Immunogenicity of novel consensus-based DNA vaccines against Chikungunya virus

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.

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.

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.

A measles virus-based vaccine induces robust chikungunya virus-specific CD4+ T-cell responses in a phase II clinical trial

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitos that causes a debilitating disease characterized by fever and long-lasting polyarthralgia. To date, no vaccine has been licensed, but multiple vaccine candidates are under evaluation in clinical trials. One of these vaccines is based on a measles virus vector encoding for the CHIKV structural genes C, E3, E2, 6K, and E1 (MV-CHIK), which proved safe in phase I and II clinical trials and elicited CHIKV-specific antibody responses in adult measles seropositive vaccine recipients. Here, we predicted T-cell epitopes in the CHIKV structural genes and investigated whether MV-CHIK vaccination induced CHIKV-specific CD4+ and/or CD8+ T-cell responses. Immune-dominant regions containing multiple epitopes in silico predicted to bind to HLA class II molecules were found for four of the five structural proteins, while no such regions were predicted for HLA class I. Experimentally, CHIKV-specific CD4+ T-cells were detected in six out of twelve participants after a single MV-CHIK vaccination and more robust responses were found 4 weeks after two vaccinations (ten out of twelve participants). T-cells were mainly directed against the three large structural proteins C, E2 and E1. Next, we sorted and expanded CHIKV-specific T cell clones (TCC) and identified human CHIKV T-cell epitopes by deconvolution. Interestingly, eight out of nine CD4+ TCC recognized an epitope in accordance with the in silico prediction. CHIKV-specific CD8+ T-cells induced by MV-CHIK vaccination were inconsistently detected. Our data show that the MV-CHIK vector vaccine induced a functional transgene-specific CD4+ T cell response which, together with the evidence of neutralizing antibodies as correlate of protection for CHIKV, makes MV-CHIK a promising vaccine candidate in the prevention of chikungunya.

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.

Heterologous DNA Prime- Subunit Protein Boost with Chikungunya Virus E2 Induces Neutralizing Antibodies and Cellular-Mediated Immunity

Chikungunya virus (CHIKV) has become a significant public health concern due to the increasing number of outbreaks worldwide and the associated comorbidities. Despite substantial efforts, there is no specific treatment or licensed vaccine against CHIKV to date. The E2 glycoprotein of CHIKV is a promising vaccine candidate as it is a major target of neutralizing antibodies during infection. In this study, we evaluated the immunogenicity of two DNA vaccines (a non-targeted and a dendritic cell-targeted vaccine) encoding a consensus sequence of E2_CHIKV and a recombinant protein (E2*_CHIKV). Mice were immunized with different homologous and heterologous DNAprime-E2* protein boost strategies, and the specific humoral and cellular immune responses were accessed. We found that mice immunized with heterologous non-targeted DNA prime- E2*_CHIKV protein boost developed high levels of neutralizing antibodies, as well as specific IFN-γ producing cells and polyfunctional CD4⁺ and CD8⁺ T cells. We also identified 14 potential epitopes along the E2_CHIKV protein. Furthermore, immunization with recombinant E2*_CHIKV combined with the adjuvant AS03 presented the highest humoral response with neutralizing capacity. Finally, we show that the heterologous prime-boost strategy with the non-targeted pVAX-E2 DNA vaccine as the prime followed by E2* protein + AS03 boost is a promising combination to elicit a broad humoral and cellular immune response. Together, our data highlights the importance of E2_CHIKV for the development of a CHIKV vaccine.

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.

PCP consensus protein/peptide alphavirus antigens stimulate broad spectrum neutralizing antibodies

Vaccines based on proteins and peptides may be safer and if calculated based on many sequences, more broad-spectrum than those designed based on single strains. Physicochemical Property Consensus (PCP_con) alphavirus (AV) antigens from the B-domain of the E2 envelope protein were designed, synthesized recombinantly and shown to be immunogenic (i.e. sera after inoculation detected the antigen in dotspots and ELISA). Antibodies in sera after inoculation with B-region antigens based on individual AV species (eastern or Venezuelan equine encephalitis (EEEV_con, VEEV_con), or chikungunya (CHIKV_con) bound only their cognate protein, while those designed against multiple species (Mosaik_con and EVC_con) recognized all three serotype specific antigens. The VEEV_con and EEEV_con sera only showed antiviral activity against their related strains (in plaque reduction neutralization assays (PRNT_50/80). Peptides designed to surface exposed areas of the E2-A-domain of CHIKV_con were added to CHIKV_con inocula to provide anti-CHIKV antibodies. EVC_con, based on three different alphavirus species, combined with E2-A-domain peptides from AllAV_con, a PCPcon of 24 diverse AV, generated broad spectrum, antiviral antibodies against VEEV, EEEV and CHIKV, AV with less than 35% amino acid identity to each other (>65% diversity). This is a promising start to a molecularly defined vaccine against all AV. Further study with these antigens can illuminate what areas are most important for a robust immune response, resistant to mutations in rapidly evolving viruses. The validated computational methods can also be used to design broad spectrum antigens against many other pathogen families.

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.

Immune profile and responses of a novel dengue DNA vaccine encoding an EDIII-NS1 consensus design based on Indo-African sequences

The ongoing COVID-19 pandemic highlights the need to tackle viral variants, expand the number of antigens, and assess diverse delivery systems for vaccines against emerging viruses. In the present study, a DNA vaccine candidate was generated by combining in tandem envelope protein domain III (EDIII) of dengue virus serotypes 1-4 and a dengue virus (DENV)-2 non-structural protein 1 (NS1) protein-coding region. Each domain was designed as a serotype-specific consensus coding sequence derived from different genotypes based on the whole genome sequencing of clinical isolates in India and complemented with data from Africa. This sequence was further optimized for protein expression. In silico structural analysis of the EDIII consensus sequence revealed that epitopes are structurally conserved and immunogenic. The vaccination of mice with this construct induced pan-serotype neutralizing antibodies and antigen-specific T cell responses. Assaying intracellular interferon (IFN)-γ staining, immunoglobulin IgG2(a/c)/IgG1 ratios, and immune gene profiling suggests a strong Th1-dominant immune response. Finally, the passive transfer of immune sera protected AG129 mice challenged with a virulent, non-mouse-adapted DENV-2 strain. Our findings collectively suggest an alternative strategy for dengue vaccine design by offering a novel vaccine candidate with a possible broad-spectrum protection and a successful clinical translation either as a stand alone or in a mix and match strategy.

A high-dose inoculum size results in persistent viral infection and arthritis in mice infected with chikungunya virus

Chikungunya virus (CHIKV) is an emerging mosquito-transmitted alphavirus that leads to acute fever and chronic debilitating polyarthralgia. To date, the mechanism underlying chronic recurrent arthralgia is unknown. In the present study, newborn wild-type C57BL/6 mice were infected with CHIKV, and the virological and pathological features of CHIKV infection were analyzed over a period of 50 days. Acute viral infection was readily established by footpad inoculation of CHIKV at doses ranging from 10 plaque forming unit (PFU) to 106 PFU, during which inoculation dose-dependent viral RNA and skeletal muscle damage were detected in the foot tissues. However, persistent CHIKV was observed only when the mice were infected with a high dose of 106 PFU of CHIKV, in which low copy numbers (103−104) of viral positive strand RNA were continuously detectable in the feet from 29 to 50 dpi, along with a low level and progressive reduction in virus-specific CD8+ T cell responses. In contrast, viral negative strand RNA was detected at 50 dpi but not at 29 dpi and was accompanied by significant local skeletal muscle damage at 50 dpi when mild synovial hyperplasia appeared in the foot joints, although the damage was briefly repaired at 29 dpi. These results demonstrated that a high viral inoculation dose leads to viral persistence and progression to chronic tissue damage after recovery from acute infection. Taken together, these results provide a useful tool for elucidating the pathogenesis of persistent CHIKV infection and viral relapse-associated chronic arthritis.

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.

Optimized production and immunogenicity of an insect virus-based chikungunya virus candidate vaccine in cell culture and animal models

A chimeric Eilat/ Chikungunya virus (EILV/CHIKV) was previously reported to replicate only in mosquito cells but capable of inducing robust adaptive immunity in animals. Here, we initially selected C7/10 cells to optimize the production of the chimeric virus. A two-step procedure produced highly purified virus stocks, which was shown to not cause hypersensitive reactions in a mouse sensitization study. We further optimized the dose and characterized the kinetics of EILV/CHIKV-induced immunity. A single dose of 10⁸ PFU was sufficient for induction of high levels of CHIKV-specific IgM and IgG antibodies, memory B cell and CD8⁺ T cell responses. Compared to the live-attenuated CHIKV vaccine 181/25, EILV/CHIKV induced similar levels of CHIKV-specific memory B cells, but higher CD8⁺ T cell responses at day 28. It also induced stronger CD8⁺, but lower CD4⁺ T cell responses than another live-attenuated CHIKV strain (CHIKV/IRES) at day 55 post-vaccination. Lastly, the purified EILV/CHIKV triggered antiviral cytokine responses and activation of antigen presenting cell (APC)s in vivo, but did not induce APCs alone upon in vitro exposure. Overall, our results demonstrate that the EILV/CHIKV vaccine candidate is safe, inexpensive to produce and a potent inducer of both innate and adaptive immunity in mice.

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.

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.

Co-Immunization With CHIKV VLP and DNA Vaccines Induces a Promising Humoral Response in Mice

Chikungunya fever is an acute infectious disease that is mediated by the mosquito-transmitted chikungunya virus (CHIKV), for which no licensed vaccines are currently available. Here, we explored several immunization protocols and investigated their immunity and protective effects in mice, with DNA- and virus-like particle (VLP)- vaccines, both alone and in combination. Both DNA and VLP vaccine candidates were developed and characterized, which express CHIKV structural genes (C-E3-E2-6K-E1). Mice were immunized twice, with different protocols, followed by immunological detection and CHIKV Ross challenge. The highest antigen-specific IgG and neutralizing activity were induced by DNA and VLP co-immunization, while the highest cellular immunity was induced by DNA vaccination alone. Although all vaccine groups could protect mice from lethal CHIKV challenge, demonstrated as reduced viral load in various tissues, without weight loss, mice co-immunized with DNA and VLP exhibited the mildest histopathological changes and lowest International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) scores, in comparison to mice with either DNA or VLP vaccination alone. We concluded that co-immunization with DNA and VLP is a promising strategy to inducing better protective immunity against CHIKV infection.

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.

Prime-boost with Chikungunya virus E2 envelope protein combined with Poly (I:C) induces specific humoral and cellular immune responses

Chikungunya virus (CHIKV) is an arbovirus transmitted to humans mainly by the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. CHIKV illness is characterized by fever and long-lasting arthritic symptoms, and in some cases it is a deadly disease. The CHIKV envelope E2 (E2_CHIKV) glycoprotein is crucial for virus attachment to the cell. Furthermore, E2_CHIKV is the immunodominant protein and the main target of neutralizing antibodies. To date, there is no available prophylactic vaccine or specific treatment against CHIKV infection. Here, we designed and produced a DNA vaccine and a recombinant protein containing a consensus sequence of E2_CHIKV. C57BL/6 mice immunized twice with the E2_CHIKV recombinant protein in the presence of the adjuvant Poly (I:C) induced the highest E2_CHIKV-specific humoral and cellular immune responses, while the immunization with the homologous DNA vaccine pVAX-E2_CHIKV was able to induce specific IFN-γ producing cells. The heterologous prime-boost strategy was also able to induce specific cellular and humoral immune responses that were, in general, lower than the responses induced by the homologous E2_CHIKV recombinant protein immunization. Furthermore, recombinant E2_CHIKV induced the highest titers of neutralizing antibodies. Collectively, we believe this is the first report to analyze E2_CHIKV-specific humoral and cellular immune responses after immunization with E2_CHIKV recombinant protein and DNA pVAX-E2_CHIKV vaccine platforms.

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There is no current licensed vaccine available against CHIKV.

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CHIKV Envelope E2 (E2_CHIKV) protein is a promising antigen to a vaccine candidate.

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Evaluation of vaccine platforms, adjuvants and strategies were performed.

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Homologous E2_CHIKV ​+ ​Poly (I:C) induced the highest humoral and cellular responses.

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Recombinant E2_CHIKV ​+ ​Poly (I:C) immunized mice presented the highest sera neutralization capacity.

Stimulation of dendritic cell functional maturation by capsid protein from chikungunya virus

Objective(s):

Chikungunya virus (ChikV) infection is characterized by persistent infection in joints and lymphoid organs. The ChikV Capsid protein plays an important role in regulating virus replication. In this study, we hypothesized that capsid protein may stimulate dendritic cell (DC) activation and maturation and trigger an inflammatory response in mice.

Materials and Methods:

Mice were intraperitoneally injected with capsid protein and examined for changes in immunophenotype in lymph nodes (LNs). Next, DCs were treated with capsid protein or LPS and then expression of maturation markers, cytokine production, and ability to stimulate CD4⁺ T cells in allo-MLR were analyzed.

Results:

Injection of mice with capsid protein led to recruitment of myeloid cells and increased activation of T lymphocytes in LNs. Importantly, treatment of DCs with capsid protein prolonged the activation of IKB-α and up-regulated the number of CD11c⁺CD86⁺DCs and release of TNF-α and IL-12p70 as well as reducing DC apoptosis, all effects were abolished in the presence of Bay 11-7082. In addition, IL-2 production was higher by CD4⁺ T cells stimulated with capsid-treated as compared with LPS-induced DCs.

Conclusion:

The observations revealed that capsid protein participates in the regulation of NF-κB signaling and maturation of DCs.

Producing physicochemical property consensus alphavirus protein antigens for broad spectrum vaccine design

There is a pressing need for new vaccines against alphaviruses, which can cause fatal encephalitis (Venezuelan equine encephalitis virus (VEEV) and others) and severe arthralgia (e.g. Chikungunya virus, CHIKV). These positive-strand RNA viruses are diverse and evolve rapidly, meaning that the sequence of any vaccine should cover multiple strains that may be quite different from any previous isolate. Here, consensus proteins were produced to represent the common physicochemical properties (PCPs) of the epitope rich, B domain of the E2 envelope protein. PCP-consensus proteins were based on multiple strains of VEEV (VEEVcon) and CHIKV (CHIKVcon) or the conserved PCPs of 24 different alphaviruses (AllAVcon). The AllAVcon was altered to include binding sites for neutralizing antibodies of both VEEV and CHIKV strains (Mosaikcon). All four designed proteins were produced solubly in E. coli and purified. They formed the β-strand core expected from experimental structures of this region of the wild type E2 proteins as indicated by circular dichroism (CD) spectra. Furthermore, the CHIKVcon protein bound to a structure dependent, CHIKV neutralizing monoclonal antibody. The AllAVcon and Mosaikcon proteins bound to polyclonal antibodies generated during natural infection with either VEEV or CHIKV, indicating they contained epitopes of both serotypes. The Mosaikcon antigen induced antibodies in rabbit sera that recognized both the VEEVcon and CHIKVcon spike proteins. These PCP-consensus antigens are promising starting points for novel, broad-spectrum alphavirus vaccines.

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.

Vaccine-Induced Skewing of T Cell Responses Protects Against Chikungunya Virus Disease

Chikungunya virus (CHIKV) infections can cause severe and debilitating joint and muscular pain that can be long lasting. Current CHIKV vaccines under development rely on the generation of neutralizing antibodies for protection; however, the role of T cells in controlling CHIKV infection and disease is still unclear. Using an overlapping peptide library, we identified the CHIKV-specific T cell receptor epitopes recognized in C57BL/6 infected mice at 7 and 14 days post-infection. A fusion protein containing peptides 451, 416, a small region of nsP4, peptide 47, and an HA tag (CHKVf5) was expressed using adenovirus and cytomegalovirus-vectored vaccines. Mice vaccinated with CHKVf5 elicited robust T cell responses to higher levels than normally observed following CHIKV infection, but the vaccine vectors did not elicit neutralizing antibodies. CHKVf5-vaccinated mice had significantly reduced infectious viral load when challenged by intramuscular CHIKV injection. Depletion of both CD4+ and CD8+ T cells in vaccinated mice rendered them fully susceptible to intramuscular CHIKV challenge. Depletion of CD8+ T cells alone reduced vaccine efficacy, albeit to a lesser extent, but depletion of only CD4+ T cells did not reverse the protective phenotype. These data demonstrated a protective role for CD8+ T cells in CHIKV infection. However, CHKVf5-vaccinated mice that were challenged by footpad inoculation demonstrated equal viral loads and increased footpad swelling at 3 dpi, which we attributed to the presence of CD4 T cell receptor epitopes present in the vaccine. Indeed, vaccination of mice with vectors expressing only CHIKV-specific CD8+ T cell epitopes followed by CHIKV challenge in the footpad prevented footpad swelling and reduced proinflammatory cytokine and chemokines associated with disease, indicating that CHIKV-specific CD8+ T cells prevent CHIKV disease. These results also indicate that a T cell-biased prophylactic vaccination approach is effective against CHIKV challenge and reduces CHIKV-induced disease in mice.

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.

Establishment and Comparison of Pathogenicity and Related Neurotropism in Two Age Groups of Immune Competent Mice, C57BL/6J Using an Indian Isolate of Chikungunya Virus (CHIKV)

Chikungunya (CHIK) is a febrile arboviral illness caused by chikungunya virus (CHIKV) and has been identified in more than 60 countries across the globe. A major public health concern, the infection occurs as an acute febrile phase and a chronic arthralgic phase. The disease manifests differently in different age groups that can range from asymptomatic infection in the younger age group to a prolonged chronic phase in the elderly population. The present study was undertaken to evaluate strain-specific pathogenesis of ECSA genotype of CHIKV strains derived from clinical isolates in adult C57BL/6J mice model. The strain that was pathogenic and developed distinct acute and post-acute phase of CHIK infection was further evaluated for dose-dependent pathogenesis. Upon arriving on the optimal dose to induce clinical symptoms in the mice, the disease progression was evaluated across the acute and the post-acute phase of infection for a period of 15 days post-infection in two age groups of mice, namely eight weeks old and 20 weeks old mice groups. Biochemical, hematological, and virology attributes were measured and correlated to morbidity and linked neurotropism and limb thickness in the two age groups. Our results show that CHIKV exhibit strain-specific pathogenesis in C57BL/6J mice. Distinct dissimilarities were observed between the two age groups in terms of pathogenesis, viral clearance and host response to CHIKV infection.

P38 and JNK Mitogen-Activated Protein Kinases Interact With Chikungunya Virus Non-structural Protein-2 and Regulate TNF Induction During Viral Infection in Macrophages

Chikungunya virus (CHIKV), a mosquito-borne Alphavirus, is endemic in different parts of the globe. The host macrophages are identified as the major cellular reservoirs of CHIKV during infection and this virus triggers robust TNF production in the host macrophages, which might be a key mediator of virus induced inflammation. However, the molecular mechanism underneath TNF induction is not understood yet. Accordingly, the Raw264.7 cells, a mouse macrophage cell line, were infected with CHIKV to address the above-mentioned question. It was observed that CHIKV induces both p38 and JNK phosphorylation in macrophages in a time-dependent manner and p-p38 inhibitor, SB203580 is effective in reducing infection even at lower concentration as compared to the p-JNK inhibitor, SP600125. However, inhibition of p-p38 and p-JNK decreased CHIKV induced TNF production in the host macrophages. Moreover, CHIKV induced macrophage derived TNF was found to facilitate TCR driven T cell activation. Additionally, it was noticed that the expressions of key transcription factors involved mainly in antiviral responses (p-IRF3) and TNF production (p-c-jun) were induced significantly in the CHIKV infected macrophages as compared to the corresponding mock cells. Further, it was demonstrated that CHIKV mediated TNF production in the macrophages is dependent on p38 and JNK MAPK pathways linking p-c-jun transcription factor. Interestingly, it was found that CHIKV nsP2 interacts with both p-p38 and p-JNK MAPKs in the macrophages. This observation was supported by the in silico protein-protein docking analysis which illustrates the specific amino acids responsible for the nsP2-MAPKs interactions. A strong polar interaction was predicted between Thr-180 (within the phosphorylation lip) of p38 and Gln-273 of nsP2, whereas, no such polar interaction was predicted for the phosphorylation lip of JNK which indicates the differential roles of p-p38 and p-JNK during CHIKV infection in the host macrophages. In summary, for the first time it has been shown that CHIKV triggers robust TNF production in the host macrophages via both p-p38 and p-JNK/p-c-jun pathways and the interaction of viral protein, nsP2 with these MAPKs during infection. Hence, this information might shed light in rationale-based drug designing strategies toward a possible control measure of CHIKV infection in future.

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.

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.

A scoping review of Chikungunya virus infection: epidemiology, clinical characteristics, viral co-circulation complications, and control

Chikungunya fever is a mosquito-borne viral illness characterized by a sudden onset of fever associated with joint pains. It was first described in the 1950s during a Chikungunya virus (CHIKV) outbreak in southern Tanzania and has since (re-) emerged and spread to several other geographical areas, reaching large populations and causing massive epidemics. In recent years, CHIKV has gained considerable attention due to its quick spread to the Caribbean and then in the Americas, with many cases reported between 2014 and 2017. CHIKV has further garnered attention due to the clinical diagnostic difficulties when Zika (ZIKV) and dengue (DENV) viruses are simultaneously present. In this review, topical CHIKV-related issues, such as epidemiology and transmission, are examined. The different manifestations of infection (acute, chronic and atypical) are described and a particular focus is placed upon the diagnostic handling in the case of ZIKV and DENV co-circulating. Natural and synthetic compounds under evaluation for treatment of chikungunya disease, including drugs already licensed for other purposes, are also discussed. Finally, previous and current vaccine strategies, as well as the control of the CHIKV transmission through an integrated vector management, are reviewed in some detail.

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.

Depleting the carboxy-terminus of human Wnt5a attenuates collagen-induced arthritis in DBA/1 mice

Wnt5a signalling plays pathological roles in synovial inflammation and bone destruction. In the present study, we designed four human Wnt5a-based DNA recombinants and detected their effects on immunogenicity and anti-rheumatism in a collagen-induced arthritis (CIA) model. Histomorphometry and micro-CT scanning showed that the phWnt5a-NL was superior to other recombinants because it resulted in decreased severity of arthritis, histopathological scores of synovial inflammation and bone erosion in CIA mice. In addition, ELISA and TRAP staining showed that the phWnt5a-NL-immunized CIA mice had reductions in the serum concentrations of the rheumatoid-associated cytokines IL-1β and RANKL and in osteoclastogenesis. Furthermore, flow cytometry showed that the phWnt5a-NL treatment increased the percentage of Treg cells. Finally, western blotting analysis showed that the phWnt5a-NL-immunization interrupted β-catenin and JNK expression in osteoclast precursors derived from the CIA mice. The results suggest that depleting the carboxy-terminus in hWnt5a-based DNA recombinants may be beneficial for the treatment of chronic inflammatory disorders involving bone resorption.

Fingolimod treatment abrogates chikungunya virus-induced arthralgia

Chikungunya virus (CHIKV) is one of the many rheumatic arthropod-borne alphaviruses responsible for debilitating joint inflammation in humans. Despite the severity in many endemic regions, clinically approved intervention targeting the virus remains unavailable. CD4⁺ T cells have been shown to mediate CHIKV-induced joint inflammation in mice. We demonstrate here that transfer of splenic CD4⁺ T cells from virus-infected C57BL/6 mice into virus-infected T cell receptor-deficient (TCR^-/-) mice recapitulated severe joint pathology including inflammation, vascular leakages, subcutaneous edema, and skeletal muscle necrosis. Proteome-wide screening identified dominant CD4⁺ T cell epitopes in nsP1 and E2 viral antigens. Transfer of nsP1- or E2-specific primary CD4⁺ T cell lines into CHIKV-infected TCR^-/- recipients led to severe joint inflammation and vascular leakage. This pathogenic role of virus-specific CD4⁺ T cells in CHIKV infections led to the assessment of clinically approved T cell-suppressive drugs for disease intervention. Although drugs targeting interleukin-2 pathway were ineffective, treatment with fingolimod, an agonist of sphingosine 1-phosphate receptor, successfully abrogated joint pathology in CHIKV-infected animals by blocking the migration of CD4⁺ T cells into the joints without any effect on viral replication. These results set the stage for further clinical evaluation of fingolimod in the treatment of CHIKV-induced joint pathologies.

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.

Protocols for Developing Novel Chikungunya Virus DNA Vaccines

To date, there have been several million infections by the Chikungunya virus (CHIKV), a mosquito-transmitted emerging pathogen that is considered to be taxonomically an Old World RNA virus. Although original CHIKV outbreaks were restricted to India, East Asian countries, Northern Italy, and France, a recent sharp rise had been identified in 41 countries or territories in the Caribbean, Central America, South America, and North America. A total of 1,012,347 suspected and 22,579 laboratory-confirmed CHIKV cases have been reported from these areas, which signals an increasing risk to the US mainland. Unlike past epidemics that were usually associated with Ae. aegypti transmission, the Caribbean outbreak was associated with Ae. albopictus transmission as the principal mosquito vector. In addition, the substantial increase in the number of deaths during this epidemic, as well as incidence of neurologic disease, suggests that CHIKV may have become more virulent. Currently, there are no licensed vaccines or therapeutics available for CHIKV or its associated disease pathologies. Therefore, development of new vaccines and therapies that could confer immunity and/or treat clinical symptoms of CHIKV is greatly desired. This chapter describes the use of entirely cutting edge technologies/methodologies developed by our group for the development and evaluation of novel DNA vaccines against CHIKV.

Single Dose of Consensus Hemagglutinin-Based Virus-Like Particles Vaccine Protects Chickens against Divergent H5 Subtype Influenza Viruses

The H5 subtype highly pathogenic avian influenza (HPAI) virus is one of the greatest threats to global poultry industry. To develop broadly protective H5 subunit vaccine, a recombinant consensus HA sequence (rHA) was constructed and expressed in virus-like particles (rHA VLPs) in the baculovirus-insect cell system. The efficacy of the rHA VLPs vaccine with or without immunopotentiator (CVCVA5) was assessed in chickens. Compared to the commercial Re6 or Re6-CVCVA5 vaccines, single dose immunization of chickens with rHA VLPs or rHA-CVCVA5 vaccines induced higher levels of serum hemagglutinin inhibition titers and neutralization titers, mucosal antibodies, IFN-γ and IL-4 cytokines in sera, and cytotoxic T lymphocyte responses. The rHA VLPs vaccine was superior to the commercial Re6 vaccine in conferring cross-protection against different clades of H5 subtype viruses. This study reports that H5 subtype consensus HA VLP single dose vaccination provides broad protection against HPAI virus in chickens.

Development and application of a bioluminescent imaging mouse model for Chikungunya virus based on pseudovirus system

Chikungunya virus (CHIKV) is an arthropod-borne virus that is transmitted to humans primarily via the bite of an infected mosquito. Infection of humans by CHIKV can cause chikungunya fever which is an acute febrile illness associated with severe, often debilitating polyarthralgias. Since a re-emergence of CHIKV in 2004, the virus has spread into novel locations in nearly 40 countries including non-endemic regions and has led to millions of cases of disease throughout countries. Handling of CHIKV is restricted to the high-containment Biosafety Level 3 (BSL-3) facilities, which greatly impede the research progress of this virus. In this study, an envelope-pseudotyped virus expressing the firefly luciferase reporter protein (pHIV-CHIKV-Fluc) was generated. An in vitro sensitive neutralizing assay and an in vivo bioluminescent-imaging-based mouse infection model had been developed based on the CHIKV pseudovirus. Utilizing the platform, protection effect of DNA vaccine was evaluated. Therefore, this study provides a safe, sensitive and visualizing model for evaluating vaccines and antiviral therapies against CHIKV in low containment BSL-2 laboratories.

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: Current Perspectives on a Reemerging Virus

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus in the family Togaviridae that causes outbreaks of debilitating acute and chronic arthralgia in humans. Although historically associated with localized outbreaks in Africa and Asia, recent epidemics in the Indian Ocean region and the Americas have led to the recognition that CHIKV is capable of moving into previously unaffected areas and causing significant levels of human suffering. The severity of CHIKV rheumatic disease, which can severely impact life quality of infected individuals for weeks, months, or even years, combined with the explosive nature of CHIKV outbreaks and its demonstrated ability to quickly spread into new regions, has led to renewed interest in developing strategies for the prevention or treatment of CHIKV-induced disease. Therefore, this chapter briefly discusses the biology of CHIKV and the factors contributing to CHIKV dissemination, while also discussing the pathogenesis of CHIKV-induced disease and summarizing the status of efforts to develop safe and effective therapies and vaccines against CHIKV and related viruses.

Whole-Inactivated and Virus-Like Particle Vaccine Strategies for Chikungunya Virus

Chikungunya virus (CHIKV) is a global public health threat, having been identified in >60 countries in Asia, Africa, Europe, and the Americas. There is no cure for or licensed vaccine against CHIKV infection. Initial attempts at CHIKV vaccine development began in the early 1960s. Whole-inactivated and virus-like particle (VLP) vaccines are 2 of the current approaches being evaluated. Success of these approaches is dependent on a safe, well-tolerated vaccine that is immunogenic and deployable in regard to manufacturing, stability, and delivery characteristics.

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.

Animal Models of Chikungunya Virus Infection and Disease

Chikungunya virus (CHIKV) is a reemerging alphavirus that causes acute febrile illness and severe joint pain in humans. Although acute symptoms often resolve within a few days, chronic joint and muscle pain can be long lasting. In the last decade, CHIKV has caused widespread outbreaks of unprecedented scale in the Americas, Asia, and the Indian Ocean island regions. Despite these outbreaks and the continued expansion of CHIKV into new areas, mechanisms of chikungunya pathogenesis and disease are not well understood. Experimental animal models are indispensable to the field of CHIKV research. The most commonly used experimental animal models of CHIKV infection are mice and nonhuman primates; each model has its advantages for studying different aspects of CHIKV disease. This review will provide an overview of animal models used to study CHIKV infection and disease and major advances in our understanding of chikungunya obtained from studies performed in these models.

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.

A chikungunya fever vaccine utilizing an insect-specific virus platform

Traditionally, vaccine development involves tradeoffs between immunogenicity and safety. Live-attenuated vaccines typically offer rapid and durable immunity but have reduced safety when compared to inactivated vaccines. In contrast, the inability of inactivated vaccines to replicate enhances safety at the expense of immunogenicity, often necessitating multiple doses and boosters. To overcome these tradeoffs, we developed the insect-specific alphavirus, Eilat virus (EILV), as a vaccine platform. To address the chikungunya fever (CHIKF) pandemic, we used an EILV cDNA clone to design a chimeric virus containing the chikungunya virus (CHIKV) structural proteins. The recombinant EILV/CHIKV was structurally identical at 10 Å to wild-type CHIKV, as determined by single-particle cryo-electron microscopy, and it mimicked the early stages of CHIKV replication in vertebrate cells from attachment and entry to viral RNA delivery. Yet the recombinant virus remained completely defective for productive replication, providing a high degree of safety. A single dose of EILV/CHIKV produced in mosquito cells elicited rapid (within 4 d) and long-lasting (>290 d) neutralizing antibodies that provided complete protection in two different mouse models. In nonhuman primates, EILV/CHIKV elicited rapid and robust immunity that protected against viremia and telemetrically monitored fever. Our EILV platform represents the first structurally native application of an insect-specific virus in preclinical vaccine development and highlights the potential application of such viruses in vaccinology.

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.

Immunogenicity of a novel enhanced consensus DNA vaccine encoding the leptospiral protein LipL45

Leptospirosis is a bacterial zoonotic disease caused by an infection with a spirochete belonging to the genus Leptospira. In animals, leptospirosis displays a wide range of pathologies, including fever, abortion, icterus, and uveitis. Conversely, infection in humans is associated with multi-organ injury, resulting in an increased rate of fatalities. Pathogenic leptospires are able to translocate through cell monolayers at a rate significantly greater than that of non-pathogenic leptospires. Thus, vaccine approaches have been focused on targeting bacterial motility, lipopolysaccharides (LPSs), lipoproteins, outer-membrane proteins (OMPs) and other potential virulence factors. Previous studies have indicated that leptospiral proteins elicit long-lasting immunological memory in infected humans. In the study reported here, the efficacy of a synthetic consensus DNA vaccine developed against the Leptospira membrane lipoprotein LipL45 was tested. After in vivo electroporation (EP) mediated intramuscular immunization with a synthetic LipL45 DNA vaccine (pLipL45) immunized mice developed a significant cellular response along with the development of anti-LipL45-specific antibodies. Specifically, the pLipL45 vaccine induced a significant Th1 type immune response, indicated by the higher production of IL-12 and IFN-γ cytokines. The results presented here are the first demonstration that a LipL45 based DNA immunogen has potential as a anti-Leptospira vaccine.

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.

Rapid and Long-Term Immunity Elicited by DNA-Encoded Antibody Prophylaxis and DNA Vaccination Against Chikungunya Virus

Background. Vaccination and passive antibody therapies are critical for controlling infectious diseases. Passive antibody administration has limitations, including the necessity for purification and multiple injections for efficacy. Vaccination is associated with a lag phase before generation of immunity. Novel approaches reported here utilize the benefits of both methods for the rapid generation of effective immunity.

Methods. A novel antibody-based prophylaxis/therapy entailing the electroporation-mediated delivery of synthetic DNA plasmids encoding biologically active anti–chikungunya virus (CHIKV) envelope monoclonal antibody (dMAb) was designed and evaluated for antiviral efficacy, as well as for the ability to overcome shortcomings inherent with conventional active vaccination and passive immunotherapy.

Results. One intramuscular injection of dMAb produced antibodies in vivo more rapidly than active vaccination with an anti-CHIKV DNA vaccine. This dMAb neutralized diverse CHIKV clinical isolates and protected mice from viral challenge. Combination of dMAb and the CHIKV DNA vaccine afforded rapid and long-lived protection.

Conclusions. A DNA-based dMAb strategy induced rapid protection against an emerging viral infection. This method can be combined with DNA vaccination as a novel strategy to provide both short- and long-term protection against this emerging infectious disease. These studies have implications for pathogen treatment and control strategies.