Safety and immunogenicity of adenovirus-vectored nasal and epicutaneous influenza vaccines in humans

Adenovirus-vectored drug-vaccine duo as a rapid-response tool for conferring seamless protection against influenza

Few other diseases exert such a huge toll of suffering as influenza. We report here that intranasal (i.n.) administration of E1/E3-defective (ΔE1E3) adenovirus serotype 5 (Ad5) particles rapidly induced an anti-influenza state as a means of prophylactic therapy which persisted for several weeks in mice. By encoding an influenza virus (IFV) hemagglutinin (HA) HA1 domain, an Ad5-HA1 vector conferred rapid protection as a prophylactic drug followed by elicitation of sustained protective immunity as a vaccine for inducing seamless protection against influenza as a drug-vaccine duo (DVD) in a single package. Since Ad5 particles induce a complex web of host responses, which could arrest influenza by activating a specific arm of innate immunity to impede IFV growth in the airway, it is conceivable that this multi-pronged influenza DVD may escape the fate of drug resistance that impairs the current influenza drugs.

Immune correlates of protection against influenza: challenges for licensure of seasonal and pandemic influenza vaccines, Miami, FL, USA, March 1-3, 2010

The emergence of a novel swine-origin pandemic influenza virus in 2009, together with the continuing circulation of highly pathogenic avian H5N1 viruses and the urgent global need to produce effective vaccines against such public health threats, has prompted a renewed interest in improving our understanding of the immune correlates of protection against influenza. As new influenza vaccine technologies, including non-HA based approaches and novel production platforms are developed and undergo clinical evaluation, it has become clear that existing immune correlates such as serum hemagglutination-inhibition antibodies may be unsuitable to estimate vaccine immunogenicity and protective efficacy of such vaccines. This International Society for Influenza and other Respiratory Virus Diseases (ISIRV) sponsored international meeting held in Miami, Florida USA on March 1-3, 2010, brought together scientists from industry, academia, and government agencies that develop and evaluate seasonal and pandemic influenza vaccines and scientists from regulatory authorities that approve them, to identify approaches to develop expanded immune correlates of protection to aid in vaccine licensure.

Evaluation of oral immunization with recombinant avian influenza virus HA1 displayed on the Lactococcus lactis surface and combined with the mucosal adjuvant cholera toxin subunit B

The development of safe and efficient avian influenza vaccines for human and animal uses is essential for preventing virulent outbreaks and pandemics worldwide. In this study, we constructed a recombinant (pgsA-HA1 gene fusion) Lactococcus lactis strain that expresses and displays the avian influenza virus HA1 antigens on its surface. The vectors were administered by oral delivery with or without the addition of cholera toxin subunit B (CTB). The resulting immune responses were analyzed, and the mice were eventually challenged with lethal doses of H5N1 viruses. Significant titers of hemagglutinin (HA)-specific serum IgG and fecal IgA were detected in the group that also received CTB. Cellular immunities were also shown in both cell proliferation and gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) assays. Most importantly, the mice that received the L. lactis pgsA-HA1 strain combined with CTB were completely protected from lethal challenge of the H5N1 virus. These findings support the further development of L. lactis-based avian influenza virus vaccines for human and animal uses.

The extent of the uptake of plasmid into the skin determines the immune responses induced by a DNA vaccine applied topically onto the skin

OBJECTIVES

Non-invasive immunization by application of plasmid DNA topically onto the skin is an attractive immunization approach. However, the immune responses induced are generally weak. Previously, we showed that the antibody responses induced by topical DNA vaccine are significantly enhanced when hair follicles in the application area are induced into the anagen (growth) stage by hair plucking. In the present study, we further investigated the mechanism of immune enhancement.

METHODS

Three different methods--hair plucking or treatment with retinoic acid (RA) or O-tetradecanoylphorbol-13-acetate (TPA)--were used to induce mice hair follicles into the anagen stage before they were dosed with a β-galactosidase-encoding plasmid, and the specific antibody responses induced were evaluated.

KEY FINDINGS

The hair-plucking method was more effective at enhancing the resultant antibody responses. Treatment with RA or TPA caused more damage to the skin and induced more severe local inflammation than hair plucking. However, hair plucking was most effective at enhancing the uptake or retention of the DNA in the application area.

CONCLUSIONS

The uptake of plasmid DNA in the application area correlated with the antibody responses induced by a topically applied DNA.

Strategies for preventing influenza: future perspectives in influenza vaccine technology

Prevention of influenza transmission and containment of epidemics and pandemics require effective strategies that can be efficiently and easily addressed to the whole population. Annual vaccination is undoubtedly the most effective way to provide protection against influenza infection. Numbers of vaccines are actually available for yearly immunisation. However, the continuous increasing demand for rapidly available vaccine doses for immunisation of a larger proportion of population represents the stimulus for study and development of more efficient vaccine production technologies, which can guarantee reduction of vaccine manufacture times and better compliance by availability of easier routes of administration. New perspectives in influenza vaccination technology are making their way in the future panorama of influenza prevention strategies.

Delivery systems for intradermal vaccination

Intradermal (ID) vaccination can offer improved immunity and simpler logistics of delivery, but its use in medicine is limited by the need for simple, reliable methods of ID delivery. ID injection by the Mantoux technique requires special training and may not reliably target skin, but is nonetheless used currently for BCG and rabies vaccination. Scarification using a bifurcated needle was extensively used for smallpox eradication, but provides variable and inefficient delivery into the skin. Recently, ID vaccination has been simplified by introduction of a simple-to-use hollow microneedle that has been approved for ID injection of influenza vaccine in Europe. Various designs of hollow microneedles have been studied preclinically and in humans. Vaccines can also be injected into skin using needle-free devices, such as jet injection, which is receiving renewed clinical attention for ID vaccination. Projectile delivery using powder and gold particles (i.e., gene gun) have also been used clinically for ID vaccination. Building off the scarification approach, a number of preclinical studies have examined solid microneedle patches for use with vaccine coated onto metal microneedles, encapsulated within dissolving microneedles or added topically to skin after microneedle pretreatment, as well as adapting tattoo guns for ID vaccination. Finally, technologies designed to increase skin permeability in combination with a vaccine patch have been studied through the use of skin abrasion, ultrasound, electroporation, chemical enhancers, and thermal ablation. The prospects for bringing ID vaccination into more widespread clinical practice are encouraging, given the large number of technologies for ID delivery under development.

Development of adenoviral vector-based mucosal vaccine against influenza

The recent pandemic threat of the influenza virus makes the increased safety and efficiency of vaccination against the pathogen a most important issue. It has been well established that for maximum protective effect, the vaccination should mimic natural infection. Therefore, recent efforts to develop a new influenza vaccine have focused on intranasal immunization strategies. Intranasal immunization is capable of inducing secretory IgA and serum IgG responses to provide a double defense against mucosal pathogens. On the other hand, it is desirable that a live pathogen is not present in the vaccine. In addition, for optimal induction of the immune responses via the nasal route, efficient and safe mucosal adjuvants are also required. This is possible to attain using an adenoviral vector for vaccine development. Adenoviral vectors are capable of delivering and protecting the antigen encoding sequence. They also possess a natural mechanism for penetrating into the nasal mucous membrane and are capable of activating the innate immune response. This review describes the basic prerequisites for the involvement of recombinant adenoviruses for mucosal (nasal) vaccine development against the influenza virus.

A complex adenovirus vaccine against chikungunya virus provides complete protection against viraemia and arthritis

Chikungunya virus, a mosquito-borne alphavirus, recently caused the largest epidemic ever seen for this virus. Chikungunya disease primarily manifests as a painful and debilitating arthralgia/arthritis, and no effective drug or vaccine is currently available. Here we describe a recombinant chikungunya virus vaccine comprising a non-replicating complex adenovirus vector encoding the structural polyprotein cassette of chikungunya virus. A single immunisation with this vaccine consistently induced high titres of anti-chikungunya virus antibodies that neutralised both an old Asian isolate and a Réunion Island isolate from the recent epidemic. The vaccine also completely protected mice against viraemia and arthritic disease caused by both virus isolates.

In vivo function of airway epithelial TLR2 in host defense against bacterial infection

Decreased Toll-like receptor 2 (TLR2) expression has been reported in patients with chronic obstructive pulmonary disease and in a murine asthma model, which may predispose the hosts to bacterial infections, leading to disease exacerbations. Since airway epithelial cells serve as the first line of respiratory mucosal defense, the present study aimed to reveal the role of airway epithelial TLR2 signaling to lung bacterial [i.e., Mycoplasma pneumoniae (Mp)] clearance. In vivo TLR2 gene transfer via intranasal inoculation of adenoviral vector was performed to reconstitute TLR2 expression in airway epithelium of TLR2(-/-) BALB/c mice, with or without ensuing Mp infection. TLR2 and lactotransferrin (LTF) expression in airway epithelial cells and lung Mp load were assessed. Adenovirus-mediated TLR2 gene transfer to airway epithelial cells of TLR2(-/-) mice reconstituted 30-40% TLR2 expression compared with TLR2(+/+) cells. Such airway epithelial TLR2 reconstitution in TLR2(-/-) mice significantly reduced lung Mp load (an appropriate 45% reduction), coupled with elevated LTF expression. LTF expression in mice was shown to be mainly dependent on TLR2 signaling in response to Mp infection. Exogenous human LTF protein dose-dependently decreased lung bacterial load in Mp-infected TLR2(-/-) mice. In addition, human LTF protein directly dose-dependently decreased Mp levels in vitro. These data indicate that reconstitution of airway epithelial TLR2 signaling in TLR2(-/-) mice significantly restores lung defense against bacteria (e.g., Mp) via increased lung antimicrobial protein LTF production. Our findings may offer a deliverable approach to attenuate bacterial infections in airways of asthma or chronic obstructive pulmonary disease patients with impaired TLR2 function.

Production of adenovirus vectors and their use as a delivery system for influenza vaccines

IMPORTANCE OF THE FIELD

With the emergence of highly pathogenic avian influenza H5N1 viruses that have crossed species barriers and are responsible for lethal infections in humans in many countries, there is an urgent need for the development of effective vaccines which can be produced in large quantities at a short notice and confer broad protection against these H5N1 variants. In order to meet the potential global vaccine demand in a pandemic scenario, new vaccine-production strategies must be explored in addition to the currently used egg-based technology for seasonal influenza.

AREAS COVERED IN THIS REVIEW

Adenovirus (Ad) based influenza vaccines represent an attractive alternative/supplement to the currently licensed egg-based influenza vaccines. Ad-based vaccines are relatively inexpensive to manufacture, and their production process does not require either chicken eggs or labor-intensive and time-consuming processes necessitating enhanced biosafety facilities. Most importantly, in a pandemic situation, this vaccine strategy could offer a stockpiling option to reduce the response time before a strain-matched vaccine could be developed.

WHAT THE READER WILL GAIN

This review discusses Ad-vector technology and the current progress in the development of Ad-based influenza vaccines.

TAKE HOME MESSAGE

Ad vector-based influenza vaccines for pandemic preparedness are under development to meet global vaccine demand.

Avian CD154 enhances humoral and cellular immune responses induced by an adenovirus vector-based vaccine in chickens

Recombinant adenoviral vectors have emerged as an attractive system for veterinary vaccines development. However, for poultry vaccination a very important criterion for an ideal vaccine is its low cost. The objective of this study was to test the ability of chicken CD154 to enhance the immunogenicity of an adenoviral vector-based vaccine against avian influenza virus in order to reduce the amount of antigen required to induce an effective immune response in avian. Chickens were vaccinated with three different doses of adenoviral vectors encoding either HA (AdHA), or HA fused to extracellular domain chicken's CD154 (AdHACD). Hemagglutination inhibition (HI) assay and relative quantification of IFN-γ showed that the adenoviral vector encoding for the chimeric antigen is able to elicit an improved humoral and cellular immune response, which demonstrated that CD154 can be used as a molecular adjuvant allowing to reduce in about 50-fold the amount of adenoviral vector vaccine required to induce an effective immune response.

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.

Comparative immunogenicity of recombinant adenovirus-vectored vaccines expressing different forms of hemagglutinin (HA) proteins from the H5 serotype of influenza A viruses in mice

Recent outbreaks of highly pathogenic avian influenza (HPAI) H5N1 viruses in poultry and their subsequent transmission to humans have highlighted an urgent need to develop preventive vaccines in the event of a pandemic. In this paper we constructed recombinant adenovirus (rAd)-vectored influenza vaccines expressing different forms of H5 hemagglutinin (HA) from the A/Vietnam/1194/04 (VN/1194/04) virus, a wild-type HA, a sequence codon-optimized HA and a transmembrane (TM) domain-truncated HA. Compared to the rAd vectors expressing the wild-type HA (rAd-04wtHA) and the TM-truncated form of HA (rAd-04optHA-dTM), the rAd vectored vaccine with the sequence codon-optimized HA (rAd-04optHA) showed a tendency to induce much higher hemagglutinin inhibition (HI) antibody titers in mice immunized with a prime-boost vaccine. Furthermore, administration of the rAd-04optHA vaccine to mice could elicit cross-reactive immune responses against the antigenically distinct HK/482/97 virus. Additionally, we constructed another vector containing the codon-optimized HA of the A/Hong Kong/482/97 (HK/482/97) virus. Administration of a bivalent immunization formulation including the rAd-04optHA and rAd-97optHA vaccines to mice induced a stronger immune response against HK/482/97 virus than the monovalent formulation. Taken together, these findings may have some implications for the development of rAd-vectored vaccines in the event of the pandemic spread of HPAI.

Impact of ETIF deletion on safety and immunogenicity of equine herpesvirus type 1-vectored vaccines

Heterologous gene transfer by viral vector systems is often limited by factors such as preexisting immunity, toxicity, low packaging capacity, or weak immunogenic potential. A novel viral vector system derived from equine herpesvirus type 1 (EHV-1) not only overcomes some of these obstacles but also promotes the robust expression of a delivered transgene and the induction of antigen-specific immune responses. Regarding an enhanced safety profile, we assessed the impact of the gene encoding the sole essential tegument protein, ETIF, on the replication and immunogenicity of recombinant EHVs. The deletion of ETIF severely attenuates replication in permissive RK13 cells and a human lung epithelial cell line but without influencing transgene expression. Whereas the intranasal administration of a recombinant luciferase EHV in BALB/c mice resulted in transgene expression in nasal cavities and lungs for 5 to 6 days, the ETIF deletion limited expression to 2 days and resulted in 30-fold-less luminescence. Attenuated replication was accompanied by a decreased capacity to induce CD8(+) T cells against a delivered HIV Gag transgene in BALB/c mice following repeated intranasal application. However, a single subcutaneous immunization with a gag DNA vaccine primed specific T cells for substantial expansion by two subsequent intranasal booster immunizations with either the gag recombinant ETIF mutant or the parental virus. In addition to inducing Gag-specific serum antibodies, this prime-boost strategy clearly outperformed three sequential immunizations with the parental or EHV-ΔETIF virus or repeated DNA vaccination by inducing substantial specific secretory IgA (sIgA) titers.

Mucosal delivery of human papillomavirus pseudovirus-encapsidated plasmids improves the potency of DNA vaccination

Mucosal immunization may be important for protection against pathogens whose transmission and pathogenesis target the mucosal tissue. The capsid proteins of human papillomavirus (HPV) confer tropism for the basal epithelium and can encapsidate DNA during self-assembly to form pseudovirions (PsVs). Therefore, we produced mucosal vaccine vectors by HPV PsV encapsidation of DNA plasmids expressing an experimental antigen derived from the M and M2 proteins of respiratory syncytial virus (RSV). Intravaginal (IVag) delivery elicited local and systemic M-M2-specific CD8+ T-cell and antibody responses in mice that were comparable to an approximately 10,000-fold higher dose of naked DNA. A single HPV PsV IVag immunization primed for M-M2-specific-IgA in nasal and vaginal secretions. Based on light emission and immunofluorescent microscopy, immunization with HPV PsV-encapsidated luciferase- and red fluorescent protein (RFP)-expressing plasmids resulted in transient antigen expression (<5 days), which was restricted to the vaginal epithelium. HPV PsV encapsidation of plasmid DNA is a novel strategy for mucosal immunization that could provide new vaccine options for selected mucosal pathogens.

Construction and immunogenicity of recombinant adenovirus vaccines expressing the HMW1, HMW2, or Hia adhesion protein of nontypeable Haemophilus influenzae

The objective of the present study was to construct and assess the immunogenicity of recombinant adenovirus vectors expressing the HMW1, HMW2, or Hia protein of nontypeable Haemophilus influenzae (NTHi). These proteins are critical adhesins and potential protective antigens expressed by NTHi. Segments of the hmw1A and hmw2A structural genes that encode the distal one-half of mature HMW1 or HMW2 were cloned into the T7 expression vector pGEMEX-2. These constructs encoded stable HMW1 or HMW2 recombinant fusion protein that expresses B-cell epitopes common to most NTHi strains. A segment of the hia gene that encodes the surface-exposed portion of mature Hia was also cloned into pGEMEX-2. The resulting T7 gene 10 translational fusions were excised from the parent plasmids and cloned into the shuttle plasmid pDC316. Cotransfection of HEK 293 cells with the pDC316 derivatives and pBHGloxΔE1,3Cre resulted in the production of viral plaques from which recombinant adenoviruses expressing fusion proteins were recovered. Chinchillas immunized intraperitoneally with a single 10(8)-PFU dose of either the HMW2 or Hia adenoviral construct developed high anti-HMW2 or anti-Hia serum antibody titers within 4 weeks of immunization. Chinchillas immunized intranasally with a single 10(7)- to 10(9)-PFU dose of the Hia adenoviral construct also developed high anti-Hia serum antibody titers within 8 weeks of immunization. Recombinant adenoviruses represent a promising system to induce mucosal and systemic immunity and protection against mucosal diseases such as otitis media. Recombinant adenoviruses expressing recombinant HMW1, HMW2, or Hia protein will be important new tools in NTHi vaccine development efforts.

Assessment of route of administration and dose escalation for an adenovirus-based influenza A Virus (H5N1) vaccine in chickens

Highly pathogenic avian influenza (HPAI) virus causes one of the most economically devastating poultry diseases. An HPAI vaccine to prevent the disease in commercial and backyard birds must be effective, safe, and inexpensive. Recently, we demonstrated the efficacy of an adenovirus-based H5N1 HPAI vaccine (Ad5.HA) in chickens. To further evaluate the potential of the Ad5.HA vaccine and its cost-effectiveness, studies to determine the minimal effective dose and optimal route of administration in chickens were performed. A dose as low as 10(7) viral particles (vp) of adenovirus-based H5N1 vaccine per chicken was sufficient to generate a robust humoral immune response, which correlated with the previously reported level of protection. Several routes of administration, including intratracheal, conjunctival, subcutaneous, and in ovo routes, were evaluated for optimal vaccine administration. However, only the subcutaneous route of immunization induced a satisfactory level of influenza virus-specific antibodies. Importantly, these studies established that the vaccine-induced immunity was cross-reactive against an H5N1 strain from a different clade, emphasizing the potential of cross-protection. Our results suggest that the Ad5.HA HPAI vaccine is safe and effective, with the potential of cross-clade protection. The ease of manufacturing and cost-effectiveness make Ad5.HA an excellent avian influenza vaccine candidate with the ability to protect poultry from HPAI virus infection. Considering the limitations of the influenza vaccine technology currently used for poultry applications, any effort aimed at overcoming those limitations is highly significant.

Platycodin d improves the immunogenicity of newcastle disease virus-based recombinant avian influenza vaccine in mice

The development of an effective influenza vaccine is urgently important for controlling outbreaks of the highly pathogenic avian influenza virus (HPAIV) and reducing the impact of pandemics. The use of an adjuvant in such a vaccine can significantly contribute to improve the immunogenicity. To explore a novel and safe adjuvant for improving the potency of influenza vaccines, platycodin D (1), a saponin from the root of Platycodon grandiflorum, was evaluated for the adjuvant potentials on the specific cellular and humoral immune responses to Newcastle disease virus-based recombinant avian influenza vaccine (rL-H5) in mice. Compound 1 significantly promoted the concanavalin A (Con A)-, the lipopolysaccharide (LPS)-, and the antigen-induced splenocyte proliferation and enhanced the serum antigen-specific IgG, IgG1, IgG2a, and IgG2b antibody titers (P<0.05, P<0.01, or P<0.001) in mice immunized with rL-H5. The mRNA expressions of Th1/Th2 cytokines (IFN-gamma and IL-10) and transcription factors (T-bet and GATA-3) in splenocytes were also markedly up-regulated by 1, compared with the control group immunized with rL-H5 alone (P<0.01 or P<0.001). In addition, 1 remarkably increased the killing activities of natural killer (NK) cells from splenocytes in the immunized mice (P<0.05), which may have important implications for the vaccination against the avian influenza virus. We concluded that 1 could improve the immunogenicity of the rL-H5 vaccine by enhancing both humoral and cellular immune responses in mice, and that 1 is a promising adjuvant for influenza vaccines.

A candidate H1N1 pandemic influenza vaccine elicits protective immunity in mice

BACKGROUND

In 2009 a new pandemic disease appeared and spread globally. The recent emergence of the pandemic influenza virus H1N1 first isolated in Mexico and USA raised concerns about vaccine availability. We here report our development of an adenovirus-based influenza H1N1 vaccine tested for immunogenicity and efficacy to confer protection in animal model.

METHODS

We generated two adenovirus(Ad5)-based influenza vaccine candidates encoding the wildtype or a codon-optimized hemagglutinin antigen (HA) from the recently emerged swine influenza isolate A/California/04/2009 (H1N1)pdm. After verification of antigen expression, immunogenicity of the vaccine candidates were tested in a mouse model using dose escalations for subcutaneous immunization. Sera of immunized animals were tested in microneutalization and hemagglutination inhibition assays for the presence of HA-specific antibodies. HA-specific T-cells were measured in IFNgamma Elispot assays. The efficiency of the influenza vaccine candidates were evaluated in a challenge model by measuring viral titer in lung and nasal turbinate 3 days after inoculation of a homologous H1N1 virus.

CONCLUSIONS/SIGNIFICANCE

A single immunization resulted in robust cellular and humoral immune response. Remarkably, the intensity of the immune response was substantially enhanced with codon-optimized antigen, indicating the benefit of manipulating the genetic code of HA antigens in the context of recombinant influenza vaccine design. These results highlight the value of advanced technologies in vaccine development and deployment in response to infections with pandemic potential. Our study emphasizes the potential of an adenoviral-based influenza vaccine platform with the benefits of speed of manufacture and efficacy of a single dose immunization.

Avian influenza pandemic preparedness: developing prepandemic and pandemic vaccines against a moving target

The unprecedented global spread of highly pathogenic avian H5N1 influenza viruses within the past ten years and their extreme lethality to poultry and humans has underscored their potential to cause an influenza pandemic. Combating the threat of an impending H5N1 influenza pandemic will require a combination of pharmaceutical and nonpharmaceutical intervention strategies. The emergence of the H1N1 pandemic in 2009 emphasised the unpredictable nature of a pandemic influenza. Undoubtedly, vaccines offer the most viable means to combat a pandemic threat. Current egg-based influenza vaccine manufacturing strategies are unlikely to be able to cater to the huge, rapid global demand because of the anticipated scarcity of embryonated eggs in an avian influenza pandemic and other factors associated with the vaccine production process. Therefore, alternative, egg-independent vaccine manufacturing strategies should be evaluated to supplement the traditional egg-derived influenza vaccine manufacturing. Furthermore, evaluation of dose-sparing strategies that offer protection with a reduced antigen dose will be critical for pandemic influenza preparedness. Development of new antiviral therapeutics and other, nonpharmaceutical intervention strategies will further supplement pandemic preparedness. This review highlights the current status of egg-dependent and egg-independent strategies against an avian influenza pandemic.

The prevalence of antibodies to adenovirus serotype 5 in an adult Indian population and implications for adenovirus vector vaccines

In vivo gene delivery using human adenovirus serotype 5 (AdV5) vectors is being explored for vaccination purposes. The presence of anti-AdV5 antibodies in human serum arising from natural exposure to AdV5 can interfere potentially with and compromise the efficacy of rAdV5-based vaccine vectors. In this report, a collection of 114 sera from healthy adult Indian blood donors was analyzed for the presence of anti-AdV5 antibodies, using an AdV5 vector encoding the green fluorescent protein (GFP) to monitor the presence of anti-AdV5 neutralizing antibodies in human sera based on their ability to block virus entry into HeLa cells which express the Coxsackievirus-and-Adenovirus Receptor (CAR). In this assay all samples tested were positive for anti-AdV5 antibodies, with titers varying over a very wide range. It was also observed that these antibodies facilitated the uptake of the reporter AdV5 vector into the monocytic cell line U937 which does not express CAR, but expresses Fc receptors (FcRs) instead. These observations have implications for rAdV5-based vaccine development. J. Med. Virol. 82:407-414, 2010. (c) 2010 Wiley-Liss, Inc.

Quality of the transgene-specific CD8+ T cell response induced by adenoviral vector immunization is critically influenced by virus dose and route of vaccination

Adenoviral vectors have been widely used for experimental gene therapy and vaccination, yet there is a surprising lack of knowledge connecting the route and dose of adenovirus administration to the induced transgene-specific immune response. We have recently demonstrated polyfunctional CD8(+) T cells and protective memory responses using adenoviral vectors, which seem to contrast with recent reports suggesting that an exhausted CD8(+) T cell phenotype is induced by inoculation with adenoviral vectors. Accordingly, we investigated the route and dose interrelationship for transgene-specific CD8(+) T cells using adenoviral vectors encoding beta-galactosidase applied either s.c. or i.v. Irrespective of the route of inoculation, most of the adenoviral inoculum was found to disseminate systemically as the dose was raised beyond 10(9) particles. The number of transgene-specific CD8(+) T cells correlated positively with dissemination, whereas the functional capacity of the generated T cells correlated inversely with vector dissemination. A comparison of the immune response to s.c. or i.v. administration at moderate doses revealed that inoculation by both routes induced a transient peak of IFN-gamma-producing CD8(+) T cells 2 to 3 wk postinfection, but following i.v. administration, these cells were only detected in the liver. Two to four months after systemic, but not peripheral, immunization, dysfunctional transgene-specific CD8(+) T cells impaired in both cytokine production and important in vivo effector functions, accumulated in the spleen. These findings indicate that the localization of the adenoviral inoculum and not the total Ag load determines the quality of the CD8(+) T cell response induced with adenoviral vaccines.

Animal models for the preclinical evaluation of candidate influenza vaccines

At present, new influenza A (H1N1)2009 viruses of swine origin are responsible for the first influenza pandemic of the 21st Century. In addition, highly pathogenic avian influenza A/H5N1 viruses continue to cause outbreaks in poultry and, after zoonotic transmission, cause an ever-increasing number of human cases, of which 59% have a fatal clinical outcome. It is also feared that these viruses adapt to replication in humans and become transmissible from human to human. The development of effective vaccines against epidemic and (potentially) pandemic viruses is therefore considered a priority. In this review, we discuss animal models that are used for the preclinical evaluation of novel candidate influenza vaccines. In most cases, a tier of multiple animal models is used before the evaluation of vaccine candidates in clinical trials is considered. Commonly, vaccines are tested for safety and efficacy in mice, ferrets and/or macaques. The use of each of these species has its advantages and limitations, which are addressed here.

Egg-independent vaccine strategies for highly pathogenic H5N1 influenza viruses

The emergence of a highly pathogenic H5N1 influenza virus in Hong Kong in 1997 and the subsequent appearance of other H5N1 strains and their spread to several countries in southeast Asia, Africa, the Middle East and Europe has evoked fear of a global influenza pandemic. Vaccines offer the best hope to combat the threat of an influenza pandemic. However, the global demand for a pandemic vaccine cannot be fulfilled by the current egg-based vaccine manufacturing strategies, thus creating a need to explore alternative technologies for vaccine production and delivery. Several egg-independent vaccine approaches such as cell culture-derived whole virus or subvirion vaccines, recombinant protein-based vaccines, virus-like particle (VLP) vaccines, DNA vaccines and viral vector-based vaccines are currently being investigated and appear promising both in preclinical and clinical studies. The present review will highlight the various egg-independent alternative vaccine approaches for pandemic influenza.

Mucosal immunity induced by adenovirus-based H5N1 HPAI vaccine confers protection against a lethal H5N2 avian influenza virus challenge

Development of effective vaccines against highly pathogenic avian influenza (HPAI) H5N1 viruses is a global public health priority. Considering the difficulty in predicting HPAI H5N1 pandemic strains, one strategy used in their design includes the development of formulations with the capacity of eliciting broad cross-protective immunity against multiple viral antigens. To this end we constructed a replication-defective recombinant adenovirus-based avian influenza virus vaccine (rAdv-AI) expressing the codon-optimized M2eX-HA-hCD40L and the M1-M2 fusion genes from HPAI H5N1 human isolate. Although there were no significant differences in the systemic immune responses observed between the intramuscular prime-intramuscular boost regimen (IM/IM) and the intranasal prime-intramuscular boost regimen (IN/IM), IN/IM induced more potent CD8(+) T cell and antibody responses at mucosal sites than the IM/IM vaccination, resulting in more effective protection against lethal H5N2 avian influenza (AI) virus challenge. These findings suggest that the strategies used to induce multi-antigen-targeted mucosal immunity, such as IN/IM delivery of rAdv-AI, may be a promising approach for developing broad protective vaccines that may be more effective against the new HPAI pandemic strains.

Protective efficacy and immunogenicity of an adenoviral vector vaccine encoding the codon-optimized F protein of respiratory syncytial virus

Adenoviral vectors (AdV) have received considerable attention for vaccine development because of their high immunogenicity and efficacy. In previous studies, it was shown that DNA immunization of mice with codon-optimized expression plasmids encoding the fusion protein of respiratory syncytial virus (RSV F) resulted in enhanced protection against RSV challenge compared to immunization with plasmids carrying the wild-type cDNA sequence of RSV F. In this study, we constructed AdV carrying the codon-optimized full-length RSV F gene (AdV-F) or the soluble form of the RSV F gene (AdV-Fsol). BALB/c mice were immunized twice with AdV-F or AdV-Fsol and challenged with RSV intranasally. Substantial levels of antibody to RSV F were induced by both AdV vaccines, with peak neutralizing-antibody titers of 1:900. Consistently, the viral loads in lung homogenates and bronchoalveolar lavage fluids were significantly reduced by a factor of more than 60,000. The protection against viral challenge could be measured even 8 months after the booster immunization. AdV-F and AdV-Fsol induced similar levels of immunogenicity and protective efficacy. Therefore, these results encourage further development of AdV vaccines against RSV infection in humans.

A complex adenovirus-vectored vaccine against Rift Valley fever virus protects mice against lethal infection in the presence of preexisting vector immunity

Rift Valley fever virus (RVFV) has been cited as a potential biological-weapon threat due to the serious and fatal disease it causes in humans and animals and the fact that this mosquito-borne virus can be lethal in an aerosolized form. Current human and veterinary vaccines against RVFV, however, are outdated, inefficient, and unsafe. We have incorporated the RVFV glycoprotein genes into a nonreplicating complex adenovirus (CAdVax) vector platform to develop a novel RVFV vaccine. Mice vaccinated with the CAdVax-based vaccine produced potent humoral immune responses and were protected against lethal RVFV infection. Additionally, protection was elicited in mice despite preexisting immunity to the adenovirus vector.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.

Protection of chickens against avian influenza with nonreplicating adenovirus-vectored vaccine

Protective immunity against avian influenza (AI) virus has been elicited in chickens by single-dose in ovo or i.m. vaccination with a replication-competent adenovirus (Ad)-free human Ad vector encoding the AI virus A/Turkey/Wisconsin/68 H5 (AdTW68. H5) or the A/Chicken/New York/94 H7 (AdChNY94. H7) hemagglutinin (HA). The AdTW68.H5-vaccinated chickens were protected against both H5N1 and H5N2 highly pathogenic AI virus challenges. The AdChNY94. H7-vaccinated chickens were protected against an H7N3 highly pathogenic avian influenza virus challenge. Chickens vaccinated in ovo with AdTW68.H5 followed by posthatch i.m. vaccination with AdChNY94.H7 responded to both vaccinations, with robust antibody titers against both the H5 and H7 AI proteins. The use of a synthetic AI H5 HA gene codon optimized to match the tRNA pool found in chicken cells is more potent than the cognate H5 HA gene. Mass administration of this AI vaccine can be streamlined with available robotic in ovo injectors. In addition, Ad5-vectored vaccines can be produced rapidly and the safety margin of the nonreplicating vector is superior to that of a replicating counterpart. Furthermore, this mode of vaccination will not interfere with epidemiological surveys of natural AI infections. Finally, the demonstration that Ad-vectored vaccines can be administered repeatedly without appreciably losing potency highlights the commercial potential of this new class of vaccine in poultry.

Adenovirus as a carrier for the development of influenza virus-free avian influenza vaccines

A long-sought goal during the battle against avian influenza is to develop a new generation of vaccines capable of mass immunizing humans as well as poultry (the major source of avian influenza for human infections) in a timely manner. Although administration of the currently licensed influenza vaccine is effective in eliciting protective immunity against seasonal influenza, this approach is associated with a number of insurmountable problems for preventing an avian influenza pandemic. Many of the hurdles may be eliminated by developing new avian influenza vaccines that do not require the propagation of an influenza virus during vaccine production. Replication-competent adenovirus-free adenovirus vectors hold promise as a carrier for influenza virus-free avian influenza vaccines owing to their safety profile and rapid manufacture using cultured suspension cells in a serum-free medium. Simple and efficient mass-immunization protocols, including nasal spray for people and automated in ovo vaccination for poultry, convey another advantage for this class of vaccines. In contrast to parenteral injection of adenovirus vector, the potency of adenovirus-vectored nasal vaccine is not appreciably interfered by pre-existing immunity to adenovirus.

Making improvements in influenza vaccines: incremental change or transformational evolution?

Influenza is one of the leading causes of morbidity and mortality, with 36,000 deaths and 226,000 hospitalizations occurring annually in the USA, primarily in the elderly. The currently licensed influenza vaccines, trivalent inactivated influenza vaccine and live, attenuated influenza vaccine, although effective in many respects, need to be more efficacious for the elderly and the very young. They can also be improved upon to induce broader immunity and cross-protection against drifted or variant strains. Additionally, there is room for improvement in manufacturing technologies. Increased antigen dose, adjuvants, virus-like particles and virosomes, novel live, attenuated influenza vaccines, and universal vaccines are all being developed or have been developed to address the unmet need in the elderly. Many of these approaches may provide incremental improvements in efficacy, where transformative improvement is necessary.

Heat shock proteins HSP27 and HSP70 are present in the skin and are important mediators of allergic contact hypersensitivity

Proteomic analysis of murine skin has shown that a variety of heat shock proteins (HSPs) are constitutively expressed in the skin. Using murine allergic contact hypersensitivity as a model, we investigated the role of two heat shock proteins, HSP27 and HSP70, in the induction of cutaneous cell-mediated immune responses. Immunohistochemical examination of skin specimens showed that HSP27 was present in the epidermis and HSP70 was present in both the epidermis and dermis. Inhibition of HSP27 and HSP70 produced a reduction in the 1-fluoro-2,4-dinitrobenzene contact hypersensitivity response and resulted in the induction of Ag-specific unresponsiveness. Treatment of dendritic cell cultures with recombinant HSP27 caused in the up-regulation of IL-1beta, TNF-alpha, IL-6, IL-12p70, and IL-12p40 but not IL-23p19, which was inhibited when Abs to HSP27 were added. The 1-fluoro-2,4-dinitrobenzene-conjugated dendritic cells that had been treated with HSP27 had an increased capacity to initiate contact hypersensitivity responses compared with control dendritic cells. This augmented capacity required TLR4 signaling because neither cytokine production by dendritic cells nor the increased induction of contact hypersensitivity responses occurred in TLR4-deficient C3H/HeJ mice. Our findings indicate that a cascade of events occurs following initial interaction of hapten with the skin that includes increased activity of HSPs, their interaction with TLR4, and, in turn, increased production of cytokines that are known to enhance Ag presentation by T cells. The results suggest that HSPs form a link between adaptive and innate immunity during the early stages of contact hypersensitivity.

CpG used as an adjuvant for an adenovirus-based Venezuelan equine encephalitis virus vaccine increases the immune response to the vector, but not to the transgene product

An adenovirus-based (ad-based) vaccine delivering antigens from the Alphavirus Venezuelan equine encephalitis virus (VEEV) is a strategy that offers clinical potential. A vaccine against VEEV is desirable because of the re-emerging nature of this virus, and also the potential that it may be used as a biological weapon. This study was designed to investigate whether the co-administration of CpG oligodeoxynucleotides (ODNs) with an ad-based VEEV vaccine could enhance the protective efficacy of the vaccine. We report that the co-administration of CpG ODN was unable to increase VEEV-specific antibody responses in mice, and was unable to increase the protective efficacy of the vaccine against aerosol challenge with virulent VEEV. However, it was noted that antibody responses directed against the adenovirus vaccine vector were increased, which may be detrimental, particularly in the context of homologous boosting.

New strategies to overcome the drawbacks of currently available flu vaccines

Vaccination represents the most efficient tool to control morbidity and mortality resulting from influenza infections in humans. The currently licensed influenza vaccines provide good protection levels in healthy adults, whereas lower protection is generally achieved in ageing individuals who are at a higher risk of developing severe clinical manifestations. Future improvements in influenza vaccines should address the needs of high risk groups including the elderly, small children and chronic patients. Recently, due to the increased incidence of avian influenza pandemic outbreaks, the prevention of a potential human influenza pandemic turned into another crucial issue in the influenza vaccination field. The development and validation of manufacturing processes for efficient and safe pandemic vaccines became one of the top priorities of health, regulatory and funding agencies all over the world. In the pandemic context, the development of novel vaccines administered via the mucosal route may play a significant role by reducing virus shedding from infected individuals. This chapter provides insights in the limitations of existing manufacturing processes, new approaches to overcome limitation in vaccine production, mechanisms of action of current vaccines and discuss potential strategies to improve the immunogenicity and efficacy of influenza vaccines.

Nasal delivery of an adenovirus-based vaccine bypasses pre-existing immunity to the vaccine carrier and improves the immune response in mice

Pre-existing immunity to human adenovirus serotype 5 (Ad5) is common in the general population. Bypassing pre-existing immunity could maximize Ad5 vaccine efficacy. Vaccination by the intramuscular (I.M.), nasal (I.N.) or oral (P.O.) route with Ad5 expressing Ebola Zaire glycoprotein (Ad5-ZGP) fully protected naïve mice against lethal challenge with Ebola. In the presence of pre-existing immunity, only mice vaccinated I.N. survived. The frequency of IFN-γ+ CD8+ T cells was reduced by 80% and by 15% in animals vaccinated by the I.M. and P.O. routes respectively. Neutralizing antibodies could not be detected in serum from either treatment group. Pre-existing immunity did not compromise the frequency of IFN-γ+ CD8+ T cells (3.9±1% naïve vs. 3.6±1% pre-existing immunity, PEI) nor anti-Ebola neutralizing antibody (NAB, 40±10 reciprocal dilution, both groups). The number of INF-γ+ CD8+ cells detected in bronchioalveolar lavage fluid (BAL) after I.N. immunization was not compromised by pre-existing immunity to Ad5 (146±14, naïve vs. 120±16 SFC/million MNCs, PEI). However, pre-existing immunity reduced NAB levels in BAL by ∼25% in this group. To improve the immune response after oral vaccination, the Ad5-based vaccine was PEGylated. Mice given the modified vaccine did not survive challenge and had reduced levels of IFN-γ+ CD8+ T cells 10 days after administration (0.3±0.3% PEG vs. 1.7±0.5% unmodified). PEGylation did increase NAB levels 2-fold. These results provide some insight about the degree of T and B cell mediated immunity necessary for protection against Ebola virus and suggest that modification of the virus capsid can influence the type of immune response elicited by an Ad5-based vaccine.

Nanotechnology in vaccine delivery

With very few adjuvants currently being used in marketed human vaccines, a critical need exists for novel immunopotentiators and delivery vehicles capable of eliciting humoral, cellular and mucosal immunity. Such crucial vaccine components could facilitate the development of novel vaccines for viral and parasitic infections, such as hepatitis, HIV, malaria, cancer, etc. In this review, we discuss clinical trial results for various vaccine adjuvants and delivery vehicles being developed that are approximately nanoscale (< 1000 nm) in size. Humoral immune responses have been observed for most adjuvants and delivery platforms while only viral vectors, ISCOMs and Montanide™ ISA 51 and 720 have shown cytotoxic T cell responses in the clinic. MF59 and MPL® have elicited Th1 responses, and virus-like particles, non-degradable nanoparticles and liposomes have also generated cellular immunity. Such vaccine components have also been evaluated for alternative routes of administration with clinical successes reported for intranasal delivery of viral vectors and proteosomes and oral delivery of a VLP vaccine.

Human infection with highly pathogenic H5N1 influenza virus

Highly pathogenic H5N1 influenza A viruses have spread relentlessly across the globe since 2003, and they are associated with widespread death in poultry, substantial economic loss to farmers, and reported infections of more than 300 people with a mortality rate of 60%. The high pathogenicity of H5N1 influenza viruses and their capacity for transmission from birds to human beings has raised worldwide concern about an impending human influenza pandemic similar to the notorious H1N1 Spanish influenza of 1918. Since many aspects of H5N1 influenza research are rapidly evolving, we aim in this Seminar to provide an up-to-date discussion on select topics of interest to influenza clinicians and researchers. We summarise the clinical features and diagnosis of infection and present therapeutic options for H5N1 infection of people. We also discuss ideas relating to virus transmission, host restriction, and pathogenesis. Finally, we discuss vaccine development in view of the probable importance of vaccination in pandemic control.

Emerging vaccines for influenza

BACKGROUND

Influenza remains one of the leading causes of morbidity and mortality worldwide. The available vaccines are least effective in the populations at greatest risk--children, the elderly, and the immunocompromised. Furthermore, avian influenza and other novel strains have the potential to cause the next influenza pandemic. Research efforts have accelerated worldwide to develop new vaccines to provide better immunity against annual epidemics and a potential pandemic.

OBJECTIVE

To summarize the global research efforts at developing new influenza vaccines, adjuvants, and delivery devices.

METHOD

MEDLINE and Pharmaprojects databases were searched for publications and continuing research on new influenza vaccine technologies.

RESULTS/CONCLUSIONS

Technologies such as DNA vaccines, live recombinant viral vector vaccines, and virus-like particles have shown significant promise for immunogenicity and protection from experimental challenge to influenza. New modalities for vaccine delivery and methods for rapid vaccine production are also being investigated. With the possibility of an influenza pandemic increasing the need to develop new vaccines, the global research community has made large strides to meet this challenge.

Multi-antigen vaccines based on complex adenovirus vectors induce protective immune responses against H5N1 avian influenza viruses

There are legitimate concerns that the highly pathogenic H5N1 avian influenza virus could adapt for human-to-human transmission and cause a pandemic similar to the 1918 "Spanish flu" that killed 50 million people worldwide. We have developed pandemic influenza vaccines by incorporating multiple antigens from both avian and Spanish influenza viruses into complex recombinant adenovirus vectors. In vaccinated mice, these vaccines induced strong humoral and cellular immune responses against pandemic influenza virus antigens, and protected vaccinated mice against lethal H5N1 virus challenge. These results indicate that this multi-antigen, broadly protective vaccine may serve as a safer and more effective approach than traditional methods for development of a pandemic influenza vaccine.

Influenza vaccines and vaccination strategies in birds

Although it is well accepted that the present Asian H5N1 panzootic is predominantly an animal health problem, the human health implications and the risk of human pandemic have highlighted the need for more information and collaboration in the field of veterinary and human health. H5 and H7 avian influenza (AI) viruses have the unique property of becoming highly pathogenic (HPAI) during circulation in poultry. Therefore, the final objective of poultry vaccination against AI must be eradication of the virus and the disease. Actually, important differences exist in the control of avian and human influenza viruses. Firstly, unlike human vaccines that must be adapted to the circulating strain to provide adequate protection, avian influenza vaccination provides broader protection against HPAI viruses. Secondly, although clinical protection is the primary goal of human vaccines, poultry vaccination must also stop transmission to achieve efficient control of the disease. This paper addresses these differences by reviewing the current and future influenza vaccines and vaccination strategies in birds.

Bovine adenoviral vector-based H5N1 influenza vaccine overcomes exceptionally high levels of pre-existing immunity against human adenovirus

Because of the high prevalence of adenovirus (Ad) infections in humans, it is believed that pre-existing Ad-neutralizing antibodies (vector immunity) may negatively impact the immune response to vaccine antigens when delivered by human Ad (HAd) vectors. In order to evaluate whether bovine Ad subtype 3 (BAd3), a non-HAd vector, can effectively elude high levels of pre-existing vector immunity, naïve and HAd serotype 5 (HAd)-primed mice were immunized with BAd-H5HA [BAd3 vector expressing the hemagglutinin (HA) gene from H5N1 influenza virus]. Even in the presence of very high levels of HAd-specific neutralizing antibody, no significant reductions in HA-specific humoral and cell-mediated immune (CMI) responses were observed in HAd-primed mice immunized with BAd-H5HA. In naïve mice immunized with HAd-H5HA (HAd5 vector expressing H5N1 HA) and boosted with BAd-H5HA, the humoral responses elicited were significantly higher (P < 0.01) than with either HAd-H5HA or BAd-H5HA alone, while the CMI responses were comparable in the groups. This finding underlines the importance of a heterologous prime-boost approach for achieving an enhanced immune response. The immunization of naïve or HAd-primed mice with BAd-H5HA bestowed full protection from morbidity and mortality following a potentially lethal challenge with A/Hong Kong/483/97. These results demonstrate the importance of BAd vectors as an alternate or supplement to HAd vectors for influenza pandemic preparedness.

Organ distribution of transgene expression following intranasal mucosal delivery of recombinant replication-defective adenovirus gene transfer vector

It is believed that respiratory mucosal immunization triggers more effective immune protection than parenteral immunization against respiratory infection caused by viruses and intracellular bacteria. Such understanding has led to the successful implementation of intranasal immunization in humans with a live cold-adapted flu virus vaccine. Furthermore there has been an interest in developing effective mucosal-deliverable genetic vaccines against other infectious diseases. However, there is a concern that intranasally delivered recombinant viral-based vaccines may disseminate to the CNS via the olfactory tissue. Initial experimental evidence suggests that intranasally delivered recombinant adenoviral gene transfer vector may transport to the olfactory bulb. However, there is a lack of quantitative studies to compare the relative amounts of transgene products in the respiratory tract, lung, olfactory bulb and brain after intranasal mucosal delivery of viral gene transfer vector. To address this issue, we have used fluorescence macroscopic imaging, luciferase quantification and PCR approaches to compare the relative distribution of transgene products or adenoviral gene sequences in the respiratory tract, lung, draining lymph nodes, olfactory bulb, brain and spleen. Intranasal mucosal delivery of replication-defective recombinant adenoviral vector results in gene transfer predominantly in the respiratory system including the lung while it does lead to a moderate level of gene transfer in the olfactory bulb. However, intranasal inoculation of adenoviral vector leads to little or no viral dissemination to the major region of the CNS, the brain. These experimental findings support the efficaciousness of intranasal adenoviral-mediated gene transfer for the purpose of mucosal immunization and suggest that it may not be of significant safety concern.