AAV Vectors Vaccines Against Infectious Diseases

Potent immunogenicity and neutralization of recombinant adeno-associated virus expressing the glycoprotein of severe fever with thrombocytopenia virus

Severe fever with thrombocytopenia syndrome (SFTS) is an infectious disease caused by a tick-borne virus called severe fever with thrombocytopenia syndrome virus (SFTSV). In recent years, human infections through contact with ticks and through contact with the bodily fluids of infected dogs and cats have been reported; however, no vaccine is currently available. SFTSV has two glycoproteins (Gn and Gc) on its envelope, which are vaccine-target antigens involved in immunogenicity. In the present study, we constructed novel SFTS vaccine candidates using an adeno-associated virus (AAV) vector to transport the SFTSV glycoprotein genome. AAV vectors are widely used in gene therapy and their safety has been confirmed in clinical trials. Recently, AAV vectors have been used to develop influenza and SARS-CoV-2 vaccines. Two types of vaccines (AAV9-SFTSV Gn and AAV9-SFTSV Gc) carrying SFTSV Gn and Gc genes were produced. The expression of Gn and Gc proteins in HEK293T cells was confirmed by infection with vaccines. These vaccines were inoculated into mice, and the collected sera produced anti-SFTS antibodies. Furthermore, sera from AAV9-SFTSV Gn infected mice showed a potent neutralizing ability, similar to previously reported SFTS vaccine candidates that protected animals from SFTSV infection. These findings suggest that this vaccine is a promising candidate for a new SFTS vaccine.

Discovery and development of COVID-19 vaccine from laboratory to clinic

The world has recently experienced one of the biggest and most severe public health disasters with severe acute respiratory syndrome coronavirus (SARS-CoV-2). SARS-CoV-2 is responsible for the coronavirus disease of 2019 (COVID-19) which is one of the most widespread and powerful infections affecting human lungs. Current figures show that the epidemic had reached 216 nations, where it had killed about 6,438,926 individuals and infected 590,405,710. WHO proclaimed the outbreak of the Ebola virus disease (EVD), in 2014 that killed hundreds of people in West Africa. The development of vaccines for SARS-CoV-2 becomes more difficult due to the viral mutation in its non-structural proteins (NSPs) especially NSP2 and NSP3, S protein, and RNA-dependent RNA polymerase (RdRp). Continuous monitoring of SARS-CoV-2, dynamics of the genomic sequence, and spike protein mutations are very important for the successful development of vaccines with good efficacy. Hence, the vaccine development for SARS-CoV-2 faces specific challenges starting from viral mutation. The requirement of long-term immunity development, safety, efficacy, stability, vaccine allocation, distribution, and finally, its cost is discussed in detail. Currently, 169 vaccines are in the clinical development stage, while 198 vaccines are in the preclinical development stage. The majority of these vaccines belong to the Ps-Protein subunit type which has 54, and the minor BacAg-SPV (Bacterial antigen-spore expression vector) type, at least 1 vaccination. The use of computational methods and models for vaccine development has revolutionized the traditional methods of vaccine development. Further, this updated review highlights the upcoming vaccine development strategies in response to the current pandemic and post-pandemic era, in the field of vaccine development.

AAV Immunotoxicity: Implications in Anti-HBV Gene Therapy

Hepatitis B virus (HBV) has afflicted humankind for decades and there is still no treatment that can clear the infection. The development of recombinant adeno-associated virus (rAAV)-based gene therapy for HBV infection has become important in recent years and research has made exciting leaps. Initial studies, mainly using mouse models, showed that rAAVs are non-toxic and induce minimal immune responses. However, several later studies demonstrated rAAV toxicity, which is inextricably associated with immunogenicity. This is a major setback for the progression of rAAV-based therapies toward clinical application. Research aimed at understanding the mechanisms behind rAAV immunity and toxicity has contributed significantly to the inception of approaches to overcoming these challenges. The target tissue, the features of the vector, and the vector dose are some of the determinants of AAV toxicity, with the latter being associated with the most severe adverse events. This review discusses our current understanding of rAAV immunogenicity, toxicity, and approaches to overcoming these hurdles. How this information and current knowledge about HBV biology and immunity can be harnessed in the efforts to design safe and effective anti-HBV rAAVs is discussed.

A dual role for adeno-associated virus in human health

Adeno-associated virus (AAV) differs from most other viruses, as it requires the simultaneous presence of a helper virus for an active infection. Up to 80% of the human population is seropositive for AAV antibodies. AAV has been known to be a non-pathogenic virus and an inhibitor of carcinogenesis caused by coinfecting viruses. However, the recent reports associating AAV infection with hepatocellular carcinoma development and the mysterious cases of acute severe hepatitis in children have challenged the idea that AAV is a harmless virus. Herein, we explore the usefulness of AAV in gene therapy and the importance of AAV as a protector or perpetrator in human carcinogenesis, ultimately reflecting on the dual role of AAV in human health.

Correlating physicochemical and biological properties to define critical quality attributes of a rAAV vaccine candidate

Recombinant adeno-associated viruses (rAAVs) are a preferred vector system in clinical gene transfer. A fundamental challenge to formulate and deliver rAAVs as stable and efficacious vaccines is to elucidate interrelationships between the vector's physicochemical properties and biological potency. To this end, we evaluated an rAAV-based coronavirus disease 2019 (COVID-19) vaccine candidate that encodes the Spike antigen (AC3) and is produced by a commercially viable process. First, state-of-the-art analytical techniques were employed to determine key structural attributes of AC3, including primary and higher-order structures, particle size, empty/full capsid ratios, aggregates, and multi-step thermal degradation pathway analysis. Next, several quantitative potency measures for AC3 were implemented, and data were correlated with the physicochemical analyses on thermally stressed and control samples. Results demonstrate links between decreasing AC3 physical stability profiles, in vitro transduction efficiency in a cell-based assay, and, importantly, in vivo immunogenicity in a mouse model. These findings are discussed in the general context of future development of rAAV-based vaccine candidates as well as specifically for the rAAV vaccine application under study.

rAAV expressing recombinant antibody for emergency prevention and long-term prophylaxis of COVID-19

Introduction

Numerous agents for prophylaxis of SARS-CoV-2-induced diseases are currently registered for the clinical use. Formation of the immunity happens within several weeks following vaccine administration which is their key disadvantage. In contrast, drugs based on monoclonal antibodies, enable rapid passive immunization and therefore can be used for emergency pre- and post-exposure prophylaxis of COVID-19. However rapid elimination of antibody-based drugs from the circulation limits their usage for prolonged pre-exposure prophylaxis.

Methods

In current work we developed a recombinant adeno-associated viral vector (rAAV), expressing a SARS-CoV-2 spike receptor-binding domain (RBD)-specific antibody P2C5 fused with a human IgG1 Fc fragment (P2C5-Fc) using methods of molecular biotechnology and bioprocessing.

Results and discussions

A P2C5-Fc antibody expressed by a proposed rAAV (rAAV-P2C5-Fc) was shown to circulate within more than 300 days in blood of transduced mice and protect animals from lethal SARS-CoV-2 virus (B.1.1.1 and Omicron BA.5 variants) lethal dose of 105 TCID50. In addition, rAAV-P2C5-Fc demonstrated 100% protective activity as emergency prevention and long-term prophylaxis, respectively. It was also demonstrated that high titers of neutralizing antibodies to the SARS-CoV-2 virus were detected in the blood serum of animals that received rAAV-P2C5-Fc for more than 10 months from the moment of administration.Our data therefore indicate applicability of an rAAV for passive immunization and induction of a rapid long-term protection against various SARS-CoV-2 variants.

Displaying and delivering viral membrane antigens via WW domain-activated extracellular vesicles

Membrane proteins expressed on the surface of enveloped viruses are conformational antigens readily recognized by B cells of the immune system. An effective vaccine would require the synthesis and delivery of these native conformational antigens in lipid membranes that preserve specific epitope structures. We have created an extracellular vesicle-based technology that allows viral membrane antigens to be selectively recruited onto the surface of WW domain-activated extracellular vesicles (WAEVs). Budding of WAEVs requires secretory carrier-associated membrane protein 3, which through its proline-proline-alanine-tyrosine motif interacts with WW domains to recruit fused viral membrane antigens onto WAEVs. Immunization with influenza and HIV viral membrane proteins displayed on WAEVs elicits production of virus-specific neutralizing antibodies and, in the case of influenza antigens, protects mice from the lethal viral infection. WAEVs thus represent a versatile platform for presenting and delivering membrane antigens as vaccines against influenza, HIV, and potentially many other viral pathogens.

A Novel Engineered AAV-Based Neoantigen Vaccine in Combination with Radiotherapy Eradicates Tumors

The potency of tumor-specific antigen (TSA) vaccines, such as neoantigen (neoAg)-based cancer vaccines, can be compromised by host immune checkpoint inhibitory mechanisms, such as programmed cell death protein 1 (PD-1)/programmed death ligand 1 (PD-L1), that attenuate neoAg presentation on dendritic cells (DC) and hinder T cell-mediated cytotoxicity. To overcome PD-1/PD-L1 inhibition in DCs, we developed a novel adeno-associated virus (meAAV) neoAg vaccine, modified with TLR9 inhibitory fragments, PD-1 trap, and PD-L1 miRNA, which extend the persistence of meAAV and activate neoAg-specific T-cell responses in immune-competent colorectal and breast cancer murine models. Moreover, we found that in combination with radiotherapy, the meAAV-based neoAg cancer vaccine not only elicited higher antigen presentation ability, but also maintained neoAg-specific cytotoxic T lymphocyte (CTL) responses. These functional PD-1 traps and PD-L1 miRNAs overcome host PD-1/PD-L1 inhibitory mechanisms and boost the therapeutic efficacy of radiotherapy. More importantly, combined radiotherapy and meAAV neoAg cancer vaccines significantly enhanced neoAg-specific CTL responses, increased CTL infiltration in tumor microenvironment, and decreased tumor-associated immunosuppression. This process led to the complete elimination of colorectal cancer and delayed tumor growth of breast cancer in tumor-bearing mice. Taken together, our results demonstrated a novel strategy that combines neoAg cancer vaccine and radiotherapy to increase the therapeutic efficacy against colorectal and breast cancers.

Overcoming Barriers to Preventing and Treating P. aeruginosa Infections Using AAV Vectored Immunoprophylaxis

Pseudomonas aeruginosa is a bacterial pathogen of global concern and is responsible for 10-15% of nosocomial infections worldwide. This opportunistic bacterial pathogen is known to cause serious complications in immunocompromised patients and is notably the leading cause of morbidity and mortality in patients suffering from cystic fibrosis. Currently, the only line of defense against P. aeruginosa infections is antibiotic treatment. Due to the acquired and adaptive resistance mechanisms of this pathogen, the prevalence of multidrug resistant P. aeruginosa strains has increased, presenting a major problem in healthcare settings. To date, there are no approved licensed vaccines to protect against P. aeruginosa infections, prompting the urgent need alternative treatment options. An alternative to traditional vaccines is vectored immunoprophylaxis (VIP), which utilizes a safe and effective adeno-associated virus (AAV) gene therapy vector to produce sustained levels of therapeutic monoclonal antibodies (mAbs) in vivo from a single intramuscular injection. In this review, we will provide an overview of P. aeruginosa biology and key mechanisms of pathogenesis, discuss current and emerging treatment strategies for P. aeruginosa infections and highlight AAV-VIP as a promising novel therapeutic platform.

Recombinant adeno-associated virus serotype 9 AAV-RABVG expressing a Rabies Virus G protein confers long-lasting immune responses in mice and non-human primates

Three or four intramuscular doses of the inactivated human rabies virus vaccines are needed for pre- or post-exposure prophylaxis in humans. This procedure has made a great contribution to prevent human rabies deaths, which bring huge economic burdens in developing countries. Herein, a recombinant adeno-associated virus serotype 9, AAV9-RABVG, harbouring a RABV G gene, was generated to serve as a single dose rabies vaccine candidate. The RABV G protein was stably expressed in the 293T cells infected with AAV9-RABVG. A single dose of 2 × 10¹¹ v.p. of AAV9-RABVG induced robust and long-term positive seroconversions in BALB/c mice with a 100% survival from a lethal RABV challenge. In Cynomolgus Macaques vaccinated with a single dose of 1 × 10¹³ v.p. of AAV9-RABVG, the titres of rabies VNAs increased remarkably from 2 weeks after immunity, and maintained over 31.525 IU/ml at 52 weeks. More DCs were activated significantly for efficient antigen presentations of RABV G protein, and more B cells were activated to be responsible for antibody responses. Significantly more RABV G specific IFN-γ-secreting CD4+ and CD8+ T cells, and IL-4-secreting CD4+ T cells were activated, and significantly higher levels of IL-2, IFN-γ, IL-4, and IL-10 were secreted to aid immune responses. Overall, the AAV9-RABVG was a single dose rabies vaccine candidate with great promising by inducing robust, long-term humoral responses and both Th1 and Th2 cell-mediated immune responses in mice and non-human primates.

Synthesis and Concomitant Assembly of Adeno-Associated Virus-like Particles in Escherichia coli

Virus-like particles (VLPs) have been used for numerous pharmaceutical applications, particularly vaccination and drug delivery. Recombinant adeno-associated virus (rAAV), a leading candidate in gene therapy, has been proposed as a vaccine scaffold, but high production costs limit its use. Here we establish intracellular production of AAV VLPs in Escherichia coli. VP3 capsid proteins of AAV serotype 5 (AAV5) were expressed, and VLPs were readily purified. The correct assembly was confirmed by ELISA with an intact-capsid AAV5 antibody and an AAVR domain as well as by atomic force microscopy. Biological functionality was demonstrated with a HeLa cell internalization assay. Coexpression of the assembly-activating protein (AAP) of AAV5 in E. coli improved capsid yield. This work provides the first evidence that AAV VLPs form in E. coli, opening new opportunities for production and exploration of AAV VLPs for biomedical applications.

Intranasal application of adeno-associated viruses: a systematic review

Adeno-associated viruses (AAVs) represent some of the most commonly employed vectors for targeted gene delivery and their extensive study has resulted in the approval of multiple gene therapies to treat human diseases. The intranasal route of vector application in gene therapy offers several advantages over traditional ways of administration. In addition to targeting local tissue like the olfactory epithelium, it provides minimally invasive access to various organ systems, including the central nervous system and the respiratory tract. Through a systematic literature review, a total of 53 articles that investigated the intranasal application of AAVs were identified, included, and summarized in this manuscript. Within these studies, AAV-based gene therapy was mainly investigated for its application in various infectious, pulmonary, or neurologic and/or psychiatric diseases. This review gives a comprehensive overview of the current technological state of the art regarding the intranasal application of AAVs for gene transfer and discusses remaining hurdles, which still have to be resolved before this approach can effectively be implemented in the routine clinical setting.

Sterile protection and transmission blockade by a multistage anti-malarial vaccine in the pre-clinical study

The Malaria Vaccine Technology Roadmap 2013 (World Health Organization) aims to develop safe and effective vaccines by 2030 that will offer at least 75% protective efficacy against clinical malaria and reduce parasite transmission. Here, we demonstrate a highly effective multistage vaccine against both the pre-erythrocytic and sexual stages of Plasmodium falciparum that protects and reduces transmission in a murine model. The vaccine is based on a viral-vectored vaccine platform, comprising a highly-attenuated vaccinia virus strain, LC16m8Δ (m8Δ), a genetically stable variant of a licensed and highly effective Japanese smallpox vaccine LC16m8, and an adeno-associated virus (AAV), a viral vector for human gene therapy. The genes encoding P. falciparum circumsporozoite protein (PfCSP) and the ookinete protein P25 (Pfs25) are expressed as a Pfs25-PfCSP fusion protein, and the heterologous m8Δ-prime/AAV-boost immunization regimen in mice provided both 100% protection against PfCSP-transgenic P. berghei sporozoites and up to 100% transmission blocking efficacy, as determined by a direct membrane feeding assay using parasites from P. falciparum-positive, naturally-infected donors from endemic settings. Remarkably, the persistence of vaccine-induced immune responses were over 7 months and additionally provided complete protection against repeated parasite challenge in a murine model. We propose that application of the m8Δ/AAV malaria multistage vaccine platform has the potential to contribute to the landmark goals of the malaria vaccine technology roadmap, to achieve life-long sterile protection and high-level transmission blocking efficacy.

rAAV expressing recombinant neutralizing antibody for the botulinum neurotoxin type A prophylaxis

Botulinum neurotoxin (BoNT) is one of the most dangerous bacterial toxins and a potential biological weapon component. BoNT mechanism of pathological action is based on inhibiting the release of neurotransmitters from nerve endings. To date, anti-BoNT therapy is reduced to the use of horse hyperimmune serum, which causes many side effects, as well as FDA-approved drug BabyBig which consists of human-derived anti-BoNT antibodies (IgG) for infant botulinum treatment. Therapeutics for botulism treatment based on safer monoclonal antibodies are undergoing clinical trials. In addition, agents have been developed for the specific prevention of botulism, but their effectiveness has not been proved. In this work, we have obtained a recombinant adeno-associated virus (rAAV-B11-Fc) expressing a single-domain antibody fused to the human IgG Fc-fragment (B11-Fc) and specific to botulinum toxin type A (BoNT/A). We have demonstrated that B11-Fc antibody, expressed via rAAV-B11-Fc treatment, can protect animals from lethal doses of botulinum toxin type A, starting from day 3 and at least 120 days after administration. Thus, our results showed that rAAV-B11-Fc can provide long-term expression of B11-Fc-neutralizing antibody in vivo and provide long-term protection against BoNT/A intoxication. Consequently, our study demonstrates the applicability of rAAV expressing protective antibodies for the prevention of intoxication caused by botulinum toxins.

The use of viral vectors in vaccine development

Vaccines represent the single most cost-efficient and equitable way to combat and eradicate infectious diseases. While traditional licensed vaccines consist of either inactivated/attenuated versions of the entire pathogen or subunits of it, most novel experimental vaccines against emerging infectious diseases employ nucleic acids to produce the antigen of interest directly in vivo. These include DNA plasmid vaccines, mRNA vaccines, and recombinant viral vectors. The advantages of using nucleic acid vaccines include their ability to induce durable immune responses, high vaccine stability, and ease of large-scale manufacturing. In this review, we present an overview of pre-clinical and clinical data on recombinant viral vector vaccines and discuss the advantages and limitations of the different viral vector platforms.

Fusion Proteins CLD and CLDmut Demonstrate Potent and Broad Neutralizing Activity against HIV-1

HIV-1 envelope glycoprotein (Env) interacts with cellular receptors and mediates virus entry into target cells. Blocking Env-receptor interactions represents an effective interventional strategy for developing HIV-1 entry inhibitors. We previously designed a panel of CD4-linker-DC-SIGN (CLD) constructs by fusing the extracellular CD4 and DC-SIGN domains with various linkers. Such CLDs produced by the prokaryotic system efficiently inhibited HIV-1 infection and dissemination in vitro and ex vivo. In this study, following the construction and identification of the most promising candidate with a linker of 8 Gly₄Ser repeats (named CLD), we further designed an improved form (named CLDmut) by back mutating Cys to Ser at amino acid 60 of CD4. Both CLD and CLDmut were produced in mammalian (293F) cells for better protein translation and modification. The anti-HIV-1 activity of CLD and CLDmut was assessed against the infection of a range of HIV-1 isolates, including transmitted and founder (T/F) viruses. While both CLD and CLDmut efficiently neutralized the tested HIV-1 isolates, CLDmut demonstrated much higher neutralizing activity than CLD, with an IC₅₀ up to one log lower. The neutralizing activity of CLDmut was close to or more potent than those of the highly effective HIV-1 broadly neutralizing antibodies (bNAbs) reported to date. Findings in this study indicate that mammalian cell-expressed CLDmut may have the potential to be used as prophylaxis or/and therapeutics against HIV-1 infection.

Development of a perfusion process for serum-free adenovirus vector herpes zoster vaccine production

Herpes zoster is caused by reactivation of the varicella zoster virus (VZV). Researching and developing a herpes zoster vaccine will help to decrease the incidence of herpes zoster. To increase the bioreactor productivity, a serum-free HEK293 cell perfusion process with adenovirus vector herpes zoster (rAd-HZ) vaccine production was developed efficiently using the design of experiment (DoE) method. First, serum-free media for HEK293 cells were screened in both batch and semi-perfusion culture modes. Then, three optimal media were employed in a medium mixture design to improve cell culture performance, and the 1:1 mixture of HEK293 medium and MCD293 medium (named HM293 medium) was identified as the optimal formulation. On the basis of the HM293 medium, the relationship of critical process parameters (CPPs), including the time of infection (TOI), multiplicity of infection (MOI), pH, and critical quality attributes (CQAs) (adenovirus titer (Titer), cell-specific virus yield (CSVY), adenovirus fold expansion (Fold)) of rAd-HZ production was investigated using the DoE approach. Furthermore, the robust setpoint and design space of these CPPs were explored. Finally, the rAd-HZ production process with parameters at a robust setpoint (TOI = 7.2 × 10⁶ cells/mL, MOI = 3.7, and pH = 7.17) was successfully scaled-up to a 3-L bioreactor with an alternating tangential flow system, yielding an adenovirus titer of 3.0 × 10¹⁰ IFU/mL, a CSVY of 4167 IFU/cells, a Fold of 1117 at 2 days post infection (dpi). The DoE approach accelerated the development of a HEK293 serum-free medium and of a robust adenovirus production process.

Assessing the developing pharmacotherapeutic landscape in hepatitis B treatment: A spotlight on drugs at phase II clinical trials

INTRODUCTION

Functional cure, defined as sustained HBsAg seroclearance, is associated with favorable outcomes in chronic hepatitis B (CHB). While nucleos(t)ide analogues (NAs) are effective in suppressing HBV replication, NAs are unable to induce functional cure at high rates. A range of novel HBV antivirals, aiming to induce functional cure, are currently under development.

AREAS COVERED

This article covered novel hepatitis B virus (HBV) antivirals that have entered phase II trials. Virus-directing agents covered include entry inhibitors, transcription inhibitors, RNA silencers, core protein allosteric modulators, non-competitive polymerase inhibitors, and viral protein export inhibitors. Immunomodulators covered include innate immune stimulators, T-cell modulators, therapeutic vaccines, and monoclonal antibodies. Upcoming developmental directions would also be discussed.

EXPERT OPINION

Among novel HBV antivirals, RNA silencers, viral protein export inhibitors (with pegylated interferon) and entry inhibitors (with pegylated interferon) appear to be effective in suppressing HBsAg and may even induce functional cure. The other virus-targeting agents have variable effects on HBV DNA, HBsAg, HBeAg and HBcrAg. Immunomodulators have modest effects on HBsAg, but may have important roles in combination therapy. Upcoming trials will answer important questions on ideal dosing, long-term drug effects, and efficacy of combination regimens.

Recombinant PBP2a/autolysin conjugate as PLGA-based nanovaccine induced humoral responses with opsonophagocytosis activity, and protection versus methicillin-resistant Staphylococcus aureus infection

Objectives

Methicillin-resistant Staphylococcus aureus (MRSA) reasons extreme infections, can resist various conventional antimicrobial agents, and cause morbidity and mortality worldwide. Vaccination seems to help modulate MRSA infections. Nanovaccine is considered a novel strategy in vaccine technology. The primary purpose of the present study was to develop a conjugate vaccine based on recombinant PBP2a and MRSA autolysin formulated in PLGA as a nanoparticle capable of enhancing protective responses against MRSA in the murine model.

Materials and Methods

Recombinant PBP2a and autolysin have been expressed and purified by nickel-nitrilotriacetic acid (Ni-NTA) affinity column and characterized by SDS-PAGE and western blot. PLGA was bound to recombinant proteins by using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDAC) and adipic acid dihydrazide (ADH) as a linker and spacer, respectively. Conjugation of recombinant proteins to PLGA was confirmed by the AFM assay, zeta potential, and size distribution, and its efficacy was evaluated in mice. Total IgG, IgG1, IgG2a, IgG2b, and IgM titers were analyzed to assess immune responses. Lastly, the bioactivity of antibodies was tested by using the opsonophagocytosis assay.

Results

Mice immunized with the r-PBP2a-r-autolysin-PLGA nanovaccine led to increased levels of opsonic antibodies and IgG1, IgG2a, IgG2b, and IgM when compared with other experimental groups. Our results confirmed that vaccination with nanovaccine could reduce the mortality rate against the sub-lethal dose of MRSA challenge. Furthermore, the nanovaccine could eliminate MRSA from the kidney of infected mice.

Conclusion

This study may provide valuable insights into the protective power of the r-PBP2a-r-autolysin-PLGA conjugate vaccine against MRSA infection.

Induction of Hepatitis E Virus Anti-ORF3 Antibodies from Systemic Administration of a Muscle-Specific Adeno-Associated Virus (AAV) Vector

The hepatitis E virus (HEV) is a major global health problem, leading to large outbreaks in the developing world and chronic infections in the developed world. HEV is a non-enveloped virus, which circulates in the blood in a quasi-enveloped form. The quasi-envelope protects HEV particles from neutralising anti-capsid antibodies in the serum; however, most vaccine approaches are designed to induce an immune response against the HEV capsid. In this study, we explored systemic in vivo administration of a novel synthetic and myotropic Adeno-associated virus vector (AAVMYO3) to express the small HEV phosphoprotein ORF3 (found on quasi-enveloped HEV) in the musculature of mice, resulting in the robust and dose-dependent formation of anti-ORF3 antibodies. Neutralisation assays using the serum of ORF3 AAV-transduced mice showed a modest inhibitory effect on the infection of quasi-enveloped HEV in vivo, comparable to previously characterised anti-ORF3 antibodies used as a control. The novel AAVMYO3 capsid used in this study can serve as a versatile platform for the continued development of vector-based vaccines against HEV and other infectious agents, which could complement traditional vaccines akin to the current positive experience with SARS-CoV-2.

PCR-Based Analytical Methods for Quantification and Quality Control of Recombinant Adeno-Associated Viral Vector Preparations

Recombinant adeno-associated viral vectors (rAAV) represent a gene therapy tool of ever-increasing importance. Their utilization as a delivery vehicle for gene replacement, silencing and editing, among other purposes, demonstrate considerable versatility. Emerging vector utilization in various experimental, preclinical and clinical applications establishes the necessity of producing and characterizing a wide variety of rAAV preparations. Critically important characteristics concerning quality control are rAAV titer quantification and the detection of impurities. Differences in rAAV constructs necessitate the development of highly standardized quantification assays to make direct comparisons of different preparations in terms of assembly or purification efficiency, as well as experimental or therapeutic dosages. The development of universal methods for impurities quantification is rather complicated, since variable production platforms are utilized for rAAV assembly. However, general agreements also should be achieved to address this issue. The majority of methods for rAAV quantification and quality control are based on PCR techniques. Despite the progress made, increasing evidence concerning high variability in titration assays indicates poor standardization of the methods undertaken to date. This review summarizes successes in the field of rAAV quality control and emphasizes ongoing challenges in PCR applications for rAAV characterization. General considerations regarding possible solutions are also provided.

Structural characterization of the porcine adeno-associated virus Po1 capsid protein binding to the nuclear trafficking protein importin alpha

Adeno-associated viruses (AAVs) are key vectors for gene therapy; thus, many aspects of their cell transduction pathway have been revealed in detail. However, the specific mechanisms AAV virions use to enter the host nucleus remain largely unresolved. We therefore aimed to reveal the structural interactions between the AAV capsid (Cap) protein and the nuclear transport protein importin alpha (IMPα). A putative nuclear localization sequence (NLS) in the virion protein 1 capsid protein of the porcine AAV Po1 was identified. This region was complexed with IMPα and a structure solved at 2.26 Å. This is the first time that an NLS of AAV Cap complexed with IMPα has been determined structurally. Our results support the findings that AAV capsids enter the nucleus through binding the nuclear import adapter IMPα.

An AAV-based, room-temperature-stable, single-dose COVID-19 vaccine provides durable immunogenicity and protection in non-human primates

The SARS-CoV-2 pandemic has affected more than 185 million people worldwide resulting in over 4 million deaths. To contain the pandemic, there is a continued need for safe vaccines that provide durable protection at low and scalable doses and can be deployed easily. Here, AAVCOVID-1, an adeno-associated viral (AAV), spike-gene-based vaccine candidate demonstrates potent immunogenicity in mouse and non-human primates following a single injection and confers complete protection from SARS-CoV-2 challenge in macaques. Peak neutralizing antibody titers are sustained at 1 year and complemented by functional memory T cell responses. The AAVCOVID vector has no relevant pre-existing immunity in humans and does not elicit cross-reactivity to common AAVs used in gene therapy. Vector genome persistence and expression wanes following injection. The single low-dose requirement, high-yield manufacturability, and 1-month stability for storage at room temperature may make this technology well suited to support effective immunization campaigns for emerging pathogens on a global scale.

Liver-Directed AAV8 Booster Vaccine Expressing Plasmodium falciparum Antigen Following Adenovirus Vaccine Priming Elicits Sterile Protection in a Murine Model

Hepatocyte infection by malaria sporozoites is a bottleneck in the life-cycle of Plasmodium spp. including P. falciparum, which causes the most lethal form of malaria. Therefore, developing an effective vaccine capable of inducing the strong humoral and cellular immune responses necessary to block the pre-erythrocytic stage has potential to overcome the spatiotemporal hindrances pertaining to parasite biology and hepatic microanatomy. We recently showed that when combined with a human adenovirus type 5 (AdHu5)-priming vaccine, adeno-associated virus serotype 1 (AAV1) is a potent booster malaria vaccine vector capable of inducing strong and long-lasting protective immune responses in a rodent malaria model. Here, we evaluated the protective efficacy of a hepatotropic virus, adeno-associated virus serotype 8 (AAV8), as a booster vector because it can deliver a transgene potently and rapidly to the liver, the organ malaria sporozoites initially infect and multiply in following sporozoite injection by the bite of an infected mosquito. We first generated an AAV8-vectored vaccine expressing P. falciparum circumsporozoite protein (PfCSP). Intravenous (i.v.) administration of AAV8-PfCSP to mice initially primed with AdHu5-PfCSP resulted in a hepatocyte transduction rate ~2.5 times above that seen with intramuscular (i.m.) administration. This immunization regimen provided a better protection rate (100% sterile protection) than that of the i.m. AdHu5-prime/i.m. AAV8-boost regimen (60%, p < 0.05), i.m. AdHu5-prime/i.v. AAV1-boost (78%), or i.m. AdHu5-prime/i.m. AAV1-boost (80%) against challenge with transgenic PfCSP-expressing P. berghei sporozoites. Compared with the i.m. AdHu5-prime/i.v. AAV1-boost regimen, three other regimens induced higher levels of PfCSP-specific humoral immune responses. Importantly, a single i.v. dose of AAV8-PfCSP recruited CD8⁺ T cells, especially resident memory CD8⁺ T cells, in the liver. These data suggest that boost with i.v. AAV8-PfCSP can improve humoral and cellular immune responses in BALB/c mice. Therefore, this regimen holds great promise as a next-generation platform for the development of an effective malaria vaccine.

Current Update on Severe Acute Respiratory Syndrome Coronavirus 2 Vaccine Development with a Special Emphasis on Gene Therapy Viral Vector Design and Construction for Vaccination

Severe acute respiratory syndrome (SARS) is a newly emerging infectious disease (COVID-19) caused by the novel coronavirus SARS-coronavirus 2 (CoV-2). To combat the devastating spread of SARS-CoV-2, extraordinary efforts from numerous laboratories have focused on the development of effective and safe vaccines. Traditional live-attenuated or inactivated viral vaccines are not recommended for immunocompromised patients as the attenuated virus can still cause disease via phenotypic or genotypic reversion. Subunit vaccines require repeated dosing and adjuvant use to be effective, and DNA vaccines exhibit lower immune responses. mRNA vaccines can be highly unstable under physiological conditions. On the contrary, naturally antigenic viral vectors with well-characterized structure and safety profile serve as among the most effective gene carriers to provoke immune response via heterologous gene transfer. Viral vector-based vaccines induce both an effective cellular immune response and a humoral immune response owing to their natural adjuvant properties via transduction of immune cells. Consequently, viral vectored vaccines carrying the SARS-CoV-2 spike protein have recently been generated and successfully used to activate cytotoxic T cells and develop a neutralizing antibody response. Recent progress in SARS-CoV-2 vaccines, with an emphasis on gene therapy viral vector-based vaccine development, is discussed in this review.

Vectored Immunotherapeutics for Infectious Diseases: Can rAAVs Be The Game Changers for Fighting Transmissible Pathogens?

Conventional vaccinations and immunotherapies have encountered major roadblocks in preventing infectious diseases like HIV, influenza, and malaria. These challenges are due to the high genomic variation and immunomodulatory mechanisms inherent to these diseases. Passive transfer of broadly neutralizing antibodies may offer partial protection, but these treatments require repeated dosing. Some recombinant viral vectors, such as those based on lentiviruses and adeno-associated viruses (AAVs), can confer long-term transgene expression in the host after a single dose. Particularly, recombinant (r)AAVs have emerged as favorable vectors, given their high in vivo transduction efficiency, proven clinical efficacy, and low immunogenicity profiles. Hence, rAAVs are being explored to deliver recombinant antibodies to confer immunity against infections or to diminish the severity of disease. When used as a vaccination vector for the delivery of antigens, rAAVs enable de novo synthesis of foreign proteins with the conformation and topology that resemble those of natural pathogens. However, technical hurdles like pre-existing immunity to the rAAV capsid and production of anti-drug antibodies can reduce the efficacy of rAAV-vectored immunotherapies. This review summarizes rAAV-based prophylactic and therapeutic strategies developed against infectious diseases that are currently being tested in pre-clinical and clinical studies. Technical challenges and potential solutions will also be discussed.

Advancements in protein nanoparticle vaccine platforms to combat infectious disease

Infectious diseases are a major threat to global human health, yet prophylactic treatment options can be limited, as safe and efficacious vaccines exist only for a fraction of all diseases. Notably, devastating diseases such as acquired immunodeficiency syndrome (AIDS) and coronavirus disease of 2019 (COVID-19) currently do not have vaccine therapies. Conventional vaccine platforms, such as live attenuated vaccines and whole inactivated vaccines, can be difficult to manufacture, may cause severe side effects, and can potentially induce severe infection. Subunit vaccines carry far fewer safety concerns due to their inability to cause vaccine-based infections. The applicability of protein nanoparticles (NPs) as vaccine scaffolds is promising to prevent infectious diseases, and they have been explored for a number of viral, bacterial, fungal, and parasitic diseases. Many types of protein NPs exist, including self-assembling NPs, bacteriophage-derived NPs, plant virus-derived NPs, and human virus-based vectors, and these particular categories will be covered in this review. These vaccines can elicit strong humoral and cellular immune responses against specific pathogens, as well as provide protection against infection in a number of animal models. Furthermore, published clinical trials demonstrate the promise of applying these NP vaccine platforms, which include bacteriophage-derived NPs, in addition to multiple viral vectors that are currently used in the clinic. The continued investigations of protein NP vaccine platforms are critical to generate safer alternatives to current vaccines, advance vaccines for diseases that currently lack effective prophylactic therapies, and prepare for the rapid development of new vaccines against emerging infectious diseases. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Disruptors, a new class of oligonucleotide reagents, significantly improved PCR performance on templates containing stable intramolecular secondary structures

Intramolecular secondary structures within templates have been shown to lower PCR performance. Whereas many approaches have been developed to mitigate such impairment on PCR, their effects can vary greatly depending on template sequences. Here we present a novel, universally effective approach to improve PCR performance involving specifically designed oligonucleotides called disruptors. A disruptor contained three functional components, an anchor designed to initiate template binding, an effector to disrupt intramolecular secondary structure, and a 3' blocker to prevent its elongation by DNA polymerase. A functional mechanism for a disruptor to improve PCR efficiency was proposed where anchor first binds to template followed by effector-mediated strand displacement to unwind intramolecular secondary structure. Such a mechanism was consistent with the observation that anchor played a more critical role for disruptor function. As an example of potential disruptor applications, inverted terminal repeat sequences of recombinant adeno-associated virus vectors were successfully amplified in the presence of disruptors despite their well-known reputation as some of the most difficult templates for PCR amplification and Sanger sequencing due to their ultra-stable T-shaped hairpin structures. In stark contrast, both DMSO and betaine, two PCR additives routinely used to facilitate PCR amplification and Sanger sequencing of GC-rich templates, did not demonstrate any improving effect.

Strategies for Vaccination: Conventional Vaccine Approaches Versus New-Generation Strategies in Combination with Adjuvants

The current COVID-19 pandemic, caused by severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), has raised significant economic, social, and psychological concerns. The rapid spread of the virus, coupled with the absence of vaccines and antiviral treatments for SARS-CoV-2, has galvanized a major global endeavor to develop effective vaccines. Within a matter of just a few months of the initial outbreak, research teams worldwide, adopting a range of different strategies, embarked on a quest to develop effective vaccine that could be effectively used to suppress this virulent pathogen. In this review, we describe conventional approaches to vaccine development, including strategies employing proteins, peptides, and attenuated or inactivated pathogens in combination with adjuvants (including genetic adjuvants). We also present details of the novel strategies that were adopted by different research groups to successfully transfer recombinantly expressed antigens while using viral vectors (adenoviral and retroviral) and non-viral delivery systems, and how recently developed methods have been applied in order to produce vaccines that are based on mRNA, self-amplifying RNA (saRNA), and trans-amplifying RNA (taRNA). Moreover, we discuss the methods that are being used to enhance mRNA stability and protein production, the advantages and disadvantages of different methods, and the challenges that are encountered during the development of effective vaccines.

Immunogenicity of an AAV-based, room-temperature stable, single dose COVID-19 vaccine in mice and non-human primates

The SARS-CoV-2 pandemic has affected more than 70 million people worldwide and resulted in over 1.5 million deaths. A broad deployment of effective immunization campaigns to achieve population immunity at global scale will depend on the biological and logistical attributes of the vaccine. Here, two adeno-associated viral (AAV)-based vaccine candidates demonstrate potent immunogenicity in mouse and nonhuman primates following a single injection. Peak neutralizing antibody titers remain sustained at 5 months and are complemented by functional memory T-cells responses. The AAVrh32.33 capsid of the AAVCOVID vaccine is an engineered AAV to which no relevant pre-existing immunity exists in humans. Moreover, the vaccine is stable at room temperature for at least one month and is produced at high yields using established commercial manufacturing processes in the gene therapy industry. Thus, this methodology holds as a very promising single dose, thermostable vaccine platform well-suited to address emerging pathogens on a global scale.

Recent developments in vaccines strategies against human viral pathogens

Recently, several viruses have emerged or reemerged from obscurity to become serious global health threats, raising alarm regarding their sustained epidemic transmission. One of the main public health concerns of these emerging viruses is their sustained circulation among populations of immunologically naïve, susceptible hosts. With every new viral emergence or reemergence, comes the call for rapid vaccine development and the induction of protective immunity through vaccination can be a powerful tool to prevent this concern by conferring protection to the population at risk. Vaccines are considered a critical component of disease prevention against emerging viral infections because, in many cases, other medical options are limited or nonexistent. While the classic approaches to vaccine development are still amenable to emerging viruses, the advent of latest technologies in molecular techniques has profoundly influenced our understanding of virus biology, and immune responses and vaccination methods based on replicating, attenuated, and nonreplicating virus vector approaches have become useful vaccine platforms. Together with a growing understanding in the biology of newly emerging virus diseases, a range of new vaccine strategies, vaccines against new and reemerging viruses may become a possibility.

Alphaherpesvirus Vaccines

Prophylactic and therapeutic vaccines for the alphaherpesviruses including varicella zoster virus (VZV) and herpes simplex virus types 1 and 2 have been the focus of enormous preclinical and clinical research. A live viral vaccine for prevention of chickenpox and a subunit therapeutic vaccine to prevent zoster are highly successful. In contrast, progress towards the development of effective prophylactic or therapeutic vaccines against HSV-1 and HSV-2 has met with limited success. This review provides an overview of the successes and failures, the different types of immune responses elicited by various vaccine modalities, and the need to reconsider the preclinical models and immune correlates of protection against HSV.

Technological approaches to streamline vaccination schedules, progressing towards single-dose vaccines

Vaccines represent the most successful medical intervention in history, with billions of lives saved. Although multiple doses of the same vaccine are typically required to reach an adequate level of protection, it would be advantageous to develop vaccines that induce protective immunity with fewer doses, ideally just one. Single-dose vaccines would be ideal to maximize vaccination coverage, help stakeholders to greatly reduce the costs associated with vaccination, and improve patient convenience. Here we describe past attempts to develop potent single dose vaccines and explore the reasons they failed. Then, we review key immunological mechanisms of the vaccine-specific immune responses, and how innovative technologies and approaches are guiding the preclinical and clinical development of potent single-dose vaccines. By modulating the spatio-temporal delivery of the vaccine components, by providing the appropriate stimuli to the innate immunity, and by designing better antigens, the new technologies and approaches leverage our current knowledge of the immune system and may synergize to enable the rational design of next-generation vaccination strategies. This review provides a rational perspective on the possible development of future single-dose vaccines.

Use of Adeno-associated viral vectors to improve delivery of a DNA vaccine against dengue virus

Dengue virus (DENV) remains a significant healthcare and socioeconomic burden for endemic countries. Attempts to produce a safe and effective vaccine have been unsuccessful so far, making this task one of the top priorities in the field. We have previously shown that an EDIII-based DNA vaccine is able to induce neutralizing, long-lasting and highly specific antibody responses for all four DENV serotypes in mice using gene-gun delivery technology. Here, we describe the use of recombinant Adeno-associated viral vectors as an alternative DNA delivery platform, in combination with different immunization schedules, to simplify the vaccination protocol without compromising the induction of neutralizing antibody responses. Our results demonstrate that using viral vectored-platforms to deliver genetic vaccines could potentially reduce the number of doses required to induce a sustained DENV-neutralizing response, thus facilitating the implementation and deployment of the vaccine in developing countries.

Protection From Influenza by Intramuscular Gene Vector Delivery of a Broadly Neutralizing Nanobody Does Not Depend on Antibody Dependent Cellular Cytotoxicity

Cross-subtype neutralizing single domain antibodies against influenza present new opportunities for immunoprophylaxis and pandemic preparedness. Their simple modular structure and single open reading frame format are highly amenable to gene therapy-mediated delivery. We have previously described R1a-B6, an alpaca-derived single domain antibody (nanobody), that is capable of potent cross-subtype neutralization in vitro of H1N1, H5N1, H2N2, and H9N2 influenza viruses, through binding to a highly conserved epitope in the influenza hemagglutinin stem region. To evaluate the potential of R1a-B6 for immunoprophylaxis, we have reformatted it as an Fc fusion for adeno-associated viral (AAV) vector delivery. Our findings demonstrate that a single intramuscular injection in mice of AAV encoding R1a-B6 fused to Fc fragments of different isotypes equipped either, with or without antibody dependent cellular cytotoxicity (ADCC) activity, was able to drive sustained high-level expression (0.5-1.1 mg/mL) in sera with no evidence of reduction for up to 6 months. R1a-B6-Fc fusions of both isotypes gave complete protection against lethal challenge with both pandemic A/California/07/2009 (H1N1)pdm09 and avian influenza A/Vietnam/1194/2004 (H5N1). This data suggests that R1a-B6 is capable of cross-subtype protection and ADCC was not essential for R1a-B6 efficacy. Our findings demonstrate AAV delivery of cross-subtype neutralizing nanobodies may be an effective strategy to prevent influenza infection and provide long-term protection independent of a host induced immune response.

The Current and Future State of Vaccines, Antivirals and Gene Therapies Against Emerging Coronaviruses

Emerging coronaviruses (CoV) are constant global public health threats to society. Multiple ongoing clinical trials for vaccines and antivirals against CoVs showcase the availability of medical interventions to both prevent and treat the future emergence of highly pathogenic CoVs in human. However, given the diverse nature of CoVs and our close interactions with wild, domestic and companion animals, the next epidemic zoonotic CoV could resist the existing vaccines and antivirals developed, which are primarily focused on Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS CoV). In late 2019, the novel CoV (SARS-CoV-2) emerged in Wuhan, China, causing global public health concern. In this review, we will summarize the key advancements of current vaccines and antivirals against SARS-CoV and MERS-CoV as well as discuss the challenge and opportunity in the current SARS-CoV-2 crisis. At the end, we advocate the development of a "plug-and-play" platform technologies that could allow quick manufacturing and administration of broad-spectrum countermeasures in an outbreak setting. We will discuss the potential of AAV-based gene therapy technology for in vivo therapeutic antibody delivery to combat SARS-CoV-2 outbreak and the future emergence of severe CoVs.

Adeno-associated virus-vectored influenza vaccine elicits neutralizing and Fcγ receptor-activating antibodies

The current seasonal inactivated influenza vaccine protects only against a narrow range of virus strains as it triggers a dominant antibody response toward the hypervariable hemagglutinin (HA) head region. The discovery of rare broadly protective antibodies against conserved regions in influenza virus proteins has propelled research on distinct antigens and delivery methods to efficiently induce broad immunity toward drifted or shifted virus strains. Here, we report that adeno‐associated virus (AAV) vectors expressing influenza virus HA or chimeric HA protected mice against homologous and heterologous virus challenges. Unexpectedly, immunization even with wild‐type HA induced antibodies recognizing the HA‐stalk and activating FcγR‐dependent responses indicating that AAV‐vectored expression balances HA head‐ and HA stalk‐specific humoral responses. Immunization with AAV‐HA partially protected also ferrets against a harsh virus challenge. Results from this study provide a rationale for further clinical development of AAV vectors as influenza vaccine platform, which could benefit from their approved use in human gene therapy.

AAV-expressed G protein induces robust humoral and cellular immune response and provides durable protection from rabies virus challenges in mice

Rabies is a highly lethal infectious zoonosis caused by rabies virus (RABV), and the mortality rate is almost 100 % once clinical symptoms appear, which poses a huge threat to public health security across the many parts of the word. Vaccination is reported to be the most effective approach to prevent the disease. G protein is the only protein present on the surface of RABV, it also could induce humoral immunity to produce virus neutralizing antibodies (VNA) and stimulate T cells to produce cellular immunity. Adeno-associated viruses (AAVs) have been used as vectors for gene therapy of different human diseases for its low immunogenicity, high safety and long-term stable expression. To develop a safe and effective vaccine, recombinant AAVs containing different kind of G gene were constructed. After intramuscular (i.m.) immunization in mice, all of these rAAV-G vaccines could induce the production of high levels of VNA and effective cellular immune response. Consistently, all of the rAAV-G vaccines could provide protection against lethal RABV challenge. Our results shown that the rAAV-G vaccines could be potential candidates used in the control of RABV infection. In addition, rAAV-G as a vaccine has many advantages of low preparation cost, simple storage and transportation conditions (4 °C storage and transportation), simple immunization program (only one immunization) and so on. Thence, the rAAV-G vaccines could be potential candidates used in the control of RABV infection.

Adeno-associated viral vector-mediated immune responses: Understanding barriers to gene delivery

Adeno-associated viral (AAV) vectors have emerged as the leading gene delivery platform for gene therapy and vaccination. Three AAV-based gene therapy drugs, Glybera, LUXTURNA, and ZOLGENSMA were approved between 2012 and 2019 by the European Medicines Agency and the United States Food and Drug Administration as treatments for genetic diseases hereditary lipoprotein lipase deficiency (LPLD), inherited retinal disease (IRD), and spinal muscular atrophy (SMA), respectively. Despite these therapeutic successes, clinical trials have demonstrated that host anti-viral immune responses can prevent the long-term gene expression of AAV vector-encoded genes. Therefore, it is critical that we understand the complex relationship between AAV vectors and the host immune response. This knowledge could allow for the rational design of optimized gene transfer vectors capable of either subverting host immune responses in the context of gene therapy applications, or stimulating desirable immune responses that generate protective immunity in vaccine applications to AAV vector-encoded antigens. This review provides an overview of our current understanding of the AAV-induced immune response and discusses potential strategies by which these responses can be manipulated to improve AAV vector-mediated gene transfer.

Adeno-associated virus capsid protein expression in Escherichia coli and chemically defined capsid assembly

Research and clinical applications of recombinant adeno-associated virus (rAAV) significantly increased in recent years alongside regulatory approvals of rAAV gene therapy products. To date, all rAAV vectors as well as AAV empty capsids are produced in eukaryotic cells. We explored a new route to generate AAV capsids with the aim to analyze capsid assembly in a chemically defined setting and pave the way for new production methods and applications based on AAV virus-like particles (VLPs). We generated these empty capsids by bacterial expression and subsequent concomitant protein refolding and VLP formation. AAV serotype 2 structural protein VP3 was expressed in Escherichia coli. VLPs formed as demonstrated by dynamic light scattering, atomic force microscopy, and ELISA. Furthermore, VLPs internalized into human HeLa cells. To extend the application range of the VLPs, we tested peptide insertions, at the genetic level, in a surface loop (amino acid position 587) or at the C-terminus of VP3 and these variants also formed VLPs. VLPs developed without assembly-activating protein (AAP), but adding purified recombinant AAP to the refolding process increased capsid yield. Our findings offer a new route to understand AAV assembly biology and open a toolbox for AAV production strategies that might enable capsid display for vaccination and matching of capsids with cargoes at large scale and low cost.

Mucosal vaccines and technology

There is an urgent and unmet need to develop effective vaccines to reduce the global burden of infectious disease in both animals and humans, and in particular for the majority of pathogens that infect via mucosal sites. Here we summarise the impediments to developing mucosal vaccines and review the new and emerging technologies aimed at overcoming the lack of effective vaccine delivery systems that is the major obstacle to developing new mucosal vaccines.

Adeno-Associated Virus as an Effective Malaria Booster Vaccine Following Adenovirus Priming

An ideal malaria vaccine platform should potently induce protective immune responses and block parasite transmission from mosquito to human, and it should maintain these effects for an extended period. Here, we have focused on vaccine development based on adeno-associated virus serotype 1 (AAV1), a viral vector widely studied in the field of clinical gene therapy that is able to induce long-term transgene expression without causing toxicity in vivo. Our results show the potential utility of AAV1 vectors as an extremely potent booster vaccine to induce durable immunity when combined with an adenovirus-priming vaccine in a rodent malaria model. We generated a series of recombinant AAV1s and human adenovirus type 5 (AdHu5) expressing either Plasmodium falciparum circumsporozoite protein (PfCSP) or P25 (Pfs25) protein. Heterologous two-dose immunization with an AdHu5-prime and AAV1-boost (AdHu5-AAV1) elicited robust and durable PfCSP- or Pfs25-specific functional antibodies over 280 days. Regarding protective efficacy, AdHu5-AAV1 PfCSP achieved high sterile protection (up to 80% protection rate) against challenge with transgenic Plasmodium berghei sporozoites expressing PfCSP. When examining transmission-blocking (TB) efficacy, we found that immunization with AdHu5-AAV1 Pfs25 maintained TB activity in vivo against transgenic P. berghei expressing Pfs25 for 287 days (99% reduction in oocyst intensity, 85% reduction in oocyst prevalence). Our data indicate that AAV1-based malaria vaccines can confer potent and durable protection as well as TB efficacy when administered following an AdHu5 priming vaccine, supporting the further evaluation of this regimen in clinical trials as a next-generation malaria vaccine platform.

Vector uncoating limits adeno-associated viral vector-mediated transduction of human dendritic cells and vector immunogenicity

AAV vectors poorly transduce Dendritic cells (DC), a feature invoked to explain AAV’s low immunogenicity. However, the reason for this non-permissiveness remained elusive. Here, we performed an in-depth analysis using human monocyte-derived immature DC (iDC) as model. iDC internalized AAV vectors of various serotypes, but even the most efficient serotype failed to transduce iDC above background. Since AAV vectors reached the cell nucleus, we hypothesized that AAV’s intracellular processing occurs suboptimal. On this basis, we screened an AAV peptide display library for capsid variants more suitable for DC transduction and identified the I/VSS family which transduced DC with efficiencies of up to 38%. This property correlated with an improved vector uncoating. To determine the consequence of this novel feature for AAV’s in vivo performance, we engineered one of the lead candidates to express a cytoplasmic form of ovalbumin, a highly immunogenic model antigen, and assayed transduction efficiency as well as immunogenicity. The capsid variant clearly outperformed the parental serotype in muscle transduction and in inducing antigen-specific humoral and T cell responses as well as anti-capsid CD8⁺ T cells. Hence, vector uncoating represents a major barrier hampering AAV vector-mediated transduction of DC and impacts on its use as vaccine platform.

Cross-Presentation of Skin-Targeted Recombinant Adeno-associated Virus 2/1 Transgene Induces Potent Resident Memory CD8+ T Cell Responses

A key aspect to consider for vaccinal protection is the induction of a local line of defense consisting of nonrecirculating tissue-resident memory T cells (T_RM), in parallel to the generation of systemic memory CD8⁺ T cell responses. The potential to induce T_RM has now been demonstrated for a number of pathogens and viral vectors. This potential, however, has never been tested for recombinant adeno-associated virus (rAAV) vectors, which are weakly inflammatory and poor transducer of dendritic cells. Using a model rAAV2/1-based vaccine, we determined that a single intradermal immunization with rAAV2/1 vectors in mice induces fully functional T_RM at the local site of immunization. The optimal differentiation of rAAV-induced transgene-specific skin T_RM was dependent on local transgene expression and additional CD4⁺ T cell help. Transgene expression in dendritic cells, however, appeared to be dispensable for the priming of transgene-specific skin T_RM, suggesting that this process solely depends on the cross-presentation of transgene products. Overall, this study provides needed information to properly assess rAAV vectors as T cell-inducing vaccine carriers.IMPORTANCE rAAVs display numerous characteristics that could make them extremely attractive as vaccine carriers, including an excellent safety profile in humans and great flexibility regarding serotypes and choice of target tissue. Studies addressing the ability of rAAV to induce protective T cell responses, however, are scarce. Notably, the potential to induce a tissue-resident memory T cell response has never been described for rAAV vectors, strongly limiting further interest for their use as vaccine carriers. Using a model rAAV2/1 vaccine delivered to the skin, our study demonstrated that rAAV vectors can induce bona fide skin resident T_RM and provides additional clues regarding the cellular mechanisms underlying this process. These results will help widen the field of rAAV applications.

Advances in Designing and Developing Vaccines, Drugs and Therapeutic Approaches to Counter Human Papilloma Virus

Human papillomavirus (HPV) is a viral infection with skin-to-skin based transmission mode. HPV annually caused over 500,000 cancer cases including cervical, anogenital and oropharyngeal cancer among others. HPV vaccination has become a public-health concern, worldwide, to prevent the cases of HPV infections including precancerous lesions, cervical cancers, and genital warts especially in adolescent female and male population by launching national programs with international alliances. Currently, available prophylactic and therapeutic vaccines are expensive to be used in developing countries for vaccination programs. The recent progress in immunotherapy, biotechnology, recombinant DNA technology and molecular biology along with alternative and complementary medicinal systems have paved novel ways and valuable opportunities to design and develop effective prophylactic and therapeutic vaccines, drugs and treatment approach to counter HPV effectively. Exploration and more researches on such advances could result in the gradual reduction in the incidences of HPV cases across the world. The present review presents a current global scenario and futuristic prospects of the advanced prophylactic and therapeutic approaches against HPV along with recent patents coverage of the progress and advances in drugs, vaccines and therapeutic regimens to effectively combat HPV infections and its cancerous conditions.

Considerations for the use of virally delivered genetic tools for in-vivo circuit analysis and behavior in mutant mice: a practical guide to optogenetics

Optogenetics was the method of the year in 2010 according to Nature Neuroscience. Since then, this method has become widespread, the use of virally delivered genetic tools has extended to other fields such as pharmacogenetics, and optogenetic techniques have become frequently applied in genetically manipulated animals for in-vivo circuit analysis and behavioral studies. However, several issues should be taken into consideration when planning such experiments. We aimed to summarize the critical points concerning optogenetic manipulation of a specific brain area in mutant mice. First, the appropriate vector should be chosen to allow optimal optogenetic manipulation. Adeno-associated viral vectors are the most common carriers with different available serotypes. Light-sensitive channels are available in many forms, and the expression of the delivered genetic material can be influenced in many ways. Second, selecting the adequate stimulation protocol is also essential. The pattern, intensity, and timing could be determinative parameters. Third, the mutant strain might have a phenotype that influences the observed behavior. In conclusion, detailed preliminary experiments and numerous control groups are required to choose the best vector and stimulation protocol and to ensure that the mutant animals do not have a specific phenotype that can influence the examined behavior.

Intradermal Immunization with rAAV1 Vector Induces Robust Memory CD8+ T Cell Responses Independently of Transgene Expression in DCs

Recombinant adeno-associated viral (rAAV) vectors exhibit interesting properties as vaccine carriers for their ability to induce long-lasting antibody responses. However, rAAV-based vaccines have been suggested to trigger functionally impaired long-term memory CD8⁺ T cell responses, in part due to poor dendritic cell (DC) transduction. Such results, albeit limited to intramuscular immunization, undermined the use of rAAV as vaccine vehicles against intracellular pathogens. We report here that intradermal immunization with a model rAAV2/1-based vaccine drives the development of bona fide long-term memory CD8⁺ T cell responses. The intradermal route of immunization and the presence of potent major histocompatibility complex (MHC) class II responses showed synergistic effects on the overall quantity and quality of systemic long-term effector memory transgene-specific CD8⁺ T cells being generated against the transgene. Of key interest, we found that the induction of memory cytotoxic T lymphocytes (CTLs) following intradermal immunization was solely dependent on the cross-presentation of skin-expressed transgene products, which appeared highly enhanced as compared to muscle-expressed transgene products. Overall our results highlight key tissue-specific differences in transgene presentation pathway requirements of importance for the design of rAAV-based T cell-inducing vaccines.

Vectored immunoprophylaxis: an emerging adjunct to traditional vaccination

The successful development of effective vaccines has been elusive for many of the world's most important infectious diseases. Additionally, much of the population, such as the aged or immunocompromised, are unable to mount an effective immunologic response for existing vaccines. Vectored Immunoprophylaxis (VIP) is a novel approach designed to address these challenges. Rather than utilizing an antigen to trigger a response from the host's immune system as is normally done with traditional vaccines, VIP genetically engineers the production of tailored antibodies from non-hematopoietic cells, bypassing the humoral immune system. Direct administration of genes encoding for neutralizing antibodies has proven to be effective in both preventing and treating several infectious diseases in animal models. While, a significant amount of work has focused on HIV, including an ongoing clinical trial, the approach has also been shown to be effective for malaria, dengue, hepatitis C, influenza, and more. In addition to presenting itself as a potentially efficient approach to solving long-standing vaccine challenges, the approach may be the best, if not only, method to vaccinate immunocompromised individuals. Many issues still need to be addressed, including which tissue(s) makes the most suitable platform, which vector(s) are most efficient at transducing the platform tissue used to secrete the antibodies, and what are the long-term effects of such a treatment. Here we provide a brief overview of this approach, and its potential application in treating some of the world's most intractable infectious diseases.