Flu Universal Vaccines: New Tricks on an Old Virus

Conventional influenza vaccines are based on predicting the circulating viruses year by year,conferring limited effectiveness since the antigenicity of vaccine strains does not always match the circulating viruses.This necessitates development of universal influenza vaccines that provide broader and lasting protection against pan-influenza viruses.The discovery of the highly conserved immunogens(epitopes)of influenza viruses provides attractive targets for universal vaccine design.Here we review the current understanding with broadly protective immunogens(epitopes)and discuss several important considerations to achieve the goal of universal influenza vaccines.

Bioinformatic Analysis of SARS-CoV-2 Genomes to Develop a Universal Coronavirus Vaccine

COVID-19 is caused by the SARS-CoV-2 virus. Current RNA vaccines Pfizer/BioNTech’s BNT162b2 and Moderna’s mRNA-1273 are more than 94% successful in preventing infection. The spike protein of the virus is essential for the interaction and internalization of the virus in the host cell and is considered a prime target for vaccine development against the SARS virus. This study aims to identify highly conserved sequences in spike protein or other sections of the viral genome that can potentially be used to develop a universal coronavirus vaccine. Bioinformatic analysis of 258,269 full-length SARS-CoV-2 genomic sequences in the NCBI database was carried out using a custom Perl Script. All sequences were compared to the spike protein and full-length viral genome reference to find 100 nucleotide-long segments that were at least 99% conserved across SARS-CoV-2 sequences. The analysis resulted in a >99.5% conserved 114-nucleotide segment on the spike protein and a 99.49% conserved 104-nucleotide segment on the non-spike protein section of the viral genome. The conserved sequences from this study may be useful in developing an RNA or protein vaccine that may be effective against future SARS-CoV-2 strains or could act as a universal vaccine if these sequences are present in other coronavirus families.

Universal COVID-19 Vaccine Targeting SARS-CoV-2 Envelope Protein

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), had caused over 382 million cases and over 2.7 million deaths globally as of 23 March 2021. By that date, at least 10 SARS-CoV-2 variants had emerged. The transmissibility and lethality of the variants are higher than those of the Wuhan reference strain. Therefore, a universal vaccine for the reference strain and all variants (present and future) is indispensable. The coronavirus envelope (E) protein is an integral membrane protein crucial to the viral lifecycle and the pathogenesis of coronaviruses. The SARS-CoV-2 E protein has a postsynaptic density protein 95/Drosophila disc large tumor suppressor/zonula occludens-1 (PDZ) binding motif (PBM), and its interaction with PDZ-domain-2 of the human tight junction protein may interrupt the integrity of lung epithelium. Furthermore, the SARS-CoV-2 E protein itself is a homopentameric cation channel viroporin, which may be involved in viral release. This protein is thus a potential target for the development of a universal COVID-19 vaccine, because of its highly conserved amino acid sequence. The variant mutations occur mainly in the spike protein, and conservation of E protein remained in most Variants of Concern (VOC). Only one of the extant VOC have mutations in the E protein that P71L mutation occurs in the South African variant 501Y.V2 (B.1.351). If a vaccine is designed to target E protein, two scenarios are possible: 1) SARS-CoV-2 maintains a highly conserved E protein amino acid sequence, rendering the virus consistently or permanently susceptible to the vaccine;or 2) the E protein mutates and new variants evolve accordingly. In scenario 2, the tertiary structure and function of the E protein homopentameric cation channel viroporin, PBM, or other aspects affecting pathogenicity would be attenuated. Either scenario would thus ameliorate the pandemic. I therefore propose that a vaccine targeting the SARS-CoV-2 E protein would be effective against the Wuhan reference strain and all current and future SARS-CoV-2 variants. Efforts to create E protein-based vaccines are ongoing. Further research and clinical trials are needed to realize this universal COVID-19 vaccine.

Protective efficacy of a universal influenza mRNA vaccine against the challenge of H1 and H5 influenza A viruses in mice

Current influenza vaccines need to be updated annually owing to constant antigenic drift in the globular head of the viral surface hemagglutinin(HA)glycoprotein.The immunogenic subdominant stem domain of HA is highly conserved and can be recognized by antibodies capable of binding multiple HA subtypes.Therefore,the HA stem antigen is a promising target for the design of universal influenza vaccines.On the basis of an established lipid nanoparticle-encapsulated mRNA vaccine platform,we designed and developed a novel universal influenza mRNA vaccine(mHAs)encoding the HA stem antigen of the influenza A(H1N1)virus.We tested the efficacy of the mHAs vaccine using a mouse model.The vaccine induced robust humoral and specific cellular immune responses against the stem region of HA.Importantly,two doses of the mHAs vaccine fully protected mice from lethal challenges of the heterologous H1N1 and heterosubtypic H5N8 influenza viruses.Vacci-nated mice had less pathological lung damage and lower viral titers than control mice.These results suggest that an mRNA vaccine using the conserved stem region of HA may provide effective protection against seasonal and other possible influenza variants.

A novel heterologous receptor-binding domain dodecamer universal mRNA vaccine against SARS-CoV-2 variants

There are currently approximately 4000 mutations in the SARS-CoV-2 S protein gene and emerging SARS-CoV-2 variants continue to spread rapidly worldwide.Universal vaccines with high efficacy and safety urgently need to be developed to prevent SARS-CoV-2 variants pandemic.Here,we described a novel self-assembling universal mRNA vaccine containing a heterologous receptorbinding domain(HRBD)-based dodecamer(HRBD^(dodecamer))against SARS-CoV-2 variants,including Alpha(B.1.1.7),Beta(B.1.351),Gamma(B.1.1.28.1),Delta(B.1.617.2)and Omicron(B.1.1.529).HRBD containing four heterologous RBD(Delta,Beta,Gamma,and Wild-type)can form a stable dodecameric conformation under T4 trimerization tag(Flodon,FD).The HRBD^(dodecamer)-encoding mRNA was then encapsulated into the newly-constructed LNPs consisting of a novel ionizable lipid(4N4T).The obtained universal mRNA vaccine(4N4T-HRBD^(dodecamer))presented higher efficiency in mRNA transfection and expression than the approved ALC-0315 LNPs,initiating potent immune protection against the immune escape of SARS-CoV-2 caused by evolutionary mutation.These findings demonstrated the first evidence that structure-based antigen design and mRNA delivery carrier optimization may facilitate the development of effective universal mRNA vaccines to tackle SARS-CoV-2 variants pandemic.

Universal influenza virus vaccines： what can we learn from the human immune response following exposure to H7 subtype viruses？

Several universal influenza virus vaccine candidates based on eliciting antibodies against the hemagglutinin stalk domain are in development. Typically, these vaccines induce responses that target group 1 or group 2 hemagglutinins with Httle to no cross-group reactivity and protection. Similarly, the majority of human anti-stalk monoclonal antibodies that have been isolated are directed against group 1 or group 2 hemagglutinins with very few that bind to hemagglutinins of both groups. Here we review what is known about the human humoral immune response to vaccination and infection with H7 subtype influenza viruses on a polyclonal and monoclonal level. It seems that unlike vaccination with H5 hemagglutinin, which induces antibody responses mostly restricted to the group 1 stalk domain, H7 exposure induces both group 2 and cross-group antibody responses. A better understanding of this phenomenon and the underlying mechanisms might help to develop future universal influenza virus vaccine candidates.

A biepitope,adjuvant-free,self-assembled influenza nanovaccine provides cross-protection against H3N2 and H1N1 viruses in mice

Currently,the incorporation of multiple epitopes into vaccines is more desirable than the incorporation of a single antigen for universal influenza vaccine development.However,epitopes induce poor immune responses.Although the use of adjuvants can overcome this obstacle,it may raise new problems.Effective antigen delivery vehicles that can function as both antigen carriers and intrinsic adjuvants are highly desired for vaccine development.Here,we report a biepitope nanovaccine that provides complete protection in mice against H3N2 virus as well as partial protection against H1N1 virus.This vaccine(3MCD-f)consists of two conserved epitopes(matrix protein 2 ectodomain(M2e)and CDhelix),and these epitopes were presented on the surface of ferritin in a sequential tandem format.Subcutaneous immunization with 3MCD-f in the absence of adjuvant induces robust humoral and cellular immune responses.These results provide a proof of concept for the 3MCD-f nanovaccine that might be an ideal candidate for future influenza pandemics.