H5N1 influenza virus-like particle vaccine protects mice from heterologous virus challenge better than whole inactivated virus

Pandemic preparedness through vaccine development for avian influenza viruses

Influenza A viruses pose a significant threat to global health, impacting both humans and animals. Zoonotic transmission, particularly from swine and avian species, is the primary source of human influenza outbreaks. Notably, avian influenza viruses of the H5N1, H7N9, and H9N2 subtypes are of pandemic concern through their global spread and sporadic human infections. Preventing and controlling these viruses is critical due to their high threat level. Vaccination remains the most effective strategy for influenza prevention and control in humans, despite varying vaccine efficacy across strains. This review focuses specifically on pandemic preparedness for avian influenza viruses. We delve into vaccines tested in animal models and summarize clinical trials conducted on H5N1, H7N9, and H9N2 vaccines in humans.

A single immunization with H5N1 virus-like particle vaccine protects chickens against divergent H5N1 influenza viruses and vaccine efficacy is determined by adjuvant and dosage

The H5N1 subtype highly pathogenic avian influenza virus (HPAIV) reveals high variability and threatens poultry production and public health. To prevent the spread of H5N1 HPAIV, we developed an H5N1 virus-like particle (VLP) vaccine based on the insect cell-baculovirus expression system. Single immunization of the H5N1 VLP vaccines induced high levels of HI antibody titres and provided effective protection against homologous virus challenge comparable to the commercial inactivated vaccine. Meanwhile, we assessed the relative efficacy of different adjuvants by carrying out a head-to-head comparison of the adjuvants ISA 201 and ISA 71 and evaluated whether the two adjuvants could induce broadly protective immunity. The ISA 71 adjuvanted vaccine induced significantly higher levels of Th1 and Th2 immune responses and provided superior cross-protection against antigenically divergent H5N1 virus challenge than the ISA 201 adjuvanted vaccine. Importantly, increasing the vaccine dose could further enhance the cross-protective efficacy of H5N1 VLP vaccine and confer completely sterilizing protection against antigenically divergent H5N1 virus challenge, which was mediated by neutralizing antibodies. Our results suggest that the H5N1 VLP vaccine can provide broad-spectrum protection against divergent H5N1 influenza viruses as determined by adjuvant and vaccine dose.

Self-Assembled Virus-Like Particle Vaccines via Fluorophilic Interactions Enable Infection Mimicry and Immune Protection

Influenza epidemics persistently threaten global health. Vaccines based on virus-like particles (VLPs), which resemble the native conformation of viruses, have emerged as vaccine candidates. However, the production of VLPs via genetic engineering remains constrained by challenges such as low yields, high costs, and being time consuming. In this study, a novel VLP platform is developed that could mimic infection and confer influenza protection through fluorination-driven self-assembly. The VLPs closely mimick the key steps in viral infection including dendritic cell (DC) attachment and pH-responsive endo-lysosomal escape, which enhances DC maturation and antigen cross-presentation. It is also observed that the VLPs migrate from the injection site to the draining lymph nodes efficiently. Immunization with VLPs triggers both Th1 and Th2 cellular responses, thereby inducing an improved CD8+ T cell response along with strong antigen-specific antibody responses. In several infected mouse models, VLP vaccines ameliorate weight loss, lung virus titers, pulmonary pathologies, and confer full protection against H1N1, H6N2, H9N2, and mixed influenza viruses. Therefore, the results support the potential of VLPs as an effective influenza vaccine with improved immune potency against infection. A methodology to generate VLPs based on fluorophilic interactions, which can be a general approach for development of pathogenic VLPs, is reported.

Development and evaluation of Newcastle disease - avian influenza bivalent vector vaccines in commercial chickens

Avian influenza (AI) and Newcastle disease (ND) are regarded as the leading viral infectious diseases affecting the global poultry industry. Vaccination is a successful therapeutic intervention to safeguard birds against both ND and AI infections. In this research, ND-AI bivalent vaccines were developed through the incorporation of HA and IRES-GMCSF gene fragments at varying locations of NDV rClone30 vectors. The two constructed vaccines were rClone30-HA-IRES-GMCSF(PM) and rClone30-HA(PM)-IRES-GMCSF(NP). Next, 27-day-old Luhua chickens (the maternal antibody level was reduced to 1.4 log2) were inoculated with the same dose of the vaccines, and humoral and cellular immune responses were assessed at multiple time points. Compared to the commercial vaccine, the levels of anti-NDV antibodies following the administration of the ND-AI vaccines were above the theoretical protection value of 4 log2. The levels of anti-AIV antibodies in the bivalent vaccine group were notably higher than those in the commercial vaccine group. Furthermore, the content of inflammatory factors and transcription levels were significantly increased in chickens administered ND-AI vaccines. The ND-AI vaccines induced stronger proliferative responses of B cells or CD3+, CD8+, and CD4 + T cells. Hematoxylin and eosin staining showed that the tissue damage induced by the two recombinant vaccines was similar to that of commercial vaccines. The outcomes of the study suggest that the two bivalent ND-AI vaccine candidates produced using the reverse genetics approach are both secure and effective. This approach not only enables the multiuse of one vaccine but also provides a new concept for the development of other vaccines against infectious viral diseases.

Recent Progress in Recombinant Influenza Vaccine Development Toward Heterosubtypic Immune Response

Flu, a viral infection caused by the influenza virus, is still a global public health concern with potential to cause seasonal epidemics and pandemics. Vaccination is considered the most effective protective strategy against the infection. However, given the high plasticity of the virus and the suboptimal immunogenicity of existing influenza vaccines, scientists are moving toward the development of universal vaccines. An important property of universal vaccines is their ability to induce heterosubtypic immunity, i.e., a wide immune response coverage toward different influenza subtypes. With the increasing number of studies and mounting evidence on the safety and efficacy of recombinant influenza vaccines (RIVs), they have been proposed as promising platforms for the development of universal vaccines. This review highlights the current progress and advances in the development of RIVs in the context of heterosubtypic immunity induction toward universal vaccine production. In particular, this review discussed existing knowledge on influenza and vaccine development, current hemagglutinin-based RIVs in the market and in the pipeline, other potential vaccine targets for RIVs (neuraminidase, matrix 1 and 2, nucleoprotein, polymerase acidic, and basic 1 and 2 antigens), and deantigenization process. This review also provided discussion points and future perspectives in looking at RIVs as potential universal vaccine candidates for influenza.

Protective effect of bivalent H1N1 and H3N2 VLP vaccines against Eurasian avian-like H1N1 and recent human-like H3N2 influenza viruses in a mouse model

Eurasian avian-like (EA) H1N1 swine influenza viruses (SIVs) are currently the most prevalent SIVs in Chinese swine populations, but recent human-like H3N2 SIV subtypes have also been frequently isolated. Hence, there is an urgent need to develop an effective vaccine against both EA H1N1 and recent human-like H3N2 infections. In this study, we utilized the baculovirus expression system to produce virus-like particles (VLPs) containing hemagglutinin protein (HA) and matrix protein (M1) based on A/Swine/Guangdong/YJ4/2014 (H1N1) and A/swine/Guangdong/L22/2010 (H3N2). An immunological experiment showed that in a mouse model, bivalent VLP vaccines against H1N1 and H3N2 can induce stronger humoral and cellular immune responses than whole influenza virus vaccines. Compared with monovalent inactivated vaccines that cannot offer protection against different SIV subtypes, monovalent H1N1 or H3N2 VLP vaccines can provide partial protection against lethal challenge by viruses of different subtypes. Meanwhile, bivalent VLP vaccines against H1N1 and H3N2 can provide full protection against lethal doses of homologous and heterologous viruses belonging to the EA H1N1 or recent human-like H3N2 lineage. These results suggest a promising approach to the development of vaccines against SIVs.

Multiple Neuraminidase Containing Influenza Virus-Like Particle Vaccines Protect Mice from Avian and Human Influenza Virus Infection

Avian influenza virus remains a threat for humans, and vaccines preventing both avian and human influenza virus infections are needed. Since virus-like particles (VLPs) expressing single neuraminidase (NA) subtype elicited limited heterosubtypic protection, VLPs expressing multiple NA subtypes would enhance the extent of heterosubtypic immunity. Here, we generated avian influenza VLP vaccines displaying H5 hemagglutinin (HA) antigen with or without avian NA subtypes (N1, N6, N8) in different combinations. BALB/c mice were intramuscularly immunized with the VLPs to evaluate the resulting homologous and heterosubtypic immunity upon challenge infections with the avian and human influenza viruses (A/H5N1, A/H3N2, A/H1N1). VLPs expressing H5 alone conferred homologous protection but not heterosubtypic protection, whereas VLPs co-expressing H5 and NA subtypes elicited both homologous and heterosubtypic protection against human influenza viruses in mice. We observed that VLP induced neuraminidase inhibitory activities (NAI), virus-neutralizing activity, and virus-specific antibody (IgG, IgA) responses were strongly correlated with the number of different NA subtype expressions on the VLPs. VLPs expressing all 3 NA subtypes resulted in the highest protection, indicated by the lowest lung titer, negligible body weight changes, and survival in immunized mice. These results suggest that expressing multiple neuraminidases in avian HA VLPs is a promising approach for developing a universal influenza A vaccine against avian and human influenza virus infections.

Development and Evaluation of Vero Cell-Derived Master Donor Viruses for Influenza Pandemic Preparedness

The embryonated egg-based platform currently produces the majority of seasonal influenza vaccines by employing a well-developed master donor virus (MDV, A/PR/8/34 (PR8)) to generate high-growth reassortants (HGRs) for A/H1N1 and A/H3N2 subtypes. Although the egg-based platform can supply enough seasonal influenza vaccines, it cannot meet surging demands during influenza pandemics. Therefore, multi-purpose platforms are desirable for pandemic preparedness. The Vero cell-based production platform is widely used for human vaccines and could be a potential multi-purpose platform for pandemic influenza vaccines. However, many wild-type and egg-derived influenza viruses cannot grow efficiently in Vero cells. Therefore, it is critical to develop Vero cell-derived high-growth MDVs for pandemic preparedness. In this study, we evaluated two in-house MDVs (Vero-15 and VB5) and two external MDVs (PR8 and PR8-HY) to generate Vero cell-derived HGRs for five avian influenza viruses (AIVs) with pandemic potentials (H5N1 clade 2.3.4, H5N1 clade 2.3.2.1, American-lineage H5N2, H7N9 first wave and H7N9 fifth wave). Overall, no single MDV could generate HGRs for all five AIVs, but this goal could be achieved by employing two in-house MDVs (vB5 and Vero-15). In immunization studies, mice received two doses of Vero cell-derived inactivated H5N1 and H7N9 whole virus antigens adjuvanted with alum and developed robust antibody responses.

Progress in the development of virus-like particle vaccines against respiratory viruses

Introduction: Influenza virus, human respiratory syncytial virus (RSV), and human metapneumovirus (HMPV) are important human respiratory pathogens. Recombinant virus-like particle (VLP) vaccines are suggested to be potential promising platforms to protect against these respiratory viruses. This review updates important progress in the development of VLP vaccines against respiratory viruses.Areas Covered: This review summarizes progress in developing VLP and nanoparticle-based vaccines against influenza virus, RSV, and HMPV. The PubMed was mainly used to search for important research articles published since 2010 although earlier key articles were also referenced. The research area covered includes VLP and nanoparticle platform vaccines against seasonal, pandemic, and avian influenza viruses as well as RSV and HMPV respiratory viruses. The production methods, immunogenic properties, and vaccine efficacy of respiratory VLP vaccines in preclinical animal models and clinical studies were reviewed in this article.Expert opinion: Previous and current preclinical and clinical studies suggest that recombinant VLP and nanoparticle vaccines are expected to be developed as promising alternative platforms against respiratory viruses in future. Therefore, continued research efforts are warranted.

Prime-pull vaccination with a plant-derived virus-like particle influenza vaccine elicits a broad immune response and protects aged mice from death and frailty after challenge

Background

Administered intramuscularly (IM), plant-derived, virus-like-particle (VLP) vaccines based on the influenza hemagglutinin (HA) protein elicit both humoral and cellular responses that can protect aged mice from lethal challenge. Unlike split virus vaccines, VLPs can be administered by different routes including intranasally (IN). We evaluated novel vaccine strategies such as prime-pull (IM boosted by IN) and multi-modality vaccination (IM and IN given simultaneously). We wished to determine if these approaches would provide better quality protection in old mice after less severe (borderline-lethal) challenge (ie: immunogenicity, frailty and survival).

Results

Survival rates were similar in all vaccinated groups. Antibody responses were modest in all groups but tended to be higher in VLP groups compared to inactivated influenza vaccine (IIV) recipients. All VLP groups had higher splenocyte T cell responses than the split virus group. Lung homogenate chemokine/cytokine levels and virus loads were lower in the VLP groups compared to IIV recipients 3 days after challenge (p < 0.05 for viral load vs all VLP groups combined). The VLP-vaccinated groups also had less weight loss and recovered more rapidly than the IIV recipients. There was limited evidence of an immunologic or survival advantage with IN delivery of the VLP vaccine.

Conclusion

Compared to IIV, the plant-derived VLP vaccine induced a broader immune response in aged mice (cellular and humoral) using either traditional (IM/IM) or novel schedules (multi-modality, prime-pull).

A plant-derived VLP influenza vaccine elicits a balanced immune response even in very old mice with co-morbidities

BACKGROUND

The elderly are at high risk from influenza, in part because immunity wanes with age and through the accumulation of comorbidities. A novel plant-derived virus-like-particle (VLP) vaccine bearing influenza hemagglutinin can induce a balanced humoral and cellular response in old mice (16-18 months) while split virion vaccines elicit mostly antibodies. Because mice also collect comorbidities and lose immune competence as they age, we wished to determine how the plant-derived VLP vaccine would perform in animals approaching the end of their life-span.

MATERIALS AND METHODS

Old (24-26 months) female BALB/c mice received two intramuscular doses of H1-VLP vaccine, an inactivated H1N1 vaccine (IIV) (both based on A/H1N1/California/07/09) (3μg each) or PBS. Serum was collected on day 42 and humoral responses were measured by enzyme-linked immunosorbent assay (ELISA), microneutralization (MN) and hemagglutination inhibition (HI) assays. Influenza-specific splenocyte CD4+ & CD8+ T cell responses were measured by flow cytometry. Full body computed tomography (CT) and structured necropsies were performed on day 42. Comorbidities including reduced lung volume (kyphosis), masses, abscesses, etc. were assessed using a standard scoring system (1-21) and mice with scores ≥5 were considered to have important comorbidities.

RESULTS

Overall, 53.3% of the animals had significant comorbidities. Three weeks post-boost, HI and MN titres were mostly undetectable but ELISA titres were significantly higher in the H1-VLP animals compared to the IIV group (GMT (95% CI): 961 (427, 2163) vs 425 (200, 903): p = 0.03). Both CD4+(TNFα, IFNγ) and CD8+ (IFNγ) T cell responses were also greater in the H1-VLP group than the IIV.

CONCLUSIONS

Even in very old mice with comorbidities, the plant-made H1-VLP vaccine elicited a stronger and more balanced immune response than IIV. Animals with fewer comorbidities tended to have the better composite (humoral and cellular) responses. These novel vaccines have the potential to address some of the limitations of current vaccines in the elderly.

Inclusion of membrane-anchored LTB or flagellin protein in H5N1 virus-like particles enhances protective responses following intramuscular and oral immunization of mice

We previously demonstrated that intramuscular immunization with virus-like particles (VLPs) composed of the haemagglutinin (HA), neuraminidase (NA), and matrix (M1) proteins of A/meerkat/Shanghai/SH-1/2012 (clade 2.3.2.1) protected mice from lethal challenge with viruses from other H5 HPAI clades. The inclusion of additional proteins that can serve as immunological adjuvants in VLPs may enhance adaptive immune responses following vaccination, and oral vaccines may represent the safest choice. Here, we report the generation of H5N1 VLPs composed of the viral HA, NA, and M1 proteins and membrane-anchored forms of the Escherichia coli heat-labile enterotoxin B subunit protein (LTB) or the Toll-like receptor 5 ligand flagellin (Flic). Mice intramuscularly or orally immunized with VLPs containing LTB or Flic generated greater humoural and cellular immune responses than those administered H5N1 VLPs without LTB or Flic. Intramuscular immunization with VLPs protected mice from lethal challenge with homologous or heterologous H5N1 viruses irrespective of whether the VLPs additionally included LTB or Flic. In contrast, oral immunization of mice with LTB- or Flic-VLPs conferred substantial protection against lethal challenge with both homologous and heterologous H5N1 influenza viruses, whereas mice immunized orally with VLPs lacking LTB and Flic universally succumbed to infection. Mice immunized orally with LTB- or Flic-VLPs showed 10-fold higher virus-specific IgG titres than mice immunized with H5N1-VLPs lacking LTB or Flic. Collectively, these results indicate that the inclusion of immunostimulatory proteins, such as LTB and Flic, in VLP-based vaccines may represent a promising new approach for the control of current H5N1 HPAI outbreaks by eliciting higher humoural and cellular immune responses and conferring improved cross-clade protection.

Influenza virus-like particles composed of conserved influenza proteins and GPI-anchored CCL28/GM-CSF fusion proteins enhance protective immunity against homologous and heterologous viruses

Influenza viruses cause significant morbidity and mortality and pose a substantial threat to public health. Vaccination represents the principle means of preventing influenza virus infection. Current vaccine approaches are hindered by the need to routinely reformulate vaccine compositions in an effort to account for the progressive antigenic changes that occur as influenza viruses circulate in the human population. In this study, we evaluated chimeric virus-like particle (cVLP) vaccines containing conserved elements of influenza proteins (HL5M2e (HA stem gene with 5M2e gene inserted) and NP), with or without glycosylphosphatidylinositol-anchored CCL28 (GPI-CCL28) and/or GM-CSF (GPI-GM-CSF) fusion proteins as molecular adjuvants. cVLPs elicited strong humoral and cellular immune responses against homologous and heterologous viruses, and improved survival following lethal challenge with both homologous and heterologous viruses. Inclusion of GPI-anchored adjuvants in cVLP vaccines augmented the generation of influenza-specific humoral and cellular immune responses in mice in comparison to the non-adjuvanted cVLP vaccines. VLPs containing GPI-anchored adjuvants reduced morbidity and improved survival to lethal challenge with homologous and heterologous influenza viruses. This work suggests that VLP vaccines incorporating conserved influenza virus proteins and GPI-anchored molecular adjuvants may serve as a platform for a broadly protective "universal" influenza vaccine.

Avian Influenza A Virus Pandemic Preparedness and Vaccine Development

Influenza A viruses can infect a wide range of hosts, creating opportunities for zoonotic transmission, i.e., transmission from animals to humans, and placing the human population at constant risk of potential pandemics. In the last hundred years, four influenza A virus pandemics have had a devastating effect, especially the 1918 influenza pandemic that took the lives of at least 40 million people. There is a constant risk that currently circulating avian influenza A viruses (e.g., H5N1, H7N9) will cause a new pandemic. Vaccines are the cornerstone in preparing for and combating potential pandemics. Despite exceptional advances in the design and development of (pre-)pandemic vaccines, there are still serious challenges to overcome, mainly caused by intrinsic characteristics of influenza A viruses: Rapid evolution and a broad host range combined with maintenance in animal reservoirs, making it near impossible to predict the nature and source of the next pandemic virus. Here, recent advances in the development of vaccination strategies to prepare against a pandemic virus coming from the avian reservoir will be discussed. Furthermore, remaining challenges will be addressed, setting the agenda for future research in the development of new vaccination strategies against potentially pandemic influenza A viruses.

Intramuscular and intranasal immunization with an H7N9 influenza virus-like particle vaccine protects mice against lethal influenza virus challenge

The H7N9 influenza virus epidemic has been associated with a high mortality rate in China. Therefore, to prevent the H7N9 virus from causing further damage, developing a safe and effective vaccine is necessary. In this study, a vaccine candidate consisting of virus-like particles (VLPs) based on H7N9 A/Shanghai/2/2013 and containing hemagglutinin (HA), neuraminidase (NA), and matrix protein (M1) was successfully produced using a baculovirus (BV) expression system. Immunization experiments showed that strong humoral and cellular immune responses could be induced by the developed VLPs when administered via either the intramuscular (IM) or intranasal (IN) immunization routes. Notably, VLPs administered via both immunization routes provided 100% protection against lethal infection caused by the H7N9 virus. The IN immunization with 40μg of H7N9 VLPs induced strong lung IgA and lung tissue resident memory (TRM) cell-mediated local immune responses. These results provide evidence for the development of an effective preventive vaccine against the H7N9 virus based on VLPs administered through both the IM and IN immunization routes.

Construction and immunological characterization of CD40L or GM-CSF incorporated Hantaan virus like particle

Infection of Hantaan virus (HTNV) usually causes hemorrhagic fever with renal syndrome (HFRS). China has the worst epidemic incidence of HFRS as well as high fatality. Inactivated whole virus has been used for HFRS vaccination, however there are still problems such as safety concerns. CD40 ligand (CD40L) and granulocyte macrophage colony-stimulating factor (GM-CSF) are well-known immune stimulating molecules that can enhance antigen presenting, lymphocytes activation and maturation, incorporation of CD40L and GM-CSF to the surface of virus like particles (VLPs) can greatly improve the vaccination effect. We constructed eukaryotic vectors expressing HTNV M segment and S segment, as well as vectors expressing HTNV M segment with CD40L or GM-CSF, our results showed successful production of CD40L or GM-CSF incorporated HTNV VLPs. In vitro stimulation with CD40L or GM-CSF anchored HTNV VLP showed enhanced activation of macrophages and DCs. CD40L/GM-CSF incorporated VLP can induce higher level of HTNV specific antibody and neutralizing antibody in mice. Immunized mice splenocytes showed higher ability of secreting IFN-γ and IL-2, as well as enhancing CTL activity. These results suggest CD40L/GM-CSF incorporated VLP can serve as prospective vaccine candidate.

A Single Intramuscular Dose of a Plant-Made Virus-Like Particle Vaccine Elicits a Balanced Humoral and Cellular Response and Protects Young and Aged Mice from Influenza H1N1 Virus Challenge despite a Modest/Absent Humoral Response

Virus-like-particle (VLP) influenza vaccines can be given intramuscularly (i.m.) or intranasally (i.n.) and may have advantages over split-virion formulations in the elderly. We tested a plant-made VLP vaccine candidate bearing the viral hemagglutinin (HA) delivered either i.m. or i.n. in young and aged mice. Young adult (5- to 8-week-old) and aged (16- to 20-month-old) female BALB/c mice received a single 3-μg dose based on the HA (A/California/07/2009 H1N1) content of a plant-made H1-VLP (i.m. or i.n.) split-virion vaccine (i.m.) or were left naive. After vaccination, humoral and splenocyte responses were assessed, and some mice were challenged. Both VLP and split vaccines given i.m. protected 100% of the young animals, but the VLP group lost the least weight and had stronger humoral and cellular responses. Compared to split-vaccine recipients, aged animals vaccinated i.m. with VLP were more likely to survive challenge (80% versus 60%). The lung viral load postchallenge was lowest in the VLP i.m. groups. Mice vaccinated with VLP i.n. had little detectable immune response, but survival was significantly increased. In both age groups, i.m. administration of the H1-VLP vaccine elicited more balanced humoral and cellular responses and provided better protection from homologous challenge than the split-virion vaccine.

Preparation and immunogenicity of influenza virus-like particles using nitrocellulose membrane filtration

Purpose

Nitrocellulose membrane–based filtration system (NCFS) is widely used for protein concentration. In this study, we applied NCFS for production of virus-like particle (VLP) as a vaccine candidate and evaluated yield property and immunogenicity.

Materials and Methods

Influenza VLPs were generated by baculovirus-insect cell protein expression system. NCFS and sucrose gradient ultracentrifugation were used for purification of VLP. Immunogenicity of VLP was evaluated by animal experiment.

Results

Influenza VLPs expressing hemagglutinin (HA) and neuraminidase proteins derived from highly pathogenic influenza virus (H5N8) were effectively produced and purified by NCFS. HA activity of VLP which correlated with antigenicity was well conserved during multiple purification steps. This NCFS based purified VLPs induced influenza virus–specific antibody responses.

Conclusion

Our results indicate that the influenza VLP vaccine could be prepared by NCFS without loss of immunogenicity and elicit antigen-specific immune responses.

Virus-based nanoparticles as platform technologies for modern vaccines

Nanoscale engineering is revolutionizing the development of vaccines and immunotherapies. Viruses have played a key role in this field because they can function as prefabricated nanoscaffolds with unique properties that are easy to modify. Viruses are immunogenic via multiple pathways, and antigens displayed naturally or by engineering on the surface can be used to create vaccines against the cognate virus, other pathogens, specific molecules or cellular targets such as tumors. This review focuses on the development of virus-based nanoparticle systems as vaccines indicated for the prevention or treatment of infectious diseases, chronic diseases, cancer, and addiction. WIREs Nanomed Nanobiotechnol 2016, 8:554-578. doi: 10.1002/wnan.1383 For further resources related to this article, please visit the WIREs website.

Progress in developing virus-like particle influenza vaccines

Recombinant vaccines based on virus-like particles (VLPs) or nanoparticles have been successful in their safety and efficacy in preclinical and clinical studies. The technology of expressing enveloped VLP vaccines has combined with molecular engineering of proteins in membrane-anchor and immunogenic forms mimicking the native conformation of surface proteins on the enveloped viruses. This review summarizes recent developments in influenza VLP vaccines against seasonal, pandemic, and avian influenza viruses from the perspective of use in humans. The immunogenicity and efficacies of influenza VLP vaccine in the homologous and cross-protection were reviewed. Discussions include limitations of current influenza vaccination strategies and future directions to confer broadly cross protective new influenza vaccines as well as vaccination.

Intranasal Immunization with Influenza Virus-Like Particles Containing Membrane-Anchored Cholera Toxin B or Ricin Toxin B Enhances Adaptive Immune Responses and Protection against an Antigenically Distinct Virus

Vaccination is the most effective means to prevent influenza virus infection, although current approaches are associated with suboptimal efficacy. Here, we generated virus-like particles (VLPs) composed of the hemagglutinin (HA), neuraminidase (NA) and matrix protein (M1) of A/Changchun/01/2009 (H1N1) with or without either membrane-anchored cholera toxin B (CTB) or ricin toxin B (RTB) as molecular adjuvants. The intranasal immunization of mice with VLPs containing membrane-anchored CTB or RTB elicited stronger humoral and cellular immune responses when compared to mice immunized with VLPs alone. Administration of VLPs containing CTB or RTB significantly enhanced virus-specific systemic and mucosal antibody responses, hemagglutination inhibiting antibody titers, virus neutralizing antibody titers, and the frequency of virus-specific IFN-γ and IL-4 secreting splenocytes. VLPs with and without CTB or RTB conferred complete protection against lethal challenge with a mouse-adapted homologous virus. When challenged with an antigenically distinct H1N1 virus, all mice immunized with VLPs containing CTB or RTB survived whereas mice immunized with VLPs alone showed only partial protection (80% survival). Our results suggest that membrane-anchored CTB and RTB possess strong adjuvant properties when incorporated into an intranasally-delivered influenza VLP vaccine. Chimeric influenza VLPs containing CTB or RTB may represent promising vaccine candidates for improved immunological protection against homologous and antigenically distinct influenza viruses.