recombinant plasmid pET/c-2Aβ15-c. Transmission electron microscope (TEM) showed that fusion protein could form virus-like particles (VLPs). After 7-weeks immunization with Aβ-HBc VLPs through subcutaneous injection, the titer of anti-Aβ antibody in sera of BALB/c mice reached up to 10(5), higher than Aβ peptide immunization. Aβ-HBc VLPs immunization did not elicit Aβ-specific T cell proliferation. The main isotypes of antibody in mice immunized with Aβ-HBc VLPs were IgG1 and IgG2b, while isotype in mice immunized with Aβ1-42 was IgG2a. When the antisera from mice immunized with Aβ-HBc VLPs were co-incubated for 1 week at 37°C with Aβ, fibers of aggregated Aβ was reduced or diminished. The antibodies also prevented PC12 cells from injury by toxicity of Aβ. In conclusion, recombinant c-2Aβ15-c gene can be expressed in E. coli. The expressed protein could form VLPs and has strong immunogenicity. The antisera prevented Aβ fiber formation and protected the PC12 cells against toxicity of Aβ. This study lays the foundation for the experimental study of AD gene engineering vaccine.

M2e-displaying virus-like particles with associated RNA promote T helper 1 type adaptive immunity against influenza A

The ectodomain of influenza A matrix protein 2 (M2e) is a candidate for a universal influenza A vaccine. We used recombinant Hepatitis B core antigen to produce virus-like particles presenting M2e (M2e-VLPs). We produced the VLPs with and without entrapped nucleic acids and compared their immunogenicity and protective efficacy. Immunization of BALB/c mice with M2e-VLPs containing nucleic acids induced a stronger, Th1-biased antibody response compared to particles lacking nucleic acids. The former also induced a stronger M2e-specific CD4(+) T cell response, as determined by ELISPOT. Mice vaccinated with alum-adjuvanted M2e-VLPs containing the nucleic acid-binding domain were better protected against influenza A virus challenge than mice vaccinated with similar particles lacking this domain, as deduced from the loss in body weight following challenge with X47 (H3N2) or PR/8 virus. Challenge of mice that had been immunized with M2e-VLPs with or without nucleic acids displayed significantly lower mortality, morbidity and lung virus titers than control-immunized groups. We conclude that nucleic acids present in M2e-VLPs correlate with improved immune protection.

Th2-Th1 shift with the multiantigenic formulation TERAVAC-HIV-1 in Balb/c mice

In chronic HIV infection a progressive Th1 to Th2/Th0 cytokine-profile shift is related to disease progression. One of the possible benefits of a therapeutic vaccination might be to counterbalance this phenomenon to allow viral replication control under a Th1-type immune response. TERAVAC-HIV-1 is a multiantigenic formulation vaccine candidate against HIV-1 which comprises the recombinant protein CR3 that contains T cell epitopes and the surface and nucleocapsid antigens of Hepatitis B Virus (HBV). Previous studies showed that such virus like particles of the HBV provide a Th1 adjuvant effect. The present studies examined the capacity of TERAVAC to elicit a Th1 response in the presence of an ongoing HIV-specific Th2-type response in Balb/c mice. To examine this issue, we injected subcutaneously the animals with CR3 or viral lysate in alum which resulted in a Th2-type response. The CR3-specific Th2-type response was verified by induction of IL-4 and IL-10 secretion in ex vivo stimulated splenocytes without secretion of IFN-γ and IgG2a antibodies in serum. Further subcutaneous and simultaneous subcutaneous-nasal immunizations of the same mice with TERAVAC promoted IFN-γ secretion and production of IgG2a antibodies in accordance with a Th1-type response. This result suggests a therapeutic benefit of this vaccine candidate in the restoration of the Th1-type HIV-specific cellular response in seropositive patients.

A vaccine formulation consisting of nucleocapsid-like particles from Dengue-2 and the fusion protein P64k-domain III from Dengue-1 induces a protective immune response against the homologous serotypes in mice

In previous studies we reported the cloning, expression and purification of the capsid protein from Dengue-2 virus. Subsequently, we described an in vitro-assembly process for the capsid protein, which resulted in nucleocapsid-like particles (recNLPs) that induced functional cell-mediated immunity and protection in mice. Moreover, our group reported the evaluation in non-human primates of the fusion protein P64k-domain III from Dengue-1 (PD10). This protein proved to be immunogenic and protective when Freund's adjuvant, but not alum, was used. Based on the previously demonstrated capacity of recNLPs to potentiate the immunogenicity of heterologous proteins, in this study we assess the immune response elicited by the formulation PD10-recNLPs-alum and its protective capacity against Dengue-1 and Dengue-2 virus. As expected, the humoral immune response was mainly directed against Dengue-1, while high levels of IFN-γ secretion were detected after stimulation with Dengue-1 and Dengue-2. Consistently, animals immunized with the bivalent formulation were significantly protected against challenge with either Dengue serotype. In conclusion, this report describes a novel formulation based on recombinant proteins and alum, which is protective against Dengue-1 and Dengue-2 in mice.

Purified and highly aggregated chimeric protein DIIIC-2 induces a functional immune response in mice against dengue 2 virus

It was previously reported that DIIIC-2 (a fusion protein composed of domain III of the envelope protein and the capsid protein from dengue 2 virus), as an aggregate antigen from a partially purified preparation, induced a functional protective immune response against dengue 2 virus in the mouse encephalitis model. In the present work, a purification procedure was developed for DIIIC-2, and soluble and aggregated fractions of the purified protein were characterized and evaluated in mice. The purification process rendered a protein preparation of 91 % purity, and the remaining 9 % consisted of fragments and aggregates of the same recombinant protein. After the in vitro aggregation process, upon addition of oligodeoxynucleotides, 80 % of the protein formed aggregates, whereas 20 % remained as soluble protein. An immunological evaluation revealed the proper immunogenicity of the aggregated purified protein in terms of induction of antiviral and neutralizing antibodies, cell-mediated immunity and protection upon dengue 2 virus challenge in the mouse encephalitis model. Based on these results, we can assert that the purified protein DIIIC-2 is functional and could be used for further scalable steps and preclinical studies in non-human primates.

Hepatitis B virus nucleocapsid but not free core antigen controls viral clearance in mice

We have recently shown that hepatitis B virus (HBV) core antigen (HBcAg) is the major viral factor for HBV clearance using a hydrodynamics-based mouse model. Knockout of HBcAg hampers the development of antiviral immune responses and thus promotes HBV persistence. Here, we further demonstrated that only in the capsid form, but not the free or dimer form, can HBcAg exert its contributory role in HBV clearance. HBcAg is the main structural protein of HBV icosahedral nucleocapsid. A mutant HBV DNA which expresses an assembly-defective HBcAg, HBcAgY132A, surprisingly prolonged HBV surface antigenemia in both C57BL/6 and BALB/c mice without affecting viral transcription and translation. This result was not due to a loss of the possible immune epitope caused by the single-amino-acid substitution of HBcAg. Moreover, the particular HBV mutant failed to induce robust humoral and cellular immunity against HBV. These data revealed the requirement of capsid structure for inducing adequate immunity that leads to HBV clearance in mice.

Recombinant nucleocapsid-like particles from dengue-2 induce functional serotype-specific cell-mediated immunity in mice

The interplay of different inflammatory cytokines induced during dengue virus infection plays a role in either protection or increased disease severity. In this sense, vaccine strategies incorporating whole virus are able to elicit both functional and pathological responses. Therefore, an ideal tetravalent vaccine candidate against dengue should be focused on serotype-specific sequences. In the present work, a new formulation of nucleocapsid-like particles (NLPs) obtained from the recombinant dengue-2 capsid protein was evaluated in mice to determine the level of protection against homologous and heterologous viral challenge and to measure the cytotoxicity and cytokine-secretion profiles induced upon heterologous viral stimulation. As a result, a significant protection rate was achieved after challenge with lethal dengue-2 virus, which was dependent on CD4(+) and CD8(+) cells. In turn, no protection was observed after heterologous challenge. In accordance, in vitro-stimulated spleen cells from mice immunized with NLPs from the four dengue serotypes showed a serotype-specific response of gamma interferon- and tumour necrosis factor alpha-secreting cells. A similar pattern was detected when spleen cells from dengue-immunized animals were stimulated with the capsid protein. Taking these data together, we can assert that NLPs constitute an attractive vaccine candidate against dengue. They induce a functional immune response mediated by CD4(+) and CD8(+) cells in mice, which is protective against viral challenge. In turn, they are potentially safe due to two important facts: induction of serotype specific cell-mediated immunity and lack of induction of antiviral antibodies. Further studies in non-human primates or humanized mice should be carried out to elucidate the usefulness of the NLPs as a potential vaccine candidate against dengue disease.

Improving reverse vaccinology with a machine learning approach

Reverse vaccinology aims to accelerate subunit vaccine design by rapidly predicting which proteins in a pathogenic bacterial proteome are putative protective antigens. Support vector machine classification is a machine learning approach that has been applied to solve numerous classification problems in biological sciences but has not previously been incorporated into a reverse vaccinology approach. A training data set of 136 bacterial protective antigens paired with 136 non-antigens was constructed and bioinformatic tools were used to annotate this data for predicted protein features, many of which are associated with antigenicity (i.e. extracellular localization, signal peptides and B-cell epitopes). Annotation was used to train support vector machine classifiers that exhibited a maximum accuracy of 92% for discriminating protective antigens from non-antigens as assessed by a leave-tenth-out cross-validation approach. These accuracies were superior to those achieved when annotating training data with auto and cross covariance transformations of z-descriptors for hydrophobicity, molecular size and polarity, or when classification was performed using regression methods. To further validate support vector machine classifiers, they were used to rank all the proteins in six bacterial proteomes for their antigenicity. Protective antigens from the training data were significantly recalled (enriched) in the top 75 ranked proteins for all six proteomes as assessed by a Fisher's exact test (p<0.05). This paper describes a superior workflow for performing reverse vaccinology studies and provides a benchmark training data set that can be used to evaluate future methodological improvements.

Hepatitis B virus core particles displaying Mycobacterium tuberculosis antigen ESAT-6 enhance ESAT-6-specific immune responses

Early secreted antigenic target-6 (ESAT-6), an important Mycobacterium tuberculosis T-cell antigen, is an attractive candidate antigen for tuberculosis subunit vaccine development. Because ESAT-6 has a low inherent immunogenicity, we used Hepatitis B virus core (HBc) protein as an immune carrier to enhance ESAT-6 immunogenicity. The ESAT-6 gene was inserted into the major immunodominant region of the HBc molecule by fusion PCR. The recombinant protein, HBc-ESAT-6 (HE6), was expressed in Escherichia coli, and electron microscopy confirmed the formation of virus-like particles. The immunogenicity of the chimeric particles was assessed in mice. Serological assays and in vitro Th1-biased cytokine assays found that immunization with HE6 particles elicited significantly higher ESAT-6-specific antibodies and CD4⁺/CD8⁺ T cell responses in mice compared to immunization with recombinant ESAT-6 protein. These data demonstrate the feasibility of HBc particles serving as an efficient immune carrier for ESAT-6 and suggest that HE6 has potential for use in a tuberculosis subunit vaccine.

The effect of the parenteral route of administration on the immune response to simultaneous nasal and parenteral immunizations using a new HBV therapeutic vaccine candidate

Chronic hepatitis B is a major health problem, with more than 350 million people infected worldwide. Available therapies have limited efficacy and require long-term continuous and expensive treatments, which often lead to the selection of resistant viral variants and rarely eliminate the virus. Immunotherapies have been investigated as a promising new approach. Several vaccine formulations have been clinically tested in chronic patients, none of which have clearly demonstrated efficacy so far. In this study we evaluated a new vaccination strategy comprising the simultaneous co-administration by the nasal and parenteral routes of a multicomponent vaccine formulation in BALB/C and HBsAg-transgenic mice. The formulation under study contains the surface and nucleocapsid antigens of the HBV, and was co-administered by the nasal route and three parenteral routes. For parenteral administration we also evaluated the immunogenicity of the antigenic mixture with alum or without the adjuvant. The immune response was evaluated by ELISA and IFN-γ ELISPOT assays. Our results indicate that all variants generated a strong antibody response in the sera against both antigens, but differed in their capacity to induce cellular immune responses against the surface antigen. Mice immunized by the nasal and subcutaneous routes without alum generated the highest IFN-γ-secreting CD8+ T-cell response, and results in this transgenic mouse model showed that there is no need to include alum. In conclusion, our results indicate that the immunization routes have to be carefully selected before carrying out clinical trials to optimize the immune response and promote further clinical development.

Nucleocapsid-like particles of dengue-2 virus enhance the immune response against a recombinant protein of dengue-4 virus

In this study, we evaluate in mice a novel formulation containing nucleocapsid-like particles of dengue-2 virus (recNLP) co-immunized with a chimeric protein composed of the dengue-4 envelope domain III fused twice within the meningococcal P64k protein of Neisseria meningitidis (PD24). The animals receiving the PD24-recNLP mixture showed the highest levels of antiviral antibodies. Similar results were obtained for IFNγ secretion levels, indicating a functional Th1 cellular response. Consistently, the percentage of mice surviving after viral challenge was significantly higher for those immunized with the mixture than for those inoculated with PD24 protein alone. In addition, in vivo depletion experiments demonstrated the decisive role of CD4(+) and CD8(+) cells in the protection conferred by immunization with PD24-recNLP. In conclusion, this report demonstrates for the first time the adjuvant capacity of dengue-2 virus recNLP. Additionally, the evidence presented highlights the potential of these particles for enhancing the immune response against heterologous recombinant proteins.

Construction and immunological evaluation of multivalent hepatitis B virus (HBV) core virus-like particles carrying HBV and HCV epitopes

A multivalent vaccine candidate against hepatitis B virus (HBV) and hepatitis C virus (HCV) infections was constructed on the basis of HBV core (HBc) virus-like particles (VLPs) as carriers. Chimeric VLPs that carried a virus-neutralizing HBV pre-S1 epitope corresponding to amino acids (aa) 20 to 47 in the major immunodominant region (MIR) and a highly conserved N-terminal HCV core epitope corresponding to aa 1 to 60 at the C terminus of the truncated HBcDelta protein (N-terminal aa 1 to 144 of full-length HBc) were produced in Escherichia coli cells and examined for their antigenicity and immunogenicity. The presence of two different foreign epitopes within the HBc molecule did not interfere with its VLP-forming ability, with the HBV pre-S1 epitope exposed on the surface and the HCV core epitope buried within the VLPs. After immunization of BALB/c mice, specific T-cell activation by both foreign epitopes and a high-titer antibody response against the pre-S1 epitope were found, whereas an antibody response against the HBc carrier was notably suppressed. Both inserted epitopes also induced a specific cytotoxic-T-lymphocyte (CTL) response, as shown by the gamma interferon (IFN-gamma) production profile.

Stimulation of the immune system by therapeutic antisense oligodeoxynucleotides and small interfering RNAs via nucleic acid receptors

Most of the therapeutic applications for synthetic oligodeoxynucleotides (ODN) and oligoribonucleotides (ORN) relate to mechanisms of manipulating gene expression based on Watson-Crick base pairing to endogenous nucleic acids. However, in recent years it has become apparent that the immune system has evolved defense mechanisms against infections that are based on the detection of infecting viral and bacterial nucleic acids. In some cases, synthetic ODN and ORN can trigger these defenses and, therefore, can interfere with or distort the mechanism of action of antisense ODN or small interfering RNAs.

Recombinant nucleocapsid-like particles from dengue-2 virus induce protective CD4+ and CD8+ cells against viral encephalitis in mice

Virus-like particles are a highly effective type of subunit vaccine that mimics the overall structure of virus particles without containing infectious genetic material. In this work, a particulate form of the recombinant capsid protein from dengue-2 was evaluated in mice to determine the level of protection against viral challenge and to measure the antigen-induced cell-mediated immunity (CMI). The nucleocapsid-like particles (NLPs) adjuvanted with alum did not induce antiviral antibodies. However, splenocytes from the immunized animals secreted high levels of IFN-gamma upon virus stimulation, and a significant protection rate was achieved after challenge with lethal dengue-2 virus. Finally, both IFN-gamma secretion and protection against viral encephalitis were demonstrated to be dependent on CD4(+) and CD8(+) cells. This study provides new evidences regarding the protective role of the CMI in the mouse model without the induction of neutralizing antibodies. Further studies in non-human primates or humanized mice should be carried out to elucidate the usefulness of the NLPs as a potential vaccine candidate against dengue disease.

Interaction of the hepatitis B core antigen and the innate immune system

Previous studies demonstrated that the primary APCs for the hepatitis B core Ag (HBcAg) were B cells and not dendritic cells (DC). We now report that splenic B1a and B1b cells more efficiently present soluble HBcAg to naive CD4(+) T cells than splenic B2 cells. This was demonstrated by direct HBcAg-biotin-binding studies and by HBcAg-specific T cell activation in vitro in cultures of naive HBcAg-specific T cells and resting B cell subpopulations. The inability of DC to function as APCs for exogenous HBcAg relates to lack of uptake of HBcAg, not to processing or presentation, because HBcAg/anti-HBc immune complexes can be efficiently presented by DC. Furthermore, HBcAg-specific CD4(+) and CD8(+) T cell priming with DNA encoding HBcAg does not require B cell APCs. TLR activation, another innate immune response, was also examined. Full-length (HBcAg(183)), truncated (HBcAg(149)), and the nonparticulate HBeAg were screened for TLR stimulation via NF-kappaB activation in HEK293 cells expressing human TLRs. None of the HBc/HBeAgs activated human TLRs. Therefore, the HBc/HBeAg proteins are not ligands for human TLRs. However, the ssRNA contained within HBcAg(183) does function as a TLR-7 ligand, as demonstrated at the T and B cell levels in TLR-7 knockout mice. Bacterial, yeast, and mammalian ssRNA encapsidated within HBcAg(183) all function as TLR-7 ligands. These studies indicate that innate immune mechanisms bridge to and enhance the adaptive immune response to HBcAg and have important implications for the use of hepadnavirus core proteins as vaccine carrier platforms.

Autoimmunogenicity of the helix-loop-helix DNA-binding domain

Nonimmunogenic character of native DNA, and its high immunogenicity when presented in complex with the DNA-binding proteins indicate that the latter might contain molecular triggers of anti-DNA response. To find if this is the case, we have evaluated the autoimmunogenic potential of the main DNA-binding domain of HIV-1 reverse transcriptase that belongs to the canonical helix-loop-helix type. BALB/c mice were immunized with a peptide representing the domain, alone or in complex with the fragmented human DNA in the presence of an adjuvant. Mice were assessed for specific antibodies, autoantibodies against a panel of self-antigens; glomerular immunoglobulin deposition; and for the signs of autoimmune disease, such as proteinuria, and changes in the blood components. Immunization with the adjuvanted peptide-DNA complex induced autoantibodies against double-stranded DNA, histones, heterochromatin, and kidney proteins; glomerular IgG and IgA deposition; proteinuria; thrombocytopenia, and anemia. Altogether, this identifies the helix-loop-helix DNA-binding domain as one of the molecular triggers of autoimmunity to DNA and DNA-associated proteins. The experiments cast new light on the role of the DNA-binding retroviral proteins in the induction of autoimmunity, and on the origins of autoimmune complications in the microbial infections in general. It also implies that choosing the DNA-binding proteins as vaccine candidates should be done with precaution.

RNA recognition via TLR7 and TLR8

In this chapter we focus on immunorecognition of RNA by two members of the family of Toll-like receptors (TLRs), TLR7, and TLR8. While any long single-stranded RNA is readily recognized by both TLR7 and TLR8, sequencedependent activation of TLR7 and TLR8 becomes more evident when using short RNA oligonucleotides. RNA oligonucleotides containing sequence motifs for TLR7 and TLR8 are termed is RNA (immunostimulatory RNA). Moreover, short doublestranded RNA oligonucleotides as used for siRNA (short interfering RNA) containing such sequences function primarily as ligands for TLR7 but not TLR8. Even in the presence of appropriate sequence motifs, RNA is not detected by TLR7 and TLR8 when certain chemical modifications are present. Both immunological recognition and ignorance are relevant for the development of RNA-based therapeutics, depending on the clinical setting for which they are developed.

A potential immunotherapy approach: mucosal immunization with an IL-13 peptide-based virus-like particle vaccine in a mouse asthma model

Interleukin (IL)-13 is critical in asthma pathogenesis. Previously, we have developed an IL-13 peptide-based vaccine and confirmed that subcutaneous immunization with the vaccine suppressed airway allergic inflammatory responses in a mouse asthma model. In the present study, we sought to test if mucosal immunization with the vaccine could be a potential approach, by inducing specific autoantibodies of both local IgA in the airway and systemic IgG in serum, to provide an overall suppression of redundant IL-13 effects. The results show that intranasal vaccination induces IL-13-specific IgA responses in multiple mucosal tissues and higher titers of IgG in serum than subcutaneous vaccination. This approach leads to a more effective suppression of ovalbumin-driven Th2 patterns of antibody responses and airway IL-13 and eosinophil accumulation than subcutaneous immunization, even when the induced IL-13 IgG responses were at a similar level. In conclusion, mucosal vaccination may be an innovative potential approach in the treatment of asthma.

Vaccine adjuvants revisited

The development of new adjuvants for human vaccines has become an expanding field of research in the last thirty years, for generating stronger vaccines capable of inducing protective and long-lasting immunity in humans. Instead of such efforts, with several adjuvant strategies approaching to requirements for their clinical application, limitations like adjuvant toxicity remain to be fully surpassed. Here we summarize the current status of adjuvant development, including regulatory recommendations, adjuvant requirements, and adjuvant categories like mineral salts, tensoactive compounds, microorganism-derived adjuvants, emulsions, cytokines, polysaccharides, nucleic acid-based adjuvants, and a section dedicated to particulate antigen delivery systems. The mechanisms of adjuvanticity are also discussed in the light of recent findings on Toll-like receptors' biology and their involvement on immune activation.

Type 1 and 2 immunity following vaccination is influenced by nanoparticle size: formulation of a model vaccine for respiratory syncytial virus

Previous studies compared uptake by dendritic cells (DC) of 20, 40, 100, 200, 500, 1000, and 2000 nm beads in vivo. When beads were used as antigen carriers, bead size influenced antibody responses and induction of IFN-gamma-producing CD4 and CD8 T cells. Beads of 40-50 nm were taken up preferentially by DC and induced particularly strong immunity. Herein, we examine immunity induced by minute differences in nanobead size, specifically within a narrow viral-sized range (20, 40, 49, 67, 93, 101, and 123 nm), to see if bead carrier size influenced the induction of type 1 or type 2 cells as demonstrated by the production of IFN-gamma or IL-4. In vivo uptake by DC was assessed for selected sizes in this range. Responses to whole ovalbumin (OVA) or the OVA-derived CD8 T cell peptide epitope (SIINFEKL) were tested. After one immunization with beads-OVA, IFN-gamma responses to both OVA and SIINFEKL were significantly better with 40 and 49 nm beads than other sizes, while, in contrast, IL-4 responses to OVA were higher after immunization with OVA conjugated to larger beads (93, 101, and 123 nm). Thus IFN-gamma induction from CD8 T cells was limited to 40-49 nm beads, while CD4 T cell activation and IL-4 were induced by 93-123 nm beads-OVA. After two immunizations, there were comparable high levels of IFN-gamma produced with 40 and 49 beads and IL-4 reactivity was still higher for larger beads (93, 101, 123 nm). Production of IgG1 was seen across the full range of bead sizes, increasing after two immunizations. Since protection against respiratory syncytial virus (RSV) depends on strong IFN responses, while IL-4 responses are reported to cause asthma-like symptoms, immunization with RSV antigens on the 49 nm carrier beads could provide the basis for a suitable vaccine. When the 49 nm beads were conjugated to RSV proteins G88 (surface) or M2.1 (internal capsid), one immunization with G88 induced high levels of IFN-gamma and low levels of IL-4. IL-4 increased with two immunizations. Beads-M2.1 induced only moderate levels of IFN-gamma and low titer antibody after two immunizations. Mice vaccinated once with G88-conjugated 49 nm beads and challenged intranasally with RSV strain A2 subtype showed reduced viral titers and recovered from weight loss more rapidly than mice immunized with M2.1-conjugated 49 nm beads or naive control mice. These results show that precise selection of nanobead size for vaccination can influence the type 1/type 2 cytokine balance after one immunization, and this will be useful in the development of effective vaccines against common human pathogens such as RSV.

Influence of aluminum-based adjuvant on the immune response to multiantigenic formulation

Several adjuvants have been described and tested in humans. However, the aluminum-based adjuvants remain the most widely used component in vaccines today. Emerging data suggest that aluminum phosphate and aluminum hydroxide adjuvants do not promote a strong commitment to the helper T cell type 2 (Th2) pathway when they are coadministered with some Th1 adjuvants. In this regard, subtle differences between both aluminum-based adjuvants have been demonstrated. We have previously shown that subcutaneous immunization, in aluminum phosphate, of a mixture comprising the surface and core antigens of hepatitis B virus (HBV) and the multiepitopic protein CR3 of human immunodeficiency virus type 1 elicits a CR3-specific Th1 immune response. In these experiments, the antigens were adjuvated at the same time. As the final selection of the best adjuvant should be based on experimental evidence, we asked whether aluminum hydroxide allows a better Th1 immune deviation than aluminum phosphate. We also studied several ways to mix the antigens and the impact on CR3-specific interferon (IFN)-gamma secretion. Our findings indicate that aluminum hydroxide allows better Th1 immunodeviation than aluminum phosphate adjuvant for the mixture of HBV antigens and CR3. In addition, CR3-specific IFN-gamma secretion of the various formulations tested was the same irrespective of the order in which the antigens were combined.

Expression, purification and characterization of full-length RNA-free hepatitis B core particles

The nucleocapsid or core particle of the hepatitis B virus has become one of the favourite recombinant vaccine carriers for foreign peptides, proteins and stimulatory oligonucleotides. The core protein consists of three regions: an N-terminal, a central and a C-terminal region that can accommodate the addition or insertion of the foreign sequences. The protamine-like C-terminal region that binds host RNA randomly during recombinant particle formation is often truncated. It is commonly thought that these truncations do not affect particle assembly. Recent studies have demonstrated that the C-terminal domains mediate a glycosaminoglycan-dependent attachment of nucleocapsids to the plasma membranes of host cells. This interaction might well contribute to the immunogenicity of nucleocapsids. Testing the hypothesis that full-length particles might be safer and superior for the induction of an immune response against the nucleocapsids and inserted sequences, requires the availability of purified particles. In this report, we detail a novel method for the synthesis and purification of full-length core particles essentially free of RNA from Escherichia coli.

Nucleic acid agonists for Toll-like receptor 7 are defined by the presence of uridine ribonucleotides

Toll-like receptor 7 (TLR7) mediates innate responses by responding to viral RNA in endocytic compartments. However, the molecular pattern recognised by TLR7 and whether it differs between RNA of viral and self origin remains unclear. Here, we identify nucleic acids that act as TLR7 agonists for mouse and human cells. We show that uridine and ribose, the two defining features of RNA, are both necessary and sufficient for TLR7 stimulation, and that short single-stranded RNA (ssRNA) act as TLR7 agonists in a sequence-independent manner as long as they contain several uridines in close proximity. Consistent with the notion that TLR7 lacks specificity for sequence motifs, we show that it is triggered equally efficiently by viral or self RNA delivered to endosomes. Our results support the notion that TLR7 recognises uracil repeats in RNA and that it discriminates between viral and self ligands on the basis of endosomal accessibility rather than sequence.

Microparticle-based technologies for vaccines

Microparticles have been effectively used for many years as delivery systems for drugs and therapeutic proteins. Their application to the delivery of vaccines is not as extensive, but is growing. Utility has been demonstrated for the delivery of various types of vaccines (e.g., recombinant proteins, plasmid DNA, and peptides) and other vaccine components (e.g., immune potentiators). With respect to delivery of immune potentiators, synergistic effects are often observed whereby much more potent immune responses are induced with a combination than with either component alone. Hence, the prospects for broad application of microparticle-based delivery systems for vaccines are excellent.

The 3' CCACCA sequence of tRNAAla(UGC) is the motif that is important in inducing Th1-like immune response, and this motif can be recognized by Toll-like receptor 3

In this article, the immunogenicity of tRNA and the recognition of tRNA by Toll-like receptors (TLRs) are analyzed. Analyses of the effects of different tRNA(Ala)(UGC) fragments (tRNA(Ala)1-76 [corresponding to positions 1 through 76], tRNA(Ala)26-76, tRNA(Ala)40-76, tRNA(Ala)62-76, tRNA(Ala)1-70, tRNA(Ala)26-70, tRNA(Ala)40-70, and tRNA(Ala)62-70) on the immune responses of hepatitis B surface antigen (HBsAg) were performed with BALB/c mice. Results show that tRNA(Ala)1-76, tRNA(Ala)26-76, tRNA(Ala)40-76, and tRNA(Ala)62-76 adjuvants not only induced stronger T helper (Th) 1 immune responses but also cytotoxic-T-lymphocyte (CTL) responses relative to tRNA(Ala)1-70, tRNA(Ala)26-70, tRNA(Ala)40-70, and tRNA(Ala)62-70 adjuvants in HBsAg immunization. A deletion of the D loop (tRNA(Ala)26-76), anticodon loop (tRNA(Ala)40-76), or TpsiC (tRNA(Ala)62-76) loop of tRNA(Ala)(UGC) does not significantly decrease the adjuvant characteristic of tRNA(Ala)(UGC). However a deletion of the 3'-end CCACCA sequence (tRNA(Ala)1-70, tRNA(Ala)26-70, tRNA(Ala)40-70, and tRNA(Ala)62-70) of tRNA(Ala)(UGC) significantly decreased the adjuvant characteristic in Th1 and CTL immune responses. Moreover, the recognitions of different tRNA(Ala)(UGC) fragments by TLR3, TLR7, TLR8, and TLR9 were analyzed. Results show that a deletion of the 3' CCACCA sequence of tRNA(Ala)(UGC) significantly decreased the recognition by TLR3. We concluded that the 3' CCACCA sequence of tRNA(Ala)(UGC) is the important motif to induce Th1 and CTL responses and this motif can be effectively recognized by TLR3.