A preliminary and comparative evaluation of a novel Ad5 [E1-, E2b-] recombinant-based vaccine used to induce cell mediated immune responses

[Neurological complications after covid-19 vaccination]

The aim of our work was to study the relevance and incidence of neurological post-vaccination complications during the COVID-19 pandemic. Based on the results of a systematic literature search of several databases, the current review describes the diagnosed complications, including neurological, that occurred after the administration of the COVID-19 vaccine during the pandemic period. To fully establish the pathophysiological mechanisms of the development of a causal relationship of neurological complications with vaccines against COVID-19, it becomes necessary to continue long-term studies. This will make it possible to carry out a pharmacological correction of the quality of vaccine safety.

Mucosal COVID-19 vaccines: Risks, benefits and control of the pandemic

Based on mucosal immunization to promote both mucosal and systemic immune responses, next-generation coronavirus disease 2019 (COVID-19) vaccines would be administered intranasally or orally. The goal of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines is to provide adequate immune protection and avoid severe disease and death. Mucosal vaccine candidates for COVID-19 including vector vaccines, recombinant subunit vaccines and live attenuated vaccines are under development. Furthermore, subunit protein vac-cines and virus-vectored vaccines have made substantial progress in preclinical and clinical settings, resulting in SARS-CoV-2 intranasal vaccines based on the previously successfully used nasal vaccines. Additional to their ability to trigger stable, protective immune responses at the sites of pathogenic infection, the development of ‘specific’ mucosal vaccines targeting coronavirus antigens could be an excellent option for preventing future pandemics. However, their efficacy and safety should be confirmed.

Frequency and Associations of Adverse Reactions of COVID-19 Vaccines Reported to Pharmacovigilance Systems in the European Union and the United States

Introduction

This study aims to provide a risk assessment of the adverse reactions related to the COVID-19 vaccines manufactured by AstraZeneca, Janssen, Moderna, and Pfizer-BioNTech which have been in use in the European Union and the United States between December 2020 and October 2021.

Methods

Data from the European Database of Suspected Adverse Drug Reaction (EudraVigilance) and the Vaccine Adverse Events Reporting System (VAERS) from 2020 to October 2021 are analysed. More than 7.8 million adverse reactions of about 1.6 million persons are included. The adverse reactions are classified with the Common Toxicity Criteria (CTC) categories. COVID-19 vaccine exposures and adverse reactions reported between December 2020 and October 2021 are compared to influenza vaccine exposures and adverse reactions reported between 2020 and 2021. The population-level vaccine exposures to COVID-19 and influenza vaccines comprised about 451 million and 437 million exposures, respectively. Absolute and relative risk estimates are calculated by CTC categories and COVID-19 vaccines for the EU and US populations aged 18 years and older.

Results

A higher risk of reporting serious adverse reactions was observed for the COVID-19 vaccines in comparison to the influenza vaccines. Individuals age 65 and older were associated with a higher frequency of death, hospitalisations, and life-threatening reactions than younger individuals (relative risk estimates between 1.49 99% CI [1.44–1.55] and 8.61 99% CI [8.02–9.23]). Outcome onset of serious adverse reactions occurred within the first 7 days after vaccination in about 77.6–89.1% of cases. The largest absolute risks were observed for allergic, constitutional reactions, dermatological, gastrointestinal, neurological reactions, and localised and non-localised pain. The largest relative risks between COVID-19 vs. influenza vaccines were observed for allergic reactions, arrhythmia, general cardiovascular events, coagulation, haemorrhages, gastrointestinal, ocular, sexual organs reactions, and thrombosis.

Conclusion

The present study provides an overview of adverse reactions frequently reported to the pharmacovigilance systems following COVID-19 vaccination in the EU and US populations. Despite the limitations of passive reporting systems, these results may inform further clinical research investigating in more detail the pathophysiological mechanisms potentially associated with the COVID-19 vaccines.

Dual-Antigen COVID-19 Vaccine Subcutaneous Prime Delivery With Oral Boosts Protects NHP Against SARS-CoV-2 Challenge

We have developed a dual-antigen COVID-19 vaccine incorporating genes for a modified SARS-CoV-2 spike protein (S-Fusion) and the viral nucleocapsid (N) protein with an Enhanced T-cell Stimulation Domain (N-ETSD) to increase the potential for MHC class II responses. The vaccine antigens are delivered by a human adenovirus serotype 5 platform, hAd5 [E1-, E2b-, E3-], previously demonstrated to be effective in the presence of Ad immunity. Vaccination of rhesus macaques with the hAd5 S-Fusion + N-ETSD vaccine by subcutaneous prime injection followed by two oral boosts elicited neutralizing anti-S IgG and T helper cell 1-biased T-cell responses to both S and N that protected the upper and lower respiratory tracts from high titer (1 x 106 TCID50) SARS-CoV-2 challenge. Notably, viral replication was inhibited within 24 hours of challenge in both lung and nasal passages, becoming undetectable within 7 days post-challenge.

Phase I study of a multitargeted recombinant Ad5 PSA/MUC-1/brachyury-based immunotherapy vaccine in patients with metastatic castration-resistant prostate cancer (mCRPC)

Background

Antitumor vaccines targeting tumor-associated antigens (TAAs) can generate antitumor immune response. A novel vaccine platform using adenovirus 5 (Ad5) vectors [E1–, E2b–] targeting three TAAs—prostate-specific antigen (PSA), brachyury, and MUC-1—has been developed. Both brachyury and the C-terminus of MUC-1 are overexpressed in metastatic castration-resistant prostate cancer (mCRPC) and have been shown to play an important role in resistance to chemotherapy, epithelial–mesenchymal transition, and metastasis. The transgenes for PSA, brachyury, and MUC-1 all contain epitope modifications for the expression of CD8+ T-cell enhancer agonist epitopes. We report here the first-in-human trial of this vaccine platform.

Methods

Patients with mCRPC were given concurrently three vaccines targeting PSA, brachyury, and MUC-1 at 5×10¹¹ viral particles (VP) each, subcutaneously every 3 weeks for a maximum of three doses (dose de-escalation cohort), followed by a booster vaccine every 8 weeks for 1 year (dose-expansion cohort only). The primary objective was to determine the safety and the recommended phase II dose. Immune assays and clinical responses were evaluated.

Results

Eighteen patients with mCRPC were enrolled between July 2018 and September 2019 and received at least one vaccination. Median PSA was 25.58 ng/mL (range, 0.65–1006 ng/mL). The vaccine was tolerable and safe, and no grade >3 treatment-related adverse events or dose-limiting toxicities (DLTs) were observed. One patient had a partial response, while five patients had confirmed PSA decline and five had stable disease for >6 months. Median progression-free survival was 22 weeks (95% CI: 19.1 to 34). Seventeen (100%) of 17 patients mounted T-cell responses to at least one TAA, whereras 8 (47%) of 17 patients mounted immune responses to all three TAAs. Multifunctional T-cell responses to PSA, MUC-1, and brachyury were also detected after vaccination in the majority of the patients.

Conclusions

Ad5 PSA/MUC-1/brachyury vaccine is well tolerated. The primary end points were met and there were no DLTs. The recommended phase II dose is 5×10¹¹ VP. The vaccine demonstrated clinical activity, including one partial response and confirmed PSA responses in five patients. Three patients with prolonged PSA responses received palliative radiation therapy. Further research is needed to evaluate the clinical benefit and immunogenicity of this vaccine in combination with other immuno-oncology agents and/or palliative radiation therapy.

Trial registration number

NCT03481816.

Vaccine formulations in clinical development for the prevention of severe acute respiratory syndrome coronavirus 2 infection

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an unprecedented effort toward the development of an effective and safe vaccine. Aided by extensive research efforts into characterizing and developing countermeasures towards prior coronavirus epidemics, as well as recent developments of diverse vaccine platform technologies, hundreds of vaccine candidates using dozens of delivery vehicles and routes have been proposed and evaluated preclinically. A high demand coupled with massive effort from researchers has led to the advancement of at least 31 candidate vaccines in clinical trials, many using platforms that have never before been approved for use in humans. This review will address the approach and requirements for a successful vaccine against SARS-CoV-2, the background of the myriad of vaccine platforms currently in clinical trials for COVID-19 prevention, and a summary of the present results of those trials. It concludes with a perspective on formulation problems which remain to be addressed in COVID-19 vaccine development and antigens or adjuvants which may be worth further investigation.

Adenoviral vector-based vaccine is fully protective against lethal Lassa fever challenge in Hartley guinea pigs

Lassa virus (LASV), the causative agent of Lassa fever (LF), was first identified in 1969. Since then, outbreaks in the endemic countries of Nigeria, Liberia, and Sierra Leone occur on an annual basis resulting in a case-fatality rate of 15-70% in hospitalized patients. There is currently no licensed vaccine and there are limited animal models to test vaccine efficacy. An estimated 37.7 million people are at risk of contracting LASV; therefore, there is an urgent need for the development of a safe, effective vaccine against LASV infection. The LF endemic countries are also inflicted with HIV, Ebola, and malaria infections. The safety in immunocompromised populations must be considered in LASV vaccine development. The novel adenovirus vector-based platform, Ad5 (E1-,E2b-) has been used in clinical trial protocols for treatment of immunocompromised individuals, has been shown to exhibit high stability, low safety risk in humans, and induces a strong cell-mediated and pro-inflammatory immune response even in the presence of pre-existing adenovirus immunity. To this nature, our lab has developed an Ad5 (E1-,E2b-) vector-based vaccine expressing the LASV-NP or LASV-GPC. We found that guinea pigs vaccinated with two doses of Ad5 (E1-,E2b-) LASV-NP and Ad5 (E1-,E2b-) LASV-GPC were protected against lethal LASV challenge. The Ad5 (E1-,E2b-) LASV-NP and LASV-GPC vaccine represents a potential vaccine candidate against LF.

Decreased Vector Gene Expression from E2b Gene-Deleted Adenovirus Serotype 5 Vaccines Intensifies Proinflammatory Immune Responses

Recombinant adenovirus serotype 5 (Ad5) vectors are promising vaccine candidates due to their intrinsic immunogenicity and potent transgene expression; however, widespread preexisting Ad5 immunity has been considered a developmental impediment to the use of traditional, or conventional, E1 and E3 gene-deleted Ad5 (Ad5[E1-]) vaccines. Even in the presence of anti-Ad5 immunity, recent murine and human studies have confirmed E2b gene-deleted Ad5 (Ad5[E1-,E2b-]) vaccines to be highly efficacious inducers of transgene-specific memory responses and significantly less toxic options than Ad5[E1-] vaccines. While these findings have been substantially confirmed, the molecular mechanisms underlying the different reactions to these vaccine platforms are unknown. Using cultures of human peripheral blood mononuclear cells (hPBMCs) derived from multiple human donors, we found that Ad5[E1-,E2b-] vaccines trigger higher levels of hPBMC proinflammatory cytokine secretion than Ad5[E1-] vaccines. Interestingly, these responses were generated regardless of the donors' preexisting anti-Ad5 humoral and cell-mediated immune response status. In vitro hPBMC infection with the Ad5[E1-,E2b-] vaccine also provoked greater Th1-dominant gene responses yet smaller amounts of Ad-derived gene expression than Ad5[E1-] vaccines. These results suggest that Ad5[E1-,E2b-] vaccines, in contrast to Ad5[E1-] vaccines, do not promote activities that suppress innate immune signaling, thereby allowing for improved vaccine efficacy and a superior safety profile independently of previous Ad5 immunity.

Development of Cancer Vaccines Targeting Brachyury, a Transcription Factor Associated with Tumor Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is recognized as a relevant process during the progression of carcinomas towards metastatic disease. Epithelial cancer cells undergoing an EMT program may acquire mesenchymal features, motility, invasiveness, and resistance to a variety of anticancer therapeutics. Preventing or reverting the EMT process in carcinomas has the potential to minimize tumor dissemination and the emergence of therapeutic resistance. One of the strategies currently under investigation to target tumor cells undergoing EMT is the generation of a sustained immune response directed against an essential molecular driver of the process. This review focuses on the current development of immune-mediated anticancer interventions aimed at targeting a transcription factor, brachyury, associated with human tumor EMT. Also presented here is a summary of recent studies demonstrating a role for EMT in tumor resistance to immune effector cytotoxicity, and the study of novel strategies aimed at reverting the EMT to be used in combination with immune-mediated anticancer interventions.

The generation and analyses of a novel combination of recombinant adenovirus vaccines targeting three tumor antigens as an immunotherapeutic

Phenotypic heterogeneity of human carcinoma lesions, including heterogeneity in expression of tumor-associated antigens (TAAs), is a well-established phenomenon. Carcinoembryonic antigen (CEA), MUC1, and brachyury are diverse TAAs, each of which is expressed on a wide range of human tumors. We have previously reported on a novel adenovirus serotype 5 (Ad5) vector gene delivery platform (Ad5 [E1-, E2b-]) in which regions of the early 1 (E1), early 2 (E2b), and early 3 (E3) genes have been deleted. The unique deletions in this platform result in a dramatic decrease in late gene expression, leading to a marked reduction in host immune response to the vector. Ad5 [E1-, E2b-]-CEA vaccine (ETBX-011) has been employed in clinical studies as an active vaccine to induce immune responses to CEA in metastatic colorectal cancer patients. We report here the development of novel recombinant Ad5 [E1-, E2b-]-brachyury and-MUC1 vaccine constructs, each capable of activating antigen-specific human T cells in vitro and inducing antigen-specific CD4⁺ and CD8⁺ T cells in vaccinated mice. We also describe the use of a combination of the three vaccines (designated Tri-Ad5) of Ad5 [E1-, E2b-]-CEA, Ad5 [E1-, E2b-]-brachyury and Ad5 [E1-, E2b-]-MUC1, and demonstrate that there is minimal to no “antigenic competition” in in vitro studies of human dendritic cells, or in murine vaccination studies. The studies reported herein support the rationale for the application of Tri-Ad5 as a therapeutic modality to induce immune responses to a diverse range of human TAAs for potential clinical studies.

In Vivo Synthesis of Cyclic-di-GMP Using a Recombinant Adenovirus Preferentially Improves Adaptive Immune Responses against Extracellular Antigens

There is a compelling need for more effective vaccine adjuvants to augment induction of Ag-specific adaptive immune responses. Recent reports suggested the bacterial second messenger bis-(3'-5')-cyclic-dimeric-guanosine monophosphate (c-di-GMP) acts as an innate immune system modulator. We recently incorporated a Vibrio cholerae diguanylate cyclase into an adenovirus vaccine, fostering production of c-di-GMP as well as proinflammatory responses in mice. In this study, we recombined a more potent diguanylate cyclase gene, VCA0848, into a nonreplicating adenovirus serotype 5 (AdVCA0848) that produces elevated amounts of c-di-GMP when expressed in mammalian cells in vivo. This novel platform further improved induction of type I IFN-β and activation of innate and adaptive immune cells early after administration into mice as compared with control vectors. Coadministration of the extracellular protein OVA and the AdVCA0848 adjuvant significantly improved OVA-specific T cell responses as detected by IFN-γ and IL-2 ELISPOT, while also improving OVA-specific humoral B cell adaptive responses. In addition, we found that coadministration of AdVCA0848 with another adenovirus serotype 5 vector expressing the HIV-1-derived Gag Ag or the Clostridium difficile-derived toxin B resulted in significant inhibitory effects on the induction of Gag and toxin B-specific adaptive immune responses. As a proof of principle, these data confirm that in vivo synthesis of c-di-GMP stimulates strong innate immune responses that correlate with enhanced adaptive immune responses to concomitantly administered extracellular Ag, which can be used as an adjuvant to heighten effective immune responses for protein-based vaccine platforms against microbial infections and cancers.

Extended evaluation of a phase 1/2 trial on dosing, safety, immunogenicity, and overall survival after immunizations with an advanced-generation Ad5 [E1-, E2b-]-CEA(6D) vaccine in late-stage colorectal cancer

A phase 1/2 clinical trial evaluating dosing, safety, immunogenicity, and overall survival on metastatic colorectal cancer (mCRC) patients after immunotherapy with an advanced-generation Ad5 [E1-, E2b-]-CEA(6D) vaccine was performed. We report our extended observations on long-term overall survival and further immune analyses on a subset of treated patients including assessment of cytolytic T cell responses, T regulatory (Treg) to T effector (Teff) cell ratios, flow cytometry on peripheral blood mononuclear cells (PBMCs), and determination of HLA-A2 status. An overall survival of 20 % (median survival 11 months) was observed during long-term follow-up, and no long-term adverse effects were reported. Cytolytic T cell responses increased after immunizations, and cell-mediated immune (CMI) responses were induced whether or not patients were HLA-A2 positive or Ad5 immune. PBMC samples from a small subset of patients were available for follow-up immune analyses. It was observed that the levels of carcinoembryonic antigen (CEA)-specific CMI activity decreased from their peak values during follow-up in five patients analyzed. Preliminary results revealed that activated CD4+ and CD8+ T cells were detected in a post-immunization sample exhibiting high CMI activity. Treg to Teff cell ratios were assessed, and samples from three of five patients exhibited a decrease in Treg to Teff cell ratio during the treatment protocol. Based upon the favorable safety and immunogenicity data obtained, we plan to perform an extensive immunologic and survival analysis on mCRC patients to be enrolled in a randomized/controlled clinical trial that investigates Ad5 [E1-, E2b-]-CEA(6D) as a single agent with booster immunizations.

Adenovirus-mediated co-expression of the TRAIL and HN genes inhibits growth and induces apoptosis in Marek's disease tumor cell line MSB-1

Background

The objective of this study was to determine the in vitro tumor-inhibitory effect of a recombinant adenovirus expressing a fusion protein of tumor necrosis factor (TNF) related apoptosis inducing ligand (TRAIL) and hemagglutinin-neuraminidase (HN) genes on the MSB-1 Marek’s disease tumor cell line.

Methods

TRAIL and HN genes were amplified from lymphocytes in the peripheral blood of chickens and the LaSota strain of Newcastle disease virus (NDV), respectively, using RT-PCR. The two genes were connected with a 2A connecting peptide by site-directed mutagenesis and gene splicing by overlap extension (SOE). The target gene TRAIL-2A-HN was cloned into the shuttle vector pShuttle-CMV. Homologous recombination was carried out with the vector pAdeasy-1 in the bacterium BJ5183 to construct the recombinant adenovirus plasmid pAd-TRAIL-2A-HN. After linearization, the plasmid was transfected into AD293 cells and packaged. Real-time quantitative PCR (RT-PCR) and fluorescence microscopy confirmed the introduction of the recombinant adenovirus into AD293 cells. The TCID₅₀ method (50% tissue culture infectious dose) was employed to determine viral titers for the exprimental and control viruses, which met criteria for use. The Marek’s disease tumor cell line MSB-1 was transfected with the constructed recombinant adenovirus. The infectivity of the recombinant adenovirus and the expression levels of exogenous genes were detected with RT-PCR and western blotting. The effects of the recombinant adenovirus on the growth of MSB-1 cells and cellular apoptosis were determined using flow cytometry.

Results

The recombinant adenovirus infected the cultured cells in vitro, and replicated and expressed exogenous genes in the cells. The recombinant adenovirus Ad-TRAIL-2A-HN inhibited the growth of MSB-1 cells and induced apoptosis by expressing exogenous genes. The rate of induced MSB-1 cell apoptosis reached 11.61%, which indicated that TRAIL and HN produced synergistic tumor-inhibiting effects.

Conclusion

The constructed TRAIL-2A-HN fusion gene combined the apoptosis-inducing function of TRAIL and the adsorptive capacity of HN from NDV for tumor cells, and the capacity of the recombinant adenovirus expressing this fusion gene to induce tumor cell apoptosis was reported. These results provide a basis for future in vivo tumor suppression studies using recombinant adenoviruses.

Novel adenoviral vector induces T-cell responses despite anti-adenoviral neutralizing antibodies in colorectal cancer patients

First-generation, E1-deleted adenovirus subtype 5 (Ad5)-based vectors, although promising platforms for use as cancer vaccines, are impeded in activity by naturally occurring or induced Ad-specific neutralizing antibodies. Ad5-based vectors with deletions of the E1 and the E2b regions (Ad5 [E1-, E2b-]), the latter encoding the DNA polymerase and the pre-terminal protein, by virtue of diminished late phase viral protein expression, were hypothesized to avoid immunological clearance and induce more potent immune responses against the encoded tumor antigen transgene in Ad-immune hosts. Indeed, multiple homologous immunizations with Ad5 [E1-, E2b-]-CEA(6D), encoding the tumor antigen carcinoembryonic antigen (CEA), induced CEA-specific cell-mediated immune (CMI) responses with antitumor activity in mice despite the presence of preexisting or induced Ad5-neutralizing antibody. In the present phase I/II study, cohorts of patients with advanced colorectal cancer were immunized with escalating doses of Ad5 [E1-, E2b-]-CEA(6D). CEA-specific CMI responses were observed despite the presence of preexisting Ad5 immunity in a majority (61.3 %) of patients. Importantly, there was minimal toxicity, and overall patient survival (48 % at 12 months) was similar regardless of preexisting Ad5 neutralizing antibody titers. The results demonstrate that, in cancer patients, the novel Ad5 [E1-, E2b-] gene delivery platform generates significant CMI responses to the tumor antigen CEA in the setting of both naturally acquired and immunization-induced Ad5-specific immunity.

Control of SIV infection and subsequent induction of pandemic H1N1 immunity in rhesus macaques using an Ad5 [E1-, E2b-] vector platform

Anti-vector immunity mitigates immune responses induced by recombinant adenovirus vector vaccines, limiting their prime-boost capabilities. We have developed a novel gene delivery and expression platform (Ad5 [E1-, E2b-]) that induces immune responses despite pre-existing and/or developed concomitant Ad5 immunity. In the present study, we evaluated if this new Ad5 platform could overcome the adverse condition of pre-existing Ad5 immunity to induce effective immune responses in prime-boost immunization regimens against two different infectious diseases in the same animal. Ad5 immune rhesus macaques (RM) were immunized multiple times with the Ad5 [E1-, E2b-] platform expressing antigens from simian immunodeficiency virus (SIV). Immunized RM developed cell-mediated immunity against SIV antigens Gag, Pol, Nef and Env as well as antibody against Env. Vaccinated and vector control RMs were challenged intra-rectally with homologous SIVmac239. During a 7-week follow-up, there was perturbation of SIV load in some immunized RM. At 7 weeks post-challenge, eight immunized animals (53%) did not have detectable SIV, compared to two RM controls (13%) (P<0.02; log-rank Mantel-Cox test). There was no correlation of protective MHC contributing to infection control. The RM without detectable circulating SIV, now hyper immune to Ad5, were then vaccinated with the same Ad5 [E1-, E2b-] platform expressing H1N1 influenza hemagglutinin (HA). Thirty days post Ad5 [E1-, E2b-]-HA vaccination, significant levels of influenza neutralizing antibody were induced in all animals that increased after an Ad5 [E1-, E2b-]-HA homologous boost. These data demonstrate the versatility of this new vector platform to immunize against two separate disease targets in the same animal despite the presence of immunity against the delivery platform, permitting homologous repeat immunizations with an Ad5 gene delivery platform.

A non-oncogenic HPV 16 E6/E7 vaccine enhances treatment of HPV expressing tumors

Human papillomaviruses (HPVs) are the causative factor for >90% of cervical cancers and 25% of head and neck cancers. The incidence of HPV positive (+) head and neck squamous cell carcinomas has greatly increased in the last 30 years. E6 and E7 are the two key viral oncoproteins that induce and propagate cellular transformation. An immune response generated during cisplatin/radiation therapy improves tumor clearance of HPV(+) cancers. Augmenting this induced response during therapy with an adenoviral HPV16 E6/E7 vaccine improves long-term survival in pre-clinical models. Here, we describe the generation of an HPV16 E6/E7 construct, which contains mutations that render E6/E7 non-oncogenic, while preserving antigenicity. These mutations do not allow E6/E7 to degrade p53, pRb, PTPN13, or activate telomerase. Non-oncogenic E6/E7 (E6(Δ)/E7(Δ)) expressed as a stable integrant, or in the [E1-, E2b-] adenovirus, lacks the ability to transform human cells while retaining the ability to induce an HPV-specific immune response. Moreover, E6(Δ)/E7(Δ) plus chemotherapy/radiation statistically enhances clearance of established HPV(+) cancer in vivo.

Novel recombinant alphaviral and adenoviral vectors for cancer immunotherapy

Although cellular immunotherapy based on autolgous dendritic cells (DCs) targeting antigens expressed by metastatic cancer has demonstrated clinical efficacy, the logistical challenges in generating an individualized cell product create an imperative to develop alternatives to DC-based cancer vaccines. Particularly attractive alternatives include in situ delivery of antigen and activation signals to resident antigen-presenting cells (APCs), which can be achieved by novel fusion molecules targeting the mannose receptor and by recombinant viral vectors expressing the antigen of interest and capable of infecting DCs. A particular challenge in the use of viral vectors is the well-appreciated clinical obstacles to their efficacy, specifically vector-specific neutralizing immune responses. Because heterologous prime and boost strategies have been demonstrated to be particularly potent, we developed two novel recombinant vectors based on alphaviral replicon particles and a next-generation adenovirus encoding an antigen commonly overexpressed in many human cancers, carcinoembryonic antigen (CEA). The rationale for developing these vectors, their unique characteristics, the preclinical studies and early clinical experience with each, and opportunities to enhance their effectiveness will be reviewed. The potential of each of these potent recombinant vectors to efficiently generate clinically active anti-tumor immune response alone, or in combination, will be discussed.

Therapeutic live vaccines as a potential anticancer strategy

The design of efficient cancer treatments is one of the major challenges of medical science. Therapeutic vaccines of cancer have been emerged as an attractive approach for their capacity of breaking the immune tolerance and invoking long-term immune response targeting cancer cells without autoimmunity. An efficient antigen delivery system is the key issue of developing an effective cancer vaccine. In this regard, live vaccination strategies including various live bacterial and viral vectors have attracted a great attention. Several bacterial strains such as Salmonella, Listeria monocytogenes and Lactococcus lactis effectively colonize solid tumors and act as antitumor therapeutics. On the other hand, the use of viruses as vaccine vectors such as Vaccinia, Adenovirus, Herpes simplex virus, Paramyxovirus and Retroviruses utilizes mechanisms that evolved in these microbes for entering cells and capturing the cellular machinery to express viral proteins. Viral/bacterial-vectored vaccines induce systemic T-cell responses including polyfunctional cytokine-secreting CD4+ and CD8+ T-cells. However, there is an urgent need for the development of new safe live vaccine vectors that are capable of enhancing antigen presentation and eliciting potent immune responses without the risk of development of disease in humans. Recently, nonpathogenic parasites including Leishmania tarentolae, Toxoplasma gondii and Trypanosoma cruzi have emerged to be a novel candidate for gene delivery and heterologous genes expression. In this review, recent researches on cancer therapy using genetically modified bacteria and virus are summarized. In addition, live parasite-based vectors will be discussed as a novel anticancer therapeutic approach.

Malaria vaccines: focus on adenovirus based vectors

Protection against malaria through vaccination is known to be achievable, as first demonstrated over 30 years ago. Vaccination via repeated bites with Plasmodium falciparum infected and irradiated mosquitoes provided short lived protection from malaria infection to these vaccinees. Though this method still remains the most protective malaria vaccine to date, it is likely impractical for widespread use. However, recent developments in sub-unit malaria vaccine platforms are bridging the gap between high levels of protection and feasibility. The current leading sub-unit vaccine, RTS,S (which consists of a fusion of a portion of the P. falciparum derived circumsporozoite protein to the Hepatitis B surface antigen), has demonstrated the ability to induce protection from malaria infection in up 56% of RTS,S vaccinees. Though encouraging, these results may fall short of protection levels generally considered to be required to achieve eradication of malaria. Therefore, the use of viral vectored vaccine platforms has recently been pursued to further improve the efficacy of malaria targeted vaccines. Adenovirus based vaccine platforms have demonstrated potent anti-malaria immune responses when used alone, as well when utilized in heterologous prime boost regimens. This review will provide an update as to the current advancements in malaria vaccine development, with a focus on the use of adenovirus vectored malaria vaccines.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

Immune recognition of gene transfer vectors: focus on adenovirus as a paradigm

Recombinant Adenovirus (Ad) based vectors have been utilized extensively as a gene transfer platform in multiple pre-clinical and clinical applications. These applications are numerous, and inclusive of both gene therapy and vaccine based approaches to human or animal diseases. The widespread utilization of these vectors in both animal models, as well as numerous human clinical trials (Ad-based vectors surpass all other gene transfer vectors relative to numbers of patients treated, as well as number of clinical trials overall), has shed light on how this virus vector interacts with both the innate and adaptive immune systems. The ability to generate and administer large amounts of this vector likely contributes not only to their ability to allow for highly efficient gene transfer, but also their elicitation of host immune responses to the vector and/or the transgene the vector expresses in vivo. These facts, coupled with utilization of several models that allow for full detection of these responses has predicted several observations made in human trials, an important point as lack of similar capabilities by other vector systems may prevent detection of such responses until only after human trials are initiated. Finally, induction of innate or adaptive immune responses by Ad vectors may be detrimental in one setting (i.e., gene therapy) and be entirely beneficial in another (i.e., prophylactic or therapeutic vaccine based applications). Herein, we review the current understanding of innate and adaptive immune responses to Ad vectors, as well some recent advances that attempt to capitalize on this understanding so as to further broaden the safe and efficient use of Ad-based gene transfer therapies in general.

Induction and comparison of SIV immunity in Ad5 naïve and Ad5 immune non-human primates using an Ad5 [E1-, E2b-] based vaccine

The effectiveness of recombinant Adenovirus serotype 5 (Ad5) vectors to induce immune responses against targeted antigens has been limited by the presence of pre-existing or Ad5 vaccine induced anti-vector immunity. The Ad5 [E1-, E2b-] platform, a recombinant Ad5 with additional deletions, has been previously reported by us to induce immune responses in the presence of Ad5 immunity. In an Ad5 immune non-human primate (NHP) model, an Ad5 [E1-, E2b-] construct expressing HIV-1 Gag induced immune responses in the presence of pre-existing Ad5 immunity. In the present study we expand on these prior observations by comparing the cell mediated immune (CMI) responses induced by Ad5 [E1-, E2b-]-SIV-gag/nef in Ad5 naïve and Ad5 immune NHP. Additionally, NHP were immunized with an Ad5 [E1-, E2b-]-HIV-pol construct following two homologous administrations of Ad5 [E1-, E2b-]-SIV-gag/nef to determine if an immune response could be induced against a third antigen in the presence of vaccine induced Ad5 immunity. Positive CMI responses, as assessed by interferon-gamma (IFN-γ) secreting lymphocytes, were induced against all three antigens. These CMI responses increased over a course of multiple immunizations and the response profiles observed in Ad5 naïve and Ad5 immune NHP were similar. No influence of the major histocompatibility complex on CMI responses was observed. These data indicate that the new Ad5 [E1-, E2b-] platform based vaccine could be used for homologous vaccination regimes to induce robust CMI responses in the presence of Ad5 vector immunity.

Prevention of influenza virus shedding and protection from lethal H1N1 challenge using a consensus 2009 H1N1 HA and NA adenovirus vector vaccine

Vaccines against emerging pathogens such as the 2009 H1N1 pandemic virus can benefit from current technologies such as rapid genomic sequencing to construct the most biologically relevant vaccine. A novel platform (Ad5 [E1-, E2b-]) has been utilized to induce immune responses to various antigenic targets. We employed this vector platform to express hemagglutinin (HA) and neuraminidase (NA) genes from 2009 H1N1 pandemic viruses. Inserts were consensuses sequences designed from viral isolate sequences and the vaccine was rapidly constructed and produced. Vaccination induced H1N1 immune responses in mice, which afforded protection from lethal virus challenge. In ferrets, vaccination protected from disease development and significantly reduced viral titers in nasal washes. H1N1 cell mediated immunity as well as antibody induction correlated with the prevention of disease symptoms and reduction of virus replication. The Ad5 [E1-, E2b-] should be evaluated for the rapid development of effective vaccines against infectious diseases.

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 Ad5[E1-, E2b-]-HER2/neu vector induces immune responses and inhibits HER2/neu expressing tumor progression in Ad5 immune mice

Immunotherapy is a promising approach for the treatment of cancers. Modified adenovirus 5 (Ad5) vectors have been used as a platform to deliver genes encoding tumor associated antigens (TAA). A major obstacle to Ad5 vector immunotherapy has been the induction of vector immunity following administration or the presence of pre-existing Ad5 immunity, which results in vector mitigation. It has been reported by us that the Ad5[E1-, E2b-] platform with unique deletions in the E1, E2b and E3 regions can induce potent cell mediated immunity (CMI) against delivered transgene products in the presence of pre-existing Ad5 immunity. Here we report the use of an Ad5[E1-, E2b-] vector platform expressing the TAA HER2/neu as a breast cancer immunotherapeutic agent. Ad5[E1-, E2b-]-HER2/neu induced potent CMI against HER2/neu in Ad5 naïve and Ad5 immune mice. Humoral responses were also induced and antibodies could lyse HER2/neu expressing tumor cells in the presence of complement in vitro. Ad5[E1-, E2b-]-HER2/neu prevented establishment of HER2/neu-expressing tumors and significantly inhibited progression of established tumors in Ad5 naïve and Ad5 immune murine models. These data demonstrate that in vivo delivery of Ad5[E1-, E2b-]-HER2/neu can induce anti-TAA immunity and inhibit progression of HER2/neu expressing cancers.

Improving adenovirus based gene transfer: strategies to accomplish immune evasion

Adenovirus (Ad) based gene transfer vectors continue to be the platform of choice for an increasing number of clinical trials worldwide. In fact, within the last five years, the number of clinical trials that utilize Ad based vectors has doubled, indicating growing enthusiasm for the numerous positive characteristics of this gene transfer platform. For example, Ad vectors can be easily and relatively inexpensively produced to high titers in a cGMP compliant manner, can be stably stored and transported, and have a broad applicability for a wide range of clinical conditions, including both gene therapy and vaccine applications. Ad vector based gene transfer will become more useful as strategies to counteract innate and/or pre-existing adaptive immune responses to Ads are developed and confirmed to be efficacious. The approaches attempting to overcome these limitations can be divided into two broad categories: pre-emptive immune modulation of the host, and selective modification of the Ad vector itself. The first category of methods includes the use of immunosuppressive drugs or specific compounds to block important immune pathways, which are known to be induced by Ads. The second category comprises several innovative strategies inclusive of: (1) Ad-capsid-display of specific inhibitors or ligands; (2) covalent modifications of the entire Ad vector capsid moiety; (3) the use of tissue specific promoters and local administration routes; (4) the use of genome modified Ads; and (5) the development of chimeric or alternative serotype Ads. This review article will focus on both the promise and the limitations of each of these immune evasion strategies, and in the process delineate future directions in developing safer and more efficacious Ad-based gene transfer strategies.

Anti-tumor immunotherapy despite immunity to adenovirus using a novel adenoviral vector Ad5 [E1-, E2b-]-CEA

Adenovirus serotype 5 (Ad5) has been widely used in clinical trials because it expresses inserted transgenes robustly and augments the innate immune response. Strategies to improve Ad5 vectors that can circumvent Ad5 immunity have become a critical issue, especially for use as a cancer immunotherapeutic in which repeated immunization is required. In this study, we constructed a novel Ad5 vector with unique deletions of the viral DNA polymerase and the pre-terminal protein region (Ad5 [E1-, E2b-]). This vector contains the carcinoembryonic antigen (CEA) gene insert and is designed to induce cell-mediated immunity (CMI) against the tumor-associated target. The CEA immunogenicity and in vivo anti-tumor effects of repeated immunizations with Ad5 [E1-, E2b-]-CEA compared with those observed with current generation Ad5 [E1-]-CEA were tested in Ad5 pre-immunized mice. We report that Ad5-immune mice immunized multiple times with Ad5 [E1-, E2b-]-CEA induced CEA-specific CMI responses that were significantly increased over those detected in Ad5-immune mice immunized multiple times with a current generation Ad5 [E1-]-CEA. Ad5 immune mice bearing CEA-expressing tumors that were treated with Ad5 [E1-, E2b-]-CEA had increased anti-tumor response as compared with Ad5 [E1-]-CEA treated mice. These results demonstrate that Ad5 [E1-, E2b-]-CEA can induce CMI immune responses which result in tumor growth inhibition despite the presence of pre-existing Ad5 immunity. Multiple re-immunizations using the same vector platform are now possible with the novel Ad5 [E1-, E2b-] platform.

Overcoming pre-existing adenovirus immunity by genetic engineering of adenovirus-based vectors

Adenovirus (Ad)-based vectors offer several benefits showing their potential for use in a variety of vaccine applications. Recombinant Ad-based vaccines possess potent immunogenic potential, capable of generating humoral and cellular immune responses to a variety of pathogen-specific antigens expressed by the vectors. Ad5 vectors can be readily produced, allowing for usage in thousands of clinical trial subjects. This is now coupled with a history of safe clinical use in the vaccine setting. However, traditional Ad5-based vaccines may not be generating optimal antigen-specific immune responses, and generate diminished antigen-specific immune responses when pre-existing Ad5 immunity is present. These limitations have driven initiation of several approaches to improve the efficacy of Ad-based vaccines, and/or allow modified vaccines to overcome pre-existing Ad immunity. These include: generation of chemically modified Ad5 capsids; generation of chimeric Ads; complete replacement of Ad5-based vaccine platforms with alternative (human and non-human origin) Ad serotypes, and Ad5 genome modification approaches that attempt to retain the native Ad5 capsid, while simultaneously improving the efficacy of the platform as well as minimizing the effect of pre-existing Ad immunity. Here we discuss recent advances in- and limitations of each of these approaches, relative to their abilities to overcome pre-existing Ad immunity.

Safety and immunogenicity of the Merck adenovirus serotype 5 (MRKAd5) and MRKAd6 human immunodeficiency virus type 1 trigene vaccines alone and in combination in healthy adults

Preexisting immunity to adenovirus serotype 5 (Ad5) diminishes immune responses to vaccines using Ad5 as a vector. Alternate Ad serotypes as vaccine vectors might overcome Ad5-specific neutralizing antibodies and enhance immune responses in populations with a high prevalence of Ad5 immunity. To test this hypothesis, healthy human immunodeficiency virus (HIV)-seronegative adults were enrolled in a blinded, randomized, dose-escalating, placebo-controlled study. In part A, subjects with baseline Ad6 titers of < or = 18 received the Merck Ad6 (MRKAd6) HIV type 1 (HIV-1) trigene vaccine at weeks 0, 4, and 26. In part B, subjects stratified by Ad5 titers (< or = 200 or >200) and Ad6 titers (< or = 18 or >18) received the MRKAd5-plus-MRKAd6 (MRKAd5+6) HIV-1 trigene vaccine at weeks 0, 4, and 26. Immunogenicity was assessed by an enzyme-linked immunospot (ELISPOT) assay at week 30. No serious adverse events occurred. MRKAd6 trigene vaccine recipients responded more often to Nef than to Gag or Pol. In part A, ELISPOT response rates to > or = 2 vaccine antigens were 14%, 63%, and 71% at 10(9), 10(10), and 10(11) viral genomes (vg)/dose, respectively. All responders had positive Nef-specific ELISPOT results. In part B, Nef-ELISPOT response rates at 10(10) vg/dose of the MRKAd5+6 trigene vaccine were 50% in the low-Ad5/low-Ad6 stratum (n = 8), 78% in the low-Ad5/high-Ad6 stratum (n = 9), 75% in the high-Ad5/low-Ad6 stratum (n = 8), and 44% in the high-Ad5/high-Ad6 stratum (n = 9). The MRKAd6 and MRKAd5+6 trigene vaccines elicited dose-dependent responses predominantly to Nef and were generally well tolerated, indicating that Ad6 should be considered a candidate vector for future vaccines. Although small sample sizes limit the conclusions that can be drawn from this exploratory study, combining two Ad vectors may be a useful vaccine strategy for circumventing isolated immunity to a single Ad serotype.