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

Reverse Genetics System for Crimean-Congo Hemorrhagic Fever Virus

Reverse genetic systems are powerful tools in molecular virology that allow the generation of infectious recombinant virus and the manipulation of viral genomes. Reverse genetic systems enable the incorporation of reporter genes, facilitating many virological assays, including high-throughput screening. Additionally, reverse genetic systems can be used to introduce targeted mutations into the viral genome, allowing investigations of viral genetic elements and protein functions in virus pathogenesis and biology. Here we describe in detail the materials and methods required for the Crimean-Congo hemorrhagic fever virus (CCHFV) reverse genetic system. This system can be used to generate complete infectious recombinant virus, and virus-like replicon particles (VRPs) lacking the M segment but complemented with an exogenous source of glycoprotein precursor (GPC); resulting in single-round replicon particles that can be used to study components of the viral replicative cycle at a lower biosafety level.

Crimean-Congo hemorrhagic fever virus replicon particle vaccine is safe and elicits functional, non-neutralizing anti-nucleoprotein antibodies and T cell activation in rhesus macaques

Advancement of vaccine candidates that demonstrate protective efficacy in screening studies necessitates detailed safety and immunogenicity investigations in pre-clinical models. A non-spreading Crimean-Congo hemorrhagic fever virus (CCHFV) viral replicon particle (VRP) vaccine was developed for single-dose administration to protect against disease. To date, several studies have supported safety, immunogenicity, and efficacy of the CCHF VRP in multiple highly sensitive murine models of lethal disease, but the VRP had yet to be evaluated in large animals. Here, we performed studies in non-human primates to further evaluate clinical utility of the VRP vaccine. Twelve adult male and female rhesus macaques were vaccinated intramuscularly and clinical monitoring was performed daily for 28 days. At 3, 7, 14, 21, and 28 days post vaccination, animals were sedated for more detailed clinical assessment; for quantification of vaccine presence in blood and mucosal samples; and for evaluation of hematology, plasma inflammatory markers, and immunogenicity. Consistent with findings in mice, vaccination was well tolerated, with no clinical alterations nor indication of vaccine spread or shedding. In addition, vaccination induced both humoral and cell-mediated responses, with immune profile and kinetics also corroborating data from small animal models. These studies provide key data in non-human primates further supporting development of the VRP for human clinical use.

Replicating RNA vaccine confers durable immunity against Crimean Congo hemorrhagic fever virus challenge in mice

Spread by Hyalomma genus ticks, Crimean-Congo hemorrhagic fever virus (CCHFV) causes a severe hemorrhagic disease endemic throughout Southern and Eastern Europe, Asia, and Africa. To date, there are no widely approved vaccines for CCHFV and treatment for disease is largely supportive. Due to this lack of intervention, the WHO lists CCHFV as a high-priority pathogen. Recently, we described a highly efficacious self-replicating RNA vaccine which is protective against CCHFV disease in mice and non-human primates. This vaccine induces high titers of non-neutralizing anti-nucleoprotein (NP) antibodies and a robust T-cell response against the viral glycoprotein. Here, we assess the durability of this vaccine in mice by monitoring the immunogenicity and efficacy of this vaccine up to 1 year post vaccination. We found that while glycoprotein-specific T-cell responses and anti-NP antibody titers waned over time, mice remained protected against lethal CCHFV challenge for at least 1 year post vaccination.

Crimean-Congo haemorrhagic fever (CCHF): present and future therapeutic armamentarium

Crimean-Congo haemorrhagic fever (CCHF) is an emerging severe tick-borne illness. The expanding habitat of Hyalomma ticks, coupled with migratory birds harbouring CCHF-infected ticks, contributes to an increasing number of potential hosts. The seroprevalence of anti-CCHF virus antibodies in livestock is approximately one-quarter, with a noticeable upward trend in recent years. The management of CCHF patients predominantly relies on supportive therapy, although a potential arsenal of antivirals, convalescent and hyperimmune plasma, monoclonal antibodies, and vaccines exists, both currently and in the future. This review aims to critically examine the current therapeutic approaches to managing CCHF, highlighting both the potential and limitations of existing treatments, and identifying future directions for improving patient outcomes.

Interventions for the control of Crimean-Congo hemorrhagic fever and tick vectors

Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic disease associated with its principal tick vector, Hyalomma spp. with increasing fatal incidence worldwide. Accordingly, CCHF is a World Health Organization-prioritized disease with the absence of effective preventive interventions and approved vaccines or effective treatments. This perspective raised from a multidisciplinary gap analysis considering a One Health approach beneficial for human and animal health and the environment exploring international collaborations, gaps and recommendations.

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.

Cellular immunity to nucleoproteins (NP) of Crimean-Congo hemorrhagic fever virus (CCHFV) and Hazara Virus (HAZV)

Crimean-Congo Hemorrhagic Fever Virus (CCHFV) is a globally significant vector-borne pathogen with no internationally-licensed preventative and therapeutic interventions. Hazara virus (HAZV), on the other hand, a related Orthonairovirus, has not been reported as a human pathogen. HAZV has been proposed as a surrogate model for studying CCHFV, bisosafety level 4 (BSL-4) agent. Previously, we investigated the humoral immune responses between NPs of these viruses and in this study, we extended the scrutiny to cellular immune responses elicited by NPs of CCHFV and HAZV. Here, mice were immunized with recombinant CCHFV NP and HAZV NP to evaluate the correlates of cell-mediated immunity (CMI). Delayed-type hypersensitivity (DTH) responses were assessed by challenging immunized mice with CCHFV-rNP or HAZV-rNP on the footpad and lymphocyte proliferation assays (LPAs) were performed by stimulating splenocytes in vitro with CCHFV-rNP or HAZV-rNP to compare cellular immune responses. In all test groups, strong DTH and LPA responses were detected against homologous and heterologous challenging antigens. To assess the cytokine response, an RT-qPCR -specific for cytokine mRNAs was utilized. Interestingly, CCHFV NP stimulated groups exhibited a significantly elevated mRNA level of interleukin 17 A (IL-17) compared to HAZV NP, indicating a notable difference in immune responses. This study presents comparison between CMI elicited by NPs of CCHFV and HAZV and contributes to the understanding of a highly pathogenic virus, particularly in the context of the declaration of CCHFV by World Health Organization's (WHO) as a major viral threat to the world.

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.

Replicon particle vaccination induces non-neutralizing anti-nucleoprotein antibody-mediated control of Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever virus (CCHFV) can cause severe human disease and is considered a WHO priority pathogen due to the lack of efficacious vaccines and antivirals. A CCHF virus replicon particle (VRP) has previously shown protective efficacy in a lethal Ifnar-/- mouse model when administered as a single dose at least 3 days prior to challenge. Here, we determine that non-specific immune responses are not sufficient to confer short-term protection, since Lassa virus VRP vaccination 3 days prior to CCHFV challenge was not protective. We also investigate how CCHF VRP vaccination confers protective efficacy by examining viral kinetics, histopathology, clinical analytes and immunity early after challenge (3 and 6 days post infection) and compare to unvaccinated controls. We characterize how these effects differ based on vaccination period and correspond to previously reported CCHF VRP-mediated protection. Vaccinating Ifnar-/- mice with CCHF VRP 28, 14, 7, or 3 days prior to challenge, all known to confer complete protection, significantly reduced CCHFV viral load, mucosal shedding, and markers of clinical disease, with greater reductions associated with longer vaccination periods. Interestingly, there were no significant differences in innate immune responses, T cell activation, or antibody titers after challenge between groups of mice vaccinated a week or more before challenge, but higher anti-NP antibody avidity and effector function (ADCD) were positively associated with longer vaccination periods. These findings support the importance of antibody-mediated responses in VRP vaccine-mediated protection against CCHFV infection.

Third International Conference on Crimean-Congo Hemorrhagic Fever in Thessaloniki, Greece, September 19-21, 2023

The Third International Conference on Crimean-Congo Hemorrhagic Fever (CCHF) was held in Thessaloniki, Greece, September 19-21, 2023, bringing together a diverse group of international partners, including public health professionals, clinicians, ecologists, epidemiologists, immunologists, and virologists. The conference was attended by 118 participants representing 24 countries and the World Health Organization (WHO). Meeting sessions covered the epidemiology of CCHF in humans; Crimean-Congo hemorrhagic fever virus (CCHFV) in ticks; wild and domestic animal hosts; molecular virology; pathogenesis and animal models; immune response related to therapeutics; and CCHF prevention in humans. The concluding session focused on recent WHO recommendations regarding disease prevention, control strategies, and innovations against CCHFV outbreaks. This meeting report summarizes lectures by the invited speakers and highlights advances in the field.