A chimeric vesiculo/alphavirus is an effective alphavirus vaccine

Chikungunya virus and other emerging arthritogenic alphaviruses

Arthritogenic alphaviruses are arboviruses (arthropod-borne viruses) that are genetically and serologically related positive-strand RNA viruses and cause epidemics on a global scale. They are transmitted by mosquitoes and cause diseases in humans that are mainly characterized by fever and often debilitating, sometimes chronic polyarthralgia. At present, approved treatments or vaccines are not available for most arthritogenic alphaviruses, and recently licensed vaccines against chikungunya virus are awaiting implementation in endemic areas. Most arthritogenic alphaviruses are currently limited to specific geographic areas due to vector distributions and availability of amplifying hosts, but they pose a substantial risk of emergence in other regions. The exception is chikungunya virus, which has emerged repeatedly from Africa, established sustained and efficient transmission in urban areas (including in temperate climates) and has caused major epidemics across the world. In this Review, we highlight recent advances in our understanding of the transmission cycles of arthritogenic alphaviruses, their vectors, epidemiology, transmission dynamics, evolution, pathophysiology and immune responses. We also outline strategies and countermeasures to anticipate and mitigate the impact of arthritogenic alphaviruses on human health.

The Current Progress in the Quest for Vaccines Against the Semliki Forest Virus Complex

The Semliki Forest virus (SFV) complex comprises of arboviruses that are transmitted by arthropod vectors and cause acute febrile illness in humans. In the last seven decades, re-emergence of these viruses has resulted in numerous outbreaks globally, affecting regions including Africa, Americas, Asia, Europe and the Caribbean. These viruses are transmitted to humans by the bite of infected mosquitoes. Symptoms of infection include high fever, severe joint pain, skin rash, muscle pain and headache. Fatal cases were reported, and mortality rate increased during the epidemic of these viruses. There is therefore a need to control the spread of these emerging arboviruses. Given that vaccination is one of the most effective ways to protect populations against viral outbreaks, efforts have been made to develop and test potential vaccine candidates. However, there are still no licensed vaccines available against the medically important viruses in the SFV complex. This review first summarizes the current knowledge of the SFV complex disease pathogenesis. Next, seven strategies that have been applied in vaccine development against these viruses are reviewed, indicating the immune response and efficacies of these vaccine candidates in in vivo models of infection. Finally, the more promising candidates that have entered clinical trials are discussed and insights into the future development of vaccines for viruses of the SFV complex are given.

Revolutionizing Chikungunya Vaccines: mRNA Breakthroughs With Molecular and Immune Simulations

With the ability to cause massive epidemics that have consequences on millions of individuals globally, the Chikungunya virus (CHIKV) emerges as a severe menace. Developing an effective vaccine is urgent as no effective therapeutics are available for such viral infections. Therefore, we designed a novel mRNA vaccine against CHIKV with a combination of highly antigenic and potential MHC-I, MHC-II, and B-cell epitopes from the structural polyprotein. The vaccine demonstrated well-characterized physicochemical properties, indicating its solubility and potential functional stability within the body (GRAVY score of -0.639). Structural analyses of the vaccine revealed a well-stabilized secondary and tertiary structure (Ramachandran score of 82.8% and a Z-score of -4.17). Docking studies of the vaccine with TLR-2 (-1027.7 KJ/mol) and TLR-4 (-1212.4 KJ/mol) exhibited significant affinity with detailed hydrogen bond interactions. Molecular dynamics simulations highlighted distinct conformational dynamics among the vaccine, "vaccine-TLR-2" and "vaccine-TLR-4" complexes. The vaccine's ability to elicit both innate and adaptive immune responses, including the presence of memory B-cells and T-cells, persistent B-cell immunity for a year, and the activation of TH cells leading to the release of IFN-γ and IL-2, has significant implications for its potential effectiveness. The CHIKV vaccine developed in this study shows promise as a potential candidate for future vaccine production against CHIKV, suggesting its suitability for further clinical advancement, including in vitro and in vivo experiments.

Vaccines Against Urban Epidemic Arboviruses: The State of the Art

Arboviruses represent a contemporary global challenge, prompting coordinated efforts from health organizations and governments worldwide. Dengue, chikungunya, and Zika viruses have become endemic in the tropics, resulting in the so-called "triple arbovirus epidemic". These viruses are transmitted typically through the bites of infected mosquitoes, especially A. aegypti and A. albopictus. These mosquito species are distributed across all continents and exhibit a high adaptive capacity in diverse environments. When combined with unplanned urbanization, uncontrolled population growth, and international travel-the so-called "triad of the modern world"-the maintenance and spread of these pathogens to new areas are favored. This review provides updated information on vaccine candidates targeting dengue, chikungunya, and Zika viruses. Additionally, we discuss the challenges, perspectives, and issues associated with their successful production, testing, and deployment within the context of public health.

A safe insect-based chikungunya fever vaccine affords rapid and durable protection in cynomolgus macaques

Eilat (EILV)/chikungunya virus (CHIKV), an insect-based chimeric alphavirus was previously reported to protect mice months after a single dose vaccination. The underlying mechanisms of host protection are not clearly defined. Here, we assessed the capacity of EILV/CHIKV to induce quick and durable protection in cynomolgus macaques. Both EILV/CHIKV and the live attenuated CHIKV 181/25 vaccine protected macaques from wild-type (WT) CHIKV infection 1 year after a single dose vaccination. Transcriptome and functional analyses reveal that EILV/CHIKV triggered T cell, memory B cell and antibody responses in a dose-dependent manner. EILV/CHIKV induced more robust, durable, and broader repertoire of CHIKV-specific T cell responses than CHIKV 181/25; whereas the latter group induced more durable memory B cells and comparable or higher CHIKV -specific neutralization and binding antibodies. EILV/CHIKV and an inactivated WT CHIKV protected macaques from WT CHIKV infection and CHIK fever (CHIKF) within 6 days post vaccination. Transcriptome analysis showed that the chimeric virus induced multiple innate immune pathways, including Toll-like receptor signaling, antigen presenting cell activation, and NK receptor signaling. EILV/CHIKV triggered quicker and more robust type I interferon and NK cell responses than the inactivated WT virus vaccine. Lastly, we developed a guinea pig sensitization model and demonstrated that the chimeric virus produced in insect cells, did not cause skin hypersensitivity reactions. Overall, EILV/CHIKV is safe, and confers rapid and long-lasting protection in cynomolgus macaques via preferential induction of robust innate immune signaling and superior T cell immunity.

A safe insect-based Chikungunya fever vaccine affords rapid and durable protection in cynomolgus macaques

Chikungunya virus (CHIKV), which induces chikungunya fever and chronic arthralgia, is an emerging public health concern. Safe and efficient vaccination strategies are needed to prevent or mitigate virus-associated acute and chronic morbidities for preparation of future outbreaks. Eilat (EILV)/CHIKV, a chimeric alphavirus which contains the structural proteins of CHIKV and the non-structural proteins of EILV, does not replicate in vertebrate cells. The chimeric virus was previously reported to induce protective adaptive immunity in mice. Here, we assessed the capacity of the virus to induce quick and durable protection in cynomolgus macaques. EILV/CHIKV protected macaques from wild-type (WT) CHIKV infection one year after a single dose vaccination. Transcriptome and in vitro functional analyses reveal that the chimeric virus triggered toll-like receptor signaling and T cell, memory B cell and antibody responses in a dose-dependent manner. Notably, EILV/CHIKV preferentially induced more durable, robust, and broader repertoire of CHIKV-specific T cell responses, compared to a live attenuated CHIKV 181/25 vaccine strain. The insect-based chimeric virus did not cause skin hypersensitivity reactions in guinea pigs sensitized to mosquito bites. Furthermore, EILV/CHIKV induced strong neutralization antibodies and protected cynomolgus macaques from WT CHIKV infection within six days post vaccination. Transcriptome analysis also suggest that the chimeric virus induction of multiple innate immune pathways, including Toll-like receptor signaling, type I IFN and IL-12 signaling, antigen presenting cell activation, and NK receptor signaling. Our findings suggest that EILV/CHIKV is a safe, highly efficacious vaccine, and provides both rapid and long-lasting protection in cynomolgus macaques.

Chikungunya fever

Chikungunya virus is widespread throughout the tropics, where it causes recurrent outbreaks of chikungunya fever. In recent years, outbreaks have afflicted populations in East and Central Africa, South America and Southeast Asia. The virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes. Chikungunya fever is characterized by severe arthralgia and myalgia that can persist for years and have considerable detrimental effects on health, quality of life and economic productivity. The effects of climate change as well as increased globalization of commerce and travel have led to growth of the habitat of Aedes mosquitoes. As a result, increasing numbers of people will be at risk of chikungunya fever in the coming years. In the absence of specific antiviral treatments and with vaccines still in development, surveillance and vector control are essential to suppress re-emergence and epidemics.

Chikungunya Virus: Priority Pathogen or Passing Trend?

Chikungunya virus (CHIKV) is considered a priority pathogen and a major threat to global health. While CHIKV infections may be asymptomatic, symptomatic patients can develop chikungunya fever (CHIKF) characterized by severe arthralgia which often transitions into incapacitating arthritis that could last for years and lead to significant loss in health-related quality of life. Yet, Chikungunya fever (CHIKF) remains a neglected tropical disease due to its complex epidemiology and the misrepresentation of its incidence and disease burden worldwide. Transmitted to humans by infected Aedes mosquitoes, CHIKV has dramatically expanded its geographic distribution to over 100 countries, causing large-scale outbreaks around the world and putting more than half of the population of the world at risk of infection. More than 50 years have passed since the first CHIKV vaccine was reported to be in development. Despite this, there is no licensed vaccine or antiviral treatments against CHIKV to date. In this review, we highlight the clinical relevance of developing chikungunya vaccines by discussing the poor understanding of long-term disease burden in CHIKV endemic countries, the complexity of CHIKV epidemiological surveillance, and emphasising the impact of the global emergence of CHIKV infections. Additionally, our review focuses on the recent progress of chikungunya vaccines in development, providing insight into the most advanced vaccine candidates in the pipeline and the potential implications of their roll-out.

Vaccine development for zoonotic viral diseases caused by positive‑sense single‑stranded RNA viruses belonging to the Coronaviridae and Togaviridae families (Review)

Outbreaks of zoonotic viral diseases pose a severe threat to public health and economies worldwide, with this currently being more prominent than it previously was human history. These emergency zoonotic diseases that originated and transmitted from vertebrates to humans have been estimated to account for approximately one billion cases of illness and have caused millions of deaths worldwide annually. The recent emergence of severe acute respiratory syndrome coronavirus-2 (coronavirus disease 2019) is an excellent example of the unpredictable public health threat causing a pandemic. The present review summarizes the literature data regarding the main vaccine developments in human clinical phase I, II and III trials against the zoonotic positive-sense single-stranded RNA viruses belonging to the Coronavirus and Alphavirus genera, including severe acute respiratory syndrome, Middle east respiratory syndrome, Venezuelan equine encephalitis virus, Semliki Forest virus, Ross River virus, Chikungunya virus and O'nyong-nyong virus. That there are neither vaccines nor effective antiviral drugs available against most of these viruses is undeniable. Therefore, new explosive outbreaks of these zoonotic viruses may surely be expected. The present comprehensive review provides an update on the status of vaccine development in different clinical trials against these viruses, as well as an overview of the present results of these trials.

Chikungunya Vaccine Candidates: Current Landscape and Future Prospects

Chikungunya virus (CHIKV) is an alphavirus that has spread globally in the last twenty years. Although mortality is rather low, infection can result in debilitating arthralgia that can persist for years. Unfortunately, no treatments or preventive vaccines are currently licensed against CHIKV infections. However, a large range of promising preclinical and clinical vaccine candidates have been developed during recent years. This review will give an introduction into the biology of CHIKV and the immune responses that are induced by infection, and will summarize CHIKV vaccine development.

Construction and Evaluation of Recombinant Adenovirus Candidate Vaccines for Chikungunya Virus

Chikungunya virus (CHIKV) is a mosquito-borne virus. The emergence of CHIKV infection has raised global concern, and there is a growing need to develop safe and effective vaccines. Here, adenovirus 5 was used as the vaccine vector to construct recombinant adenoviruses expressing CHIKV E2, E1, and E2-6K-E1, respectively. And then the immunogenicity and protective efficiency against CHIKV were evaluated in BALB/c mice. Compared to the ad-wt control group, all three vaccines elicited significant humoral and cellar immune responses. The levels of neutralizing antibodies in the rAd-CHIKV-E2-6K-E1 and rAd-CHIKV-E2 groups both reached 1:256, which were 3.2 times higher than those in the rAd-CHIKV-E1 group. Furthermore, the levels of lymphocyte proliferation in rAd-CHIKV-E2-6K-E1 group were the highest. Besides, the concentrations of IFN-γ and IL-4 in mice immunized with rAd-CHIKV-E2-6K-E1 were 1.37 and 1.20 times higher than those in ad-wt immunized mice, respectively. After the challenge, mice in the rAd-CHIKV-E2-6K-E1 and rAd-CHIKV-E2 groups lost 2% of their body weight compared with 5% in the ad-wt control group. And low viral loads were detected in the heart, kidney, and blood of mice immunized with rAd-CHIKV-E2-6K-E1 and rAd-CHIKV-E2 at 3–5 dpc, which decreased by 0.4–0.7 orders of magnitude compared with the ad-wt control. Overall, these data suggest that the recombinant adenovirus is a potential candidate vaccine against CHIKV.

The emerging roles of retromer and sorting nexins in the life cycle of viruses

Retromer and sorting nexins (SNXs) transport cargoes from endosomes to the trans-Golgi network or plasma membrane. Recent studies have unveiled the emerging roles for retromer and SNXs in the life cycle of viruses, including members of Coronaviridae, Flaviviridae and Retroviridae. Key components of retromer/SNXs, such as Vps35, Vps26, SNX5 and SNX27, can affect multiple steps of the viral life cycle, including facilitating the entry of viruses into cells, participating in viral replication, and promoting the assembly of virions. Here we present a comprehensive updated review on the interplay between retromer/SNXs and virus, which will shed mechanistic insights into controlling virus infection.

Insights into Antibody-Mediated Alphavirus Immunity and Vaccine Development Landscape

Alphaviruses are mosquito-borne pathogens distributed worldwide in tropical and temperate areas causing a wide range of symptoms ranging from inflammatory arthritis-like manifestations to the induction of encephalitis in humans. Historically, large outbreaks in susceptible populations have been recorded followed by the development of protective long-lasting antibody responses suggesting a potential advantageous role for a vaccine. Although the current understanding of alphavirus antibody-mediated immunity has been mainly gathered in natural and experimental settings of chikungunya virus (CHIKV) infection, little is known about the humoral responses triggered by other emerging alphaviruses. This knowledge is needed to improve serology-based diagnostic tests and the development of highly effective cross-protective vaccines. Here, we review the role of antibody-mediated immunity upon arthritogenic and neurotropic alphavirus infections, and the current research efforts for the development of vaccines as a tool to control future alphavirus outbreaks.

Designing multivalent immunogens for alphavirus vaccine optimization

There is a pressing need for vaccines against mosquito-borne alphaviruses such as Venezualen and eastern equine encephalitis viruses (VEEV, EEEV). We demonstrate an approach to vaccine development based on physicochemical properties (PCP) of amino acids to design a PCP-consensus sequence of the epitope-rich B domain of the VEEV major antigenic E2 protein. The consensus "spike" domain was incorporated into a live-attenuated VEEV vaccine candidate (ZPC/IRESv1). Mice inoculated with either ZPC/IRESv1 or the same virus containing the consensus E2 protein fragment (VEEVconE2) were protected against lethal challenge with VEEV strains ZPC-738 and 3908, and Mucambo virus (MUCV, related to VEEV), and had comparable neutralizing antibody titers against each virus. Both vaccines induced partial protection against Madariaga virus (MADV), a close relative of EEEV, lowering mortality from 60% to 20%. Thus PCP-consensus sequences can be integrated into a replicating virus that could, with further optimization, provide a broad-spectrum vaccine against encephalitic alphaviruses.

Chikungunya Virus Evades Antiviral CD8+ T Cell Responses To Establish Persistent Infection in Joint-Associated Tissues

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes explosive epidemics of a febrile illness characterized by debilitating arthralgia and arthritis that can endure for months to years following infection. In mouse models, CHIKV persists in joint tissues for weeks to months and is associated with chronic synovitis. Using a recombinant CHIKV strain encoding a CD8+ T cell receptor epitope from ovalbumin, as well as a viral peptide-specific major histocompatibility complex class I tetramer, we interrogated CD8+ T cell responses during CHIKV infection. Epitope-specific CD8+ T cells, which were reduced in Batf3-/- and Wdfy4-/- mice with known defects in antigen cross-presentation, accumulated in joint tissue and the spleen. Antigen-specific ex vivo restimulation assays and in vivo killing assays demonstrated that CD8+ T cells produce cytokine and have cytolytic activity. Despite the induction of a virus-specific CD8+ T cell response, the CHIKV burden in joint-associated tissues and the spleen were equivalent in wild-type (WT) and CD8α-/- mice during both the acute and the chronic phases of infection. In comparison, CD8+ T cells were essential for the control of acute and chronic lymphocytic choriomeningitis virus infection in the joint and spleen. Moreover, adoptive transfer of virus-specific effector CD8+ T cells or immunization with a vaccine that induces virus-specific effector CD8+ T cells prior to infection enhanced the clearance of CHIKV infection in the spleen but had a minimal impact on CHIKV infection in the joint. Collectively, these data suggest that CHIKV establishes and maintains a persistent infection in joint-associated tissue in part by evading CD8+ T cell immunity.IMPORTANCE CHIKV is a reemerging mosquito-transmitted virus that in the last decade has spread into Europe, Asia, the Pacific Region, and the Americas. Joint pain, swelling, and stiffness can endure for months to years after CHIKV infection, and epidemics have a severe economic impact. Elucidating the mechanisms by which CHIKV subverts antiviral immunity to establish and maintain a persistent infection may lead to the development of new therapeutic strategies against chronic CHIKV disease. In this study, we found that CHIKV establishes and maintains a persistent infection in joint-associated tissue in part by evading antiviral CD8+ T cell immunity. Thus, immunomodulatory therapies that improve CD8+ T cell immune surveillance and clearance of CHIKV infection could be a strategy for mitigating chronic CHIKV disease.

Current Efforts in the Development of Vaccines for the Prevention of Zika and Chikungunya Virus Infections

Arboviruses represent major challenges to public health, particularly in tropical, and subtropical regions, and a substantial risk to other parts of the world as respective vectors extend their habitats. In recent years, two viruses transmitted by Aedes mosquitoes, Chikungunya and Zika virus, have gathered increased interest. After decades of regionally constrained outbreaks, both viruses have recently caused explosive outbreaks on an unprecedented scale, causing immense suffering and massive economic burdens in affected regions. Chikungunya virus causes an acute febrile illness that often transitions into a chronic manifestation characterized by debilitating arthralgia and/or arthritis in a substantial subset of infected individuals. Zika infection frequently presents as a mild influenza-like illness, often subclinical, but can cause severe complications such as congenital malformations in pregnancy and neurological disorders, including Guillain-Barré syndrome. With no specific treatments or vaccines available, vector control remains the most effective measure to manage spread of these diseases. Given that both viruses cause antibody responses that confer long-term, possibly lifelong protection and that such responses are cross-protective against the various circulating genetic lineages, the development of Zika and Chikungunya vaccines represents a promising route for disease control. In this review we provide a brief overview on Zika and Chikungunya viruses, the etiology and epidemiology of the illnesses they cause and the host immune response against them, before summarizing past and current efforts to develop vaccines to alleviate the burden caused by these emerging diseases. The development of the urgently needed vaccines is hampered by several factors including the unpredictable epidemiology, feasibility of rapid clinical trial implementation during outbreaks and regulatory pathways. We will give an overview of the current developments.

Chikungunya: Epidemiology, Pathogenesis, Clinical Features, Management, and Prevention

Chikungunya, a zoonotic disease caused by the Chikungunya virus (CHIKV), is transmitted by infected Aedes spp mosquitoes. CHIKV has now spread to more than 100 countries and is listed on the WHO Blueprint priority pathogens. After an incubation period of 1 to 12 days, symptoms similar to other febrile infections appear, with a sudden onset of high fever, nausea, polyarthralgia, myalgia, widespread skin rash, and conjunctivitis. Serious complications include myocarditis, uveitis, retinitis, hepatitis, acute renal disease, severe bullous lesions, meningoencephalitis, Guillain-Barré syndrome, myelitis, and cranial nerve palsies. Treatment is supportive; there is no specific antiviral treatment and no effective vaccine.

Recent Progress in Vaccine Development Against Chikungunya Virus

Chikungunya fever (CHIKF) is an acute infectious disease that is mediated by the mosquito-transmitted chikungunya virus (CHIKV). People infected with CHIKV may experience high fever, severe joint pain, skin rash, and headache. In recent years, this disease has become a global public health problem. However, there is no licensed vaccine available for CHIKV. Accumulating research data have provided novel approaches and new directions for the development of CHIKV vaccines. Our review focuses on recent progress in CHIKV vaccine studies. The potential vaccine candidates are classified into seven types: inactivated vaccine, subunit vaccine, live-attenuated vaccine, recombinant virus-vectored vaccine, virus-like particle vaccine, chimeric vaccine, and nucleic acid vaccine. These studies will provide important insights into the future development of CHIKV vaccines.

Human monoclonal antibodies against chikungunya virus target multiple distinct epitopes in the E1 and E2 glycoproteins

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes persistent arthritis in a subset of human patients. We report the isolation and functional characterization of monoclonal antibodies (mAbs) from two patients infected with CHIKV in the Dominican Republic. Single B cell sorting yielded a panel of 46 human mAbs of diverse germline lineages that targeted epitopes within the E1 or E2 glycoproteins. MAbs that recognized either E1 or E2 proteins exhibited neutralizing activity. Viral escape mutations localized the binding epitopes for two E1 mAbs to sites within domain I or the linker between domains I and III; and for two E2 mAbs between the β-connector region and the B-domain. Two of the E2-specific mAbs conferred protection in vivo in a stringent lethal challenge mouse model of CHIKV infection, whereas the E1 mAbs did not. These results provide insight into human antibody response to CHIKV and identify candidate mAbs for therapeutic intervention.

Chikungunya virus modulates the miRNA expression patterns in human synovial fibroblasts

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitoes. CHIKV infection leads to polyarthritis and polyarthralgia among patients. The synovial fibroblasts are the primary target for CHIKV. The microRNAs (miRNAs) are the small endogenous noncoding RNAs which posttranscriptionally regulate the expression of genes by binding to their target messenger RNAs (mRNAs) through their 3'-untranslated regions. The miRNAs are the key regulators for various pathological processes including viral infection, cancer, cardiovascular disease, and neurodegeneration. This study was designed to dissect out the roles of miRNAs during CHIKV (Ross Strain E1: A226V) infection in primary human synovial fibroblasts. The miRNA microarray profiling was performed on the primary human synovial fibroblasts infected by CHIKV. The gene target prediction analysis, enrichment, and network analysis were performed by various bioinformatics analyses. The subset of 26 differentially expressed microRNAs (DEMs) were identified through microarray profiling and were further screened for gene predictions, Gene Ontology, pathway enrichment, and miRNA-mRNA network using various bioinformatics tools. The bioinformatics analysis indicates the role of DEMs by suppressing the immune response which may contribute to CHIKV persistence in human primary synovial fibroblasts. Our study provides the plausible roles of DEMs, miRNAs, and mRNA interactions and pathways involved in the molecular pathogenesis of CHIKV.

Recombinant vesicular stomatitis virus vector vaccines for WHO blueprint priority pathogens

The devastating Ebola virus (EBOV) outbreak in West Africa in 2013-2016 has flagged the need for the timely development of vaccines for high-threat pathogens. To be better prepared for new epidemics, the WHO has compiled a list of priority pathogens that are likely to cause future outbreaks and for which R&D efforts are, therefore, paramount (R&D Blueprint: https://www.who.int/blueprint/priority-diseases/en/ ). To this end, the detailed characterization of vaccine platforms is needed. The vesicular stomatitis virus (VSV) has been established as a robust vaccine vector backbone for infectious diseases for well over a decade. The recent clinical trials testing the vaccine candidate VSV-EBOV against EBOV disease now have added a substantial amount of clinical data and suggest VSV to be an ideal vaccine vector candidate for outbreak pathogens. In this review, we discuss insights gained from the clinical VSV-EBOV vaccine trials as well as from animal studies investigating vaccine candidates for Blueprint pathogens.

Infectious Chikungunya Virus (CHIKV) with a Complete Capsid Deletion: a New Approach for a CHIKV Vaccine

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes epidemics of debilitating disease worldwide. Currently, there are no licensed vaccines or antivirals available against CHIKV infection. In this study, we generated a novel live attenuated vaccine (LAV) candidate for CHIKV with a complete deficiency of capsid (ΔC-CHIKV). It could propagate in BHK-21 cells, and had antigenic properties similar to those of native CHIKV. Vaccination of either immunocompromised IFNAR^-/- mice or immunocompetent C57BL/6 mice with a single dose of ΔC-CHIKV conferred complete protection upon challenge with wild-type (WT) CHIKV. Taken together, this vaccine candidate appeared to be safe and efficacious, representing a novel strategy for CHIKV vaccine design.IMPORTANCE Currently, there is no licensed vaccine against CHIKV infection. An ideal CHIKV vaccine should generate an optimal balance between efficacy and safety. Live attenuated vaccines that can elicit strong immune responses often involve a trade-off of reduced safety. Here, a novel live attenuated vaccine candidate for CHIKV lacking the entire capsid gene, ΔC-CHIKV, was developed. It was demonstrated to be genetically stable, highly attenuated, immunogenic, and able to confer complete protection against lethal CHIKV challenge after a single dose of immunization. Such an infectious vaccine candidate devoid of capsid provides a novel strategy for the development of a live attenuated CHIKV vaccine.

Arthritogenic Alphaviruses: A Worldwide Emerging Threat?

Arthritogenic alphaviruses are responsible for a dengue-like syndrome associated with severe debilitating polyarthralgia that can persist for months or years and impact life quality. Chikungunya virus is the most well-known member of this family since it was responsible for two worldwide epidemics with millions of cases in the last 15 years. However, other arthritogenic alphaviruses that are as of yet restrained to specific territories are the cause of neglected tropical diseases: O'nyong'nyong virus in Sub-Saharan Africa, Mayaro virus in Latin America, and Ross River virus in Australia and the Pacific island countries and territories. This review evaluates their emerging potential in light of the current knowledge for each of them and in comparison to chikungunya virus.

rVSVΔG-ZEBOV-GP (also designated V920) recombinant vesicular stomatitis virus pseudotyped with Ebola Zaire Glycoprotein: Standardized template with key considerations for a risk/benefit assessment

The Brighton Collaboration Viral Vector Vaccines Safety Working Group (V3SWG) was formed to evaluate the safety and characteristics of live, recombinant viral vector vaccines. A recent publication by the V3SWG described live, attenuated, recombinant vesicular stomatitis virus (rVSV) as a chimeric virus vaccine for HIV-1 (Clarke et al., 2016). The rVSV vector system is being explored as a platform for development of multiple vaccines. This paper reviews the molecular and biological features of the rVSV vector system, followed by a template with details on the safety and characteristics of a rVSV vaccine against Zaire ebolavirus (ZEBOV). The rVSV-ZEBOV vaccine is a live, replication competent vector in which the VSV glycoprotein (G) gene is replaced with the glycoprotein (GP) gene of ZEBOV. Multiple copies of GP are expressed and assembled into the viral envelope responsible for inducing protective immunity. The vaccine (designated V920) was originally constructed by the National Microbiology Laboratory, Public Health Agency of Canada, further developed by NewLink Genetics Corp. and Merck & Co., and is now in final stages of registration by Merck. The vaccine is attenuated by deletion of the principal virulence factor of VSV (the G protein), which also removes the primary target for anti-vector immunity. The V920 vaccine caused no toxicities after intramuscular (IM) or intracranial injection of nonhuman primates and no reproductive or developmental toxicity in a rat model. In multiple studies, cynomolgus macaques immunized IM with a wide range of virus doses rapidly developed ZEBOV-specific antibodies measured in IgG ELISA and neutralization assays and were fully protected against lethal challenge with ZEBOV virus. Over 20,000 people have received the vaccine in clinical trials; the vaccine has proven to be safe and well tolerated. During the first few days after vaccination, many vaccinees experience a mild acute-phase reaction with fever, headache, myalgia, and arthralgia of short duration; this period is associated with a low-level viremia, activation of anti-viral genes, and increased levels of chemokines and cytokines. Oligoarthritis and rash appearing in the second week occur at a low incidence, and are typically mild-moderate in severity and self-limited. V920 vaccine was used in a Phase III efficacy trial during the West African Ebola epidemic in 2015, showing 100% protection against Ebola Virus Disease, and it has subsequently been deployed for emergency control of Ebola outbreaks in central Africa. The template provided here provides a comprehensive picture of the first rVSV vector to reach the final stage of development and to provide a solution to control of an alarming human disease.

Assessment of Immunogenicity and Neutralisation Efficacy of Viral-Vectored Vaccines Against Chikungunya Virus

Chikungunya virus (CHIKV) has caused extensive outbreaks in several countries within the Americas, Asia, Oceanic/Pacific Islands, and Europe. In humans, CHIKV infections cause a debilitating disease with acute febrile illness and long-term polyarthralgia. Acute and chronic symptoms impose a major economic burden to health systems and contribute to poverty in affected countries. An efficacious vaccine would be an important step towards decreasing the disease burden caused by CHIKV infection. Despite no licensed vaccine is yet available for CHIKV, there is strong evidence of effective asymptomatic viral clearance due to neutralising antibodies against the viral structural proteins. We have designed viral-vectored vaccines to express the structural proteins of CHIKV, using the replication-deficient chimpanzee adenoviral platform, ChAdOx1. Expression of the CHIKV antigens results in the formation of chikungunya virus-like particles. Our vaccines induce high frequencies of anti-chikungunya specific T-cell responses as well as high titres of anti-CHIKV E2 antibodies with high capacity for in vitro neutralisation. Our results indicate the potential for further clinical development of the ChAdOx1 vaccine platform in CHIKV vaccinology.

51 years in of Chikungunya clinical vaccine development: A historical perspective

Chikungunya fever (CHIKF) is a mosquito-borne disease caused by Chikungunya virus (CHIKV). This virus is considered a priority pathogen to the UK government, the US National Institute of Allergy and Infectious Diseases (NIAID) and the US military personnel, due to the potential of CHIKV to cause major outbreaks. Nearly all CHIKV infections are symptomatic, often incapacitating and patients experience severe joint pain and inflammation that can last for more than one year with 0.4-0.5% fatality rates. Mother-to-child transmission has also been described. Despite this re-emerging disease has been documented in more than 100 countries in Europe, Oceania, Africa, Asia, the Caribbean, South and North America, no licensed vaccine is yet available to prevent CHIKF. Nevertheless, various developments have entered phase I and II trials and are now viable options to fight this incapacitating disease. This review focuses on the development of CHIKV vaccines that have reached the stage of clinical trials since the late 1960s up until 2018.

Conformational plasticity of the VEEV macro domain is important for binding of ADP-ribose

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ADPr’s binding triggers conformational changes to the whole VEEV macro domain.

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High flexibility of the loops β5-α3 and α3-β6 assist the ADPr’s binding.

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Loops around ADPr site undergo a transition pathway between apo and complex state.

Venezuelan equine encephalitis virus (VEEV) is a new world alphavirus which can be involved in several central nervous system disorders such as encephalitis and meningitis. The VEEV genome codes for 4 non-structural proteins (nsP), of which nsP3 contains a Macro domain. Macro domains (MD) can be found as stand-alone proteins or embedded within larger proteins in viruses, bacteria and eukaryotes. Their most common feature is the binding of ADP-ribose (ADPr), while several macro domains act as ribosylation writers, erasers or readers. Alphavirus MD erase ribosylation but their precise contribution in viral replication is still under investigation. NMR-driven titration experiments of ADPr in solution with the VEEV macro domain (in apo- and complex state) show that it adopts a suitable conformation for ADPr binding. Specific experiments indicate that the flexibility of the loops β5-α3 and α3-β6 is critical for formation of the complex and assists a wrapping mechanism for ADPr binding. Furthermore, along with this sequence of events, the VEEV MD undergoes a conformational exchange process between the apo state and a low-populated “dark” conformational state.

Chikungunya Virus Vaccines: Platforms, Progress, and Challenges

Chikungunya is a clinically and economically important arbovirus that has spread globally in the twenty-first century. While uncommonly fatal, infection with the virus can lead to incapacitating arthralgia that can persist for months to years. The adverse impacts of viral spread are most severe in developing low- and middle-income countries in which medical infrastructure is insufficient and manual labor is an economic driver. Unfortunately, no prophylactic or therapeutic treatments are approved for human use to combat the virus. Historically, vaccination has proven to be the most efficient and successful strategy for protecting populations and eradicating infectious disease. A large and diverse range of promising vaccination approaches for use against Chikungunya has emerged in recent years and been shown to safely elicit protective immune responses in animal models and humans. Importantly, many of these are based on technologies that have been clinically approved for use against other pathogens. Furthermore, clinical trials are currently ongoing for a subset of these. The purpose of this review is to provide a description of the relevant immunobiology of Chikungunya infection, to present immune-stimulating technologies that have been successfully employed to protect against infection, and discuss priorities and challenges regarding the future development of a vaccine for clinical use.

Defining a correlate of protection for chikungunya virus vaccines

Chikungunya virus infection causes a debilitating febrile illness that in many affected individuals is associated with long-term sequelae that can persist for months or years. Over the past decade a large number of candidate vaccines have been developed, several of which have now entered clinical trials. The rapid and sporadic nature of chikungunya outbreaks poses challenges for planning of large clinical efficacy trials suggesting that licensure of chikungunya vaccines may utilize non-traditional approval pathways based on identification of immunological endpoint(s) predictive of clinical benefit. This report reviews the current status of nonclinical and clinical testing and potential challenges for defining a suitable surrogate or correlate of protection.

Peptide vaccine against chikungunya virus: immuno-informatics combined with molecular docking approach

BACKGROUND

Chikungunya virus (CHIKV), causes massive outbreaks of chikungunya infection in several regions of Asia, Africa and Central/South America. Being positive sense RNA virus, CHIKV replication within the host resulting in its genome mutation and led to difficulties in creation of vaccine, drugs and treatment strategies. Vector control strategy has been a gold standard to combat spreading of CHIKV infection, but to eradicate a species from the face of earth is not an easy task. Therefore, alongside vector control, there is a dire need to prevent the infection through vaccine as well as through antiviral strategies.

METHODS

This study was designed to find out conserved B cell and T cell epitopes of CHIKV structural proteins through immuno-informatics and computational approaches, which may play an important role in evoking the immune responses against CHIKV.

RESULTS

Several conserved cytotoxic T-lymphocyte epitopes, linear and conformational B cell epitopes were predicted for CHIKV structural polyprotein and their antigenicity was calculated. Among B-cell epitopes "PPFGAGRPGQFGDI" showed a high antigenicity score and it may be highly immunogenic. In case of T cell epitopes, MHC class I peptides 'TAECKDKNL' and MHC class II peptides 'VRYKCNCGG' were found extremely antigenic.

CONCLUSION

The study led to the discovery of various epitopes, conserved among various strains belonging to different countries. The potential antigenic epitopes can be successfully utilized in designing novel vaccines for combating and eradication of CHIKV disease.

Cellular and Molecular Immune Response to Chikungunya Virus Infection

Chikungunya virus (CHIKV) is a re-emergent arthropod-borne virus (arbovirus) that causes a disease characterized primarily by fever, rash and severe persistent polyarthralgia. In the last decade, CHIKV has become a serious public health problem causing several outbreaks around the world. Despite the fact that CHIKV has been around since 1952, our knowledge about immunopathology, innate and adaptive immune response involved in this infectious disease is incomplete. In this review, we provide an updated summary of the current knowledge about immune response to CHIKV and about soluble immunological markers associated with the morbidity, prognosis and chronicity of this arbovirus disease. In addition, we discuss the progress in the research of new vaccines for preventing CHIKV infection and the use of monoclonal antibodies as a promising therapeutic strategy.

Chikungunya-vesicular stomatitis chimeric virus targets and eliminates brain tumors

Vesicular stomatitis virus (VSV) shows potential for targeting and killing cancer cells, but can be dangerous in the brain due to its neurotropic glycoprotein. Here we test a chimeric virus in which the VSV glycoprotein is replaced with the Chikungunya polyprotein E3-E2-6K-E1 (VSVΔG-CHIKV). Control mice with brain tumors survived a mean of 40 days after tumor implant. VSVΔG-CHIKV selectively infected and eliminated the tumor, and extended survival substantially in all tumor-bearing mice to over 100 days. VSVΔG-CHIKV also targeted intracranial primary patient derived melanoma xenografts. Virus injected into one melanoma spread to other melanomas within the same brain with little detectable infection of normal cells. Intravenous VSVΔG-CHIKV infected tumor cells but not normal tissue. In immunocompetent mice, VSVΔG-CHIKV selectively infected mouse melanoma cells within the brain. These data suggest VSVΔG-CHIKV can target and destroy brain tumors in multiple animal models without the neurotropism associated with the wild type VSV glycoprotein.

Comparative Characterization of the Sindbis Virus Proteome from Mammalian and Invertebrate Hosts Identifies nsP2 as a Component of the Virion and Sorting Nexin 5 as a Significant Host Factor for Alphavirus Replication

Recent advances in mass spectrometry methods and instrumentation now allow for more accurate identification of proteins in low abundance. This technology was applied to Sindbis virus, the prototypical alphavirus, to investigate the viral proteome. To determine if host proteins are specifically packaged into alphavirus virions, Sindbis virus (SINV) was grown in multiple host cells representing vertebrate and mosquito hosts, and total protein content of purified virions was determined. This analysis identified host factors not previously associated with alphavirus entry, replication, or egress. One host protein, sorting nexin 5 (SNX5), was shown to be critical for the replication of three different alphaviruses, Sindbis, Mayaro, and Chikungunya viruses. The most significant finding was that in addition to the host proteins, SINV nonstructural protein 2 (nsP2) was detected within virions grown in all host cells examined. The protein and RNA-interacting capabilities of nsP2 coupled with its presence in the virion support a role for nsP2 during packaging and/or entry of progeny virus. This function has not been identified for this protein. Taken together, this strategy identified at least one host factor integrally involved in alphavirus replication. Identification of other host proteins provides insight into alphavirus-host interactions during viral replication in both vertebrate and invertebrate hosts. This method of virus proteome analysis may also be useful for the identification of protein candidates for host-based therapeutics.

IMPORTANCE Pathogenic alphaviruses, such as Chikungunya and Mayaro viruses, continue to plague public health in developing and developed countries alike. Alphaviruses belong to a group of viruses vectored in nature by hematophagous (blood-feeding) insects and are termed arboviruses (arthropod-borne viruses). This group of viruses contains many human pathogens, such as dengue fever, West Nile, and Yellow fever viruses. With few exceptions, there are no vaccines or prophylactics for these agents, leaving one-third of the world population at risk of infection. Identifying effective antivirals has been a long-term goal for combating these diseases not only because of the lack of vaccines but also because they are effective during an ongoing epidemic. Mass spectrometry-based analysis of the Sindbis virus proteome can be effective in identifying host genes involved in virus replication and novel functions for virus proteins. Identification of these factors is invaluable for the prophylaxis of this group of viruses.

A recombinant virus vaccine that protects against both Chikungunya and Zika virus infections

Chikungunya virus (CHIKV) and Zika virus (ZIKV) have recently expanded their range in the world and caused serious and widespread outbreaks of near pandemic proportions. There are no licensed vaccines that protect against these co-circulating viruses that are transmitted by invasive mosquito vectors. We report here on the development of a single-dose, bivalent experimental vaccine for CHIKV and ZIKV. This vaccine is based on a chimeric vesicular stomatitis virus (VSV) that expresses the CHIKV envelope polyprotein (E3-E2-6K-E1) in place of the VSV glycoprotein (G) and also expresses the membrane-envelope (ME) glycoproteins of ZIKV. This vaccine induced neutralizing antibody responses to both CHIKV and ZIKV in wild-type mice and in interferon receptor-deficient A129 mice, animal models for CHIKV and ZIKV infection. A single vaccination of A129 mice with the vector protected these mice against infection with both CHIKV and ZIKV. Our single-dose vaccine could provide durable, low-cost protection against both CHIKV and ZIKV for people traveling to or living in areas where both viruses are circulating, which include most tropical regions in the world.

Rhabdoviruses as vaccine platforms for infectious disease and cancer

The family Rhabdoviridae (RV) comprises a large, genetically diverse collection of single-stranded, negative sense RNA viruses from the order Mononegavirales. Several RV members are being developed as live-attenuated vaccine vectors for the prevention or treatment of infectious disease and cancer. These include the prototype recombinant Vesicular Stomatitis Virus (rVSV) and the more recently developed recombinant Maraba Virus, both species within the genus Vesiculoviridae. A relatively strong safety profile in humans, robust immunogenicity and genetic malleability are key features that make the RV family attractive vaccine platforms. Currently, the rVSV vector is in preclinical development for vaccination against numerous high-priority infectious diseases, with clinical evaluation underway for HIV/AIDS and Ebola virus disease. Indeed, the success of the rVSV-ZEBOV vaccine during the 2014-15 Ebola virus outbreak in West Africa highlights the therapeutic potential of rVSV as a vaccine vector for acute, life-threatening viral illnesses. The rVSV and rMaraba platforms are also being tested as 'oncolytic' cancer vaccines in a series of phase 1-2 clinical trials, after being proven effective at eliciting immune-mediated tumour regression in preclinical mouse models. In this review, we discuss the biological and genetic features that make RVs attractive vaccine platforms and the development and ongoing testing of rVSV and rMaraba strains as vaccine vectors for infectious disease and cancer.

Assessment of the ability of V920 recombinant vesicular stomatitis-Zaire ebolavirus vaccine to replicate in relevant arthropod cell cultures and vector species

V920, rVSVΔG-ZEBOV-GP, is a recombinant vesicular stomatitis-Zaire ebolavirus vaccine which has shown an acceptable safety profile and provides a protective immune response against Ebola virus disease (EVD) induced by Zaire ebolavirus in humans. The purpose of this study was to determine whether the V920 vaccine is capable of replicating in arthropod cell cultures of relevant vector species and of replicating in live mosquitoes. While the V920 vaccine replicated well in Vero cells, no replication was observed in Anopheles or Aedes mosquito, Culicoides biting midge, or Lutzomyia sand fly cells, nor in live Culex or Aedes mosquitoes following exposure through intrathoracic inoculation or feeding on a high-titer infectious blood meal. The insect taxa selected for use in this study represent actual and potential epidemic vectors of VSV. V920 vaccine inoculated into Cx. quinquefasciatus and Ae. aegypti mosquitoes demonstrated persistence of replication-competent virus following inoculation, consistent with the recognized biological stability of the vaccine, but no evidence for active virus replication in live mosquitoes was observed. Following administration of an infectious blood meal to Ae. aegypti and Cx. quinquefasciatus mosquitoes at a titer several log₁₀ PFU more concentrated than would be observed in vaccinated individuals, no infection or dissemination of V920 was observed in either mosquito species. In vitro and in vivo data gathered during this study support minimal risk of the vector-borne potential of the V920 vaccine.

Vaccine and Therapeutic Options To Control Chikungunya Virus

Beginning in 2004, chikungunya virus (CHIKV) went from an endemic pathogen limited to Africa and Asia that caused periodic outbreaks to a global pathogen. Given that outbreaks caused by CHIKV have continued and expanded, serious consideration must be given to identifying potential options for vaccines and therapeutics. Currently, there are no licensed products in this realm, and control relies completely on the use of personal protective measures and integrated vector control, which are only minimally effective. Therefore, it is prudent to urgently examine further possibilities for control. Vaccines have been shown to be highly effective against vector-borne diseases. However, as CHIKV is known to rapidly spread and generate high attack rates, therapeutics would also be highly valuable. Several candidates are currently being developed; this review describes the multiple options under consideration for future development and assesses their relative advantages and disadvantages.

Chikungunya vaccines in development

Chikungunya virus has become a global health threat, spreading to the industrial world of Europe and the Americas; no treatment or prophylactic vaccine is available. Since the late 1960s much effort has been put into the development of a vaccine, and several heterogeneous strategies have already been explored. Only two candidates have recently qualified to enter clinical phase II trials, a chikungunya virus-like particle-based vaccine and a recombinant live attenuated measles virus-vectored vaccine.

This review focuses on the current status of vaccine development against chikungunya virus in humans and discusses the diversity of immunization strategies, results of recent human trials and promising vaccine candidates.

Chikungunya Virus Vaccines: Viral Vector-Based Approaches

In 2013, a major chikungunya virus (CHIKV) epidemic reached the Americas. In the past 2 years, >1.7 million people have been infected. In light of the current epidemic, with millions of people in North and South America at risk, efforts to rapidly develop effective vaccines have increased. Here, we focus on CHIKV vaccines that use viral-vector technologies. This group of vaccine candidates shares an ability to potently induce humoral and cellular immune responses by use of highly attenuated and safe vaccine backbones. So far, well-described vectors such as modified vaccinia virus Ankara, complex adenovirus, vesicular stomatitis virus, alphavirus-based chimeras, and measles vaccine Schwarz strain (MV/Schw) have been described as potential vaccines. We summarize here the recent data on these experimental vaccines, with a focus on the preclinical and clinical activities on the MV/Schw-based candidate, which is the first CHIKV-vectored vaccine that has completed a clinical trial.

Development of Vaccines for Chikungunya Fever

Chikungunya fever, an acute and often chronic arthralgic disease caused by the mosquito-borne chikungunya virus (CHIKV), has reemerged since 2004 to cause millions of cases. Because CHIKV exhibits limited antigenic diversity and is not known to be capable of reinfection, a vaccine could serve to both prevent disease and diminish human amplification during epidemic circulation. Here, we review the many promising vaccine platforms and candidates developed for CHIKV since the 1970s, including several in late preclinical or clinical development. We discuss the advantages and limitations of each, as well as the commercial and regulatory challenges to bringing a vaccine to market.

Development of a micro-neutralization assay for ebolaviruses using a replication-competent vesicular stomatitis hybrid virus and a quantitative PCR readout

Development of vaccines against highly pathogenic viruses that could also be used as agents of bioterrorism is both a public health issue and a national security priority. Methods that can quantify neutralizing antibodies will likely be crucial in demonstrating vaccine effectiveness, as most licensed viral vaccines are effective due to their capacity to elicit neutralizing antibodies. Assays to determine whether antibodies are neutralizing traditionally involve infectious virus, and the assay most commonly used is the plaque-reduction neutralization test (PRNT). However, when the virus is highly pathogenic, this assay must be done under the appropriate level of containment; for tier one select agents, such as Ebola virus (EBOV), it is performed under Biological Safety Level 4 (BSL-4) conditions. Developing high-throughput neutralization assays for these viruses that can be done in standard BSL-2 laboratories should facilitate vaccine development. Our approach is to use a replication-competent hybrid virus whose genome carries the envelope gene from the pathogenic virus on the genetic backbone of a non-pathogenic virus, such as vesicular stomatitis virus (VSV). We have generated hybrid VSVs carrying the envelope genes for several species of ebolavirus. The readout for infectivity is a one-step reverse transcriptase quantitative PCR (RT-qPCR), an approach that we have used for other viruses that allows robustness and adaptability to automation. Using this method, we have shown that neutralization can be assessed within 6-16h after infection. Importantly, the titers obtained in our assay with two characterized antibodies were in agreement with titers obtained in other assays. Finally, although in this paper we describe the VSV platform to quantify neutralizing antibodies to ebolaviruses, the platform should be directly applicable to any virus whose envelope is compatible with VSV biology.

Recombinant Isfahan Virus and Vesicular Stomatitis Virus Vaccine Vectors Provide Durable, Multivalent, Single-Dose Protection against Lethal Alphavirus Challenge

The demonstrated clinical efficacy of a recombinant vesicular stomatitis virus (rVSV) vaccine vector has stimulated the investigation of additional serologically distinct Vesiculovirus vectors as therapeutic and/or prophylactic vaccine vectors to combat emerging viral diseases. Among these viral threats are the encephalitic alphaviruses Venezuelan equine encephalitis virus (VEEV) and Eastern equine encephalitis virus (EEEV), which have demonstrated potential for natural disease outbreaks, yet no licensed vaccines are available in the event of an epidemic. Here we report the rescue of recombinant Isfahan virus (rISFV) from genomic cDNA as a potential new vaccine vector platform. The rISFV genome was modified to attenuate virulence and express the VEEV and EEEV E2/E1 surface glycoproteins as vaccine antigens. A single dose of the rISFV vaccine vectors elicited neutralizing antibody responses and protected mice from lethal VEEV and EEEV challenges at 1 month postvaccination as well as lethal VEEV challenge at 8 months postvaccination. A mixture of rISFV vectors expressing the VEEV and EEEV E2/E1 glycoproteins also provided durable, single-dose protection from lethal VEEV and EEEV challenges, demonstrating the potential for a multivalent vaccine formulation. These findings were paralleled in studies with an attenuated form of rVSV expressing the VEEV E2/E1 glycoproteins. Both the rVSV and rISFV vectors were attenuated by using an approach that has demonstrated safety in human trials of an rVSV/HIV-1 vaccine. Vaccines based on either of these vaccine vector platforms may present a safe and effective approach to prevent alphavirus-induced disease in humans.IMPORTANCE This work introduces rISFV as a novel vaccine vector platform that is serologically distinct and phylogenetically distant from VSV. The rISFV vector has been attenuated by an approach used for an rVSV vector that has demonstrated safety in clinical studies. The vaccine potential of the rISFV vector was investigated in a well-established alphavirus disease model. The findings indicate the feasibility of producing a safe, efficacious, multivalent vaccine against the encephalitic alphaviruses VEEV and EEEV, both of which can cause fatal disease. This work also demonstrates the efficacy of an attenuated rVSV vector that has already demonstrated safety and immunogenicity in multiple HIV-1 phase I clinical studies. The absence of serological cross-reactivity between rVSV and rISFV and their phylogenetic divergence within the Vesiculovirus genus indicate potential for two stand-alone vaccine vector platforms that could be used to target multiple bacterial and/or viral agents in successive immunization campaigns or as heterologous prime-boost agents.

Chikungunya, Influenza, Nipah, and Semliki Forest Chimeric Viruses with Vesicular Stomatitis Virus: Actions in the Brain

Recombinant vesicular stomatitis virus (VSV)-based chimeric viruses that include genes from other viruses show promise as vaccines and oncolytic viruses. However, the critical safety concern is the neurotropic nature conveyed by the VSV glycoprotein. VSVs that include the VSV glycoprotein (G) gene, even in most recombinant attenuated strains, can still show substantial adverse or lethal actions in the brain. Here, we test 4 chimeric viruses in the brain, including those in which glycoprotein genes from Nipah, chikungunya (CHIKV), and influenza H5N1 viruses were substituted for the VSV glycoprotein gene. We also test a virus-like vesicle (VLV) in which the VSV glycoprotein gene is expressed from a replicon encoding the nonstructural proteins of Semliki Forest virus. VSVΔG-CHIKV, VSVΔG-H5N1, and VLV were all safe in the adult mouse brain, as were VSVΔG viruses expressing either the Nipah F or G glycoprotein. In contrast, a complementing pair of VSVΔG viruses expressing Nipah G and F glycoproteins were lethal within the brain within a surprisingly short time frame of 2 days. Intranasal inoculation in postnatal day 14 mice with VSVΔG-CHIKV or VLV evoked no adverse response, whereas VSVΔG-H5N1 by this route was lethal in most mice. A key immune mechanism underlying the safety of VSVΔG-CHIKV, VSVΔG-H5N1, and VLV in the adult brain was the type I interferon response; all three viruses were lethal in the brains of adult mice lacking the interferon receptor, suggesting that the viruses can infect and replicate and spread in brain cells if not blocked by interferon-stimulated genes within the brain.IMPORTANCE Vesicular stomatitis virus (VSV) shows considerable promise both as a vaccine vector and as an oncolytic virus. The greatest limitation of VSV is that it is highly neurotropic and can be lethal within the brain. The neurotropism can be mostly attributed to the VSV G glycoprotein. Here, we test 4 chimeric viruses of VSV with glycoprotein genes from Nipah, chikungunya, and influenza viruses and nonstructural genes from Semliki Forest virus. Two of the four, VSVΔG-CHIKV and VLV, show substantially attenuated neurotropism and were safe in the healthy adult mouse brain. VSVΔG-H5N1 was safe in the adult brain but lethal in the younger brain. VSVΔG Nipah F+G was even more neurotropic than wild-type VSV, evoking a rapid lethal response in the adult brain. These results suggest that while chimeric VSVs show promise, each must be tested with both intranasal and intracranial administration to ensure the absence of lethal neurotropism.

Chikungunya virus: an update on the biology and pathogenesis of this emerging pathogen

Re-emergence of chikungunya virus, a mosquito-transmitted pathogen, is of serious public health concern. In the past 15 years, after decades of infrequent, sporadic outbreaks, the virus has caused major epidemic outbreaks in Africa, Asia, the Indian Ocean, and more recently the Caribbean and the Americas. Chikungunya virus is mainly transmitted by Aedes aegypti mosquitoes in tropical and subtropical regions, but the potential exists for further spread because of genetic adaptation of the virus to Aedes albopictus, a species that thrives in temperate regions. Chikungunya virus represents a substantial health burden to affected populations, with symptoms that include severe joint and muscle pain, rashes, and fever, as well as prolonged periods of disability in some patients. The inflammatory response coincides with raised levels of immune mediators and infiltration of immune cells into infected joints and surrounding tissues. Animal models have provided insights into disease pathology and immune responses. Although host innate and adaptive responses have a role in viral clearance and protection, they can also contribute to virus-induced immune pathology. Understanding the mechanisms of host immune responses is essential for the development of treatments and vaccines. Inhibitory compounds targeting key inflammatory pathways, as well as attenuated virus vaccines, have shown some success in animal models, including an attenuated vaccine strain based on an isolate from La Reunion incorporating an internal ribosome entry sequence that prevents the virus from infecting mosquitoes and a vaccine based on virus-like particles expressing envelope proteins. However, immune correlates of protection, as well as the safety of prophylactic and therapeutic candidates, are important to consider for their application in chikungunya infections. In this Review, we provide an update on chikungunya virus with regard to its epidemiology, molecular virology, virus-host interactions, immunological responses, animal models, and potential antiviral therapies and vaccines.

Vaccines against chikungunya, Zika and other emerging Aedes mosquito-borne viruses: unblocking existing bottlenecks

The emergence of Aedes mosquito-borne viral diseases is a global public health challenge. Since mosquito control programs are not highly efficient for outbreak containment, vaccines are essential to limit disease burden. Besides yellow fever vaccines, a vaccine against dengue is now available, while research on vaccines against Zika has just started. Several vaccine candidates against chikungunya are undergoing preclinical studies, and few of them have been tested in Phase II trials. To overcome hurdles and speed-up the development of vaccines against these viral diseases, several actions should be planned: first, the ‘animal rule’ could be considered for regulatory purposes; second, public–private partnership should be stimulated; third, countries, international organizations and donors commitment should be strengthened, and potential markets identified.

Plant expression systems, a budding way to confront chikungunya and Zika in developing countries?

Plant expression systems could be used as biofactories of heterologous proteins that have the potential to be used with biopharmaceutical aims and vaccine design. This technology is scalable, safe and cost-effective and it has been previously proposed as an option for vaccine and protein pharmaceutical development in developing countries. Here we present a proposal of how plant expression systems could be used to address Zika and chikungunya outbreaks through development of vaccines and rapid diagnostic kits.

Recombinant vesicular stomatitis virus-based dengue-2 vaccine candidate induces humoral response and protects mice against lethal infection

Dengue is the most important arbovirus disease throughout the world and it is responsible for more than 500,000 dengue hemorrhagic cases and 22,000 deaths every year. One vaccine was recently licensed for human use in Brazil, Mexico and Philippines and although at least seven candidates have been in clinical trials the results of the most developed CYD vaccine have demonstrated immunization problems, such as uneven protection and interference between serotypes. We constructed a vaccine candidate based on vesicular stomatitis virus (VSV) expression of pre-membrane (prM) and envelope (E) proteins of dengue-2 virus (DENV-2) and tested it in mice to evaluate immunogenicity and protection against DENV-2 infection. VSV has been successfully used as vaccine vectors for several viruses to induce strong humoral and cellular immune responses. The VSV-DENV-2 recombinant was constructed by inserting the DENV-2 structural proteins into a VSV plasmid DNA for recombinant VSV-DENV-2 recovery. Infectious recombinant VSV viruses were plaque purified and prM and E expression were confirmed by immunofluorescence and radiolabeling of proteins of infected cells. Forty Balb/C mice were inoculated through subcutaneous (s.c.) route with VSV-DENV-2 vaccine in a two doses schedule 15 d apart and 29 d after first inoculation, sera were collected and the mice were challenged with 50 lethal doses (LD50) of a neurovirulent DENV-2. The VSV-DENV-2 induced anti-DENV-2 antibodies and protected animals in the challenge experiment comparable to DENV-2 immunization control group. We conclude that VSV is a promising platform to test as a DENV vaccine and perhaps against others Flaviviridae.

Therapeutics and vaccines against chikungunya virus

Currently, there are no licensed vaccines or therapies available against chikungunya virus (CHIKV), and these were subjects discussed during a CHIKV meeting recently organized in Langkawi, Malaysia. In this review, we chart the approaches taken in both areas. Because of a sharp increase in new data in these fields, the present paper is complementary to previous reviews by Weaver et al. in 2012 and Kaur and Chu in 2013 . The most promising antivirals so far discovered are reviewed, with a special focus on the virus-encoded replication proteins as potential targets. Within the vaccines in development, our review emphasizes the various strategies in parallel development that are unique in the vaccine field against a single disease.

Molecular epidemiology, evolution and phylogeny of Chikungunya virus: An updating review

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus belonging to the Togaviridae family, causing a febrile illness associated with severe arthralgia and rash. In this review, we summarized a series of articles published from 2013 to 2016 concerning CHIKV epidemiology, phylogeny, vaccine and therapies, to give an update of our most recent article written in 2014 (Lo Presti et al.,2014). CHIKV infection was first reported in 1952 from Makonde plateaus and since this time caused many outbreaks worldwide, involving the Indian Ocean region, African countries, American continent and Italy. CHIKV infection is still underestimated and it is normally associated with clinical symptoms overlapping with dengue virus, recurring epidemics and mutations within the viral genome. These characteristics promote the geographical spread and the inability to control vector-mediated transmission of the virus. For these reasons, the majority of studies were aimed to describe outbreaks and to enhance knowledge on CHIKV biology, pathogenesis, infection treatment, and prevention. In this review, 16 studies on CHIKV phylogenetic and phylodinamics were considered, during the years 2013-2016. Phylogenetic and phylodinamic analysis are useful tools to investigate how the genealogy of a pathogen population is influenced by pathogen's demographic history, host immunological milieu and environmental/ecological factors. Phylogenetic tools were revealed important to reconstruct the geographic spread of CHIKV during the epidemics wave and to have information on the circulating strains of the virus, that are important for the prediction and control of the epidemics, as well as for vaccines and antiviral drugs development. In conclusion, this updating review can give a critical appraisal of the epidemiology, therapeutic and phylogenesis of CHIKV, reinforcing the need to monitor the geographic spread of virus and vectors.