A novel M2e based flu vaccine formulation for dogs

An experimental universal swine influenza a virus (IAV) vaccine candidate based on the M2 ectodomain (M2e) peptide does not provide protection against H1N1 IAV challenge in pigs

Swine flu is a common disease problem in North American pig populations and swine influenza A viruses (IAV) are extremely diverse and the lack of cross protection between heterologous strains is impacting vaccine efficacy in the field. The objective of this study was to design and test a novel swine flu vaccine targeting the M2 ectodomain (M2e) of IAV, a highly conserved region within the IAV proteome. In brief, an M2e peptide was designed to match the predominant swine IAV M2 sequence based on global analysis of sequences from pigs and humans. The resulting sequence was used to synthesize the M2e peptide coupled to a carrier protein. The final vaccine concentration was 200 µg per dose, and a commercial, microemulsion-based aqueous adjuvant was added. Nine 3-week-old IAV negative piglets were randomly assigned to three groups and rooms including non-vaccinated pigs (NEG-CONTROLs) and vaccinated pigs using the intramuscular (M2e-IM) or the intranasal route (M2e-IN). Vaccinations were done at weaning and again at 2 weeks later. An in-house enzyme-linked immunosorbent assay (ELISA) was developed and validated to study the M2e IgG antibody response and demonstrated M2e-IM pigs had a higher systemic antibody response compared to M2e-IN pigs. Subsequently, an IAV challenge study was conducted. The results indicated that M2e-IM vaccinated pigs were not protected from H1N1 (US pandemic clade, global clade 1A.3.3.2) challenge despite having a strong humoral anti-M2e immune response. In conclusion, while the experimental IAV vaccine was able to induce anti-M2e antibodies, when challenged with H1N1, the vaccinated pigs were not protected, perhaps indicating that reactivity to the M2e antigen alone is not sufficient to reduce clinical signs, lesions or shedding associated with experimental IAV challenge.

Virus-like Particle Vaccines and Platforms for Vaccine Development

Virus-like particles (VLPs) have gained a lot of interest within the past two decades. The use of VLP-based vaccines to protect against three infectious agents-hepatitis B virus, human papillomavirus, and hepatitis E virus-has been approved; they are very efficacious and offer long-lasting immune responses. Besides these, VLPs from other viral infectious agents (that infect humans, animals, plants, and bacteria) are under development. These VLPs, especially those from human and animal viruses, serve as stand-alone vaccines to protect against viruses from which the VLPs were derived. Additionally, VLPs, including those derived from plant and bacterial viruses, serve as platforms upon which to display foreign peptide antigens from other infectious agents or metabolic diseases such as cancer, i.e., they can be used to develop chimeric VLPs. The goal of chimeric VLPs is to enhance the immunogenicity of foreign peptides displayed on VLPs and not necessarily the platforms. This review provides a summary of VLP vaccines for human and veterinary use that have been approved and those that are under development. Furthermore, this review summarizes chimeric VLP vaccines that have been developed and tested in pre-clinical studies. Finally, the review concludes with a snapshot of the advantages of VLP-based vaccines such as hybrid/mosaic VLPs over conventional vaccine approaches such as live-attenuated and inactivated vaccines.

A nanoparticle-based COVID-19 vaccine candidate elicits broad neutralizing antibodies and protects against SARS-CoV-2 infection

A vaccine candidate to SARS-CoV-2 was constructed by coupling the viral receptor binding domain (RBD) to the surface of the papaya mosaic virus (PapMV) nanoparticle (nano) to generate the RBD-PapMV vaccine. Immunization of mice with the coupled RBD-PapMV vaccine enhanced the antibody titers and the T-cell mediated immune response directed to the RBD antigen as compared to immunization with the non-coupled vaccine formulation (RBD + PapMV nano). Anti-RBD antibodies, generated in vaccinated animals, neutralized SARS-CoV-2 infection in vitro against the ancestral, Delta and the Omicron variants. At last, immunization of mice susceptible to the infection by SARS-CoV-2 (K18-hACE2 transgenic mice) with the RBD-PapMV vaccine induced protection to the ancestral SARS-CoV-2 infectious challenge. The induction of the broad neutralization against SARS-CoV-2 variants induced by the RBD-PapMV vaccine demonstrate the potential of the PapMV vaccine platform in the development of efficient vaccines against viral respiratory infections.

A Novel Mechanism Underlying Antiviral Activity of an Influenza Virus M2-Specific Antibody

Protective immunity against influenza A viruses (IAVs) generally depends on antibodies to the major envelope glycoprotein, hemagglutinin (HA), whose antigenicity is distinctive among IAV subtypes. On the other hand, the matrix 2 (M2) protein is antigenically highly conserved and has been studied as an attractive vaccine antigen to confer cross-protective immunity against multiple subtypes of IAVs. However, antiviral mechanisms of M2-specific antibodies are not fully understood. Here, we report the molecular basis of antiviral activity of an M2-specific monoclonal antibody (MAb), rM2ss23. We first found that rM2ss23 inhibited A/Aichi/2/1968 (H3N2) (Aichi) but not A/PR/8/1934 (H1N1) (PR8) replication. rM2ss23 altered the cell surface distribution of M2, likely by cross-linking the molecules, and interfered with the colocalization of HA and M2, resulting in reduced budding of progeny viruses. However, these effects were not observed for another strain, PR8, despite the binding capacity of rM2ss23 to PR8 M2. Interestingly, HA was also involved in the resistance of PR8 to rM2ss23. We also found that two amino acid residues at positions 54 and 57 in the M2 cytoplasmic tail were critical for the insensitivity of PR8 to rM2ss2. These findings suggest that the disruption of the M2-HA colocalization on infected cells and subsequent reduction of virus budding is one of the principal mechanisms of antiviral activity of M2-specific antibodies and that anti-M2 antibody-sensitive and -resistant IAVs have different properties in the interaction between M2 and HA.IMPORTANCE Although the IAV HA is the major target of neutralizing antibodies, most of the antibodies are HA subtype specific, restricting the potential of HA-based vaccines. On the contrary, the IAV M2 protein has been studied as a vaccine antigen to confer cross-protective immunity against IAVs with multiple HA subtypes, since M2 is antigenically conserved. Although a number of studies highlight the protective role of anti-HA neutralizing and nonneutralizing antibodies, precise information on the molecular mechanism of action of M2-specific antibodies is still obscure. In this study, we found that an anti-M2 antibody interfered with the HA-M2 association, which is important for efficient budding of progeny virus particles from infected cells. The antiviral activity was IAV strain dependent despite the similar binding capacity of the antibody to M2, and, interestingly, HA was involved in susceptibility to the antibody. Our data provide a novel mechanism underlying antiviral activity of M2-specific antibodies.

Influenza-Host Interplay and Strategies for Universal Vaccine Development

Influenza is an annual epidemic and an occasional pandemic caused by pathogens that are responsible for infectious respiratory disease. Humans are highly susceptible to the infection mediated by influenza A viruses (IAV). The entry of the virus is mediated by the influenza virus hemagglutinin (HA) glycoprotein that binds to the cellular sialic acid receptors and facilitates the fusion of the viral membrane with the endosomal membrane. During IAV infection, virus-derived pathogen-associated molecular patterns (PAMPs) are recognized by host intracellular specific sensors including toll-like receptors (TLRs), C-type lectin receptors, retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) either on the cell surface or intracellularly in endosomes. Herein, we comprehensively review the current knowledge available on the entry of the influenza virus into host cells and the molecular details of the influenza virus–host interface. We also highlight certain strategies for the development of universal influenza vaccines.

M2e-based universal influenza vaccines: a historical overview and new approaches to development

The influenza A virus was isolated for the first time in 1931, and the first attempts to develop a vaccine against the virus began soon afterwards. In addition to causing seasonal epidemics, influenza viruses can cause pandemics at random intervals, which are very hard to predict. Vaccination is the most effective way of preventing the spread of influenza infection. However, seasonal vaccination is ineffective against pandemic influenza viruses because of antigenic differences, and it takes approximately six months from isolation of a new virus to develop an effective vaccine. One of the possible ways to fight the emergence of pandemics may be by using a new type of vaccine, with a long and broad spectrum of action. The extracellular domain of the M2 protein (M2e) of influenza A virus is a conservative region, and an attractive target for a universal influenza vaccine. This review gives a historical overview of the study of M2 protein, and summarizes the latest developments in the preparation of M2e-based universal influenza vaccines.

The Quest for a Truly Universal Influenza Vaccine

There is an unmet public health need for a universal influenza vaccine (UIV) to provide broad and durable protection from influenza virus infections. The identification of broadly protective antibodies and cross-reactive T cells directed to influenza viral targets present a promising prospect for the development of a UIV. Multiple targets for cross-protection have been identified in the stalk and head of hemagglutinin (HA) to develop a UIV. Recently, neuraminidase (NA) has received significant attention as a critical component for increasing the breadth of protection. The HA stalk-based approaches have shown promising results of broader protection in animal studies, and their feasibility in humans are being evaluated in clinical trials. Mucosal immune responses and cross-reactive T cell immunity across influenza A and B viruses intrinsic to live attenuated influenza vaccine (LAIV) have emerged as essential features to be incorporated into a UIV. Complementing the weakness of the stand-alone approaches, prime-boost vaccination combining HA stalk, and LAIV is under clinical evaluation, with the aim to increase the efficacy and broaden the spectrum of protection. Preexisting immunity in humans established by prior exposure to influenza viruses may affect the hierarchy and magnitude of immune responses elicited by an influenza vaccine, limiting the interpretation of preclinical data based on naive animals, necessitating human challenge studies. A consensus is yet to be achieved on the spectrum of protection, efficacy, target population, and duration of protection to define a “universal” vaccine. This review discusses the recent advancements in the development of UIVs, rationales behind cross-protection and vaccine designs, and challenges faced in obtaining balanced protection potency, a wide spectrum of protection, and safety relevant to UIVs.

Application of built-in adjuvants for epitope-based vaccines

Several studies have shown that epitope vaccines exhibit substantial advantages over conventional vaccines. However, epitope vaccines are associated with limited immunity, which can be overcome by conjugating antigenic epitopes with built-in adjuvants (e.g., some carrier proteins or new biomaterials) with special properties, including immunologic specificity, good biosecurity and biocompatibility, and the ability to vastly improve the immune response of epitope vaccines. When designing epitope vaccines, the following types of built-in adjuvants are typically considered: (1) pattern recognition receptor ligands (i.e., toll-like receptors); (2) virus-like particle carrier platforms; (3) bacterial toxin proteins; and (4) novel potential delivery systems (e.g., self-assembled peptide nanoparticles, lipid core peptides, and polymeric or inorganic nanoparticles). This review primarily discusses the current and prospective applications of these built-in adjuvants (i.e., biological carriers) to provide some references for the future design of epitope-based vaccines.

A Perspective on Nanoparticle Universal Influenza Vaccines

Annually recurring seasonal influenza causes massive economic loss and poses severe threats to public health worldwide. The current seasonal influenza vaccines are the most effective means of preventing influenza infections but possess major weaknesses. Seasonal influenza vaccines require annual updating of the vaccine strains. However, it is an unreachable task to accurately predict the future circulating strains. Vaccines with mismatched strains dramatically compromise the vaccine efficacy. In addition, the seasonal influenza vaccines are ineffective against an unpredictable pandemic. A universal influenza vaccine would overcome these weaknesses of the seasonal vaccines and abolish the threat of influenza pandemics. One approach under investigation is to design influenza vaccine immunogens based on conserved, type-specific amino acid sequences and conformational epitopes, rather than strain-specific. Such vaccines can elicit broadly reactive humoral and cellular immunity. Universal influenza vaccine development has intensively employed nanotechnology because the structural and morphological properties of nanoparticles dramatically improve vaccine immunogenicity and the induced immunity duration. Layered protein nanoparticles can decrease off-target immune responses, fine-tune antigen recognition and processing, and facilitate comprehensive immune response induction. Herein, we review the designs of effective nanoparticle universal influenza vaccines, the recent discoveries of specific nanoparticle features that contribute to immunogenicity enhancement, and recent progress in clinical trials.

Plant-made vaccines and reagents for the One Health initiative

The One Health initiative is increasingly becoming a prominent discussion topic in animal and human health, with its focus on prevention of spread of zoonotic diseases, both in animals, and from animals to humans. An important part of One Health is that diagnostics and vaccines for diseases may be the same thing - and be used for both humans and animals. One potential problem standing in the way of wider adoption of One Health principles, though, is that use of conventional cell fermentation systems for production of the recombinant proteins that could be used as diagnostics or vaccines is often expensive and is not easily scalable. A solution to this may be the use of plants or plant cells as bioreactors: molecular farming, or the production of biologics in plants, is now a well-established science with many proofs of principle and important proofs of efficacy for especially animal vaccines. This review discusses how molecular farming could enable important advances in One Health, using as examples plant-made vacccines, reagents and therapeutics for influenza viruses, ebolaviruses, rabies virus, bunyaviruses and flaviviruses.

M2e-Based Universal Influenza A Vaccines

The successful isolation of a human influenza virus in 1933 was soon followed by the first attempts to develop an influenza vaccine. Nowadays, vaccination is still the most effective method to prevent human influenza disease. However, licensed influenza vaccines offer protection against antigenically matching viruses, and the composition of these vaccines needs to be updated nearly every year. Vaccines that target conserved epitopes of influenza viruses would in principle not require such updating and would probably have a considerable positive impact on global human health in case of a pandemic outbreak. The extracellular domain of Matrix 2 (M2e) protein is an evolutionarily conserved region in influenza A viruses and a promising epitope for designing a universal influenza vaccine. Here we review the seminal and recent studies that focused on M2e as a vaccine antigen. We address the mechanism of action and the clinical development of M2e-vaccines. Finally, we try to foresee how M2e-based vaccines could be implemented clinically in the future.

Universal influenza vaccines, a dream to be realized soon

Due to frequent viral antigenic change, current influenza vaccines need to be re-formulated annually to match the circulating strains for battling seasonal influenza epidemics. These vaccines are also ineffective in preventing occasional outbreaks of new influenza pandemic viruses. All these challenges call for the development of universal influenza vaccines capable of conferring broad cross-protection against multiple subtypes of influenza A viruses. Facilitated by the advancement in modern molecular biology, delicate antigen design becomes one of the most effective factors for fulfilling such goals. Conserved epitopes residing in virus surface proteins including influenza matrix protein 2 and the stalk domain of the hemagglutinin draw general interest for improved antigen design. The present review summarizes the recent progress in such endeavors and also covers the encouraging progress in integrated antigen/adjuvant delivery and controlled release technology that facilitate the development of an affordable universal influenza vaccine.