Adenoviral-vectored universal influenza vaccines administered intranasally reduce lung inflammatory responses upon viral challenge 15 months post-vaccination.

IMPORTANCE: Vaccines targeting highly conserved proteins can protect broadly against diverse viral strains. When a vaccine is administered to the respiratory tract, protection against disease is especially powerful. However, it is important to establish that this approach is safe. When vaccinated animals later encounter viruses, does reactivation of powerful local immunity, including T cell responses, damage the lungs? This study investigates the safety of mucosal vaccination of the respiratory tract. Non-replicating adenoviral vaccine vectors expressing conserved influenza virus proteins were given intranasally. This vaccine-induced protection persists for at least 15 months. Vaccination did not exacerbate inflammatory responses or tissue damage upon influenza virus infection. Instead, vaccination with nucleoprotein reduced cytokine responses and histopathology, while neutrophil and T cell responses resolved earlier. The results are promising for safe vaccination at the site of infection and thus have implications for the control of influenza and other respiratory viruses.

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-JHD-/- 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.

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.

Effect of an Adenovirus-Vectored Universal Influenza Virus Vaccine on Pulmonary Pathophysiology in a Mouse Model.

Current influenza vaccines, live attenuated or inactivated, do not protect against antigenically novel influenza A viruses (IAVs) of pandemic potential, which has driven interest in the development of universal influenza vaccines. Universal influenza vaccine candidates targeting highly conserved antigens of IAV nucleoprotein (NP) are promising as vaccines that induce T cell immunity, but concerns have been raised about the safety of inducing robust CD8 T cell responses in the lungs. Using a mouse model, we systematically evaluated effects of recombinant adenovirus vectors (rAd) expressing IAV NP (A/NP-rAd) or influenza B virus (IBV) NP (B/NP-rAd) on pulmonary inflammation and function after vaccination and following live IAV challenge. After A/NP-rAd or B/NP-rAd vaccination, female mice exhibited robust systemic and pulmonary vaccine-specific B cell and T cell responses and experienced no morbidity (e.g., body mass loss). Both in vivo pulmonary function testing and lung histopathology scoring revealed minimal adverse effects of intranasal rAd vaccination compared with unvaccinated mice. After IAV challenge, A/NP-rAd-vaccinated mice experienced significantly less morbidity, had lower pulmonary virus titers, and developed less pulmonary inflammation than unvaccinated or B/NP-rAd-vaccinated mice. Based on analysis of pulmonary physiology using detailed testing not previously applied to the question of T cell damage, mice protected by vaccination also had better lung function than controls. Results provide evidence that, in this model, adenoviral universal influenza vaccine does not damage pulmonary tissue. In addition, adaptive immunity, in particular, T cell immunity in the lungs, does not cause damage when restimulated but instead mitigates pulmonary damage following IAV infection.IMPORTANCE Respiratory viruses can emerge and spread rapidly before vaccines are available. It would be a tremendous advance to use vaccines that protect against whole categories of viruses, such as universal influenza vaccines, without the need to predict which virus will emerge. The nucleoprotein (NP) of influenza virus provides a target conserved among strains and is a dominant T cell target. In animals, vaccination to NP generates powerful T cell immunity and long-lasting protection against diverse influenza strains. Concerns have been raised, but not evaluated experimentally, that potent local T cell responses might damage the lungs. We analyzed lung function in detail in the setting of such a vaccination. Despite CD8 T cell responses in the lungs, lungs were not damaged and functioned normally after vaccination alone and were protected upon subsequent infection. This precedent provides important support for vaccines based on T cell-mediated protection, currently being considered for both influenza and SARS-CoV-2 vaccines.

The effect of respiratory viruses on immunogenicity and protection induced by a candidate universal influenza vaccine in mice.

Current approaches to influenza control rely on vaccines matched to viruses in circulation. Universal influenza vaccines would offer the advantage of providing broad protection against diverse strains of influenza virus. Candidate universal vaccines are developed using model systems, often testing in naïve animals. Yet the human population is not naïve, having varied immune histories that include exposure to viruses. We studied a candidate universal influenza vaccine (replication deficient adenoviruses expressing the conserved influenza A antigens NP and M2 [A/NP+M2-rAd]) given intranasally, the route previously shown to be most effective. To model recipients exposed to viruses, we used mice given rhinovirus (RV1B), respiratory syncytial virus (RSV-A2), influenza B virus, or influenza A virus before or after universal influenza vaccine. Vaccine performance was assessed by measuring immune responses to NP and M2, and monitoring weight loss and survival following influenza A challenge. Prior influenza A virus infection enhanced the response to the vaccine by priming to conserved influenza A antigens. RSV-A2 or RV1B had no effect on antibody responses to NP and M2 in serum. None of the viruses inhibited the ability of the vaccine to protect against influenza A virus challenge. The study demonstrates that the usefulness of this universal vaccine is not confined to the immunologically naïve and supports possible use in a human population with a varied history of respiratory infections.

Reduction of influenza virus transmission from mice immunized against conserved viral antigens is influenced by route of immunization and choice of vaccine antigen.

Transmission of influenza virus between susceptible hosts mediates spread of infection in the population and can occur via direct-contact or airborne routes. Mathematical models suggest that vaccines that reduce viral transmission from infected individuals could substantially reduce viral spread in an epidemic or pandemic, even if they do not completely protect against infection. Vaccines targeting conserved nucleoprotein (A/NP) and matrix 2 (M2) antigens of influenza virus do not completely prevent infection upon influenza virus challenge, but reduce viral replication, morbidity, and mortality. Using a mouse model of influenza virus transmission, we have previously shown that immunization with recombinant adenovirus vectors expressing the combination of A/NP and M2 can reduce viral transmission to unimmunized contacts. Here we demonstrate that transmission reduction is more effective when mice are immunized against A/NP and M2 intranasally than via the intramuscular route. We show that immunization against the combination of A/NP and M2 is more effective at reducing transmission than either antigen alone, with a clear hierarchy of effectiveness (A/NP + M2 > A/NP > M2). Transmission reduction is seen to a similar degree under both direct-contact and airborne transmission conditions. Finally, using seroconversion as an indicator of infection, we show that immunizing contact mice against A/NP and M2 prevents a significant fraction (∼50%) from becoming infected under direct-contact conditions. These findings suggest that when strain-matched vaccines are unavailable, conserved antigen vaccines could not only reduce severity of disease in vaccinated individuals but also limit the spread of virus during influenza epidemics or pandemics.

Conventional influenza vaccines influence the performance of a universal influenza vaccine in mice.

Universal influenza vaccines are designed to protect against diverse strains of influenza virus. Preclinical testing of new vaccine candidates is usually done in naïve animals, despite intended use in the human population with its varied immune history including responses to previous vaccinations. As an approach more relevant to human use, we tested a candidate universal influenza vaccine in mice with a history of conventional vaccination. Female BALB/c mice were given two intramuscular doses of inactivated influenza vaccine (IIV) or diphtheria and tetanus toxoids vaccine (DT), one month apart. Another group was given two intranasal doses of live attenuated influenza virus (LAIV). One month after the second dose, mice were given the universal influenza vaccine: recombinant adenoviruses expressing influenza A nucleoprotein (A/NP) and matrix 2 (M2) (A/NP + M2-rAd). Immune responses to universal vaccine antigens A/NP and M2 were assessed by ELISA and interferon-γ ELISPOT. Protection was tested by challenge with mouse-adapted A/FM/1/47 (H1N1) and monitoring for weight loss and survival. Universal vaccine performance was enhanced, inhibited or unaffected by particular prior vaccinations. Mice given Afluria IIV and LAIV had greater antibody and T-cell response to A/NP than mice without prior vaccination, providing examples of enhanced A/NP + M2-rAd performance. Though Fluvirin IIV partially inhibited, the universal vaccine still provided considerable protection unlike conventional vaccination. Fluzone IIV and DT had no effect on A/NP + M2-rAd performance. Thus our results demonstrate that universal vaccine candidate A/NP + M2-rAd was at least partially effective in mice with diverse prior histories. However, the degree of protection and nature of the immune responses may be affected by a history of conventional vaccination and suggests that performance in humans would be influenced by immune history.

Surveillance Study of Influenza Occurrence and Immunity in a Wisconsin Cohort During the 2009 Pandemic.

BACKGROUND: Antibody and T-cell immunity to conserved influenza virus antigens can protect animals against infection with diverse influenza strains. Although immunity against conserved antigens occurs in humans, whether such responses provide cross-protection in humans and could be harnessed as the basis for universal influenza vaccines is controversial. The 2009 pandemic provided an opportunity to investigate whether pre-existing cross-reactive immunity affected susceptibility to infection. METHODS: In 2009, we banked sera and peripheral blood mononuclear cells (PBMC) from blood donors, then monitored them for pandemic influenza infection (pH1N1) by polymerase chain reaction or seroconversion. Antibodies to hemagglutinin (HA), neuraminidase (NA), nucleoprotein (NP), matrix 2 (M2), and HA-pseudotypes were measured in sera. T-cell inteferon-γ enzyme-linked immunospot responses were measured in PBMC. RESULTS: There were 13 infections in 117 evaluable donors. Pre-existing T-cell reactivity to pH1N1 was substantial (of 153 donors tested, 146 had >100 spot-forming cells/106 cells). Antibodies reactive with pH1N1 were common: anti-NP (all donors) and anti-M2 (44% of donors). Pseudotype-neutralizing antibodies to H1 were detected, but not to highly conserved HA epitopes. Unexpectedly, donors with symptomatic pH1N1 infection had sharp rises in HA pseudotype-neutralizing antibodies, not only pH1N1 but also against multiple seasonal H1s. In addition, an exploratory study of a T-cell marker (response to NP418-426) identified probable infection missed by standard criteria. CONCLUSIONS: Although the number of infections was inadequate for conclusions about mechanisms of protection, this study documents the wide variety of pre-existing, cross-reactive, humoral and cellular immune responses to pandemic influenza virus antigens in humans. These responses can be compared with results of other studies and explored in universal influenza vaccine studies.

Age Dependence of Immunity Induced by a Candidate Universal Influenza Vaccine in Mice.

Influenza has a major impact on the elderly due to increased susceptibility to infection with age and poor response to current vaccines. We have studied universal influenza vaccine candidates based on influenza A nucleoprotein and matrix 2 (A/NP+M2). Long-lasting protection against influenza virus strains of divergent subtypes is induced, especially with mucosal immunization. Here, we tested universal vaccination in BALB/c mice of different ages. Vaccination used intramuscular DNA priming to A/NP+M2 followed by intranasal (i.n.) boosting with recombinant adenoviruses (rAd) expressing the same antigens, or only A/NP+M2-rAd given i.n. Antigen-specific systemic antibody responses were induced in young, middle-aged, and elderly mice (2, 11-17, and 20 months old, respectively), but decreased with age. Antibody responses in bronchoalveolar lavage (BAL) were detected only in young mice. Antigen-specific T cell responses were seen in young and middle-aged but not elderly mice. A/NP+M2 vaccination by the two regimens above protected against stringent challenge in young and middle-aged mice, but not in elderly mice. However, mice vaccinated with A/NP-rAd or A/M2-rAd during their youth were partially protected against challenge 16 months later when they were elderly. In addition, a regimen of two doses of A/NP+M2-rAd given i.n. one month apart beginning in old age protected elderly mice against stringent challenge. This study highlights the potential benefit of cross-protective vaccines through middle age, and suggests that their performance might be enhanced in elderly individuals who had been exposed to influenza antigens early in life, as most humans have been, or by a two-dose rAd regimen given later in life.

Mucosal immunization with a candidate universal influenza vaccine reduces virus transmission in a mouse model.

UNLABELLED: Pandemic influenza is a major public health concern, but conventional strain-matched vaccines are unavailable early in a pandemic. Candidate "universal" vaccines targeting the viral antigens nucleoprotein (NP) and matrix 2 (M2), which are conserved among all influenza A virus strains and subtypes, could be manufactured in advance for use at the onset of a pandemic. These vaccines do not prevent infection but can reduce disease severity, deaths, and virus titers in the respiratory tract. We hypothesized that such immunization may reduce virus transmission from vaccinated, infected animals. To investigate this hypothesis, we studied mouse models for direct-contact and airborne transmission of H1N1 and H3N2 influenza viruses. We established conditions under which virus transmission occurs and showed that transmission efficiency is determined in part at the level of host susceptibility to infection. Our findings indicate that virus transmission between mice has both airborne and direct-contact components. Finally, we demonstrated that immunization with recombinant adenovirus vectors expressing NP and M2 significantly reduced the transmission of virus to cohoused, unimmunized mice in comparison to controls. These findings have broad implications for the impact of conserved-antigen vaccines, not only in protecting the vaccinated individual but also in protecting others by limiting influenza virus transmission and potentially reducing the size of epidemics. IMPORTANCE: Using a mouse model of influenza A virus transmission, we demonstrate that a candidate "universal" influenza vaccine both protects vaccinated animals from lethal infection and reduces the transmission of virus from vaccinated to nonvaccinated mice. This vaccine induces immunity against proteins conserved among all known influenza A virus strains and subtypes, so it could be used early in a pandemic before conventional strain-matched vaccines are available and could potentially reduce the spread of infection in the community.

Vaccination to conserved influenza antigens in mice using a novel Simian adenovirus vector, PanAd3, derived from the bonobo Pan paniscus.

Among approximately 1000 adenoviruses from chimpanzees and bonobos studied recently, the Pan Adenovirus type 3 (PanAd3, isolated from a bonobo, Pan paniscus) has one of the best profiles for a vaccine vector, combining potent transgene immunogenicity with minimal pre-existing immunity in the human population. In this study, we inserted into a replication defective PanAd3 a transgene expressing a fusion protein of conserved influenza antigens nucleoprotein (NP) and matrix 1 (M1). We then studied antibody and T cell responses as well as protection from challenge infection in a mouse model. A single intranasal administration of PanAd3-NPM1 vaccine induced strong antibody and T cell responses, and protected against high dose lethal influenza virus challenge. Thus PanAd3 is a promising candidate vector for vaccines, including universal influenza vaccines.

Intranasal administration of adeno-associated virus type 12 (AAV12) leads to transduction of the nasal epithelia and can initiate transgene-specific immune response.

A critical aspect in defining the utility of a vector for gene therapy applications is the cell tropism and biodistribution of the vector. Adeno-associated virus type 12 (AAV12) has several unique biological and immunological properties that could be exploited for gene therapy purposes, including a unique cell surface receptor, transduction of epithelial cells, and limited neutralization by pooled human antibodies. However, little is known about its cell tropism and biodistribution in vivo. In vivo biodistribution studies with AAV12 vectors encoding a cytomegalovirus promoted luciferase transgene indicated preferential transduction of the nasal epithelia which was not observed with AAV2-based vectors. Expression peaked 2 weeks postadministration, before decreasing to a persistent level. The level of neutralizing antibodies (Nab) induced was sevenfold lower for AAV12 than for AAV2, an advantage for use in repeat administration. Furthermore, vectors encoding influenza A nucleoprotein (NP), an antigen which has previously been shown to induce immune protection against challenge, resulted in generation of both anti-A/NP antibodies and lung anti-A/NP T cells. Our findings suggest further evaluation of AAV12 as a vector for gene therapy and as a potential nasal vaccine.

Cold-adapted influenza and recombinant adenovirus vaccines induce cross-protective immunity against pH1N1 challenge in mice.

BACKGROUND: The rapid spread of the 2009 H1N1 pandemic influenza virus (pH1N1) highlighted problems associated with relying on strain-matched vaccines. A lengthy process of strain identification, manufacture, and testing is required for current strain-matched vaccines and delays vaccine availability. Vaccines inducing immunity to conserved viral proteins could be manufactured and tested in advance and provide cross-protection against novel influenza viruses until strain-matched vaccines became available. Here we test two prototype vaccines for cross-protection against the recent pandemic virus. METHODOLOGY/PRINCIPAL FINDINGS: BALB/c and C57BL/6 mice were intranasally immunized with a single dose of cold-adapted (ca) influenza viruses from 1977 or recombinant adenoviruses (rAd) expressing 1934 nucleoprotein (NP) and consensus matrix 2 (M2) (NP+M2-rAd). Antibodies against the M2 ectodomain (M2e) were seen in NP+M2-rAd immunized BALB/c but not C57BL/6 mice, and cross-reacted with pH1N1 M2e. The ca-immunized mice did not develop antibodies against M2e. Despite sequence differences between vaccine and challenge virus NP and M2e epitopes, extensive cross-reactivity of lung T cells with pH1N1 peptides was detected following immunization. Both ca and NP+M2-rAd immunization protected BALB/c and C57BL/6 mice against challenge with a mouse-adapted pH1N1 virus. CONCLUSION/SIGNIFICANCE: Cross-protective vaccines such as NP+M2-rAd and ca virus are effective against pH1N1 challenge within 3 weeks of immunization. Protection was not dependent on recognition of the highly variable external viral proteins and could be achieved with a single vaccine dose. The rAd vaccine was superior to the ca vaccine by certain measures, justifying continued investigation of this experimental vaccine even though ca vaccine is already available. This study highlights the potential for cross-protective vaccines as a public health option early in an influenza pandemic.

Single-dose mucosal immunization with a candidate universal influenza vaccine provides rapid protection from virulent H5N1, H3N2 and H1N1 viruses.

BACKGROUND: The sudden emergence of novel influenza viruses is a global public health concern. Conventional influenza vaccines targeting the highly variable surface glycoproteins hemagglutinin and neuraminidase must antigenically match the emerging strain to be effective. In contrast, "universal" vaccines targeting conserved viral components could be used regardless of viral strain or subtype. Previous approaches to universal vaccination have required protracted multi-dose immunizations. Here we evaluate a single dose universal vaccine strategy using recombinant adenoviruses (rAd) expressing the conserved influenza virus antigens matrix 2 and nucleoprotein. METHODOLOGY/PRINCIPAL FINDINGS: In BALB/c mice, administration of rAd via the intranasal route was superior to intramuscular immunization for induction of mucosal responses and for protection against highly virulent H1N1, H3N2, or H5N1 influenza virus challenge. Mucosally vaccinated mice not only survived, but had little morbidity and reduced lung virus titers. Protection was observed as early as 2 weeks post-immunization, and lasted at least 10 months, as did antibodies and lung T cells with activated phenotypes. Virus-specific IgA correlated with but was not essential for protection, as demonstrated in studies with IgA-deficient animals. CONCLUSION/SIGNIFICANCE: Mucosal administration of NP and M2-expressing rAd vectors provided rapid and lasting protection from influenza viruses in a subtype-independent manner. Such vaccines could be used in the interval between emergence of a new virus strain and availability of strain-matched vaccines against it. This strikingly effective single-dose vaccination thus represents a candidate off-the-shelf vaccine for emergency use during an influenza pandemic.

Genetic control of immune responses to influenza A matrix 2 protein (M2).

Vaccines should protect genetically diverse populations. Therefore we tested the candidate "universal" influenza A matrix protein 2 (M2) vaccine in multiple mouse strains. Mice were primed with M2 DNA and boosted with M2 recombinant adenovirus (rAd). C57BL/6 (B6) mice developed no antibody or T-cell response to M2, while BALB/c responded strongly. CBA responses were intermediate. Both MHC and background genes influenced responsiveness. To improve low responses we immunized with adjuvanted peptide-carrier conjugates, or co-immunized with nucleoprotein (NP), which can augment T-cell help. The conjugate vaccine enhanced some outcomes but not others. Co-immunizing with NP improved outcomes over either NP or M2 immunizations alone. These results have implications for vaccination of genetically diverse populations.

Vaccination focusing immunity on conserved antigens protects mice and ferrets against virulent H1N1 and H5N1 influenza A viruses.

Immunization against conserved virus components induces broad, heterosubtypic protection against diverse influenza A viruses, providing a strategy for controlling unexpected outbreaks or pandemics until strain-matched vaccines become available. This study characterized immunization to nucleoprotein (NP) and matrix 2 (M2) by DNA priming followed by parenteral or mucosal boosting in mice and ferrets. DNA vaccination followed by boosting with antigen-matched recombinant adenovirus (rAd) or cold-adapted (ca) influenza virus provided robust protection against virulent H1N1 and H5N1 challenges. Compared to other boosts, mucosal rAd induced stronger IgA responses, more virus-specific activated T-cells in the lung, and better protection against morbidity following challenge even eight months post-boost. In ferrets, both mucosal and parenteral rAd boosting protected from lethal H5N1 challenge. These findings demonstrate potent protection by vaccination highly focused on conserved antigens and identify immune response measures in mice that differed among vaccinations and correlated with outcome.

Comparison of vaccines for induction of heterosubtypic immunity to influenza A virus: cold-adapted vaccine versus DNA prime-adenovirus boost strategies.

Influenza epidemics or pandemics can arise for which strain- or subtype-matched vaccines are unavailable. Heterosubtypic immunity (Het-I) targeting conserved influenza A antigens could reduce morbidity and mortality during preparation of matched vaccines. Various vaccines inducing Het-I in animals have been studied separately using different viruses and conditions, but effectiveness for inducing Het-I has not been directly compared. The present studies compared immunization with cold-adapted (ca) viruses to DNA prime-recombinant adenovirus (rAd) boost vaccination to conserved antigens nucleoprotein (NP), matrix-2 (M2), or A/NP+M2. Both ca and DNA-rAd vaccinations induced antibody and T cell responses, and protected against lethal H1N1 challenge. Only A/NP+M2 DNA-rAd protected against challenge with highly pathogenic A/Vietnam/1203/2004 (H5N1); ca vaccine did not. Existing ca vaccines may provide some Het-I, but experimental vaccination focusing on conserved antigens was more effective in this model for protection against a divergent, highly pathogenic virus.

Matrix protein 2 vaccination and protection against influenza viruses, including subtype H5N1.

Changes in influenza viruses require regular reformulation of strain-specific influenza vaccines. Vaccines based on conserved antigens provide broader protection. Influenza matrix protein 2 (M2) is highly conserved across influenza A subtypes. To evaluate its efficacy as a vaccine candidate, we vaccinated mice with M2 peptide of a widely shared consensus sequence. This vaccination induced antibodies that cross-reacted with divergent M2 peptide from an H5N1 subtype. A DNA vaccine expressing full-length consensus-sequence M2 (M2-DNA) induced M2-specific antibody responses and protected against challenge with lethal influenza. Mice primed with M2-DNA and then boosted with recombinant adenovirus expressing M2 (M2-Ad) had enhanced antibody responses that crossreacted with human and avian M2 sequences and produced T-cell responses. This M2 prime-boost vaccination conferred broad protection against challenge with lethal influenza A, including an H5N1 strain. Vaccination with M2, with key sequences represented, may provide broad protection against influenza A.

Protection against multiple influenza A subtypes by vaccination with highly conserved nucleoprotein.

Influenza epidemic and pandemic strains cannot be predicted with certainty. Current vaccines elicit antibodies effective against specific strains, but new strategies are urgently needed for protection against unexpected strains. DNA vaccines encoding conserved antigens protect animals against diverse subtypes, but their potency needs improvement. We tested DNA prime-recombinant adenoviral boost immunization to nucleoprotein (NP). Strong antibody and T cell responses were induced. Protection against challenge was T cell-dependent and substantially more potent than DNA vaccination alone. Importantly, vaccination protected against lethal challenge with highly pathogenic H5N1 virus. Thus, gene-based vaccination with NP may contribute to protective immunity against diverse influenza viruses through its ability to stimulate cellular immunity.

Protection against lethal influenza virus challenge by RNA interference in vivo.

Influenza virus infection is responsible for hundreds of thousands of deaths annually. Current vaccination strategies and antiviral drugs provide limited protection; therefore, new strategies are needed. RNA interference is an effective means of suppressing virus replication in vitro. Here we demonstrate that treatment with small interfering RNAs (siRNAs) specific for highly conserved regions of the nucleoprotein or acidic polymerase inhibits influenza A virus replication in vivo. Delivery of these siRNAs significantly reduced lung virus titers in infected mice and protected animals from lethal challenge. This protection was specific and not mediated by an antiviral IFN response. Moreover, influenza-specific siRNA treatment was broadly effective and protected animals against lethal challenge with highly pathogenic avian influenza A viruses of the H5 and H7 subtypes. These results indicate that RNA interference is promising for control of influenza virus infection, as well as other viral infections.