Intranasal administration of peptide vaccine protects human/mouse radiation chimera from influenza infection

Virus-like particle vaccines with epitopes from porcine epidemic virus and transmissible gastroenteritis virus incorporated into self-assembling ADDomer platform provide clinical immune responses in piglets

Introduction

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are major intestinal coronaviruses that cause vomiting, diarrhea, dehydration, and mortality in piglets. These viruses coexist and lead to significant economic losses in the swine industry. Virus-like particles (VLPs) have emerged as promising alternatives to conventional inactivated vaccines due to their exceptional safety, efficacy, and ability to provide multi-disease protection with a single dose.

Methods

Our study focused on specific antigenic epitopes from the PEDV S protein (SS2 and 2C10 regions) and the TGEV S protein (A and D sites) as target candidates. These epitopes were integrated into the ADDomer framework, and we successfully generated recombinant proteins AD, AD-P, AD-T, and AD-PT using the baculovirus expression vector system (BEVS). By meticulously optimizing conditions in High Five cells, we successfully expressed and purified the recombinant proteins. Subsequently, we developed the recombinant ADDomer-VLP vaccine and conducted a comprehensive evaluation of its efficacy in piglets.

Results

Following ultrafiltration concentration and sucrose gradient centrifugation purification, the recombinant proteins self-assembled into VLPs as observed by transmission electron microscopy (TEM). Administration of the vaccine did not result in any adverse reactions in the immunized piglets. Additionally, no significant instances of fever were detected in any of the experimental groups, and there were no notable changes in average daily weight gain compared to the control group that received PBS. The recombinant ADDomer-VLP vaccines demonstrated strong immunogenicity, effectively stimulating the production of neutralizing antibodies against both PEDV and TGEV. Moreover, the recombinant ADDomer-VLP vaccine induced elevated levels of IFN-γ, IL-2, and IL-4, and enhanced cytotoxic T lymphocyte (CTL) activity in the peripheral blood of piglets.

Discussion

These recombinant VLPs have demonstrated the ability to induce strong cellular and humoral immune responses in piglets, making them an incredibly promising platform for the rapid and simplified development of epitope vaccines.

Flagellin from Salmonella enteritidis Enhances the Immune Response of Fused F18 from Enterotoxigenic Escherichia coli

F18 plays an important role in helping Enterotoxigenic Escherichia coli (ETEC) binds to specific receptors on small intestinal enterocytes, followed by secreting of toxins causing diarrhea in post-weaning piglets (post-weaning diarrhea, PWD). However, the F18 subunit vaccine is not sufficient to stimulate an immune response that can protect weaning pigs from F18-positive ETEC (F18⁺ETEC). Recently, a body of evidence shows that flagellin protein (FliC) helps to increase the immunity of fused proteins. Therefore, in this study, we combined FliC with F18 to enhance the immune response of F18. The f18 gene was obtained from F18⁺ETEC, then was fused with the fliC gene. The expression of recombinant FliC-F18 protein was induced by Isopropyl-beta-D-Thiogalactopyranoside (IPTG). The purified protein was tested in vivo in mouse models to evaluate the immunostimulation. Results showed that the fusion of FliC and F18 protein increased the production of anti-F18 antibodies. Besides, the anti-F18 antibody in the collected antiserum specifically identified F18⁺ETEC. This result provides proof-of-concept for the development of subunit vaccine to prevent PWD using F18 antigen.

A recombinant protein containing influenza viral conserved epitopes and superantigen induces broad-spectrum protection

Influenza pandemics pose public health threats annually for lacking vaccine that provides cross-protection against novel and emerging influenza viruses. Combining conserved antigens that induce cross-protective antibody responses with epitopes that activate cross-protective T cell responses might be an attractive strategy for developing a universal vaccine. In this study, we constructed a recombinant protein named NMHC that consists of influenza viral conserved epitopes and a superantigen fragment. NMHC promoted the maturation of bone marrow-derived dendritic cells and induced CD4+ T cells to differentiate into Th1, Th2, and Th17 subtypes. Mice vaccinated with NMHC produced high levels of immunoglobulins that cross-bound to HA fragments from six influenza virus subtypes with high antibody titers. Anti-NMHC serum showed potent hemagglutinin inhibition effects to highly divergent group 1 (H1 subtype) and group 2 (H3 subtype) influenza virus strains. Furthermore, purified anti-NMHC antibodies bound to multiple HAs with high affinities. NMHC vaccination effectively protected mice from infection and lung damage when exposed to two subtypes of H1N1 influenza virus. Moreover, NMHC vaccination elicited CD4+ and CD8+ T cell responses that cleared the virus from infected tissues and prevented virus spread. In conclusion, this study provides proof of concept that NMHC vaccination triggers B and T cell immune responses against multiple influenza virus infections. Therefore, NMHC might be a candidate universal broad-spectrum vaccine for the prevention and treatment of multiple influenza viruses.

Multi-Epitope Peptide-Based and Vaccinia-Based Universal Influenza Vaccine Candidates Subjected to Clinical Trials

In light of the limited protection conferred by current influenza vaccines, immunisation using universal influenza vaccines has been proposed for protection against all or most influenza sub-types. The fundamental principle of universal influenza vaccines is based on conserved antigens found in most influenza strains, such as matrix 2, nucleocapsid, matrix 1 and stem of hemagglutinin proteins. These antigens trigger cross-protective immunity against different influenza strains. Many researchers have attempted to produce the conserved epitopes of these antigens in the form of peptides in the hope of generating universal influenza vaccine candidates that can broadly induce cross-reactive protection against influenza viral infections. However, peptide vaccines are poorly immunogenic when applied individually owing to their small molecular sizes. Hence, strategies, such as combining peptides as multi-epitope vaccines or presenting peptides on vaccinia virus particles, are employed. This review discusses the clinical and laboratory findings of several multi-epitope peptide vaccine candidates and vaccinia-based peptide vaccines. The majority of these vaccine candidates have reached the clinical trial phase. The findings in this study will indeed shed light on the applicability of universal influenza vaccines to prevent seasonal and pandemic influenza outbreaks in the near future.

Inflammasomes as Targets for Adjuvants

Inflammasomes are an essential part of the innate immune system. They are necessary for the development of a healthy immune response against infectious diseases. Inflammasome activation leads to the secretion of pro-inflammatory cytokines such as IL-1β and IL-18, which stimulate the adaptive immune system. Inflammasomes activators can be used as adjuvants to provide and maintain the strength of the immune response. This review is focused on the mechanisms of action and the effects of adjuvants on inflammasomes. The therapeutic and prophylaxis significance of inflammasomes in infectious diseases is also discussed.

Broadly Protective Strategies Against Influenza Viruses: Universal Vaccines and Therapeutics

Influenza virus is a respiratory pathogen that can cause disease in humans, with symptoms ranging from mild to life-threatening. The vast majority of influenza virus infections in humans are observed during seasonal epidemics and occasional pandemics. Given the substantial public health burden associated with influenza virus infection, yearly vaccination is recommended for protection against seasonal influenza viruses. Despite vigilant surveillance for new variants and careful selection of seasonal vaccine strains, the efficacy of seasonal vaccines can vary widely from year to year. This often results in lowered protection within the population, regardless of vaccination status. In order to broaden the protection afforded by seasonal influenza vaccines, the National Institute of Allergy and Infectious Diseases (NIAID) has deemed the development of a universal influenza virus vaccine to be a priority in influenza virus vaccine research. This universal vaccine would provide protection against all influenza virus strains, eliminating the need for the yearly reformulations of seasonal influenza vaccines. In addition to universal influenza vaccine efforts, substantial progress has been made in developing novel influenza virus therapeutics that utilize broadly neutralizing antibodies to provide protection against influenza virus infection and to mitigate disease outcomes during infection. In this review, we discuss various approaches toward the goal of improving influenza virus vaccine efficacy through a universal influenza virus vaccine. We also address the novel methods of discovery and utilization of broadly neutralizing antibodies to improve influenza disease outcomes.

Is a universal influenza vaccine feasible?

The influenza virus causes significant human morbidity and mortality annually and poses a pandemic threat. In addition, the virus frequently mutates, contributing to thousands of identified strains. Current influenza vaccine solutions are strain specific, target existing strains, and achieve only approximately 40% vaccine effectiveness (VE). The need for broadly protective Universal Influenza Vaccines (UIVs) is clear. UIV research and development efforts focus on widely conserved (i.e. not strain specific) influenza epitopes. The most clinically advanced UIV candidate, the Multimeric-001 (M-001), is currently undergoing a pivotal, clinical efficacy, phase III trial. Completed clinical trials indicate M-001 is safe, well tolerated, and immunogenic to a broad range of influenza strains. Additional candidates are also under development, supported by public and private funding. Research results suggest that it is only a matter of time until a broadly protective influenza vaccine is approved for licensure.

Development of Universal Influenza Vaccines Targeting Conserved Viral Proteins

Vaccination is still the most efficient way to prevent an infection with influenza viruses. Nevertheless, existing commercial vaccines face serious limitations such as availability during epidemic outbreaks and their efficacy. Existing seasonal influenza vaccines mostly induce antibody responses to the surface proteins of influenza viruses, which frequently change due to antigenic shift and or drift, thus allowing influenza viruses to avoid neutralizing antibodies. Hence, influenza vaccines need a yearly formulation to protect against new seasonal viruses. A broadly protective or universal influenza vaccine must induce effective humoral as well as cellular immunity against conserved influenza antigens, offer good protection against influenza pandemics, be safe, and have a fast production platform. Nanotechnology has great potential to improve vaccine delivery, immunogenicity, and host immune responses. As new strains of human epidemic influenza virus strains could originate from poultry and swine viruses, development of a new universal influenza vaccine will require the immune responses to be directed against viruses from different hosts. This review discusses how the new vaccine platforms and nanoparticles can be beneficial in the development of a broadly protective, universal influenza vaccine.

Lessons from next generation influenza vaccines for inflammatory disease therapies

Lessons can be learned for treating inflammatory diseases such as rheumatoid arthritis (RA) from next generation approaches for development of universal influenza vaccines. Immunomodulation of inflammatory diseases, rather than ablation of cytokine or cellular responses, can address the root cause of the disease and provide potential cure. Like influenza, there are different antigenic 'strains' and inflammatory T cell responses, Th1 or Th17, that drive each person's disease. As such, next generation vaccine-like antigen specific therapies for inflammatory diseases can be developed but will need to be customized to the patient depending upon the antigen and T cell response that is driving the disease.

Towards a universal influenza vaccine: different approaches for one goal

Influenza virus infection is an ongoing health and economic burden causing epidemics with pandemic potential, affecting 5–30% of the global population annually, and is responsible for millions of hospitalizations and thousands of deaths each year. Annual influenza vaccination is the primary prophylactic countermeasure aimed at limiting influenza burden. However, the effectiveness of current influenza vaccines are limited because they only confer protective immunity when there is antigenic similarity between the selected vaccine strains and circulating influenza isolates. The major targets of the antibody response against influenza virus are the surface glycoprotein antigens hemagglutinin (HA) and neuraminidase (NA). Hypervariability of the amino acid sequences encoding HA and NA is largely responsible for epidemic and pandemic influenza outbreaks, and are the consequence of antigenic drift or shift, respectively. For this reason, if an antigenic mismatch exists between the current vaccine and circulating influenza isolates, vaccinated people may not be afforded complete protection. There is currently an unmet need to develop an effective “broadly-reactive” or “universal” influenza vaccine capable of conferring protection against both seasonal and newly emerging pre-pandemic strains. A number of novel influenza vaccine approaches are currently under evaluation. One approach is the elicitation of an immune response against the “Achille’s heel” of the virus, i.e. conserved viral proteins or protein regions shared amongst seasonal and pre-pandemic strains. Alternatively, other approaches aim toward eliciting a broader immune response capable of conferring protection against the diversity of currently circulating seasonal influenza strains.

In this review, the most promising under-development universal vaccine approaches are discussed with an emphasis on those targeting the HA glycoprotein. In particular, their strengths and potential short-comings are discussed. Ultimately, the upcoming clinical evaluation of these universal vaccine approaches will be fundamental to determine their effectiveness against preventing influenza virus infection and/or reducing transmission and disease severity.

Bacterial flagellin-a potent immunomodulatory agent

Flagellin is a subunit protein of the flagellum, a whip-like appendage that enables bacterial motility. Traditionally, flagellin was viewed as a virulence factor that contributes to the adhesion and invasion of host cells, but now it has emerged as a potent immune activator, shaping both the innate and adaptive arms of immunity during microbial infections. In this review, we summarize our understanding of bacterial flagellin and host immune system interactions and the role flagellin as an adjuvant, anti-tumor and radioprotective agent, and we address important areas of future research interests.

Intranasal immunization with a peptide conjugated to Salmonella flagellin induces both systemic and mucosal peptide-specific antibody responses in mice

In this study, the mucosal adjuvant activity of Salmonella flagellin as a carrier in a conjugate of EXP153-rFliC was investigated. EXP153-rFliC was made by conjugation of a synthetic B-cell epitope peptide derived from Plasmodium falciparum exported protein-1(EXP153) to recombinant phase 1 flagellin of Salmonella enterica serovar Typhimurium expressed in Escherichia coli (rFliC), and used to immunize BALB/c mice via intranasal instillation. It was found that robust EXP153-specific serum IgG antibodies were induced without additional adjuvant. EXP153-specific sIgA antibodies were also induced, these being detected in bronchoalveolar, nasal, vaginal and intestinal washes. These observations demonstrate that Salmonella flagellin as a carrier is an effective mucosal adjuvant in that its conjugated peptide induces antibody responses.

Computational Identification and Characterization of a Promiscuous T-Cell Epitope on the Extracellular Protein 85B of Mycobacterium spp. for Peptide-Based Subunit Vaccine Design

Tuberculosis (TB) is a reemerging disease that remains as a leading cause of morbidity and mortality in humans. To identify and characterize a T-cell epitope suitable for vaccine design, we have utilized the Vaxign server to assess all antigenic proteins of Mycobacterium spp. recorded to date in the Protegen database. We found that the extracellular protein 85B displayed the most robust antigenicity among the proteins identified. Computational tools for identifying T-cell epitopes predicted an epitope, 181-QQFIYAGSLSALLDP-195, that could bind to at least 13 major histocompatibility complexes, revealing the promiscuous nature of the epitope. Molecular docking simulation demonstrated that the epitope could bind to the binding groove of MHC II and MHC I molecules by several hydrogen bonds. Molecular docking analysis further revealed that the epitope had a distinctive binding pattern to all DRB1 and A and B series of MHC molecules and presented almost no polymorphism in its binding site. Moreover, using "Allele Frequency Database," we checked the frequency of HLA alleles in the worldwide population and found a higher frequency of both class I and II HLA alleles in individuals living in TB-endemic regions. Our results indicate that the identified peptide might be a universal candidate to produce an efficient epitope-based vaccine for TB.

Production of Epitope-Specific Antibodies by Immunization with Synthetic Epitope Peptide Formulated with CpG-DNA-Liposome Complex Without Carriers

Antibody production using synthetic peptides has been investigated extensively to develop therapeutic antibodies and prophylactic vaccines. Previously, we reported that a complex of CpG-DNA and synthetic peptides corresponding to B cell epitopes, encapsulated in a phosphatidyl-β-oleoyl-γ-palmitoyl ethanolamine (DOPE):cholesterol hemisuccinate (CHEMS) complex, significantly enhanced the synthetic peptide-specific IgG production. Here, we describe synthetic peptide-based epitope screening and antibody production without conventional carriers.

Immunogenicity of Pseudomonas aeruginosa recombinant b-type fagellin as a vaccine candidate: Protective efficacy in a murine burn wound sepsis model

Pseudomonas aeruginosa (PA) is a formidable opportunistic pathogen among patients with burn wound infections. Antimicrobial therapy is often unsuccessful because PA can develop multi-drug resistance; thus, immunotherapy can be a rational alternative. The goal of this study was to evaluate the immunogenicity recombinant type b flagellin (r-b-flagellin) as a potential vaccine against P. aeruginosa in a mouse model for burn wound sepsis. Primary immunization with r-b-flagellin (10μg) followed by two booster shots was sufficient to generate a robust humoral response, which was predominantly a T helper 2 (Th2) type response consisting mainly of subtype IgG1 and low levels of IgG2a. Analysis of the Th1-Th2 response among immunized mice showed an increased production of IL-4, INF-γ and IL-17 by splenocytes upon stimulation by r-b-flagellin. Opsono-phagocytosis assays confirmed the enhanced killing of bacteria by anti r-b-flagellin immune sera. These antibodies were also able to inhibit motility of P. aeruginosa and afforded protection to immunized mice by reducing bacterial load in the site of original infection into the liver of challenged mice. The reduction of systemic bacterial spread resulted in an increase in the survival rate of challenged immunized mice. In conclusion, immunization of mice with r-b-flagellin protein increased the level of humoral and cellular immune response and led to an efficacious protection against P. aeruginosa infection in the burn mouse model.

Cloning of fliC Gene From Salmonella typhimurium in the Expression Vector pVAX1 and Evaluation of its Expression in Eukaryotic Cells

Background:

Flagellin is the main structural protein of the flagella of many pathogens including Salmonella typhimurium. It is a potent trigger of innate immune responses that enhance adaptive immune responses to a variety of protein antigens. Flagellin has intrinsic adjuvant activity mediated through toll-like receptor (TLR) 5 and is an attractive candidate for highly effective vaccine adjuvant conferring enhanced antibody and cellular immune responses to proteins or peptides. In the present study, we cloned the fliC gene from S. entericatyphimurium in eukaryote vector pVAX1 and evaluated its expression in eukaryotic cells.

Objectives:

The main aim of the present study was to construct a DNA vaccine expressing fliC as an adjuvant.

Materials and Methods:

The fliC gene of S. typhimurium (ATCC 14028) was amplified by PCR with specific primers and cloned into the pPrime cloning vector and successfully subcloned into expression vector pVAX1. The recombinant plasmid pVAX-fliC was finally expressed in eukaryotic cells.

Results:

Cloning and subcloning of the fliC gene were confirmed by colony PCR, restriction enzymes digestion and DNA sequencing of the recombinant plasmids pPrime-fliC and pVAX-fliC. The expression of flagellin protein in eukaryotic cells was approved by immunofluorescence assay (IFA), western blotting analysis and the reverse transcriptase polymerase chain reaction (RT-PCR) method.

Conclusions:

The results of this study demonstrated that the fliC gene in recombinant plasmid pVAX-fliC was successfully expressed in eukaryotic cells and produced flagellin protein, which could be used as an effective adjuvant for DNA vaccine research.

Toward a universal influenza virus vaccine: prospects and challenges

Current influenza virus vaccines are annually reformulated to elicit protection by generating an immune response toward the virus strains that are predicted to circulate in the upcoming influenza season. These vaccines provide limited protection in cases of antigenic mismatch, when the vaccine and the circulating viral strains differ. The emergence of unexpected pandemic viruses presents an additional challenge to vaccine production. To increase influenza virus preparedness, much work has been dedicated to the development of a universal vaccine. Focusing on regions of viral proteins that are highly conserved across virus subtypes, vaccine strategies involving the matrix 2 protein, stalk domain of the hemagglutinin, and multivalent approaches have provided broad-based protection in animal models and show much promise. This review summarizes the most encouraging advances in the field with a focus on novel vaccine designs that have yielded promising preclinical and clinical data.

Intranasal immunization of lambs with serine/threonine phosphatase 2A against gastrointestinal nematodes

Seven 3-month-old, female, helminth-free lambs were immunized intranasally with three doses (1 mg total) of a recombinant part of the catalytic region of the serine/threonine phosphatase 2A (PP2Ar) (group 1 [G1]). In addition, four lambs were used as an adjuvant control group (G2), four as unimmunized, infected controls (G3), and four as unimmunized, uninfected controls (G4). Fifteen days after the last immunization, lambs from G1, G2, and G3 were challenged with 10,000 larval stage 3 (L3) organisms in a plurispecific nematode infection composed of ca. 40% Trichostrongylus colubriformis, 40% Haemonchus contortus, and 20% Teladorsagia circumcincta. All the lambs were clinically monitored throughout the experiment. Parasitological (fecal egg output and immunological response), biopathological (packed-cell volume and leukocyte and eosinophil counts), and zootechnical (live-weight gain) analyses were conducted. On day 105 of the experiment, all the animals were slaughtered and the adult worm population in their abomasa examined. Intranasal administration of PP2Ar with bacterial walls as an adjuvant elicited a strong immune response in the immunized lambs, as evidenced by their humoral immune response. Immunized animals and animals receiving the adjuvant shed significantly (P < 0.001) fewer numbers of parasites' eggs in their feces. The immunization significantly reduced the helminth burden in the abomasa by the end of the experiment (>68%), protection being provided against both Haemonchus and Teladorsagia. Live-weight gain in the immunized lambs was similar to that in the uninfected controls versus the infected or adjuvanted animal groups. Our results suggest that heterologous immunization of ruminants by intranasal administration may be efficacious in the struggle to control gastrointestinal helminths in these livestock.

DNA-vaccine platform development against H1N1 subtype of swine influenza A viruses

Swine influenza virus (SIV) is an important viral pathogen in pig populations. However, commercial vaccines cannot provide complete protection with induced humoral immunity only, and require frequent updates to fight against current isolates. DNA vaccination is an effective means of eliciting both arms of the immune system, the humoral and cellular immune responses. In this study, DNA vector pcDNA3.1 was inserted with a chimeric intron downstream of the CMV promoter region followed by a Kozak sequence to enhance the expression of gene inserts. The C-terminal of the VP22 gene (VP22c), encoding the tegument protein of bovine herpesvirus-1, was fused separately to the N-terminal of four quadruplicated epitopes: two B-cell epitopes (HA91-108 and M2e), and two T-cell epitopes (NP366-374 and NP380-393), which were conserved, at least among the three SIV subtypes prevailing in pig populations in North America. Linker -KK- was used to space between each copy of the two B-cell epitopes, and -RVKR- was used for the two T-cell epitopes, in order to enhance the presentation of epitopes to the immune system. The expression of epitopes was confirmed in in vitro transfection of 293FT cells, and higher percentages of epitope-positive cells were achieved from the plasmids containing VP22c than those without. After the DNA plasmids were administered to mice intramuscularly in combination or separately, or boosted with recombinant proteins of quadruplicated epitopes fused to VP22c, the vaccine stimulated the desired epitope-specific humoral immunity to the two B-cell epitopes, and cellular immunity to the epitope NP380-393. Our results indicate that plasmids with quadruplicated epitopes fused to the VP22c may be a potential vehicle in developing epitopes as vaccines against SIV.

Prevention and therapy of hepatocellular carcinoma by vaccination with TM4SF5 epitope-CpG-DNA-liposome complex without carriers

Although peptide vaccines have been actively studied in various animal models, their efficacy in treatment is limited. To improve the efficacy of peptide vaccines, we previously formulated an efficacious peptide vaccine without carriers using the natural phosphodiester bond CpG-DNA and a special liposome complex (Lipoplex(O)). Here, we show that immunization of mice with a complex consisting of peptide and Lipoplex(O) without carriers significantly induces peptide-specific IgG2a production in a CD4⁺ cells- and Th1 differentiation-dependent manner. The transmembrane 4 superfamily member 5 protein (TM4SF5) has gained attention as a target for hepatocellular carcinoma (HCC) therapy because it induces uncontrolled growth of human HCC cells via the loss of contact inhibition. Monoclonal antibodies specific to an epitope of human TM4SF5 (hTM4SF5R2-3) can recognize native mouse TM4SF5 and induce functional effects on mouse cancer cells. Pre-immunization with a complex of the hTM4SF5R2-3 epitope and Lipoplex(O) had prophylactic effects against tumor formation by HCC cells implanted in an mouse tumor model. Furthermore, therapeutic effects were revealed regarding the growth of HCC when the vaccine was injected into mice after tumor formation. These results suggest that our improved peptide vaccine technology provides a novel prophylaxis measure as well as therapy for HCC patients with TM4SF5-positive tumors.

Production of antibodies with peptide-CpG-DNA-liposome complex without carriers

Background

The screening of peptide-based epitopes has been studied extensively for the purpose of developing therapeutic antibodies and prophylactic vaccines that can be potentially useful for treating cancer and infectious diseases such as influenza virus, malaria, hepatitis B, and HIV. To improve the efficacy of antibody production by epitope-based immunization, researchers evaluated liposomes as a means of delivering vaccines; they also formulated adjuvants such as flagella and CpG-DNA to enhance the magnitude of immune responses. Here, we provide a potent method for peptide-based epitope screening and antibody production without conventional carriers.

Results

We present that a particular form of natural phosphodiester bond CpG-DNA encapsulated in a specific liposome complex (Lipoplex(O)) induces potent immunomodulatory activity in humans as well as in mice. Additionally, Lipoplex(O) enhances the production of IgG2a specific to antigenic protein in mice. Most importantly, immunization of mice with several peptides co-encapsulated with Lipoplex(O) without carriers significantly induces each peptide-specific IgG2a production in a TLR9-dependent manner. A peptide-specific monoclonal antibody produced against hepatocellular carcinoma-associated antigen has functional effects on the cancer cells.

Conclusions

Our overall results show that Lipoplex(O) is a potent adjuvant and that complexes of peptide and Lipoplex(O) are extremely useful for B cell epitope screening and antibody production without carriers. Therefore, our strategy may be promptly used for the development of therapeutic antibodies by rapid screening of potent B cell epitopes.

Progress towards a universal influenza vaccine

Seasonal influenza is a common and highly transmissible disease, characterized by frequent and unpredictable mutations occurring in the viral envelope glycoproteins. Owing to this high variability, annual reformulation and immunization are required and still, the vaccine is not effective enough when there is an antigenic mismatch with circulating strains. A solution could come from the construction of a universal vaccine that would be based on highly conserved antigens and would be effective against many strains: some universal vaccine developers focus on the Matrix 2 protein, whereas others use additional conserved proteins, such as the nucleoprotein and Matrix 1, or even a range of peptides from these proteins and others to induce cross-strain immunity. This article aims to highlight recent significant advances in the development of a universal vaccine against influenza and focuses mainly on studies using the epitope-based approach that have also entered the clinical trial stage; it includes a brief summary of current vaccines against influenza as well as the ongoing efforts to develop a universal vaccine.

Flagellin as an adjuvant: cellular mechanisms and potential

Flagellin is a potent activator of a broad range of cell types involved in innate and adaptive immunity. An increasing number of studies have demonstrated the effectiveness of flagellin as an adjuvant, as well as its ability to promote cytokine production by a range of innate cell types, trigger a generalized recruitment of T and B lymphocytes to secondary lymphoid sites, and activate TLR5(+)CD11c(+) cells and T lymphocytes in a manner that is distinct from cognate Ag recognition. The plasticity of flagellin has allowed for the generation of a range of flagellin-Ag fusion proteins that have proven to be effective vaccines in animal models. This review summarizes the state of our current understanding of the adjuvant effect of flagellin and addresses important areas of current and future research interest.

Fusion protein of TLR5-ligand and allergen potentiates activation and IL-10 secretion in murine myeloid DC

Toll-like receptor ligands are immune-modulatory components linking innate and adaptive immune responses and are considered to be promising vaccine components. Objective of this study was to investigate the adjuvant activity of Listeria monocytogenesis-derived TLR5-ligand flagellin A (flaA) genetically fused to ovalbumin (Ova, major chicken white egg allergen) in a murine in vitro system. Recombinant flaA, rOva, and a fusion protein of rflaA and rOva (rflaA:Ova) were over-expressed in Escherchia coli and purified by FPLC. LPS depletion was confirmed by LAL test. TLR5-binding was evaluated by human and murine TLR5-transgenic HEK 293 cells. The immune-modulatory effect of rflaA:Ova and rflaA:Ova modified by reduction and alkylation on purified BALB/c bone marrow-derived myeloid (mDC) and plasmacytoid dendritic cells (pDC) was investigated by flow cytometry and intracellular cytokine staining (ICS). Dose-dependent IL-8 secretion from transgenic HEK 293 cells confirmed binding of rflaA and rflaA:Ova molecules to human and murine TLR5. Recombinant flaA showed similar biological reactivity to TLR5-ligand fliC derived from Salmonella typhimurium applied as positive control. Compared to rflaA, both rflaA:Ova preparations induced higher expression of maturation markers (CD40, CD69, CD80, and CD86) on mDC, whereas only CD69 and CD40 were upregulated on pDC. Moreover, IL-6 and IL-10 production by mDC was enhanced upon stimulation with rflaA:Ova constructs in comparison to an equimolar mixture of both proteins whereas pDC did not show secretion of the investigated cytokines. Any immunological effects of LPS can be excluded by depletion of endotoxins and the lack of IL-10 production upon proteinase K digestion of rflaA:Ova. In summary, the rflaA:Ova fusion proteins showed an enhanced immune modulating capacity in comparison to rflaA or the mixture of rflaA and antigen. Since the rflaA:Ova fusion proteins induce strong IL-10 induction they are considered as potential vaccine candidates to improve allergen-specific immunotherapy.

A recombinant flagellin-poxvirus fusion protein vaccine elicits complement-dependent protection against respiratory challenge with vaccinia virus in mice

Bacterial flagellin is a potent adjuvant that enhances adaptive immune responses to a variety of protein antigens. The vaccinia virus antigens L1R and B5R are highly immunogenic in the context of the parent virus, but recombinant forms of the proteins are only weakly immunogenic. Therefore we evaluated the humoral response to these antigens in mice when flagellin was used as an adjuvant. Flagellin-L1R and flagellin-B5R fusion proteins were more potent than flagellin, L1R, and B5R as separate proteins. At least three immunizations with flagellin-L1R and flagellin-B5R fusion proteins were required to confer protection in mice against challenge with vaccinia virus. Immune mice exhibited only limited signs of disease following challenge. Additionally, virus neutralization titers correlated with protection. Depletion of complement using cobra venom factor resulted in a marked decrease in the survival of immunized mice after challenge with vaccinia virus. Our results are consistent with the conclusion that flagellin-L1R and flagellin-B5R fusion proteins are effective in eliciting protective immunity against vaccinia virus that is dependent, in large part, on complement.

Identification of a dual-specific T cell epitope of the hemagglutinin antigen of an h5 avian influenza virus in chickens

Avian influenza viruses (AIV) of the H5N1 subtype have caused morbidity and mortality in humans. Although some migratory birds constitute the natural reservoir for this virus, chickens may play a role in transmission of the virus to humans. Despite the importance of avian species in transmission of AIV H5N1 to humans, very little is known about host immune system interactions with this virus in these species. The objective of the present study was to identify putative T cell epitopes of the hemagglutinin (HA) antigen of an H5 AIV in chickens. Using an overlapping peptide library covering the HA protein, we identified a 15-mer peptide, H5_246–260, within the HA1 domain which induced activation of T cells in chickens immunized against the HA antigen of an H5 virus. Furthermore, H5_246–260 epitope was found to be presented by both major histocompatibility complex (MHC) class I and II molecules, leading to activation of CD4+ and CD8+ T cell subsets, marked by proliferation and expression of interferon (IFN)-γ by both of these cell subsets as well as the expression of granzyme A by CD8+ T cells. This is the first report of a T cell epitope of AIV recognized by chicken T cells. Furthermore, this study extends the previous finding of the existence of dual-specific epitopes in other species to chickens. Taken together, these results elucidate some of the mechanisms of immune response to AIV in chickens and provide a platform for creation of rational vaccines against AIV in this species.

Flagellin-F1-V fusion protein is an effective plague vaccine in mice and two species of nonhuman primates

A number of studies have clearly demonstrated that flagellin is a potent adjuvant that promotes robust immune responses when it is given with a protein antigen. In view of the potential biological and practical benefits of a recombinant protein vaccine composed of a single fusion protein containing flagellin and antigen, we have evaluated the efficacy of a fusion protein composed of flagellin and two protective antigens of Yersinia pestis (F1 and V) in eliciting protection against respiratory challenge with Y. pestis. Flagellin-F1-V was produced and purified in high yield under good manufacturing practices conditions. The fusion protein retains full Toll-like receptor 5-stimulating activity in vitro. Using a prime-boost immunization protocol, we found that flagellin-F1-V elicits robust antigen-specific humoral immunity in mice and two species of nonhuman primates. Immune mice were fully protected against intranasal challenge with 150 mean tolerated doses of Y. pestis CO92. In immune mice, the bacteria were completely cleared within 3 days after challenge. Flagellin-F1-V exhibited full stability for at least 297 days at 4 degrees C and at least 168 days at 25 degrees C. At between 29 and 84 days at 37 degrees C, the protein exhibited a loss of biological activity that appeared to be associated with a substantial change in protein diameter, possibly due to oligomerization. On the basis of our results, we believe that flagellin-F1-V is an outstanding candidate for evaluation in studies with humans.

Effects of flagellin on innate and adaptive immunity

Flagella are locomotive organelles present on a wide range of bacteria and are important for the pathogenesis of many species. Cells of the innate immune system lack memory per se, but recognize conserved pathogen-associated molecular patterns (PAMPs) through a family of type I membrane receptors known as Toll-like receptors (TLRs). Flagellin, the major structural component of flagella, is a highly conserved protein recognized in hosts by TLR5. Signaling of flagellin via TLR5/TLR4 heteromeric complexes enhances the diversity of the response, likely by engaging MyD88-independent adaptors to activate the interferon pathway. Flagellin is a potent immune activator, stimulating diverse biologic effects that mediate both innate inflammatory responses as well as the development of adaptive immunity. Binding of flagellin to the extracellular domain of TLR5 rapidly induces a signal cascade that culminates in the production of proinflammatory mediators such as cytokines, chemokines, and costimulatory molecules. This review focuses on the mechanisms of action of flagellin and its effects on both innate and adaptive immunity.

Mouse models for HIV-1 infection

The generation of small animal models, which preserve the ability for the generation of primary and memory immune responses of the engrafted human immune cells and in which a robust HIV-1 infection may occur, may enable the rapid screening, development and evaluation of HIV-1 protective vaccines and adjuvants. This manuscript reviews the existing mouse HIV-1 models used to study virologic, immunologic and pathogenic aspects of HIV-1 infection and disease and discusses their limitations and advantages, especially in the context of vaccine development, with special focus on the recently developed Trimera-HIV-1 animal model.

Enhanced HIV-1 specific immune response by CpG ODN and HIV-1 immunogen-pulsed dendritic cells confers protection in the Trimera murine model of HIV-1 infection

We have recently developed a novel small animal model for HIV-1 infection (Ayash-Rashkovsky et al., http://www.fasebj.org/cgi/doi/10.1096/fj.04-3184fje; doi:10.1096/fj.04-3184fje). The mice were successfully infected with HIV-1 for 4-6 wk with different clades of either T- or M-tropic isolates. HIV-1 infection was accompanied by rapid loss of human CD4+ T cells, decrease in CD4/CD8 ratio, and increased T cell activation. HIV specific human humoral and cellular immune responses were observed in all HIV-1 infected animals. In the present study, HIV specific human immune responses, both humoral and cellular, were generated in noninfected Trimera mice, after their immunization with gp120-depleted HIV-1 antigen, presented by autologous human dendritic cells. Addition of CpG ODN to the antigen-pulsed DCs significantly enhanced (by 2- to 30-fold) the humoral and cellular HIV-1 specific immune responses. Only mice immunized with the HIV-1 immunogen and CpG were completely protected from infection with HIV-1 after challenge with high infection titers of the virus. This novel small animal model for HIV-1 infection may thus serve as an attractive platform for rapid testing of candidate HIV-1 vaccines and of adjuvants and may shorten the time needed for the development and final assessment of protective HIV-1 vaccines in human trials.

A novel small animal model for HIV-1 infection

Lethally irradiated normal BALB/c mice, reconstituted with murine SCID bone marrow and engrafted with human PBMC (Trimera mice), were used to establish a novel murine model for HIV-1 infection. The Trimera mice were successfully infected with different clades and primary isolates of T- and M-tropic HIV-1, with the infection persisting in the animals for 4-6 wk. Rapid loss of the human CD4+ T cells, decrease in CD4/CD8 ratio, and increased T cell activation accompanied the viral infection. All HIV-1 infected animals were able to generate both primary and secondary immune responses, including HIV specific human humoral and cellular responses. In addition to testing the efficacy of new antiviral compounds, this new murine HIV-1 model may be used for studying host-virus interactions and, most importantly, for screening and developing potential HIV-1 protective vaccines and adjuvants (Ayash-Rashkovsky et al., http://www.fasebj.org/cgi/doi/10.1096/fj.04-3185fje; doi:10.1096/fj.04-3185fje.).

Host and bacterial factors affecting induction of immune responses to flagellin expressed by attenuated Salmonella vaccine strains

Previous observations demonstrated that the delivery of recombinant Salmonella enterica serovar Dublin strains to mice via mucosal routes did not efficiently activate systemic and secreted antibody responses to either type d flagellin or genetically fused heterologous B-cell epitopes, thus reducing the usefulness of the protein as a carrier of epitopes for vaccine purposes. In this work, we investigated murine systemic and mucosal flagellin immunogenicity after oral immunization with attenuated Salmonella strains. The reduced anti-type d flagellin antibody responses in mice immunized via mucosal routes with three doses of flagellated S. enterica serovar Dublin strains were not caused by oral tolerance and could not be restored by coadministration of a mucosal adjuvant. The induction of antibody responses to Salmonella flagellins was shown to differ according to the genetic background, but not the haplotype, of the mouse lineage. Moreover, BALB/c mice orally immunized with S. enterica serovar Typhimurium strains developed anti-type i flagellin sera and secreted antibody responses, which indicated that the serovar of the Salmonella vaccine strain also affected flagellin immunogenicity. Analyses of cytokine responses of BALB/c mice immunized with three oral doses of flagellated S. enterica serovar Dublin vaccine strains showed that, in spite of the lack of antibody responses, elevated type d flagellin-specific CD4-cell-activation-dependent gamma interferon (IFN-gamma) and interleukin-10 responses were elicited after the administration of the vaccine strains via either parenteral or mucosal routes. Similar cytokine production patterns were detected to a T-cell heterologous epitope, derived from the CFA/I fimbriae of enterotoxigenic Escherichia coli (ETEC), in mice orally immunized with a Salmonella vaccine strain expressing hybrid flagella. These results indicate that the immunogenicities of Salmonella flagellins can differ significantly, depending on the murine host and on the bacterial vector used, and demonstrate that the induction of CD4-cell-activation-dependent IFN-gamma production represents a major immune response triggered by flagellin and in-frame fused heterologous T-cell epitopes after the oral administration of recombinant S. enterica serovar Dublin vaccine strains.

Old and new vaccine approaches

The conventional, currently available vaccines, though quite successful, suffer from a few shortcomings which hamper future vaccine development. We present herewith some of the new approaches that are presently being pursued, including (1) the development of recombinant, or genetically engineered, vaccines which are based either on the expression of the relevant protective antigen and its formulation into vaccine, or the production of live vaccines, where an appropriate live vector (virus or bacterium) presents the foreign antigen. (2) The development of naked DNA vaccines that include the gene(s) coding for the relevant protective antigen(s). (3) Peptide vaccines that include defined B cell and T cell epitopes, either in a chemically synthesized molecule or in a synthetic recombinant construct. The efficacy of such vaccines is usually dependent on adequate presentation and delivery, namely, carrier/adjuvant technology. (4) Therapeutic vaccines, based on all of the above approaches, may be applied for chronic or long-term infections, or for noninfectious diseases including autoimmune diseases, various neurological disorders, allergy and cancer.

Intranasal immunotherapy for the treatment of Alzheimer's disease: Escherichia coli LT and LT(R192G) as mucosal adjuvants

Alzheimer's disease (AD) is the most common form of dementia worldwide, yet there is currently no effective treatment or cure. Extracellular deposition of amyloid-beta protein (Abeta) in brain is a key neuropathological characteristic of AD. In 1999, Schenk et al. first reported that an injected Abeta vaccine given to PDAPP mice, an AD mouse model displaying Abeta deposition in brain, led to the lowering of Abeta levels in brain. In 2000, we demonstrated that intranasal (i.n.) immunization with human synthetic Abeta1-40 peptide for 7 months led to a 50-60% reduction in cerebral Abeta burden in PDAPP mice; serum Abeta antibody titers were low (approximately 26 microg/ml). More recently, we have optimized our i.n. Abeta immunization protocol in wild-type (WT) mice. When low doses Escherichia coli heat-labile enterotoxin (LT) were given as a mucosal adjuvant with Abeta i.n., there was a dramatic 12-fold increase in Abeta antibody titers in WT B6D2F1 mice treated two times per week for 8 weeks compared to those of mice receiving i.n. Abeta without adjuvant. A non-toxic form of LT, designated LT(R192G), showed even better adjuvanticity; anti-Abeta antibody titers were 16-fold higher than those seen in mice given i.n. Abeta without adjuvant. In both cases, the serum Abeta antibodies recognized epitopes within Abeta1-15 and were of the immunoglobulin (Ig) isotypes IgG2b, IgG1, IgG2a and low levels of IgA. This new and improved Abeta vaccine protocol is now being tested in AD mouse models with the expectation that higher Abeta antibody titers may be more effective in reducing cerebral Abeta levels.

Immunization with influenza virus hemagglutinin globular region containing the receptor-binding pocket

The globular region of hemagglutinin (residues 91-261) membrane glycoprotein of influenza virus that encompasses the binding zone to the oligosaccharide receptor of target cells has been cloned by reverse transcriptase-polymerase chain reaction (RT-PCR). This protein segment (denoted HA91-261 peptide) induced significant immune response in mice. The serum antibodies and lung homogenates from the immunized mice cross-reacted with native virus particles. The cellular immunity was manifested by proliferative splenocyte responses and cytokine release indicating T helper type 1 activity. The plasmid DNA containing this segment (denoted pHA91-261) provoked, in addition, a significant cytotoxic T lymphocyte (CTL) response, whereas the HA91-261 protein fragment led to no such response. Both the DNA and the protein fragment of HA91-261 induced significant protection against viral challenge, although the immune response they induce might be along different pathways. Interestingly, the combined DNA priming-protein boosting immunization regimen did not induce protection against viral challenges even though it led to significant humoral immune responses similar to that induced by the peptide vaccine.

Intranasal immunization with synthetic recombinant vaccine containing multiple epitopes of influenza virus

The oligonucleotides coding for three epitopes (HA91-108, NP55-69, and NP 147-158) of influenza virus, stimulating B-cells, T-helper cells and cytotoxic T lymphocytes (CTLs), respectively, were previously employed for expressing each epitope in flagella that induced specific humoral and cellular immune responses. We have constructed new plasmids expressing all three epitopes as a single recombinant product. Two versions have been prepared-a longer one (Fla-HNN) comprising hybrid flagella containing the epitopes, and a shorter version (HNN). Immunization of BALB/c mice with either constructs induced significant humoral immune response against influenza virus. The mice immunized with these peptides also induced higher T-helper activity, including Th1 type-cytokine (IL-2 and IFN-gamma) release. In addition, the mice immunized with HNN peptide demonstrated significant protection against sublethal viral challenge. Furthermore, this vaccine fully protected mice from lethal challenge and enhanced their recovery process. Our results indicate that a single construct expressing multiple epitopes, which stimulate different arms of the immune system, might be an appropriate candidate when the synthetic recombinant vaccine approach is considered.

Nasal vaccination with beta-amyloid peptide for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a severe neurodegenerative disease for which there is currently no effective prevention or treatment. The prediction that the number of U.S. patients with AD will triple to approximately 14 million over the next 50 years underscores the urgent need to explore novel therapeutic strategies for AD. The beta-amyloid protein (Abeta) accumulation and accompanying inflammation appear to play key roles in initiating the neuronal degeneration that underlies the signs and symptoms of AD. Interventions geared toward reducing Abeta accumulation and inflammatory responses should delay or prevent the onset of the clinical disease. Recently, several research groups, including ours, have shown that vaccination with Abeta results in a significant lowering of the Abeta burden in the brains of APP transgenic mice and, in some studies, improvement in their cognitive deficits. Our study described a novel approach, namely mucosal (intranasal) Abeta vaccination. Precisely how Abeta vaccination chronically lowers Abeta levels and reduces Abeta-associated pathology remains unclear. Here, we provide an overview of these studies, with particular emphasis on our work with intranasal Abeta vaccination. Examples of other intranasal vaccines and mucosal adjuvants are presented. Taken together, these data have implications for the future development of an intranasal Abeta vaccine for humans.

Peptide-based synthetic recombinant vaccines with anti-viral efficacy

Synthetic recombinant vaccines are constructs in which a synthetic oligonucleotide coding for a protective epitope is inserted into an adequate gene for expression of the epitope. We report the results obtained using recombinant flagella of Salmonella vaccine strain expressing epitopes of influenza virus or of the parasite Schistosoma mansoni. In the case of influenza virus, three conserved epitopes of the haemagglutinin and the nucleoprotein of the virus inducing B- and T-cell immune response, were expressed and the flagella were used for intranasal immunization without any adjuvant. Both humoral and cellular immune responses specific to the virus induced in mice cross-strain long-term protection against challenge infection. Aged mice were also able to resist infection. For the design of a human influenza vaccine, epitopes recognized by the HLAs prevalent in Caucasian populations were used, and the resulting vaccine was evaluated in human/mouse radiation chimaera in which human PBMC are functionally engrafted. The vaccinated mice demonstrated efficient clearance of the virus after challenge and resistance to lethal infection. In the case of the parasitic disease schistosomiasis, a 14-residue peptide denoted 9B peptide 1 was expressed in the flagella. Intranasal vaccination of mice with this construct, without the use of adjuvant, resulted in 40% protection against challenge infection.

Induction of strong hepatitis B virus (HBV) specific T helper cell and cytotoxic T lymphocyte responses by therapeutic vaccination in the trimera mouse model of chronic HBV infection

Humanized BALB/c mice (termed trimera mice) conditioned by lethal total body irradiation and bone marrow transplantation from SCID mice have been described to support rapid engraftment of human peripheral blood mononuclear cells (PBMC) and the induction of strong B and T cell responses after immunization in vivo. Moreover, these mice can be infected with the hepatitis B and C viruses (HBV, HCV). The current study employed this model to study therapeutic vaccination approaches against the HBV. Thus, strong primary Th cell responses against the HBV core (HBc) and the Borrelia burgdorferi control antigen were induced by transfer of antigen-loaded dendritic cells together with autologous PBMC from HBV-naive donors as well as by vaccination with high doses of antigen or a DNA plasmid encoding for HBcAg. Moreover, primary peptide-specific CTL responses against the immunodominant epitope HBc(18 - 27) were induced by HBc particle or DNA vaccination of chimera engrafted with HBV-naive PBMC. Finally, strong HBc-specific Th cell and antibody responses were induced by HBc or DNA vaccination of mice reconstituted with PBMC from a chronic HBV patient. Thus, since HBc represents the immunodominant antigen in self-limited HBV infection, HBc particles or DNA vectors are good candidates for therapeutic vaccination, that will be further studied in our model and clinical studies.