Single mucosal vaccination targeting nucleoprotein provides broad protection against two lineages of influenza B virus

Cross-protective efficacy and safety of an adenovirus-based universal influenza vaccine expressing nucleoprotein, hemagglutinin, and the ectodomain of matrix protein 2

It is necessary to develop universal vaccines that act broadly and continuously to combat regular seasonal epidemics of influenza and rare pandemics. The aim of this study was to find the optimal dose regimen for the efficacy and safety of a mixture of previously developed recombinant adenovirus-based vaccines that expressed influenza nucleoprotein, hemagglutinin, and ectodomain of matrix protein 2 (rAd/NP and rAd/HA-M2e). The vaccine efficacy and safety were measured in the immunized mice with the mixture of rAd/NP and rAd/HA-M2e intranasally or intramuscularly. The minimum dose that would be efficacious in a single intranasal administration of the vaccine mixture and cross-protective efficacy against various influenza strains were examined. In addition, the immune responses that may affect the cross-protective efficacy were measured. We found that intranasal administration is an optimal route for 107 pfu of vaccine mixture, which is effective against pre-existing immunity against adenovirus. In a study to find the minimum dose with vaccine efficacy, the 106 pfu of vaccine mixture showed higher antibody titers to the nucleoprotein than did the same dose of rAd/NP alone in the serum of immunized mice. The 106 pfu of vaccine mixture overcame the morbidity and mortality of mice against the lethal dose of pH1N1, H3N2, and H5N1 influenza infections. No noticeable side effects were observed in single and repeated toxicity studies. We found that the mucosal administration of adenovirus-based universal influenza vaccine has both efficacy and safety, and can provide cross-protection against various influenza infections even at doses lower than those previously known to be effective.

Nucleoprotein as a Promising Antigen for Broadly Protective Influenza Vaccines

Annual vaccination is considered as the main preventive strategy against seasonal influenza. Due to the highly variable nature of major viral antigens, such as hemagglutinin (HA) and neuraminidase (NA), influenza vaccine strains should be regularly updated to antigenically match the circulating viruses. The influenza virus nucleoprotein (NP) is much more conserved than HA and NA, and thus seems to be a promising target for the design of improved influenza vaccines with broad cross-reactivity against antigenically diverse influenza viruses. Traditional subunit or recombinant protein influenza vaccines do not contain the NP antigen, whereas live-attenuated influenza vaccines (LAIVs) express the viral NP within infected cells, thus inducing strong NP-specific antibodies and T-cell responses. Many strategies have been explored to design broadly protective NP-based vaccines, mostly targeted at the T-cell mode of immunity. Although the NP is highly conserved, it still undergoes slow evolutionary changes due to selective immune pressure, meaning that the particular NP antigen selected for vaccine design may have a significant impact on the overall immunogenicity and efficacy of the vaccine candidate. In this review, we summarize existing data on the conservation of the influenza A viral nucleoprotein and review the results of preclinical and clinical trials of NP-targeting influenza vaccine prototypes, focusing on the ability of NP-specific immune responses to protect against diverse influenza viruses.

Intranasal delivery of an adenovirus-vector vaccine co-expressing a modified spike protein and a genetic adjuvant confers lasting mucosal immunity against SARS-CoV-2

The ongoing COVID-19 pandemic caused by SARS-CoV-2 infection has threatened global health. Since the first case of infection was reported in December 2019, SARS-CoV-2 has rapidly spread worldwide and caused millions of deaths. As vaccination is the best way to protect the host from invading pathogens, several vaccines have been developed to prevent the infection of SARS-CoV-2, saving numerous lives thus far. However, SARS-CoV-2 constantly changes its antigens, resulting in escape from vaccine-induced protection, and the longevity of immunity induced by vaccines remains an issue. Additionally, traditional intramuscular COVID-19 vaccines are insufficient at evoking mucosal-specific immune responses. Because the respiratory tract is the primary route of SARS-CoV-2 entry, the need for mucosal vaccines is strong. Using an adenoviral (Ad) vector platform, we generated Ad5-S.Mod, a recombinant COVID-19 vaccine that encodes modified-spike (S) antigen and the genetic adjuvant human CXCL9. Intranasal delivery of Ad5-S.Mod elicited superior airway humoral and T-cell responses over traditional intramuscular vaccines and protected mice from lethal SARS-CoV-2 infection. cDC1 cells were required for the generation of antigen-specific CD8⁺ T-cell responses and CD8⁺ tissue-resident memory T-cell development in intranasal Ad5-S.Mod vaccinated mice. Furthermore, we confirmed the efficacy of the intranasal Ad5-S.Mod vaccine in terms of transcriptional changes and identified lung macrophages as a key supporter of maintenance of lung-resident memory T and B cells. Our study demonstrates Ad5-S.Mod has the potential to confer protective immunity against SARS-CoV-2 and that lung macrophages support the maintenance of vaccine-induced tissue-resident memory lymphocytes.

Development of a pentavalent broadly protective nucleoside-modified mRNA vaccine against influenza B viruses

Messenger RNA (mRNA) vaccines represent a new, effective vaccine platform with high capacity for rapid development. Generation of a universal influenza virus vaccine with the potential to elicit long-lasting, broadly cross-reactive immune responses is a necessity for reducing influenza-associated morbidity and mortality. Here we focus on the development of a universal influenza B virus vaccine based on the lipid nanoparticle-encapsulated nucleoside-modified mRNA (mRNA-LNP) platform. We evaluate vaccine candidates based on different target antigens that afford protection against challenge with ancestral and recent influenza B viruses from both antigenic lineages. A pentavalent vaccine combining all tested antigens protects mice from morbidity at a very low dose of 50 ng per antigen after a single vaccination. These findings support the further advancement of nucleoside-modified mRNA-LNPs expressing multiple conserved antigens as universal influenza virus vaccine candidates.

The public health concern caused by influenza B virus is often overlooked, yet represents a significant global burden. Here, the authors evaluate the cellular and humoral immune responses of multivalent vaccine candidates, based on the lipid nanoparticle-encapsulated nucleoside-modified mRNA platform, and demonstrate protection of mice from challenge with a broad panel of influenza B viruses.

Layered protein nanoparticles containing influenza B HA stalk induced sustained cross-protection against viruses spanning both viral lineages

The influenza epidemics pose a significant threat to public health. Of them, type B influenza coincided with several severe flu outbreaks. The efficacy of the current seasonal flu vaccine is limited due to the antigenicity changes of circulating strains. In this study, we generated structure-stabilized HA stalk antigens from influenza B and fabricated double-layered protein nanoparticles as universal influenza B vaccine candidates. In vitro studies found that the resulting protein nanoparticles were effectively taken up to activate dendritic cells. Nanoparticle immunization induced broadly reactive immune responses conferring robust and sustained cross-immune protection against influenza B virus strains of both lineages. The results reveal the potential of layered protein nanoparticles incorporated with structure-stabilized constant antigens as a universal influenza vaccine with improved immune protective potency and breadth.

Progress towards the Development of a Universal Influenza Vaccine

Influenza viruses are responsible for millions of cases globally and significantly threaten public health. Since pandemic and zoonotic influenza viruses have emerged in the last 20 years and some of the viruses have resulted in high mortality in humans, a universal influenza vaccine is needed to provide comprehensive protection against a wide range of influenza viruses. Current seasonal influenza vaccines provide strain-specific protection and are less effective against mismatched strains. The rapid antigenic drift and shift in influenza viruses resulted in time-consuming surveillance and uncertainty in the vaccine protection efficacy. Most recent universal influenza vaccine studies target the conserved antigen domains of the viral surface glycoproteins and internal proteins to provide broader protection. Following the development of advanced vaccine technologies, several innovative strategies and vaccine platforms are being explored to generate robust cross-protective immunity. This review provides the latest progress in the development of universal influenza vaccines.

Cross-Protection Induced by Virus-like Particles Derived from the Influenza B Virus

The mismatch between the circulating influenza B virus (IBV) and the vaccine strain contributes to the rapid emergence of IBV infection cases throughout the globe, which necessitates the development of effective vaccines conferring broad protection. Here, we generated influenza B virus-like particle (VLP) vaccines expressing hemagglutinin, neuraminidase, or both antigens derived from the influenza B virus (B/Washington/02/2019 (B/Victoria lineage)-like virus, B/Phuket/3073/2013 (B/Yamagata lineage)-like virus. We found that irrespective of the derived antigen lineage, immunizing mice with the IBV VLPs significantly reduced lung viral loads, minimized bodyweight loss, and ensured 100% survival upon Victoria lineage virus B/Colorado/06/2017 challenge infection. These results were closely correlated with the vaccine-induced antibody responses and HI titer in sera, IgG, IgA antibody responses, CD4+ and CD8+ T cell responses, germinal center B cell responses, and inflammatory cytokine responses in the lungs. We conclude that hemagglutinin, neuraminidase, or both antigen-expressing VLPs derived from these influenza B viruses that were circulating during the 2020/21 season provide cross-protections against mismatched Victoria lineage virus (B/Colorado/06/2017) challenge infections.

Influenza B: Prospects for the Development of Cross-Protective Vaccines

In this review, we analyze the epidemiological and ecological features of influenza B, one of the most common and severe respiratory infections. The review presents various strategies for cross-protective influenza B vaccine development, including recombinant viruses, virus-like particles, and recombinant proteins. We provide an overview of viral proteins as cross-protective vaccine targets, along with other updated broadly protective vaccine strategies. The importance of developing such vaccines lies not only in influenza B prevention, but also in the very attractive prospect of eradicating the influenza B virus in the human population.

Reduction of Influenza A Virus Transmission in Mice by a Universal Intranasal Vaccine Candidate is Long-Lasting and Does Not Require Antibodies

Vaccination against influenza virus infection can protect the vaccinee and also reduce transmission to contacts. Not all types of vaccines induce sterilizing immunity via neutralizing antibodies; some instead permit low-level, transient infection. There has been concern that infection-permissive influenza vaccines may allow continued spread in the community despite minimizing symptoms in the vaccinee. We have explored that issue for a universal influenza vaccine candidate that protects recipients by inducing T cell responses and nonneutralizing antibodies. Using a mouse model, we have shown previously that an adenoviral vectored vaccine expressing nucleoprotein (NP) and matrix 2 (M2) provides broad protection against diverse strains and subtypes of influenza A viruses and reduces transmission to contacts in an antigen-specific manner. Here, we use this mouse model to further explore the mechanism and features of that reduction in transmission. Passive immunization did not reduce transmission from infected donors to naive contact animals to whom passive serum had been transferred. Vaccination of antibody-deficient mIgTg-J_HD^-/- mice, which have intact T cell responses and antigen presentation, reduced transmission in an antigen-specific manner, despite the presence of some virus in the lungs and nasal wash, pointing to a role for cellular immunity. Vaccination at ages ranging from 8 to 60 weeks was able to achieve reduction in transmission. Finally, the immune-mediated reduction in transmission persisted for at least a year after a single-dose intranasal vaccination. Thus, this infection-permissive vaccine reduces virus transmission in a long-lasting manner that does not require antibodies. IMPORTANCE Universal influenza virus vaccines targeting antigens conserved among influenza A virus strains can protect from severe disease but do not necessarily prevent infection. Despite allowing low-level infection, intranasal immunization with adenovirus vectors expressing the conserved antigens influenza nucleoprotein (A/NP) and M2 reduces influenza virus transmission from vaccinated to unvaccinated contact mice. Here, we show that antibodies are not required for this transmission reduction, suggesting a role for T cells. We also show that transmission blocking could be achieved in recipients of different ages and remained effective for at least a year following a single-dose vaccination. Such vaccines could have major public health impacts by limiting viral transmission in the community.

The Role of Nucleoprotein in Immunity to Human Negative-Stranded RNA Viruses—Not Just Another Brick in the Viral Nucleocapsid

Negative-stranded RNA viruses (NSVs) are important human pathogens, including emerging and reemerging viruses that cause respiratory, hemorrhagic and other severe illnesses. Vaccine design traditionally relies on the viral surface glycoproteins. However, surface glycoproteins rarely elicit effective long-term immunity due to high variability. Therefore, an alternative approach is to include conserved structural proteins such as nucleoprotein (NP). NP is engaged in myriad processes in the viral life cycle: coating and protection of viral RNA, regulation of transcription/replication processes and induction of immunosuppression of the host. A broad heterosubtypic T-cellular protection was ascribed very early to this protein. In contrast, the understanding of the humoral immunity to NP is very limited in spite of the high titer of non-neutralizing NP-specific antibodies raised upon natural infection or immunization. In this review, the data with important implications for the understanding of the role of NP in the immune response to human NSVs are revisited. Major implications of the elicited T-cell immune responses to NP are evaluated, and the possible multiple mechanisms of the neglected humoral response to NP are discussed. The intention of this review is to remind that NP is a very promising target for the development of future vaccines.

Development of a Mouse Model to Explore CD4 T Cell Specificity, Phenotype, and Recruitment to the Lung after Influenza B Infection

The adaptive T cell response to influenza B virus is understudied, relative to influenza A virus, for which there has been considerable attention and progress for many decades. Here, we have developed and utilized the C57BL/6 mouse model of intranasal infection with influenza B (B/Brisbane/60/2008) virus and, using an iterative peptide discovery strategy, have identified a series of robustly elicited individual CD4 T cell peptide specificities. The CD4 T cell repertoire encompassed at least eleven major epitopes distributed across hemagglutinin, nucleoprotein, neuraminidase, and non-structural protein 1 and are readily detected in the draining lymph node, spleen, and lung. Within the lung, the CD4 T cells are localized to both lung vasculature and tissue but are highly enriched in the lung tissue after infection. When studied by flow cytometry and MHC class II: peptide tetramers, CD4 T cells express prototypical markers of tissue residency including CD69, CD103, and high surface levels of CD11a. Collectively, our studies will enable more sophisticated analyses of influenza B virus infection, where the fate and function of the influenza B-specific CD4 T cells elicited by infection and vaccination can be studied as well as the impact of anti-viral reagents and candidate vaccines on the abundance, functionality, and localization of the elicited CD4 T cells.

A "Prime and Deploy" Strategy for Universal Influenza Vaccine Targeting Nucleoprotein Induces Lung-Resident Memory CD8 T cells

Lung-resident memory T cells (T_RM) play an essential role in protecting against pulmonary virus infection. Parenteral administration of DNA vaccine is generally not sufficient to induce lung CD8 T_RM cells. This study investigates whether intramuscularly administered DNA vaccine expressing the nucleoprotein (NP) induces lung T_RM cells and protects against the influenza B virus. The results show that DNA vaccination poorly generates lung T_RM cells and massive secondary effector CD8 T cells entering the lungs after challenge infection do not offer sufficient protection. Nonetheless, intranasal administration of non-replicating adenovirus vector expressing no Ag following priming DNA vaccination deploys NP-specific CD8 T_RM cells in the lungs, which subsequently offers complete protection. This novel 'prime and deploy' strategy could be a promising regimen for a universal influenza vaccine targeting the conserved NP Ag.

Universal influenza vaccine based on conserved antigens provides long-term durability of immune responses and durable broad protection against diverse challenge virus strains in mice

Current influenza vaccines rely on inducing antibody responses to the rapidly evolving hemagglutinin (HA) and neuraminidase (NA) proteins, and thus need to be strain-matched. However, predictions of strains that will circulate are imperfect, and manufacturing of new vaccines based on them takes months. As an alternative, universal influenza vaccines target highly conserved antigens. In proof of concept studies of universal vaccine candidates in animal models challenge is generally conducted only a short time after vaccination, but protective immunity lasting far longer is important for the intended public health impact. We address the challenge of providing long-term protection. We demonstrate here broad, powerful, and long-lasting immune protection for a promising universal vaccine candidate. A single intranasal dose of recombinant adenoviruses (rAd) expressing influenza A nucleoprotein (A/NP) and matrix 2 (M2) was used. Extending our previous studies of this type of vaccine, we show that antibody and T-cell responses persist for over a year without boosting, and that protection against challenge persists a year after vaccination and remains broad, covering both group 1 and 2 influenza A viruses. In addition, we extend the work to influenza B. Immunization with influenza B nucleoprotein (B/NP)-rAd also gives immune responses that last a year without boosting and protect against challenge with influenza B viruses of mismatched HA lineages. Despite host immunity to adenoviral antigens, effective readministration is possible a year after primary vaccination, as shown by successful immunization to a transgene product the animals had not seen before. Protection against challenge with divergent and highly pathogenic A/H7N9 virus was weaker but was enhanced by a second dose of vaccine. Thus, this mucosal vaccination to conserved influenza antigens confers very long-lasting immune protection in animals against a broad range of influenza A and B viruses.

Invaplex functions as an intranasal adjuvant for subunit and DNA vaccines co-delivered in the nasal cavity of nonhuman primates

Development of intranasal vaccines for HIV-1 and other mucosal pathogens has been hampered by the lack of adjuvants that can be given safely to humans. We have found that an intranasal Shigella vaccine (Invaplex) which is well tolerated in humans can also function as an adjuvant for intranasal protein and DNA vaccines in mice. To determine whether Invaplex could potentially adjuvant similar vaccines in humans, we simultaneously administered a simian immunodeficiency virus (SIV) envelope (Env) protein and DNA encoding simian-human immunodeficiency virus (SHIV) with or without Invaplex in the nasal cavity of female rhesus macaques. Animals were intranasally boosted with adenoviral vectors expressing SIV env or gag,pol to evaluate memory responses. Anti-SIV antibodies in sera and nasal, genital tract and rectal secretions were quantitated by ELISA. Intracellular cytokine staining was used to measure Th1-type T cells in blood. Macaques given DNA/protein immunizations with 0.5 mg Invaplex developed greater serum IgG, nasal IgA and cervicovaginal IgA responses to SIV Env and SHIV Gag,Pol proteins when compared to non-adjuvanted controls. Rectal IgA responses to Env were only briefly elevated and not observed to Gag,Pol. Invaplex increased frequencies of IFNγ-producing CD4 and CD8 T cells to the Env protein, but not T cell responses induced by the DNA. Ad-SIV boosting increased Env-specific polyfunctional T cells and Env- and Gag,Pol-specific antibodies in serum and all secretions. The data suggest that Invaplex could be highly effective as an adjuvant for intranasal protein vaccines in humans, especially those intended to prevent infections in the genital or respiratory tract.

Adenovirus Vectors: Excellent Tools for Vaccine Development

Adenovirus was originally used as a vector for gene therapy. In recent years, with the development of the next-generation vectors with increased safety and high immunogenicity to transgene products, its utility as a vaccine vector has continued to increase. Adenovirus-based vaccines are currently being tested not only to prevent various infectious diseases but also to be applied as cancer vaccines. In this review, I discuss the innate and adaptive aspects of the immunological characteristics of adenovirus vectors and further examine the current status of advanced adenovirus-based vaccine development. Various methods that can overcome the limitations of currently used adenoviruses as vaccine vehicles are also discussed. Through this study, I hope that vaccine development using adenovirus vectors will be expedited and more successful.

Progress in the Development of Universal Influenza Vaccines

Influenza viruses pose a significant threat to human health. They are responsible for a large number of deaths annually and have a serious impact on the global economy. There are numerous influenza virus subtypes, antigenic variations occur continuously, and epidemic trends are difficult to predict—all of which lead to poor outcomes of routine vaccination against targeted strain subtypes. Therefore, the development of universal influenza vaccines still constitutes the ideal strategy for controlling influenza. This article reviews the progress in development of universal vaccines directed against the conserved regions of hemagglutinin (HA), neuraminidase (NA), and other structural proteins of influenza viruses using new technologies and strategies with the goals of enhancing our understanding of universal influenza vaccines and providing a reference for research into the exploitation of natural immunity against influenza viruses.

Insights from the comparison of genomic variants from two influenza B viruses grown in the presence of human antibodies in cell culture

Understanding the extent and limitation of viral genome evolution can provide insight about potential drug and vaccine targets. Influenza B Viruses (IBVs) infect humans in a seasonal manner and causes significant morbidity and mortality. IBVs are negative-sense single-stranded RNA viruses with a segmented genome and can be divided into two antigenically distinct lineages. The two lineages have been circulating and further evolving for almost four decades. The immune response to IBV infection can lead to antibodies that target the strain causing the infection. Some antibodies are cross-reactive and are able to bind strains from both lineages but, because of antigenic drift and immunodominance, both lineages continue to evolve and challenge human health. Here we investigate changes in the genomes of an IBVs from each lineage after passage in tissue culture in the presence of human sera containing polyclonal antibodies directed toward antigenically and temporally distinct viruses. Our previous analysis of the fourth segment, which encodes the major surface protein HA, revealed a pattern of change in which signature sequences from one lineage mutated to the signature sequences of the other lineage. Here we analyze genes from the other genomic segments and observe that most of the quasispecies’ heterogeneity occurs at the same loci in each lineage. The nature of the variants at these loci are investigated and possible reasons for this pattern are discussed. This work expands our understanding of the extent and limitations of genomic change in IBV.

Innate and adaptive immunity toward influenza B viruses

Despite annual vaccination, influenza B viruses (IBV) cause significant disease with substantial health and socio-economic impacts. Novel vaccination strategies inducing broadly protective and long-lasting immunity across IBV lineages are needed. However, as immune responses toward IBV are largely understudied, host–virus interactions and protective immune mechanisms need to be defined to rationally design such vaccines. Here, we summarize recent advances in our understanding of immunological mechanisms underpinning protection from IBV. We discuss how innate antiviral host factors inhibit IBV replication and the ways by which IBV escapes such restriction. We review the specificity of broadly cross-reactive antibodies and universal T cells, and the mechanisms by which they mediate protection. We highlight important knowledge gaps needing to be addressed to design improved IBV vaccines.

Superior immune responses induced by intranasal immunization with recombinant adenovirus-based vaccine expressing full-length Spike protein of Middle East respiratory syndrome coronavirus

Middle East respiratory syndrome coronavirus (MERS-CoV) causes an acute and severe lower respiratory illness as well as vomiting, diarrhea, and renal failure. Because no licensed MERS-CoV vaccines are currently available, preventive and therapeutic measures are urgently needed. The surface spike (S) glycoprotein of MERS-CoV, which binds to the cellular receptor dipeptidyl peptidase 4 (DPP4), is considered as a major target for MERS-CoV vaccine development. Here, we designed recombinant replication-deficient adenovirus-based vaccines expressing the N-terminal domain (rAd/NTD) and receptor-binding domain (rAd/RBD) of the MERS-CoV S1 subunit and full-length Spike protein (rAd/Spike). We found that immunization with candidate vaccines via intranasal route induced S1-specific IgG antibodies and neutralizing antibodies against MERS spike pseudotyped virus. Especially, rAd/Spike induced the highest neutralizing antibody titer and the strongest cytokine-induced T cell responses among the three candidate vaccines. To compare the immune responses induced by different administration routes, rAd/Spike was administered via intranasal, sublingual, or intramuscular route. All these administration routes exhibited neutralizing effects in the serum. MERS-CoV-specific neutralizing IgA antibodies in the bronchoalveolar lavage fluid were only induced by intranasal and sublingual administration but not by intramuscular administration. Intranasal administration with rAd/Spike also created resident memory CD8 T cells in the airway and lung parenchyma. Taken together, our results showed that both the humoral and cellular immune responses are highly induced by rAd/Spike administration, suggesting that rAd/Spike may confer protection against MERS-CoV infection.

Nucleoprotein vaccine induces cross-protective cytotoxic T lymphocytes against both lineages of influenza B virus

Purpose

The influenza B virus diverges into two antigenically distinct lineages: B/Yamagata and B/Victoria. Influenza B is the dominant circulating virus during some influenza seasons, and recent data demonstrated that influenza A and B infection similarly cause severe clinical symptoms in hospitalized patients. Nucleoprotein (NP) is a good target for a universal influenza vaccine. This study investigated whether NP epitope variation within two lineages affects the dominant cytotoxic T lymphocyte (CTL) responses induced by vaccination and the resultant protective immunity.

Materials and Methods

The NP of B/Yamagata/16/1988, the representative strain of the Yamagata lineage, includes a dominant CTL epitope, FSPIRITFL, while B/Shangdong/7/1997 from the Victoria lineage has one amino acid difference in this sequence, FSPIRVTFL. Two recombinant replication-deficient adenovirus (rAd)-vectored vaccines expressing either NP were prepared (rAd/B-NP(I) and rAd/B-NP(V), respectively) and administered to BALB/c mice intranasally. To examine the efficacy of vaccination, antibody responses, CTL responses, and morbidity/mortality after challenge were measured.

Results

Both vaccines induce similar antibody and CD8 T-cell responses cross-reacting to both epitopes, and also confer cross-protection against both lineages regardless of amino acid difference.

Conclusion

The rAd-vectored vaccine expressing the NP could be developed as universal influenza B vaccine which provides broader protection.