Immunological Analysis of a CCHFV mRNA Vaccine Candidate in Mouse Models

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.

Vaccine approaches and treatment aspects against Crimean Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever [CCHF] is a severe infectious viral disease caused by a tick borne virus which can lead to fatal hemorrhagic disease in humans. It has been reported from some continents including Africa, Asia and Europe. Virus is transmitted to human mainly through tick bite, whose acquire infection from reservoirs wild and domesticated mammalians and ostriches. Currently no approved vaccine or drug is available for CCHF and prevention is mainly based on biosecurity measures. Ribavirin is the only approved drug that has been used in some countries to treat human disease, however some new studies did not prove the Ribavirin efficacy. Different strategies to design effective vaccines, have been conducted through years, from inactivated virus to nucleotide-based ones including DNA and mRNA vaccines. In this study we review of pioneering vaccine candidate platforms.

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.

Nucleocapsid protein-specific monoclonal antibodies protect mice against Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever virus (CCHFV) is a WHO priority pathogen. Antibody-based medical countermeasures offer an important strategy to mitigate severe disease caused by CCHFV. Most efforts have focused on targeting the viral glycoproteins. However, glycoproteins are poorly conserved among viral strains. The CCHFV nucleocapsid protein (NP) is highly conserved between CCHFV strains. Here, we investigate the protective efficacy of a CCHFV monoclonal antibody targeting the NP. We find that an anti-NP monoclonal antibody (mAb-9D5) protected female mice against lethal CCHFV infection or resulted in a significant delay in mean time-to-death in mice that succumbed to disease compared to isotype control animals. Antibody protection is independent of Fc-receptor functionality and complement activity. The antibody bound NP from several CCHFV strains and exhibited robust cross-protection against the heterologous CCHFV strain Afg09-2990. Our work demonstrates that the NP is a viable target for antibody-based therapeutics, providing another direction for developing immunotherapeutics against CCHFV.

Lipid Nanoparticle-Based Delivery System-A Competing Place for mRNA Vaccines

mRNA, as one of the foci of biomedical research in the past decade, has become a candidate vaccine solution for various infectious diseases and tumors and for regenerative medicine and immunotherapy due to its high efficiency, safety, and effectiveness. A stable and effective delivery system is needed to protect mRNAs from nuclease degradation while also enhancing immunogenicity. The success of mRNA lipid nanoparticles in treating COVID-19, to a certain extent, marks a milestone for mRNA vaccines and also promotes further research on mRNA delivery systems. Here, we explore mRNA vaccine delivery systems, especially lipid nanoparticles (LNPs), considering the current research status, prospects, and challenges of lipid nanoparticles, and explore other mRNA delivery systems.

Nano-bio interactions in mRNA nanomedicine: Challenges and opportunities for targeted mRNA delivery

Upon entering the biological milieu, nanomedicines swiftly interact with the surrounding tissue fluid, subsequently being enveloped by a dynamic interplay of biomacromolecules, such as carbohydrates, nucleic acids, and cellular metabolites, but with predominant serum proteins within the biological corona. A notable consequence of the protein corona phenomenon is the unintentional loss of targeting ligands initially designed to direct nanomedicines toward particular cells or organs within the in vivo environment. mRNA nanomedicine displays high demand for specific cell and tissue-targeted delivery to effectively transport mRNA molecules into target cells, where they can exert their therapeutic effects with utmost efficacy. In this review, focusing on the delivery systems and tissue-specific applications, we aim to update the nanomedicine population with the prevailing and still enigmatic paradigm of nano-bio interactions, a formidable hurdle in the pursuit of targeted mRNA delivery. We also elucidate the current impediments faced in mRNA therapeutics and, by contemplating prospective avenues-either to modulate the corona or to adopt an 'ally from adversary' approach-aim to chart a course for advancing mRNA nanomedicine.

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.

Induced protection from a CCHFV-M DNA vaccine requires CD8+ T cells

Crimean-Congo hemorrhagic fever (CCHF) is a World Health Organization prioritized disease because its broad distribution and severity of disease make it a global health threat. Despite advancements in preclinical vaccine development for CCHF virus (CCHFV), including multiple platforms targeting multiple antigens, a clear definition of the adaptive immune correlates of protection is lacking. Levels of neutralizing antibodies in vaccinated animal models do not necessarily correlate with protection, suggesting that cellular immunity, such as CD8+ T cells, might have an important role in protection in this model. Using a well-established IFN-I antibody blockade mouse model (IS) and a DNA-based vaccine encoding the CCHFV M-segment glycoprotein precursor, we investigated the role of humoral and T cell immunity in vaccine-mediated protection in mice genetically devoid of these immune compartments. We found that in the absence of the B-cell compartment (µMT knockout mice), protection provided by the vaccine was not reduced. In contrast, in the absence of CD8+ T cells (CD8+ knockout mice) the vaccine-mediated protection was significantly diminished. Importantly, humoral responses to the vaccine in CD8+ T-cell knockout mice were equivalent to wild-type mice. These findings indicated that CD8+ T-cell responses are necessary and sufficient to promote protection in mice vaccinated with the M-segment DNA vaccine. Identifying a crucial role of the cellular immunity to protect against CCHFV should help guide the development of CCHFV-targeting vaccines.

Crimean-Congo Hemorrhagic Fever Virus: Progress in Vaccine Development

Crimean-Congo hemorrhagic fever virus (CCHFV), a member of the Nairoviridae family and Bunyavirales order, is transmitted to humans via tick bites or contact with the blood of infected animals. It can cause severe symptoms, including hemorrhagic fever, with a mortality rate between 5 to 30%. CCHFV is classified as a high-priority pathogen by the World Health Organization (WHO) due to its high fatality rate and the absence of effective medical countermeasures. CCHFV is endemic in several regions across the world, including Africa, Europe, the Middle East, and Asia, and has the potential for global spread. The emergence of the disease in new areas, as well as the presence of the tick vector in countries without reported cases, emphasizes the need for preventive measures to be taken. In the past, the lack of a suitable animal model susceptible to CCHFV infection has been a major obstacle in the development of vaccines and treatments. However, recent advances in biotechnology and the availability of suitable animal models have significantly expedited the development of vaccines against CCHF. These advancements have not only contributed to an enhanced understanding of the pathogenesis of CCHF but have also facilitated the evaluation of potential vaccine candidates. This review outlines the immune response to CCHFV and animal models utilized for the study of CCHFV and highlights the progress made in CCHFV vaccine studies. Despite remarkable advancements in vaccine development for CCHFV, it remains crucial to prioritize continued research, collaboration, and investment in this field.

Evaluation of the immunogenicity of a Crimean-Congo hemorrhagic fever virus vaccine candidate in mice developed based on a baculovirus Zera nanoparticle delivery system

Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic disease caused by Crimean-Congo hemorrhagic fever virus (CCHFV), which can cause severe clinical disease and even death in humans. In recent years, the disease has spread to a wider area, posing a major public health threat to China as well as the Middle East, Europe and Africa, and there is no safe and effective vaccine to prevent the disease. Recently, it has been shown that using the Zera fusion to target proteins can enhance immunogenicity and improve the potential for developing viral vaccines. Based on this finding, in this study, two vaccine candidates, Zera-Gn and Zera-Np, were prepared using an insect baculovirus system expressing CCHFV glycoprotein (Gn) and nucleocapsid protein (Np) fused with Zera tags, and evaluated for immunogenicity in BALB/c mice. The obtainedresults showed that both Zera-Gn and Zera-Np recombinant nanoparticles were successfully expressed, and Zera-Gn had good induction of humoral and cellular immunity in mice, and its immunogenicity was significantly higher than that of Zera-Np. The results indicated that Zera-Gn self-assembled nanoparticles prepared by fusing Zera tags with CCHFV spike-in protein Gn have the potential to be a candidate vaccine for CCHF, and this study provides a reference for the development of Zera self-assembled nanoparticle vaccine for CCHF.

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.

Adenoviral vectored vaccination protects against Crimean-Congo Haemorrhagic Fever disease in a lethal challenge model

BACKGROUND

The tick-borne bunyavirus, Crimean-Congo Haemorrhagic Fever virus (CCHFV), can cause severe febrile illness in humans and has a wide geographic range that continues to expand due to tick migration. Currently, there are no licensed vaccines against CCHFV for widespread usage.

METHODS

In this study, we describe the preclinical assessment of a chimpanzee adenoviral vectored vaccine (ChAdOx2 CCHF) which encodes the glycoprotein precursor (GPC) from CCHFV.

FINDINGS

We demonstrate here that vaccination with ChAdOx2 CCHF induces both a humoral and cellular immune response in mice and 100% protection in a lethal CCHF challenge model. Delivery of the adenoviral vaccine in a heterologous vaccine regimen with a Modified Vaccinia Ankara vaccine (MVA CCHF) induces the highest levels of CCHFV-specific cell-mediated and antibody responses in mice. Histopathological examination and viral load analysis of the tissues of ChAdOx2 CCHF immunised mice reveals an absence of both microscopic changes and viral antigen associated with CCHF infection, further demonstrating protection against disease.

INTERPRETATION

There is the continued need for an effective vaccine against CCHFV to protect humans from lethal haemorrhagic disease. Our findings support further development of the ChAd platform expressing the CCHFV GPC to seek an effective vaccine against CCHFV.

FUNDING

This research was supported by funding from the Biotechnology and Biological Sciences Research Council (UKRI-BBSRC) [BB/R019991/1 and BB/T008784/1].

Mutational analysis of catalytic site domain of CCHFV L RNA segment

INTRODUCTION

Crimean-Congo haemorrhagic fever virus (CCHFV) has tripartite RNA genome and is endemic in various countries of Asia, Africa and Europe.

METHOD

The present study is focused on mutation profiling of CCHFV L segment and phylogenetic clustering of protein dataset into six CCHFV genotypes.

RESULTS

Phylogenetic tree rooted with NCBI reference sequence (YP_325663.1) indicated less divergence from genotype III and the sequences belonging to same genotypes have shown less divergence among each other. Mutation frequency at 729 mutated positions was calculated and 563, 49, 33, 46 and 38 amino acid positions were found to be mutated at mutation frequency intervals of 0-0.2, 0.21-0.4, 0.41-0.6, 0.61-0.8 and 0.81-1.0 respectively. Thirty-eight highly frequent mutations (0.81-1.0 interval) were found in all genotypes and mapping in L segment (encoded for RdRp) revealed four mutations (V2074I, I2134T/A, V2148A and Q2695H/R) in catalytic site domain and no mutation in OTU domain. Molecular dynamic simulation and in silico analysis showed that catalytic site domain displayed large deviation and fluctuation upon introduction of these point mutations.

CONCLUSION

Overall study provides strong evidence that OTU domain is highly conserved and less prone to mutation whereas point mutations recorded in catalytic domain have affected the stability of protein and were found to be persistent in the large population.

Crimean-Congo hemorrhagic fever: Immunopathogenesis and recent advances in the development of vaccines

Crimean-Congo hemorrhagic fever is a serious vector-borne zoonotic viral infection which leads to severe illness and fatalities in people living in endemic regions and becoming infected sporadically. Hyalomma ticks are responsible for the transmission of the virus which belongs to the family Nairoviridae. This disease spreads through ticks bite, infected tissues, or blood of viremic animals, and from infected humans to others. Serological studies also indicate the presence of the virus in various domestic and wild animals to be a risk factor for the transmission of the disease. Crimean-Congo hemorrhagic fever virus elicits many immune responses during the infection including inflammatory, innate, and adaptive immune responses. The development of an effective vaccine could be a promising method for the control and prevention of disease in endemic areas. The purpose of this review is to highlight the importance of CCHF, its mode of transmission, the interaction of the virus with the hosts and ticks, immunopathogenesis, and advances in immunization.

Construction and evaluation of DNA vaccine encoding Crimean Congo hemorrhagic fever virus nucleocapsid protein, glycoprotein N-terminal and C-terminal fused with LAMP1

Crimean-Congo hemorrhagic fever virus (CCHFV) can cause severe hemorrhagic fever in humans and is mainly transmitted by ticks. There is no effective vaccine for Crimean-Congo hemorrhagic fever (CCHF) at present. We developed three DNA vaccines encoding CCHFV nucleocapsid protein (NP), glycoprotein N-terminal (Gn) and C-terminal (Gc) fused with lysosome-associated membrane protein 1 (LAMP1) and assessed their immunogenicity and protective efficacy in a human MHC (HLA-A11/DR1) transgenic mouse model. The mice that were vaccinated three times with pVAX-LAMP1-CCHFV-NP induced balanced Th1 and Th2 responses and could most effectively protect mice from CCHFV transcription and entry-competent virus-like particles (tecVLPs) infection. The mice vaccinated with pVAX-LAMP1-CCHFV-Gc mainly elicited specific anti-Gc and neutralizing antibodies and provided a certain protection from CCHFV tecVLPs infection, but the protective efficacy was less than that of pVAX-LAMP1-CCHFV-NP. The mice vaccinated with pVAX-LAMP1-CCHFV-Gn only elicited specific anti-Gn antibodies and could not provide sufficient protection from CCHFV tecVLPs infection. These results suggest that pVAX-LAMP1-CCHFV-NP would be a potential and powerful candidate vaccine for CCHFV.

Vaccine efficacy trials for Crimean-Congo haemorrhagic fever: Insights from modelling different epidemiological settings

BACKGROUND

Crimean-Congo haemorrhagic fever (CCHF) is a priority emerging pathogen for which a licensed vaccine is not yet available. We aim to assess the feasibility of conducting phase III vaccine efficacy trials and the role of varying transmission dynamics.

METHODS

We calibrate models of CCHF virus (CCHFV) transmission among livestock and spillover to humans in endemic areas in Afghanistan, Turkey and South Africa. We propose an individual randomised controlled trial targeted to high-risk population, and use the calibrated models to simulate trial cohorts to estimate the minimum necessary number of cases (trial endpoints) to analyse a vaccine with a minimum efficacy of 60%, under different conditions of sample size and follow-up time in the three selected settings.

RESULTS

A mean follow-up of 160,000 person-month (75,000-550,000) would be necessary to accrue the required 150 trial endpoints for a target vaccine efficacy of 60 % and clinically defined endpoint, in a setting like Herat, Afghanistan. For Turkey, the same would be achieved with a mean follow-up of 175,000 person-month (50,000-350,000). The results suggest that for South Africa the low endemic transmission levels will not permit achieving the necessary conditions for conducting this trial within a realistic follow-up time. In the scenario of CCHFV vaccine trial designed to capture infection as opposed to clinical case as a trial endpoint, the required person-months is reduced by 70 % to 80 % in Afghanistan and Turkey, and in South Africa, a trial becomes feasible for a large number of person-months of follow-up (>600,000). Increased expected vaccine efficacy > 60 % will reduce the required number of trial endpoints and thus the sample size and follow-time in phase III trials.

CONCLUSIONS

Underlying endemic transmission levels will play a central role in defining the feasibility of phase III vaccine efficacy trials. Endemic settings in Afghanistan and Turkey offer conditions under which such studies could feasibly be conducted.

Replicating RNA vaccination elicits an unexpected immune response that efficiently protects mice against lethal Crimean-Congo hemorrhagic fever virus challenge

Background

Crimean-Congo hemorrhagic fever virus is the cause of a severe hemorrhagic fever with cases reported throughout a wide-geographic region. Spread by the bite of infected ticks, contact with infected livestock or in the health care setting, disease begins as a non-specific febrile illness that can rapidly progress to hemorrhagic manifestations. Currently, there are no approved vaccines and antivirals such as ribavirin have unclear efficacy. Thus treatment is mostly limited to supportive care.

Methods

In this report we evaluated an alphavirus-based replicon RNA vaccine expressing either the CCHFV nucleoprotein or glycoprotein precursor in a stringent, heterologous lethal challenge mouse model.

Findings

Vaccination with the RNA expressing the nucleoprotein alone could confer complete protection against clinical disease, but vaccination with a combination of both the nucleoprotein and glycoprotein precursor afforded robust protection against disease and viral replication. Protection from lethal challenge required as little as a single immunization with 100ng of RNA. Unexpectedly, analysis of the immune responses elicited by the vaccine components showed that vaccination resulted in antibodies against the internal viral nucleoprotein and cellular immunity against the virion-exposed glycoproteins.

Interpretation

Cumulatively this vaccine conferred robust protection against Crimean-Congo hemorrhagic fever virus and supports continued development of this vaccine candidate.

Funding

This research was supported by the Intramural Research Program of the NIAID/NIH and HDT Bio.

GEM-PA-Based Subunit Vaccines of Crimean Congo Hemor-Rhagic Fever Induces Systemic Immune Responses in Mice

The Crimean Congo Hemorrhagic Fever Virus (CCHFV) is a tick-borne bunyavirus of the Narovirus genus, which is the causative agent of Crimean Congo Hemorrhagic Fever (CCHF). CCHF is endemic in Africa, the Middle East, Eastern Europe and Asia, with a high case-fatality rate of up to 50% in humans. Currently, there are no approved vaccines or effective therapies available for CCHF. The GEM-PA is a safe, versatile and effective carrier system, which offers a cost-efficient, high-throughput platform for recovery and purification of subunit proteins for vaccines. In the present study, based on a GEM-PA surface display system, a GEM-PA based vaccine expressing three subunit vaccine candidates (G-GP, including G-eG_N, G-eG_C and G-NAb) of CCHFV was developed, displaying the ectodomains of the structural glycoproteins eG_N, eG_C and NAb, respectively. According to the immunological assays including indirect-ELISA, a micro-neutralization test of pseudo-virus and ELISpot, 5 μg GPBLP₃ combined with Montanide ISA 201VG plus Poly (I:C) adjuvant (A-G-GP-5 μg) elicited GP-specific humoral and cellular immunity in BALB/c mice after three vaccinations via subcutaneous injection (s.c.). The consistent data between IgG subtype and cytokine detection, ELISpot and cytokine detection indicated balanced Th1 and Th2 responses, of which G-eG_N vaccines could elicit a stronger T-cell response post-vaccination, respectively. Moreover, all three vaccine candidates elicited high TNF-α, IL-6, and IL-10 cytokine levels in the supernatant of stimulated splenocytes in vitro. However, the neutralizing antibody (nAb) was only detected in A-G-eG_C and A-G-eG_C vaccination groups with the highest neutralizing titer of 128, suggesting that G-eG_C could elicit a stronger humoral immune response. In conclusion, the GEM-PA surface display system could provide an efficient and convenient purification method for CCHFV subunit antigens, and the G-GP subunit vaccine candidates will be promising against CCHFV infections with excellent immunogenicity.

Transmission dynamics and vaccination strategies for Crimean-Congo haemorrhagic fever virus in Afghanistan: A modelling study

Background

Crimean-Congo haemorrhagic fever virus (CCHFV) is a highly pathogenic virus for which a safe and effective vaccine is not yet available, despite being considered a priority emerging pathogen. Understanding transmission patterns and the use of potential effective vaccines are central elements of the future plan against this infection.

Methods

We developed a series of models of transmission amongst livestock, and spillover infection into humans. We use real-world human and animal data from a CCHFV endemic area in Afghanistan (Herat) to calibrate our models. We assess the value of environmental drivers as proxy indicators of vector activity, and select the best model using deviance information criteria. Finally we assess the impact of vaccination by simulating campaigns targeted to humans or livestock, and to high-risk subpopulations (i.e, farmers).

Findings

Saturation deficit is the indicator that better explains tick activity trends in Herat. Recent increments in reported CCHFV cases in this area are more likely explained by increased surveillance capacity instead of changes in the background transmission dynamics. Modelling suggests that clinical cases only represent 31% (95% CrI 28%-33%) of total infections in this area. Vaccination campaigns targeting humans would result in a much larger impact than livestock vaccination (266 vs 31 clinical cases averted respectively) and a more efficient option when assessed in courses per case averted (35 vs 431 respectively). Targeted vaccination of farmers is impactful and more efficient, resulting in 19 courses per case averted (95% CrI 7–62) compared to targeting the general population (35 courses 95% CrI 16–107)

Conclusions

CCHFV is endemic in Herat, and transmission cycles are well predicted by environmental drivers like saturation deficit. Vaccinating humans is likely to be more efficient and impactful than animals, and importantly targeted interventions to high risk groups like farmers can offer a more efficient approach to vaccine roll-out.

Crimean-Congo haemorrhagic fever virus (CCHF) is an understudied emerging pathogen and the cause of increasingly frequent outbreaks of haemorrhagic fever in humans in several parts of the world. Here we bring together an important body of work in different aspects of the ecology and epidemiology of CCHF to shed light on its transmission dynamics into humans and the role of environmental drivers. These results show that over the years an endemic pattern of CCHFV transmission has been established within livestock, and the frequency of human cases mirrors the seasonal pattern of livestock transmission. Our analysis further suggests that an important fraction of cases in humans might be subclinical, and the volume of transmission into humans might be much larger than previously thought. We examine the potential impact of vaccination, which suggest that not only human vaccination could be more impactful than animal vaccination, but also that targeted strategies in human high risk groups could be very effective. Our results raise important insights for future vaccine development and important questions on the optimal conditions for conducting Phase III vaccine trials in humans.

Immunobiology of Crimean-Congo hemorrhagic fever

Human infection with Crimean-Congo hemorrhagic fever virus (CCHFV), a tick-borne pathogen in the family Nairoviridae, can result in a spectrum of outcomes, ranging from asymptomatic infection through mild clinical signs to severe or fatal disease. Studies of CCHFV immunobiology have investigated the relationship between innate and adaptive immune responses with disease severity, attempting to elucidate factors associated with differential outcomes. In this article, we begin by highlighting unanswered questions, then review current efforts to answer them. We discuss in detail current clinical studies and research in laboratory animals on CCHF, including immune targets of infection and adaptive and innate immune responses. We summarize data about the role of the immune response in natural infections of animals and humans and experimental studies in vitro and in vivo and from evaluating immune-based therapies and vaccines, and present recommendations for future research.

Nucleoside-Modified mRNA Vaccines Protect IFNAR-/- Mice against Crimean-Congo Hemorrhagic Fever Virus Infection

Crimean-Congo hemorrhagic fever (CCHF), caused by Crimean-Congo hemorrhagic fever virus (CCHFV), is on the World Health Organizations' list of prioritized diseases and pathogens. With global distribution, high fatality rate, and no approved vaccine or effective treatment, CCHF constitutes a threat against global health. In the current study, we demonstrate that vaccination with nucleoside-modified mRNA-lipid nanoparticles (mRNA-LNP), encoding for the CCHFV nucleoprotein (N) or glycoproteins (GcGn) protect IFNAR-/- mice against lethal CCHFV infection. In addition, we found that both mRNA-LNP induced strong humoral and cellular immune responses in IFNAR-/- and immunocompetent mice and that neutralizing antibodies are not necessary for protection. When evaluating immune responses induced by immunization including CCHFV Gc and Gn antigens, we found the Gc protein to be more immunogenic compared with the Gn protein. Hepatic injury is prevalent in CCHF and contributes to the severity and mortality of the disease in humans. Thus, to understand the immune response in the liver after infection and the potential effect of the vaccine, we performed a proteomic analysis on liver samples from vaccinated and control mice after CCHFV infection. Similar to observations in humans, vaccination affected the metabolic pathways. In conclusion, this study shows that a CCHFV mRNA-LNP vaccine, based on viral nucleo- or glycoproteins, mediate protection against CCHFV induced disease. Consequently, genetic immunization is an attractive approach to prevent disease caused by CCHFV and we believe we have necessary evidence to bring this vaccine platform to the next step in the development of a vaccine against CCHFV infection. IMPORTANCE Crimean-Congo hemorrhagic fever virus (CCHFV) is a zoonotic pathogen causing Crimean-Congo hemorrhagic fever (CCHF), a severe fever disease. CCHFV has a wide distribution and is endemic in several areas around the world. Cases of CCHF are also being reported in new areas, indicating an expansion of the disease, which is of high concern. Dispersion of the disease, high fatality rate, and no approved vaccine makes CCHF a threat to global health. The development of a vaccine is thus of great importance. Here we show 100% protection against lethal CCHFV infection in mice immunized with mRNA-LNP encoding for different CCHFV proteins. The vaccination showed both robust humoral and cellular immunity. mRNA-LNP vaccines combine the ability to induce an effective immune response, the safety of a transient carrier, and the flexibility of genetic vaccines. This and our results from the current study support the development of a mRNA-LNP based vaccine against CCHFV.

Immune responses in multiple hosts to Nucleocapsid Protein (NP) of Crimean-Congo Hemorrhagic Fever Virus (CCHFV)

In 2019, the World Health Organization declared 3 billion to be at risk of developing Crimean Congo Hemorrhagic Fever (CCHF). The causative agent of this deadly infection is CCHFV. The data related to the biology and immunology of CCHFV are rather scarce. Due to its indispensable roles in the viral life cycle, NP becomes a logical target for detailed viral immunology studies. In this study, humoral immunity to NP was investigated in CCHF survivors, as well as in immunized mice and rabbits. Abundant antibody response against NP was demonstrated both during natural infection in humans and following experimental immunizations in mice and rabbits. Also, cellular immune responses to recombinant NP (rNP) was detected in multispecies. This study represents the most comprehensive investigation on NP as an inducer of both humoral and cellular immunity in multiple hosts and proves that rNP is an excellent candidate warranting further immunological studies specifically on vaccine investigations.

Crimean Congo Hemorrhagic Fever Virus (CCHFV) is the most lethal human pathogen of medical importance after the dengue virus among arboviruses. The increasing geographic spread of Hyalomma ticks, which are responsible for viral transmission widespread, threatens billions of people. WHO currently declares the field of research on CCHFV as the second most urgently needed areas of investigations on emerging pathogens. About 10 to 40% of those infected with the virus lose their life due to the rapidly developing severe clinical manifestations. Pandemic potential and the lack of any approved treatment or vaccine make raise the studies on CCHFV as critical. The studies on CCHFV are challenging due to the necessities of BSL-4 facilities and the immunological characterization of individual structural proteins will lay the groundwork for the steps to be taken to treat and prevent this emerging disease. As is known from other RNA viruses, nucleoprotein (NP) has crucial roles in the viral life cycle, both in viral replication and transcription and in the formation of the virion structure. So far, detailed and comprehensive immunological characterizations on NP in multiple are not undertaken. Our study was set out to embark such detailed investigation. The strong humoral and cellular immune response to NP demonstrated by this study indicates that NP might be an excellent candidate for future scrutinies on vaccines and diagnostic reagents.

Development of a protective inactivated vaccine against Crimean-Congo hemorrhagic fever infection

Crimean-Congo hemorrhagic fever (CCHF) is an emerging zoonotic infectious disease caused by Crimean-Congo hemorrhagic fever virus (CCHFV). The first clinical CCHF infection was described in 1944 in the Crimean Peninsula, exclusively in humans, with case-fatality rates exceeding 30%. The increasing number of cases, high mortality rate, and lack of effective therapy make CCHF a serious threat to public health and a potential bioterrorism agent. The present study evaluated the development, immunogenicity, and immune response durations for cell-culture-derived inactivated vaccine (CCVax) formulations in comparison with those of mouse-brain-derived vaccine (MBVax) formulations. In this study, the Kelkit06 CCHF virus strain was propagated in both suckling mice and Vero E6 cells, and purified with a sucrose gradient. Formalin-inactivated vaccine candidates were formulated at various doses [low dose (LD), 5 μg; medium dose (MD), 10 μg; high dose (HD), 20 μg)] and mixed with an alum adjuvant. BALB/c mice received the same doses of the vaccine formulations three times at 3-week intervals. The humoral endpoint IgG responses were evaluated and compared for the MBVax and CCVax treatments. The duration of the presence of IgG and neutralizing antibody (Ab) titers was evaluated and compared until up to 1 year after immunization. The humoral IgG responses indicated that the CCVax and MBVax candidates enhanced the IgG endpoint titers in a dose-dependent manner, which were induced more strongly in all the CCVax groups than in the MBVax mice. The fold changes in neutralizing Ab levels were also found to be higher in the CCVax groups: between 2- and 7.6-fold after the second week of the last immunization. The neutralization titers peaked 4 months after immunization in all the vaccine-receiving groups, but these were still comparable at the end of the first year. The CCVax formulations induced higher IgG and neutralizing Ab titers at all the measured time points. In this study, we showed that cell-culture-purified and formalin-inactivated vaccine candidates induced strong and robust immunity in vaccinated mice dose-dependently, more so than mouse-brain-derived vaccines.

Development of a BoHV-4 viral vector expressing tgD of BoHV-1 and evaluation of its immunogenicity in mouse model

In recent years, Bovine herpesvirus 4 (BoHV-4) has emerged as an attractive gene delivery viral vector, mainly for vaccination purposes in the veterinary field. In the present study, a new infectious clone of the BoHV-4 genome carrying a bacterial artificial chromosome vector (BoHV-4-BAC) was developed by homologous recombination in mammalian cell culture and bacterial systems, and exploited to express a truncated form of glycoprotein D (tgD) of Bovine herpesvirus 1 (BoHV-1) (BoHV-4-tgD∆TK) as a vaccine candidate. This construct's immunogenicity was compared to a DNA vector expressing the same antigen (pC-tgD) in a BALB/c mouse model. After the mice were immunized, total and specific antibody responses, cytokine responses, total splenocyte cells proliferation/cytotoxicity, and virus neutralization assays were conducted to analyze the immune response elicited by both constructs. Mice from both vaccine groups developed significant humoral and cellular immune responses after a booster dose regime was conducted on day 28 post-injection. In almost all immunological assays, BoHV-4-tgDΔTK induced as high an immune response as pC-tgD. In both vaccine constructs, neutralizing antibodies were a significant determining factor in protection against BoHV-1, even after the first injection. We conclude that a BoHV-4-based viral vector offers an effective immunization strategy as an alternative to DNA-based immunization platforms, at least to combat BoHV-1.

The Integration of Human and Veterinary Studies for Better Understanding and Management of Crimean-Congo Haemorrhagic Fever

Outbreaks that occur as a result of zoonotic spillover from an animal reservoir continue to highlight the importance of studying the disease interface between species. One Health approaches recognise the interdependence of human and animal health and the environmental interplay. Improving the understanding and prevention of zoonotic diseases may be achieved through greater consideration of these relationships, potentially leading to better health outcomes across species. In this review, special emphasis is given on the emerging and outbreak pathogen Crimean-Congo Haemorrhagic Fever virus (CCHFV) that can cause severe disease in humans. We discuss the efforts undertaken to better understand CCHF and the importance of integrating veterinary and human research for this pathogen. Furthermore, we consider the use of closely related nairoviruses to model human disease caused by CCHFV. We discuss intervention approaches with potential application for managing CCHFV spread, and how this concept may benefit both animal and human health.

A CCHFV DNA vaccine protects against heterologous challenge and establishes GP38 as immunorelevant in mice

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus that causes severe hemorrhagic fever disease in humans. Currently, no licensed CCHF vaccines exist, and the protective epitopes remain unclear. Previously, we tested a DNA vaccine expressing the M-segment glycoprotein precursor gene of the laboratory CCHFV strain IbAr 10200 (CCHFV-M₁₀₂₀₀). CCHFV-M₁₀₂₀₀ provided >60% protection against homologous CCHFV-IbAr 10200 challenge in mice. Here, we report that increasing the dose of CCHFV-M₁₀₂₀₀ provides complete protection from homologous CCHFV challenge in mice, and significant (80%) protection from challenge with the clinically relevant heterologous strain CCHFV-Afg09-2990. We also report complete protection from CCHFV-Afg09-2990 challenge following vaccination with a CCHFV-Afg09-2990 M-segment DNA vaccine (CCHFV-M_Afg09). Finally, we show that the non-structural M-segment protein, GP38, influences CCHF vaccine immunogenicity and provides significant protection from homologous CCHFV challenge. Our results demonstrate that M-segment DNA vaccines elicit protective CCHF immunity and further illustrate the immunorelevance of GP38.

Evaluation of the cell culture based and the mouse brain derived inactivated vaccines against Crimean-Congo hemorrhagic fever virus in transiently immune-suppressed (IS) mouse model

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus in the Nairoviridae family within the Bunyavirales order of viruses. Crimean-Congo hemorrhagic fever (CCHF) is the most widespread among tick-borne human viral diseases. It is endemic in many areas of Africa, Asia, the Middle East, in the Balkans, Russia and countries of the former Soviet Union. The confirmed CCHF cases were seen in Spain in 2016 to signify expansion of the virus into new geographical areas. CCHFV causes a viral human disease characterized by sudden onset of fever, headache, abdominal pain, nausea, hypotension, hemorrhage, and hepatic dysfunction with fatality rates up to 30%. Currently, there are no spesific treatments or licensed vaccines available for CCHFV. The absence of a susceptible animal model for CCHFV infection was severely hindered work on the development of vaccines. However, several animal models of CCHFV infection have been recently developed and used to assess vaccine efficacy. In this study, we have used the transiently immune-suppressed (IS) mouse model that MAb-5A3 was used to block IFN-I signaling in immune intact, wild-type mice at the time of CCHFV infection to evaluate the immune response and efficacy of the cell culture based and the mouse brain derived inactivated vaccines against CCHFV. Both vaccine preparations have provided complete protection but the cell culture based vaccine more effectively induced to CCFHV spesific antibodies and T cell responses. This is the first comparison of the cell culture based and the mouse brain derived vaccines for assessing the protective efficacy and the immunogenicity in the IS mouse CCHFV model.

Optimization of an mRNA vaccine assisted with cyclodextrin-polyethyleneimine conjugates

Messenger RNA (mRNA) vaccines have attracted great interest in recent years due to their high potency, safety profile, and potential of rapid development. Although a number of mRNA vaccines have entered clinical trials, there remain several challenges. Inefficient in vivo delivery of mRNA is the foremost one. Here we synthesized a conjugate composed of β-cyclodextrin (β-CD) and branched polyethyleneimine (molecular weight 2 kDa, bPEI2k) to deliver an mRNA vaccine. The CD-PEI (CP) conjugate helped the encapsulated mRNA molecules pass through the plasma membranes and escape from the endosomes, which consequently ensured high transfection efficiency. On this basis, we optimized several structural elements of mRNA molecules via synthesizing an advanced cap structure and incorporating untranslated regions (UTRs) and an extended poly(A) tail into the sequence. These modifications led to a higher expression level of encoded proteins, which was expected to induce potent immune responses with a relatively low dosage. We also investigated the relevance of the administration route to the immune responses induced by CP-assisted mRNA vaccines with in vivo evidence, providing a basis for the selection of optimum administration route in specific cases. This CP-based mRNA vaccine platform, with an optimized mRNA structure and administrated in a most appropriate route, holds a promise to be applied to specific antigens in the future. Graphical abstract.

Crimean-Congo Hemorrhagic Fever Virus: Advances in Vaccine Development

Crimean-Congo hemorrhagic fever (CCHF) is a severe human disease with mortality rates of up to 30%. The disease is widespread in Africa, Asia, the Middle East and Eastern Europe. The last few years have seen disease emergence in Spain for the first time and disease re-emergence in other regions of the world after periods of inactivity. Factors, such as climate change, movement of infected ticks, animals, and changes in human activity, are likely to broaden endemic foci. There are therefore concerns that CCHF might emerge in currently nonendemic regions. The absence of approved vaccines or therapies heightens these concerns; thus Crimean-Congo hemorrhagic fever virus (CCHFV) is listed by the World Health Organization as a priority organism. However, the current sporadic nature of CCHF cases may call for targeted vaccination of risk groups as opposed to mass vaccinations. CCHF vaccine development has accelerated in recent years, partly because of the discovery of CCHF animal models. In this review, we discuss CCHF risk groups who are most likely to benefit from vaccine development, the merits and demerits of available CCHF animal models, and the various approaches which have been explored for CCHF vaccine development. Lastly, we present concluding remarks and research areas which can be further explored to enhance the available CCHFV vaccine data.

The use of mice lacking type I or both type I and type II interferon responses in research on hemorrhagic fever viruses. Part 2: Vaccine efficacy studies

For more than 20 years, researchers have used laboratory mice lacking type I or both type I and II interferon (IFN) responses to study high-containment viruses that cause hemorrhagic fevers (HF) in humans. With the exception of Rift Valley fever virus, agents that cause viral HF in humans, such as Ebola and Lassa virus, do not cause disease in mature immunocompetent mice. In contrast, IFN-deficient mice typically develop severe or fatal disease when inoculated with these agents. The sensitivity of IFN-deficient mice to disease has led to their widespread use in biocontainment laboratories to assess the efficacy of novel vaccines against HF viruses, often without considering whether adaptive immune responses in IFN-deficient mice accurately mirror those in immunocompetent humans. Failure to recognize these questions may lead to inappropriate expectations of the predictive value of mouse experiments. In two invited articles, we investigate these questions. The present article reviews the use of IFN-deficient mice for assessing novel vaccines against HF viruses, including Ebola, Lassa, Crimean-Congo hemorrhagic fever and Rift Valley fever viruses. A companion paper examines the general question of how the lack of IFN signaling may affect adaptive immune responses and the outcome of vaccine studies in mice.