Vector-based genetically modified vaccines: Exploiting Jenner's legacy

Adaptation of an rVSV Ebola vaccine purification process for rapid development of a viral vaccine candidate for SARS-CoV-2

During the COVID-19 pandemic, long development timelines typically associated with vaccines were challenged. The urgent need for a vaccine provided a strong driver to reevaluate existing vaccine development approaches. Innovative approaches to regulatory approval were realized, including the use of platform-based technology. In collaboration with the International AIDS Vaccine Initiative, Inc. (IAVI), Merck & Co., Inc., Rahway, NJ, USA rapidly advanced an investigational SARS-CoV-2 vaccine based on the recombinant vesicular stomatitis virus (rVSV) platform used for the Ebola vaccine ERVEBO (rVSV∆G-ZEBOV-GP). An rVSV∆G-SARS-CoV-2 vaccine candidate was generated using the SARS-CoV-2 spike protein to replace the VSV G protein. The purification process development for this vaccine candidate was detailed in this paper. Areas were highlighted where the ERVEBO platform process was successfully adopted and where additional measures were needed for the SARS-CoV-2 vaccine candidate. These included: (i) endonuclease addition directly into the bioreactor prior to harvest, (ii) inclusion of a core-shell chromatography step for improved purification, and (iii) incorporation of a terminal, sterile filtration step to eliminate the need for aseptic, closed processing. High infectious virus titers were achieved in Phase 3 clinical drug substance (>108 PFU mL-1 ), and process consistency was demonstrated across four large scale batches that were completed in 6 months from clone selection.

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.

Respiratory Syncytial Virus Vaccines: A Review of the Candidates and the Approved Vaccines

Respiratory syncytial virus (RSV) is responsible for a significant proportion of global morbidity and mortality affecting young children and older adults. In the aftermath of formalin-inactivated RSV vaccine development, the effort to develop an immunizing agent was carefully guided by epidemiologic and pathophysiological evidence of the virus, including various vaccine technologies. The pipeline of RSV vaccine development includes messenger ribonucleic acid (mRNA), live-attenuated (LAV), subunit, and recombinant vector-based vaccine candidates targeting different virus proteins. The availability of vaccine candidates of various technologies enables adjustment to the individualized needs of each vulnerable age group. Arexvy® (GSK), followed by Abrysvo® (Pfizer), is the first vaccine available for market use as an immunizing agent to prevent lower respiratory tract disease in older adults. Abrysvo is additionally indicated for the passive immunization of infants by maternal administration during pregnancy. This review presents the RSV vaccine pipeline, analyzing the results of clinical trials. The key features of each vaccine technology are also mentioned. Currently, 24 vaccines are in the clinical stage of development, including the 2 licensed vaccines. Research in the field of RSV vaccination, including the pharmacovigilance methods of already approved vaccines, promotes the achievement of successful prevention.

Adenoviral Vector-Based Vaccine Platform for COVID-19: Current Status

The coronavirus disease (COVID-19) breakout had an unimaginable worldwide effect in the 21st century, claiming millions of lives and putting a huge burden on the global economy. The potential developments in vaccine technologies following the determination of the genetic sequence of SARS-CoV-2 and the increasing global efforts to bring potential vaccines and therapeutics into the market for emergency use have provided a small bright spot to this tragic event. Several intriguing vaccine candidates have been developed using recombinant technology, genetic engineering, and other vaccine development technologies. In the last decade, a vast amount of the vaccine development process has diversified towards the usage of viral vector-based vaccines. The immune response elicited by such vaccines is comparatively higher than other approved vaccine candidates that require a booster dose to provide sufficient immune protection. The non-replicating adenoviral vectors are promising vaccine carriers for infectious diseases due to better yield, cGMP-friendly manufacturing processes, safety, better efficacy, manageable shipping, and storage procedures. As of April 2022, the WHO has approved a total of 10 vaccines around the world for COVID-19 (33 vaccines approved by at least one country), among which three candidates are adenoviral vector-based vaccines. This review sheds light on the developmental summary of all the adenoviral vector-based vaccines that are under emergency use authorization (EUA) or in the different stages of development for COVID-19 management.

Adenovirus vector-based vaccines as forefront approaches in fighting the battle against flaviviruses

Flaviviruses are arthropod-borne viruses (arboviruses) that have been recently considered among the significant public health problems in defined geographical regions. In this line, there have been vaccines approved for some flaviviruses including dengue virus (DENV), Japanese encephalitis virus (JEV), yellow fever virus (YFV), and tick-borne encephalitis virus (TBEV), although the efficiency of such vaccines thought to be questionable. Surprisingly, there are no effective vaccine for many other hazardous flaviviruses, including West Nile and Zika viruses. Furthermore, in spite of approved vaccines for some flaviviruses, for example DENV, alternative prophylactic vaccines seem to be still needed for the protection of a broader population, and it originates from the unsatisfying safety, and the efficacy of vaccines that have been introduced. Thus, adenovirus vector-based vaccine candidates are suggested to be effective, safe, and reliable. Interestingly, recent widespread use of adenovirus vector-based vaccines for the COVID-19 pandemic have highlighted the importance and feasibility of their widespread application. In this review, the applicability of adenovirus vector-based vaccines, as promising approaches to harness the diseases caused by Flaviviruses, is discussed.

Viral Vector Vaccines Against ASF: Problems and Prospectives

African swine fever (ASF) is a highly contagious viral disease affecting pigs, with mortality rates a primary focus as they can reach up to 100%. The widespread and colossal economic losses from ASF have impacts on the development of animal husbandry practices in most countries within Africa, Asia, and Europe. Currently, a variety of approaches toward the development of vaccines against ASF are being employed. A promising new concept centered around more economical and time-consuming vaccine production is based on the use of viral vectors to deliver selected immunogens. This review discusses the results obtained from testing various viral vectors as carriers of targeted ASF virus genes. The safety and prospects of viral vectors, the possibilities around modulating cellular and humoral immune responses by choosing genes expressing immunodominant antigens, and the degree of protection in experimental animals from infection with a lethal dose of virulent ASF virus strains have been shown and discussed.

Therapeutic cancer vaccines revamping: technology advancements and pitfalls

Cancer vaccines (CVs) represent a long-sought therapeutic and prophylactic immunotherapy strategy to obtain antigen (Ag)-specific T-cell responses and potentially achieve long-term clinical benefit. However, historically, most CV clinical trials have resulted in disappointing outcomes, despite promising signs of immunogenicity across most formulations. In the past decade, technological advances regarding vaccine delivery platforms, tools for immunogenomic profiling, and Ag/epitope selection have occurred. Consequently, the ability of CVs to induce tumor-specific and, in some cases, remarkable clinical responses have been observed in early-phase clinical trials. It is notable that the record-breaking speed of vaccine development in response to the coronavirus disease-2019 pandemic mainly relied on manufacturing infrastructures and technological platforms already developed for CVs. In turn, research, clinical data, and infrastructures put in place for the severe acute respiratory syndrome coronavirus 2 pandemic can further speed CV development processes. This review outlines the main technological advancements as well as major issues to tackle in the development of CVs. Possible applications for unmet clinical needs will be described, putting into perspective the future of cancer vaccinology.

Evolving pharmacovigilance requirements with novel vaccines and vaccine components

This paper explores the pipeline of new and upcoming vaccines as it relates to monitoring their safety. Compared with most currently available vaccines, that are constituted of live attenuated organisms or inactive products, future vaccines will also be based on new technologies. Several products that include such technologies are either already licensed or at an advanced stage of clinical development. Those include viral vectors, genetically attenuated live organisms, nucleic acid vaccines, novel adjuvants, increased number of antigens present in a single vaccine, novel mode of vaccine administration and thermostabilisation. The Global Advisory Committee on Vaccine Safety (GACVS) monitors novel vaccines, from the time they become available for large scale use. GACVS maintains their safety profile as evidence emerges from post-licensure surveillance and observational studies. Vaccines and vaccine formulations produced with novel technologies will have different safety profiles that will require adapting pharmacovigilance approaches. For example, GACVS now considers viral vector templates developed on the model proposed by Brighton Collaboration. The characteristics of those novel products will also have implications for the risk management plans (RMPs). Questions related to the duration of active monitoring for genetic material, presence of adventitious agents more easily detected with enhanced biological screening, or physiological mechanisms of novel adjuvants are all considerations that will belong to the preparation of RMPs. In addition to assessing those novel products and advising experts, GACVS will also consider how to more broadly communicate about risk assessment, so vaccine users can also benefit from the committee’s advice.

Comparison of regulatory framework of clinical trial with genetically modified organism-containing vaccines in the Europe, Australia, and Switzerland

New vaccines production and manufacture have revolutionized by recombinant technology. Various regulatory associations are engaged with the appraisal of a clinical trial with genetically modified organisms. At present safe, effective vaccines are needed in order to control the various emerging diseases which are a major cause of mortality. In reality, most vaccines raise biosafety worries with respect to human wellbeing. "Federal Office for Environment" is the competent authority for environmental risk assessments in Switzerland. Gene Technology Act 2000 is the fundamental direction that provides the necessary information to carry the clinical trials with genetically modified organism-containing vaccines. In addition, regulatory framework for "clinical trial with genetically modified organisms-containing vaccines" is stringent and partially harmonized in Switzerland, the European Union and Australia. In this study, we mainly concerned with regulatory aspects of "clinical trial with genetically modified organism" containing vaccine in three regions. This review includes various aspects like ethics, guidelines related to clinical trials of vaccines with genetically modified organisms.

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.

Multi-epitope vaccine expressed in Leishmania tarentolae confers protective immunity to Toxoplasma gondii in BALB/c mice

Current study deals with a novel multi-epitope vaccine designed in silico and its confirmation experiments for potential efficacy in BALB/c mice. Major histocompatibility complex (MHC)-binding and B-cell binding epitopes of five Toxoplasma antigens (SAG1, ROP16, GRA12, MIC4 and M2AP) were predicted. Selected epitopes were fused together using SAPGTP linker, and antigenicity, allergenicity, physico-chemical features, secondary and tertiary structures and validations were all performed via bioinformatics servers. Then, vaccine construct was cloned into pLEXSY-neo 2.1 vector. After Leishmania tarentolae transfection, live recombinant and wild parasites were subcutaneously injected into 6-8 week female BALB/c mice and immune responses were measured. Results showed that the peptide possessed 282 amino acid residues with average molecular weight of 28.06 kDa. About 90% of the peptide residues were incorporated in favored and allowed regions of the Ramachandran plot. Vaccinated mice showed remarkably elevated levels of specific antibodies (P < 0.05) with predominance of IgG2a production. Also, a Th₁ immune response with production of IFN-γ and relatively increased survival rate against intraperitoneal challenge with RH strain was demonstrated in immunized mice than control groups (P < 0.05). Also, very low levels of IL-4 were demonstrated, which showed statistically significant association with controls (P < 0.05). The findings clarified that multi-epitope vaccine expressed in Leishmania tarentolae induced significant immune responses against acute toxoplasmosis.

Developmental Landscape of Potential Vaccine Candidates Based on Viral Vector for Prophylaxis of COVID-19

Severe acute respiratory syndrome coronavirus 2, SARS-CoV-2, arose at the end of 2019 as a zoonotic virus, which is the causative agent of the novel coronavirus outbreak COVID-19. Without any clear indications of abatement, the disease has become a major healthcare threat across the globe, owing to prolonged incubation period, high prevalence, and absence of existing drugs or vaccines. Development of COVID-19 vaccine is being considered as the most efficient strategy to curtail the ongoing pandemic. Following publication of genetic sequence of SARS-CoV-2, globally extensive research and development work has been in progress to develop a vaccine against the disease. The use of genetic engineering, recombinant technologies, and other computational tools has led to the expansion of several promising vaccine candidates. The range of technology platforms being evaluated, including virus-like particles, peptides, nucleic acid (DNA and RNA), recombinant proteins, inactivated virus, live attenuated viruses, and viral vectors (replicating and non-replicating) approaches, are striking features of the vaccine development strategies. Viral vectors, the next-generation vaccine platforms, provide a convenient method for delivering vaccine antigens into the host cell to induce antigenic proteins which can be tailored to arouse an assortment of immune responses, as evident from the success of smallpox vaccine and Ervebo vaccine against Ebola virus. As per the World Health Organization, till January 22, 2021, 14 viral vector vaccine candidates are under clinical development including 10 nonreplicating and four replicating types. Moreover, another 39 candidates based on viral vector platform are under preclinical evaluation. This review will outline the current developmental landscape and discuss issues that remain critical to the success or failure of viral vector vaccine candidates against COVID-19.

Vaccine Development for Severe Fever with Thrombocytopenia Syndrome

Severe fever with thrombocytopenia syndrome (SFTS), which is caused by SFTS virus (SFTSV), is a tick-borne emerging zoonosis with a high case-fatality rate. At present, there is no approved SFTS vaccine, although the development of a vaccine would be one of the best strategies for preventing SFTS. This article focused on studies aimed at establishing small animal models of SFTS that are indispensable for evaluating vaccine candidates, developing these vaccine candidates, and establishing more practical animal models for evaluation. Innate immune-deficient mouse models, a hamster model, an immunocompetent ferret model and a cat model have been developed for SFTS. Several vaccine candidates for SFTS have been developed, and their efficacy has been confirmed using these animal models. The candidates consist of live-attenuated virus-based, viral vector-based, or DNA-based vaccines. SFTS vaccines are expected to be used for humans and companion dogs and cats. Hence for practical use, the vaccine candidates should be evaluated for efficacy using not only nonhuman primates but also dogs and cats. There is no practical nonhuman primate model of SFTS; however, the cat model is available to evaluate the efficacy of these candidate SFTS vaccines on domesticated animals.

Rational Vaccine Design in Times of Emerging Diseases: The Critical Choices of Immunological Correlates of Protection, Vaccine Antigen and Immunomodulation

Vaccines are the most effective medical intervention due to their continual success in preventing infections and improving mortality worldwide. Early vaccines were developed empirically however, rational design of vaccines can allow us to optimise their efficacy, by tailoring the immune response. Establishing the immune correlates of protection greatly informs the rational design of vaccines. This facilitates the selection of the best vaccine antigens and the most appropriate vaccine adjuvant to generate optimal memory immune T cell and B cell responses. This review outlines the range of vaccine types that are currently authorised and those under development. We outline the optimal immunological correlates of protection that can be targeted. Finally we review approaches to rational antigen selection and rational vaccine adjuvant design. Harnessing current knowledge on protective immune responses in combination with critical vaccine components is imperative to the prevention of future life-threatening diseases.

One or two injections of MVA-vectored vaccine shields hACE2 transgenic mice from SARS-CoV-2 upper and lower respiratory tract infection

Modified vaccinia virus Ankara (MVA) is a replication-restricted smallpox vaccine, and numerous clinical studies of recombinant MVAs (rMVAs) as vectors for prevention of other infectious diseases, including COVID-19, are in progress. Here, we characterize rMVAs expressing the S protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Modifications of full-length S individually or in combination included two proline substitutions, mutations of the furin recognition site, and deletion of the endoplasmic retrieval signal. Another rMVA in which the receptor binding domain (RBD) is flanked by the signal peptide and transmembrane domains of S was also constructed. Each modified S protein was displayed on the surface of rMVA-infected cells and was recognized by anti-RBD antibody and soluble hACE2 receptor. Intramuscular injection of mice with the rMVAs induced antibodies, which neutralized a pseudovirus in vitro and, upon passive transfer, protected hACE2 transgenic mice from lethal infection with SARS-CoV-2, as well as S-specific CD3+CD8+IFNγ+ T cells. Antibody boosting occurred following a second rMVA or adjuvanted purified RBD protein. Immunity conferred by a single vaccination of hACE2 mice prevented morbidity and weight loss upon intranasal infection with SARS-CoV-2 3 wk or 7 wk later. One or two rMVA vaccinations also prevented detection of infectious SARS-CoV-2 and subgenomic viral mRNAs in the lungs and greatly reduced induction of cytokine and chemokine mRNAs. A low amount of virus was found in the nasal turbinates of only one of eight rMVA-vaccinated mice on day 2 and none later. Detection of low levels of subgenomic mRNAs in turbinates indicated that replication was aborted in immunized animals.

A highly attenuated vaccinia virus strain LC16m8-based vaccine for severe fever with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) caused by a species Dabie bandavirus (formerly SFTS virus [SFTSV]) is an emerging hemorrhagic infectious disease with a high case-fatality rate. One of the best strategies for preventing SFTS is to develop a vaccine, which is expected to induce both humoral and cellular immunity. We applied a highly attenuated but still immunogenic vaccinia virus strain LC16m8 (m8) as a recombinant vaccine for SFTS. Recombinant m8s expressing SFTSV nucleoprotein (m8-N), envelope glycoprotein precursor (m8-GPC), and both N and GPC (m8-N+GPC) in the infected cells were generated. Both m8-GPC- and m8-N+GPC-infected cells were confirmed to produce SFTSV-like-particles (VLP) in vitro, and the N was incorporated in the VLP produced by the infection of cells with m8-N+GPC. Specific antibodies to SFTSV were induced in mice inoculated with each of the recombinant m8s, and the mice were fully protected from lethal challenge with SFTSV at both 10³ TCID₅₀ and 10⁵ TCID₅₀. In mice that had been immunized with vaccinia virus strain Lister in advance of m8-based SFTSV vaccine inoculation, protective immunity against the SFTSV challenge was also conferred. The pathological analysis revealed that mice immunized with m8-GPC or m8-N+GPC did not show any histopathological changes without any viral antigen-positive cells, whereas the control mice showed focal necrosis with inflammatory infiltration with SFTSV antigen-positive cells in tissues after SFTSV challenge. The passive serum transfer experiments revealed that sera collected from mice inoculated with m8-GPC or m8-N+GPC but not with m8-N conferred protective immunity against lethal SFTSV challenge in naïve mice. On the other hand, the depletion of CD8-positive cells in vivo did not abrogate the protective immunity conferred by m8-based SFTSV vaccines. Based on these results, the recombinant m8-GPC and m8-N+GPC were considered promising vaccine candidates for SFTS.

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging viral hemorrhagic fever with a high case-fatality rate (approximately 5% to >40%). Indigenous SFTS has been reported in China, Japan, South Korea, and Vietnam. Thus, the development of an effective vaccine for SFTS is urgently needed. Vaccinia virus (VAC) was previously used as a vaccine for smallpox. Unfortunately, after these strains, the so-called second generation of VAC used during the eradication campaign was associated with severe adverse events, and the third generation of VAC strains such as LC16m8 (m8) and modified vaccinia Ankara (MVA) was established. m8 is confirmed to be highly attenuated while still maintaining immunogenicity. m8 is licensed for use in healthy people in Japan. At the present time, approximately 100,000 people have undergone vaccination with m8 without experiencing any severe postvaccine complications. At present, third-generation VAC strains are attractive for a recombinant vaccine vector, especially for viral hemorrhagic infectious diseases, such as Ebola virus disease, Lassa fever, Crimean-Congo hemorrhagic fever, and SFTS. We investigated the practicality of an m8-based recombinant vaccine for SFTS as well as other promising recombinant VAC-based vaccines for viral hemorrhagic infectious diseases.

Principles and Challenges in anti-COVID-19 Vaccine Development

The number of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected patients keeps rising in most of the European countries despite the pandemic precaution measures. The current antiviral and anti-inflammatory therapeutic approaches are only supportive, have limited efficacy, and the prevention in reducing the transmission of SARS-CoV-2 virus is the best hope for public health. It is presumed that an effective vaccination against SARS-CoV-2 infection could mobilize the innate and adaptive immune responses and provide a protection against severe forms of coronavirus disease 2019 (COVID-19) disease. As the race for the effective and safe vaccine has begun, different strategies were introduced. To date, viral vector-based vaccines, genetic vaccines, attenuated vaccines, and protein-based vaccines are the major vaccine types tested in the clinical trials. Over 80 clinical trials have been initiated; however, only 18 vaccines have reached the clinical phase II/III or III, and 4 vaccine candidates are under consideration or have been approved for the use so far. In addition, the protective effect of the off-target vaccines, such as Bacillus Calmette-Guérin and measles vaccine, is being explored in randomized prospective clinical trials with SARS-CoV-2-infected patients. In this review, we discuss the most promising anti-COVID-19 vaccine clinical trials and different vaccination strategies in order to provide more clarity into the ongoing clinical trials.

Membrane Microvesicles as Potential Vaccine Candidates

The prevention and control of infectious diseases is crucial to the maintenance and protection of social and public healthcare. The global impact of SARS-CoV-2 has demonstrated how outbreaks of emerging and re-emerging infections can lead to pandemics of significant public health and socio-economic burden. Vaccination is one of the most effective approaches to protect against infectious diseases, and to date, multiple vaccines have been successfully used to protect against and eradicate both viral and bacterial pathogens. The main criterion of vaccine efficacy is the induction of specific humoral and cellular immune responses, and it is well established that immunogenicity depends on the type of vaccine as well as the route of delivery. In addition, antigen delivery to immune organs and the site of injection can potentiate efficacy of the vaccine. In light of this, microvesicles have been suggested as potential vehicles for antigen delivery as they can carry various immunogenic molecules including proteins, nucleic acids and polysaccharides directly to target cells. In this review, we focus on the mechanisms of microvesicle biogenesis and the role of microvesicles in infectious diseases. Further, we discuss the application of microvesicles as a novel and effective vaccine delivery system.

MVA Vector Vaccines Inhibit SARS CoV-2 Replication in Upper and Lower Respiratory Tracts of Transgenic Mice and Prevent Lethal Disease

Replication-restricted modified vaccinia virus Ankara (MVA) is a licensed smallpox vaccine and numerous clinical studies investigating recombinant MVAs (rMVAs) as vectors for prevention of other infectious diseases have been completed or are in progress. Two rMVA COVID-19 vaccine trials are at an initial stage, though no animal protection studies have been reported. Here, we characterize rMVAs expressing the S protein of CoV-2. Modifications of full length S individually or in combination included two proline substitutions, mutations of the furin recognition site and deletion of the endoplasmic retrieval signal. Another rMVA in which the receptor binding domain (RBD) flanked by the signal peptide and transmembrane domains of S was also constructed. Each modified S protein was displayed on the surface of rMVA-infected human cells and was recognized by anti-RBD antibody and by soluble hACE2 receptor. Intramuscular injection of mice with the rMVAs induced S-binding and pseudovirus-neutralizing antibodies. Boosting occurred following a second homologous rMVA but was higher with adjuvanted purified RBD protein. Weight loss and lethality following intranasal infection of transgenic hACE2 mice with CoV-2 was prevented by one or two immunizations with rMVAs or by passive transfer of serum from vaccinated mice. One or two rMVA vaccinations also prevented recovery of infectious CoV-2 from the lungs. A low amount of virus was detected in the nasal turbinates of only one of eight rMVA-vaccinated mice on day 2 and none later. Detection of subgenomic mRNA in turbinates on day 2 only indicated that replication was abortive in immunized animals.

Use of a small DNA virus model to investigate mechanisms of CpG dinucleotide-induced attenuation of virus replication

Suppression of the CpG dinucleotide is widespread in RNA viruses infecting vertebrates and plants, and in the genomes of retroviruses and small mammalian DNA viruses. The functional basis for CpG suppression in the latter was investigated through the construction of mutants of the parvovirus, minute virus of mice (MVM) with increased CpG or TpA dinucleotides in the VP gene. CpG-high mutants displayed extraordinary attenuation in A9 cells compared to wild-type MVM (>six logs), while TpA elevation showed no replication effect. Attenuation was independent of Toll-like receptor 9 and STING-mediated DNA recognition pathways and unrelated to effects on translation efficiency. While translation from codon-optimized VP RNA was enhanced in a cell-free assay, MVM containing this sequence was highly attenuated. Further mutational analysis indicated that this arose through its increased numbers of CpG dinucleotides (7→70) and separately from its increased G+C content (42.3→57.4 %), which independently attenuated replication. CpG-high viruses showed impaired NS mRNA expression by qPCR and reduced NS and particularly VP protein expression detected by immunofluorescence and replication in A549 cells, effects reversed in zinc antiviral protein (ZAP) knockout cells, even though nuclear relocalization of VP remained defective. The demonstrated functional basis for CpG suppression in MVM and potentially other small DNA viruses and the observed intolerance of CpGs in coding sequences, even after codon optimization, has implications for the use of small DNA virus vectors in gene therapy and immunization.

ΦX174 Attenuation by Whole-Genome Codon Deoptimization

Natural selection acting on synonymous mutations in protein-coding genes influences genome composition and evolution. In viruses, introducing synonymous mutations in genes encoding structural proteins can drastically reduce viral growth, providing a means to generate potent, live-attenuated vaccine candidates. However, an improved understanding of what compositional features are under selection and how combinations of synonymous mutations affect viral growth is needed to predictably attenuate viruses and make them resistant to reversion. We systematically recoded all nonoverlapping genes of the bacteriophage ΦX174 with codons rarely used in its Escherichia coli host. The fitness of recombinant viruses decreases as additional deoptimizing mutations are made to the genome, although not always linearly, and not consistently across genes. Combining deoptimizing mutations may reduce viral fitness more or less than expected from the effect size of the constituent mutations and we point out difficulties in untangling correlated compositional features. We test our model by optimizing the same genes and find that the relationship between codon usage and fitness does not hold for optimization, suggesting that wild-type ΦX174 is at a fitness optimum. This work highlights the need to better understand how selection acts on patterns of synonymous codon usage across the genome and provides a convenient system to investigate the genetic determinants of virulence.

The Race for a COVID-19 Vaccine: Current Trials, Novel Technologies, and Future Directions

The Coronavirus Disease 2019 (COVID-19) pandemic has presented a major threat to public health worldwide alongside unprecedented global economic and social implications. In the absence of a “gold standard” treatment, the rapid development of a safe and effective vaccine is considered the most promising way to control the pandemic. In recent years, traditional vaccine technologies have seemed insufficient to provide global protection against the rapid spread of emerging pandemics. Therefore, the establishment of novel approaches that are independent of whole pathogen cultivation, cost-effective, and able to be rapidly developed and produced on a large scale are of paramount importance for global health. This article summarizes the current efforts to develop a COVID-19 vaccine, including the ongoing and future anticipated clinical trials. We also provide plastic and reconstructive surgeons with insight into the novel technologies currently utilized for COVID-19 vaccine development, focusing on the very promising viral-vector-based and gene-based vaccine technologies. Each platform has its own advantages and disadvantages related to its efficacy and ability to induce certain immune responses, manufacturing capacity, and safety for human use. Once the fundamental key challenges have been addressed for viral-vector-based and gene-based vaccines, these novel technologies may become helpful in winning the fight against COVID-19 and transforming the future of health care.

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.

Regulatory aspects of quality and safety for live recombinant viral vaccines against infectious diseases in Japan

Recombinant viral vaccines expressing antigens of pathogenic microbes (e.g., HIV, Ebola virus, and malaria) have been designed to overcome the insufficient immune responses induced by the conventional vaccines. Our knowledge of and clinical experience with the new recombinant viral vaccines are insufficient, and a clear regulatory pathway is needed for the further development and evaluation of recombinant viral vaccines. In 2018, the research group supported by the Ministry of Health, Labour and Welfare, Japan (MHLW) published a concept paper to address the development of recombinant viral vaccines against infectious diseases. Herein we summarize the concept paper-which explains the Japanese regulatory concerns about recombinant viral vaccines-and provide a focus of discussion about the development of recombinant viral vaccines.

Clinical trials with GMO-containing vaccines in Europe: Status and regulatory framework

Recombinant technology has revolutionised the way novel vaccines are developed and manufactured. The possibility to genetically modify micro-organisms to bring immunogenic material (antigens/epitopes) to the human (or animal) immune system to provoke an immune response, provides new hope to producing prophylactic vaccines against HIV, malaria and tuberculosis and emerging diseases. Regulatory requirements associated with the development of genetically-modified organism (GMO)-containing vaccines in Europe add an additional burden to the clinical trial application procedure and to the preparation and initiation of a clinical trial of such vaccines. Moreover, the GMO regulatory framework is complex and only partially harmonised across Europe, which may hamper multi-country clinical trials with GMO-containing vaccines. This paper provides an overview of clinical trial applications with GMO-containing vaccines in Europe and reviews the regulatory framework in countries where GMO-containing vaccine clinical trial authorisation (CTA) applications were submitted between 2004 and 2017.

Poxvirus-based vector systems and the potential for multi-valent and multi-pathogen vaccines

INTRODUCTION

With the increasing number of vaccines and vaccine-preventable diseases, the pressure to generate multi-valent and multi-pathogen vaccines grows. Combining individual established vaccines to generate single-shot formulations represents an established path, with significant ensuing public health and cost benefits. Poxvirus-based vector systems have the capacity for large recombinant payloads and have been widely used as platforms for the development of recombinant vaccines encoding multiple antigens, with considerable clinical trials activity and a number of registered and licensed products.

AREAS COVERED

Herein we discuss design strategies, production processes, safety issues, regulatory hurdles and clinical trial activities, as well as pertinent new technologies such as systems vaccinology and needle-free delivery. Literature searches used PubMed, Google Scholar and clinical trials registries, with a focus on the recombinant vaccinia-based systems, Modified Vaccinia Ankara and the recently developed Sementis Copenhagen Vector.

EXPERT COMMENTARY

Vaccinia-based platforms show considerable promise for the development of multi-valent and multi-pathogen vaccines, especially with recent developments in vector technologies and manufacturing processes. New methodologies for defining immune correlates and human challenge models may also facilitate bringing such vaccines to market.

New Vaccine Technologies to Combat Outbreak Situations

Ever since the development of the first vaccine more than 200 years ago, vaccinations have greatly decreased the burden of infectious diseases worldwide, famously leading to the eradication of small pox and allowing the restriction of diseases such as polio, tetanus, diphtheria, and measles. A multitude of research efforts focuses on the improvement of established and the discovery of new vaccines such as the HPV (human papilloma virus) vaccine in 2006. However, radical changes in the density, age distribution and traveling habits of the population worldwide as well as the changing climate favor the emergence of old and new pathogens that bear the risk of becoming pandemic threats. In recent years, the rapid spread of severe infections such as HIV, SARS, Ebola, and Zika have highlighted the dire need for global preparedness for pandemics, which necessitates the extremely rapid development and comprehensive distribution of vaccines against potentially previously unknown pathogens. What is more, the emergence of antibiotic resistant bacteria calls for new approaches to prevent infections. Given these changes, established methods for the identification of new vaccine candidates are no longer sufficient to ensure global protection. Hence, new vaccine technologies able to achieve rapid development as well as large scale production are of pivotal importance. This review will discuss viral vector and nucleic acid-based vaccines (DNA and mRNA vaccines) as new approaches that might be able to tackle these challenges to global health.

Effects of pre-existing orthopoxvirus-specific immunity on the performance of Modified Vaccinia virus Ankara-based influenza vaccines

The replication-deficient orthopoxvirus modified vaccinia virus Ankara (MVA) is a promising vaccine vector against various pathogens and has an excellent safety record. However, pre-existing vector-specific immunity is frequently suggested to be a drawback of MVA-based vaccines. To address this issue, mice were vaccinated with MVA-based influenza vaccines in the presence or absence of orthopoxvirus-specific immunity. Importantly, protective efficacy of an MVA-based influenza vaccine against a homologous challenge was not impaired in the presence of orthopoxvirus-specific pre-existing immunity. Nonetheless, orthopoxvirus-specific pre-existing immunity reduced the induction of antigen-specific antibodies under specific conditions and completely prevented induction of antigen-specific T cell responses by rMVA-based vaccination. Notably, antibodies induced by vaccinia virus vaccination, both in mice and humans, were not capable of neutralizing MVA. Thus, when using rMVA-based vaccines it is important to consider the main correlate of protection induced by the vaccine, the vaccine dose and the orthopoxvirus immune status of vaccine recipients.

Understanding modern-day vaccines: what you need to know

Vaccines are considered to be one of the greatest public health achievements of the last century. Depending on the biology of the infection, the disease to be prevented, and the targeted population, a vaccine may require the induction of different adaptive immune mechanisms to be effective. Understanding the basic concepts of different vaccines is therefore crucial to understand their mode of action, benefits, risks, and their potential real-life impact on protection. This review aims to provide healthcare professionals with background information about the main vaccine designs and concepts of protection in a simplified way to improve their knowledge and understanding, and increase their confidence in the science of vaccination ( Supplementary Material ). KEY MESSAGE Different vaccine designs, each with different advantages and limitations, can be applied for protection against a particular disease. Vaccines may contain live-attenuated pathogens, inactivated pathogens, or only parts of pathogens and may also contain adjuvants to stimulate the immune responses. This review explains the mode of action, benefits, risks and real-life impact of vaccines by highlighting key vaccine concepts. An improved knowledge and understanding of the main vaccine designs and concepts of protection will help support the appropriate use and expectations of vaccines, increase confidence in the science of vaccination, and help reduce vaccine hesitancy.

Newcastle disease virus co-expressing interleukin 7 and interleukin 15 modified tumor cells as a vaccine for cancer immunotherapy

Interleukin 15 (IL15) and IL7 are two cytokines essential for T cell development and homeostasis. In order to improve the antitumor activity by Newcastle disease virus (NDV)-modified tumor vaccine, we generated a recombinant NDV co-expressing IL15 and IL7 (LX/IL(15+7)) through incorporation of a 2A self-processing peptide into IL15 and IL7 using reverse genetics. B16 cells infected with LX/IL(15+7) expressed both IL15 and IL7 stably. The cytotoxicity assay showed that murine melanoma cells modified with LX/IL(15+7) could significantly enhance the antitumor immune response in vitro. Then, the antitumor effects of tumor vaccine modified with recombinant virus were tested in the murine tumor models. We observed strong antitumor responses induced by LX/IL(15+7)-modified tumor cells both in prophylaxis and therapeutic models. Although the tumor-infiltrating CD4⁺ T cells and CD8⁺ T cells were both increased, the antitumor activity of the tumor vaccine modified with LX/IL(15+7) was dependent on CD8⁺ T cells. Taken together, our data strongly indicated that tumor vaccine modified with NDV strain LX/IL(15+7) is a promising agent for cancer immunotherapy.

Hazard Characterization of Modified Vaccinia Virus Ankara Vector: What Are the Knowledge Gaps?

Modified vaccinia virus Ankara (MVA) is the vector of choice for human and veterinary applications due to its strong safety profile and immunogenicity in vivo. The use of MVA and MVA-vectored vaccines against human and animal diseases must comply with regulatory requirements as they pertain to environmental risk assessment, particularly the characterization of potential adverse effects to humans, animals and the environment. MVA and recombinant MVA are widely believed to pose low or negligible risk to ecosystem health. However, key aspects of MVA biology require further research in order to provide data needed to evaluate the potential risks that may occur due to the use of MVA and MVA-vectored vaccines. The purpose of this paper is to identify knowledge gaps in the biology of MVA and recombinant MVA that are of relevance to its hazard characterization and discuss ongoing and future experiments aimed at providing data necessary to fill in the knowledge gaps. In addition, we presented arguments for the inclusion of uncertainty analysis and experimental investigation of verifiable worst-case scenarios in the environmental risk assessment of MVA and recombinant MVA. These will contribute to improved risk assessment of MVA and recombinant MVA vaccines.

Investigating Tick-borne Flaviviral-like Particles as a Delivery System for Gene Therapy

Background

Research on the biogenesis of tick-borne encephalitis virus (TBEV) would benefit gene therapy. Due to specific arrangements of genes along the TBEV genome, its viral-like particles (VLPs) could be exploited as shuttles to deliver their replicon, which carries therapeutic genes, to immune system cells.

Objective

To develop a flaviviral vector for gene delivery as a part of gene therapy research that can be expressed in secretable VLP suicidal shuttles and provide abundant unique molecular and structural data supporting this gene therapy concept.

Method

TBEV structural gene constructs of a Swedish Torö strain were cloned into plasmids driven by the promoters CAG and CMV and then transfected into various cell lines, including COS-1 and BHK-21. Time-course sampling of the cells, culture fluid, cell lysate supernatant, and pellet specimens were performed. Western blotting and electron microscopy analyses of collected specimens were used to investigate molecular and structural processing of TBEV structural proteins.

Results

Western blotting analysis showed differences between promoters in directing the gene expression of the VLPs constructs. The premature flaviviral polypeptides as well as mature VLPs could be traced. Using electron microscopy, the premature and mature VLP accumulation in cellular compartments—and also endoplasmic reticulum proliferation as a virus factory platform—were observed in addition to secreted VLPs.

Conclusions

The abundant virologic and cellular findings in this study show the natural processing and safety of inserting flaviviral structural genes into suicidal VLP shuttles. Thus, we propose that these VLPs are a suitable gene delivering system model in gene therapy.

Modified Vaccinia Virus Ankara Preferentially Targets Antigen Presenting Cells In Vitro, Ex Vivo and In Vivo

Modified Vaccinia virus Ankara (MVA) is a promising vaccine vector with an excellent safety profile. However, despite extensive pre-clinical and clinical testing, surprisingly little is known about the cellular tropism of MVA, especially in relevant animal species. Here, we performed in vitro, ex vivo and in vivo experiments with recombinant MVA expressing green fluorescent protein (rMVA-GFP). In both human peripheral blood mononuclear cells and mouse lung explants, rMVA-GFP predominantly infected antigen presenting cells. Subsequent in vivo experiments performed in mice, ferrets and non-human primates indicated that preferential targeting of dendritic cells and alveolar macrophages was observed after respiratory administration, although subtle differences were observed between the respective animal species. Following intramuscular injection, rMVA-GFP was detected in interdigitating cells between myocytes, but also in myocytes themselves. These data are important in advancing our understanding of the basis for the immunogenicity of MVA-based vaccines and aid rational vaccine design and delivery strategies.

Protein and modified vaccinia virus Ankara-based influenza virus nucleoprotein vaccines are differentially immunogenic in BALB/c mice

Because of the high variability of seasonal influenza viruses and the eminent threat of influenza viruses with pandemic potential, there is great interest in the development of vaccines that induce broadly protective immunity. Most probably, broadly protective influenza vaccines are based on conserved proteins, such as nucleoprotein (NP). NP is a vaccine target of interest as it has been shown to induce cross-reactive antibody and T cell responses. Here we tested and compared various NP-based vaccine preparations for their capacity to induce humoral and cellular immune responses to influenza virus NP. The immunogenicity of protein-based vaccine preparations with Matrix-M™ adjuvant as well as recombinant viral vaccine vector modified Vaccinia virus Ankara (MVA) expressing the influenza virus NP gene, with or without modifications that aim at optimization of CD8⁺ T cell responses, was addressed in BALB/c mice. Addition of Matrix-M™ adjuvant to NP wild-type protein-based vaccines significantly improved T cell responses. Furthermore, recombinant MVA expressing the influenza virus NP induced strong antibody and CD8⁺ T cell responses, which could not be improved further by modifications of NP to increase antigen processing and presentation.