Accelerated DNA vaccine regimen provides protection against Crimean-Congo hemorrhagic fever virus challenge in a macaque model

Antibodies targeting the Crimean-Congo Hemorrhagic Fever Virus nucleoprotein protect via TRIM21

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) is a negative-sense RNA virus spread by Hyalomma genus ticks across Europe, Asia, and Africa. CCHF disease begins as a non-specific febrile illness which may progress into a severe hemorrhagic disease with no widely approved or highly efficacious interventions currently available. Recently, we reported a self-replicating, alphavirus-based RNA vaccine that expresses the CCHFV nucleoprotein and is protective against lethal CCHFV disease in mice. This vaccine induces high titers of non-neutralizing anti-NP antibodies and we show here that protection does not require Fc-gamma receptors or complement. Instead, vaccinated mice deficient in the intracellular Fc-receptor TRIM21 were unable to control the infection despite mounting robust CCHFV-specific immunity. We also show that passive transfer of NP-immune sera confers significant TRIM21-dependent protection against lethal CCHFV challenge. Together our data identifies TRIM21-mediated mechanisms as the Fc effector function of protective antibodies against the CCHFV NP and provides mechanistic insight into how vaccines against the CCHFV NP confer protection.

The Role of Nucleocapsid Protein (NP) in the Immunology of Crimean-Congo Hemorrhagic Fever Virus (CCHFV)

Crimean-Congo hemorrhagic fever virus (CCHFV) is an orthonairovirus from the Bunyavirales order that is widely distributed geographically and causes severe or fatal infections in humans. The viral genome consists of three segmented negative-sense RNA molecules. The CCHFV nucleocapsid protein (CCHFV NP) is encoded by the smallest segment of the virus. CCHFV NP, the primary function of which is the encapsidation of viral RNA molecules, plays a critical role in various mechanisms important for viral replication and pathogenesis. This review is an attempt to revisit the literature available on the highly immunogenic and highly conserved CCHFV NP, summarizing the multifunctional roles of this protein in the immunology of CCHFV. Specifically, the review addresses the impact of CCHFV NP on innate, humoral, and cellular immune responses, epitopes recognized by B and T cells that limit viral spread, and its role as a target for diagnostic tests and for vaccine design. Based on the extensive information generated by many research groups, it could be stated that NP constitutes a significant and critical player in the immunology of CCHFV.

Crimean Congo hemorrhagic fever virus nucleoprotein and GP38 subunit vaccine combination prevents morbidity in mice

Immunizing mice with Crimean-Congo hemorrhagic fever virus (CCHFV) nucleoprotein (NP), glycoprotein precursor (GPC), or with the GP38 domain of GPC, can be protective when the proteins are delivered with viral vectors or as a DNA or RNA vaccine. Subunit vaccines are a safe and cost-effective alternative to some vaccine platforms, but Gc and Gn glycoprotein subunit vaccines for CCHFV fail to protect despite eliciting high levels of neutralizing antibodies. Here, we investigated humoral and cellular immune responses and the protective efficacy of recombinant NP, GP38, and GP38 forms (GP85 and GP160) associated with the highly glycosylated mucin-like (MLD) domain, as well as the NP + GP38 combination. Vaccination with GP160, GP85, or GP38 did not confer protection, and vaccination with the MLD-associated GP38 forms blunted the humoral immune responses to GP38, worsened clinical chemistry, and increased viral RNA in the blood compared to the GP38 vaccination. In contrast, NP vaccination conferred 100% protection from lethal outcome and was associated with mild clinical disease, while the NP + GP38 combination conferred even more robust protection by reducing morbidity compared to mice receiving NP alone. Thus, recombinant CCHFV NP alone is a promising vaccine candidate conferring 100% survival against heterologous challenge. Moreover, incorporation of GP38 should be considered as it further enhances subunit vaccine efficacy by reducing morbidity in surviving animals.

Recent Advances in Crimean-Congo Hemorrhagic Fever Virus Detection, Treatment, and Vaccination: Overview of Current Status and Challenges

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus, and zoonosis, and affects large regions of Asia, Southwestern and Southeastern Europe, and Africa. CCHFV can produce symptoms, including no specific clinical symptoms, mild to severe clinical symptoms, or deadly infections. Virus isolation attempts, antigen-capture enzyme-linked immunosorbent assay (ELISA), and reverse transcription polymerase chain reaction (RT-PCR) are all possible diagnostic tests for CCHFV. Furthermore, an efficient, quick, and cheap technology, including biosensors, must be designed and developed to detect CCHFV. The goal of this article is to offer an overview of modern laboratory tests available as well as other innovative detection methods such as biosensors for CCHFV, as well as the benefits and limits of the assays. Furthermore, confirmed cases of CCHF are managed with symptomatic assistance and general supportive care. This study examined the various treatment modalities, as well as their respective limitations and developments, including immunotherapy and antivirals. Recent biotechnology advancements and the availability of suitable animal models have accelerated the development of CCHF vaccines by a substantial margin. We examined a range of potential vaccines for CCHF in this research, comprising nucleic acid, viral particles, inactivated, and multi-epitope vaccines, as well as the present obstacles and developments in this field. Thus, the purpose of this review is to present a comprehensive summary of the endeavors dedicated to advancing various diagnostic, therapeutic, and preventive strategies for CCHF infection in anticipation of forthcoming hazards.

A replicating RNA vaccine confers protection in a rhesus macaque model of Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne febrile illness with a wide geographic distribution. In recent years the geographic range of Crimean-Congo hemorrhagic fever virus (CCHFV) and its tick vector have increased, placing an increasing number of people at risk of CCHFV infection. Currently, there are no widely available vaccines, and although the World Health Organization recommends ribavirin for treatment, its efficacy is unclear. Here we evaluate a promising replicating RNA vaccine in a rhesus macaque (Macaca mulatta) model of CCHF. This model provides an alternative to the established cynomolgus macaque model and recapitulates mild-to-moderate human disease. Rhesus macaques infected with CCHFV consistently exhibit viremia, detectable viral RNA in a multitude of tissues, and moderate pathology in the liver and spleen. We used this model to evaluate the immunogenicity and protective efficacy of a replicating RNA vaccine. Rhesus macaques vaccinated with RNAs expressing the CCHFV nucleoprotein and glycoprotein precursor developed robust non-neutralizing humoral immunity against the CCHFV nucleoprotein and had significant protection against the CCHFV challenge. Together, our data report a model of CCHF using rhesus macaques and demonstrate that our replicating RNA vaccine is immunogenic and protective in non-human primates after a prime-boost immunization.

Crimean-Congo Hemorrhagic Fever Virus for Clinicians-Diagnosis, Clinical Management, and Therapeutics

Crimean-Congo hemorrhagic fever virus (CCHFV) is the most geographically widespread tickborne viral infection worldwide and has a fatality rate of up to 62%. Despite its widespread range and high fatality rate, no vaccines or treatments are currently approved by regulatory agencies in the United States or Europe. Supportive treatment remains the standard of care, but the use of antiviral medications developed for other viral infections have been considered. We reviewed published literature to summarize the main aspects of CCHFV infection in humans. We provide an overview of diagnostic testing and management and medical countermeasures, including investigational vaccines and limited therapeutics. CCHFV continues to pose a public health threat because of its wide geographic distribution, potential to spread to new regions, propensity for genetic variability, potential for severe and fatal illness, and limited medical countermeasures for prophylaxis and treatment. Clinicians should become familiar with available diagnostic and management tools for CCHFV infections in humans.

Single dose, dual antigen RNA vaccines protect against lethal Crimean-Congo haemorrhagic fever virus infection in mice

BACKGROUND

Crimean-Congo Haemorrhagic Fever Virus is a tick-borne bunyavirus prevalent across Asia, Africa, the Middle East, and Europe. The virus causes a non-specific febrile illness which may develop into severe haemorrhagic disease. To date, there are no widely approved therapeutics. Recently, we reported an alphavirus-based replicon RNA vaccine which expresses the CCHFV nucleoprotein (repNP) or glycoprotein precursor (repGPC) and is protective against lethal disease in mice.

METHODS

Here, we evaluated engineered GPC constructs to find the minimal enhancing epitope of repGPC and test two RNA vaccine approaches to express multiple antigens in vivo to optimize protective efficacy of our repRNA.

FINDINGS

Vaccination with repNP and a construct expressing just the Gc antigen (repGc-FL) resulted in equivalent immunogenicity and protective efficacy compared to original repNP + repGPC vaccination. This vaccine was protective when prepared in either of two vaccine approaches, a mixed synthesis reaction producing two RNAs in a single tube and a single RNA expressing two antigens.

INTERPRETATION

Overall, our data illustrate two vaccine approaches to deliver two antigens in a single immunization. Both approaches induced protective immune responses against CCHFV in this model. These approaches support their continued development for this and future vaccine candidates for CCHFV and other vaccines where inclusion of multiple antigens would be optimal.

FUNDING

This work was supported by the Intramural Research Program, NIAID/NIH, HDT Bio and MCDC Grant #MCDC2204-011.

A mRNA Vaccine for Crimean-Congo Hemorrhagic Fever Virus Expressing Non-Fusion GnGc Using NSm Linker Elicits Unexpected Immune Responses in Mice

Crimean-Congo hemorrhagic fever (CCHF), caused by Crimean-Congo Hemorrhagic virus (CCHFV), is listed in the World Health Organization's list of priority diseases. The high fatality rate in humans, the widespread distribution of CCHFV, and the lack of approved specific vaccines are the primary concerns regarding this disease. We used microfluidic technology to optimize the mRNA vaccine delivery system and demonstrated that vaccination with nucleoside-modified CCHFV mRNA vaccines encoding GnNSmGc (vLMs), Gn (vLMn), or Gc (vLMc) induced different immune responses. We found that both T-cell and B-cell immune responses induced by vLMc were better than those induced by vLMn. Interestingly, immune responses were found to be lower for vLMs, which employed NSm to link Gn and Gc for non-fusion expression, compared to those for vLMc. In conclusion, our results indicated that NSm could be a factor that leads to decreased specific immune responses in the host and should be avoided in the development of CCHFV vaccine antigens.

CD8+ T-cells target the Crimean-Congo haemorrhagic fever virus Gc protein to control the infection in wild-type mice

BACKGROUND

Crimean-Congo haemorrhagic fever (CCHF) is a serious viral hemorrhagic fever caused by the CCHF virus (CCHFV). Spread by the bites of infected ticks or handling of viremic livestock, human disease is characterized by a non-specific febrile illness that can rapidly progress to fatal hemorrhagic disease. No vaccines or antivirals are available. Case fatality rates can vary but can be higher than 30%, although sub-clinical infections are often unrecognized and unreported. Yet, while most humans infected with CCHFV will survive the infection, often with little-to-no symptoms, the host responses that control the infection are unknown.

METHODS

Here we investigated the role of cellular immunity in control of CCHFV infection in an immunocompetent mouse model.

FINDINGS

We found that CD8+ T-cells are crucial for efficient control of the acute infection and rapidly acquired CCHFV-specific antiviral effector functions such as production of antiviral cytokines and degranulating in response to CCHFV peptides. We further identified the minimal CD8+ T-cell epitopes in the viral Gc proteins and that infection of mice lacking IFNγ resulted in worsened disease and higher viral loads.

INTERPRETATION

Together our data suggest that CD8+ T-cells are important for control of acute CCHFV infection likely through production of antiviral cytokines.

FUNDING

This work was supported by the Intramural Research Program of the NIH.

Identification of T cell responses to the nonstructural glycoproteins in survivors of Crimean-Congo hemorrhagic fever in South Africa

Crimean-Congo hemorrhagic fever orthonairovirus (CCHFV) is listed as a priority pathogen by the World Health Organization due to the severity of disease, propensity for spread to nonendemic regions, and absence of a vaccine or specific treatment. The immune correlates of protection are not clearly defined and hence the importance of investigating host immune responses in survivors. We have previously shown that survivors generate memory T cell responses that are long-lived and this study aimed to further define specific viral proteins targeted by the T cell response. The NSM , GP38, highly variable mucin-like domain, and N-terminus of GC regions in CCHFV are considered immunogenic regions and were investigated using peptide libraries representing regions of interest. An interferon gamma ELISpot assay was used to identify responses in peripheral blood mononuclear cells isolated from 12 survivors of laboratory confirmed CCHFV infections. IFN-γ responses were detected from eight survivors, against nine peptides, including four peptides located in the NSM region and five peptides located in the GP38 protein. No response was detected against peptides representing the mucin-like domain. In conclusion, the results suggest the presence of a long-lasting T cell memory response upon stimulation with viral epitopes in survivors of infection.

CCHFV vaccine development, current challenges, limitations, and future directions

Crimean-Congo hemorrhagic fever (CCHF) is the most prevalent tick-borne viral disease affecting humans. The disease is life-threatening in many regions of the developing world, including Africa, Asia, the Middle East, and Southern Europe. In line with the rapidly increasing disease prevalence, various vaccine strategies are under development. Despite a large number of potential vaccine candidates, there are no approved vaccines as of yet. This paper presents a detailed comparative analysis of current efforts to develop vaccines against CCHFV, limitations associated with current efforts, and future research directions.

Vaccination with the Crimean-Congo hemorrhagic fever virus viral replicon vaccine induces NP-based T-cell activation and antibodies possessing Fc-mediated effector functions

Crimean-Congo hemorrhagic fever virus (CCHFV; family Nairoviridae) is a tick-borne pathogen that frequently causes lethal disease in humans. CCHFV has a wide geographic distribution, and cases have been reported in Africa, Asia, the Middle East, and Europe. Availability of a safe and efficacious vaccine is critical for restricting outbreaks and preventing disease in endemic countries. We previously developed a virus-like replicon particle (VRP) vaccine that provides complete protection against homologous and heterologous lethal CCHFV challenge in mice after a single dose. However, the immune responses induced by this vaccine are not well characterized, and correlates of protection remain unknown. Here we comprehensively characterized the kinetics of cell-mediated and humoral immune responses in VRP-vaccinated mice, and demonstrate that they predominantly target the nucleoprotein (NP). NP antibodies are not associated with protection through neutralizing activity, but VRP vaccination results in NP antibodies possessing Fc-mediated antibody effector functions, such as complement activation (ADCD) and antibody-mediated cellular phagocytosis (ADCP). This suggests that Fc-mediated effector functions may contribute to this vaccine's efficacy.

Proceedings of the Online Conference "Vaccines and Vaccination during and Post COVID Pandemics" (7-9 December 2022)

The COVID-19 pandemic put focus on various aspects of vaccine research and development. These include mass vaccination strategies, vaccination compliance and hesitancy, acceptance of novel vaccine approaches, preclinical and animal models used to assess vaccine safety and efficacy, and many other related issues. These issues were addressed by the international online conference "Vaccines and Vaccination During and Post COVID Pandemics" (VAC&VAC 2022) held on the platform of Riga Stradins University, Riga, Latvia. Conference was supported by the International Society for Vaccines, the National Cancer Institute "Fondazione Pascale" (Naples, Italy), and the scientific journal VACCINES (mdpi). VAC&VAC 2022 attracted nearly 150 participants from 14 countries. This report summarizes conference presentations and their discussion. Sessions covered the topics of (1) COVID-19 vaccine development, evaluation, and attitude towards these vaccines, (2) HPV and cancer vaccines, (3) progress and challenges of HIV vaccine development, (4) new and re-emerging infectious threats, and (5) novel vaccine vehicles, adjuvants, and carriers. Each session was introduced by a plenary lecture from renowned experts from leading research institutions worldwide. The conference also included sessions on research funding and grant writing and an early career researcher contest in which the winners received monetary awards and a chance to publish their results free of charge in the special issue of VACCINES covering the meeting.

A roadmap for developing Venezuelan equine encephalitis virus (VEEV) vaccines: Lessons from the past, strategies for the future

Venezuelan equine encephalitis (VEE) is a zoonotic infectious disease caused by the Venezuelan equine encephalitis virus (VEEV), which can lead to severe central nervous system infections in both humans and animals. At present, the medical community does not possess a viable means of addressing VEE, rendering the prevention of the virus a matter of paramount importance. Regarding the prevention and control of VEEV, the implementation of a vaccination program has been recognized as the most efficient strategy. Nevertheless, there are currently no licensed vaccines or drugs available for human use against VEEV. This imperative has led to a surge of interest in vaccine research, with VEEV being a prime focus for researchers in the field. In this paper, we initially present a comprehensive overview of the current taxonomic classification of VEEV and the cellular infection mechanism of the virus. Subsequently, we provide a detailed introduction of the prominent VEEV vaccine types presently available, including inactivated vaccines, live attenuated vaccines, genetic, and virus-like particle vaccines. Moreover, we emphasize the challenges that current VEEV vaccine development faces and suggest urgent measures that must be taken to overcome these obstacles. Notably, based on our latest research, we propose the feasibility of incorporation codon usage bias strategies to create the novel VEEV vaccine. Finally, we prose several areas that future VEEV vaccine development should focus on. Our objective is to encourage collaboration between the medical and veterinary communities, expedite the translation of existing vaccines from laboratory to clinical applications, while also preparing for future outbreaks of new VEEV variants.

Comparative characterization of Crimean-Congo hemorrhagic fever virus cell culture systems with application to propagation and titration methods

Crimean-Congo hemorrhagic fever orthonairovirus (CCHFV) is a biosafety level 4 and World Health Organization top priority pathogen. Infection leads to an often fatal hemorrhagic fever disease in humans. The tick-borne virus is endemic in countries across Asia, Europe and Africa, with signs of spreading into new regions. Despite the severity of disease and the potential of CCHFV geographic expansion to cause widespread outbreaks, no approved vaccine or treatment is currently available. Critical for basic research and the development of diagnostics or medical countermeasures, CCHFV viral stocks are commonly produced in Vero E6 and SW-13 cell lines. While a variety of in-house methods are being used across different laboratories, there has been no clear, specific consensus on a standard, optimal system for CCHFV growth and titration. In this study, we perform a systematic, side-by-side characterization of Vero E6 and SW-13 cell lines concerning the replication kinetics of CCHFV under different culture conditions. SW-13 cells are typically cultured in a CO₂-free condition (SW-13 CO₂^-) according to the American Type Culture Collection. However, we identify a CO₂-compatible culture condition (SW-13 CO₂⁺) that demonstrates the highest viral load (RNA concentration) and titer (infectious virus concentration) in the culture supernatants, in comparison to SW-13 CO₂^- and Vero E6 cultures. This optimal viral propagation system also leads to the development of two titration methods: an immunostaining-based plaque assay using a commercial CCHFV antibody and a colorimetric readout, and an antibody staining-free, cytopathic effect-based median tissue culture infectious dose assay using a simple excel calculator. These are anticipated to serve as a basis for a reproducible, standardized and user-friendly platform for CCHFV propagation and titration.

Advances and perspectives in the development of vaccines against highly pathogenic bunyaviruses

Increased human activities around the globe and the rapid development of once rural regions have increased the probability of contact between humans and wild animals. A majority of bunyaviruses are of zoonotic origin, and outbreaks may result in the substantial loss of lives, economy contraction, and social instability. Many bunyaviruses require manipulation in the highest levels of biocontainment, such as Biosafety Level 4 (BSL-4) laboratories, and the scarcity of this resource has limited the development speed of vaccines for these pathogens. Meanwhile, new technologies have been created, and used to innovate vaccines, like the mRNA vaccine platform and bioinformatics-based antigen design. Here, we summarize current vaccine developments for three different bunyaviruses requiring work in the highest levels of biocontainment: Crimean-Congo Hemorrhagic Fever Virus (CCHFV), Rift Valley Fever Virus (RVFV), and Hantaan virus (HTNV), and provide perspectives and potential future directions that can be further explored to advance specific vaccines for humans and livestock.

Crimean-Congo haemorrhagic fever virus

Crimean-Congo haemorrhagic fever (CCHF) is a severe tick-borne illness with a wide geographical distribution and case fatality rates of 30% or higher. Caused by infection with the CCHF virus (CCHFV), cases are reported throughout Africa, the Middle East, Asia and southern and eastern Europe. The expanding range of the Hyalomma tick vector is placing new populations at risk for CCHF, and no licensed vaccines or specific antivirals exist to treat CCHF. Furthermore, despite cases of CCHF being reported annually, the host and viral determinants of CCHFV pathogenesis are poorly understood. CCHFV can productively infect a multitude of animal species, yet only humans develop a severe illness. Within human populations, subclinical infections are underappreciated and may represent a substantial proportion of clinical outcomes. Compared with other members of the Bunyavirales order, CCHFV has a more complex genomic organization, with many viral proteins having unclear functions in viral pathogenesis. In recent years, improved animal models have led to increased insights into CCHFV pathogenesis, and several antivirals and vaccines for CCHFV have shown robust efficacy in preclinical models. Translation of these insights and candidate therapeutics to the clinic will hopefully reduce the morbidity and mortality caused by CCHFV.