Phase 1 Trials of rVSV Ebola Vaccine in Africa and Europe

Ebolavirus: Infection, Vaccination and Control

Members of the genus Ebolavirus (family Filoviridae) are among the deadliest viral pathogens spread throughout the world with severe rate of mortality, at least 90% in some outbreaks. Their virions are filamentous and enveloped with enclosed negative-sense single-stranded RNA genome. The genome potentially expresses seven structural and nonstructural proteins. The replication cycle is complex consisting of multiple molecular processes and interactions with human-host factors and proteins. Due to high mortality rate of infection, the studies regarding cure is still infancy. This review covers the current understanding of the virus replication cycle and vaccine development, and herbal treatments to control Ebola covering the available literature on the subject.

Therapeutic vaccination strategies against EBOV by rVSV-EBOV-GP: the role of innate immunity

Zaire Ebola virus (EBOV) is a member of the Filoviridae family. Infection with EBOV causes Ebola virus disease (EVD) characterized by excessive inflammation, lymphocyte death, coagulopathy, and multi-organ failure. In 2019, the FDA-approved the first anti-EBOV vaccine, rVSV-EBOV-GP (Ervebo® by Merck). This live-recombinant vaccine confers both prophylactic and therapeutic protection to nonhuman primates and humans. While mechanisms conferring prophylactic protection are well-investigated, those underlying protection conferred shortly before and after exposure to EBOV remain poorly understood. In this review, we review data from in vitro and in vivo studies analyzing early immune responses to rVSV-EBOV-GP and discuss the role of innate immune activation in therapeutic protection.

mRNA vaccines for infectious diseases: principles, delivery and clinical translation

Over the past several decades, messenger RNA (mRNA) vaccines have progressed from a scepticism-inducing idea to clinical reality. In 2020, the COVID-19 pandemic catalysed the most rapid vaccine development in history, with mRNA vaccines at the forefront of those efforts. Although it is now clear that mRNA vaccines can rapidly and safely protect patients from infectious disease, additional research is required to optimize mRNA design, intracellular delivery and applications beyond SARS-CoV-2 prophylaxis. In this Review, we describe the technologies that underlie mRNA vaccines, with an emphasis on lipid nanoparticles and other non-viral delivery vehicles. We also overview the pipeline of mRNA vaccines against various infectious disease pathogens and discuss key questions for the future application of this breakthrough vaccine platform.

Filovirus Neutralising Antibodies: Mechanisms of Action and Therapeutic Application

Filoviruses, especially Ebola virus, cause sporadic outbreaks of viral haemorrhagic fever with very high case fatality rates in Africa. The 2013–2016 Ebola epidemic in West Africa provided large survivor cohorts spurring a large number of human studies which showed that specific neutralising antibodies played a key role in protection following a natural Ebola virus infection, as part of the overall humoral response and in conjunction with the cellular adaptive response. This review will discuss the studies in survivors and animal models which described protective neutralising antibody response. Their mechanisms of action will be detailed. Furthermore, the importance of neutralising antibodies in antibody-based therapeutics and in vaccine-induced responses will be explained, as well as the strategies to avoid immune escape from neutralising antibodies. Understanding the neutralising antibody response in the context of filoviruses is crucial to furthering our understanding of virus structure and function, in addition to improving current vaccines & antibody-based therapeutics.

Cancer Clinical Trials in Africa-An Untapped Opportunity: Recommendations From AORTIC 2019 Conference Special Interest Group in Clinical Trials

Cancer is now a formidable health care burden in sub-Saharan Africa (SSA) due to lifestyle westernization and longer life expectancy. The exponential increase in cancer incidence coupled with high mortality rate is not comparable with that seen in westernized countries. To address global cancer disparity, globalization of cancer clinical trials to involve sub-Saharan Africa can serve as a platform where innovative targeted therapies can be made available to patients in the environ. In the 2019 African Organization for Research and Training in Cancer (AORTIC) conference held at Maputo, Mozambique, a group of clinical trialists spanning across multiple continents highlighted the opportunities in Africa for the conduct of cancer clinical trials. The secondary purpose of the meeting was to address the belief that Africa was incapable of conducting interventional cancer trials but showed the in-continent strengths, such as available capacities, trained local clinical trialists with clinical trial experiences, clinical trial consortia, local capabilities, mapping out logistics, ethical consideration, political will, real-time benefits of clinical trials to clinical practice, and future directions for trials.

Vesicular Stomatitis Virus: From Agricultural Pathogen to Vaccine Vector

Vesicular stomatitis virus (VSV), which belongs to the Vesiculovirus genus of the family Rhabdoviridae, is a well studied livestock pathogen and prototypic non-segmented, negative-sense RNA virus. Although VSV is responsible for causing economically significant outbreaks of vesicular stomatitis in cattle, horses, and swine, the virus also represents a valuable research tool for molecular biologists and virologists. Indeed, the establishment of a reverse genetics system for the recovery of infectious VSV from cDNA transformed the utility of this virus and paved the way for its use as a vaccine vector. A highly effective VSV-based vaccine against Ebola virus recently received clinical approval, and many other VSV-based vaccines have been developed, particularly for high-consequence viruses. This review seeks to provide a holistic but concise overview of VSV, covering the virus's ascension from perennial agricultural scourge to promising medical countermeasure, with a particular focus on vaccines.

Immunogenicity and safety of Ebola virus vaccines in healthy adults: a systematic review and network meta-analysis

Clinical development of Ebola virus vaccines (EVV) was accelerated by the West African Ebola virus epidemic which remains the deadliest in history. To compare and rank the EVV according to their immunogenicity and safety. A total of 21 randomized controlled trial, evaluating seven different vaccines with different doses, and 5,275 participants were analyzed. The rVSVΔG-ZEBOV-GP (2 × 10 ⁷) vaccine was more immunogenic (P-score 0.80). For pain, rVSVΔG-ZEBOV-GP (≤10 ⁵) had few events (P-score 0.90). For fatigue and headache, the DNA-EBOV (≤ 4 mg) was the best one with P-scores of 0.94 and 0.87, respectively. For myalgia, the ChAd3 (10 ¹⁰) had a lower risk (P-score 0.94). For fever, the Ad5.ZEBOV (≤ 8 × 10 ¹⁰) was the best one (P-score 0.80). The best vaccine to be used to stop future outbreak of Ebola is the rVSVDG-ZEBOV-GP vaccine at dose of 2 × 10⁷ PFU.

Development and Evaluation of an Ebola Virus Glycoprotein Mucin-Like Domain Replacement System as a New Dendritic Cell-Targeting Vaccine Approach against HIV-1

The development of efficient vaccine approaches against HIV infection remains challenging in the vaccine field. Here, we developed an Ebola virus envelope glycoprotein (EboGP)-based chimeric fusion protein system and demonstrated that replacement of the mucin-like domain (MLD) of EboGP with HIV C2-V3-C3 (134 amino acids [aa]) or C2-V3-C3-V4-C4-V5-C5 (243 aa) polypeptides (EbGPΔM-V3 and EbGPΔM-V3-V5, respectively) still maintained the efficiency of EboGP-mediated viral entry into human macrophages and dendritic cells (DCs). Animal studies using mice revealed that immunization with virus-like particles (VLPs) containing the above chimeric proteins, especially EbGPΔM-V3, induced significantly more potent anti-HIV antibodies than HIV gp120 alone in mouse serum and vaginal fluid. Moreover, the splenocytes isolated from mice immunized with VLPs containing EbGPΔM-V3 produced significantly higher levels of gamma interferon (IFN-γ), interleukin 2 (IL-2), IL-4, IL-5, and macrophage inflammatory protein 1α (MIP-1α). Additionally, we demonstrated that coexpression of EbGPΔM-V3 and the HIV Env glycoprotein in a recombinant vesicular stomatitis virus (rVSV) vector elicited robust anti-HIV antibodies that may have specifically recognized epitopes outside or inside the C2-V3-C3 region of HIV-1 gp120 and cross-reacted with the gp120 from different HIV strains. Thus, this study has demonstrated the great potential of this DC-targeting vaccine platform as a new vaccine approach for improving immunogen delivery and increasing vaccine efficacy.

IMPORTANCE Currently, there are more than 38.5 million reported cases of HIV globally. To date, there is no approved vaccine for HIV-1 infection. Thus, the development of an effective vaccine against HIV infection remains a global priority. This study revealed the efficacy of a novel dendritic cell (DC)-targeting vaccination approach against HIV-1. The results clearly show that the immunization of mice with virus-like particles (VLPs) and VSVs containing HIV Env and a fusion protein composed of a DC-targeting domain of Ebola virus GP with HIV C2-V3-C3 polypeptides (EbGPΔM-V3) could induce robust immune responses against HIV-1 Env and/or Gag in serum and vaginal mucosa. These findings provide a proof of concept of this novel and efficient DC-targeting vaccine approach in delivering various antigenic polypeptides of HIV-1 and/or other emergent infections to the host antigen-presenting cells to prevent HIV and other viral infections.

Vaccine Development Throughout History

The emergence of the coronavirus disease 2019 (COVID-19) pandemic has made us appreciate how important it is to quickly develop treatments and save lives. The race to develop a vaccine for this novel coronavirus began as soon as the pandemic emerged. Time was the only limiting factor. From the first vaccine developed in 1796 against smallpox to the latest COVID-19 vaccine, there have been several vaccines that have reduced the burden of disease, with the associated mortality and morbidity. Over the years we have seen many new advancements in organism isolation, cell culture, whole-genome sequencing, and recombinant nuclear techniques. These techniques have greatly facilitated the development of vaccines. Each vaccine has its own development story and there is much wisdom to be gained from learning about breakthroughs in vaccine development.

Ebola Virus Neutralizing Antibodies in Dogs from Sierra Leone, 2017

Ebola virus (EBOV) is a highly pathogenic zoonotic virus for which the reservoir host has not been identified. To study the role of dogs as potential hosts, we screened 300 serum samples from dogs in Sierra Leone and found EBOV neutralizing antibodies in 12, suggesting their susceptibility to natural infection.

Viewpoint of a WHO Advisory Group Tasked to Consider Establishing a Closely-monitored Challenge Model of Coronavirus Disease 2019 (COVID-19) in Healthy Volunteers

WHO convened an Advisory Group (AG) to consider the feasibility, potential value, and limitations of establishing a closely-monitored challenge model of experimental severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease 2019 (COVID-19) in healthy adult volunteers. The AG included experts in design, establishment, and performance of challenges. This report summarizes issues that render a COVID-19 model daunting to establish (the potential of SARS-CoV-2 to cause severe/fatal illness, its high transmissibility, and lack of a "rescue treatment" to prevent progression from mild/moderate to severe clinical illness) and it proffers prudent strategies for stepwise model development, challenge virus selection, guidelines for manufacturing challenge doses, and ways to contain SARS-CoV-2 and prevent transmission to household/community contacts. A COVID-19 model could demonstrate protection against virus shedding and/or illness induced by prior SARS-CoV-2 challenge or vaccination. A limitation of the model is that vaccine efficacy in experimentally challenged healthy young adults cannot per se be extrapolated to predict efficacy in elderly/high-risk adults.

Effects of Gamma Irradiation of Human Serum Samples from rVSVΔG-ZEBOV-GP (V920) Ebola Virus Vaccine Recipients on Plaque-Reduction Neutralization Assays

Gamma irradiation (GI) is included in the CDC guidance on inactivation procedures to render a group of select agents and toxins nonviable. The Ebola virus falls within this group because it potentially poses a severe threat to public health and safety. To evaluate the impact of GI at a target dose of 50 kGy on neutralizing antibody titers induced by the rVSVΔG-ZEBOV-GP vaccine (V920), we constructed a panel of 48 paired human serum samples (GI-treated versus non-GI-treated) from healthy participants selected from a phase 3 study of V920 (study V920-012; NCT02503202). Neutralizing antibody titers were determined using a validated plaque-reduction neutralization test. GI of sera from V920 recipients was associated with approximately 20% reduction in postvaccination neutralizing antibody titers. GI was not associated with any change in pre-vaccination neutralizing antibody titers.

Postexposure Prophylaxis With rVSV-ZEBOV Following Exposure to a Patient With Ebola Virus Disease Relapse in the United Kingdom: An Operational, Safety, and Immunogenicity Report

Background

In October 2015, 65 people came into direct contact with a healthcare worker presenting with a late reactivation of Ebola virus disease (EVD) in the United Kingdom. Vaccination was offered to 45 individuals with an initial assessment of high exposure risk.

Methods

Approval for rapid expanded access to the recombinant vesicular stomatitis virus–Zaire Ebola virus (rVSV-ZEBOV) vaccine as an unlicensed emergency medicine was obtained from the relevant authorities. An observational follow-up study was carried out for 1 year following vaccination.

Results

Twenty-six of 45 individuals elected to receive vaccination between 10 and 11 October 2015 following written informed consent. By day 14, 39% had seroconverted, increasing to 87% by day 28 and 100% by 3 months, although these responses were not always sustained. Neutralizing antibody responses were detectable in 36% by day 14 and 73% at 12 months. Common side effects included fatigue, myalgia, headache, arthralgia, and fever. These were positively associated with glycoprotein-specific T-cell but not immunoglobulin (Ig) M or IgG antibody responses. No severe vaccine-related adverse events were reported. No one exposed to the virus became infected.

Conclusions

This paper reports the use of the rVSV-ZEBOV vaccine given as an emergency intervention to individuals exposed to a patient presenting with a late reactivation of EVD. The vaccine was relatively well tolerated, but a high percentage developed a fever ≥37.5°C, necessitating urgent screening for Ebola virus, and a small number developed persistent arthralgia.

Under consent: participation of people with HIV in an Ebola vaccine trial in Canada

BACKGROUND

Little is known about volunteers from Northern research settings who participate in vaccine trials of highly infectious diseases with no approved treatments. This article explores the motivations of HIV immunocompromised study participants in Canada who volunteered in a Phase II clinical trial that evaluated the safety and immunogenicity of an Ebola vaccine candidate.

METHODS

Observation at the clinical study site and semi-structured interviews employing situational and discursive analysis were conducted with clinical trial participants and staff over one year. Interviews were recorded, transcribed and analysed using critical qualitative interpretivist thematic analytical techniques. Patterns were identified, clustered and sorted to generate distinct and comprehensive themes. We then reassembled events and contexts from the study participants' stories to develop two ideal portraits based on "composite characters" based on study participants features. These provide ethnographically rich details of participants' meaningful social worlds while protecting individual identities.

RESULTS

Ten of the 14 clinical trial participants, and 3 study staff were interviewed. Participant demographics and socio-economic profiles expressed limited contextual diversity. Half were men who have sex with men, half were former injection drug users experiencing homelessness, one was female, none were racialized minorities and there were no people from HIV endemic countries. Fully 90% had previous involvement in other clinical studies. Their stories point to particular socio-economic situations that motivated their participation as clinical labor through trial participation.

CONCLUSIONS

Our findings support Fisher's argument of "structural coercion" in clinical trial recruitment of vulnerable individuals experiencing precarious living conditions. Clinical trials should provide more detail of the structural socio-economic conditions and healthcare needs which lie "under consent" of study participants. Going well beyond an overly convenient narrative of altruism, ethical deliberation frameworks need to sufficiently address the structural conditions of clinical trials. We offer concrete possibilities for this and acknowledge that further research and clinical data should be made available underlying study participant contexts with regards to recruitment and participation in resource poor settings, in both the South and the North.

High dose of vesicular stomatitis virus-vectored Ebola virus vaccine causes vesicular disease in swine without horizontal transmission

ABSTRACTThe recent impact of Ebola virus disease (EVD) on public health in Africa clearly demonstrates the need for a safe and efficacious vaccine to control outbreaks and mitigate its threat to global health. ERVEBO® is an effective recombinant Vesicular Stomatitis Virus (VSV)-vectored Ebola virus vaccine (VSV-EBOV) that was approved by the FDA and EMA in late 2019 for use in prevention of EVD. Since the parental virus VSV, which was used to construct VSV-EBOV, is pathogenic for livestock and the vaccine virus may be shed at low levels by vaccinated humans, widespread deployment of the vaccine requires investigation into its infectivity and transmissibility in VSV-susceptible livestock species. We therefore performed a comprehensive clinical analysis of the VSV-EBOV vaccine virus in swine to determine its infectivity and potential for transmission. A high dose of VSV-EBOV resulted in VSV-like clinical signs in swine, with a proportion of pigs developing ulcerative vesicular lesions at the nasal injection site and feet. Uninoculated contact control pigs co-mingled with VSV-EBOV-inoculated pigs did not become infected or display any clinical signs of disease, indicating the vaccine is not readily transmissible to naïve pigs during prolonged close contact. In contrast, virulent wild-type VSV Indiana had a shorter incubation period and was transmitted to contact control pigs. These results indicate that the VSV-EBOV vaccine causes vesicular illness in swine when administered at a high dose. Moreover, the study demonstrates the VSV-EBOV vaccine is not readily transmitted to uninfected pigs, encouraging its safe use as an effective human vaccine.

Longitudinal antibody and T cell responses in Ebola virus disease survivors and contacts: an observational cohort study

BACKGROUND

The 2013-16 Ebola virus disease epidemic in west Africa caused international alarm due to its rapid and extensive spread resulting in a significant death toll and social unrest within the affected region. The large number of cases provided an opportunity to study the long-term kinetics of Zaire ebolavirus-specific immune response of survivors in addition to known contacts of those infected with the virus.

METHODS

In this observational cohort study, we worked with leaders of Ebola virus disease survivor associations in two regions of Guinea, Guéckédou and Coyah, to recruit survivors of Ebola virus disease, contacts from households of individuals known to have had Ebola virus disease, and individuals who were not knowingly associated with infected individuals or had not had Ebola virus disease symptoms to serve as negative controls. We did Zaire ebolavirus glycoprotein-specific T cell analysis on peripheral blood mononuclear cells (PBMCs) on location in Guinea and transported plasma and PBMCs back to Europe for antibody quantification by ELISA, functional neutralising antibody analysis using live Zaire ebolavirus, and T cell phenotype studies. We report on the longitudinal cellular and humoral response among Ebola virus disease survivors and highlight potentially paucisymptomatic infection.

FINDINGS

We recruited 117 survivors of Ebola virus disease, 66 contacts, and 23 negative controls. The mean neutralising antibody titre among the Ebola virus disease survivors 3-14 months after infection was 1/174 (95% CI 1/136-1/223). Individual results varied greatly from 1/10 to more than 1/1000 but were on average ten times greater than that induced after 1 month by single dose Ebola virus vaccines. Following reactivation with glycoprotein peptide, the mean T cell responses among 116 Ebola virus disease survivors as measured by ELISpot was 305 spot-forming units (95% CI 257-353). The dominant CD8+ polyfunctional T cell phenotype, as measured among 53 Ebola virus disease survivors, was interferon γ+, tumour necrosis factor+, interleukin-2-, and the mean response was 0·046% of total CD8+ T cells (95% CI 0·021-0·071). Additionally, both neutralising antibody and T cell responses were detected in six (9%) of 66 Ebola virus disease contacts. We also noted that four (3%) of 117 individuals with Ebola virus disease infections did not have circulating Ebola virus-specific antibodies 3 months after infection.

INTERPRETATION

The continuous high titre of neutralising antibodies and increased T cell response might support the concept of long-term protective immunity in survivors. The existence of antibody and T cell responses in contacts of individuals with Ebola virus disease adds further evidence to the existence of sub-clinical Ebola virus infection.

FUNDING

US Food & Drug Administration, Horizon 2020 EU EVIDENT, Wellcome, UK Department for International Development.

TRANSLATION

For the French translation of the abstract see Supplementary Materials section.

Prominent Neutralizing Antibody Response Targeting the Ebolavirus Glycoprotein Subunit Interface Elicited by Immunization

The severe death toll caused by the recent outbreak of Ebola virus disease reinforces the importance of developing ebolavirus prevention and treatment strategies. Here, we have explored the immunogenicity of a novel immunization regimen priming with vesicular stomatitis virus particles bearing Sudan Ebola virus (SUDV) glycoprotein (GP) that consists of GP1 & GP2 subunits and boosting with soluble SUDV GP in macaques, which developed robust neutralizing antibody (nAb) responses following immunizations. Moreover, EB46, a protective nAb isolated from one of the immune macaques, is found to target the GP1/GP2 interface, with GP-binding mode and neutralization mechanism similar to a number of ebolavirus nAbs from human and mouse, indicating that the ebolavirus GP1/GP2 interface is a common immunological target in different species. Importantly, selected immune macaque polyclonal sera showed nAb specificity similar to EB46 at substantial titers, suggesting that the GP1/GP2 interface region is a viable target for ebolavirus vaccine.Importance: The elicitation of sustained neutralizing antibody (nAb) responses against diverse ebolavirus strains remains as a high priority for the vaccine field. The most clinically advanced rVSV-ZEBOV vaccine could elicit moderate nAb responses against only one ebolavirus strain, EBOV, among the five ebolavirus strains, which last less than 6 months. Boost immunization strategies are desirable to effectively recall the rVSV vector-primed nAb responses to prevent infections in prospective epidemics, while an in-depth understanding of the specificity of immunization-elicited nAb responses is essential for improving vaccine performance. Here, using non-human primate animal model, we demonstrated that booster immunization with a stabilized trimeric soluble form of recombinant glycoprotein derived from the ebolavirus Sudan strain following the priming rVSV vector immunization led to robust nAb responses that substantially map to the subunit interface of ebolavirus glycoprotein, a common B cell repertoire target of multiple species including primates and rodents.

Development of Pandemic Vaccines: ERVEBO Case Study

Preventative vaccines are considered one of the most cost-effective and efficient means to contain outbreaks and prevent pandemics. However, the requirements to gain licensure and manufacture a vaccine for human use are complex, costly, and time-consuming. The 2013-2016 Ebola virus disease (EVD) outbreak was the largest EVD outbreak to date and the third Public Health Emergency of International Concern in history, so to prevent a pandemic, numerous partners from the public and private sectors combined efforts and resources to develop an investigational Zaire ebolavirus (EBOV) vaccine candidate (rVSVΔG-ZEBOV-GP) as quickly as possible. The rVSVΔG-ZEBOV-GP vaccine was approved as ERVEBOTM by the European Medicines Authority (EMA) and the United States Food and Drug Administration (FDA) in December 2019 after five years of development. This review describes the development program of this EBOV vaccine, summarizes what is known about safety, immunogenicity, and efficacy, describes ongoing work in the program, and highlights learnings applicable to the development of pandemic vaccines.

Ebolavirus: Comparison of Survivor Immunology and Animal Models in the Search for a Correlate of Protection

Ebola viruses are enveloped, single-stranded RNA viruses belonging to the Filoviridae family and can cause Ebola virus disease (EVD), a serious haemorrhagic illness with up to 90% mortality. The disease was first detected in Zaire (currently the Democratic Republic of Congo) in 1976. Since its discovery, Ebola virus has caused sporadic outbreaks in Africa and was responsible for the largest 2013-2016 EVD epidemic in West Africa, which resulted in more than 28,600 cases and over 11,300 deaths. This epidemic strengthened international scientific efforts to contain the virus and develop therapeutics and vaccines. Immunology studies in animal models and survivors, as well as clinical trials have been crucial to understand Ebola virus pathogenesis and host immune responses, which has supported vaccine development. This review discusses the major findings that have emerged from animal models, studies in survivors and vaccine clinical trials and explains how these investigations have helped in the search for a correlate of protection.

Randomized, Blinded, Dose-Ranging Trial of an Ebola Virus Glycoprotein Nanoparticle Vaccine With Matrix-M Adjuvant in Healthy Adults

BACKGROUND

Ebola virus (EBOV) epidemics pose a major public health risk. There currently is no licensed human vaccine against EBOV. The safety and immunogenicity of a recombinant EBOV glycoprotein (GP) nanoparticle vaccine formulated with or without Matrix-M adjuvant were evaluated to support vaccine development.

METHODS

A phase 1, placebo-controlled, dose-escalation trial was conducted in 230 healthy adults to evaluate 4 EBOV GP antigen doses as single- or 2-dose regimens with or without adjuvant. Safety and immunogenicity were assessed through 1-year postdosing.

RESULTS

All EBOV GP vaccine formulations were well tolerated. Receipt of 2 doses of EBOV GP with adjuvant showed a rapid increase in anti-EBOV GP immunoglobulin G titers with peak titers observed on Day 35 representing 498- to 754-fold increases from baseline; no evidence of an antigen dose response was observed. Serum EBOV-neutralizing and binding antibodies using wild-type Zaire EBOV (ZEBOV) or pseudovirion assays were 3- to 9-fold higher among recipients of 2-dose EBOV GP with adjuvant, compared with placebo on Day 35, which persisted through 1 year.

CONCLUSIONS

Ebola virus GP vaccine with Matrix-M adjuvant is well tolerated and elicits a robust and persistent immune response. These data suggest that further development of this candidate vaccine for prevention of EBOV disease is warranted.

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

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

No Evidence of rVSV-Ebola Virus Vaccine Replication or Dissemination in the Sand Fly Phlebotomus papatasi

Following vaccination with the live attenuated, recombinant vesicular stomatitis virus Indiana serotype Ebola virus (rVSV-EBOV) vaccine, persons may exhibit a transient vaccine-associated viremia. To investigate the potential for Old World sand flies to transmit this vaccine following feeding on a viremic person, we fed laboratory-reared Phlebotomus papatasi an artificial blood meal containing 7.2 log10 plaque-forming units of rVSV-EBOV. Replication or dissemination was not detected in the body or legs of any P. papatasi collected at seven (n = 75) or 15 (n = 75) days post-feed. These results indicate a low potential for rVSV-EBOV to replicate and disseminate in P. papatasi, a species whose geographic distribution ranges from Morocco to southwest Asia and as far north as southern Europe.

Integrin Alpha E (CD103) Limits Virus-Induced IFN-I Production in Conventional Dendritic Cells

Early and strong production of IFN-I by dendritic cells is important to control vesicular stomatitis virus (VSV), however mechanisms which explain this cell-type specific innate immune activation remain to be defined. Here, using a genome wide association study (GWAS), we identified Integrin alpha-E (Itgae, CD103) as a new regulator of antiviral IFN-I production in a mouse model of vesicular stomatitis virus (VSV) infection. CD103 was specifically expressed by splenic conventional dendritic cells (cDCs) and limited IFN-I production in these cells during VSV infection. Mechanistically, CD103 suppressed AKT phosphorylation and mTOR activation in DCs. Deficiency in CD103 accelerated early IFN-I in cDCs and prevented death in VSV infected animals. In conclusion, CD103 participates in regulation of cDC specific IFN-I induction and thereby influences immune activation after VSV infection.

Human Transcriptomic Response to the VSV-Vectored Ebola Vaccine

Ebolavirus Disease (EVD) is a severe haemorrhagic fever that occurs in epidemic outbreaks, with a high fatality rate and no specific therapies available. rVSVΔG-ZEBOV-GP (Ervebo^®), a live-attenuated recombinant vesicular stomatitis virus vector expressing the glycoprotein G of Zaire Ebolavirus, is the first vaccine approved for prevention of EVD. Both innate and adaptive responses are deemed to be involved in vaccine-induced protection, yet the mechanisms are not fully elucidated. A global transcriptomic approach was used to profile the blood host-response in 51 healthy volunteers enrolled in a phase 1/2 clinical trial. Signatures of the host responses were investigated assessing the enrichment in differentially expressed genes (DEGs) of specific “blood transcription modules” (BTM). Comparison of gene-expression levels showed that vaccination produces a peak of 5469 DEGs at day one, representing 38.6% of the expressed genes. Out of 346 BTMs, 144 were significantly affected by vaccination. Innate immunity pathways were induced from day 1 to day 14. At days 2 and 3, neutrophil modules were downregulated and complement-related modules upregulated. T-cell and cell-cycle associated modules were upregulated at days 7 and 14, while at day 28, no modules remained activated. At day 14, a direct correlation was observed between ZEBOV glycoprotein-specific antibody titres and activation of seven BTMs, including two related to B-cell activation and B cell receptor signalling. Transcriptomic analysis identified an rVSVΔG-ZEBOV-GP-induced signature and demonstrated a direct correlation of blood transcriptomic changes with ZEBOV glycoprotein-specific antibody titres.

Use of Ebola Vaccine: Recommendations of the Advisory Committee on Immunization Practices, United States, 2020

This report summarizes the recommendations of the Advisory Committee on Immunization Practices (ACIP) for use of the rVSVΔG-ZEBOV-GP Ebola vaccine (Ervebo) in the United States. The vaccine contains rice-derived recombinant human serum albumin and live attenuated recombinant vesicular stomatitis virus (VSV) in which the gene encoding the glycoprotein of VSV was replaced with the gene encoding the glycoprotein of Ebola virus species Zaire ebolavirus. Persons with a history of severe allergic reaction (e.g., anaphylaxis) to rice protein should not receive Ervebo. This is the first and only vaccine currently licensed by the Food and Drug Administration for the prevention of Ebola virus disease (EVD). These guidelines will be updated based on availability of new data or as new vaccines are licensed to protect against EVD.ACIP recommends preexposure vaccination with Ervebo for adults aged ≥18 years in the U.S. population who are at highest risk for potential occupational exposure to Ebola virus species Zaire ebolavirus because they are responding to an outbreak of EVD, work as health care personnel at federally designated Ebola treatment centers in the United States, or work as laboratorians or other staff at biosafety level 4 facilities in the United States. Recommendations for use of Ervebo in additional populations at risk for exposure and other settings will be considered and discussed by ACIP in the future.

Development of sustainable research excellence with a global perspective on infectious diseases: Centre de Recherches Médicales de Lambaréné (CERMEL), Gabon

Medical research in sub-Saharan Africa is of high priority for societies to respond adequately to local health needs. Often enough it remains a challenge to build up capacity in infrastructure and human resources to highest international standards and to sustain this over mid-term to long-term periods due to difficulties in obtaining long-term institutional core funding, attracting highly qualified scientists for medical research and coping with ever changing structural and political environments. The Centre de Recherches Médicales de Lambaréné (CERMEL) serves as model for how to overcome such challenges and to continuously increase its impact on medical care in Central Africa and beyond. Starting off as a research annex to the Albert Schweitzer Hospital in Lambaréné, Gabon, it has since then expanded its activities to academic and regulatory clinical trials for drugs, vaccines and diagnostics in the field of malaria, tuberculosis, and a wide range of poverty related and neglected tropical infectious diseases. Advancing bioethics in medical research in Africa and steadily improving its global networks and infrastructures, CERMEL serves as a reference centre for several international consortia. In close collaboration with national authorities, CERMEL has become one of the main training hubs for medical research in Central Africa. It is hoped that CERMEL and its leitmotiv “to improve medical care for local populations” will serve as an inspiration to other institutions in sub-Saharan Africa to further increase African capacity to advance medicine.

Is there a role for childhood vaccination against COVID-19?

Tremendous efforts are undertaken to quickly develop COVID-19 vaccines that protect vulnerable individuals from severe disease and thereby limit the health and socioeconomic impacts of the pandemic. Potential candidates are tested in adult populations, and questions arise of whether COVID-19 vaccination should be implemented in children. Compared to adults, the incidence and disease severity of COVID-19 are low in children, and despite their infectiveness, their role in disease propagation is limited. Therefore, COVID-19 vaccines will need to have fully demonstrated safety and efficacy in preventing not only complications but transmission to justify childhood vaccination. This work summarizes currently tested vaccine platforms and debates practical and ethical considerations for their potential use in children. It also discusses the already deleterious effect of the pandemic on routine childhood vaccine coverage, calling for action to limit the risks for a rise in vaccine-preventable diseases.

Environmental Risk Assessment for rVSVΔG-ZEBOV-GP, a Genetically Modified Live Vaccine for Ebola Virus Disease

rVSVΔG-ZEBOV-GP is a live, attenuated, recombinant vesicular stomatitis virus (rVSV)-based vaccine for the prevention of Ebola virus disease caused by Zaire ebolavirus. As a replication-competent genetically modified organism, rVSVΔG-ZEBOV-GP underwent various environmental evaluations prior to approval, the most in-depth being the environmental risk assessment (ERA) required by the European Medicines Agency. This ERA, as well as the underlying methodology used to arrive at a sound conclusion about the environmental risks of rVSVΔG-ZEBOV-GP, are described in this review. Clinical data from vaccinated adults demonstrated only infrequent, low-level shedding and transient, low-level viremia, indicating a low person-to-person infection risk. Animal data suggest that it is highly unlikely that vaccinated individuals would infect animals with recombinant virus vaccine or that rVSVΔG-ZEBOV-GP would spread within animal populations. Preclinical studies in various hematophagous insect vectors showed that these species were unable to transmit rVSVΔG-ZEBOV-GP. Pathogenicity risk in humans and animals was found to be low, based on clinical and preclinical data. The overall risk for non-vaccinated individuals and the environment is thus negligible and can be minimized further through defined mitigation strategies. This ERA and the experience gained are relevant to developing other rVSV-based vaccines, including candidates under investigation for prevention of COVID-19.

New viral vectors for infectious diseases and cancer

Since the discovery in 1796 by Edward Jenner of vaccinia virus as a way to prevent and finally eradicate smallpox, the concept of using a virus to fight another virus has evolved into the current approaches of viral vectored genetic vaccines. In recent years, key improvements to the vaccinia virus leading to a safer version (Modified Vaccinia Ankara, MVA) and the discovery that some viruses can be used as carriers of heterologous genes encoding for pathological antigens of other infectious agents (the concept of 'viral vectors') has spurred a new wave of clinical research potentially providing for a solution for the long sought after vaccines against major diseases such as HIV, TB, RSV and Malaria, or emerging infectious diseases including those caused by filoviruses and coronaviruses. The unique ability of some of these viral vectors to stimulate the cellular arm of the immune response and, most importantly, T lymphocytes with cell killing activity, has also reawakened the interest toward developing therapeutic vaccines against chronic infectious diseases and cancer. To this end, existing vectors such as those based on Adenoviruses have been improved in immunogenicity and efficacy. Along the same line, new vectors that exploit viruses such as Vesicular Stomatitis Virus (VSV), Measles Virus (MV), Lymphocytic choriomeningitis virus (LCMV), cytomegalovirus (CMV), and Herpes Simplex Virus (HSV), have emerged. Furthermore, technological progress toward modifying their genome to render some of these vectors incompetent for replication has increased confidence toward their use in infant and elderly populations. Lastly, their production process being the same for every product has made viral vectored vaccines the technology of choice for rapid development of vaccines against emerging diseases and for 'personalised' cancer vaccines where there is an absolute need to reduce time to the patient from months to weeks or days. Here we review the recent developments in viral vector technologies, focusing on novel vectors based on primate derived Adenoviruses and Poxviruses, Rhabdoviruses, Paramixoviruses, Arenaviruses and Herpesviruses. We describe the rationale for, immunologic mechanisms involved in, and design of viral vectored gene vaccines under development and discuss the potential utility of these novel genetic vaccine approaches in eliciting protection against infectious diseases and cancer.

Severe fever with thrombocytopenia syndrome virus: a highly lethal bunyavirus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel bunyavirus. Since 2007, SFTS disease has been reported in China with high fatality rate up to 30%, which drew high attention from Centre for Disease Control and Prevention and government. SFTSV is endemic in the centra l and eastern China, Korea and Japan. There also have been similar cases reported in Vietnam. The number of SFTSV infection cases has a steady growth in these years. As SFTSV could transmitted from person to person, it will expose the public to infectious risk. In 2018 annual review of the Blueprint list of priority diseases, World Health Organisation has listed SFTSV infection as prioritised diseases for research and development in emergency contexts. However, the pathogenesis of SFTSV remains largely unclear. Currently, there are no specific therapeutics or vaccines to combat infections of SFTSV. This review discusses recent findings of epidemiology, transmission pathway, pathogenesis and treatments of SFTS disease.

[Ebola, the first vaccines available]

In the recent years, Ebola virus has been responsible for several major epidemics. Research efforts have allowed the development and evaluation in the field of several vaccine candidates. At present, two of them are already approved and used in the fight against the virus in the Democratic Republic of Congo. This review aims to describe the different candidates, the clinical trials that have been conducted as well as the first results in the field.

Evaluation of novel HIV vaccine candidates using recombinant vesicular stomatitis virus vector produced in serum-free Vero cell cultures

Acquired Immune Deficiency Syndrome (AIDS) in humans is a result of the destruction of the immune system caused by Human Immunodeficiency Virus (HIV) infection. This serious epidemic is still progressing world-wide. Despite advances in treatment, a safe and effective preventive HIV vaccine is desired to combat this disease, and to save millions of lives. However, such a vaccine is not available yet although extensive amounts of resources in research and development have been invested over three decades. In light of the recently approved Ebola virus disease vaccine based on a recombinant vesicular stomatitis virus (rVSV-ZEBOV), we present the results of our work on three novel VSV-vectored HIV vaccine candidates. We describe the design, rescue, production and purification method and evaluate their immunogenicity in mice prior to preclinical studies that will be performed in non-human primates. The production of each of the three candidate vaccines (rVSV-B6-NL4.3Env/SIVtm, rVSV-B6-NL4.3Env/Ebtm and rVSV-B6-A74Env(PN6)/SIVtm) was evaluated in small scale in Vero cells and it was found that production kinetics on Vero cells vary depending on the HIV gp surface protein used. Purified virus preparations complied with the WHO restrictions for the residual DNA and host cell protein contents. Finally, when administered to mice, all three rVSV-HIV vaccine candidates induced an HIV gp140-specific antibody response.

Method feasibility for cross-species testing, qualification, and validation of the Filovirus Animal Nonclinical Group anti-Ebola virus glycoprotein immunoglobulin G enzyme-linked immunosorbent assay for non-human primate serum samples

An anti-Zaire Ebola virus (EBOV) glycoprotein (GP) immunoglobulin G (IgG) enzyme linked immunosorbent assay (ELISA) was developed to quantify the serum levels of anti-EBOV IgG in human and non-human primate (NHP) serum following vaccination and/or exposure to EBOV. This method was validated for testing human serum samples as previously reported. However, for direct immunobridging comparability between humans and NHPs, additional testing was warranted. First, method feasibility experiments were performed to assess cross-species reactivity and parallelism between human and NHP serum samples. During these preliminary assessments, the goat anti-human IgG secondary antibody conjugate used in the previous human validation was found to be favorably cross-reactive with NHP samples when tested at the same concentrations previously used in the validated assay for human sample testing. Further, NHP serum samples diluted in parallel with human serum when tested side-by-side in the ELISA. A subsequent NHP matrix qualification and partial validation in the anti-GP IgG ELISA were performed based on ICH and FDA guidance, to characterize assay performance for NHP test samples and supplement the previous validation for human sample testing. Based on our assessments, the anti-EBOV GP IgG ELISA method is considered suitable for the intended use of testing with both human and NHP serum samples in the same assay for immunobridging purposes.

Characterization of Antigenic MHC-Class-I-Restricted T Cell Epitopes in the Glycoprotein of Ebolavirus

Ebolavirus causes highly lethal hemorrhagic fever in humans. The envelope-displayed viral glycoprotein (GP) is the primary target of humoral immunity induced by natural exposure and vaccination. No T cell epitopes in the GP have been characterized in humans. A phase I clinical trial of a heterologous prime-boost vaccination regime with viral vectors encoding filovirus antigens elicits humoral and T cell responses in vaccinees. The most frequently recognized peptide pools are deconvoluted to identify the minimal epitopes recognized by antigen-specific T cells. We characterize nine immunogenic epitopes on the Ebolavirus GP. Histocompatibility leukocyte antigen (HLA) typing with in silico epitope analysis determines the likely MHC class I restriction elements. Thirteen HLA-A and -B alleles are predicted to present the identified CD8⁺ T cell epitopes, suggesting promiscuous recognition and a broad immune response. Delivery of the Ebolavirus GP antigen by using a heterologous prime-boost approach is immunogenic in genetically diverse human populations, with responses against multiple epitopes.

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Vaccination induces high T cell responses to the Ebola virus glycoprotein in humans

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Eight CD8⁺ epitopes were defined, recognized through multiple MHC class I alleles

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Responses match those observed in Ebola survivors and could boost vaccine efficacy

Immunological Perspective for Ebola Virus Infection and Various Treatment Measures Taken to Fight the Disease

Ebolaviruses, discovered in 1976, belongs to the Filoviridae family, which also includes Marburg and Lloviu viruses. They are negative-stranded RNA viruses with six known species identified to date. Ebola virus (EBOV) is a member of Zaire ebolavirus species and can cause the Ebola virus disease (EVD), an emerging zoonotic disease that results in homeostatic imbalance and multi-organ failure. There are three EBOV outbreaks documented in the last six years resulting in significant morbidity (> 32,000 cases) and mortality (> 13,500 deaths). The potential factors contributing to the high infectivity of this virus include multiple entry mechanisms, susceptibility of the host cells, employment of multiple immune evasion mechanisms and rapid person-to-person transmission. EBOV infection leads to cytokine storm, disseminated intravascular coagulation, host T cell apoptosis as well as cell mediated and humoral immune response. In this review, a concise recap of cell types targeted by EBOV and EVD symptoms followed by detailed run-through of host innate and adaptive immune responses, virus-driven regulation and their combined effects contributing to the disease pathogenesis has been presented. At last, the vaccine and drug development initiatives as well as challenges related to the management of infection have been discussed.

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.

To B or Not to B: Mechanisms of Protection Conferred by rVSV-EBOV-GP and the Roles of Innate and Adaptive Immunity

Zaire Ebola virus (EBOV) is a member of the Filoviridae family of negative sense, single-stranded RNA viruses. EBOV infection causes Ebola virus disease (EVD), characterized by coagulopathy, lymphopenia, and multi-organ failure, which can culminate in death. In 2019, the FDA approved the first vaccine against EBOV, a recombinant live-attenuated viral vector wherein the G protein of vesicular stomatitis virus is replaced with the glycoprotein (GP) of EBOV (rVSV-EBOV-GP, Ervebo^® by Merck). This vaccine demonstrates high efficacy in nonhuman primates by providing prophylactic, rapid, and post-exposure protection. In humans, rVSV-EBOV-GP demonstrated 100% protection in several phase III clinical trials in over 10,000 individuals during the 2013–2016 West Africa epidemic. As of 2020, over 218,000 doses of rVSV-EBOV-GP have been administered to individuals with high risk of EBOV exposure. Despite licensure and robust preclinical studies, the mechanisms of rVSV-EBOV-GP-mediated protection are not fully understood. Such knowledge is crucial for understanding vaccine-mediated correlates of protection from EVD and to aid the further design and development of therapeutics against filoviruses. Here, we summarize the current literature regarding the host response to vaccination and EBOV exposure, and evidence regarding innate and adaptive immune mechanisms involved in rVSV-EBOV-GP-mediated protection, with a focus on the host transcriptional response. Current data strongly suggest a protective synergy between rapid innate and humoral immunity.

Pseudotyping of VSV with Ebola virus glycoprotein is superior to HIV-1 for the assessment of neutralising antibodies

Ebola virus (EBOV) is an enveloped, single-stranded RNA virus that can cause Ebola virus disease (EVD). It is thought that EVD survivors are protected against subsequent infection with EBOV and that neutralising antibodies to the viral surface glycoprotein (GP) are potential correlates of protection. Serological studies are vital to assess neutralising antibodies targeted to EBOV GP; however, handling of EBOV is limited to containment level 4 laboratories. Pseudotyped viruses can be used as alternatives to live viruses, which require high levels of bio-containment, in serological and viral entry assays. However, neutralisation capacity can differ among pseudotyped virus platforms. We evaluated the suitability of EBOV GP pseudotyped human immunodeficiency virus type 1 (HIV-1) and vesicular stomatitis virus (VSV) to measure the neutralising ability of plasma from EVD survivors, when compared to results from a live EBOV neutralisation assay. The sensitivity, specificity and correlation with live EBOV neutralisation were greater for the VSV-based pseudotyped virus system, which is particularly important when evaluating EBOV vaccine responses and immuno-therapeutics. Therefore, the EBOV GP pseudotyped VSV neutralisation assay reported here could be used to provide a better understanding of the putative correlates of protection against EBOV.

Ebola Virus Disease Survivors Show More Efficient Antibody Immunity than Vaccinees Despite Similar Levels of Circulating Immunoglobulins

The last seven years have seen the greatest surge of Ebola virus disease (EVD) cases in equatorial Africa, including the 2013-2016 epidemic in West Africa and the recent epidemics in the Democratic Republic of Congo (DRC). The vaccine clinical trials that took place in West Africa and the DRC, as well as follow-up studies in collaboration with EVD survivor communities, have for the first time allowed researchers to compare immune memory induced by natural infection and vaccination. These comparisons may be relevant to evaluate the putative effectiveness of vaccines and candidate medical countermeasures such as convalescent plasma transfer. In this study, we compared the long-term functionality of anti-EBOV glycoprotein (GP) antibodies from EVD survivors with that from volunteers who received the recombinant vesicular stomatitis virus vectored vaccine (rVSV-ZEBOV) during the Phase I clinical trial in Hamburg. Our study highlights important differences between EBOV vaccination and natural infection and provides a framework for comparison with other vaccine candidates.

Ervebo (Ebola Zaire Vaccine, Live/rVSVΔG-ZEBOV-GP): The First Licensed Vaccine for the Prevention of Ebola Virus Disease

Objective: To review the clinical data regarding the safety and efficacy of the Ervebo (Ebola Zaire vaccine, live/rVSVΔG-ZEBOV-GP) vaccine for the prevention of the Ebola virus disease. Data Sources: A literature search through PubMed, MEDLINE, and Cochrane Library was conducted for clinical trials published between January 2014 and June 2020 in the English language using the keywords Ervebo, rVSVΔG-ZEBOV, rVSVΔG-ZEBOV-GP, Ebola Zaire, and vaccine. Study Selection and Data Extraction: Articles were selected if they were related to the Food and Drug Administration (FDA) approval of Ervebo (Ebola Zaire vaccine, live/rVSVΔG-ZEBOV-GP) or provided novel data regarding this entity. Twelve articles noted in the FDA approval were chosen, along with 2 additional articles identified as providing novel information. Data Synthesis: The findings of the review show that Ervebo (Ebola Zaire vaccine, live/rVSVΔG-ZEBOV-GP) is a safe, immunogenic, and likely effective vaccine for the prevention of Ebola virus disease. Relevance to Patient Care and Clinical Practice: Ebola virus disease is highly infectious and often fatal. There have been multiple large outbreaks in the past 5 years, with no licensed treatments or vaccines. An effective vaccine could largely curtail current outbreaks and prevent further ones. Conclusion: The recent FDA approval of Ervebo (Ebola Zaire vaccine, live/rVSVΔG-ZEBOV-GP) offers the first approved vaccine for the prevention of Ebola virus disease. It has been shown to be safe, immunogenic, and likely effective for use in real-world applications for those at risk of contracting the disease.

A Modified Case Definition to Facilitate Essential Hospital Care During Ebola Outbreaks

During the late phase of the large West-African Ebola virus disease (EVD) outbreak, the majority of patients were cared for in designated treatment centers. However, the preexisting healthcare infrastructure was already overwhelmed by the outbreak. This had a huge impact on other, non-EVD-related diseases, causing an unprecedented increase in morbidity and mortality, which most likely exceeded the toll due to EVD directly. Consequently, a crucial question is how to provide appropriate healthcare and safeguard functionality of a healthcare system that also serves patients not suspected or diagnosed to have EVD. Here, we report on the Lion Heart Medical Center's experience in Sierra Leone and note that a case definition of Ebola that is broader than those commonly applied may be better suited when it is necessary to identify atypically presenting, pauci-symptomatic cases.

A tool with many applications: vesicular stomatitis virus in research and medicine

INTRODUCTION

Vesicular stomatitis virus (VSV) has long been a useful research tool in virology and recently become an essential part of medicinal products. Vesiculovirus research is growing quickly following its adaptation to clinical gene and cell therapy and oncolytic virotherapy.

AREAS COVERED

This article reviews the versatility of VSV as a research tool and biological reagent, its use as a viral and vaccine vector delivering therapeutic and immunogenic transgenes and an oncolytic virus aiding cancer treatment. Challenges such as the immune response against such advanced therapeutic medicinal products and manufacturing constraints are also discussed.

EXPERT OPINION

The field of in vivo gene and cell therapy is advancing rapidly with VSV used in many ways. Comparison of VSV's use as a versatile therapeutic reagent unveils further prospects and problems for each application. Overcoming immunological challenges to aid repeated administration of viral vectors and minimizing harmful host-vector interactions remains one of the major challenges. In the future, exploitation of reverse genetic tools may assist the creation of recombinant viral variants that have improved onco-selectivity and more efficient vaccine vector activity. This will add to the preferential features of VSV as an excellent advanced therapy medicinal product (ATMP) platform.

Ebola vaccine trials: progress in vaccine safety and immunogenicity

Introduction: Ebolaviruses are non-segmented negative-strand RNA viruses in the Filoviridae family that cause a neglected infectious disease designated as Ebola virus disease (EVD). The most prominent member is the Ebola virus (EBOV), representing the Zaire ebolavirus species that has been responsible for the largest reported EVD outbreaks including the West African epidemic and the current outbreak in the Democratic Republic of the Congo. Today, the most advanced EVD vaccine approaches target EBOV and multiple phase 1-4 human trials have been performed over the past few years. The most advanced platforms include vectored vaccines based on vesicular stomatitis virus (VSV-EBOV), distinct human (Ad5 and Ad26) and chimpanzee (ChAd3) adenoviruses and modified vaccinia Ankara (MVA) as well as DNA-based vaccines administered as a prime-only or homologous or combined prime-boost immunization.Areas covered: Here, we review and discuss human trials with a focus on vaccine safety and immunogenicity.Expert opinion: Despite obvious progress and promising success in EBOV vaccine development, many shortcomings and challenges remain to be tackled in the future.

A Perspective on Emerging Therapeutic Interventions for COVID-19

Coronaviruses are enveloped positive-sense RNA viruses with an unusual large RNA genome and a unique replication mechanism, which are characterized by club-like spikes that protrude from their surface. An outbreak of a novel coronavirus 2019 infection has posed significant threat to the health and economies in the whole world. This article reviewed the viral replication, pathogenicity, prevention and treatment strategies. With a lack of approved treatment options for this virus, alternative approaches to control the spread of disease is in urgent need. This article also covers some management strategies which may be applied to this virus outbreak. Ongoing clinical studies related to possible treatments for COVID-19, potential vaccines, and alternative medication such as natural compounds are also discussed.

Ebola Virus: Pathogenesis and Countermeasure Development

Since its discovery in 1976, Ebola virus (EBOV) has caused numerous outbreaks of fatal hemorrhagic disease in Africa. The biggest outbreak on record is the 2013-2016 epidemic in west Africa with almost 30,000 cases and over 11,000 fatalities, devastatingly affecting Guinea, Liberia, and Sierra Leone. The epidemic highlighted the need for licensed drugs or vaccines to quickly combat the disease. While at the beginning of the epidemic no licensed countermeasures were available, several experimental drugs with preclinical efficacy were accelerated into human clinical trials and used to treat patients with Ebola virus disease (EVD) toward the end of the epidemic. In the same manner, vaccines with preclinical efficacy were administered primarily to known contacts of EVD patients on clinical trial protocols using a ring-vaccination strategy. In this review, we describe the pathogenesis of EBOV and summarize the current status of EBOV vaccine development and treatment of EVD.

An effective CTL peptide vaccine for Ebola Zaire Based on Survivors' CD8+ targeting of a particular nucleocapsid protein epitope with potential implications for COVID-19 vaccine design

The 2013-2016 West Africa EBOV epidemic was the biggest EBOV outbreak to date. An analysis of virus-specific CD8+ T-cell immunity in 30 survivors showed that 26 of those individuals had a CD8+ response to at least one EBOV protein. The dominant response (25/26 subjects) was specific to the EBOV nucleocapsid protein (NP). It has been suggested that epitopes on the EBOV NP could form an important part of an effective T-cell vaccine for Ebola Zaire. We show that a 9-amino-acid peptide NP44-52 (YQVNNLEEI) located in a conserved region of EBOV NP provides protection against morbidity and mortality after mouse adapted EBOV challenge. A single vaccination in a C57BL/6 mouse using an adjuvanted microsphere peptide vaccine formulation containing NP44-52 is enough to confer immunity in mice. Our work suggests that a peptide vaccine based on CD8+ T-cell immunity in EBOV survivors is conceptually sound and feasible. Nucleocapsid proteins within SARS-CoV-2 contain multiple Class I epitopes with predicted HLA restrictions consistent with broad population coverage. A similar approach to a CTL vaccine design may be possible for that virus.

Comparative evaluation of pathogenicity of three isolates of vesicular stomatitis virus (Indiana serotype) in pigs

Vesicular stomatitis (VS) is a notifiable disease of livestock affecting cattle, horses, pigs and humans. Vesicular stomatitis virus (VSV) serotypes Indiana and New Jersey are endemic to Central America; however, they also cause sporadic and scattered outbreaks in various countries in South and North America, including the USA. In order to develop an effective experimental challenge model for VSV, we compared the pathogenicity of three VSV serotype Indiana isolates in 36 4-5 week-old pigs. Two bovine isolates of Central American origin and one equine isolate from the USA were used for the experimental infections. Each pig was inoculated with a single isolate by both the intradermal and intranasal routes. Clinical signs of VSV infection were recorded daily for 10 days post-inoculation (days p.i.). Nasal and tonsillar swab samples and blood were collected to monitor immune responses, virus replication and shedding. Post-challenge, characteristic signs of VS were observed, including vesicles on the nasal planum and coronary bands, lameness, loss of hoof walls and pyrexia. Pigs inoculated with the Central American isolates showed consistently more severe clinical signs in comparison to the pigs infected with the USA isolate. Genomic RNA was isolated from the original challenge virus stocks, sequenced and compared to VSV genomes available in GenBank. Comparative genome analysis demonstrated significant differences between the VSV isolate from the USA and the two Central American isolates. Our results indicate that the Central American isolates of VSV serotype Indiana used in this study are more virulent in swine than the USA VSV serotype Indiana isolate and represent good candidate challenge strains for future VSV studies.

Epitopes of Naturally Acquired and Vaccine-Induced Anti-Ebola Virus Glycoprotein Antibodies in Single Amino Acid Resolution

The Ebola virus (EBOV) can cause severe infections in humans, leading to a fatal outcome in a high percentage of cases. Neutralizing antibodies against the EBOV surface glycoprotein (GP) can prevent infections, demonstrating a straightforward way for an efficient vaccination strategy. Meanwhile, many different anti-EBOV antibodies have been identified, whereas the exact binding epitopes are often unknown. Here, the analysis of serum samples from an EBOV vaccine trial with the recombinant vesicular stomatitis virus-Zaire ebolavirus (rVSV-ZEBOV) and an Ebola virus disease survivor, using high-density peptide arrays, is presented. In this proof-of-principle study, distinct IgG and IgM antibodies binding to different epitopes of EBOV GP is detected: By mapping the whole GP as overlapping peptide fragments, new epitopes and confirmed epitopes from the literature are found. Furthermore, the highly selective binding epitope of a neutralizing monoclonal anti-EBOV GP antibody could be validated. This shows that peptide arrays can be a valuable tool to study the humoral immune response to vaccines in patients and to support Ebola vaccine development.