Ebola: Lessons on Vaccine Development

Heterologous cAd3-Ebola and MVA-EbolaZ vaccines are safe and immunogenic in US and Uganda phase 1/1b trials

Ebola virus disease (EVD) is a filoviral infection caused by virus species of the Ebolavirus genus including Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV). We investigated the safety and immunogenicity of a heterologous prime-boost regimen involving a chimpanzee adenovirus 3 vectored Ebola vaccine [either monovalent (cAd3-EBOZ) or bivalent (cAd3-EBO)] prime followed by a recombinant modified vaccinia virus Ankara EBOV vaccine (MVA-EbolaZ) boost in two phase 1/1b randomized open-label clinical trials in healthy adults in the United States (US) and Uganda (UG). Trial US (NCT02408913) enrolled 140 participants, including 26 EVD vaccine-naïve and 114 cAd3-Ebola-experienced participants (April-November 2015). Trial UG (NCT02354404) enrolled 90 participants, including 60 EVD vaccine-naïve and 30 DNA Ebola vaccine-experienced participants (February-April 2015). All tested vaccines and regimens were safe and well tolerated with no serious adverse events reported related to study products. Solicited local and systemic reactogenicity was mostly mild to moderate in severity. The heterologous prime-boost regimen was immunogenic, including induction of durable antibody responses which peaked as early as two weeks and persisted up to one year after each vaccination. Different prime-boost intervals impacted the magnitude of humoral and cellular immune responses. The results from these studies demonstrate promising implications for use of these vaccines in both prophylactic and outbreak settings.

High-titer manufacturing of SARS-CoV-2 Spike-pseudotyped VSV in stirred-tank bioreactors

The severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) pandemic highlighted the importance of vaccine innovation in public health. Hundreds of vaccines built on numerous technology platforms have been rapidly developed against SARS-CoV-2 since 2020. Like all vaccine platforms, an important bottleneck to viral-vectored vaccine development is manufacturing. Here, we describe a scalable manufacturing protocol for replication-competent SARS-CoV-2 Spike-pseudotyped vesicular stomatitis virus (S-VSV)-vectored vaccines using Vero cells grown on microcarriers in a stirred-tank bioreactor. Using Cytodex 1 microcarriers over 6 days of fed-batch culture, Vero cells grew to a density of 3.95 ± 0.42 ×106 cells/mL in 1-L stirred-tank bioreactors. Ancestral strain S-VSV reached a peak titer of 2.05 ± 0.58 ×108 plaque-forming units (PFUs)/mL at 3 days postinfection. When compared to growth in plate-based cultures, this was a 29-fold increase in virus production, meaning a 1-L bioreactor produces the same amount of virus as 1,284 plates of 15 cm. In addition, the omicron BA.1 S-VSV reached a peak titer of 5.58 ± 0.35 × 106 PFU/mL. Quality control testing showed plate- and bioreactor-produced S-VSV had similar particle-to-PFU ratios and elicited comparable levels of neutralizing antibodies in immunized hamsters. This method should enhance preclinical and clinical development of pseudotyped VSV-vectored vaccines in future pandemics.

Design of universal Ebola virus vaccine candidates via immunofocusing

The Ebola virus causes hemorrhagic fever in humans and poses a significant threat to global public health. Although two viral vector vaccines have been approved to prevent Ebola virus disease, they are distributed in the limited ring vaccination setting and only indicated for prevention of infection from orthoebolavirus zairense (EBOV)-one of three orthoebolavirus species that have caused previous outbreaks. Ebola virus glycoprotein GP mediates viral infection and serves as the primary target of neutralizing antibodies. Here, we describe a universal Ebola virus vaccine approach using a structure-guided design of candidates with hyperglycosylation that aims to direct antibody responses away from variable regions and toward conserved epitopes of GP. We first determined the hyperglycosylation landscape on Ebola virus GP and used that to generate hyperglycosylated GP variants with two to four additional glycosylation sites to mask the highly variable glycan cap region. We then created vaccine candidates by displaying wild-type or hyperglycosylated GP variants on ferritin nanoparticles (Fer). Immunization with these antigens elicited potent neutralizing antisera against EBOV in mice. Importantly, we observed consistent cross-neutralizing activity against Bundibugyo virus and Sudan virus from hyperglycosylated GP-Fer with two or three additional glycans. In comparison, elicitation of cross-neutralizing antisera was rare in mice immunized with wild-type GP-Fer. These results demonstrate a potential strategy to develop universal Ebola virus vaccines that confer cross-protective immunity against existing and emerging filovirus species.

[Vaccines to prevent Ebola virus disease: current challenges and perspectives]

RELEVANCE

Ebola virus disease (EVD) is an acute infectious disease with an extremely high case fatality rate reaching up to 90%. EVD has become widely known since 2014-2016, when outbreak in West Africa occurred and led to epidemic, which caused travel-related cases on the territory of other continents. There are two vaccines against EVD, prequalified by WHO for emergency use, as well as a number of vaccines, approved by local regulators in certain countries. However, even with the availability of effective vaccines, the lack of data on immune correlates of protection and duration of protective immune response in humans and primates is limiting factor for effectively preventing the spread of EVD outbreaks.

AIMS

This review highlights experience of use of EVD vaccines during outbreaks in endemic areas, summarizes data on vaccine immunogenicity in clinical trials, and discusses perspectives for further development and use of effective EVD vaccines.

Design of universal Ebola virus vaccine candidates via immunofocusing

Ebola virus causes hemorrhagic fever in humans and poses a significant threat to global public health. Although two viral vector vaccines have been approved to prevent Ebola virus disease, they are distributed in the limited ring vaccination setting and only indicated for prevention of infection from orthoebolavirus zairense (EBOV) - one of three orthoebolavirus species that have caused previous outbreaks. Ebola virus glycoprotein GP mediates viral infection and serves as the primary target of neutralizing antibodies. Here we describe a universal Ebola virus vaccine approach using structure-guided design of candidates with hyperglycosylation that aims to direct antibody responses away from variable regions and toward conserved epitopes of GP. We first determined the hyperglycosylation landscape on Ebola virus GP and used that to generate hyperglycosylated GP variants with two to four additional glycosylation sites to mask the highly variable glycan cap region. We then created vaccine candidates by displaying wild-type or hyperglycosylated GP variants on ferritin nanoparticles (Fer). Immunization with these antigens elicited potent neutralizing antisera against EBOV in mice. Importantly, we observed consistent cross-neutralizing activity against Bundibugyo virus and Sudan virus from hyperglycosylated GP-Fer with two or three additional glycans. In comparison, elicitation of cross-neutralizing antisera was rare in mice immunized with wild-type GP-Fer. These results demonstrate a potential strategy to develop universal Ebola virus vaccines that confer cross-protective immunity against existing and emerging filovirus species.

Effects of adjuvants in a rabies-vectored Ebola virus vaccine on protection from surrogate challenge

Ebola virus is the primary contributor to the global threat of filovirus severe hemorrhagic fever, and Ebola virus disease has a case fatality rate of 50-90%. An inactivated, bivalent filovirus/rabies virus vaccine, FILORAB1, consists of recombinant rabies virus virions expressing the Ebola virus glycoprotein. FILORAB1 is immunogenic and protective from Ebola virus challenge in mice and non-human primates, and protection is enhanced when formulated with toll-like receptor 4 agonist Glucopyranosyl lipid adjuvant (GLA) in a squalene oil-in-water emulsion (SE). Through an adjuvant comparison in mice, we demonstrate that GLA-SE improves FILORAB1 efficacy by activating the innate immune system and shaping a Th1-biased adaptive immune response. GLA-SE adjuvanted mice and those adjuvanted with the SE component are better protected from surrogate challenge, while Th2 alum adjuvanted mice are not. Additionally, the immune response to FILORAB1 is long-lasting, as exhibited by highly-maintained serum antibody titers and long-lived cells in the spleen and bone marrow.

Epidemiology of Ebolaviruses from an Etiological Perspective

Since the inception of the ebolavirus in 1976, 32 outbreaks have resulted in nearly 15,350 deaths in more than ten countries of the African continent. In the last decade, the largest (2013-2016) and second largest (2018-2020) ebolavirus outbreaks have occurred in West Africa (mainly Guinea, Liberia, and Sierra Leone) and the Democratic Republic of the Congo, respectively. The 2013-2016 outbreak indicated an alarming geographical spread of the virus and was the first to qualify as an epidemic. Hence, it is imperative to halt ebolavirus progression and develop effective countermeasures. Despite several research efforts, ebolaviruses' natural hosts and secondary reservoirs still elude the scientific world. The primary source responsible for infecting the index case is also unknown for most outbreaks. In this review, we summarize the history of ebolavirus outbreaks with a focus on etiology, natural hosts, zoonotic reservoirs, and transmission mechanisms. We also discuss the reasons why the African continent is the most affected region and identify steps to contain this virus.

Ebola Virus Disease Vaccines: Development, Current Perspectives & Challenges

The global outgoing outbreaks of Ebola virus disease (EVD) in different regions of Sudan, Uganda, and Western Africa have brought into focus the inadequacies and restrictions of pre-designed vaccines for use in the battle against EVD, which has affirmed the urgent need for the development of a systematic protocol to produce Ebola vaccines prior to an outbreak. There are several vaccines available being developed by preclinical trials and human-based clinical trials. The group of vaccines includes virus-like particle-based vaccines, DNA-based vaccines, whole virus recombinant vaccines, incompetent replication originated vaccines, and competent replication vaccines. The limitations and challenges faced in the development of Ebola vaccines are the selection of immunogenic, rapid-responsive, cross-protective immunity-based vaccinations with assurances of prolonged protection. Another issue for the manufacturing and distribution of vaccines involves post authorization, licensing, and surveillance to ensure a vaccine's efficacy towards combating the Ebola outbreak. The current review focuses on the development process, the current perspective on the development of an Ebola vaccine, and future challenges for combatting future emerging Ebola infectious disease.

An introduction to the Marburg virus vaccine consortium, MARVAC

The emergence of Marburg virus (MARV) in Guinea and Ghana triggered the assembly of the MARV vaccine "MARVAC" consortium representing leaders in the field of vaccine research and development aiming to facilitate a rapid response to this infectious disease threat. Here, we discuss current progress, challenges, and future directions for MARV vaccines.

Nonhuman Primates Are Protected against Marburg Virus Disease by Vaccination with a Vesicular Stomatitis Virus Vector-Based Vaccine Prepared under Conditions to Allow Advancement to Human Clinical Trials

Vaccines are needed to disrupt or prevent continued outbreaks of filoviruses in humans across Western and Central Africa, including outbreaks of Marburg virus (MARV). As part of a filovirus vaccine product development plan, it is important to investigate dose response early in preclinical development to identify the dose range that may be optimal for safety, immunogenicity, and efficacy, and perhaps demonstrate that using lower doses is feasible, which will improve product access. To determine the efficacious dose range for a manufacturing-ready live recombinant vesicular stomatitis virus vaccine vector (rVSV∆G-MARV-GP) encoding the MARV glycoprotein (GP), a dose-range study was conducted in cynomolgus macaques. Results showed that a single intramuscular injection with as little as 200 plaque-forming units (PFUs) was 100% efficacious against lethality and prevented development of viremia and clinical pathologies associated with MARV Angola infection. Across the vaccine doses tested, there was nearly a 2000-fold range of anti-MARV glycoprotein (GP) serum IgG titers with seroconversion detectable even at the lowest doses. Virus-neutralizing serum antibodies also were detected in animals vaccinated with the higher vaccine doses indicating that vaccination induced functional antibodies, but that the assay was a less sensitive indicator of seroconversion. Collectively, the data indicates that a relatively wide range of anti-GP serum IgG titers are observed in animals that are protected from disease implying that seroconversion is positively associated with efficacy, but that more extensive immunologic analyses on samples collected from our study as well as future preclinical studies will be valuable in identifying additional immune responses correlated with protection that can serve as markers to monitor in human trials needed to generate data that can support vaccine licensure in the future.

Multimerization of Ebola GPΔmucin on protein nanoparticle vaccines has minimal effect on elicitation of neutralizing antibodies

Ebola virus (EBOV), a member of the Filoviridae family of viruses and a causative agent of Ebola Virus Disease (EVD), is a highly pathogenic virus that has caused over twenty outbreaks in Central and West Africa since its formal discovery in 1976. The only FDA-licensed vaccine against Ebola virus, rVSV-ZEBOV-GP (Ervebo®), is efficacious against infection following just one dose. However, since this vaccine contains a replicating virus, it requires ultra-low temperature storage which imparts considerable logistical challenges for distribution and access. Additional vaccine candidates could provide expanded protection to mitigate current and future outbreaks. Here, we designed and characterized two multimeric protein nanoparticle subunit vaccines displaying 8 or 20 copies of GPΔmucin, a truncated form of the EBOV surface protein GP. Single-dose immunization of mice with GPΔmucin nanoparticles revealed that neutralizing antibody levels were roughly equivalent to those observed in mice immunized with non-multimerized GPΔmucin trimers. These results suggest that some protein subunit antigens do not elicit enhanced antibody responses when displayed on multivalent scaffolds and can inform next-generation design of stable Ebola virus vaccine candidates.

Fast Tracking—Vaccine Safety, Efficacy, and Lessons Learned: A Narrative Review

(1) Background: The COVID-19 pandemic has led to the fast-tracked development of vaccines under emergency use authorization. In light of the growing concerns about fast-tracked vaccines, this article reviews the safety, efficacy, and lessons learned of previously fast-tracked vaccines. (2) Methods: An article search regarding the safety and efficacy of fast-tracked vaccines was done in PubMed, Embase, Web of Science, and ScienceDirect. Of the 104 results, 24 articles were included. Five articles about BiovaxID, THERATOPE^®, Sipuleucel-T, and AIDSVAX were also reviewed. (3) Results: The overall efficacy was shown to be 77–100%, with seroprotection against the viruses ranging from 87 to 100%. The antibody responses for optimal protection against the viruses fall within 85–97%. Generally, the fast-tracked vaccines were well-tolerated and had few significant adverse events, except for the H1N1 pandemic vaccine and its association with narcolepsy. To have accurate, precise, and timely fast-tracked vaccines, communication, sharing resources/data, and improving the current structures/outbreak operations are crucial. (4) Conclusions: This review found the FDA’s fast-tracking process for vaccines to have rigorous standards similar to the normal process. The previous fast-tracked vaccines were safe and efficacious. The lessons drawn from previous studies highlighted the significance of planning and utilizing global resources during significant outbreaks.

Seq-BEL: Sequence-Based Ensemble Learning for Predicting Virus-Human Protein-Protein Interaction

Infectious diseases are currently the most important and widespread health problem, and identifying viral infection mechanisms is critical for controlling diseases caused by highly infectious viruses. Because of the lack of non-interactive protein pairs and serious imbalance between positive and negative sample ratios, the supervised learning algorithm is not suitable for prediction. At the same time, due to the lack of information on viral proteins and significant dissimilarity in sequence, some ensemble learning models have poor generalization ability. In this paper, we propose a Sequence-Based Ensemble Learning (Seq-BEL) method to predict the potential virus-human PPIs. Specifically, based on the amino acid sequence of proteins and the currently known virus-human PPI network, Seq-BEL calculates various features and similarities of human proteins and viral proteins, and then combines these similarities and features to score the potential of virus-human PPIs. The computational results show that Seq-BEL achieves success in predicting potential virus-human PPIs and outperforms other state-of-the-art methods. More importantly, Seq-BEL also has good predictive performance for new human proteins and new viral proteins. In addition, the model has the advantages of strong robustness and good generalization ability, and can be used as an effective tool for virus-human PPI prediction.

Does infection with or vaccination against SARS-CoV-2 lead to lasting immunity?

Many nations are pursuing the rollout of SARS-CoV-2 vaccines as an exit strategy from unprecedented COVID-19-related restrictions. However, the success of this strategy relies critically on the duration of protective immunity resulting from both natural infection and vaccination. SARS-CoV-2 infection elicits an adaptive immune response against a large breadth of viral epitopes, although the duration of the response varies with age and disease severity. Current evidence from case studies and large observational studies suggests that, consistent with research on other common respiratory viruses, a protective immunological response lasts for approximately 5-12 months from primary infection, with reinfection being more likely given an insufficiently robust primary humoral response. Markers of humoral and cell-mediated immune memory can persist over many months, and might help to mitigate against severe disease upon reinfection. Emerging data, including evidence of breakthrough infections, suggest that vaccine effectiveness might be reduced significantly against emerging variants of concern, and hence secondary vaccines will need to be developed to maintain population-level protective immunity. Nonetheless, other interventions will also be required, with further outbreaks likely to occur due to antigenic drift, selective pressures for novel variants, and global population mobility.

Mapping the global research output on Ebola vaccine from research indexed in web of science and scopus: a comprehensive bibliometric analysis

Introduction: The Ebola Virus outbreak in Africa is believed to be one of the deadliest viral infections that causes severe hemorrhagic fever in human and nonhuman primates, which has resulted in increased mortality rates in the affected African countries. Thus, the current study mapped and quantified global research output and trends in the EBOV vaccine publications via a bibliometric analysis.Methods: Publications about the Ebola virus vaccine were extracted from the Web of Science and Scopus databases. HistCite, Bibliometrix, an R package, and VOSviewer.Var1.6.6 were used for data mapping and analysis.Results: A total of 541 (WoS) and 511 (Scopus) documents were included, with a cumulation of 24,611 citations in both databases. These documents were published in 141 journals in the Wos and 185 in Scopus. The USA was the most productive country with 206 (38.08%) publications in the Wos. Although the top-cited authors are from the USA, the United Kingdom, and Canada, only one author from Africa "Samai M" from the University of Sierra Leone contributed 13 publications. Meanwhile, the Journal of Infectious Diseases was the most productive (45, 8.32%) in this field.Conclusion: The study provides insight for researchers and health policy on the trends and progress of the EBOV vaccine research and development, focusing on the hot topics, research collaboration, and research dearth that requires urgent redress to fast-track an all-inclusive EBOV vaccine development.

Construction and evaluation of DNA vaccine encoding Ebola virus glycoprotein fused with lysosome-associated membrane protein

Ebola virus (EBOV) of the genus Ebolavirus belongs to the family Filoviridae, which cause disease in both humans and non-human primates. Zaire Ebola virus accounts for the highest fatality rate, reaching 90%. Considering that EBOV has a high infection and fatality rate, the development of a highly effective vaccine has become a top public health priority. Glycoprotein (GP) plays a critical role during infection and protective immune responses. Herein, we developed an EBOV GP recombinant DNA vaccine that targets the major histocompatibility complex (MHC) class II compartment by fusing with lysosomal-associated membrane protein 1 (LAMP1). Through lysosome trafficking and antigen presentation transferring, the LAMP1 targeting strategy successfully improved both humoral and cellular EBOV-GP-specific immune responses. After three consecutive immunizations, the serum antibody titers, especially the neutralizing activity of mice immunized with the pVAX-LAMP/GPEBO vaccine were significantly higher than those of the other groups. Antigen-specific T cells showed positive activity against three dominant peptides, EAAVSHLTTLATIST, IGEWAFWETKKNLTR, and ELRTFSILNRKAIDF, with high affinity for MHC class II molecules predicted by IEDB-recommended. Preliminary safety observation denied histological alterations. DNA vaccine candidate pVAX-LAMP/GPEBO shows promise against Ebola epidemic and further evaluation is guaranteed.

Biodefence research two decades on: worth the investment?

For the past 20 years, the notion of bioterror has been a source of considerable fear and panic worldwide. In response to the terror attacks of 2001 in the USA, extensive research funding was awarded to investigate bioterror-related pathogens. The global scientific legacy of this funding has extended into the present day, highlighted by the ongoing COVID-19 pandemic. Unsurprisingly, the surge in biodefence-related research and preparedness has been met with considerable apprehension and opposition. Here, we briefly outline the history of modern bioterror threats and biodefence research, describe the scientific legacy of biodefence research by highlighting advances pertaining to specific bacterial and viral pathogens, and summarise the future of biodefence research and its relevance today. We sought to address the sizeable question: have the past 20 years of investment into biodefence research and preparedness been worth it? The legacy of modern biodefence funding includes advancements in biosecurity, biosurveillence, diagnostics, medical countermeasures, and vaccines. In summary, we feel that these advances justify the substantial biodefence funding trend of the past two decades and set a precedent for future funding.

Conserved immunogenic peptides of Ebola glycoprotein elicit immune response in human peripheral blood mononuclear cells

In the past 45 years, ebolaviruses have periodically caused epidemics on the African continent. In December 2019, approval of a recombinant vector-based EBOV vaccine, named Ervebo, came as encouraging news; still, there is a long way to go in the development of an accessible, global, and pan-ebolavirus vaccine. The current study expanded our previous in silico work which was conducted on ebolavirus glycoprotein and this resulted in the identification of three potentially immunogenic peptides (P1 - FKRTSFFLWVIILFQRTFSIPL, P2 - LANETTQALQLF, and P3 - RATTELRTFSILNRKAIDF). An analysis to estimate the number of expected human leukocyte antigen (HLA) responders revealed that P1, P2, and P3 can potentially interact with 2540, 2150, and 2802 HLA alleles, respectively. Further, these peptides were subject to in vitro analysis wherein the human peripheral blood mononuclear cell proliferation and interferon-gamma (IFN-γ) production by peptide stimulated cells was studied in 10 healthy human blood samples with the help of a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and a sandwich enzyme-linked immunosorbent assay (ELISA) respectively. P3 presented the best results, a significant (P < 0.05) peptide induced cell proliferation and IFN-γ stimulation for 8 and 10 samples, respectively, followed by P1 (5 and 6) and P2 (5 and 7). The in silico and in vitro results obtained in this study indicate the immunogenic potential of these peptides and warrant exploration of the effects on other cytokines as well as in vivo experimental validation.

Ebola Virus Glycoprotein Domains Associated with Protective Efficacy

Ebola virus (EBOV) is the cause of sporadic outbreaks of human hemorrhagic disease in Africa, and the best-characterized virus in the filovirus family. The West African epidemic accelerated the clinical development of vaccines and therapeutics, leading to licensure of vaccines and antibody-based therapeutics for human use in recent years. The most widely used vaccine is based on vesicular stomatitis virus (VSV) expressing the EBOV glycoprotein (GP) (VSV-EBOV). Due to its favorable immune cell targeting, this vaccine has also been used as a base vector for the development of second generation VSV-based vaccines against Influenza, Nipah, and Zika viruses. However, in these situations, it may be beneficial if the immunogenicity against EBOV GP is minimized to induce a better protective immune response against the other foreign immunogen. Here, we analyzed if EBOV GP can be truncated to be less immunogenic, yet still able to drive replication of the vaccine vector. We found that the EBOV GP glycan cap and the mucin-like domain are both dispensable for VSV-EBOV replication. The glycan cap, however, appears critical for mediating a protective immune response against lethal EBOV challenge in mice.

Single-component multilayered self-assembling nanoparticles presenting rationally designed glycoprotein trimers as Ebola virus vaccines

Ebola virus (EBOV) glycoprotein (GP) can be recognized by neutralizing antibodies (NAbs) and is the main target for vaccine design. Here, we first investigate the contribution of the stalk and heptad repeat 1-C (HR1_C) regions to GP metastability. Specific stalk and HR1_C modifications in a mucin-deleted form (GPΔmuc) increase trimer yield, whereas alterations of HR1_C exert a more complex effect on thermostability. Crystal structures are determined to validate two rationally designed GPΔmuc trimers in their unliganded state. We then display a modified GPΔmuc trimer on reengineered protein nanoparticles that encapsulate a layer of locking domains (LD) and a cluster of helper T-cell epitopes. In mice and rabbits, GP trimers and nanoparticles elicit cross-ebolavirus NAbs, as well as non-NAbs that enhance pseudovirus infection. Repertoire sequencing reveals quantitative profiles of vaccine-induced B-cell responses. This study demonstrates a promising vaccine strategy for filoviruses, such as EBOV, based on GP stabilization and nanoparticle display.

Single-component multilayered self-assembling nanoparticles presenting rationally designed glycoprotein trimers as Ebola virus vaccines

Ebola virus (EBOV) glycoprotein (GP) can be recognized by neutralizing antibodies (NAbs) and is the main target for vaccine design. Here, we first investigate the contribution of the stalk and heptad repeat 1-C (HR1_C) regions to GP metastability. Specific stalk and HR1_C modifications in a mucin-deleted form (GPΔmuc) increase trimer yield, whereas alterations of HR1_C exert a more complex effect on thermostability. Crystal structures are determined to validate two rationally designed GPΔmuc trimers in their unliganded state. We then display a modified GPΔmuc trimer on reengineered protein nanoparticles that encapsulate a layer of locking domains (LD) and a cluster of helper T-cell epitopes. In mice and rabbits, GP trimers and nanoparticles elicit cross-ebolavirus NAbs, as well as non-NAbs that enhance pseudovirus infection. Repertoire sequencing reveals quantitative profiles of vaccine-induced B-cell responses. This study demonstrates a promising vaccine strategy for filoviruses, such as EBOV, based on GP stabilization and nanoparticle display.

Ebola virus glycoprotein (GP) is a major target for vaccine design. Here, the authors identify mutations to improve GP stability and yield, design two multilayered nanoparticle carriers, and demonstrate good immunogenicity of the modified GP on nanoparticles in mice and rabbits.

Targeting Ebola virus replication through pharmaceutical intervention

Introduction. The consistent emergence/reemergence of filoviruses into a world that previously lacked an approved pharmaceutical intervention parallels an experience repeatedly played-out for most other emerging pathogenic zoonotic viruses. Investment to preemptively develop effective and low-cost prophylactic and therapeutic interventions against viruses that have high potential for emergence and societal impact should be a priority.Areas covered. Candidate drugs can be characterized into those that interfere with cellular processes required for Ebola virus (EBOV) replication (host-directed), and those that directly target virally encoded functions (direct-acting). We discuss strategies to identify pharmaceutical interventions for EBOV infections. PubMed/Web of Science databases were searched to establish a detailed catalog of these interventions.Expert opinion. Many drug candidates show promising in vitro inhibitory activity, but experience with EBOV shows the general lack of translation to in vivo efficacy for host-directed repurposed drugs. Better translation is seen for direct-acting antivirals, in particular monoclonal antibodies. The FDA-approved monoclonal antibody treatment, Inmazeb™ is a success story that could be improved in terms of impact on EBOV-associated disease and mortality, possibly by combination with other direct-acting agents targeting distinct aspects of the viral replication cycle. Costs need to be addressed given EBOV emergence primarily in under-resourced countries.

Vaccine development for emerging infectious diseases

Examination of the vaccine strategies and technical platforms used for the COVID-19 pandemic in the context of those used for previous emerging and reemerging infectious diseases and pandemics may offer some mutually beneficial lessons. The unprecedented scale and rapidity of dissemination of recent emerging infectious diseases pose new challenges for vaccine developers, regulators, health authorities and political constituencies. Vaccine manufacturing and distribution are complex and challenging. While speed is essential, clinical development to emergency use authorization and licensure, pharmacovigilance of vaccine safety and surveillance of virus variants are also critical. Access to vaccines and vaccination needs to be prioritized in low- and middle-income countries. The combination of these factors will weigh heavily on the ultimate success of efforts to bring the current and any future emerging infectious disease pandemics to a close.

Sequence diversity analyses of an improved rhesus macaque genome enhance its biomedical utility

The rhesus macaque (Macaca mulatta) is the most widely studied nonhuman primate (NHP) in biomedical research. We present an updated reference genome assembly (Mmul_10, contig N50 = 46 Mbp) that increases the sequence contiguity 120-fold and annotate it using 6.5 million full-length transcripts, thus improving our understanding of gene content, isoform diversity, and repeat organization. With the improved assembly of segmental duplications, we discovered new lineage-specific genes and expanded gene families that are potentially informative in studies of evolution and disease susceptibility. Whole-genome sequencing (WGS) data from 853 rhesus macaques identified 85.7 million single-nucleotide variants (SNVs) and 10.5 million indel variants, including potentially damaging variants in genes associated with human autism and developmental delay, providing a framework for developing noninvasive NHP models of human disease.

Development of a Multivalent Kunjin Virus Reporter Virus-Like Particle System Inducing Seroconversion for Ebola and West Nile Virus Proteins in Mice

Kunjin virus (KUNV) is an attenuated strain of the severe neurotropic West Nile virus (WNV). The virus has a single-strand positive-sense RNA genome that encodes a polyprotein. Following gene expression, the polyprotein is cleaved into structural proteins for viral packaging and nonstructural proteins for viral replication and expression. Removal of the structural genes generate subgenomic replicons that maintain replication capacity. Co-expression of these replicons with the viral structural genes produces reporter virus-like particles (RVPs) which infect cells in a single round. In this study, we aimed to develop a system to generate multivalent RVPs based on KUNV to elicit an immune response against different viruses. We selected the Ebola virus (EBOV) glycoprotein (GP) and the matrix protein (VP40) genes, as candidates to be delivered by KUNV RVPs. Initially, we enhanced the production of KUNV RVPs by generating a stable cell line expressing the KUNV packaging system comprising capsid, precursor membrane, and envelope. Transfection of the DNA-based KUNV replicon into this cell line resulted in an enhanced RVP production. The replicon was expressed in the stable cell line to produce the RVPs that allowed the delivery of EBOV GP and VP40 genes into other cells. Finally, we immunized BALB/cN mice with RVPs, resulting in seroconversion for EBOV GP, EBOV VP40, WNV nonstructural protein 1, and WNV E protein. Thus, our study shows that KUNV RVPs may function as a WNV vaccine candidate and RVPs can be used as a gene delivery system in the development of future EBOV vaccines.

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.

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.

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.

Addressing challenges for clinical research responses to emerging epidemics and pandemics: a scoping review

BACKGROUND

Major infectious disease outbreaks are a constant threat to human health. Clinical research responses to outbreaks generate evidence to improve outcomes and outbreak control. Experiences from previous epidemics have identified multiple challenges to undertaking timely clinical research responses. This scoping review is a systematic appraisal of political, economic, administrative, regulatory, logistical, ethical and social (PEARLES) challenges to clinical research responses to emergency epidemics and solutions identified to address these.

METHODS

A scoping review. We searched six databases (MEDLINE, Embase, Global Health, PsycINFO, Scopus and Epistemonikos) for articles published from 2008 to July 2018. We included publications reporting PEARLES challenges to clinical research responses to emerging epidemics and pandemics and solutions identified to address these. Two reviewers screened articles for inclusion, extracted and analysed the data.

RESULTS

Of 2678 articles screened, 76 were included. Most presented data relating to the 2014-2016 Ebola virus outbreak or the H1N1 outbreak in 2009. The articles related to clinical research responses in Africa (n = 37), Europe (n = 8), North America (n = 5), Latin America and the Caribbean (n = 3) and Asia (n = 1) and/or globally (n = 22). A wide range of solutions to PEARLES challenges was presented, including a need to strengthen global collaborations and coordination at all levels and develop pre-approved protocols and equitable frameworks, protocols and standards for emergencies. Clinical trial networks and expedited funding and approvals were some solutions implemented. National ownership and community engagement from the outset were a key enabler for delivery. Despite the wide range of recommended solutions, none had been formally evaluated.

CONCLUSIONS

To strengthen global preparedness and response to the COVID-19 pandemic and future epidemics, identified solutions for rapid clinical research deployment, delivery, and dissemination must be implemented. Improvements are urgently needed to strengthen collaborations, funding mechanisms, global and national research capacity and capability, targeting regions vulnerable to epidemics and pandemics. Solutions need to be flexible to allow timely adaptations to context, and research led by governments of affected regions. Research communities globally need to evaluate their activities and incorporate lessons learnt to refine and rehearse collaborative outbreak response plans in between epidemics.

Applying lessons from the Ebola vaccine experience for SARS-CoV-2 and other epidemic pathogens

The world is experiencing an unprecedented global pandemic of coronavirus disease 2019 (COVID-19) caused by a novel coronavirus, Severe Acute Respiratory Syndrome-coronavirus-2 (SARS-CoV-2). Development of new vaccines and therapeutics are important to achieve long-term prevention and control of the virus. Experience gained in the development of vaccines for Ebola virus disease provide important lessons in the regulatory, clinical, and manufacturing process that can be applied to SARS-CoV-2 and other epidemic pathogens. This report outlines the main lessons learned by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA (MSD) during development of an Ebola Zaire vaccine (ERVEBO®) and looks ahead to critical lessons beyond vaccine development. It highlights focus areas for public-private partnership and regulatory harmonization that can be directly applied to current vaccine development efforts for SARS-CoV-2, while drawing attention to the need for parallel consideration of issues beyond development that are equally important to achieve global preparedness and response goals.

In Vitro Characterization and In Vivo Effectiveness of Ebola Virus Specific Equine Polyclonal F(ab')2

There is no vaccine or approved therapy against lethal Ebola virus (EBOV). We investigated a proven technology platform to produce polyclonal IgG fragments, F(ab')2, against EBOV. Horses immunized with nanoparticles harboring surface glycoprotein trimers of EBOV-Zaire/Makona produced anti-Ebola IgG polyclonal antibodies with high neutralization activity. Highly purified equine anti-Ebola F(ab')2 showed strong cross-neutralization of 2 Zaire EBOV strains (Gabon 2001 and Makona) and in vivo 3 or 5 daily F(ab')2 intraperitoneal injections provided 100% protection to BALB/c mice against lethal EBOV challenge. Rapid preparation of purified equine anti-Ebola F(ab')2 offers a potentially efficient therapeutic approach against EBOV disease in humans.

A single dose of a vesicular stomatitis virus-based influenza vaccine confers rapid protection against H5 viruses from different clades

The avian influenza virus outbreak in 1997 highlighted the potential of the highly pathogenic H5N1 virus to cause severe disease in humans. Therefore, effective vaccines against H5N1 viruses are needed to counter the potential threat of a global pandemic. We have previously developed a fast-acting and efficacious vaccine against Ebola virus (EBOV) using the vesicular stomatitis virus (VSV) platform. In this study, we generated recombinant VSV-based H5N1 influenza virus vectors to demonstrate the feasibility of this platform for a fast-acting pan-H5 influenza virus vaccine. We chose multiple approaches regarding antigen design and genome location to define a more optimized vaccine approach. After the VSV-based H5N1 influenza virus constructs were recovered and characterized in vitro, mice were vaccinated by a single dose or prime/boost regimen followed by challenge with a lethal dose of the homologous H5 clade 1 virus. We found that a single dose of VSV vectors expressing full-length hemagglutinin (HAfl) were sufficient to provide 100% protection. The vaccine vectors were fast-acting as demonstrated by uniform protection when administered 3 days prior to lethal challenge. Moreover, single vaccination induced cross-protective H5-specific antibodies and protected mice against lethal challenge with various H5 clade 2 viruses, highlighting the potential of the VSV-based HAfl as a pan-H5 influenza virus emergency vaccine.

A rapid and label-free platform for virus capture and identification from clinical samples

Viruses evolve rapidly and unpredictably, challenging the effectiveness of disease diagnostics. To help control outbreaks and understand their origins, the first step is often isolating viruses from infected samples for characterization. We demonstrate that multiple emerging virus strains can be simultaneously enriched and optically detected in only a few minutes without using any labels. A portable platform that captures viruses by their size, coupled to Raman spectroscopy, resulted in successful virus identification with 90% accuracy in real time directly from clinical samples. Furthermore, this viable enrichment process enables further culturing and characterization by electron microscopy and deep sequencing. This microplatform is an effective disease-monitoring system and broadens virus surveillance by enabling real-time virus identification.

Emerging and reemerging viruses are responsible for a number of recent epidemic outbreaks. A crucial step in predicting and controlling outbreaks is the timely and accurate characterization of emerging virus strains. We present a portable microfluidic platform containing carbon nanotube arrays with differential filtration porosity for the rapid enrichment and optical identification of viruses. Different emerging strains (or unknown viruses) can be enriched and identified in real time through a multivirus capture component in conjunction with surface-enhanced Raman spectroscopy. More importantly, after viral capture and detection on a chip, viruses remain viable and get purified in a microdevice that permits subsequent in-depth characterizations by various conventional methods. We validated this platform using different subtypes of avian influenza A viruses and human samples with respiratory infections. This technology successfully enriched rhinovirus, influenza virus, and parainfluenza viruses, and maintained the stoichiometric viral proportions when the samples contained more than one type of virus, thus emulating coinfection. Viral capture and detection took only a few minutes with a 70-fold enrichment enhancement; detection could be achieved with as little as 10² EID₅₀/mL (50% egg infective dose per microliter), with a virus specificity of 90%. After enrichment using the device, we demonstrated by sequencing that the abundance of viral-specific reads significantly increased from 4.1 to 31.8% for parainfluenza and from 0.08 to 0.44% for influenza virus. This enrichment method coupled to Raman virus identification constitutes an innovative system that could be used to quickly track and monitor viral outbreaks in real time.

Dendritic Cells Generated From Mops condylurus, a Likely Filovirus Reservoir Host, Are Susceptible to and Activated by Zaire Ebolavirus Infection

Ebola virus infection of human dendritic cells (DCs) induces atypical adaptive immune responses and thereby exacerbates Ebola virus disease (EVD). Human DCs, infected with Ebola virus aberrantly express low levels of the DC activation markers CD80, CD86, and MHC class II. The T cell responses ensuing are commonly anergic rather than protective against EVD. We hypothesize that DCs derived from potential reservoir hosts such as bats, which do not develop disease signs in response to Ebola virus infection, would exhibit features associated with activation. In this study, we have examined Zaire ebolavirus (EBOV) infection of DCs derived from the Angolan free-tailed bat species, Mops condylurus. This species was previously identified as permissive to EBOV infection in vivo, in the absence of disease signs. M. condylurus has also been recently implicated as the reservoir host for Bombali ebolavirus, a virus species that is closely related to EBOV. Due to the absence of pre-existing M. condylurus species-specific reagents, we characterized its de novo assembled transcriptome and defined its phylogenetic similarity to other mammals, which enabled the identification of cross-reactive reagents for M. condylurus bone marrow-derived DC (bat-BMDC) differentiation and immune cell phenotyping. Our results reveal that bat-BMDCs are susceptible to EBOV infection as determined by detection of EBOV specific viral RNA (vRNA). vRNA increased significantly 72 h after EBOV-infection and was detected in both cells and in culture supernatants. Bat-BMDC infection was further confirmed by the observation of GFP expression in DC cultures infected with a recombinant GFP-EBOV. Bat-BMDCs upregulated CD80 and chemokine ligand 3 (CCL3) transcripts in response to EBOV infection, which positively correlated with the expression levels of EBOV vRNA. In contrast to the aberrant responses to EBOV infection that are typical for human-DC, our findings from bat-BMDCs provide evidence for an immunological basis of asymptomatic EBOV infection outcomes.

Intranasal immunization with recombinant Vaccinia virus Tiantan harboring Zaire Ebola virus gp elicited systemic and mucosal neutralizing antibody in mice

Accumulating literature revealed that human mucosa was likely one of the important routes for EBOV attachment and further infection. Therefore inducing effective mucosal immune responses play key role in preventing the virus infection. Vaccinia virus Tiantan strain (VV) was a remarkably attenuated poxvirus, which has been broadly exploited as a multifunctional vector during the development of genetically recombinant vaccine and cancer therapeutic agent. In this study, we generated a recombinant VV harboring EBOV gp (VV-_Egp) that was used to immunize mice, followed by assessing immune responses, particularly the mucosal immune responses to EBOV GP. A stable and further attenuated VV-_Egp, in which the VV ha gene was replaced with the EBOV gp, was generated. In BALB/c mouse model, intranasal immunization with VV-_Egp elicited robust humoral and cellular immune responses, including high level of neutralizing serum IgG and IgA against EBOV, and a large amount of GP-specific IFN-γ secreting lymphocytes. More importantly, EBOV GP-specific neutralizing secreted IgA (sIgA) in nasal wash and both sIgA and IgG in vaginal wash were induced. In summary, immunization with a safe and stable recombinant VV carrying a single EBOV gp conferred robust systemic immune response and mucosal neutralizing antibodies, indicating that the recombinant virus could be utilized as a viral vector for plug-and-play universal platform in mucosal vaccine development.