Protective efficacy of baculovirus-derived influenza virus-like particles bearing H5 HA alone or in combination with M1 in chickens

The transmembrane replacement H7N9-VLP vaccine displays high levels of protection in mice

The incidence of infections caused by the H7N9 subtype of the influenza virus has expanded rapidly in China in recent decades, generating massive economic loss and posing a significant threat to public health. In the absence of specialized antiviral treatments or long-term effective preventative vaccinations, it is critical to constantly enhance vaccines and create effective antiviral drugs to prevent the recurrence of pandemics. In the present study, a transmembrane-substituted (TM) virus-like particle (VLP)-based vaccine was created by replacing the transmembrane region of hemagglutinin (HA) protein with the transmembrane region of the H3 HA protein and then used to immunize BALB/c mice. Sera and T cells were collected from the immunized mice to evaluate the passive immune effects. Our results showed that naïve mice achieved 80–100% protection against homologous and heterologous H7N9 influenza strains after receiving passive serum immunization; the protective effect of the TM VLPs was more evident than that of the wild-type HA VLPs. In contrast, mice immunized with passive T cells achieved only 20 to 80% protection against homologous or heterologous strains. Our findings significantly contribute to understanding the control of the H7N9 virus and the development of a vaccine.

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.

Characterization of Immune Response towards Generation of Universal Anti-HA-Stalk Antibodies after Immunization of Broiler Hens with Triple H5N1/NA-HA-M1 VLPs

(1) Background: Avian influenza viruses (AIVs) promptly evade preexisting immunity by constantly altering the immunodominant neutralizing antibody epitopes (antigenic drift) or by procuring new envelope serotypes (antigenic shift). As a consequence, the majority of antibodies elicited by infection or vaccination protect only against closely related strains. The immunodominance of the globular head of the main glycoprotein has been shown to mask the immunogenicity of the conserved regions located within the hemagglutinin (HA) protein. It has been shown that the broadly neutralizing universal antibodies recognize the HA2 domain in headless hemagglutinin (HA-stalk). Therefore, the HA-stalk is a highly conserved antigen, which makes it a good candidate to be used in universal vaccine development against AIVs. (2) Methods: Sf9 insect cells were used to produce triple H5N1/NA-HA-M1 influenza virus-like particles (VLPs) via co-expression of neuraminidase, hemagglutinin and matrix proteins from a tricistronic expression cassette. Purified influenza VLPs were used to immunize broiler hens. An in-depth characterization of the immune response was performed with an emphasis on the pool of elicited universal antibodies. (3) Results: Our findings suggest, that after vaccination with triple H5N1/NA-HA-M1 VLPs, hens generate a pool of broad-spectrum universal anti-HA-stalk antibodies. Furthermore, these universal antibodies are able to recognize the mammalian-derived HA-stalk recombinant proteins from homologous H5N1 and heterologous H7N9 AIVs as well as from the heterosubtypic human H1N1 influenza strain. (4) Conclusions: Our findings may suggest that highly pathogenic avian influenza H5 HA protein contain functional epitopes that are attractive targets for the generation of broad-spectrum antibodies against AIVs in their native hosts.

Single Dose of Bivalent H5 and H7 Influenza Virus-Like Particle Protects Chickens Against Highly Pathogenic H5N1 and H7N9 Avian Influenza Viruses

Both H5N1 and H7N9 subtype avian influenza viruses cause enormous economic losses and pose considerable threats to public health. Bivalent vaccines against both two subtypes are more effective in control of H5N1 and H7N9 viruses in poultry and novel egg-independent vaccines are needed. Herein, H5 and H7 virus like particle (VLP) were generated in a baculovirus expression system and a bivalent H5+H7 VLP vaccine candidate was prepared by combining these two antigens. Single immunization of the bivalent VLP or commercial inactivated vaccines elicited effective antibody immune responses, including hemagglutination inhibition, virus neutralizing and HA-specific IgG antibodies. All vaccinated birds survived lethal challenge with highly pathogenic H5N1 and H7N9 viruses. Furthermore, the bivalent VLP significantly reduced viral shedding and virus replication in chickens, which was comparable to that observed for the commercial inactivated vaccine. However, the bivalent VLP was better than the commercial vaccine in terms of alleviating pulmonary lesions caused by H7N9 virus infection in chickens. Therefore, our study suggests that the bivalent H5+H7 VLP vaccine candidate can serve as a critical alternative for the traditional egg-based inactivated vaccines against H5N1 and H7N9 avian influenza virus infection in poultry.

AIV polyantigen epitope expressed by recombinant baculovirus induces a systemic immune response in chicken and mouse models

BACKGROUND

The protective efficacy of avian influenza virus (AIV) vaccines is unsatisfactory due to the presence of various serotypes generated by genetic reassortment. Thus, immunization with a polyantigen chimeric epitope vaccine may be an effective strategy for protecting poultry from infection with different AIV subtypes.

METHODS

Baculovirus has recently emerged as a novel and attractive gene delivery vehicle for animal cells. In the present study, a recombinant baculovirus BmNPV-CMV/THB-P10/CTLT containing a fused codon-optimized sequence (CTLT) of T lymphocyte epitopes from H1HA, H9HA, and H7HA AIV subtypes, and another fused codon-optimized sequence (THB) of Th and B cell epitopes from H1HA, H9HA, and H7HA AIV subtypes, driven by a baculovirus P10 promoter and cytomegalovirus CMV promoter, respectively, was constructed.

RESULTS

Western blotting and cellular immunofluorescence demonstrated that the CTLT (THB) can be expressed in rBac-CMV/THB-P10/CTLT-infected silkworm cells (mammalian HEK293T cells). Furthermore, the recombinant virus, rBac-CMV-THB-CTLT, was used to immunize both chickens and mice.

CONCLUSIONS

The results of an indirect ELISA, immunohistochemistry, and T lymphocyte proliferation assay indicated that specific humoral and cellular responses were detected in both chicken and mice. These results suggest that rBac-CMV/THB-P10/CTLT can be developed as a potential vaccine against different AIV subtypes.

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.

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.

Sequential Immunizations with heterosubtypic virus-like particles elicit cross protection against divergent influenza A viruses in mice

Seasonal influenza vaccines have proven to be effective against well-matched viruses in healthy adults. However, rapid accumulation of mutations in the main antigenic surface proteins of influenza can compromise the efficiency of flu vaccines. Occasionally, influenza pandemics arise and present a different type of challenge to current seasonal vaccines. Novel vaccination strategies that can educate the host immune system to generate immune responses focusing on conserved epitopes on theses antigenic surface proteins are crucial for controlling and limiting influenza epidemics and pandemics. In this study, we have sequentially vaccinated mice with heterosubtypic influenza HA virus-like particles (VLPs) harboring H1, H8, and H13 from the HA phylogenetic group 1, or H3, H4, and H10 from the HA phylogenetic group 2, or in various combinations. The immunized animals were fully protected when challenged with lethal doses of heterosubtypic viruses from either phylogenetic group. Our vaccination approach demonstrates a promising strategy for the development of a ‘universal influenza vaccine’.

Immune responses to highly conserved influenza A virus matrix 1 peptides

Influenza vaccine development is considered to be complicated and challenging. Constantly evolving influenza viruses require continuous global monitoring and reformulation of the vaccine strains. Peptides that are conserved among different strains and subtypes of influenza A virus are strongly considered to be attractive targets for development of cross protective influenza vaccines that stimulate cellular responses. In this study, three highly conserved (>90%) matrix 1 peptides that contain multiple T cell epitopes, ILGFVFTLTVPSERGLQRRRF (P_M 1), LIRHENRMVLASTTAKA (P_M 2) and LQAYQKRMGVQMQR (P_M 3), were assessed for their immunogenic potential in vitro by subjecting peripheral blood mononuclear cells from healthy volunteers to repetitive stimulation with these chemically synthesised peptides and measuring their IFN-γ concentrations, proliferation by ELISA, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, respectively. Seven samples were screened for immunogenicity of P_M 1 and P_M 2, and six for that of P_M 3. All six samples had positive responses (IFN-γ secretion) to P_M 3 stimulation, as did five and three for P_M 2 and P_M 1 respectively. In contrast, seven (P_M 1 and P_M 2) and four (P_M 3) samples showed proliferative response as compared with unstimulated cells. The encouraging immunogenic response generated by these highly conserved matrix 1 peptides indicates they are prospective candidates for development of broadly reactive influenza vaccines.

A genetically engineered H5 protein expressed in insect cells confers protection against different clades of H5N1 highly pathogenic avian influenza viruses in chickens

The evolution of highly pathogenic H5N1 avian influenza viruses (HPAI-H5N1) has resulted in the appearance of a number of diverse groups of HPAI-H5N1 based on the presence of genetically similar clusters of their haemagglutinin sequences (clades). An H5 antigen encoded by a recombinant baculovirus and expressed in insect cells was used for oil-emulsion-based vaccine prototypes. In several experiments, vaccination was performed at 10 days of age, followed by challenge infection on day 21 post vaccination (PV) with HPAI-H5N1 clades 2.2, 2.2.1, and 2.3.2. A further challenge infection with HPAI-H5N1 clade 2.2.1 was performed at day 42 PV. High haemagglutination inhibition titres were observed for the recH5 vaccine antigen, and lower haemagglutination inhibition titres for the challenge virus antigens. Nevertheless, the rate of protection from mortality and clinical signs was 100% when challenged at 21 days PV and 42 days PV, indicating protection over the entire broiler chicken rearing period without a second vaccination. The unvaccinated control chickens mostly died between two and five days after challenge infection. A low level of viral RNA was detected by reverse transcription followed by a quantitative polymerase chain reaction in a limited number of birds for a short period after challenge infection, indicating a limited spread of HPAI-H5N1 at flock level. Furthermore, it was observed that the vaccine can be used in a differentiation infected from vaccinated animals (DIVA) approach, based on the detection of nucleoprotein antibodies in vaccinated/challenged chickens. The vaccine fulfilled all expectations of an inactivated vaccine after one vaccination against challenge with different clades of H5N1-HPAI and is suitable for a DIVA approach.

Multi-antigen avian influenza a (H7N9) virus-like particles: particulate characterizations and immunogenicity evaluation in murine and avian models

BACKGROUND

Human infection with avian influenza A virus (H7N9) was first reported in China in March 2013. Since then, hundreds of cases have been confirmed showing severe symptoms with a high mortality rate. The virus was transmitted from avian species to humans and has spread to many neighboring areas, raising serious concerns over its pandemic potential. Towards containing the disease, the goal of this study is to prepare a virus-like particle (VLP) that consists of hemagglutinin (HA), neuraminidase (NA) and matrix protein 1 (M1) derived from the human isolate A/Taiwan/S02076/2013(H7N9) for potential vaccine development.

RESULTS

Full length HA, NA, and M1 protein genes were cloned and expressed using a baculoviral expression system, and the VLPs were generated by co-infecting insect cells with three respective recombinant baculoviruses. Nanoparticle tracking analysis and transmission electron microscopy were applied to verify the VLPs' structure and antigenicity, and the multiplicity of infection of the recombinant baculoviruses was adjusted to achieve the highest hemagglutination activity. In animal experiments, BALB/c mice and specific-pathogen-free chickens receiving the VLP immunization showed elevated hemagglutination inhibition serum titer and antibodies against NA and M1 proteins. In addition, examination of cellular immunity showed the VLP-immunized mice and chickens exhibited an increased splenic antigen-specific cytokines production.

CONCLUSIONS

The H7N9 VLPs possess desirable immunogenicity in vivo and may serve as a candidate for vaccine development against avian influenza A (H7N9) infection.

Particle and subunit-based hemagglutinin vaccines provide protective efficacy against H1N1 influenza in pigs

The increasing diversity of influenza strains circulating in swine herds escalates the potential for the emergence of novel pandemic viruses and highlights the need for swift development of new vaccines. Baculovirus has proven to be a flexible platform for the generation of recombinant forms of hemagglutinin (HA) including subunit, VLP-displayed, and baculovirus-displayed antigens. These presentations have been shown to be efficacious in mouse, chicken, and ferret models but little is known about their immunogenicity in pigs. To assess the utility of these HA presentations in swine, Baculovirus constructs expressing HA fused to swine IgG2a Fc, displayed in a FeLV gag VLP, or displayed in the baculoviral envelope were generated. Vaccines formulated with these antigens wer The e administered to groups of pigs who were subsequently challenged with H1α cluster H1N1 swine influenza virus (SIV) A/Swine/Indiana/1726/88. Our results demonstrate that vaccination with any of these three vaccines elicits robust hemagglutinin inhibition titers in the serum and decreased the severity of SIV-associated lung lesions after challenge when compared to placebo-vaccinated controls. In addition, the number of pigs with virus detected in the lungs and nasal passages was reduced. Taken together, the results demonstrate that these recombinant approaches expressed with the baculovirus expression vector system may be viable options for development of SIV vaccines for swine.

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.

Identification of Conserved Peptides Comprising Multiple T Cell Epitopes of Matrix 1 Protein in H1N1 Influenza Virus

Cell mediated immune response plays a key role in combating viral infection and thus identification of new vaccine targets manifesting T cell mediated response may serve as an ideal approach for influenza vaccine. The present study involves the application of an immunoinformatics-based consensus approach for epitope prediction (three epitope prediction tools each for CD4+ and CD8+ T cell epitopes) and molecular docking to identify peptide sequences containing T cell epitopes using the conserved sequences from all the Matrix 1 protein sequences of H1N1 virus available until April 2015. Three peptides comprising CD4+ and CD8+ T cell epitopes were obtained, which were not exactly reported in earlier studies. Population coverage study of these multi-epitope peptides revealed that they are capable of inducing a potent immune response belonging to individuals from different populations and ethnicity distributed around the globe. Conservation study with other subtypes of influenza virus infecting humans (H2N2, H5N1, H7N9, and H3N2) revealed that these three peptides were conserved (>90%), with 100% identity in most of these strains. Hence, these peptides can impart immunity against H1N1 as well as other subtypes of influenza virus. A molecular docking study of the predicted peptides with class I and II human leukocyte antigen (HLA) molecules has shown that the majority of them have comparable binding energies to that of native peptides. Hence, these peptides from Matrix 1 protein of H1N1 appear to be promising candidates for universal vaccine design.

Vaccines against influenza A viruses in poultry and swine: Status and future developments

Influenza A viruses are important pathogens with a very broad host spectrum including domestic poultry and swine. For preventing clinical disease and controlling the spread, vaccination is one of the most efficient tools. Classical influenza vaccines for domestic poultry and swine are conventional inactivated preparations. However, a very broad range of novel vaccine types ranging from (i) nucleic acid-based vaccines, (ii) replicon particles, (iii) subunits and virus-like particles, (iv) vectored vaccines, or (v) live-attenuated vaccines has been described, and some of them are now also used in the field. The different novel approaches for vaccines against avian and swine influenza virus infections are reviewed, and additional features like universal vaccines, novel application approaches and the "differentiating infected from vaccinated animals" (DIVA)-strategy are summarized.

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

The highly pathogenic avian influenza (HPAI) H5N1 virus has become highly enzootic since 2003 and has dynamically evolved to undergo substantial evolution. Clades 2.3.2.1 and 2.3.4 have become the most dominant lineage in recent years, and H5N8 avian influenza outbreaks have been reported Asia. The current approach to generate influenza virus vaccines uses embryonated chicken eggs for large-scale production, although such vaccines have been poorly immunogenic to heterologous virus challenge. In the current study, virus-like particles (VLP) based on A/meerkat/Shanghai/SH-1/2012 (clade 2.3.2.1) and comprising hemagglutinin (HA), neuraminidase (NA), and matrix (M1) were produced using a baculovirus expression system to develop effective protection for different H5 HPAI clade challenges. Mice immunized with VLP demonstrated stronger humoral and cellular immune responses than mice immunized with whole influenza virus (WIV), with 20-fold higher IgG antibody titers against A/meerkat/Shanghai/SH-1/2012 after boost. Notably, the WIV vaccine group showed partial protection (80% survival) to homologous challenge, little protection (40% survival) to heterologous challenge, and 20% survival to H5N8 challenge, whereas all mice in the VLP+CFA group survived. These results provide insight for the development of effective prophylactic vaccines based on VLPs with cross-clade protection for the control of current H5 HPAI outbreaks in humans.

Self-assembly and release of peste des petits ruminants virus-like particles in an insect cell-baculovirus system and their immunogenicity in mice and goats

Peste des petits ruminants (PPR) is an acute, febrile, viral disease of small ruminants that has a significant economic impact. For many viral diseases, vaccination with virus-like particles (VLPs) has shown considerable promise as a prophylactic approach; however, the processes of assembly and release of peste des petits ruminants virus (PPRV) VLPs are not well characterized, and their immunogenicity in the host is unknown. In this study, VLPs of PPRV were generated in a baculovirus system through simultaneous expression of PPRV matrix (M) protein and hemaglutin in (H) or fusion (F) protein. The released VLPs showed morphology similar to that of the native virus particles. Subcutaneous injection of these VLPs (PPRV-H, PPRV-F) into mice and goats elicited PPRV-specific IgG production, increased the levels of virus neutralizing antibodies, and promoted lymphocyte proliferation. Without adjuvants, the immune response induced by the PPRV-H VLPs was comparable to that obtained using equivalent amounts of PPRV vaccine. Thus, our results demonstrated that VLPs containing PPRV M protein and H or F protein are potential “differentiating infected from vaccinated animals” (DIVA) vaccine candidates for the surveillance and eradication of PPR.

Self-adjuvanting influenza candidate vaccine presenting epitopes for cell-mediated immunity on a proteinaceous multivalent nanoplatform

We exploit the features of a virus-like particle, adenoviral dodecahedron (Ad Dd), for engineering a multivalent vaccination platform carrying influenza epitopes for cell-mediated immunity. The delivery platform, Ad Dd, is a proteinaceous, polyvalent, and biodegradable nanoparticle endowed with remarkable endocytosis activity that can be engineered to carry 60 copies of a peptide. Influenza M1 is the most abundant influenza internal protein with the conserved primary structure. Two different M1 immunodominant epitopes were separately inserted in Dd external positions without destroying the particles' dodecahedric structure. Both kinds of DdFluM1 obtained through expression in baculovirus system were properly presented by human dendritic cells triggering efficient activation of antigen-specific T cells responses. Importantly, the candidate vaccine was able to induce cellular immunity in vivo in chickens. These results warrant further investigation of Dd as a platform for candidate vaccine, able to stimulate cellular immune responses.

Use of baculovirus expression system for generation of virus-like particles: successes and challenges

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A brief overview of principles and applications of BES.

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Generation of VLPs using BES.

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Major properties of BES: promoting generation of VLPs.

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Bioprocess considerations for generation of VLPs.

The baculovirus expression system (BES) has been one of the versatile platforms for the production of recombinant proteins requiring multiple post-translational modifications, such as folding, oligomerization, phosphorylation, glycosylation, acylation, disulfide bond formation and proteolytic cleavage. Advances in recombinant DNA technology have facilitated application of the BES, and made it possible to express multiple proteins simultaneously in a single infection and to produce multimeric proteins sharing functional similarity with their natural analogs. Therefore, the BES has been used for the production of recombinant proteins and the construction of virus-like particles (VLPs), as well as for the development of subunit vaccines, including VLP-based vaccines. The VLP, which consists of one or more structural proteins but no viral genome, resembles the authentic virion but cannot replicate in cells. The high-quality recombinant protein expression and post-translational modifications obtained with the BES, along with its capacity to produce multiple proteins, imply that it is ideally suited to VLP production. In this article, we critically review the pros and cons of using the BES as a platform to produce both enveloped and non-enveloped VLPs.