Phase II safety and immunogenicity study of live chikungunya virus vaccine TSI-GSD-218

Generating prophylactic immunity against arboviruses in vertebrates and invertebrates

The World Health Organization recently declared a global initiative to control arboviral diseases. These are mainly caused by pathogenic flaviviruses (such as dengue, yellow fever and Zika viruses) and alphaviruses (such as chikungunya and Venezuelan equine encephalitis viruses). Vaccines represent key interventions for these viruses, with licensed human and/or veterinary vaccines being available for several members of both genera. However, a hurdle for the licensing of new vaccines is the epidemic nature of many arboviruses, which presents logistical challenges for phase III efficacy trials. Furthermore, our ability to predict or measure the post-vaccination immune responses that are sufficient for subclinical outcomes post-infection is limited. Given that arboviruses are also subject to control by the immune system of their insect vectors, several approaches are now emerging that aim to augment antiviral immunity in mosquitoes, including Wolbachia infection, transgenic mosquitoes, insect-specific viruses and paratransgenesis. In this Review, we discuss recent advances, current challenges and future prospects in exploiting both vertebrate and invertebrate immune systems for the control of flaviviral and alphaviral diseases.

Live-attenuated CHIKV vaccine with rearranged genome replicates in vitro and induces immune response in mice

Chikungunya fever virus (CHIKV) is a mosquito-borne alphavirus that causes wide-spread human infections and epidemics in Asia, Africa and recently, in the Americas. CHIKV is considered a priority pathogen by CEPI and WHO. Despite recent approval of a live-attenuated CHIKV vaccine, development of additional vaccines is warranted due to the worldwide outbreaks of CHIKV. Previously, we developed immunization DNA (iDNA) plasmid capable of launching live-attenuated CHIKV vaccine in vivo. Here we report the use of CHIKV iDNA plasmid to prepare a novel, live-attenuated CHIKV vaccine V5040 with rearranged RNA genome. In V5040, genomic RNA was rearranged to encode capsid gene downstream from the glycoprotein genes. Attenuated mutations derived from experimental CHIKV 181/25 vaccine were also engineered into E2 gene of V5040. The DNA copy of rearranged CHIKV genomic RNA with attenuated mutations was cloned into iDNA plasmid pMG5040 downstream from the CMV promoter. After transfection in vitro, pMG5040 launched replication of V5040 virus with rearranged genome and attenuating E2 mutations. Furthermore, V5040 virus was evaluated in experimental murine models for general safety and immunogenicity. Vaccination with V5040 virus subcutaneously resulted in elicitation of CHIKV-specific, virus-neutralizing antibodies. The results warrant further evaluation of V5040 virus with rearranged genome as a novel live-attenuated vaccine for CHIKV.

Single-Dose Immunogenic DNA Vaccines Coding for Live-Attenuated Alpha- and Flaviviruses

Single-dose, immunogenic DNA (iDNA) vaccines coding for whole live-attenuated viruses are reviewed. This platform, sometimes called immunization DNA, has been used for vaccine development for flavi- and alphaviruses. An iDNA vaccine uses plasmid DNA to launch live-attenuated virus vaccines in vitro or in vivo. When iDNA is injected into mammalian cells in vitro or in vivo, the RNA genome of an attenuated virus is transcribed, which starts replication of a defined, live-attenuated vaccine virus in cell culture or the cells of a vaccine recipient. In the latter case, an immune response to the live virus vaccine is elicited, which protects against the pathogenic virus. Unlike other nucleic acid vaccines, such as mRNA and standard DNA vaccines, iDNA vaccines elicit protection with a single dose, thus providing major improvement to epidemic preparedness. Still, iDNA vaccines retain the advantages of other nucleic acid vaccines. In summary, the iDNA platform combines the advantages of reverse genetics and DNA immunization with the high immunogenicity of live-attenuated vaccines, resulting in enhanced safety and immunogenicity. This vaccine platform has expanded the field of genetic DNA and RNA vaccines with a novel type of immunogenic DNA vaccines that encode entire live-attenuated viruses.

Immunogenicity, safety and duration of protection afforded by chikungunya virus vaccines undergoing human clinical trials

Background. Chikungunya virus (CHIKV) causes chikungunya fever and has been responsible for major global epidemics of arthritic disease over the past two decades. Multiple CHIKV vaccine candidates are currently undergoing or have undergone human clinical trials, with one vaccine candidate receiving FDA approval. This scoping review was performed to evaluate the 'efficacy', 'safety' and 'duration of protection' provided by CHIKV vaccine candidates in human clinical trials.Methods. This scoping literature review addresses studies involving CHIKV vaccine clinical trials using available literature on the PubMed, Medline Embase, Cochrane Library and Clinicaltrial.gov databases published up to 25 August 2023. Covidence software was used to structure information and review the studies included in this article.Results. A total of 1138 studies were screened and, after removal of duplicate studies, 12 relevant studies were thoroughly reviewed to gather information. This review summarizs that all seven CHIKV vaccine candidates achieved over 90 % seroprotection against CHIKV after one or two doses. All vaccines were able to provide neutralizing antibody protection for at least 28 days.Conclusions. A variety of vaccine technologies have been used to develop CHIKV vaccine candidates. With one vaccine candidate having recently received FDA approval, it is likely that further CHIKV vaccines will be available commercially in the near future.

Development of Vaccines against Emerging Mosquito-Vectored Arbovirus Infections

Among emergent climate-sensitive infectious diseases, some mosquito-vectored arbovirus infections have epidemiological, social, and economic effects. Dengue virus (DENV), West Nile virus (WNV), and Chikungunya virus (CHIKV) disease, previously common only in the tropics, currently pose a major risk to global health and are expected to expand dramatically in the near future if adequate containment measures are not implemented. The lack of safe and effective vaccines is critical as it seems likely that emerging mosquito-vectored arbovirus infections will be con-trolled only when effective and safe vaccines against each of these infections become available. This paper discusses the clinical characteristics of DENV, WNV, and CHIKV infections and the state of development of vaccines against these viruses. An ideal vaccine should be able to evoke with a single administration a prompt activation of B and T cells, adequate concentrations of protecting/neutralizing antibodies, and the creation of a strong immune memory capable of triggering an effective secondary antibody response after new infection with a wild-type and/or mutated infectious agent. Moreover, the vaccine should be well tolerated, safe, easily administrated, cost-effective, and widely available throughout the world. However, the development of vaccines against emerging mosquito-vectored arbovirus diseases is far from being satisfactory, and it seems likely that it will take many years before effective and safe vaccines for all these infections are made available worldwide.

Developing a Prototype Pathogen Plan and Research Priorities for the Alphaviruses

The Togaviridae family, genus, Alphavirus, includes several mosquito-borne human pathogens with the potential to spread to near pandemic proportions. Most of these are zoonotic, with spillover infections of humans and domestic animals, but a few such as chikungunya virus (CHIKV) have the ability to use humans as amplification hosts for transmission in urban settings and explosive outbreaks. Most alphaviruses cause nonspecific acute febrile illness, with pathogenesis sometimes leading to either encephalitis or arthralgic manifestations with severe and chronic morbidity and occasional mortality. The development of countermeasures, especially against CHIKV and Venezuelan equine encephalitis virus that are major threats, has included vaccines and antibody-based therapeutics that are likely to also be successful for rapid responses with other members of the family. However, further work with these prototypes and other alphavirus pathogens should target better understanding of human tropism and pathogenesis, more comprehensive identification of cellular receptors and entry, and better understanding of structural mechanisms of neutralization.

Live-Attenuated CHIKV Vaccine with Rearranged Genome Replicates in vitro and Induces Immune Response in Mice

Chikungunya fever virus (CHIKV) is a mosquito-borne alphavirus that causes wide-spread human infections and epidemics in Asia, Africa and recently, in the Americas. There is no approved vaccine and CHIKV is considered a priority pathogen by CEPI and WHO. Previously, we developed immunization DNA (iDNA) plasmid capable of launching live-attenuated CHIKV vaccine in vivo . Here we report the use of CHIKV iDNA plasmid to prepare a novel, live-attenuated CHIKV vaccine V5040 with rearranged RNA genome for improved safety. In V5040, genomic RNA was rearranged to encode capsid gene downstream from the glycoprotein genes. To secure safety profile, attenuated mutations derived from experimental CHIKV 181/25 vaccine were also engineered into E2 gene of V5040. The DNA copy of rearranged CHIKV genomic RNA with attenuated mutations was cloned into iDNA plasmid pMG5040 downstream from the CMV promoter. After transfection in vitro, pMG5040 launched replication of V5040 virus with rearranged genome and attenuating E2 mutations. Furthermore, V5040 virus was evaluated in experimental murine models for safety and immunogenicity. Vaccination with V5040 virus subcutaneously resulted in elicitation of CHIKV-specific, virus-neutralizing antibodies. The results warrant further evaluation of V5040 virus with rearranged genome as a novel live-attenuated vaccine for CHIKV.

A booster regime of liposome-delivered live-attenuated CHIKV vaccine RNA genome protects against chikungunya virus disease in mice

Mosquito-transmitted chikungunya virus (CHIKV) is the causal pathogen of CHIKV disease and is responsible for global epidemics of arthritic disease. CHIKV infection can lead to severe chronic and debilitating arthralgia, significantly impacting patient mobility and quality of life. Our previous studies have shown a live-attenuated CHIKV vaccine candidate, CHIKV-NoLS, to be effective in protecting against CHIKV disease in mice vaccinated with one dose. Further studies have demonstrated the value of a liposome RNA delivery system to deliver the RNA genome of CHIKV-NoLS directly in vivo, promoting de novo production of live-attenuated vaccine particles in vaccinated hosts. This system, designed to bypass live-attenuated vaccine production bottlenecks, uses CAF01 liposomes. However, one dose of CHIKV-NoLS CAF01 failed to provide systemic protection against CHIKV challenge in mice, with low levels of CHIKV-specific antibodies. Here we describe CHIKV-NoLS CAF01 booster vaccination regimes designed to increase vaccine efficacy. C57BL/6 mice were vaccinated with three doses of CHIKV-NoLS CAF01 either intramuscularly or subcutaneously. CHIKV-NoLS CAF01 vaccinated mice developed a systemic immune response against CHIKV that shared similarity to vaccination with CHIKV-NoLS, including high levels of CHIKV-specific neutralising antibodies in subcutaneously inoculated mice. CHIKV-NoLS CAF01 vaccinated mice were protected against disease signs and musculoskeletal inflammation when challenged with CHIKV. Mice given one dose of live-attenuated CHIKV-NoLS developed a long lasting protective immune response for up to 71 days. A clinically relevant CHIKV-NoLS CAF01 booster regime can overcome the challenges faced by our previous one dose strategy and provide systemic protection against CHIKV disease.

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.

Evolution and immunopathology of chikungunya virus informs therapeutic development

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, is an emerging global threat identified in more than 60 countries across continents. The risk of CHIKV transmission is rising due to increased global interactions, year-round presence of mosquito vectors, and the ability of CHIKV to produce high host viral loads and undergo mutation. Although CHIKV disease is rarely fatal, it can progress to a chronic stage, during which patients experience severe debilitating arthritis that can last from several weeks to months or years. At present, there are no licensed vaccines or antiviral drugs for CHIKV disease, and treatment is primarily symptomatic. This Review provides an overview of CHIKV pathogenesis and explores the available therapeutic options and the most recent advances in novel therapeutic strategies against CHIKV infections.

Comparative Efficacy of Mayaro Virus-Like Particle Vaccines Produced in Insect or Mammalian Cells

Mayaro virus (MAYV) is a mosquito-transmitted alphavirus that causes often debilitating rheumatic disease in tropical Central and South America. There are currently no licensed vaccines or antiviral drugs available for MAYV disease. Here, we generated Mayaro virus-like particles (VLPs) using the scalable baculovirus-insect cell expression system. High-level secretion of MAYV VLPs in the culture fluid of Sf9 insect cells was achieved, and particles with a diameter of 64 to 70 nm were obtained after purification. We characterize a C57BL/6J adult wild-type mouse model of MAYV infection and disease and used this model to compare the immunogenicity of VLPs from insect cells with that of VLPs produced in mammalian cells. Mice received two intramuscular immunizations with 1 μg of nonadjuvanted MAYV VLPs. Potent neutralizing antibody responses were generated against the vaccine strain, BeH407, with comparable activity seen against a contemporary 2018 isolate from Brazil (BR-18), whereas neutralizing activity against chikungunya virus was marginal. Sequencing of BR-18 illustrated that this virus segregates with genotype D isolates, whereas MAYV BeH407 belongs to genotype L. The mammalian cell-derived VLPs induced higher mean neutralizing antibody titers than those produced in insect cells. Both VLP vaccines completely protected adult wild-type mice against viremia, myositis, tendonitis, and joint inflammation after MAYV challenge. IMPORTANCE Mayaro virus (MAYV) is associated with acute rheumatic disease that can be debilitating and can evolve into months of chronic arthralgia. MAYV is believed to have the potential to emerge as a tropical public health threat, especially if it develops the ability to be efficiently transmitted by urban mosquito vectors, such as Aedes aegypti and/or Aedes albopictus. Here, we describe a scalable virus-like particle vaccine against MAYV that induced neutralizing antibodies against a historical and a contemporary isolate of MAYV and protected mice against infection and disease, providing a potential new intervention for MAYV epidemic preparedness.

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.

Chikungunya Virus and Its Envelope Protein E2 Induce Hyperalgesia in Mice: Inhibition by Anti-E2 Monoclonal Antibodies and by Targeting TRPV1

Chikungunya virus is an arthropod-borne infectious agent that causes Chikungunya fever disease. About 90% of the infected patients experience intense polyarthralgia, affecting mainly the extremities but also the large joints such as the knees. Chronic disease symptoms persist for months, even after clearance of the virus from the blood. Envelope proteins stimulate the immune response against the Chikungunya virus, becoming an important therapeutic target. We inactivated the Chikungunya virus (iCHIKV) and produced recombinant E2 (rE2) protein and three different types of anti-rE2 monoclonal antibodies. Using these tools, we observed that iCHIKV and rE2 protein induced mechanical hyperalgesia (electronic aesthesiometer test) and thermal hyperalgesia (Hargreaves test) in mice. These behavioral results were accompanied by the activation of dorsal root ganglia (DRG) neurons in mice, as observed by calcium influx. Treatment with three different types of anti-rE2 monoclonal antibodies and absence or blockade (AMG-9810 treatment) of transient receptor potential vanilloid 1 (TRPV1) channel diminished mechanical and thermal hyperalgesia in mice. iCHIKV and rE2 activated TRPV1+ mouse DRG neurons in vitro, demonstrating their ability to activate nociceptor sensory neurons directly. Therefore, our mouse data demonstrate that targeting E2 CHIKV protein with monoclonal antibodies and inhibiting TRPV1 channels are reasonable strategies to control CHIKV pain.

Chikungunya Virus Vaccine Candidate Incorporating Synergistic Mutations Is Attenuated and Protects Against Virulent Virus Challenge

BACKGROUND

Chikungunya virus (CHIKV) is an arbovirus that periodically emerges to cause large epidemics of arthritic disease. Although the robust immunity elicited by live-attenuated virus (LAV) vaccine candidates makes them attractive, CHIKV vaccine development has been hampered by a high threshold for acceptable adverse events.

METHODS

We evaluated the vaccine potential of a recently described LAV, skeletal muscle-restricted virus (SKE), that exhibits diminished replication in skeletal muscle due to insertion of target sequences for skeletal muscle-specific miR-206. We also evaluated whether these target sequences could augment safety of an LAV encoding a known attenuating mutation, E2 G82R. Attenuation of viruses containing these mutations was compared with a double mutant, SKE G82R.

RESULTS

SKE was attenuated in both immunodeficient and immunocompetent mice and induced a robust neutralizing antibody response, indicating its vaccine potential. However, only SKE G82R elicited diminished swelling in immunocompetent mice at early time points postinoculation, indicating that these mutations synergistically enhance safety of the vaccine candidate.

CONCLUSIONS

These data suggest that restriction of LAV replication in skeletal muscle enhances tolerability of reactogenic vaccine candidates and may improve the rational design of CHIKV vaccines.

The research progress of Chikungunya fever

Chikungunya fever, an acute infectious disease caused by Chikungunya virus (CHIKV), is transmitted by Aedes aegypti mosquitoes, with fever, rash, and joint pain as the main features. 1952, the first outbreak of Chikungunya fever was in Tanzania, Africa, and the virus was isolated in 1953. The epidemic has expanded from Africa to South Asia, the Indian Ocean islands and the Americas, and is now present in more than 100 countries and territories worldwide, causing approximately 1 million infections worldwide each year. In addition, fatal cases have been reported, making CHIKV a relevant public health disease. The evolution of the virus, globalization, and climate change may have contributed to the spread of CHIKV. 2005-2006 saw the most severe outbreak on Reunion Island, affecting nearly 35% of the population. Since 2005, cases of Chikungunya fever have spread mainly in tropical and subtropical regions, eventually reaching the Americas through the Caribbean island. Today, CHIKV is widely spread worldwide and is a global public health problem. In addition, the lack of a preventive vaccine and approved antiviral treatment makes CHIKV a major global health threat. In this review, we discuss the current knowledge on the pathogenesis of CHIKV, focusing on the atypical disease manifestations. We also provide an updated review of the current development of CHIKV vaccines. Overall, these aspects represent some of the most recent advances in our understanding of CHIKV pathogenesis and also provide important insights into the current development of CHIKV and potential CHIKV vaccines for current development and clinical trials.

The life cycle of the alphaviruses: From an antiviral perspective

The alphaviruses are a widely distributed group of positive-sense, single stranded, RNA viruses. These viruses are largely arthropod-borne and can be found on all populated continents. These viruses cause significant human disease, and recently have begun to spread into new populations, such as the expansion of Chikungunya virus into southern Europe and the Caribbean, where it has established itself as endemic. The study of alphaviruses is an active and expanding field, due to their impacts on human health, their effects on agriculture, and the threat that some pose as potential agents of biological warfare and terrorism. In this systematic review we will summarize both historic knowledge in the field as well as recently published data that has potential to shift current theories in how alphaviruses are able to function. This review is comprehensive, covering all parts of the alphaviral life cycle as well as a brief overview of their pathology and the current state of research in regards to vaccines and therapeutics for alphaviral disease.

Understanding the Biology and Immune Pathogenesis of Chikungunya Virus Infection for Diagnostic and Vaccine Development

Chikungunya virus, the causative agent of chikungunya fever, is generally characterized by the sudden onset of symptoms, including fever, rash, myalgia, and headache. In some patients, acute chikungunya virus infection progresses to severe and chronic arthralgia that persists for years. Chikungunya infection is more commonly identified in tropical and subtropical regions. However, recent expansions and epidemics in the temperate regions have raised concerns about the future public health impact of chikungunya diseases. Several underlying factors have likely contributed to the recent re-emergence of chikungunya infection, including urbanization, human travel, viral adaptation to mosquito vectors, lack of effective control measures, and the spread of mosquito vectors to new regions. However, the true burden of chikungunya disease is most likely to be underestimated, particularly in developing countries, due to the lack of standard diagnostic assays and clinical manifestations overlapping with those of other endemic viral infections in the regions. Additionally, there have been no chikungunya vaccines available to prevent the infection. Thus, it is important to update our understanding of the immunopathogenesis of chikungunya infection, its clinical manifestations, the diagnosis, and the development of chikungunya vaccines.

A molecular understanding of alphavirus entry and antibody protection

Alphaviruses are arthropod-transmitted RNA viruses that cause epidemics of human infection and disease on a global scale. These viruses are classified as either arthritogenic or encephalitic based on their genetic relatedness and the clinical syndromes they cause. Although there are currently no approved therapeutics or vaccines against alphaviruses, passive transfer of monoclonal antibodies confers protection in animal models. This Review highlights recent advances in our understanding of the host factors required for alphavirus entry, the mechanisms of action by which protective antibodies inhibit different steps in the alphavirus infection cycle and candidate alphavirus vaccines currently under clinical evaluation that focus on humoral immunity. A comprehensive understanding of alphavirus entry and antibody-mediated protection may inform the development of new classes of countermeasures for these emerging viruses.

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.

Mosquitoes and Mosquito-Borne Diseases in Vietnam

Mosquito-borne diseases pose a significant threat to humans in almost every part of the world. Key factors such as global warming, climatic conditions, rapid urbanisation, frequent human relocation, and widespread deforestation significantly increase the number of mosquitoes and mosquito-borne diseases in Vietnam, and elsewhere around the world. In southeast Asia, and notably in Vietnam, national mosquito control programmes contribute to reducing the risk of mosquito-borne disease transmission, however, malaria and dengue remain a threat to public health. The aim of our review is to provide a complete checklist of all Vietnamese mosquitoes that have been recognised, as well as an overview of mosquito-borne diseases in Vietnam. A total of 281 mosquito species of 42 subgenera and 22 genera exist in Vietnam. Of those, Anopheles, Aedes, and Culex are found to be potential vectors for mosquito-borne diseases. Major mosquito-borne diseases in high-incidence areas of Vietnam include malaria, dengue, and Japanese encephalitis. This review may be useful to entomological researchers for future surveys of Vietnamese mosquitoes and to decision-makers responsible for vector control tactics.

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.

Safety and immunogenicity of PXVX0317, an aluminium hydroxide-adjuvanted chikungunya virus-like particle vaccine: a randomised, double-blind, parallel-group, phase 2 trial

BACKGROUND

Chikungunya virus (CHIKV) disease is an ongoing public health threat. We aimed to evaluate the safety and immunogenicity of PXVX0317, an aluminium hydroxide-adjuvanted formulation of a CHIKV virus-like particle (VLP) vaccine.

METHODS

This randomised, double-blind, parallel-group, phase 2 trial was conducted at three clinical trial centres in the USA. Eligible participants were healthy CHIKV-naïve adults aged 18-45 years. Participants were stratified by site and randomly assigned (1:1:1:1:1:1:1:1) to one of the eight vaccination groups using a block size of 16. Group 1 received two doses of unadjuvanted PXVX0317 28 days apart (2 × 20 μg; standard); all other groups received adjuvanted PXVX0317: groups 2-4 received two doses 28 days apart (2 × 6 μg [group 2], 2 × 10 μg [group 3], or 2 × 20 μg [group 4]; standard); group 4 also received a booster dose 18 months after the first active injection (40 μg; standard plus booster); groups 5-7 received two doses 14 days apart (2 × 6 μg [group 5], 2 × 10 μg [group 6], or 2 × 20 μg [group 7]; accelerated); and group 8 received one dose (1 × 40 μg; single). The primary endpoint was the geometric mean titre of anti-CHIKV neutralising antibody on day 57 (28 days after the last vaccination), assessed in the immunogenicity-evaluable population. Additionally, we assessed safety. This trial is registered at ClinicalTrials.gov, NCT03483961.

FINDINGS

This trial was conducted from April 18, 2018, to Sept 21, 2020; 468 participants were assessed for eligibility. Of these, 415 participants were randomly assigned to eight groups (n=53 in groups 1, 5, and 6; n=52 in groups 2 and 8; n=51 in groups 3 and 7; and n=50 in group 4) and 373 were evaluable for immunogenicity. On day 57, serum neutralising antibody geometric mean titres were 2057·0 (95% CI 1584·8-2670·0) in group 1, 1116·2 (852·5-1461·4; p=0·0015 vs group 1 used as a reference) in group 2, 1465·3 (1119·1-1918·4; p=0·076) in group 3, 2023·8 (1550·5-2641·7; p=0·93) in group 4, 920·1 (710·9-1190·9; p<0·0001) in group 5, 1206·9 (932·4-1562·2; p=0·0045) in group 6, 1562·8 (1204·1-2028·3; p=0·14) in group 7, and 1712·5 (1330·0-2205·0; p=0·32) in group 8. In group 4, a booster dose increased serum neutralising antibody geometric mean titres from 215·7 (95% CI 160·9-289·1) on day 547 to 10 941·1 (7378·0-16 225·1) on day 575. Durability of the immune response (evaluated in groups 1, 4, and 8) was shown up to 2 years. The most common solicited adverse event was pain at the injection site, reported in 12 (23%) of 53 participants who received the unadjuvanted vaccine (group 1) and 111 (31%) of 356 who received the adjuvanted vaccine. No vaccine-related serious adverse events were reported.

INTERPRETATION

PXVX0317 was well tolerated and induced a robust and durable serum neutralising antibody immune response against CHIKV up to 2 years. A single 40 μg injection of adjuvanted PXVX0317 is being further investigated in phase 3 clinical trials (NCT05072080 and NCT05349617).

FUNDING

Emergent BioSolutions.

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.

Evaluation of monophosphoryl lipid A as an adjuvanted for inactivated chikungunya virus

Currently there is no clinically approved chikungunya virus (CHIKV) vaccine for immunization. Though definite need is felt, long disappearance of CHIKV has been a concern. Inactivated CHIKV (I-CHIKV) is an attractive antigen to develop effective vaccines within a short period of time. However, highly purified inactivated CHIKV do not contain necessary triggers for induction of robust antibody response. Monophosphoryl lipid A (MPLA) is a TLR4 ligand which is expressed on immune cells and is known to enhance immune response. Additionally, route of delivery also plays a critical role in modulating the immune response. Thus, antigen, adjuvant and route of delivery might modulate immune response if combined. Therefore in this study, we explored the immunogenicity of inactivated CHIKV-MPLA combination in mice after administration by intradermal or intramuscular route. Long term immune response study was also conducted by varying the antigen concentration and keeping the adjuvant concentration constant. Our study showed that the CHIKV-MPLA combination induced higher binding antibodies as well as neutralizing antibody titers as compared to unadjuvanted CHIKV. No difference in antibody titers was observed after delivery by either of the routes. However, difference in IFNγ and IL4 profiles was observed when a supernatant from stimulated splenocytes was analyzed. Taken together, these data show that both routes could be used for administration of the I-CHIKV-MPLA combination.

Two Conserved Phenylalanine Residues in the E1 Fusion Loop of Alphaviruses Are Essential for Viral Infectivity

Alphaviruses infect cells by a low pH-dependent fusion reaction between viral and host cell membranes that is mediated by the viral E1 glycoprotein. Most reported alphavirus E1 sequences include two phenylalanines (F87 and F95) in the fusion loop, yet the role of these residues in viral infectivity remains to be defined. Following introduction of wild type (WT), E1-F87A, and E1-F95A chikungunya virus (CHIKV) RNA genomes into cells, viral particle production was similar in magnitude. However, CHIKV E1-F87A and E1-F95A virions displayed impaired infectivity compared with WT CHIKV particles. Although WT, E1-F87A, and E1-F95A particles bound cells with similar efficiencies, E1-F87A and E1-F95A particles were unable to undergo fusion and entry into cells. Introduction of an F95A mutation in the E1 fusion loop of Mayaro virus or Venezuelan equine encephalitis virus also resulted in poorly infectious virions. We further tested whether an E1-F87A or E1-F95A mutation could be incorporated into a live-attenuated vaccine strain, CHIKV 181/25, to enhance vaccine safety. Infection of immunocompromised Ifnar1-/- and Irf3-/-Irf5-/-Irf7-/- mice with 181/25E1-F87A or 181/25E1-F95A resulted in 0% mortality, compared with 100% mortality following 181/25 infection. Despite this enhanced attenuation, surviving Ifnar1-/- and Irf3-/-Irf5-/-Irf7-/- mice were protected against virulent virus re-challenge. Moreover, single-dose immunization of WT mice with either 181/25, 181/25E1-F87A, or 181/25E1-F95A elicited CHIKV-specific antibody responses and protected against pathogenic CHIKV challenge. These studies define a critical function for residues E1-F87 and E1-F95 in alphavirus fusion and entry into target cells and suggest that incorporation of these mutations could enhance the safety of live-attenuated alphavirus vaccine candidates. IMPORTANCE Alphaviruses are human pathogens that cause both debilitating acute and chronic musculoskeletal disease and potentially fatal encephalitis. In this study, we determined that two highly conserved phenylalanine residues in the alphavirus E1 glycoprotein are required for fusion of viral and host cell membranes and viral entry into target cells. We further demonstrated that mutation of these phenylalanines results in a substantial loss of viral virulence but not immunogenicity. These data enhance an understanding of the viral determinants of alphavirus entry into host cells and could contribute to the development of new antivirals targeting these conserved phenylalanines or new live-attenuated alphavirus vaccines.

A Review on Chikungunya Virus Epidemiology, Pathogenesis and Current Vaccine Development

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that recently re-emerged in many parts of the world causing large-scale outbreaks. CHIKV infection presents as a febrile illness known as chikungunya fever (CHIKF). Infection is self-limited and characterized mainly by severe joint pain and myalgia that can last for weeks or months; however, severe disease presentation can also occur in a minor proportion of infections. Among the atypical CHIKV manifestations that have been described, severe arthralgia and neurological complications, such as encephalitis, meningitis, and Guillain–Barré Syndrome, are now reported in many outbreaks. Moreover, death cases were also reported, placing CHIKV as a relevant public health disease. Virus evolution, globalization, and climate change may have contributed to CHIKV spread. In addition to this, the lack of preventive vaccines and approved antiviral treatments is turning CHIKV into a major global health threat. In this review, we discuss the current knowledge about CHIKV pathogenesis, with a focus on atypical disease manifestations, such as persistent arthralgia and neurologic disease presentation. We also bring an up-to-date review of the current CHIKV vaccine development. Altogether, these topics highlight some of the most recent advances in our understanding of CHIKV pathogenesis and also provide important insights into the current development and clinical trials of CHIKV potential vaccine candidates.

Current Understanding of the Role of T Cells in Chikungunya, Dengue and Zika Infections

Arboviral infections such as Chikungunya (CHIKV), Dengue (DENV) and Zika (ZIKV) are a major disease burden in tropical and sub-tropical countries, and there are no effective vaccinations or therapeutic drugs available at this time. Understanding the role of the T cell response is very important when designing effective vaccines. Currently, comprehensive identification of T cell epitopes during a DENV infection shows that CD8 and CD4 T cells and their specific phenotypes play protective and pathogenic roles. The protective role of CD8 T cells in DENV is carried out through the killing of infected cells and the production of proinflammatory cytokines, as CD4 T cells enhance B cell and CD8 T cell activities. A limited number of studies attempted to identify the involvement of T cells in CHIKV and ZIKV infection. The identification of human immunodominant ZIKV viral epitopes responsive to specific T cells is scarce, and none have been identified for CHIKV. In CHIKV infection, CD8 T cells are activated during the acute phase in the lymph nodes/blood, and CD4 T cells are activated during the chronic phase in the joints/muscles. Studies on the role of T cells in ZIKV-neuropathogenesis are limited and need to be explored. Many studies have shown the modulating actions of T cells due to cross-reactivity between DENV-ZIKV co-infections and have repeated heterologous/homologous DENV infection, which is an important factor to consider when developing an effective vaccine.

An mRNA vaccine encoding Chikungunya virus E2-E1 protein elicits robust neutralizing antibody responses and CTL immune responses

Arthropod-borne chikungunya virus (CHIKV) infection can cause a debilitating arthritic disease in human. However, there are no specific antiviral drugs and effective licensed vaccines against CHIKV available for clinical use. Here, we developed an mRNA-lipid nanoparticle (mRNA-LNP) vaccine expressing CHIKV E2-E1 antigen, and compared its immunogenicity with soluble recombinant protein sE2-E1 antigen expressed in S2 cells. For comparison, we first showed that recombinant protein antigens mixed with aluminum adjuvant elicit strong antigen-specific humoral immune response and a moderate cellular immune response in C57BL/6 mice. Moreover, sE2-E1 vaccine stimulated 12–23 folds more neutralizing antibodies than sE1 vaccine and sE2 vaccine. Significantly, when E2-E1 gene was delivered by an mRNA-LNP vaccine, not only the better magnitude of neutralizing antibody responses was induced, but also greater cellular immune responses were generated, especially for CD8⁺ T cell responses. Moreover, E2-E1-LNP induced CD8⁺ T cells can perform cytotoxic effect in vivo. Considering its better immunogenicity and convenience of preparation, we suggest that more attention should be placed to develop CHIKV E2-E1-LNP mRNA vaccine.

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Heterodimer sE2-E1 is a more promising antigen than sE1 or sE2 monomer.

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CHIKV E2-E1-LNP mRNA vaccine is superior to subunit vaccine sE2-E1.

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mRNA vaccine elicits robust CTL response but modest CD4⁺ T cell response.

Prevention and control of dengue and Chikungunya in Colombia: A cost-effectiveness analysis

Background

Chikungunya and dengue are emerging diseases that have caused large outbreaks in various regions of the world. Both are both spread by Aedes aegypti and Aedes albopictus mosquitos. We developed a dynamic transmission model of chikungunya and dengue, calibrated to data from Colombia (June 2014 –December 2017).

Methodology/Principal findings

We evaluated the health benefits and cost-effectiveness of residual insecticide treatment, long-lasting insecticide-treated nets, routine dengue vaccination for children aged 9, catchup vaccination for individuals aged 10–19 or 10–29, and portfolios of these interventions. Model calibration resulted in 300 realistic transmission parameters sets that produced close matches to disease-specific incidence and deaths. Insecticide was the preferred intervention and was cost-effective. Insecticide averted an estimated 95 chikungunya cases and 114 dengue cases per 100,000 people, 61 deaths, and 4,523 disability-adjusted life years (DALYs). In sensitivity analysis, strategies that included dengue vaccination were cost-effective only when the vaccine cost was 14% of the current price.

Conclusions/Significance

Insecticide to prevent chikungunya and dengue in Colombia could generate significant health benefits and be cost-effective. Because of limits on diagnostic accuracy and vaccine efficacy, the cost of dengue testing and vaccination must decrease dramatically for such vaccination to be cost-effective in Colombia. The vectors for chikungunya and dengue have recently spread to new regions, highlighting the importance of understanding the effectiveness and cost-effectiveness of policies aimed at preventing these diseases.

Chikungunya and dengue are emerging diseases that have caused large outbreaks in various regions of the world. Both are both spread by Aedes aegypti and Aedes albopictus mosquitos. To evaluate the effectiveness and cost-effectiveness of interventions aimed at controlling either of these diseases, it is important to consider the potential effects on both diseases, as an intervention that reduces the mosquito population will reduce the spread of both diseases. We developed a dynamic transmission model of chikungunya and dengue, calibrated to data from Colombia. We evaluated the health benefits and cost-effectiveness of the following interventions: residual insecticide treatment, long-lasting insecticide-treated nets, routine dengue vaccination for children aged 9, catchup dengue vaccination for individuals aged 10–19 or 10–29, and portfolios of these interventions. In all vaccination scenarios, we considered testing for previous exposure to dengue. We found that insecticide to prevent chikungunya and dengue in Colombia could generate significant health benefits and be cost-effective. While the dengue vaccine was effective in preventing cases and deaths, costs of diagnostic testing and vaccination must decrease for dengue vaccination to be considered cost-effective.

Chikungunya and arthritis: An overview

Chikungunya is caused by CHIKV (chikungunya virus), an emerging and re-emerging arthropod-vectored viral infection that causes a febrile disease with primarily long term sequelae of arthralgia and myalgia and is fatal in a small fraction of infected patients. Sporadic outbreaks have been reported from different parts of the world chiefly Africa, Asia, the Indian and Pacific ocean regions, Europe and lately even in the Americas. Currently, treatment is primarily symptomatic as no vaccine, antibody-mediated immunotherapy or antivirals are available. Chikungunya belongs to a family of arthritogenic alphaviruses which have many pathophysiological similarities. Chikungunya arthritis has similarities and differences with rheumatoid arthritis. Although research into arthritis caused by these alphaviruses have been ongoing for decades and significant progress has been made, the mechanisms underlying viral infection and arthritis are not well understood. In this review, we give a background to chikungunya and the causative virus, outline the history of alphavirus arthritis research and then give an overview of findings on arthritis caused by CHIKV. We also discuss treatment options and the research done so far on various therapeutic intervention strategies.

The global emergence of Chikungunya infection: An integrated view

Chikungunya virus (CHIKV) is one of the emerging viruses around the globe. It belongs to the family Togaviridae and genus Alphavirus and is an arthropod borne virus that transmits by the bite of an infected mosquito, mainly through Aedes aegypti and Aedes albopcitus. It is a spherical, enveloped virus with positive single stranded RNA genome. It was first discovered during 1952-53 in Tanganyika, after which outbreaks were documented in many regions of the world. CHIKV has two transmission cycles; an enzootic sylvatic cycle and an urban cycle. CHIKV genome contains 11,900 nucleotides and two open reading frames and shows great sequence variability. Molecular mechanisms of virus host-cell interactions and the pathogenesis of disease are not fully understood. The disease involves three phases; acute, post-acute and chronic with symptoms including high-grade fever, arthralgia, macupapular rashes and headache. There is no licensed vaccine or specific treatment for CHIKV infection. This lack of specific interventions combined with difficulties in making a precise diagnosis together make the disease difficult to manage. In this review we aim to present the current knowledge of global epidemiology, transmission, structure, various aspects of diagnosis as well as highlight potential antiviral drugs and vaccines against CHIKV.

Current Status of Chikungunya in India

Chikungunya fever (CHIKF) is an arbovirus disease caused by chikungunya virus (CHIKV), an alphavirus of Togaviridae family. Transmission follows a human-mosquito-human cycle starting with a mosquito bite. Subsequently, symptoms develop after 2-6 days of incubation, including high fever and severe arthralgia. The disease is self-limiting and usually resolve within 2 weeks. However, chronic disease can last up to several years with persistent polyarthralgia. Overlapping symptoms and common vector with dengue and malaria present many challenges for diagnosis and treatment of this disease. CHIKF was reported in India in 1963 for the first time. After a period of quiescence lasting up to 32 years, CHIKV re-emerged in India in 2005. Currently, every part of the country has become endemic for the disease with outbreaks resulting in huge economic and productivity losses. Several mutations have been identified in circulating strains of the virus resulting in better adaptations or increased fitness in the vector(s), effective transmission, and disease severity. CHIKV evolution has been a significant driver of epidemics in India, hence, the need to focus on proper surveillance, and implementation of prevention and control measure in the country. Presently, there are no licensed vaccines or antivirals available; however, India has initiated several efforts in this direction including traditional medicines. In this review, we present the current status of CHIKF in India.

Live-attenuated RNA hybrid vaccine technology provides single-dose protection against Chikungunya virus

We present a live-attenuated RNA hybrid vaccine technology that uses an RNA vaccine delivery vehicle to deliver in vitro-transcribed, full-length, live-attenuated viral genomes to the site of vaccination. This technology allows ready manufacturing in a cell-free environment, regardless of viral attenuation level, and it promises to avoid many safety and manufacturing challenges of traditional live-attenuated vaccines. We demonstrate this technology through development and testing of a live-attenuated RNA hybrid vaccine against Chikungunya virus (CHIKV), comprised of an in vitro-transcribed, highly attenuated CHIKV genome delivered by a highly stable nanostructured lipid carrier (NLC) formulation as an intramuscular injection. We demonstrate that single-dose immunization of immunocompetent C57BL/6 mice results in induction of high CHIKV-neutralizing antibody titers and protection against mortality and footpad swelling after lethal CHIKV challenge.

Non-replicating adenovirus based Mayaro virus vaccine elicits protective immune responses and cross protects against other alphaviruses

Mayaro virus (MAYV) is an alphavirus endemic to South and Central America associated with sporadic outbreaks in humans. MAYV infection causes severe joint and muscle pain that can persist for weeks to months. Currently, there are no approved vaccines or therapeutics to prevent MAYV infection or treat the debilitating musculoskeletal inflammatory disease. In the current study, a prophylactic MAYV vaccine expressing the complete viral structural polyprotein was developed based on a non-replicating human adenovirus V (AdV) platform. Vaccination with AdV-MAYV elicited potent neutralizing antibodies that protected WT mice against MAYV challenge by preventing viremia, reducing viral dissemination to tissues and mitigating viral disease. The vaccine also prevented viral-mediated demise in IFN⍺R1-/- mice. Passive transfer of immune serum from vaccinated animals similarly prevented infection and disease in WT mice as well as virus-induced demise of IFN⍺R1-/- mice, indicating that antiviral antibodies are protective. Immunization with AdV-MAYV also generated cross-neutralizing antibodies against two related arthritogenic alphaviruses-chikungunya and Una viruses. These cross-neutralizing antibodies were protective against lethal infection in IFN⍺R1-/- mice following challenge with these heterotypic alphaviruses. These results indicate AdV-MAYV elicits protective immune responses with substantial cross-reactivity and protective efficacy against other arthritogenic alphaviruses. Our findings also highlight the potential for development of a multi-virus targeting vaccine against alphaviruses with endemic and epidemic potential in the Americas.

Arthritogenic Alphavirus Capsid Protein

In the past two decades Old World and arthritogenic alphavirus have been responsible for epidemics of polyarthritis, causing high morbidity and becoming a major public health concern. The multifunctional arthritogenic alphavirus capsid protein is crucial for viral infection. Capsid protein has roles in genome encapsulation, budding and virion assembly. Its role in multiple infection processes makes capsid protein an attractive target to exploit in combating alphaviral infection. In this review, we summarize the function of arthritogenic alphavirus capsid protein, and describe studies that have used capsid protein to develop novel arthritogenic alphavirus therapeutic and diagnostic strategies.

Implementation of in silico methods to predict common epitopes for vaccine development against Chikungunya and Mayaro viruses

Being a Positive sense RNA virus the recent reemergence of Chikungunya and Mayaro virus has taken the concern of the leading scientific communities of the world. Though the outbreak of Mayaro virus is limited to Neotropical region only, Chikungunya is already identified in over 60 countries around the world. Besides, the lack of a strong protective treatment, misdiagnosis issue and co-circulation of both the viruses calls for a new strategy which could potentially prevent these infections from spreading. In this study, we therefore, identified the peptide based vaccine candidates e.g. epitopes for B cell and T cell from Chikungunya virus which also showed to be homologous to the Mayaro virus through immuno-informatics and computational approaches. Final epitopes identified from the most antigenic structural polyprotein of both the viruses were 5 for CD8+ T cell Epitopes (²⁰⁹KPGDSGRPI²¹⁷, ²¹⁹TGTMGHFIL²²⁷, ²³⁹ALSVVTWNK²⁴⁷, ⁹⁸KPGRRERMC¹⁰⁶ and ¹⁰⁰GRRERMCMK¹⁰⁸), 2 epitopes for CD4+ T cell (¹⁰⁵MCMKIENDCIFEVKH¹¹⁹ and ⁵⁰²DRTLLSQQSGNVKIT⁵¹⁶) and a single epitope for B cell (⁵⁰⁴GGRFTIPTGAGKPGDSGRPI⁵¹⁸). Analysis of our predicted epitopes for population coverage showed prominent population coverage (92.43%) around the world. Finally, molecular docking simulation of the foreseen T cell epitopes with respondent HLA alleles secured good HLA-epitope interaction. This study was directed towards the discovery of potential antigenic epitopes which can open up a new skyline to design novel vaccines for combating both of the diseases at the same time.

In silico studies of fisetin and silymarin as novel chikungunya virus nonstructural proteins inhibitors

Aim: Chikungunya virus (CHIKV) infection is often characterized by fever, rash and arthralgia. Until now, there is no vaccine or antiviral drug available for this disease. Two flavonoid compounds, silymarin and fisetin, were reported to be able to inhibit CHIKV replication. Materials & methods: The interaction between the flavonoid compounds and two CHIKV nonstructural proteins (nsP2 and nsP3) were investigated through molecular docking supported with other analysis such as molecular dynamics simulation and binding free energy calculation. Results: The compounds establish potent, stable and flexible interaction with the binding pocket of the two target proteins. Conclusion: The outcomes of this study support the previously published experimental data on anti-CHIKV activity of the compounds by highlighting the interactions with the proteins’ key residues.

Prophylactic strategies to control chikungunya virus infection

Chikungunya virus (CHIKV) is a (re)emerging arbovirus and the causative agent of chikungunya fever. In recent years, CHIKV was responsible for a series of outbreaks, some of which had serious economic and public health impacts in the affected regions. So far, no CHIKV-specific antiviral therapy or vaccine has been approved. This review gives a brief summary on CHIKV epidemiology, spread, infection and diagnosis. It furthermore deals with the strategies against emerging diseases, drug development and the possibilities of testing antivirals against CHIKV in vitro and in vivo. With our review, we hope to provide the latest information on CHIKV, disease manifestation, as well as on the current state of CHIKV vaccine development and post-exposure therapy.

Injection site vaccinology of a recombinant vaccinia-based vector reveals diverse innate immune signatures

Poxvirus systems have been extensively used as vaccine vectors. Herein a RNA-Seq analysis of intramuscular injection sites provided detailed insights into host innate immune responses, as well as expression of vector and recombinant immunogen genes, after vaccination with a new multiplication defective, vaccinia-based vector, Sementis Copenhagen Vector. Chikungunya and Zika virus immunogen mRNA and protein expression was associated with necrosing skeletal muscle cells surrounded by mixed cellular infiltrates. The multiple adjuvant signatures at 12 hours post-vaccination were dominated by TLR3, 4 and 9, STING, MAVS, PKR and the inflammasome. Th1 cytokine signatures were dominated by IFNγ, TNF and IL1β, and chemokine signatures by CCL5 and CXCL12. Multiple signatures associated with dendritic cell stimulation were evident. By day seven, vaccine transcripts were absent, and cell death, neutrophil, macrophage and inflammation annotations had abated. No compelling arthritis signatures were identified. Such injection site vaccinology approaches should inform refinements in poxvirus-based vector design.

Poxvirus vector systems have been widely developed for vaccine applications. Despite considerable progress, so far only one recombinant poxvirus vectored vaccine has to date been licensed for human use, with ongoing efforts seeking to enhance immunogenicity whilst minimizing reactogenicity. The latter two characteristics are often determined by early post-vaccination events at the injection site. We therefore undertook an injection site vaccinology approach to analyzing gene expression at the vaccination site after intramuscular inoculation with a recombinant, multiplication defective, vaccinia-based vaccine. This provided detailed insights into inter alia expression of vector-encoded immunoregulatory genes, as well as host innate and adaptive immune responses. We propose that such injection site vaccinology can inform rational vaccine vector design, and we discuss how the information and approach elucidated herein might be used to improve immunogenicity and limit reactogenicity of poxvirus-based vaccine vector systems.

Evolution and epidemiologic dynamics of dengue virus in Nicaragua during the emergence of chikungunya and Zika viruses

Arthropod-borne viruses (arboviruses) comprise a significant and ongoing threat to human health, infecting hundreds of millions annually. Three such arboviruses include circumtropical dengue, Zika, and chikungunya viruses, exhibiting continuous emergence primarily via Aedes mosquito vectors. Nicaragua has experienced endemic dengue virus (DENV) transmission involving multiple serotypes since 1985, with chikungunya virus (CHIKV) reported in 2014-2015, followed by Zika virus (ZIKV) first reported in 2016. In order to identify patterns of genetic variation and selection pressures shaping the evolution of co-circulating DENV serotypes in light of the arrival of CHIKV and ZIKV, we employed whole-genome sequencing on an Illumina MiSeq platform of random-amplified total RNA libraries to characterize 42 DENV low-passage isolates, derived from viremic patients in Nicaragua between 2013 and 2016. Our approach also revealed clinically undetected co-infections with CHIKV. Of the three DENV serotypes (1, 2, and 3) co-circulating during our study, we uncovered distinct patterns of evolution using comparative phylogenetic inference. DENV-1 genetic variation was structured into two distinct co-circulating lineages with no evidence of positive selection in the origins of either lineage, suggesting they are equally fit. In contrast, the evolutionary history of DENV-2 was marked by positive selection, and a unique, divergent lineage correlated with high epidemic potential emerged in 2015 to drive an outbreak in 2016. DENV-3 genetic variation remained unstructured into lineages throughout the period of study. Thus, this study reveals insights into evolutionary and epidemiologic trends exhibited during the circulation of multiple arboviruses in Nicaragua.

Chikungunya Virus Strains from Each Genetic Clade Bind Sulfated Glycosaminoglycans as Attachment Factors

Alphavirus infections are a global health threat, contributing to outbreaks of disease in many parts of the world. Recent epidemics caused by CHIKV, an arthritogenic alphavirus, resulted in more than 8.5 million cases as the virus has spread into new geographic regions, including the Western Hemisphere. CHIKV causes disease in the majority of people infected, leading to severe and debilitating arthritis. Despite the severity of CHIKV disease, there are no licensed therapeutics. Since attachment factors and receptors are determinants of viral tropism and pathogenesis, understanding these virus-host interactions can enhance our knowledge of CHIKV infection. We analyzed over 670 glycans and identified GAGs as the main glycan bound by CHIKV. We defined specific GAG components required for CHIKV binding and assessed strain-specific differences in GAG binding capacity. These studies provide insight about cell surface molecules that CHIKV binds, which could facilitate the development of antiviral therapeutics targeting the CHIKV attachment step.

Chikungunya virus (CHIKV) is an arthritogenic alphavirus that causes debilitating musculoskeletal disease. CHIKV displays broad cell, tissue, and species tropism, which may correlate with the attachment factors and entry receptors used by the virus. Cell surface glycosaminoglycans (GAGs) have been identified as CHIKV attachment factors. However, the specific types of GAGs and potentially other glycans to which CHIKV binds and whether there are strain-specific differences in GAG binding are not fully understood. To identify the types of glycans bound by CHIKV, we conducted glycan microarray analyses and discovered that CHIKV preferentially binds GAGs. Microarray results also indicate that sulfate groups on GAGs are essential for CHIKV binding and that CHIKV binds most strongly to longer GAG chains of heparin and heparan sulfate. To determine whether GAG binding capacity varies among CHIKV strains, a representative strain from each genetic clade was tested. While all strains directly bound to heparin and chondroitin sulfate in enzyme-linked immunosorbent assays (ELISAs) and depended on heparan sulfate for efficient cell binding and infection, we observed some variation by strain. Enzymatic removal of cell surface GAGs and genetic ablation that diminishes GAG expression reduced CHIKV binding and infectivity of all strains. Collectively, these data demonstrate that GAGs are the preferred glycan bound by CHIKV, enhance our understanding of the specific GAG moieties required for CHIKV binding, define strain differences in GAG engagement, and provide further evidence for a critical function of GAGs in CHIKV cell attachment and infection.

IMPORTANCE Alphavirus infections are a global health threat, contributing to outbreaks of disease in many parts of the world. Recent epidemics caused by CHIKV, an arthritogenic alphavirus, resulted in more than 8.5 million cases as the virus has spread into new geographic regions, including the Western Hemisphere. CHIKV causes disease in the majority of people infected, leading to severe and debilitating arthritis. Despite the severity of CHIKV disease, there are no licensed therapeutics. Since attachment factors and receptors are determinants of viral tropism and pathogenesis, understanding these virus-host interactions can enhance our knowledge of CHIKV infection. We analyzed over 670 glycans and identified GAGs as the main glycan bound by CHIKV. We defined specific GAG components required for CHIKV binding and assessed strain-specific differences in GAG binding capacity. These studies provide insight about cell surface molecules that CHIKV binds, which could facilitate the development of antiviral therapeutics targeting the CHIKV attachment step.

Chikungunya infection: de-linking replication from symptomatology reveals the central role of muscle

Chikungunya virus (CHIKV) is an emerging arbovirus, endemic in many parts of the world, that is spread by travelers and adapts to new mosquito vectors that live in temperate climates. CHIKV replicates in many host tissues and initially causes a self-limiting febrile illness similar to dengue. However, in 30%-40% of cases, CHIKV also causes long-term painful and debilitating muscle and joint pain, the pathogenesis of which remains unknown. In this issue of the JCI, Lentscher et al. engineered a skeletal muscle-restricted CHIKV to show that while musculoskeletal disease requires viral replication in affected muscle, muscular pathology is mediated by host immunological factors. These findings de-link viral replication and disease symptoms, illuminate the virus-host interplay in CHIKV symptomatology, and raise the possibility that immune modulation is a therapeutic option. The results also highlight possible solutions to existing vaccine barriers and provide insights that may apply to other viral diseases.

Engineering a fidelity-variant live-attenuated vaccine for chikungunya virus

Chikungunya virus (CHIKV), which causes a febrile illness characterized by severe and prolonged polyarthralgia/polyarthritis, is responsible for a global disease burden of millions of cases each year with autochthonous transmission in over 100 countries and territories worldwide. There is currently no approved treatment or vaccine for CHIKV. One live-attenuated vaccine (LAV) developed by the United States Army progressed to Phase II human clinical trials but was withdrawn when 8% of volunteers developed joint pain associated with vaccination. Attenuation of the Army’s CHIKV LAV strain 181 clone 25 (CHIKV-181/25) relies on two mutations in the envelope 2 (E2) glycoprotein responsible for cell binding and entry, making it particularly prone to reversion, a common concern for replication-competent vaccines. High error rates associated with RNA virus replication have posed a challenge for LAV development where stable incorporation of attenuating elements is necessary for establishing safety in pre-clinical models. Herein, we incorporate two replicase mutations into CHIKV-181/25 which modulate CHIKV replication fidelity combined with additional attenuating features that cannot be eliminated by point mutation. The mutations were stably incorporated in the LAV and did not increase virulence in mice. Two fidelity-variant CHIKV LAVs generated neutralizing antibodies and were protective from CHIKV disease in adult mice. Unexpectedly, our fidelity-variant candidates were more mutable than CHIKV-181/25 and exhibited restricted replication in mice and Aedes mosquitoes, a possible consequence of hypermutation. Our data demonstrate safety and efficacy but highlight a further need to evaluate fidelity-altering phenotypes before use as a LAV given the potential for virulent reversion.

Hypervariable Domain of nsP3 of Eastern Equine Encephalitis Virus Is a Critical Determinant of Viral Virulence

Eastern equine encephalitis virus (EEEV) is the most pathogenic member of the Alphavirus genus in the Togaviridae family. This virus continues to circulate in the New World and has a potential for deliberate use as a bioweapon. Despite the public health threat, to date no attenuated EEEV variants have been applied as live EEEV vaccines. Our previous studies demonstrated the critical function of the hypervariable domain (HVD) in EEEV nsP3 for the assembly of viral replication complexes (vRCs). EEEV HVD contains short linear motifs that recruit host proteins required for vRC formation and function. In this study, we developed a set of EEEV mutants that contained combinations of deletions in nsP3 HVD and clustered mutations in capsid protein, and tested the effects of these modifications on EEEV infection in vivo These mutations had cumulative negative effects on viral ability to induce meningoencephalitis. The deletions of two critical motifs, which interact with the members of cellular FXR and G3BP protein families, made EEEV cease to be neurovirulent. The additional clustered mutations in capsid protein, which affect its ability to induce transcriptional shutoff, diminished EEEV's ability to develop viremia. Most notably, despite the inability to induce detectable disease, the designed EEEV mutants remained highly immunogenic and, after a single dose, protected mice against subsequent infection with wild-type (wt) EEEV. Thus, alterations of interactions of EEEV HVD and likely HVDs of other alphaviruses with host factors represent an important direction for development of highly attenuated viruses that can be applied as live vaccines.IMPORTANCE Hypervariable domains (HVDs) of alphavirus nsP3 proteins recruit host proteins into viral replication complexes. The sets of HVD-binding host factors are specific for each alphavirus, and we have previously identified those specific for EEEV. The results of this study demonstrate that the deletions of the binding sites of the G3BP and FXR protein families in the nsP3 HVD of EEEV make the virus avirulent for mice. Mutations in the nuclear localization signal in EEEV capsid protein have an additional negative effect on viral replication in vivo Despite the inability to cause a detectable disease, the double HVD and triple HVD/capsid mutants induce high levels of neutralizing antibodies. Single immunization protects mice against infection with the highly pathogenic North American strain of EEEV. High safety, the inability to revert to wild-type phenotype, and high immunogenicity make the designed mutants attractive vaccine candidates for EEEV infection.

Mutating chikungunya virus non-structural protein produces potent live-attenuated vaccine candidate

Currently, there are no commercially available live-attenuated vaccines against chikungunya virus (CHIKV). Here, CHIKVs with mutations in non-structural proteins (nsPs) were investigated for their suitability as attenuated CHIKV vaccines. R532H mutation in nsP1 caused reduced infectivity in mouse tail fibroblasts but an enhanced type-I IFN response compared to WT-CHIKV Adult mice infected with this nsP-mutant exhibited a mild joint phenotype with low-level viremia that rapidly cleared. Mechanistically, ingenuity pathway analyses revealed a tilt in the anti-inflammatory IL-10 versus pro-inflammatory IL-1β and IL-18 balance during CHIKV nsP-mutant infection that modified acute antiviral and cell signaling canonical pathways. Challenging CHIKV nsP-mutant-infected mice with WT-CHIKV or the closely related O'nyong-nyong virus resulted in no detectable viremia, observable joint inflammation, or damage. Challenged mice showed high antibody titers with efficient neutralizing capacity, indicative of immunological memory. Manipulating molecular processes that govern CHIKV replication could lead to plausible vaccine candidates against alphavirus infection.

Effect of a Chikungunya Virus-Like Particle Vaccine on Safety and Tolerability Outcomes: A Randomized Clinical Trial

IMPORTANCE

Chikungunya virus (CHIKV) is a mosquito-borne Alphavirus prevalent worldwide. There are currently no licensed vaccines or therapies.

OBJECTIVE

To evaluate the safety and tolerability of an investigational CHIKV virus-like particle (VLP) vaccine in endemic regions.

DESIGN, SETTING, AND PARTICIPANTS

This was a randomized, placebo-controlled, double-blind, phase 2 clinical trial to assess the vaccine VRC-CHKVLP059-00-VP (CHIKV VLP). The trial was conducted at 6 outpatient clinical research sites located in Haiti, Dominican Republic, Martinique, Guadeloupe, and Puerto Rico. A total of 400 healthy adults aged 18 through 60 years were enrolled after meeting eligibility criteria. The first study enrollment occurred on November 18, 2015; the final study visit, March 6, 2018.

INTERVENTIONS

Participants were randomized 1:1 to receive 2 intramuscular injections 28 days apart (20 µg, n = 201) or placebo (n = 199) and were followed up for 72 weeks.

MAIN OUTCOMES AND MEASURES

The primary outcome was the safety (laboratory parameters, adverse events, and CHIKV infection) and tolerability (local and systemic reactogenicity) of the vaccine, and the secondary outcome was immune response by neutralization assay 4 weeks after second vaccination.

RESULTS

Of the 400 randomized participants (mean age, 35 years; 199 [50%] women), 393 (98%) completed the primary safety analysis. All injections were well tolerated. Of the 16 serious adverse events unrelated to the study drugs, 4 (25%) occurred among 4 patients in the vaccine group and 12 (75%) occurred among 11 patients in the placebo group. Of the 16 mild to moderate unsolicited adverse events that were potentially related to the drug, 12 (75%) occurred among 8 patients in the vaccine group and 4 (25%) occurred among 3 patients in the placebo group. All potentially related adverse events resolved without clinical sequelae. At baseline, there was no significant difference between the effective concentration (EC50)-which is the dilution of sera that inhibits 50% infection in viral neutralization assay-geometric mean titers (GMTs) of neutralizing antibodies of the vaccine group (46; 95% CI, 34-63) and the placebo group (43; 95% CI, 32-57). Eight weeks following the first administration, the EC50 GMT in the vaccine group was 2005 (95% CI, 1680-2392) vs 43 (95% CI, 32-58; P < .001) in the placebo group. Durability of the immune response was demonstrated through 72 weeks after vaccination.

CONCLUSIONS AND RELEVANCE

Among healthy adults in a chikungunya endemic population, a virus-like particle vaccine compared with placebo demonstrated safety and tolerability. Phase 3 trials are needed to assess clinical efficacy.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02562482.

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.