The Ebola virus glycoprotein and its immune responses across multiple vaccine platforms

Single-dose VSV-based vaccine protects cynomolgus macaques from disease after Taï Forest virus infection

Taï Forest virus (TAFV) is a lesser-known ebolavirus that causes lethal infections in chimpanzees and is responsible for a single human case. Limited research has been done on this human pathogen; however, with the recent emergence of filoviruses in West Africa, further investigation and countermeasure development against this virus is warranted.We developed a vesicular stomatitis virus (VSV)-based vaccine expressing the TAFV glycoprotein as the viral antigen and assessed it for protective efficacy in nonhuman primates (NHPs). Following a single high-dose vaccination, NHPs developed antigen-specific binding and neutralizing antibodies as well as modest T cell responses. Importantly, all vaccinated NHPs were uniformly protected from disease after lethal TAFV challenge while the naïve control group succumbed to the disease. Histopathologic lesions consistent with filovirus disease were present in control NHPs but were not observed in vaccinated NHPs. Transcriptional analysis of whole blood samples obtained after vaccination and challenge was performed to gain insight into molecular underpinnings conferring protection. Differentially expressed genes (DEG) detected 7 days post-vaccination were enriched to processes associated with innate immunity and antiviral responses. Only a small number of DEG was detected in vaccinated NHPs post-challenge while over 1,000 DEG were detected in control NHPs at end-stage disease which mapped to gene ontology terms indicative of defense responses and inflammation. Taken together, this data demonstrates the effective single-dose protection of the VSV-TAFV vaccine, and its potential for use in outbreaks.

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.

Development of Fluorescence-Tagged SARS-CoV-2 Virus-like Particles by a Tri-Cistronic Vector Expression System for Investigating the Cellular Entry of SARS-CoV-2

Severe acute respiratory syndrome-related coronavirus-2 (SARS-CoV-2) has caused the pandemic that began late December 2019. The co-expression of SARS-CoV-2 structural proteins in cells could assemble into several types of virus-like particles (VLPs) without a viral RNA genome. VLPs containing S proteins with the structural and functional properties of authentic virions are safe materials to exploit for virus-cell entry and vaccine development. In this study, to generate SARS-CoV-2 VLPs (SCoV2-SEM VLPs) composed of three structural proteins including spike (S), envelop (E) protein and membrane (M) protein, a tri-cistronic vector expression system was established in a cell line co-expressing SARS-CoV-2 S, E and M proteins. The SCoV2-SEM VLPs were harvested from the cultured medium, and three structure proteins were confirmed by Western blot assay. A negative-stain TEM assay demonstrated the size of the SCoV2-SEM VLPs with a diameter of about 90 nm. To further characterize the infectious properties of SCoV2-SEM VLPs, the VLPs (atto647N-SCoV2-SEM VLPs) were fluorescence-labeled by conjugation with atto-647N and visualized under confocal microscopy at a single-particle resolution. The results of the infection assay revealed that atto647N-SCoV2-SEM VLPs attached to the surface of the HEK293T cells at the pre-binding phase in a ACE2-dependent manner. At the post-infection phase, atto647N-SCoV2-SEM VLPs either fused with the cellular membrane or internalized into the cytoplasm with mCherry-rab5-positive early endosomes. Moreover, fusion with the cellular membrane and the internalization with early endosomes could be inhibited by the treatment of camostat (a pharmacological inhibitor of TMPRSS2) and chlorpromazine (an endocytosis inhibitor), respectively. These results elucidated that SCoV2-SEM VLPs behave similarly to the authentic live SARS-CoV-2 virus, suggesting that the development of SCoV2-SEM VLPs provide a realistic and safe experimental model for studying the infectious mechanism of SARS-CoV-2.

Virus-Like Particle-Templated Silica-Adjuvanted Nanovaccines with Enhanced Humoral and Cellular Immunity

Virus-like particles (VLPs) are self-assembled viral proteins that represent a superior form of antigens in vaccine formulations. To enhance immunogenicity, adjuvants, especially the aluminum salts (Alum), are essentially formulated in VLP vaccines. However, Alum only induce biased humoral immune responses that limits further applications of VLP-based vaccines. To stimulate more balanced immunity, we, herein, develop a one-step strategy of using VLPs as the biotemplates to synthesize raspberry-like silica-adjuvanted VLP@Silica nanovaccines. Hepatitis B surface antigen (HBsAg) VLPs and human papillomavirus type 18 (HPV 18) VLPs are selected as model templates. Circular dichroism (CD) and affinity analyses demonstrate that HBsAg VLPs in the nanovaccines maintain their secondary structure and immunogenicity, respectively. VLP@Silica promote silica dissolution-induced lysosomal escape and cytosolic delivery of antigens, and enhance the secretion of both Th1 and Th2 type cytokines in murine bone marrow-derived dendritic cells (BMDCs). Additionally, they could improve antigen trafficking and mediate DC activation in draining lymph nodes (DLNs). Vaccination study demonstrate that both HBsAg VLP@Silica and HPV 18 VLP@Silica nanovaccines induce enhanced antigen-specific antibody productions and T-cell mediated adaptive immune responses. This design strategy can utilize VLPs derived from a diversity of viruses or their variants as templates to construct both prophylactic and therapeutic vaccines with improved immunogenicity.

World Society for Virology first international conference: Tackling global virus epidemics

This communication summarizes the presentations given at the 1st international conference of the World Society for Virology (WSV) held virtually during 16-18 June 2021, under the theme of tackling global viral epidemics. The purpose of this biennial meeting is to foster international collaborations and address important viral epidemics in different hosts. The first day included two sessions exclusively on SARS-CoV-2 and COVID-19. The other two days included one plenary and three parallel sessions each. Last not least, 16 sessions covered 140 on-demand submitted talks. In total, 270 scientists from 49 countries attended the meeting, including 40 invited keynote speakers.

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.

Recent developments and strategies of Ebola virus vaccines

The Filovirus family member, Ebola virus (EBOV), is a highly infectious pathogen responsible for viral hemorrhagic fever. EBOV has a fatality rate in the range 50%-90% in primates. The lethal viral hemorrhagic attack in 2014 by EBOV has forced the human race to look for rapid countermeasures. Fortunately, owing to continuous efforts and several vaccine platforms, few potential vaccine candidates are emerging, such as replicative and non-replicative vectored vaccines, polyepitopic or monovalent vaccines, and DNA vaccines. This article reviewed various kinds of EBOV vaccines in different clinical trial phases and their approval status. Updated knowledge of vaccine development progress might stimulate the researchers to look for more potent and effective vaccine candidates against EBOV.

Virus-like particles: preparation, immunogenicity and their roles as nanovaccines and drug nanocarriers

Virus-like particles (VLPs) are virus-derived structures made up of one or more different molecules with the ability to self-assemble, mimicking the form and size of a virus particle but lacking the genetic material so they are not capable of infecting the host cell. Expression and self-assembly of the viral structural proteins can take place in various living or cell-free expression systems after which the viral structures can be assembled and reconstructed. VLPs are gaining in popularity in the field of preventive medicine and to date, a wide range of VLP-based candidate vaccines have been developed for immunization against various infectious agents, the latest of which is the vaccine against SARS-CoV-2, the efficacy of which is being evaluated. VLPs are highly immunogenic and are able to elicit both the antibody- and cell-mediated immune responses by pathways different from those elicited by conventional inactivated viral vaccines. However, there are still many challenges to this surface display system that need to be addressed in the future. VLPs that are classified as subunit vaccines are subdivided into enveloped and non- enveloped subtypes both of which are discussed in this review article. VLPs have also recently received attention for their successful applications in targeted drug delivery and for use in gene therapy. The development of more effective and targeted forms of VLP by modification of the surface of the particles in such a way that they can be introduced into specific cells or tissues or increase their half-life in the host is likely to expand their use in the future. Recent advances in the production and fabrication of VLPs including the exploration of different types of expression systems for their development, as well as their applications as vaccines in the prevention of infectious diseases and cancers resulting from their interaction with, and mechanism of activation of, the humoral and cellular immune systems are discussed in this review.

Protein/AS01B vaccination elicits stronger, more Th2-skewed antigen-specific human T follicular helper cell responses than heterologous viral vectors

Interactions between B cells and CD4⁺ T follicular helper (Tfh) cells are key determinants of humoral responses. Using samples from clinical trials performed with the malaria vaccine candidate antigen Plasmodium falciparum merozoite protein (PfRH5), we compare the frequency, phenotype, and gene expression profiles of PfRH5-specific circulating Tfh (cTfh) cells elicited by two leading human vaccine delivery platforms: heterologous viral vector prime boost and protein with AS01_B adjuvant. We demonstrate that the protein/AS01_B platform induces a higher-magnitude antigen-specific cTfh cell response and that this correlates with peak anti-PfRH5 IgG concentrations, frequency of PfRH5-specific memory B cells, and antibody functionality. Furthermore, our data indicate a greater Th2/Tfh2 skew within the polyfunctional response elicited following vaccination with protein/AS01_B as compared to a Th1/Tfh1 skew with viral vectors. These data highlight the impact of vaccine platform on the cTfh cell response driving humoral immunity, associating a high-magnitude, Th2-biased cTfh response with potent antibody production.

CD4 Tfh comparison in malaria vaccine trials using leading human vaccine platforms

Protein/AS01_B drives stronger antigen-specific Tfh responses than viral vectors

Greater T(f)h2 skewing of antigen-specific CD4 T cells in protein/AS01_B vaccinees

Antigen-specific CD4 T(fh) cell parameters correlate with functional antibody

Investigating the Interaction between Negative Strand RNA Viruses and Their Hosts for Enhanced Vaccine Development and Production

The current pandemic has highlighted the ever-increasing risk of human to human spread of zoonotic pathogens. A number of medically-relevant zoonotic pathogens are negative-strand RNA viruses (NSVs). NSVs are derived from different virus families. Examples like Ebola are known for causing severe symptoms and high mortality rates. Some, like influenza, are known for their ease of person-to-person transmission and lack of pre-existing immunity, enabling rapid spread across many countries around the globe. Containment of outbreaks of NSVs can be difficult owing to their unpredictability and the absence of effective control measures, such as vaccines and antiviral therapeutics. In addition, there remains a lack of essential knowledge of the host–pathogen response that are induced by NSVs, particularly of the immune responses that provide protection. Vaccines are the most effective method for preventing infectious diseases. In fact, in the event of a pandemic, appropriate vaccine design and speed of vaccine supply is the most critical factor in protecting the population, as vaccination is the only sustainable defense. Vaccines need to be safe, efficient, and cost-effective, which is influenced by our understanding of the host–pathogen interface. Additionally, some of the major challenges of vaccines are the establishment of a long-lasting immunity offering cross protection to emerging strains. Although many NSVs are controlled through immunisations, for some, vaccine design has failed or efficacy has proven unreliable. The key behind designing a successful vaccine is understanding the host–pathogen interaction and the host immune response towards NSVs. In this paper, we review the recent research in vaccine design against NSVs and explore the immune responses induced by these viruses. The generation of a robust and integrated approach to development capability and vaccine manufacture can collaboratively support the management of outbreaking NSV disease health risks.

Interlaboratory comparison for the Filovirus Animal Nonclinical Group (FANG) anti-Ebola virus glycoprotein immunoglobulin G enzyme-linked immunosorbent assay

The need for an efficacious vaccine against highly pathogenic filoviruses was reinforced by the devastating 2014–2016 outbreak of Ebola virus (EBOV) disease (EVD) in Guinea, Sierra Leone, and Liberia that resulted in over 28,000 cases and over 11,300 deaths. In addition, the 2018–2020 outbreak in the Democratic Republic of the Congo currently has over 3,400 cases and over 2,200 deaths. A fully licensed vaccine and at least one other investigational vaccine are being deployed to combat this EVD outbreak. To support vaccine development and pre-clinical/clinical testing a Filovirus Animal Nonclinical Group (FANG) human anti-EBOV GP IgG ELISA was developed to measure anti-EBOV GP IgG antibodies. This ELISA is currently being used in multiple laboratories. Reported here is a characterization of an interlaboratory statistical analysis of the human anti-EBOV GP IgG ELISA as part of a collaborative study between five participating laboratories. Each laboratory used similar method protocols and reagents to measure anti-EBOV GP IgG levels in human serum samples from a proficiency panel consisting of ten serum samples created by the differential dilution of a serum sample positive for anti-GP IgG antibodies (BMIZAIRE105) with negative serum (BMI529). The total assay variability (inter- and intra-assay variability) %CVs observed at each laboratory ranged from 12.2 to 30.6. Intermediate precision (inter-assay variability) for the laboratory runs ranged from 8.9 to 21.7%CV and repeatability (intra-assay variability) %CVs ranged from 7.2 to 23.7. The estimated slope for the relationship between log₁₀(Target Concentration) and the log₁₀(Observed Concentration) across all five laboratories was 0.95 with a 90% confidence interval of (0.93, 0.97). Equivalence test results showed that the 90% confidence interval for the ratios for the sample-specific mean concentrations at the five individual labs to the overall laboratory consensus value were within the equivalence bounds of 0.80 to 1.25 for each laboratory and test sample, except for six test samples from Lab D, two samples from Lab B1, and one sample from Lab B2. The mean laboratory concentrations for Lab D were less than those from the other laboratories by 20% on average across the serum samples. The evaluation of the proficiency panel at these laboratories provides a limited assessment of assay precision (intermediate precision, repeatability, and total assay variability), dilutional linearity, and accuracy. This evaluation suggests that the within-laboratory performance of the anti-EBOV GP IgG ELISA as implemented at the five laboratories is consistent with the intended use of the assay based on the acceptance criteria used by laboratories that have validated the assay. However, the assessment of between-laboratory performance revealed lower observed concentrations at Lab D and greater variability in assay results at Lab B1 relative to other laboratories.