A novel chimpanzee serotype-based adenoviral vector as delivery tool for cancer vaccines

One HA stalk topping multiple heads as a novel influenza vaccine

Classic chimeric hemagglutinin (cHA) was designed to induce immune responses against the conserved stalk domain of HA. However, it is unclear whether combining more than one HA head domain onto one stalk domain is immunogenic and further induce immune responses against influenza viruses. Here, we constructed numerous novel cHAs comprising two or three fuzed head domains from different subtypes grafted onto one stalk domain, designated as cH1-H3, cH1-H7, cH1-H3-H7, and cH1-H7-H3. The three-dimensional structures of these novel cHAs were modelled using bioinformatics simulations. Structural analysis showed that the intact neutralizing epitopes were exposed in cH1-H7 and were predicted to be immunogenic. The immunogenicity of the cHAs constructs was evaluated in mice using a chimpanzee adenoviral vector (AdC68) vaccine platform. The results demonstrated that cH1-H7 expressed by AdC68 (AdC68-cH1-H7) induced the production of high levels of binding antibodies, neutralizing antibodies, and hemagglutinin inhibition antibodies against homologous pandemic H1N1, drifted seasonal H1N1, and H7N9 virus. Moreover, vaccinated mice were fully protected from a lethal challenge with the aforementioned influenza viruses. Hence, cH1-H7 cHAs with potent immunogenicity might be a potential novel vaccine to provide protection against different subtypes of influenza virus.

Safety, tolerability, and immunogenicity of the chimpanzee adenovirus type 3-vectored Marburg virus (cAd3-Marburg) vaccine in healthy adults in the USA: a first-in-human, phase 1, open-label, dose-escalation trial

BACKGROUND

WHO has identified Marburg virus as an emerging virus requiring urgent vaccine research and development, particularly due to its recent emergence in Ghana. We report results from a first-in-human clinical trial evaluating a replication-deficient recombinant chimpanzee adenovirus type 3 (cAd3)-vectored vaccine encoding a wild-type Marburg virus Angola glycoprotein (cAd3-Marburg) in healthy adults.

METHODS

We did a first-in-human, phase 1, open-label, dose-escalation trial of the cAd3-Marburg vaccine at the Walter Reed Army Institute of Research Clinical Trials Center in the USA. Healthy adults aged 18-50 years were assigned to receive a single intramuscular dose of cAd3-Marburg vaccine at either 1 × 1010 or 1 × 1011 particle units (pu). Primary safety endpoints included reactogenicity assessed for the first 7 days and all adverse events assessed for 28 days after vaccination. Secondary immunogenicity endpoints were assessment of binding antibody responses and T-cell responses against the Marburg virus glycoprotein insert, and assessment of neutralising antibody responses against the cAd3 vector 4 weeks after vaccination. This study is registered with ClinicalTrials.gov, NCT03475056.

FINDINGS

Between Oct 9, 2018, and Jan 31, 2019, 40 healthy adults were enrolled and assigned to receive a single intramuscular dose of cAd3-Marburg vaccine at either 1 × 1010 pu (n=20) or 1 × 1011 pu (n=20). The cAd3-Marburg vaccine was safe, well tolerated, and immunogenic. All enrolled participants received cAd3-Marburg vaccine, with 37 (93%) participants completing follow-up visits; two (5%) participants moved from the area and one (3%) was lost to follow-up. No serious adverse events related to vaccination occurred. Mild to moderate reactogenicity was observed after vaccination, with symptoms of injection site pain and tenderness (27 [68%] of 40 participants), malaise (18 [45%] of 40 participants), headache (17 [43%] of 40 participants), and myalgia (14 [35%] of 40 participants) most commonly reported. Glycoprotein-specific antibodies were induced in 38 (95%) of 40 participants 4 weeks after vaccination, with geometric mean titres of 421 [95% CI 209-846] in the 1 × 1010 pu group and 545 [276-1078] in the 1 × 1011 pu group, and remained significantly elevated at 48 weeks compared with baseline titres (39 [95% CI 13-119] in the 1 ×1010 pu group and 27 [95-156] in the 1 ×1011 pu group; both p<0·0001). T-cell responses to the glycoprotein insert and neutralising responses against the cAd3 vector were also increased at 4 weeks after vaccination.

INTERPRETATION

This first-in-human trial of this cAd3-Marburg vaccine showed the agent is safe and immunogenic, with a safety profile similar to previously tested cAd3-vectored filovirus vaccines. 95% of participants produced a glycoprotein-specific antibody response at 4 weeks after a single vaccination, which remained in 70% of participants at 48 weeks. These findings represent a crucial step in the development of a vaccine for emergency deployment against a re-emerging pathogen that has recently expanded its reach to new regions.

FUNDING

National Institutes of Health.

Novel and efficient method for the reconstruction of adenoviruses through isothermal assembly and its potential applications

Adenovirus based vectors are useful tools for vaccine development, gene therapy, and oncolytic virotherapy. Here we describe a novel approach for the genetic engineering of any portion of the adenovirus genome and the reconstruction of either fully replication competent or defective virions. This innovative strategy is rapid, effective and suitable for the manipulation of the entire genome broadening the spectrum of potential applications for the adenovirus system. Our strategy involved insertion of restriction enzyme recognition sequences absent in the native virus into the termini of the adenovirus genome in order to facilitate recovery. These restriction enzyme sites, together with the two inverted terminal repeats and packaging sequences, were synthesized and then subcloned into the pBR322 vector. The remaining internal portion of the adenovirus genome was separated and amplified via PCR into six segments, of which groups of two were joined together by PCR and then subcloned into pBR322 plasmids. During the PCR reaction, an overlap of 30-40 bp was added to the termini of the adjacent fragments, allowing for the subsequent isothermal assembly and correct orientation of all fragments. This approach allows for the genetic modification of each genomic fragment according to the specific research goals, (e.g., deletion, substitution, addition, etc.) To recreate the entire viral genome, the four engineered fragments (each comprised of two adenovirus genomic sections) as well as the pBR322 backbone, were reassembled into a single construct utilizing an isothermal assembly reaction. Finally, the reassembled plasmid containing the entire genome was linearized and transfected into HEK293 cells to recover the complete reconstructed adenoviral vector. Using this approach, we have successfully generated two recombinant reporter adenoviruses, one of human adenovirus serotype 14 and another of serotype 55. The E3 region was replaced by the reporter genes (GFP and Luciferase) to visualize and track the recovery process. Subsequent infection of A549 cells with these reconstructed adenovirus vectors demonstrated that they were replication competent. This method shortens the viral reconstruction process because the one-step isothermal assembly requires less than 4 days, and recombinant adenovirus recovery occurs within 10 days. This new method allows for single or multiple genetic modifications within any portion of the viral genome and can be used to construct or manipulate any adenovirus whose complete genome sequence is known.

Repeated-Dose Toxicity, Biodistribution, and Shedding Assessments With a ChAd155 Respiratory Syncytial Virus Vaccine Candidate Evaluated in Rabbits and Rats

Respiratory syncytial virus (RSV) is a leading cause of acute lower respiratory tract infections (LRTI) in infants, and toddlers and vaccines are not yet available. A pediatric RSV vaccine (ChAd155-RSV) is being developed to protect infants against RSV disease. The ChAd155-RSV vaccine consists of a recombinant replication-deficient chimpanzee-derived adenovirus (ChAd) group C vector engineered to express the RSV antigens F, N, and M2-1. The local and systemic effects of three bi-weekly intramuscular injections of the ChAd155-RSV vaccine was tested in a repeated-dose toxicity study in rabbits. After three intramuscular doses, the ChAd155-RSV vaccine was considered well-tolerated. Changes due to the vaccine-elicited inflammatory reaction/immune response were observed along with transient decreases in platelet count without physiological consequences, already reported for other adenovirus-based vaccines. In addition, the biodistribution and shedding of ChAd155-RSV were also characterized in two studies in rats. The distribution and persistence of the ChAd155-RSV vaccine candidate was consistent with other similar adenovector-based vaccines, with quantifiable levels of ChAd155-RSV observed at the injection site (muscle) and the draining lymph nodes up to 69 days post administration. The shedding results demonstrated that ChAd155-RSV was generally not detectable in any secretions or excreta samples. In conclusion, the ChAd155-RSV vaccine was well-tolerated locally and systemically.

Understanding Post Entry Sorting of Adenovirus Capsids; A Chance to Change Vaccine Vector Properties

Adenovirus vector-based genetic vaccines have emerged as a powerful strategy against the SARS-CoV-2 health crisis. This success is not unexpected because adenoviruses combine many desirable features of a genetic vaccine. They are highly immunogenic and have a low and well characterized pathogenic profile paired with technological approachability. Ongoing efforts to improve adenovirus-vaccine vectors include the use of rare serotypes and non-human adenoviruses. In this review, we focus on the viral capsid and how the choice of genotypes influences the uptake and subsequent subcellular sorting. We describe how understanding capsid properties, such as stability during the entry process, can change the fate of the entering particles and how this translates into differences in immunity outcomes. We discuss in detail how mutating the membrane lytic capsid protein VI affects species C viruses' post-entry sorting and briefly discuss if such approaches could have a wider implication in vaccine and/or vector development.

The potential of adenoviral vaccine vectors with altered antigen presentation capabilities

Introduction: Despite their appeal as vaccine vectors, adenoviral vectors are yet unable to induce protective immune responses against some weakly immunogenic antigens. Additionally, the maximum doses of adenovirus-based vaccines are limited by vector-induced toxicity, causing vector elimination and diminished immune responses against the target antigen. In order to increase immune responses to the transgene, while maintaining a moderate vector dose, new technologies for improved transgene presentation have been developed for adenoviral vaccine vectors.Areas covered: This review provides an overview of different genetic-fusion adjuvants that aim to improve antigen presentation in the context of adenoviral vector-based vaccines. The influence on both T cell and B cell responses are discussed, with a main focus on two technologies: MHC class II-associated invariant chain and virus-like-vaccines.Expert opinion: Different strategies have been tested to improve adenovirus-based vaccinations with varying degrees of success. The reviewed genetic adjuvants were designed to increase antigen processing and MHC presentation, or promote humoral immune responses with an improved conformational antigen display. While none of the introduced technologies is universally applicable, this review shall give an overview to identify potential improvements for future vaccination approaches.

Interaction of adenovirus with antibodies, complement, and coagulation factors

Adenovirus (AdV) is one of the most widely used vectors for gene therapy and vaccine studies due to its excellent transduction efficiency, capacity for large transgenes, and high levels of gene expression. When administered intravascularly, the fate of AdV vectors is heavily influenced by interactions with host plasma proteins. Some plasma proteins can neutralize AdV, but AdV can also specifically bind plasma proteins that protect against neutralization and preserve activity. This review summarizes the plasma proteins that interact with AdV, including antibodies, complement, and vitamin K-dependent coagulation factors. We will also review the complex interactions of these plasma proteins with each other and with cellular proteins, as well as strategies for developing better AdV vectors that evade or manipulate plasma proteins.

A recombinant bovine herpesvirus-4 vectored vaccine delivered via intranasal nebulization elicits viral neutralizing antibody titers in cattle

Recombinant herpesvirus vaccine vectors offer distinct advantages in next-generation vaccine development, primarily due to the ability to establish persistent infections to provide sustainable antigen responses in the host. Recombinant bovine herpesvirus-4 (BoHV-4) has been previously shown to elicit protective immunity in model laboratory animal species against a variety of pathogens. For the first time, we describe the induction of antigen-specific immune responses to two delivered antigens in the host species after intranasal nebulization of recombinant BoHV-4 expressing the chimeric peptide containing the bovine viral diarrhea virus (BVDV) glycoprotein E2 and the bovine herpesvirus 1 (BoHV-1) glycoprotein D (BoHV-4-A-CMV-IgK-gE2gD-TM). In this study, four cattle were immunized via intranasal nebulization with the recombinant BoHV-4 construct. Two of the cattle were previously infected with wild-type BoHV-4, and both developed detectable serologic responses to BVDV and BoHV-1. All four immunized cattle developed detectable viral neutralizing antibody responses to BVDV, and one steer developed a transient viral neutralizing response to BoHV-1. Approximately one year after immunization, immunosuppressive doses of the glucocorticoid dexamethasone were administered intravenously to all four cattle. Within two weeks of immunosuppression, all animals developed viral neutralizing antibody responses to BoHV-1, and all animals maintained BVDV viral neutralizing capacity. Overall, nebulization of BoHV-4-A-CMV-IgK-gE2gD-TM persistently infects cattle, is capable of eliciting antigen-specific immunity following immunization, including in the presence of pre-existing BoHV-4 immunity, and recrudescence of the virus boosts the immune response to BoHV-4-vectored antigens. These results indicate that BoHV-4 is a viable and attractive vaccine delivery platform for use in cattle.

Development of novel vaccine vectors: Chimpanzee adenoviral vectors

Adenoviral vector has been employed as one of the most efficient means against infectious diseases and cancer. It can be genetically modified and armed with foreign antigens to elicit specific antibody responses and T cell responses in hosts as well as engineered to induce apoptosis in cancer cells. The chimpanzee adenovirus-based vector is one kind of novel vaccine carriers whose unique features and non-reactivity to pre-existing human adenovirus neutralizing antibodies makes it an outstanding candidate for vaccine research and development. Here, we review the different strategies for constructing chimpanzee adenoviral vectors and their applications in recent clinical trials and also discuss the oncolytic virotherapy and immunotherapy based on chimpanzee adenoviral vectors.

Novel Concepts for HIV Vaccine Vector Design

The unprecedented challenges of developing effective vaccines against intracellular pathogens such as HIV, malaria, and tuberculosis have resulted in more rational approaches to vaccine development. Apart from the recent advances in the design and selection of improved epitopes and adjuvants, there are also ongoing efforts to optimize delivery platforms.

The unprecedented challenges of developing effective vaccines against intracellular pathogens such as HIV, malaria, and tuberculosis have resulted in more rational approaches to vaccine development. Apart from the recent advances in the design and selection of improved epitopes and adjuvants, there are also ongoing efforts to optimize delivery platforms. Viral vectors are the best-characterized delivery tools because of their intrinsic adjuvant capability, unique cellular tropism, and ability to trigger robust adaptive immune responses. However, a known limitation of viral vectors is preexisting immunity, and ongoing efforts are aimed at developing novel vector platforms with lower seroprevalence. It is also becoming increasingly clear that different vectors, even those derived from phylogenetically similar viruses, can elicit substantially distinct immune responses, in terms of quantity, quality, and location, which can ultimately affect immune protection. This review provides a summary of the status of viral vector development for HIV vaccines, with a particular focus on novel viral vectors and the types of adaptive immune responses that they induce.

Development of Novel Vaccines Against Infectious Diseases Based on Chimpanzee Adenoviral Vector

Vaccination is considered to be the most effective method of preventing infectious or other diseases. Adenovirus (Ad) is one the most promising vectors in vaccine research and development. It can induce not only potent humoral but also cellular immune responses, and has therefore been widely applied in basic and translational studies. Chimpanzee Ad is a rare serotype circulating in humans. This circumvents the problem of preexisting immunity to human Ad serotypes, enhancing Chimpanzee Ad prospects in vaccine development. Here we describe experimental procedures used to generate a new generation of rabies vaccine based on a chimpanzee Ad vector, which can be extended in the development of novel vaccines against other infectious diseases.

Effect of HIV-1 envelope cytoplasmic tail on adenovirus primed virus encoded virus-like particle immunizations

The low number of envelope (Env) spikes presented on native HIV-1 particles is a major impediment for HIV-1 prophylactic vaccine development. We designed virus-like particle encoding adenoviral vectors utilizing SIVmac239 Gag as an anchor for full length and truncated HIV-1 M consensus Env. Truncated Env overexpressed VRC01 and 17b binding antigen on the surface of transduced cells while the full length Env vaccine presented more and similar amounts of antigen binding to the trimer conformation sensitive antibodies PGT151 and PGT145, respectively. The adenoviral vectors were used to prime Balb/c mice followed by sequential boosting with chimpanzee type 63, and chimpanzee type 3 adenoviral vectors encoding SIVmac239 Gag and full length consensus Env. Both vaccine regimens induced increasing titers of binding antibody responses after each immunization, and significant differences in immune responses between the two groups were observed after the final immunization. Full length Env priming skewed antibody responses towards gp41, while truncated Env priming induced responses primarily targeting gp120 containing and derived antigens. Importantly, no differences in neutralizing antibody responses were found between the different priming regimens as both induced high titered tier 1 neutralizing antibodies, but no tier 2 antibodies, possibly reflecting the similar presentation of trimer specific antibody epitopes. The described vaccine regimens provide insight into the effects of the HIV-1 Env cytoplasmic tail on epitope presentation and subsequent immune responses, which is relevant for the interpretation of current clinical trials that are using truncated Env as an immunogen. The regimens described here provide similar neutralization titers, and thus are useful for investigating the importance of specificity in non-neutralizing antibody mediated protection against viral challenge.

Rapid, Efficient, and Modular Generation of Adenoviral Vectors via Isothermal Assembly

Adenoviral vectors have yielded promising results as carriers for gene transfer and vaccines in basic research and clinical applications. However, most common procedures to construct adenoviral vectors and manipulate adenovirus (Ad) genomes are complex and labor-intensive. An easy and detailed protocol for the rapid, efficient, and modular generation of chimpanzee Ad serotype 68 (AdC68) as a molecular clone via isothermal assembly, which directionally assembles multiple DNA fragments in a single isothermal reaction without restriction enzymes or ligases, is presented. Any serotype of adenovirus with the sequence of genome known can be constructed as a molecular clone by this method. Recombinant adenoviral vectors can be created via one-step isothermal assembly in <3 days, and recombinant Ads can be rescued within 8 days. This protocol is practical for manipulations of Ad genomes, because an entire Ad genome can be divided into specific fragments within modular plasmids. © 2016 by John Wiley & Sons, Inc.

Xenogenic Adenoviral Vectors

Many nonhuman adenoviruses (AdVs) of simian, bovine, porcine, canine, ovine, murine, and fowl origin are being developed as gene delivery systems for recombinant vaccines and gene therapy applications. In addition to circumventing preexisting human AdV (HAdV) immunity, nonhuman AdV vectors utilize coxsackievirus-adenovirus receptor or other receptors for vector internalization, thereby expanding the range of cell types that can be targeted. Nonhuman AdV vectors also provide excellent platforms for veterinary vaccines. A specific nonhuman AdV vector when used in its species of origin could provide an excellent animal model for evaluating the vector efficacy and pathogenesis. These vectors are useful in prime–boost approaches with other AdV vectors or with other gene delivery systems including DNA immunization and viral or bacterial vectors. When multiple vector inoculations are required, nonhuman AdV vectors could supplement HAdV or other viral vectors.

Analysis of T cell responses to chimpanzee adenovirus vectors encoding HIV gag-pol-nef antigen

Adenoviruses have been shown to be both immunogenic and efficient at presenting HIV proteins but recent trials have suggested that they may play a role in increasing the risk of HIV acquisition. This risk may be associated with the presence of pre-existing immunity to the viral vectors. Chimpanzee adenoviruses (chAd) have low seroprevalence in human populations and so reduce this risk. ChAd3 and chAd63 were used to deliver an HIV gag, pol and nef transgene. ELISpot analysis of T cell responses in mice showed that both chAd vectors were able to induce an immune response to Gag and Pol peptides but that only the chAd3 vector induced responses to Nef peptides. Although the route of injection did not influence the magnitude of immune responses to either chAd vector, the dose of vector did. Taken together these results demonstrate that chimpanzee adenoviruses are suitable vector candidates for the delivery of HIV proteins and could be used for an HIV vaccine and furthermore the chAd3 vector produces a broader response to the HIV transgene.

Taxonomy proposal for Old World monkey adenoviruses: characterisation of several non-human, non-ape primate adenovirus lineages

A species classification regarding Old World monkey adenoviruses is proposed. We determined the nucleotide sequences of PCR-amplified fragments from the genes of the IVa2, DNA-dependent DNA polymerase, penton base, and hexon proteins from every simian adenovirus (SAdV) serotype that originated from Old World monkeys for which the full genome sequence had not yet been published. We confirmed that the majority of Old Word monkey SAdVs belong to two previously established species. Interestingly, one is the most recently established human AdV species, Human mastadenovirus G, which includes a single human virus, HAdV-52, as well as SAdV-1, -2, -7, -11, -12, and -15. The other approved species, Simian mastadenovirus A includes SAdV-3, -4, -6, -9, -10, -14, and -48. Several SAdVs (SAdV-5, -8, -49, -50) together with baboon AdV-1 and rhesus monkey AdV strains A1139, A1163, A1173, A1258, A1285, A1296, A1312, A1327 and A1335 have been proposed to be classified into an additional species, Simian mastadenovirus B. Another proposed species, Simian mastadenovirus C has been described for SAdV-19, baboon AdV-2/4 and -3. Our study revealed the existence of four additional AdV lineages. The corresponding new candidate species are Simian mastadenovirus D (for SAdV-13), Simian mastadenovirus E (for SAdV-16), Simian mastadenovirus F (for SAdV-17 and -18), and Simian mastadenovirus G (for SAdV-20). Several biological and genomic properties, such as the host origin, haemagglutination profile, number of fibre genes, and G+C content of the genome, strongly support this classification. Three SAdV strains originating from the American Type Culture Collection turned out to be mixtures of at least two virus types, either of the same species (SAdV-12 and -15 types from Human mastadenovirus G) or of two different species (SAdV-5 types from Simian mastadenovirus B and Human mastadenovirus G).

Antigen expression determines adenoviral vaccine potency independent of IFN and STING signaling

Recombinant adenoviral vectors (rAds) are lead vaccine candidates for protection against a variety of pathogens, including Ebola, HIV, tuberculosis, and malaria, due to their ability to potently induce T cell immunity in humans. However, the ability to induce protective cellular immunity varies among rAds. Here, we assessed the mechanisms that control the potency of CD8 T cell responses in murine models following vaccination with human-, chimpanzee-, and simian-derived rAds encoding SIV-Gag antigen (Ag). After rAd vaccination, we quantified Ag expression and performed expression profiling of innate immune response genes in the draining lymph node. Human-derived rAd5 and chimpanzee-derived chAd3 were the most potent rAds and induced high and persistent Ag expression with low innate gene activation, while less potent rAds induced less Ag expression and robustly induced innate immunity genes that were primarily associated with IFN signaling. Abrogation of type I IFN or stimulator of IFN genes (STING) signaling increased Ag expression and accelerated CD8 T cell response kinetics but did not alter memory responses or protection. These findings reveal that the magnitude of rAd-induced memory CD8 T cell immune responses correlates with Ag expression but is independent of IFN and STING and provide criteria for optimizing protective CD8 T cell immunity with rAd vaccines.

Adenovirus-Based Vectors for the Development of Prophylactic and Therapeutic Vaccines

Emerging and reemerging infectious diseases as well as cancer pose great global health impacts on the society. Vaccines have emerged as effective treatments to prevent or reduce the burdens of already developed diseases. This is achieved by means of activating various components of the immune system to generate systemic inflammatory reactions targeting infectious agents or diseased cells for control/elimination. DNA virus-based genetic vaccines gained significant attention in the past decades owing to the development of DNA manipulation technologies, which allowed engineering of recombinant viral vectors encoding sequences for foreign antigens or their immunogenic epitopes as well as various immunomodulatory molecules. Despite tremendous progress in the past 50 years, many hurdles still remain for achieving the full clinical potential of viral-vectored vaccines. This chapter will present the evolution of vaccines from “live” or “attenuated” first-generation agents to recombinant DNA and viral-vectored vaccines. Particular emphasis will be given to human adenovirus (Ad) for the development of prophylactic and therapeutic vaccines. Ad biological properties related to vaccine development will be highlighted along with their advantages and potential hurdles to be overcome. In particular, we will discuss (1) genetic modifications in the Ad capsid protein to reduce the intrinsic viral immunogenicity, (2) antigen capsid incorporation for effective presentation of foreign antigens to the immune system, (3) modification of the hexon and fiber capsid proteins for Ad liver de-targeting and selective retargeting to cancer cells, (4) Ad-based vaccines carrying “arming” transgenes with immunostimulatory functions as immune adjuvants, and (5) oncolytic Ad vectors as a new therapeutic approach against cancer. Finally, the combination of adenoviral vectors with other non-adenoviral vector systems, the prime/boost strategy of immunization, clinical trials involving Ad-based vaccines, and the perspectives for the field development will be discussed.

Cancer vaccines targeting carcinoembryonic antigen: state-of-the-art and future promise

Concurrent with the US FDA's approval of the first therapeutic cancer vaccine, and supported by mounting clinical evidence indicating that targeting carcinoembryonic antigen (CEA) can safely overcome pre-existing tolerance, a multitude of novel CEA cancer vaccines are now in various stages of development. Since cancer-driven immune suppression often limits the efficacy of vaccines, numerous strategies are being examined in both preclinical and clinical settings to overcome immunosuppressive elements, including the combined use of vaccines with certain chemotherapies, immune checkpoint inhibitors, small-molecule targeted therapies and radiation. This review discusses the current state and future direction of therapeutic cancer vaccines targeting CEA, based on advances achieved over the last 5 years.

Development of chimpanzee adenoviruses as vaccine vectors: challenges and successes emerging from clinical trials

Replication-defective chimpanzee adenovirus vectors are emerging as a promising new class of genetic vaccine carriers. Chimpanzee adenovirus vectors have now reached the clinical stage and appear to be endowed with all the properties needed for human vaccine development, including high quality and magnitude of the immune response induced against the encoded antigens, good safety and ease of manufacturing on a large-scale basis. Here the authors review the recent findings of this novel class of adenovirus vectors and compare their properties to other clinical stage vaccine vectors derived from poxvirus, alphavirus and human adenovirus.

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

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

Comparative analysis of the magnitude, quality, phenotype, and protective capacity of simian immunodeficiency virus gag-specific CD8+ T cells following human-, simian-, and chimpanzee-derived recombinant adenoviral vector immunization

Recombinant adenoviral vectors (rAds) are the most potent recombinant vaccines for eliciting CD8(+) T cell-mediated immunity in humans; however, prior exposure from natural adenoviral infection can decrease such responses. In this study we show low seroreactivity in humans against simian- (sAd11, sAd16) or chimpanzee-derived (chAd3, chAd63) compared with human-derived (rAd5, rAd28, rAd35) vectors across multiple geographic regions. We then compared the magnitude, quality, phenotype, and protective capacity of CD8(+) T cell responses in mice vaccinated with rAds encoding SIV Gag. Using a dose range (1 × 10(7)-10(9) particle units), we defined a hierarchy among rAd vectors based on the magnitude and protective capacity of CD8(+) T cell responses, from most to least, as: rAd5 and chAd3, rAd28 and sAd11, chAd63, sAd16, and rAd35. Selection of rAd vector or dose could modulate the proportion and/or frequency of IFN-γ(+)TNF-α(+)IL-2(+) and KLRG1(+)CD127(-)CD8(+) T cells, but strikingly ∼30-80% of memory CD8(+) T cells coexpressed CD127 and KLRG1. To further optimize CD8(+) T cell responses, we assessed rAds as part of prime-boost regimens. Mice primed with rAds and boosted with NYVAC generated Gag-specific responses that approached ∼60% of total CD8(+) T cells at peak. Alternatively, priming with DNA or rAd28 and boosting with rAd5 or chAd3 induced robust and equivalent CD8(+) T cell responses compared with prime or boost alone. Collectively, these data provide the immunologic basis for using specific rAd vectors alone or as part of prime-boost regimens to induce CD8(+) T cells for rapid effector function or robust long-term memory, respectively.

Delivery of antigens by viral vectors for vaccination

Viral vectors have been developed as vaccine platforms for a number of pathogens and tumors. In particular, adenovirus (Ad)-based vectors expressing genes coding for pathogen or tumor antigens have proven efficacious to induce protective immunity. Major challenges in the use of Ad vectors are the high prevalence of anti-Ad immunity and the recent observation during an Ad-based HIV vaccine trial that led to increased HIV-1 acquisition in the presence of circulating anti-Ad5 neutralizing antibodies. In this review we summarize strategies to address these challenges and focus on modifications of the Ad capsid to enhance the adjuvant effect of anti-Ad immunogenicity and to circumvent pre-existing immunity. In addition, we summarize the current status and potential of other viral vector vaccines based on adeno-associated viruses, lentiviruses and poxviruses.

Gene-based vaccination with a mismatched envelope protects against simian immunodeficiency virus infection in nonhuman primates

The RV144 trial demonstrated that an experimental AIDS vaccine can prevent human immunodeficiency virus type 1 (HIV-1) infection in humans. Because of its limited efficacy, further understanding of the mechanisms of preventive AIDS vaccines remains a priority, and nonhuman primate (NHP) models of lentiviral infection provide an opportunity to define immunogens, vectors, and correlates of immunity. In this study, we show that prime-boost vaccination with a mismatched SIV envelope (Env) gene, derived from simian immunodeficiency virus SIVmac239, prevents infection by SIVsmE660 intrarectally. Analysis of different gene-based prime-boost immunization regimens revealed that recombinant adenovirus type 5 (rAd5) prime followed by replication-defective lymphocytic choriomeningitis virus (rLCMV) boost elicited robust CD4 and CD8 T-cell and humoral immune responses. This vaccine protected against infection after repetitive mucosal challenge with efficacies of 82% per exposure and 62% cumulatively. No effect was seen on viremia in infected vaccinated monkeys compared to controls. Protection correlated with the presence of neutralizing antibodies to the challenge viruses tested in peripheral blood mononuclear cells. These data indicate that a vaccine expressing a mismatched Env gene alone can prevent SIV infection in NHPs and identifies an immune correlate that may guide immunogen selection and immune monitoring for clinical efficacy trials.

Genetic cancer vaccines: current status and perspectives

INTRODUCTION

The recent approval of the first therapeutic cancer vaccine by the US Regulatory Agency represents a breakthrough event in the history of cancer treatment. The past scepticism towards this type of therapeutic intervention is now replaced by great expectations. The field is now moving towards the development of alternative vaccination technologies, which are capable of generating stronger, more durable and efficient immune responses against specific tumour-associated antigens (TAAs) in combination with cheaper and more standardised manufacturing.

AREAS COVERED

In this context, genetic vaccines are emerging among the most promising methodologies. Several evidences point to combinations of different genetic immunisation modalities (heterologous prime/boost) as a powerful approach to induce superior immune responses and achieve greater clinical efficacy. In this review, we provide an overview of the current status of development of genetic cancer vaccines with particular emphasis on adenoviral vector prime/DNA boost vaccination schedules.

EXPERT OPINION

We believe that therapeutic genetic cancer vaccines have the strong potential to become an established therapeutic modality for cancer in next coming years, in a manner similar to what have now become monoclonal antibodies.

T-cell-inducing vaccines - what's the future

In the twentieth century vaccine development has moved from the use of attenuated or killed micro-organisms to protein sub-unit vaccines, with vaccine immunogenicity assessed by measuring antibodies induced by vaccination. However, for many infectious diseases T cells are an important part of naturally acquired protective immune responses, and inducing these by vaccination has been the aim of much research. The progress that has been made in developing effective T-cell-inducing vaccines against viral and parasitic diseases such as HIV and malaria is discussed, along with recent developments in therapeutic vaccine development for chronic viral infections and cancer. Although many ways of inducing T cells by vaccination have been assessed, the majority result in low level, non-protective responses. Sufficient clinical research has now been conducted to establish that replication-deficient viral vectored vaccines lead the field in inducing strong and broad responses, and efficacy studies of T-cell-inducing vaccines against a number of diseases are finally demonstrating that this is a valid approach to filling the gaps in our defence against not only infectious disease, but some forms of cancer.

Emerging cancer vaccines: the promise of genetic vectors

Therapeutic vaccination against cancer is an important approach which, when combined with other therapies, can improve long-term control of cancer. In fact, the induction of adaptive immune responses against Tumor Associated Antigens (TAAs) as well as innate immunity are important factors for tumor stabilization/eradication. A variety of immunization technologies have been explored in last decades and are currently under active evaluation, such as cell-based, protein, peptide and heat-shock protein-based cancer vaccines. Genetic vaccines are emerging as promising methodologies to elicit immune responses against a wide variety of antigens, including TAAs. Amongst these, Adenovirus (Ad)-based vectors show excellent immunogenicity profile and have achieved immunological proof of concept in humans. In vivo electroporation of plasmid DNA (DNA-EP) is also a desirable vaccine technology for cancer vaccines, as it is repeatable several times, a parameter required for the long-term maintenance of anti-tumor immunity. Recent findings show that combinations of different modalities of immunization (heterologous prime/boost) are able to induce superior immune reactions as compared to single-modality vaccines. In this review, we will discuss the challenges and requirements of emerging cancer vaccines, particularly focusing on the genetic cancer vaccines currently under active development and the promise shown by Ad and DNA-EP heterologous prime-boost.

Advances and future challenges in adenoviral vector pharmacology and targeting

Adenovirus is a robust vector for therapeutic applications, but its use is limited by our understanding of its complex in vivo pharmacology. In this review we describe the necessity of identifying its natural, widespread, and multifaceted interactions with the host since this information will be crucial for efficiently redirecting virus into target cells. In the rational design of vectors, the notion of overcoming a sequence of viral "sinks" must be combined with re-targeting to target populations with capsid as well as shielding the vectors from pre-existing or toxic immune responses. It must also be noted that most known adenoviral pharmacology is deduced from the most commonly used serotypes, Ad5 and Ad2. However, these serotypes may not represent all adenoviruses, and may not even represent the most useful vectors for all purposes. Chimeras between Ad serotypes may become useful in engineering vectors that can selectively evade substantial viral traps, such as Kupffer cells, while retaining the robust qualities of Ad5. Similarly, vectorizing other Ad serotypes may become useful in avoiding immunity against Ad5 altogether. Taken together, this research on basic adenovirus biology will be necessary in developing vectors that interact more strategically with the host for the most optimal therapeutic effect.

Advances in human papilloma virus vaccines: a patent review

INTRODUCTION

Human papilloma virus (HPV) infection is the main factor associated with the development of cervical cancer. The currently available HPV vaccines, Gardasil and Cervarix, can prevent infection by certain HPV types, but not all. At present, research efforts are being devoted to developing more broad spectrum preventative vaccines, as well as therapeutic vaccines.

AREAS COVERED

Recent advances in HPV vaccine development are reviewed in this paper, with a focus on worldwide patents and patent applications. In principle, patents that have been granted since 2002 are covered. Exceptions are the patents pending at PCT stage and recent patent applications since 2009. Readers will gain insights into the cutting-edge technologies being used in the development and production of vaccines, as well as adjuvant systems.

EXPERT OPINION

In the future, the use of mosaic virus-like particles (VLPs,) comprising at least one L1 protein of each HPV type, may be able to prevent infection by all HPV types while patented codon-optimization techniques and the use of edible or DNA-based vaccines may be good places to start for reducing costs. Future vaccines should ideally have both preventive and therapeutic efficacies. Enhanced immunogenicity could be achieved by the use of more effective adjuvants, such as nanoparticle-based delivery systems, or new classes of adjuvants.

An efficient method of directly cloning chimpanzee adenovirus as a vaccine vector

Adenoviral vectors have shown great promise as vaccine carriers and in gene transfer to correct underlying genetic diseases. Traditionally, construction of adenoviral vectors is complex and time consuming. In this paper, we provide an improved method for efficient generation of novel adenoviral vectors by using direct cloning. We introduce a feasible and detailed protocol for the development of chimpanzee adenoviruses (Ads) as molecular clones, as well as for the generation of recombinant virus from the molecular clones. Recombinant viruses are genetically stable and induce potent immune responses in animals. Generation of new Ad molecular clones or new recombinant Ad can be achieved in 2 months or 2 weeks, respectively.

Nanoparticle delivery systems in cancer vaccines

Therapeutic strategies that involve the manipulation of the host's immune system are gaining momentum in cancer research. Antigen-loaded nanocarriers are capable of being actively taken up by antigen-presenting cells (APCs) and have shown promising potential in cancer immunotherapy by initiating a strong immunostimulatory cascade that results in potent antigen-specific immune responses against the cancer. Such carrier systems offer versatility in that they can simultaneously co-deliver adjuvants with the antigens to enhance APC activation and maturation. Furthermore, modifying the surface properties of these nanocarriers affords active targeting properties to APCs and/or enhanced accumulation in solid tumors. Here, we review some recent advances in these colloidal and particulate nanoscale systems designed for cancer immunotherapy and the potential for these systems to translate into clinical cancer vaccines.

Simian recombinant adenovirus delivered by the mucosal route modulates gammadelta T cells from murine genital tract

Although it has been demonstrated that mucosal immunization using vectors such as simian adenovirus (AdC) stimulates robust adaptive immune responses, there remains a paucity of information on the modulation of innate immune responses by such vectors. Using an established murine model of intravaginal immunization (Ivag), we have investigated whether mucosal gammadelta T cells participate in immune responses induced by AdC vectors. gammadelta T cell numbers were found to be increased in the vaginal tract. Moreover, gammadelta T cells isolated from the genital tract showed an activated phenotype and enhanced expression of cytokine gene. Altogether, our results demonstrate that AdC modulates gammadelta T cell responses and suggest that this cell population may influence immune responses following vaginal immunization.

Applying genomic and bioinformatic resources to human adenovirus genomes for use in vaccine development and for applications in vector development for gene delivery

Technological advances and increasingly cost-effect methodologies in DNA sequencing and computational analysis are providing genome and proteome data for human adenovirus research. Applying these tools, data and derived knowledge to the development of vaccines against these pathogens will provide effective prophylactics. The same data and approaches can be applied to vector development for gene delivery in gene therapy and vaccine delivery protocols. Examination of several field strain genomes and their analyses provide examples of data that are available using these approaches. An example of the development of HAdV-B3 both as a vaccine and also as a vector is presented.

Engineered adenovirus serotypes for overcoming anti-vector immunity

Adenovirus (Ad)-based gene transfer has been successfully utilised in gene therapy and vaccine applications. To date, an increasing number of human clinical trials utilise recombinant Ad-based vectors as a gene transfer platform. In particular, progress has been made recently in utilising Ad-based vectors as a vaccine platform in HIV, cancer immunotherapy approaches and in vaccination for other infections. Despite these successes, the scientific and bio-industrial communities have recently recognised that innate and pre-existing immunity against Ad vectors can constitute a serious obstacle to the development and application of this technology. It is essential to overcome vector-mediated immune responses, such as production of inflammatory cytokines and pre-existing immunity to Ad, because the induction of these responses not only shortens the period of gene expression but also leads to serious side effects. This review focuses on the biology of Ad infection and the approaches that are being adopted to overcome immunity against the Ad-based vectors.

Progress and prospects: immune responses to viral vectors

Viral vectors are potent gene delivery platforms used for the treatment of genetic and acquired diseases. However, just as viruses have evolved to infect cells efficiently, the immune system has evolved to fight off what it perceives as invading pathogens. Therefore, innate immunity and antigen-specific adaptive immune responses against vector-derived antigens reduce the efficacy and stability of in vivo gene transfer. In addition, a number of vectors are derived from parent viruses that humans encounter through natural infection, resulting in preexisting antibodies and possibly in memory responses against vector antigens. Similarly, antibody and T-cell responses may be directed against therapeutic gene products that often differ from the endogenous nonfunctional or absent protein that is being replaced. As details and mechanisms of such immune reactions are uncovered, novel strategies are being developed, and vectors are being specifically engineered to avoid, suppress or manipulate the response, ideally resulting in sustained expression and immune tolerance to the transgene product. This review provides a summary of our current knowledge of the interactions between the immune system adeno-associated virus, adenoviral and lentiviral vectors, and their transgene products.

Ovine atadenovirus, a novel and highly immunogenic vector in prime-boost studies of a candidate HIV-1 vaccine

Ovine adenovirus type 7 (OAdV) is the prototype member of the genus Atadenovirus. No immunity to the virus has so far been detected in human sera. We describe the construction and evaluation of a candidate HIV-1 vaccine based on OAdV and its utilisation alone and in combination with plasmid-, human adenovirus type 5 (HAdV5; a Mastadenovirus)-, and modified vaccinia Ankara (MVA)-vectored vaccines. All vectors expressed HIVA, an immunogen consisting of HIV-1 clade A consensus Gag-derived protein coupled to a T cell polyepitope. OAdV.HIVA was genetically stable, grew well and expressed high levels of protein from the Rous sarcoma virus promoter. OAdV.HIVA was highly immunogenic in mice and efficiently primed and boosted HIV-1-specific T cell responses together with heterologous HIVA-expressing vectors. There were significant differences between OAdV and HAdV5 vectors in priming of naïve CD8(+) T cell responses to HIVA and in the persistence of MHC class I-restricted epitope presentation in the local draining lymph nodes. OAdV.HIVA primed T cells more rapidly but was less persistent than AdV5.HIVA and thus induced a qualitatively distinct T cell response. Nevertheless, both vectors primed a response in mice that reduced viral titres in a surrogate challenge model by three to four orders of magnitude. Thus, OAdV is a novel, underexplored vaccine vector with potential for further development for HIV-1 and other vaccines. The data are discussed in the context of the latest HIV-1 vaccine developments.

New insights on adenovirus as vaccine vectors

Adenovirus (Ad) vectors were initially developed for treatment of genetic diseases. Their usefulness for permanent gene replacement was limited by their high immunogenicity, which resulted in rapid elimination of transduced cells through induction of T and B cells to antigens of Ad and the transgene product. The very trait that excluded their use for sustained treatment of genetic diseases made them highly attractive as vaccine carriers. Recently though results showed that Ad vectors based on common human serotypes, such as serotype 5, may not be ideal as vaccine carriers. A recently conducted phase 2b trial, termed STEP trial, with an AdHu5-based vaccine expressing antigens of human immunodeficiency virus 1 (HIV-1) not only showed lack of efficacy in spite of the vaccine's immunogenicity, but also suggested an increased trend for HIV acquisition in individuals that had circulating AdHu5 neutralizing antibodies prior to vaccination. Alternative serotypes from humans or nonhuman primates (NHPs), to which most humans lack pre-existing immunity, have been vectored and may circumvent the problems encountered with the use of AdHu5 vectors in humans. In summary, although Ad vectors have seen their share of setbacks in recent years, they remain viable tools for prevention or treatment of a multitude of diseases.