Comparison of Heterologous Prime-Boost Strategies against Human Immunodeficiency Virus Type 1 Gag Using Negative Stranded RNA Viruses

Current Progress of Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) Vaccine Development

SFTSV is an emerging tick-borne virus causing hemorrhagic fever with a case fatality rate (CFR) that can reach up to 27%. With endemic infection in East Asia and the recent spread of the vector tick to more than 20 states in the United States, the SFTSV outbreak is a globally growing public health concern. However, there is currently no targeted antiviral therapy or licensed vaccine against SFTSV. Considering the age-dependent SFTS pathogenesis and disease outcome, a sophisticated vaccine development approach is required to safeguard the elderly population from lethal SFTSV infection. Given the recent emergence of SFTSV, the establishment of animal models to study immunogenicity and protection from SFTS symptoms has only occurred recently. The latest research efforts have applied diverse vaccine development approaches-including live-attenuated vaccine, DNA vaccine, whole inactivated virus vaccine, viral vector vaccine, protein subunit vaccine, and mRNA vaccine-in the quest to develop a safe and effective vaccine against SFTSV. This review aims to outline the current progress in SFTSV vaccine development and suggest future directions to enhance the safety and efficacy of these vaccines, ensuring their suitability for clinical application.

Heterologous vaccination utilizing viral vector and protein platforms confers complete protection against SFTSV

Severe fever with thrombocytopenia syndrome virus was first discovered in 2009 as the causative agent of severe fever with thrombocytopenia syndrome. Despite its potential threat to public health, no prophylactic vaccine is yet available. This study developed a heterologous prime-boost strategy comprising priming with recombinant replication-deficient human adenovirus type 5 (rAd5) expressing the surface glycoprotein, Gn, and boosting with Gn protein. This vaccination regimen induced balanced Th1/Th2 immune responses and resulted in potent humoral and T cell-mediated responses in mice. It elicited high neutralizing antibody titers in both mice and non-human primates. Transcriptome analysis revealed that rAd5 and Gn proteins induced adaptive and innate immune pathways, respectively. This study provides immunological and mechanistic insight into this heterologous regimen and paves the way for future strategies against emerging infectious diseases.

Inactivated rabies virus vectored SARS-CoV-2 vaccine prevents disease in a Syrian hamster model

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an emergent coronavirus that has caused a worldwide pandemic. Although human disease is often asymptomatic, some develop severe illnesses such as pneumonia, respiratory failure, and death. There is an urgent need for a vaccine to prevent its rapid spread as asymptomatic infections accounting for up to 40% of transmission events. Here we further evaluated an inactivated rabies vectored SARS-CoV-2 S1 vaccine CORAVAX in a Syrian hamster model. CORAVAX adjuvanted with MPLA-AddaVax, a TRL4 agonist, induced high levels of neutralizing antibodies and generated a strong Th1-biased immune response. Vaccinated hamsters were protected from weight loss and viral replication in the lungs and nasal turbinates three days after challenge with SARS-CoV-2. CORAVAX also prevented lung disease, as indicated by the significant reduction in lung pathology. This study highlights CORAVAX as a safe, immunogenic, and efficacious vaccine that warrants further assessment in human trials.

We have developed an inactivated rabies virus vectored vaccine platform that has been used to develop a vaccine against SARS-CoV-2 (CORAVAX). CORAVAX induced high levels of neutralizing antibodies against SARS-CoV-2. Here we show that vaccinated hamsters, the best animal model for COVID-19, were protected against viral replication, indicating that this vaccine can stop transmission. CORAVAX also prevented lung disease. Rabies virus vaccines have been used in more than 100 million people worldwide, are safe and used in children and pregnant women. Therefore, it is anticipated that CORAVAX will generate robust immune responses against SARS-CoV-2 in humans that may also mimic the long-term protection seen in rabies vaccines.

Rhabdoviruses as vectors for vaccines and therapeutics

Appropriate choice of vaccine vector is crucial for effective vaccine development. Rhabdoviral vectors, such as rabies virus and vesicular stomatitis virus, have been used in a variety of vaccine strategies. These viruses have small, easily manipulated genomes that can stably express foreign glycoproteins due to a well-established reverse genetics system for virus recovery. Both viruses have well-described safety profiles and have been demonstrated to be effective vaccine vectors. This review will describe how these Rhabdoviruses can be manipulated for use as vectors, their various applications as vaccines or therapeutics, and the advantages and disadvantages of their use.

Reverse Genetics of Newcastle Disease Virus

Reverse genetics allows for the generation of recombinant viruses or vectors used in functional studies, vaccine development, and gene therapy. This technique enables genetic manipulation and cloning of viral genomes, gene mutation through site-directed mutagenesis, along with gene insertion or deletion, among other studies. An in vitro infection-based system including the highly attenuated vaccinia virus Ankara strain expressing the T7 RNA polymerase from bacteriophage T7, with co-transfection of three helper plasmids and a full-length cDNA plasmid, was successfully developed to rescue genetically modified Newcastle disease viruses in 1999. In this chapter, the materials and the methods involved in rescuing Newcastle disease virus (NDV) from cDNA, utilizing site-directed mutagenesis and gene replacement techniques, are described in detail.

Replication and Oncolytic Activity of an Avian Orthoreovirus in Human Hepatocellular Carcinoma Cells

Oncolytic viruses are cancer therapeutics with promising outcomes in pre-clinical and clinical settings. Animal viruses have the possibility to avoid pre-existing immunity in humans, while being safe and immunostimulatory. We isolated an avian orthoreovirus (ARV-PB1), and tested it against a panel of hepatocellular carcinoma cells. We found that ARV-PB1 replicated well and induced strong cytopathic effects. It was determined that one mechanism of cell death was through syncytia formation, resulting in apoptosis and induction of interferon stimulated genes (ISGs). As hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma worldwide, we investigated the effect of ARV-PB1 against cells already infected with this virus. Both HCV replicon-containing and infected cells supported ARV-PB1 replication and underwent cytolysis. Finally, we generated in silico models to compare the structures of human reovirus- and ARV-PB1-derived S1 proteins, which are the primary targets of neutralizing antibodies. Tertiary alignments confirmed that ARV-PB1 differs from its human homolog, suggesting that immunity to human reoviruses would not be a barrier to its use. Therefore, ARV-PB1 can potentially expand the repertoire of oncolytic viruses for treatment of human hepatocellular carcinoma and other malignancies.

Evaluation of protective efficacy induced by different heterologous prime-boost strategies encoding triosephosphate isomerase against Schistosoma japonicum in mice

BACKGROUND

In China, schistosomiasis japonica is a predominant zoonotic disease, and animal reservoir hosts in the environment largely sustain infections. The development of transmission-blocking veterinary vaccines is urgently needed for the prevention and efficient control of schistosomiasis. Heterologous prime-boost strategy is more effective than traditional vaccination and homologous prime-boost strategies against multiple pathogens infection. In the present study, to further improve protective efficacy, we immunized mice with three types of heterologous prime-boost combinations based on our previously constructed vaccines that encode triosphate isomerase of Schistosoma japonicum, tested the specific immune responses, and evaluated the protective efficacy through challenge infection in mice.

METHODS

DNA vaccine (pcDNA3.1-SjTPI.opt), adenoviral vectored vaccine (rAdV-SjTPI.opt), and recombinant protein vaccine (rSjTPI) were prepared and three types of heterologous prime-boost combinations, including DNA i.m. priming-rAdV i.m. boosting, rAdV i.m. priming-rAdV s.c. boosting, and rAdV i.m. priming-rSjTPI boosting strategies, were carried out. The specific immune responses and protective efficacies were evaluated in BALB/c mice RESULTS: Results show that different immune profiles and various levels of protective efficacy were elicited by using different heterologous prime-boost combinations. A synergistic effect was observed using the DNA i.m. priming-rAdV i.m. boosting strategy; however, its protective efficacy was similar to that of rAdV i.m. immunization. Conversely, an antagonistic effect was generated by using the rAd i.m. priming-s.c. boosting strategy. However, the strategy, with rAdV i.m. priming- rSjTPI s.c. boosting, generated the most optimal protective efficacy and worm or egg reduction rate reaching up to 70% in a mouse model.

CONCLUSIONS

A suitable immunization strategy, rAdV i.m. priming-rSjTPI boosting strategy, was developed, which elicits a high level of protective efficacy against Schistosoma japonicum infection in mice.

Recombinant Newcastle disease virus-vectored vaccines against human and animal infectious diseases

Recent advances in recombinant genetic engineering techniques have brought forward a leap in designing new vaccines in modern medicine. One attractive strategy is the application of reverse genetics technology to make recombinant Newcastle disease virus (rNDV) deliver protective antigens of pathogens. In recent years, numerous studies have demonstrated that rNDV-vectored vaccines can induce quicker and better humoral and mucosal immune responses than conventional vaccines and are protective against pathogen challenges. With deeper understanding of NDV molecular biology, it is feasible to develop gene-modified rNDV vaccines accompanied by good safety, high efficacy, low toxicity and better immunogenicity. This review summarizes the development of reverse genetics technology in using NDV as a promising vaccine vector to design new vaccines for human and animal use.

Enhancement of protective efficacy through adenoviral vectored vaccine priming and protein boosting strategy encoding triosephosphate isomerase (SjTPI) against Schistosoma japonicum in mice

Background

Schistosomiasis japonica is a zoonotic parasitic disease; developing transmission blocking veterinary vaccines are urgently needed for the prevention and control of schistosomiasis in China. Heterologous prime-boost strategy, a novel vaccination approach, is more effective in enhancing vaccine efficacy against multiple pathogens. In the present study, we established a novel heterologous prime-boost vaccination strategy, the rAdV-SjTPI.opt intramuscular priming and rSjTPI subcutaneous boosting strategy, and evaluated its protective efficacy against Schistosoma japonicum in mice.

Methodology/Principal Findings

Adenoviral vectored vaccine (rAdV-SjTPI.opt) and recombinant protein vaccine (rSjTPI) were prepared and used in different combinations as vaccines in a mouse model. The specific immune responses and protective efficacies were evaluated. Furthermore, the longevity of protective efficacy was also determined. Results showed that the rAdV-SjTPI.opt priming-rSjTPI boosting strategy elicited higher levels of specific IgG responses and broad-spectrum specific cellular immune responses. The protective efficacy could reach up to nearly 70% and 50% of protection could be observed at 10 weeks after the last immunization in mice.

Conclusions/Significance

The rAdV-SjTPI.opt intramuscular priming-rSjTPI subcutaneous boosting vaccination strategy is a novel, highly efficient, and stable approach to developing vaccines against Schistosoma japonicum infections in China.

Reverse genetics of Mononegavirales: How they work, new vaccines, and new cancer therapeutics

The order Mononegavirales includes five families: Bornaviridae, Filoviridae, Nyamaviridae, Paramyxoviridae, and Rhabdoviridae. The genome of these viruses is one molecule of negative-sense single strand RNA coding for five to ten genes in a conserved order. The RNA is not infectious until packaged by the nucleocapsid protein and transcribed by the polymerase and co-factors. Reverse genetics approaches have answered fundamental questions about the biology of Mononegavirales. The lack of icosahedral symmetry and modular organization in the genome of these viruses has facilitated engineering of viruses expressing fluorescent proteins, and these fluorescent proteins have provided important insights about the molecular and cellular basis of tissue tropism and pathogenesis. Studies have assessed the relevance for virulence of different receptors and the interactions with cellular proteins governing the innate immune responses. Research has also analyzed the mechanisms of attenuation. Based on these findings, ongoing clinical trials are exploring new live attenuated vaccines and the use of viruses re-engineered as cancer therapeutics.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.

Newcastle disease virus: current status and our understanding

Newcastle disease (ND) is one of the highly pathogenic viral diseases of avian species. ND is economically significant because of the huge mortality and morbidity associated with it. The disease is endemic in many third world countries where agriculture serves as the primary source of national income. Newcastle disease virus (NDV) belongs to the family Paramyxoviridae and is well characterized member among the avian paramyxovirus serotypes. In recent years, NDV has lured the virologists not only because of its pathogenic potential, but also for its oncolytic activity and its use as a vaccine vector for both humans and animals. The NDV based recombinant vaccine offers a pertinent choice for the construction of live attenuated vaccine due to its modular nature of transcription, minimum recombination frequency, and lack of DNA phase during replication. Our current understanding about the NDV biology is expanding rapidly because of the availability of modern molecular biology tools and high-throughput complete genome sequencing.