Pre-clinical evaluation of a replication-competent recombinant adenovirus serotype 4 vaccine expressing influenza H5 hemagglutinin

Role of homologous recombination/recombineering on human adenovirus genome engineering: Not the only but the most competent solution

Adenoviruses typically cause mild illnesses, but severe diseases may occur primarily in immunodeficient individuals, particularly children. Recently, adenoviruses have garnered significant interest as a versatile tool in gene therapy, tumor treatment, and vaccine vector development. Over the past two decades, the advent of recombineering, a method based on homologous recombination, has notably enhanced the utility of adenoviral vectors in therapeutic applications. This review summarizes recent advancements in the use of human adenoviral vectors in medicine and discusses the pivotal role of recombineering in the development of these vectors. Additionally, it highlights the current achievements and potential future impact of therapeutic adenoviral vectors.

A Single Oral Immunization with a Replication-Competent Adenovirus-Vectored Vaccine Protects Mice from Influenza Respiratory Infection

The development of effective and flexible vaccine platforms is a major public health challenge, especially in the context of influenza vaccines that have to be renewed every year. Adenoviruses (AdVs) are easy to produce and have a good safety and efficacy profile when administered orally, as demonstrated by the long-term use of oral AdV-4 and -7 vaccines in the U.S. military. These viruses therefore appear to be the ideal backbone for the development of oral replicating vector vaccines. However, research into these vaccines is limited by the ineffectiveness of human AdV replication in laboratory animals. The use of mouse AdV type 1 (MAV-1) in its natural host allows infection to be studied under replicating conditions. Here, we orally vaccinated mice with a MAV-1 vector expressing influenza hemagglutinin (HA) to assess the protection conferred against an intranasal challenge of influenza. We showed that a single oral immunization with this vaccine generates influenza-specific and -neutralizing antibodies and completely protects mice against clinical signs and viral replication, similar to traditional inactivated vaccines. IMPORTANCE Given the constant threat of pandemics and the need for annual vaccination against influenza and possibly emerging agents such as SARS-CoV-2, new types of vaccines that are easier to administer and therefore more widely accepted are a critical public health need. Here, using a relevant animal model, we have shown that replicative oral AdV vaccine vectors can help make vaccination against major respiratory diseases more available, better accepted, and therefore more effective. These results could be of major importance in the coming years in the fight against seasonal or emerging respiratory diseases such as COVID-19.

Adenoviral-Vectored Centralized Consensus Hemagglutinin Vaccine Provides Broad Protection against H2 Influenza a Virus

Several influenza pandemics have occurred in the past century, one of which emerged in 1957 from a zoonotic transmission of H2N2 from an avian reservoir into humans. This pandemic caused 2–4 million deaths and circulated until 1968. Since the disappearance of H2N2 from human populations, there has been waning immunity against H2, and this subtype is not currently incorporated into seasonal vaccines. However, H2 influenza remains a pandemic threat due to consistent circulation in avian reservoirs. Here, we describe a method of pandemic preparedness by creating an adenoviral-vectored centralized consensus vaccine design against human H2 influenza. We also assessed the utility of serotype-switching to enhance the protective immune responses seen with homologous prime-boosting strategies. Immunization with an H2 centralized consensus showed a wide breadth of antibody responses after vaccination, protection against challenge with a divergent human H2 strain, and significantly reduced viral load in the lungs after challenge. Further, serotype switching between two species C adenoviruses enhanced protective antibody titers after heterologous boosting. These data support the notion that an adenoviral-vectored H2 centralized consensus vaccine has the ability to provide broadly cross-reactive immune responses to protect against divergent strains of H2 influenza and prepare for a possible pandemic.

Recent Progress in Recombinant Influenza Vaccine Development Toward Heterosubtypic Immune Response

Flu, a viral infection caused by the influenza virus, is still a global public health concern with potential to cause seasonal epidemics and pandemics. Vaccination is considered the most effective protective strategy against the infection. However, given the high plasticity of the virus and the suboptimal immunogenicity of existing influenza vaccines, scientists are moving toward the development of universal vaccines. An important property of universal vaccines is their ability to induce heterosubtypic immunity, i.e., a wide immune response coverage toward different influenza subtypes. With the increasing number of studies and mounting evidence on the safety and efficacy of recombinant influenza vaccines (RIVs), they have been proposed as promising platforms for the development of universal vaccines. This review highlights the current progress and advances in the development of RIVs in the context of heterosubtypic immunity induction toward universal vaccine production. In particular, this review discussed existing knowledge on influenza and vaccine development, current hemagglutinin-based RIVs in the market and in the pipeline, other potential vaccine targets for RIVs (neuraminidase, matrix 1 and 2, nucleoprotein, polymerase acidic, and basic 1 and 2 antigens), and deantigenization process. This review also provided discussion points and future perspectives in looking at RIVs as potential universal vaccine candidates for influenza.

Breaking Entry-and Species Barriers: LentiBOOST® Plus Polybrene Enhances Transduction Efficacy of Dendritic Cells and Monocytes by Adenovirus 5

Due to their ability to trigger strong immune responses, adenoviruses (HAdVs) in general and the serotype5 (HAdV-5) in particular are amongst the most popular viral vectors in research and clinical application. However, efficient transduction using HAdV-5 is predominantly achieved in coxsackie and adenovirus receptor (CAR)-positive cells. In the present study, we used the transduction enhancer LentiBOOST^® comprising the polycationic Polybrene to overcome these limitations. Using LentiBOOST^®/Polybrene, we yielded transduction rates higher than 50% in murine bone marrow-derived dendritic cells (BMDCs), while maintaining their cytokine expression profile and their capability to induce T-cell proliferation. In human dendritic cells (DCs), we increased the transduction rate from 22% in immature (i)DCs or 43% in mature (m)DCs to more than 80%, without inducing cytotoxicity. While expression of specific maturation markers was slightly upregulated using LentiBOOST^®/Polybrene on iDCs, no effect on mDC phenotype or function was observed. Moreover, we achieved efficient HAdV5 transduction also in human monocytes and were able to subsequently differentiate them into proper iDCs and functional mDCs. In summary, we introduce LentiBOOST^® comprising Polybrene as a highly potent adenoviral transduction agent for new in-vitro applications in a set of different immune cells in both mice and humans.

Adenoviral vector-based platforms for developing effective vaccines to combat respiratory viral infections

Since the development of the first vaccine against smallpox over two centuries ago, vaccination strategies have been at the forefront of significantly impacting the incidences of infectious diseases globally. However, the increase in the human population, deforestation and climate change, and the rise in worldwide travel have favored the emergence of new viruses with the potential to cause pandemics. The ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is a cruel reminder of the impact of novel pathogens and the suboptimal capabilities of conventional vaccines. Therefore, there is an urgent need to develop new vaccine strategies that allow the production of billions of doses in a short duration and are broadly protective against emerging and re-emerging infectious diseases. Extensive knowledge of the molecular biology and immunology of adenoviruses (Ad) has favored Ad vectors as platforms for vaccine design. The Ad-based vaccine platform represents an attractive strategy as it induces robust humoral and cell-mediated immune responses and can meet the global demand in a pandemic situation. This review describes the status of Ad vector-based vaccines in preclinical and clinical studies for current and emerging respiratory viruses, particularly coronaviruses, influenza viruses and respiratory syncytial viruses.

A recombinant herpes virus expressing influenza hemagglutinin confers protection and induces antibody-dependent cellular cytotoxicity

Despite widespread yearly vaccination, influenza leads to significant morbidity and mortality across the globe. To make a more broadly protective influenza vaccine, it may be necessary to elicit antibodies that can activate effector functions in immune cells, such as antibody-dependent cellular cytotoxicity (ADCC). There is growing evidence supporting the necessity for ADCC in protection against influenza and herpes simplex virus (HSV), among other infectious diseases. An HSV-2 strain lacking the essential glycoprotein D (gD), was used to create ΔgD-2, which is a highly protective vaccine against lethal HSV-1 and HSV-2 infection in mice. It also elicits high levels of IgG2c antibodies that bind FcγRIV, a receptor that activates ADCC. To make an ADCC-eliciting influenza vaccine, we cloned the hemagglutinin (HA) gene from an H1N1 influenza A strain into the ΔgD-2 HSV vector. Vaccination with ΔgD-2::HA_PR8 was protective against homologous influenza challenge and elicited an antibody response against HA that inhibits hemagglutination (HAI⁺), is predominantly IgG2c, strongly activates FcγRIV, and protects against influenza challenge following passive immunization of naïve mice. Prior exposure of mice to HSV-1, HSV-2, or a replication-defective HSV-2 vaccine (dl5-29) does not reduce protection against influenza by ΔgD-2::HA_PR8 This vaccine also continues to elicit protection against both HSV-1 and HSV-2, including high levels of IgG2c antibodies against HSV-2. Mice lacking the interferon-α/β receptor and mice lacking the interferon-γ receptor were also protected against influenza challenge by ΔgD-2::HA_PR8 Our results suggest that ΔgD-2 can be used as a vaccine vector against other pathogens, while also eliciting protective anti-HSV immunity.

A replication-competent adenovirus-vectored influenza vaccine induces durable systemic and mucosal immunity

BACKGROUNDTo understand the features of a replicating vaccine that might drive potent and durable immune responses to transgene-encoded antigens, we tested a replication-competent adenovirus type 4 encoding influenza virus H5 HA (Ad4-H5-Vtn) administered as an oral capsule or via tonsillar swab or nasal spray.METHODSViral shedding from the nose, mouth, and rectum was measured by PCR and culturing. H5-specific IgG and IgA antibodies were measured by bead array binding assays. Serum antibodies were measured by a pseudovirus entry inhibition, microneutralization, and HA inhibition assays.RESULTSAd4-H5-Vtn DNA was shed from most upper respiratory tract-immunized (URT-immunized) volunteers for 2 to 4 weeks, but cultured from only 60% of participants, with a median duration of 1 day. Ad4-H5-Vtn vaccination induced increases in H5-specific CD4+ and CD8+ T cells in the peripheral blood as well as increases in IgG and IgA in nasal, cervical, and rectal secretions. URT immunizations induced high levels of serum neutralizing antibodies (NAbs) against H5 that remained stable out to week 26. The duration of viral shedding correlated with the magnitude of the NAb response at week 26. Adverse events (AEs) were mild, and peak NAb titers were associated with overall AE frequency and duration. Serum NAb titers could be boosted to very high levels 2 to 5 years after Ad4-H5-Vtn vaccination with recombinant H5 or inactivated split H5N1 vaccine.CONCLUSIONReplicating Ad4 delivered to the URT caused prolonged exposure to antigen, drove durable systemic and mucosal immunity, and proved to be a promising platform for the induction of immunity against viral surface glycoprotein targets.TRIAL REGISTRATIONClinicalTrials.gov NCT01443936 and NCT01806909.FUNDINGIntramural and Extramural Research Programs of the NIAID, NIH (U19 AI109946) and the Centers of Excellence for Influenza Research and Surveillance (CEIRS), NIAID, NIH (contract HHSN272201400008C).

Codon Usage and Adenovirus Fitness: Implications for Vaccine Development

Vaccination is the most effective method to date to prevent viral diseases. It intends to mimic a naturally occurring infection while avoiding the disease, exposing our bodies to viral antigens to trigger an immune response that will protect us from future infections. Among different strategies for vaccine development, recombinant vaccines are one of the most efficient ones. Recombinant vaccines use safe viral vectors as vehicles and incorporate a transgenic antigen of the pathogen against which we intend to generate an immune response. These vaccines can be based on replication-deficient viruses or replication-competent viruses. While the most effective strategy involves replication-competent viruses, they must be attenuated to prevent any health hazard while guaranteeing a strong humoral and cellular immune response. Several attenuation strategies for adenoviral-based vaccine development have been contemplated over time. In this paper, we will review them and discuss novel approaches based on the principle that protein synthesis from individual genes can be modulated by codon usage bias manipulation. We will summarize vaccine approaches that consider recoding of viral proteins to produce adenoviral attenuation and recoding of the transgene antigens for both viral attenuation and efficient viral epitope expression.

Adenoviral Vectors as Vaccines for Emerging Avian Influenza Viruses

It is evident that the emergence of infectious diseases, which have the potential for spillover from animal reservoirs, pose an ongoing threat to global health. Zoonotic transmission events have increased in frequency in recent decades due to changes in human behavior, including increased international travel, the wildlife trade, deforestation, and the intensification of farming practices to meet demand for meat consumption. Influenza A viruses (IAV) possess a number of features which make them a pandemic threat and a major concern for human health. Their segmented genome and error-prone process of replication can lead to the emergence of novel reassortant viruses, for which the human population are immunologically naïve. In addition, the ability for IAVs to infect aquatic birds and domestic animals, as well as humans, increases the likelihood for reassortment and the subsequent emergence of novel viruses. Sporadic spillover events in the past few decades have resulted in human infections with highly pathogenic avian influenza (HPAI) viruses, with high mortality. The application of conventional vaccine platforms used for the prevention of seasonal influenza viruses, such as inactivated influenza vaccines (IIVs) or live-attenuated influenza vaccines (LAIVs), in the development of vaccines for HPAI viruses is fraught with challenges. These issues are associated with manufacturing under enhanced biosafety containment, and difficulties in propagating HPAI viruses in embryonated eggs, due to their propensity for lethality in eggs. Overcoming manufacturing hurdles through the use of safer backbones, such as low pathogenicity avian influenza viruses (LPAI), can also be a challenge if incompatible with master strain viruses. Non-replicating adenoviral (Ad) vectors offer a number of advantages for the development of vaccines against HPAI viruses. Their genome is stable and permits the insertion of HPAI virus antigens (Ag), which are expressed in vivo following vaccination. Therefore, their manufacture does not require enhanced biosafety facilities or procedures and is egg-independent. Importantly, Ad vaccines have an exemplary safety and immunogenicity profile in numerous human clinical trials, and can be thermostabilized for stockpiling and pandemic preparedness. This review will discuss the status of Ad-based vaccines designed to protect against avian influenza viruses with pandemic potential.

Adenoviral Vector-Based Vaccine Platforms for Developing the Next Generation of Influenza Vaccines

Ever since the discovery of vaccines, many deadly diseases have been contained worldwide, ultimately culminating in the eradication of smallpox and polio, which represented significant medical achievements in human health. However, this does not account for the threat influenza poses on public health. The currently licensed seasonal influenza vaccines primarily confer excellent strain-specific protection. In addition to the seasonal influenza viruses, the emergence and spread of avian influenza pandemic viruses such as H5N1, H7N9, H7N7, and H9N2 to humans have highlighted the urgent need to adopt a new global preparedness for an influenza pandemic. It is vital to explore new strategies for the development of effective vaccines for pandemic and seasonal influenza viruses. The new vaccine approaches should provide durable and broad protection with the capability of large-scale vaccine production within a short time. The adenoviral (Ad) vector-based vaccine platform offers a robust egg-independent production system for manufacturing large numbers of influenza vaccines inexpensively in a short timeframe. In this review, we discuss the progress in the development of Ad vector-based influenza vaccines and their potential in designing a universal influenza vaccine.

Prolonged evolution of the memory B cell response induced by a replicating adenovirus-influenza H5 vaccine

Induction of an antibody response capable of recognizing highly diverse strains is a major obstacle to the development of vaccines for viruses such as HIV and influenza. Here, we report the dynamics of B cell expansion and evolution at the single-cell level after vaccination with a replication-competent adenovirus type 4 recombinant virus expressing influenza H5 hemagglutinin. Fluorescent H1 or H5 probes were used to quantitate and isolate peripheral blood B cells and their antigen receptors. We observed increases in H5-specific antibody somatic hypermutation and potency for several months beyond the period of active viral replication that was not detectable at the serum level. Individual broad and potent antibodies could be isolated, including one stem-specific antibody that is part of a new multidonor class. These results demonstrate prolonged evolution of the B cell response for months after vaccination and should be considered in efforts to evaluate or boost vaccine-induced immunity.

Longitudinal quantification of adenovirus neutralizing responses in Zambian mother-infant pairs: Impact of HIV-1 infection and its treatment

Vaccination offers the most cost-effective approach to limiting the adverse impact of infectious and neoplastic diseases that reduce the quality of life in sub-Saharan Africa (SSA). However, it is unclear what vaccine vectors would be most readily implementable in the setting and at what age they should be applied for maximal efficacy. Adenoviruses (Ad) and Ad-based vectors have been demonstrated to induce effective humoral and cellular immune responses in animal models and in humans. However, because immunity associated with Ad infection is lifelong, there exists a debate as to whether pre-existing immunity might decrease the efficacy of Ad vectored vaccines. In order to begin to rationally develop vaccination strategies for SSA, we have quantified neutralizing antibodies (nAb) against Ad4, Ad5, Ad7, Ad26, Ad28, Ad45 and Ad48 in 67 adult women and their infants. We are the first to define the decay kinetics of transferred maternal nAb in infants as well as the apparent initiation of de novo Ad responses. Our findings demonstrate that in Zambian adults, robust nAb responses exist against each of the Ads tested and are efficiently transferred to newborns. With few exceptions, neither the HIV-1 infection status of the mothers or the antiretroviral therapy (ART) treatment of HIV-1 disease had significant impact on maternal Ad nAb responses or their transfer to infants. However, maternal Ad nAb decays in infants to a nadir at 12 months of age such that any of the seven Ad types could function as vaccine vectors. The definition of this 'window of opportunity' provides important foundational data for rational design and implementation of Ad vectors in this setting.

Characterization of a replication-competent vector encoding DsRed based on a human adenovirus type 4 a-like strain

Human adenovirus type 4 (HAdV4) is an etiological agent of acute respiratory disease (ARD) in pediatric and adult patients. HAdV4 strains can be divided into two major genomic clusters, namely prototype (p)-like viruses and a-like viruses. Here, the complete genome sequence of HAdV4 strain GZ01, isolated from a child with ARD in southern China, is first reported and analyzed. This strain was determined to be of the 4a1 genome-type based on in silico restriction profiles. Then, a replication-competent rAd4DsRed virus, containing the HAdV4 GZ01 infectious genome and expressing the reporter molecule DsRed, was generated and characterized. Recombinant rAd4DsRed can infect AD293, hamster, and mouse cells in which DsRed protein was expressed. No changes in antigenicity and genome replication were detected for rAd4DsRed and wild-type HAdV4. Mice immunized with rAd4DsRed was elicited a marked antibody response to DsRed. A rapid method of testing neutralizing antibodies against HAdV3 and HAdV4 was also established using a mixture of rAd4DsRed and rAd3EGFP. Our results provide the foundation to develop HAdV4 vaccines, potential vector platforms for vaccine and gene therapy, and rapid methods for serological and antiviral screening.

Oral Vaccination with Replication-Competent Adenovirus in Mice Reveals Dissemination of the Viral Vaccine beyond the Gastrointestinal Tract

Since the 1970s, replication-competent human adenoviruses 4 and 7 have been used as oral vaccines to protect U.S. soldiers against the severe respiratory diseases caused by these viruses. These vaccines are thought to establish a digestive tract infection conferring protection against respiratory challenge through antibodies. The success of these vaccines makes replication-competent adenoviruses attractive candidates for use as oral vaccine vectors. However, the inability of human adenoviruses to replicate efficiently in laboratory animals has hampered the study of such vectors. Here, we used mouse adenovirus type 1 (MAV-1) in mice to study oral replication-competent adenovirus-based vaccines. We show that MAV-1 oral administration provides protection that recapitulates the protection against homologous respiratory challenge observed with adenovirus 4 and 7 vaccines. Moreover, live oral MAV-1 vaccine better protected against a respiratory challenge than inactivated vaccines. This protection was linked not only with the presence of MAV-1-specific antibodies but also with a better recruitment of effector CD8 T cells. However, unexpectedly, we found that such oral replication-competent vaccine systemically spread all over the body. Our results therefore support the use of MAV-1 to study replication-competent oral adenovirus-based vaccines but also highlight the fact that those vaccines can disseminate widely in the body.IMPORTANCE Replication-competent adenoviruses appear to be promising vectors for the development of oral vaccines in humans. However, the study and development of these vaccines suffer from the lack of any reliable animal model. In this study, mouse adenovirus type 1 was used to develop a small-animal model for oral replication-competent adenovirus vaccines. While this model reproduced in mice what is observed with human adenovirus oral vaccines, it also highlighted that oral immunization with such a replication-competent vaccine is associated with the systemic spread of the virus. This study is therefore of major importance for the future development of such vaccine platforms and their use in large human populations.

A review of 65 years of human adenovirus seroprevalence

Introduction: Human adenovirus (HAdV)-derived vectors have been used in numerous pre-clinical and clinical trials during the last 40 years. Current research in HAdV-based vaccines focuses on improving transgene immunogenicity and safety. Because pre-existing humoral immunity against HAdV types correlate with reduced vaccine efficacy and safety, many groups are exploring the development of HAdV types vectors with lower seroprevalence. However, global seroepidemiological data are incomplete. Areas covered: The goal of this review is to centralize 65 years of research on (primarily) HAdV epidemiology. After briefly addressing adenovirus biology, we chronical HAdV seroprevalence studies and highlight major milestones. Finally, we analyze data from about 50 studies with respect to HAdVs types that are currently used in the clinic, or are in the developmental pipeline. Expert opinion: Vaccination is among the most efficient tools to prevent infectious disease. HAdV-based vaccines have undeniable potential, but optimization is needed and antivector immunity remains a challenge if the same vectors are to be administrated to different populations. Here, we identify gaps in our knowledge and the need for updated worldwide epidemiological data.

Seroprevalence of Neutralizing Antibodies to Human Adenovirus Type 4 and 7 in Healthy Populations From Southern China

Human adenoviruses type 4 (HAdV4) and 7 (HAdV7) are two major respiratory pathogens and sporadically cause outbreaks of acute respiratory diseases. The neutralizing antibody (nAb) response to these two adenoviruses in civilian populations, which is important for dissecting previous circulations and predicting potential outbreaks, remains largely unknown. In this study, we generated replication-competent HAdV4 and HAdV7 reporter viruses expressing secreted-alkaline-phosphatase (SEAP), and established neutralization assays to investigate the seroprevalence of pre-existing nAb in healthy volunteers from Hunan Province, southern China. The seropositivity rates are 58.4 and 63.8% for anti-HAdV4 nAb and anti-HAdV7 nAb, respectively. High nAb titers (> 1000) were frequently detected in HAdV4-seropositive individuals, whereas most HAdV7-seropositive volunteers had moderate nAb titers (201-1000). The seropositivity rates of anti-HAdV4 nAb and anti-HAdV7 nAb increase with age, with individuals younger than 20 exhibiting the lowest seropositivity rates. Both seropositivity rates and nAb titers are comparable between different sex groups. Notably, HAdV4-seropositive individuals tend to be HAdV7-seropositive and vice versa. Because HAdV4 antisera showed no neutralizing activity to HAdV7 whereas HAdV7 antisera cannot neutralize HAdV4, a subgroup of individuals might be susceptible to infection by HAdV4 and HAdV7 and thus generate nAb to both of them. These results revealed the continuous circulation of HAdV4 and HAdV7 and the lack of protective immunity in more than 35% of people, which emphasized the surveillance of these two HAdVs and the development of prophylactic vaccines.

The Journey of in vivo Virus Engineered Dendritic Cells From Bench to Bedside: A Bumpy Road

Dendritic cells (DCs) are recognized as highly potent antigen-presenting cells that are able to stimulate cytotoxic T lymphocyte (CTL) responses with antitumor activity. Consequently, DCs have been explored as cellular vaccines in cancer immunotherapy. To that end, DCs are modified with tumor antigens to enable presentation of antigen-derived peptides to CTLs. In this review we discuss the use of viral vectors for in situ modification of DCs, focusing on their clinical applications as anticancer vaccines. Among the viral vectors discussed are those derived from viruses belonging to the families of the Poxviridae, Adenoviridae, Retroviridae, Togaviridae, Paramyxoviridae, and Rhabdoviridae. We will further shed light on how the combination of viral vector-based vaccination with T-cell supporting strategies will bring this strategy to the next level.

Combination Adenovirus and Protein Vaccines Prevent Infection or Reduce Viral Burden after Heterologous Clade C Simian-Human Immunodeficiency Virus Mucosal Challenge

HIV vaccine development is focused on designing immunogens and delivery methods that elicit protective immunity. We evaluated a combination of adenovirus (Ad) vectors expressing HIV 1086.C (clade C) envelope glycoprotein (Env), SIV Gag p55, and human pegivirus GBV-C E2 glycoprotein. We compared replicating simian (SAd7) with nonreplicating human (Ad4) adenovirus-vectored vaccines paired with recombinant proteins in a novel prime-boost regimen in rhesus macaques, with the goal of eliciting protective immunity against SHIV challenge. In both vaccine groups, plasma and buccal Env-specific IgG, tier 1 heterologous neutralizing antibodies, and antibody-dependent cell-mediated viral inhibition were readily generated. High Env-specific T cell responses elicited in all vaccinees were significantly greater than responses targeting Gag. After three intrarectal exposures to heterologous tier 1 clade C SHIV, all 10 sham-vaccinated controls were infected, whereas 4/10 SAd7- and 3/10 Ad4-vaccinated macaques remained uninfected or maintained tightly controlled plasma viremia. Time to infection was significantly delayed in SAd7-vaccinated macaques compared to the controls. Cell-associated and plasma virus levels were significantly lower in each group of vaccinated macaques compared to controls; the lowest plasma viral burden was found in animals vaccinated with the SAd7 vectors, suggesting superior immunity conferred by the replicating simian vectors. Furthermore, higher V1V2-specific binding antibody titers correlated with viral control in the SAd7 vaccine group. Thus, recombinant Ad plus protein vaccines generated humoral and cellular immunity that was effective in either protecting from SHIV acquisition or significantly reducing viremia in animals that became infected, consequently supporting additional development of replicating Ad vectors as HIV vaccines.IMPORTANCE There is a well-acknowledged need for an effective AIDS vaccine that protects against HIV infection and limits in vivo viral replication and associated pathogenesis. Although replicating virus vectors have been advanced as HIV vaccine platforms, there have not been any direct comparisons of the replicating to the nonreplicating format. The present study directly compared the replicating SAd7 to nonreplicating Ad4 vectors in macaques and demonstrated that in the SAd7 vaccine group, the time to infection was significantly delayed compared to the control group, and V1V2 Env-specific binding antibodies correlated with viral outcomes. Viral control was significantly enhanced in vaccinated macaques compared to controls, and in infected SAd7-vaccinated macaques compared to Ad4-vaccinated macaques, suggesting that this vector may have conferred more effective immunity. Because blocking infection is so difficult with current vaccines, development of a vaccine that can limit viremia if infection occurs would be valuable. These data support further development of replicating adenovirus vectors.

Identification of a Critical and Conformational Neutralizing Epitope in Human Adenovirus Type 4 Hexon

Human adenovirus type 4 (HAdV-4) is an epidemic virus that contributes to serious acute respiratory disease (ARD) in both pediatric and adult patients. However, no licensed drug or vaccine is currently available to the civilian population. The identification of neutralizing epitopes of HAdV-4 should allow the development of a novel antiviral vaccine and a novel gene transfer vector, and an effective neutralizing monoclonal antibody (MAb) will be useful in developing appropriate antiviral drugs. In this study, we report that MAb MN4b shows strong neutralizing activity against HAdV-4. MN4b recognizes a conformational epitope (418AGSEK422) within hypervariable region 7 (HVR7). Mutations within this site permitted HAdV-4 mutants to escape neutralization by MN4b and to resist neutralization by animal and human anti-HAdV-4 sera. A recombinant virus, rAd3-A4R7-1, containing the identified neutralizing epitope in the HVR7 region of HAdV-3 hexon, successfully induced antiserum that inhibited HAdV-4 infection. These results indicate that a small surface loop of HAdV-4 hexon is a critical neutralization epitope for this virus. The generation of MN4b and the identification of this neutralizing epitope may be useful in developing therapeutic treatment, a subunit vaccine, and a novel vector that can escape preexisting neutralization for HAdV-4.

IMPORTANCE Neutralizing antibodies are considered good tools for the prevention of human adenovirus type 4 (HAdV-4) infections. The identification of the epitopes recognized by such neutralizing antibodies is important for the generation of recombinant antiviral vaccines. However, until now, no neutralizing epitope has been reported for HAdV-4. Here, we developed a serotype-specific neutralizing MAb directed against HAdV-4, MN4b. We provide evidence that MN4b recognizes a conformational epitope within HVR7 of HAdV-4 hexon. Antisera generated to this conformational epitope displayed on HAdV-3 hexon inhibited infection of AD293 cells by HAdV-4. Our findings are very important for the development of therapeutic treatment, a subunit vaccine, and a novel vector for HAdV-4.

Getting genetic access to natural adenovirus genomes to explore vector diversity

Recombinant vectors based on the human adenovirus type 5 (HAdV5) have been developed and extensively used in preclinical and clinical studies for over 30 years. However, certain restrictions of HAdV5-based vectors have limited their clinical applications because they are rather inefficient in specifically transducing cells of therapeutic interest that lack the coxsackievirus and adenovirus receptor (CAR). Moreover, enhanced vector-associated toxicity and widespread preexisting immunity have been shown to significantly hamper the effectiveness of HAdV-5-mediated gene transfer. However, evolution of adenoviruses in the natural host is driving the generation of novel types with altered virulence, enhanced transmission, and altered tissue tropism. As a consequence, an increasing number of alternative adenovirus types were identified, which may represent a valuable resource for the development of novel vector types. Thus, researchers are focusing on the other naturally occurring adenovirus types, which are structurally similar but functionally different from HAdV5. To this end, several strategies have been devised for getting genetic access to adenovirus genomes, resulting in a new panel of adenoviral vectors. Importantly, these vectors were shown to have a host range different from HAdV5 and to escape the anti-HAdV5 immune response, thus underlining the great potential of this approach. In summary, this review provides a state-of-the-art overview of one essential step in adenoviral vector development.

Adenovirus-Mediated Gene Delivery: Potential Applications for Gene and Cell-Based Therapies in the New Era of Personalized Medicine

With rapid advances in understanding molecular pathogenesis of human diseases in the era of genome sciences and systems biology, it is anticipated that increasing numbers of therapeutic genes or targets will become available for targeted therapies. Despite numerous setbacks, efficacious gene and/or cell-based therapies still hold the great promise to revolutionize the clinical management of human diseases. It is wildly recognized that poor gene delivery is the limiting factor for most in vivo gene therapies. There has been a long-lasting interest in using viral vectors, especially adenoviral vectors, to deliver therapeutic genes for the past two decades. Among all currently available viral vectors, adenovirus is the most efficient gene delivery system in a broad range of cell and tissue types. The applications of adenoviral vectors in gene delivery have greatly increased in number and efficiency since their initial development. In fact, among over 2,000 gene therapy clinical trials approved worldwide since 1989, a significant portion of the trials have utilized adenoviral vectors. This review aims to provide a comprehensive overview on the characteristics of adenoviral vectors, including adenoviral biology, approaches to engineering adenoviral vectors, and their applications in clinical and pre-clinical studies with an emphasis in the areas of cancer treatment, vaccination and regenerative medicine. Current challenges and future directions regarding the use of adenoviral vectors are also discussed. It is expected that the continued improvements in adenoviral vectors should provide great opportunities for cell and gene therapies to live up to its enormous potential in personalized medicine.

Adenovirus serotype 5 vaccine vectors trigger IL-27-dependent inhibitory CD4+ T cell responses that impair CD8+ T cell function

Adenovirus serotype 5 (Ad5) vaccine vectors elicit robust CD8⁺ T cell responses, but these responses typically exhibit a partially exhausted phenotype. However, the immunologic mechanism by which Ad5 vectors induce dysfunctional CD8⁺ T cells has not previously been elucidated. Here we demonstrate that, following immunization of B6 mice, Ad5 vectors elicit antigen-specific IL-10⁺CD4⁺ T cells with a distinct transcriptional profile in a dose-dependent fashion. In rhesus monkeys, we similarly observed upregulated expression of IL-10 and PD-1 by CD4⁺ T cells following Ad5 vaccination. These cells markedly suppressed vaccine-elicited CD8⁺ T cell responses in vivo and IL-10 blockade increased the frequency and functionality of antigen-specific CD8⁺ T cells as well as improved protective efficacy against challenge with recombinant Listeria monocytogenes. Moreover, induction of these inhibitory IL-10⁺CD4⁺ T cells correlated with IL-27 expression and IL-27 blockade substantially improved CD4⁺ T cell functionality. These data highlight a role for IL-27 in the induction of inhibitory IL-10⁺CD4⁺ T cells, which suppress CD8⁺ T cell magnitude and function following Ad5 vector immunization. A deeper understanding of the cytokine networks and transcriptional profiles induced by vaccine vectors should lead to strategies to improve the immunogenicity and protective efficacy of viral vector-based vaccines.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

Beyond Oncolytics: E1B55K-Deleted Adenovirus as a Vaccine Delivery Vector

Type 5 human adenoviruses (Ad5) deleted of genes encoding the early region 1B 55-kDa (E1B55K) protein including Onyx-015 (dl1520) and H101 are best known for their oncolytic potential. As a vaccine vector the E1B55K deletion may allow for the insertion of a transgene nearly 1,000 base pairs larger than now possible. This has the potential of extending the application for which the vectors are clinically known. However, the immune priming ability of E1B55K-deleted vectors is unknown, undermining our ability to gauge their usefulness in vaccine applications. For this reason, we created an E1B55K-deleted Ad5 vector expressing full-length single chain HIV_BaLgp120 attached to a flexible linker and the first two domains of rhesus CD4 (rhFLSC) in exchange for the E3 region. In cell-based experiments the E1B55K-deleted vector promoted higher levels of innate immune signals including chemokines, cytokines, and the NKG2D ligands MIC A/B compared to an E1B55K wild-type vector expressing the same immunogen. Based on these results we evaluated the immune priming ability of the E1B55K-deleted vector in mice. The E1B55K-deleted vector promoted similar levels of Ad5-, HIVgp120, and rhFLSC-specific cellular and humoral immune responses as the E1B55K wild-type vector. In pre-clinical HIV-vaccine studies the wild-type vector has been employed as part of a very effective prime-boost strategy. This study demonstrates that E1B55K-deleted adenoviruses may serve as effective vaccine delivery vectors.

Permissive growth of human adenovirus type 4 vaccine strain-based vector in porcine cell lines

In recent years, there has been considerable interest in using adenoviruses as live vectors to develop recombinant vaccines. Previous studies have demonstrated the safety and effectiveness of HIV/SIV and influenza vaccine candidates based on human adenovirus type 4 (Ad4) replication-competent vectors in rhesus macaque and human model. To explore the possibility of human Ad4 vaccine strain used as a vector in developing porcine vaccines, the growth properties of replication-competent human Ad4 vaccine strain recombinant encoding EGFP in different porcine cell lines were investigated. All tested cell lines are permissive for Ad4 vaccine strain vector with varied replication efficiency. Thus, human Ad4 based vectors would be promising supplement to adenovirus vectors as a delivery vehicle for recombinant vaccines in swine industry.

DNA-based influenza vaccines as immunoprophylactic agents toward universality

Influenza is an illness of global public health concern. Influenza viruses have been responsible for several pandemics affecting humans. Current influenza vaccines have proved satisfactory safety; however, they have limitations and do not provide protection against unexpected emerging influenza virus strains. Therefore, there is an urgent need for alternative approaches to conventional influenza vaccines. The development of universal influenza vaccines will help alleviate the severity of influenza pandemics. Influenza DNA vaccines have been the subject of many studies over the past decades due to their ability to induce broad-based protective immune responses in various animal models. The present review highlights the recent advances in influenza DNA vaccine research and its potential as an affordable universal influenza vaccine.

Development of Novel Adenoviral Vectors to Overcome Challenges Observed With HAdV-5-based Constructs

Recombinant vectors based on human adenovirus serotype 5 (HAdV-5) have been extensively studied in preclinical models and clinical trials over the past two decades. However, the thorough understanding of the HAdV-5 interaction with human subjects has uncovered major concerns about its product applicability. High vector-associated toxicity and widespread preexisting immunity have been shown to significantly impede the effectiveness of HAdV-5–mediated gene transfer. It is therefore that the in-depth knowledge attained working on HAdV-5 is currently being used to develop alternative vectors. Here, we provide a comprehensive overview of data obtained in recent years disqualifying the HAdV-5 vector for systemic gene delivery as well as novel strategies being pursued to overcome the limitations observed with particular emphasis on the ongoing vectorization efforts to obtain vectors based on alternative serotypes.

Attenuation of Replication-Competent Adenovirus Serotype 26 Vaccines by Vectorization

Replication-competent adenovirus (rcAd)-based vaccine vectors may theoretically provide immunological advantages over replication-incompetent Ad vectors, but they also raise additional potential clinical and regulatory issues. We produced replication-competent Ad serotype 26 (rcAd26) vectors by adding the E1 region back into a replication-incompetent Ad26 vector backbone with the E3 or E3/E4 regions deleted. We assessed the effect of vectorization on the replicative capacity of the rcAd26 vaccines. Attenuation occurred in a stepwise fashion, with E3 deletion, E4 deletion, and human immunodeficiency virus type 1 (HIV-1) envelope (Env) gene insertion all contributing to reduced replicative capacity compared to that with the wild-type Ad26 vector. The rcAd26 vector with E3 and E4 deleted and containing the Env transgene exhibited 2.7- to 4.4-log-lower replicative capacity than that of the wild-type Ad26 in vitro. This rcAd26 vector is currently being evaluated in a phase 1 clinical trial. Attenuation as a result of vectorization and transgene insertion has implications for the clinical development of replication-competent vaccine vectors.

Current and emerging cell culture manufacturing technologies for influenza vaccines

Annually, influenza virus infects millions of people worldwide. Vaccination programs against seasonal influenza infections require the production of hundreds of million doses within a very short period of time. The influenza vaccine is currently produced using a technology developed in the 1940s that relies on replicating the virus in embryonated hens' eggs. The monovalent viral preparation is inactivated and purified before being formulated in trivalent or tetravalent influenza vaccines. The production process has depended on a continuous supply of eggs. In the case of pandemic outbreaks, this mode of production might be problematic because of a possible drastic reduction in the egg supply and the low flexibility of the manufacturing process resulting in a lack of supply of the required vaccine doses in a timely fashion. Novel production systems using mammalian or insect cell cultures have emerged to overcome the limitations of the egg-based production system. These industrially well-established production systems have been primarily selected for a faster and more flexible response to pandemic threats. Here, we review the most important cell culture manufacturing processes that have been developed in recent years for mass production of influenza vaccines.

Efficacy and immunogenicity of single-dose AdVAV intranasal anthrax vaccine compared to anthrax vaccine absorbed in an aerosolized spore rabbit challenge model

AdVAV is a replication-deficient adenovirus type 5-vectored vaccine expressing the 83-kDa protective antigen (PA83) from Bacillus anthracis that is being developed for the prevention of disease caused by inhalation of aerosolized B. anthracis spores. A noninferiority study comparing the efficacy of AdVAV to the currently licensed Anthrax Vaccine Absorbed (AVA; BioThrax) was performed in New Zealand White rabbits using postchallenge survival as the study endpoint (20% noninferiority margin for survival). Three groups of 32 rabbits were vaccinated with a single intranasal dose of AdVAV (7.5 × 10(7), 1.5 × 10(9), or 3.5 × 10(10) viral particles). Three additional groups of 32 animals received two doses of either intranasal AdVAV (3.5 × 10(10) viral particles) or intramuscular AVA (diluted 1:16 or 1:64) 28 days apart. The placebo group of 16 rabbits received a single intranasal dose of AdVAV formulation buffer. All animals were challenged via the inhalation route with a targeted dose of 200 times the 50% lethal dose (LD50) of aerosolized B. anthracis Ames spores 70 days after the initial vaccination and were followed for 3 weeks. PA83 immunogenicity was evaluated by validated toxin neutralizing antibody and serum anti-PA83 IgG enzyme-linked immunosorbent assays (ELISAs). All animals in the placebo cohort died from the challenge. Three of the four AdVAV dose cohorts tested, including two single-dose cohorts, achieved statistical noninferiority relative to the AVA comparator group, with survival rates between 97% and 100%. Vaccination with AdVAV also produced antibody titers with earlier onset and greater persistence than vaccination with AVA.

Adenovirus-based vaccines against avian-origin H5N1 influenza viruses

Since 1997, human infection with avian H5N1, having about 60% mortality, has posed a threat to public health. In this review, we describe the epidemiology of H5N1 transmission, advantages and disadvantages of different influenza vaccine types, and characteristics of adenovirus, finally summarizing advances in adenovirus-based H5N1 systemic and mucosal vaccines.

Virus-vectored influenza virus vaccines

Despite the availability of an inactivated vaccine that has been licensed for >50 years, the influenza virus continues to cause morbidity and mortality worldwide. Constant evolution of circulating influenza virus strains and the emergence of new strains diminishes the effectiveness of annual vaccines that rely on a match with circulating influenza strains. Thus, there is a continued need for new, efficacious vaccines conferring cross-clade protection to avoid the need for biannual reformulation of seasonal influenza vaccines. Recombinant virus-vectored vaccines are an appealing alternative to classical inactivated vaccines because virus vectors enable native expression of influenza antigens, even from virulent influenza viruses, while expressed in the context of the vector that can improve immunogenicity. In addition, a vectored vaccine often enables delivery of the vaccine to sites of inductive immunity such as the respiratory tract enabling protection from influenza virus infection. Moreover, the ability to readily manipulate virus vectors to produce novel influenza vaccines may provide the quickest path toward a universal vaccine protecting against all influenza viruses. This review will discuss experimental virus-vectored vaccines for use in humans, comparing them to licensed vaccines and the hurdles faced for licensure of these next-generation influenza virus vaccines.

Immune responses in macaques to a prototype recombinant adenovirus live oral human papillomavirus 16 vaccine

Immunization with human papillomavirus (HPV) L1 virus-like particles (VLPs) prevents infection with HPV. However, the expense and logistical demands of current VLP vaccines will limit their widespread use in resource-limited settings, where most HPV-induced cervical cancer occurs. Live oral adenovirus vaccines have properties that are well-suited for use in such settings. We have described a live recombinant adenovirus vaccine prototype that produces abundant HPV16 L1 protein from the adenovirus major late transcriptional unit and directs the assembly of HPV16 VLPs in tissue culture. Recombinant-derived VLPs potently elicit neutralizing antibodies in mice. Here, we characterize the immune response to the recombinant after dual oral and intranasal immunization of pigtail macaques, in which the virus replicates as it would in immunized humans. The immunization of macaques induced vigorous humoral responses to adenovirus capsid and nonstructural proteins, although, surprisingly, not against HPV L1. In contrast, immunization elicited strong T-cell responses to HPV VLPs as well as adenovirus virions. T-cell responses arose immediately after the primary immunization and were boosted by a second immunization with recombinant virus. T-cell immunity contributes to protection against a wide variety of pathogens, including many viruses. The induction of a strong cellular response by the recombinant indicates that live adenovirus recombinants have potential as vaccines for those agents. These studies encourage and will inform the continued development of viable recombinant adenovirus vaccines.

Longitudinal requirement for CD4+ T cell help for adenovirus vector-elicited CD8+ T cell responses

Despite the widespread use of replication-incompetent recombinant adenovirus (Ad) vectors as candidate vaccine platforms, the mechanism by which these vectors elicit CD8(+) T cell responses remains poorly understood. Our data demonstrate that induction and maintenance of CD8(+) T cell responses by Ad vector immunization is longitudinally dependent on CD4(+) T cell help for a prolonged period. Depletion of CD4(+) T cells in wild type mice within the first 8 d following Ad immunization resulted in dramatically reduced induction of Ag-specific CD8(+) T cells, decreased T-bet and eomesodermin expression, impaired KLRG1(+) effector differentiation, and atypical expression of the memory markers CD127, CD27, and CD62L. Moreover, these CD8(+) T cells failed to protect against a lethal recombinant Listeria monocytogenes challenge. Depletion of CD4(+) T cells between weeks 1 and 4 following immunization resulted in increased contraction of memory CD8(+) T cells. These data demonstrate a prolonged temporal requirement for CD4(+) T cell help for vaccine-elicited CD8(+) T cell responses in mice. These findings have important implications in the design of vaccines aimed at eliciting CD8(+) T cell responses and may provide insight into the impaired immunogenicity of vaccines in the context of AIDS and other CD4(+) T cell immune deficiencies.

H5N1 vaccines in humans

The spread of highly pathogenic avian H5N1 influenza viruses since 1997 and their virulence for poultry and humans has raised concerns about their potential to cause an influenza pandemic. Vaccines offer the most viable means to combat a pandemic threat. However, it will be a challenge to produce, distribute and implement a new vaccine if a pandemic spreads rapidly. Therefore, efforts are being undertaken to develop pandemic vaccines that use less antigen and induce cross-protective and long-lasting responses, that can be administered as soon as a pandemic is declared or possibly even before, in order to prime the population and allow for a rapid and protective antibody response. In the last few years, several vaccine manufacturers have developed candidate pandemic and pre-pandemic vaccines, based on reverse genetics and have improved the immunogenicity by formulating these vaccines with different adjuvants. Some of the important and consistent observations from clinical studies with H5N1 vaccines are as follows: two doses of inactivated vaccine are generally necessary to elicit the level of immunity required to meet licensure criteria, less antigen can be used if an oil-in-water adjuvant is included, in general antibody titers decline rapidly but can be boosted with additional doses of vaccine and if high titers of antibody are elicited, cross-reactivity against other clades is observed. Prime-boost strategies elicit a more robust immune response. In this review, we discuss data from clinical trials with a variety of H5N1 influenza vaccines. We also describe studies conducted in animal models to explore the possibility of reassortment between pandemic live attenuated vaccine candidates and seasonal influenza viruses, since this is an important consideration for the use of live vaccines in a pandemic setting.

Pre-clinical development of a recombinant, replication-competent adenovirus serotype 4 vector vaccine expressing HIV-1 envelope 1086 clade C

BACKGROUND

There is a well-acknowledged need for an effective AIDS vaccine that protects against HIV-1 infection or limits in vivo viral replication. The objective of these studies is to develop a replication-competent, vaccine vector based on the adenovirus serotype 4 (Ad4) virus expressing HIV-1 envelope (Env) 1086 clade C glycoprotein. Ad4 recombinant vectors expressing Env gp160 (Ad4Env160), Env gp140 (Ad4Env140), and Env gp120 (Ad4Env120) were evaluated.

METHODS

The recombinant Ad4 vectors were generated with a full deletion of the E3 region of Ad4 to accommodate the env gene sequences. The vaccine candidates were assessed in vitro following infection of A549 cells for Env-specific protein expression and for posttranslational transport to the cell surface as monitored by the binding of broadly neutralizing antibodies (bNAbs). The capacity of the Ad4Env vaccines to induce humoral immunity was evaluated in rabbits for Env gp140 and V1V2-specific binding antibodies, and HIV-1 pseudovirus neutralization. Mice immunized with the Ad4Env160 vaccine were assessed for IFNγ T cell responses specific for overlapping Env peptide sets.

RESULTS

Robust Env protein expression was confirmed by western blot analysis and recognition of cell surface Env gp160 by multiple bNAbs. Ad4Env vaccines induced humoral immune responses in rabbits that recognized Env 1086 gp140 and V1V2 polypeptide sequences derived from 1086 clade C, A244 clade AE, and gp70 V1V2 CASE A2 clade B fusion protein. The immune sera efficiently neutralized tier 1 clade C pseudovirus MW965.26 and neutralized the homologous and heterologous tier 2 pseudoviruses to a lesser extent. Env-specific T cell responses were also induced in mice following Ad4Env160 vector immunization.

CONCLUSIONS

The Ad4Env vaccine vectors express high levels of Env glycoprotein and induce both Env-specific humoral and cellular immunity thus supporting further development of this new Ad4 HIV-1 Env vaccine platform in Phase 1 clinical trials.

Vaccines within vaccines: the use of adenovirus types 4 and 7 as influenza vaccine vectors

Adenovirus Types 4 and 7 (Ad4 and Ad7) are associated with acute respiratory distress (ARD). In order to prevent widespread Ad-associated ARD (Ad-ARD) the United States military immunizes new recruits using a safe and effective lyophilized wildtype Ad4 and Ad7 delivered orally in an enteric-coated capsule. We cloned Ad4 and Ad7 and modified them to express either a GFP-Luciferase (GFPLuc) fusion gene or a centralized influenza H1 hemagglutinin (HA1-con). BALB/c mice were injected with GFPLuc expressing viruses intramuscularly (i.m.) and intranasally (i.n.). Ad4 induced significantly higher luciferase expression levels as compared with Ad7 by both routes. Ad7 transduction was restored using a human CD46+ transgenic mouse model. Mice immunized with serial dilutions of viruses expressing the HA1-con influenza vaccine gene were challenged with 100 MLD 50 of influenza virus. Ad4 protected BALB/c mice at a lower dose by i.m. immunization as compared with Ad7. Unexpectedly, there was no difference in protection by i.n. immunization. Although Ad7 i.m. transduction was restored in CD46+ transgenic mice, protection against influenza challenge required even higher doses as compared with the BALB/c mice. However, Ad7 i.n. immunized CD46+ transgenic mice were better protected as compared with Ad4. Interestingly, the restoration of Ad7 transduction in CD46+ mice did not increase vaccine efficacy and indicates that Ad7 may transduce a different subset of cells through alternative receptors in the absence of CD46. These data indicate that both Ad4 and Ad7 can effectively induce anti-H1N1 immunity against a heterologous challenge using a centralized H1 gene. Future studies in non-human primates or human clinical trials will determine the overall effectiveness of Ad4 and Ad7 as vaccines for influenza.

Effects of the deletion of early region 4 (E4) open reading frame 1 (orf1), orf1-2, orf1-3 and orf1-4 on virus-host cell interaction, transgene expression, and immunogenicity of replicating adenovirus HIV vaccine vectors

The global health burden engendered by human immunodeficiency virus (HIV)-induced acquired immunodeficiency syndrome (AIDS) is a sobering reminder of the pressing need for a preventative vaccine. In non-human primate models replicating adenovirus (Ad)-HIV/SIV recombinant vaccine vectors have been shown to stimulate potent immune responses culminating in protection against challenge exposures. Nonetheless, an increase in the transgene carrying capacity of these Ad vectors, currently limited to approximately 3000 base pairs, would greatly enhance their utility. Using a replicating, E3-deleted Ad type 5 host range mutant (Ad5 hr) encoding full-length single-chain HIVBaLgp120 linked to the D1 and D2 domains of rhesus macaque CD4 (rhFLSC) we systematically deleted the genes encoding early region 4 open reading frame 1 (E4orf1) through E4orf4. All the Ad-rhFLSC vectors produced similar levels of viral progeny. Cell cycle analysis of infected human and monkey cells revealed no differences in virus-host interaction. The parental and E4-deleted viruses expressed comparable levels of the transgene with kinetics similar to Ad late proteins. Similar levels of cellular immune responses and transgene-specific antibodies were elicited in vaccinated mice. However, differences in recognition of Ad proteins and induced antibody subtypes were observed, suggesting that the E4 gene products might modulate antibody responses by as yet unknown mechanisms. In short, we have improved the transgene carrying capacity by one thousand base pairs while preserving the replicability, levels of transgene expression, and immunogenicity critical to these vaccine vectors. This additional space allows for flexibility in vaccine design that could not be obtained with the current vector and as such should facilitate the goal of improving vaccine efficacy. To the best of our knowledge, this is the first report describing the effects of these E4 deletions on transgene expression and immunogenicity in a replicating Ad vector.

Prospects for oral replicating adenovirus-vectored vaccines

Orally delivered replicating adenovirus (Ad) vaccines have been used for decades to prevent adenovirus serotype 4 and 7 respiratory illness in military recruits, demonstrating exemplary safety and high efficacy. That experience suggests that oral administration of live recombinant Ads (rAds) holds promise for immunization against other infectious diseases, including those that have been refractory to traditional vaccination methods. Live rAds can express intact antigens from free-standing transgenes during replication in infected cells. Alternatively, antigenic epitopes can be displayed on the rAd capsid itself, allowing presentation of the epitope to the immune system both prior to and during replication of the virus. Such capsid-display rAds offer a novel vaccine approach that could be used either independently of or in combination with transgene expression strategies to provide a new tool in the search for protection from infectious disease.

Recombinant vaccines against T. gondii: comparison between homologous and heterologous vaccination protocols using two viral vectors expressing SAG1

The use of recombinant viral vectors expressing T. gondii antigens is a safe and efficient approach to induce immune response against the parasite and a valuable tool for vaccine development. We have previously protected mice from toxoplasmosis by immunizing the animals with an adenovirus expressing the protein SAG1 (AdSAG1) of T. gondii. We are now looking for ways to improve the vaccination strategy and enhance protection. One limitation of homologous vaccinations (sequential doses of the same vector) is induction of anti-vector immune response that blocks cell transduction, restricts transgene expression and, consequently, compromises the overall outcome of vaccination. One way to avert the effects of anti-vector response is to use different viruses in prime and boost (heterologous vaccination). Bearing this in mind, we generated a modified Vaccinia Virus Ankara encoding SAG1 (MVASAG1), to be tested as boost agent after prime with AdSAG1. Although minor differences were observed in the magnitude of the anti-SAG1 immune response induced by each vaccination protocol, the heterologous immunization with AdSAG1 followed by MVASAG1 resulted in improved capacity to control brain cyst formation in a model of chronic toxoplasmosis in C57BL/6 mice.

Safety and immunogenicity of an oral, replicating adenovirus serotype 4 vector vaccine for H5N1 influenza: a randomised, double-blind, placebo-controlled, phase 1 study

Background

Replication-competent virus vector vaccines might have advantages compared with non-replicating vector vaccines. We tested the safety and immunogenicity of an oral adenovirus serotype 4 vector vaccine candidate (Ad4-H5-Vtn) expressing the haemagglutinin from an avian influenza A H5N1 virus.

Methods

We did this phase 1 study at four sites in the USA. We used a computer-generated randomisation list (block size eight, stratified by site) to assign healthy volunteers aged 18–40 years to receive one of five doses of Ad4-H5-Vtn (10⁷ viral particles [VP], 10⁸ VP, 10⁹ VP, 10¹⁰ VP, 10¹¹ VP) or placebo (3:1). Vaccine or placebo was given on three occasions, about 56 days apart. Participants, investigators, and study-site personnel were masked to assignment throughout the study. Subsequently, volunteers received a boost dose with 90 μg of an inactivated parenteral H5N1 vaccine. Primary immunogenicity endpoints were seroconversion by haemagglutination-inhibition (HAI), defined as a four-times rise compared with baseline titre, and HAI geometric mean titre (GMT). We solicited symptoms of reactogenicity daily for 7 days after each vaccination and recorded symptoms that persisted beyond 7 days as adverse events. Primary analysis was per protocol. This trial is registered with ClinicalTrials.gov, number NCT01006798.

Findings

We enrolled 166 participants (125 vaccine; 41 placebo) between Oct 19, 2009, and Sept 9, 2010. HAI responses were low: 13 of 123 vaccinees (11%, 95% CI 6–17) and three of 41 placebo recipients (7%, 2–20) seroconverted. HAI GMT was 6 (95% CI 5–7) for vaccinees, and 5 (5–6) for placebo recipients. However, when inactivated H5N1 vaccine became available, one H5N1 boost was offered to all participants. In this substudy, HAI seroconversion occurred in 19 of 19 participants in the 10¹¹ VP cohort (100%; 95% CI 82–100) and eight of 22 placebo recipients (36%; 17–59); 17 of 19 participants in the 10¹¹ VP cohort (89%; 67–99) achieved seroprotection compared with four of 22 placebo recipients (18%; 5–40); GMT was 135 (89–205) with 10¹¹ VP, compared with 13 (7–21) with placebo. The cumulative frequency of abdominal pain, diarrhoea, and nasal congestion after all three vaccinations was significantly higher in vaccinees than placebo recipients (21 [16·8%] of 125 vs one [2·4%] of 41, p=0·017; 24 [19·2%] of 125 vs two [4·9%] of 41, p=0·027; 41 [32·8%] of 125 vs six [14·6%] of 41, p=0·028; respectively). No serious treatment-related adverse events occurred.

Interpretation

Oral Ad4 vector priming might enhance the efficacy of poorly immunogenic vaccines such as H5N1.

Funding

Wellcome Trust Foundation, PaxVax.

Recent advances in molecular medicine techniques for the diagnosis, prevention, and control of infectious diseases

In recent years we have observed great advances in our ability to combat infectious diseases. Through the development of novel genetic methodologies, including a better understanding of pathogen biology, pathogenic mechanisms, advances in vaccine development, designing new therapeutic drugs, and optimization of diagnostic tools, significant infectious diseases are now better controlled. Here, we briefly describe recent reports in the literature concentrating on infectious disease control. The focus of this review is to describe the molecular methods widely used in the diagnosis, prevention, and control of infectious diseases with regard to the innovation of molecular techniques. Since the list of pathogenic microorganisms is extensive, we emphasize some of the major human infectious diseases (AIDS, tuberculosis, malaria, rotavirus, herpes virus, viral hepatitis, and dengue fever). As a consequence of these developments, infectious diseases will be more accurately and effectively treated; safe and effective vaccines are being developed and rapid detection of infectious agents now permits countermeasures to avoid potential outbreaks and epidemics. But, despite considerable progress, infectious diseases remain a strong challenge to human survival.

Current and novel approaches to vaccine development against tuberculosis

Antibiotics and vaccines are the two most successful medical countermeasures that humans have created against a number of pathogens. However a select few e.g., Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB) have evaded eradication by vaccines and therapeutic approaches. TB is a global public health problem that kills 1.4 million people per year. The past decade has seen significant progress in developing new vaccine candidates, but the most fundamental questions in understanding disease progression and protective host responses that are responsible for controlling Mtb infection still remain poorly resolved. Current TB treatment requires intense chemotherapy with several antimicrobials, while the only approved vaccine is the classical viable whole-cell based Bacille-Calmette-Guerin (BCG) that protects children from severe forms of TB, but fails to protect adults. Taken together, there is a growing need to conduct basic and applied research to develop novel vaccine strategies against TB. This review is focused on the discussion surrounding current strategies and innovations being explored to discover new protective antigens, adjuvants, and delivery systems in the hopes of creating an efficacious TB vaccine.

Pre-existing immunity against vaccine vectors--friend or foe?

Over the last century, the successful attenuation of multiple bacterial and viral pathogens has led to an effective, robust and safe form of vaccination. Recently, these vaccines have been evaluated as delivery vectors for heterologous antigens, as a means of simultaneous vaccination against two pathogens. The general consensus from published studies is that these vaccine vectors have the potential to be both safe and efficacious. However, some of the commonly employed vectors, for example Salmonella and adenovirus, often have pre-existing immune responses in the host and this has the potential to modify the subsequent immune response to a vectored antigen. This review examines the literature on this topic, and concludes that for bacterial vectors there can in fact, in some cases, be an enhancement in immunogenicity, typically humoral, while for viral vectors pre-existing immunity is a hindrance for subsequent induction of cell-mediated responses.

Advances and future challenges in recombinant adenoviral vectored H5N1 influenza vaccines

The emergence of a highly pathogenic avian influenza virus H5N1 has increased the potential for a new pandemic to occur. This event highlights the necessity for developing a new generation of influenza vaccines to counteract influenza disease. These vaccines must be manufactured for mass immunization of humans in a timely manner. Poultry should be included in this policy, since persistent infected flocks are the major source of avian influenza for human infections. Recombinant adenoviral vectored H5N1 vaccines are an attractive alternative to the currently licensed influenza vaccines. This class of vaccines induces a broadly protective immunity against antigenically distinct H5N1, can be manufactured rapidly, and may allow mass immunization of human and poultry. Recombinant adenoviral vectors derived from both human and non-human adenoviruses are currently being investigated and appear promising both in nonclinical and clinical studies. This review will highlight the current status of various adenoviral vectored H5N1 vaccines and will outline novel approaches for the future.

Recombinant influenza vaccines

This review covers the problems encountered in the construction and production of new recombinant influenza vaccines. New approaches to the development of influenza vaccines are investigated; they include reverse genetics methods, production of virus-like particles, and DNA- and viral vector-based vaccines. Such approaches as the delivery of foreign genes by DNA- and viral vector-based vaccines can preserve the native structure of antigens. Adenoviral vectors are a promising gene-delivery platform for a variety of genetic vaccines. Adenoviruses can efficiently penetrate the human organism through mucosal epithelium, thus providing long-term antigen persistence and induction of the innate immune response. This review provides an overview of the practicability of the production of new recombinant influenza cross-protective vaccines on the basis of adenoviral vectors expressing hemagglutinin genes of different influenza strains.