Regulatory considerations in development of vaccines to prevent disease caused by Chikungunya virus

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus. Chikungunya disease (CHIK) in humans is characterized by sudden onset of high fever, cutaneous rash, myalgia and debilitating polyarthralgia. Until recently the virus was considered endemic to only Africa and Asia, but since 2004 CHIK has spread to previously non-endemic regions, including Europe and the Americas, thereby emerging as a global health threat. Although a variety of CHIKV vaccine candidates have been tested in animals, and a few have advanced to human clinical trials, no licensed vaccine is currently available for prevention of disease. In this article, we review recent efforts in CHIKV vaccine development and discuss regulatory considerations for CHIKV vaccine licensure under U.S. FDA regulations. Several licensure pathways are available, and the most appropriate licensure pathway for a CHIK vaccine will depend on the type of evidence that can be generated to demonstrate the vaccine’s effectiveness. If “traditional approval” following demonstration of direct benefit in adequate and well-controlled clinical disease endpoint studies is not possible, the Accelerated Approval and Animal Rule pathways are potential alternatives. In terms of vaccine safety, the potential for vaccine associated arthralgia and antibody-dependent enhancement of infectivity and disease severity are important issues that should be addressed in both pre-clinical and clinical studies. CHIK vaccine developers are encouraged to communicate with the FDA during all stages of vaccine development.     

A Brighton Collaboration standardized template with key considerations for a benefit/risk assessment for an inactivated viral vaccine against Chikungunya virus

Inactivated viral vaccines have long been used in humans for diseases of global health threat (e.g., poliomyelitis and pandemic and seasonal influenza) and the technology of inactivation has more recently been used for emerging diseases such as West Nile, Chikungunya, Ross River, SARS and especially for COVID-19.The Brighton Collaboration Benefit-Risk Assessment of VAccines by TechnolOgy (BRAVATO) Working Group has prepared standardized templates to describe the key considerations for the benefit and risk of several vaccine platform technologies, including inactivated viral vaccines. This paper uses the BRAVATO inactivated virus vaccine template to review the features of an inactivated whole chikungunya virus (CHIKV) vaccine that has been evaluated in several preclinical studies and clinical trials.The inactivated whole CHIKV vaccine was cultured on Vero cells and inactivated by ß-propiolactone. This provides an effective, flexible system for high-yield manufacturing. The inactivated whole CHIKV vaccine has favorable thermostability profiles, compatible with vaccine supply chains.Safety data are compiled in the current inactivated whole CHIKV vaccine safety database with unblinded data from the ongoing studies: 850 participants from phase II study (parts A and B) outside of India, and 600 participants from ongoing phase II study in India, and completed phase I clinical studies for 60 subjects. Overall, the inactivated whole CHIKV vaccine has been well tolerated, with no significant safety issues identified. Evaluation of the inactivated whole CHIKV vaccine is continuing, with 1410 participants vaccinated as of 20 April 2022. Extensive evaluation of immunogenicity in humans shows strong, durable humoral immune responses.     

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.     

Cross-protective immunity against o'nyong-nyong virus afforded by a novel recombinant chikungunya vaccine

Emerging mosquito-borne alphavirus infections caused by chikungunya virus (CHIKV) or o'nyong-nyong virus (ONNV) are responsible for sporadic and sometimes explosive urban outbreaks. Currently, there is no licensed vaccine against either virus. We have developed a highly attenuated recombinant CHIKV candidate vaccine (CHIKV/IRES) that in preclinical studies was demonstrated to be safe, immunogenic and efficacious. In this study we investigated the potential of this vaccine to induce cross-protective immunity against the antigenically related ONNV. Our studies demonstrated that a single dose of CHIKV/IRES elicited a strong cross-neutralizing antibody response and conferred protection against ONNV challenge in the A129 mouse model. Moreover, CHIKV/IRES immune A129 dams transferred antibodies to their offspring that were protective, and passively transferred anti-CHIKV/IRES immune serum protected AG129 mice, independently of a functional IFN response. These findings highlight the potential of the CHIKV/IRES vaccine to protect humans against not only CHIKV but also against ONNV-induced disease.     

Status of research and development of vaccines for chikungunya

Chikungunya virus (CHIKV) is an arthritogenic alphavirus that during the last decade has significantly expanded its geographical range and caused large outbreaks of human disease around the world. Although mortality rates associated with CHIKV outbreaks are low, acute and chronic illnesses caused by CHIKV represent a significant burden of disease largely affecting low and middle income countries. This report summarizes the current status of vaccine development for CHIKV.     

A recombinant measles vaccine expressing chikungunya virus-like particles is strongly immunogenic and protects mice from lethal challenge with chikungunya virus

Chikungunya virus (CHIKV), a mosquito-transmitted alphavirus, recently reemerged in the Indian Ocean, India and Southeast Asia, causing millions of cases of severe polyarthralgia. No specific treatment to prevent disease or vaccine to limit epidemics is currently available. Here we describe a recombinant live-attenuated measles vaccine (MV) expressing CHIKV virus-like particles comprising capsid and envelope structural proteins from the recent CHIKV strain La Reunion. Immunization of mice susceptible to measles virus induced high titers of CHIKV antibodies that neutralized several primary isolates. Specific cellular immune responses were also elicited. A single immunization with this vaccine candidate protected all mice from a lethal CHIKV challenge, and passive transfer of immune sera conferred protection to naïve mice. Measles vaccine is one of the safest and most effective human vaccines. A recombinant MV-CHIKV virus could make a safe and effective vaccine against chikungunya that deserves to be further tested in human trials.     

Deciphering the protective role of adaptive immunity to CHIKV/IRES a novel candidate vaccine against Chikungunya in the A129 mouse model

Chikungunya virus (CHIKV), a mosquito-borne alphavirus, recently re-emerged in Africa and spread to islands in the Indian Ocean, the Indian subcontinent, and to South East Asia. Viremic travelers have also imported CHIKV to the Western hemisphere highlighting the importance of CHIKV in public health. In addition to the great burden of arthralgic disease, which can persist for months or years, epidemiologic studies have estimated case-fatality rates of ∼0.1%, principally from neurologic disease in older patients. There are no licensed vaccines or effective therapies to prevent or treat human CHIKV infections. We have developed a live CHIKV vaccine (CHIKV/IRES) that is highly attenuated yet immunogenic in mouse models, and is incapable of replicating in mosquito cells. In this study we sought to decipher the role of adaptive immunity elicited by CHIKV/IRES in protection against wild-type CHIKV infection. A single dose of vaccine effectively activated T cells with an expansion peak on day 10 post immunization and elicited memory CD4⁺ and CD8⁺ T cells that produced IFN-γ, TNF-α and IL-2 upon restimulation with CHIKV/IRES. Adoptive transfer of CHIKV/IRES-immune CD4⁺ or CD8⁺ T cells did not confer protection against wtCHIKV-LR challenge. By contrast, passive immunization with anti-CHIKV/IRES immune serum provided protection, and a correlate of a minimum protective neutralizing antibody titer was established. Overall, our findings demonstrate the immunogenic potential of the CHIKV/IRES vaccine and highlight the important role that neutralizing antibodies play in protection against an acute CHIKV infection.     

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.     

Immunological implications of diverse production approaches for Chikungunya virus-like particle vaccines

Chikungunya virus (CHIKV), an arbovirus from the Alphavirus genus, causes sporadic outbreaks and epidemics and can cause acute febrile illness accompanied by severe long-term arthralgias. Over 20 CHIKV vaccine candidates have been developed over the last two decades, utilizing a wide range of vaccine platforms, including virus-like particles (VLP). A CHIKV VLP vaccine candidate is among three candidates in late-stage clinical testing and has potentially promising data in nonclinical and clinical studies exploring safety and vaccine immunogenicity. Despite the consistency of the CHIKV VLP structure, vaccine candidates vary significantly in protein sequence identity, structural protein expression cassettes and their mode of production. Here, we explore the impact of CHIKV VLP coding sequence variation and the chosen expression platform, which affect VLP expression yields, antigenicity and overall vaccine immunogenicity. Additionally, we explore the potential of the CHIKV VLP platform to be modified to elicit protection against other pathogens.     

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

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

Deinococcus Mn2+-peptide complex: A novel approach to alphavirus vaccine development

Over the last ten years, Chikungunya virus (CHIKV), an Old World alphavirus has caused numerous outbreaks in Asian and European countries and the Americas, making it an emerging pathogen of great global health importance. Venezuelan equine encephalitis virus (VEEV), a New World alphavirus, on the other hand, has been developed as a bioweapon in the past due to its ease of preparation, aerosol dispersion and high lethality in aerosolized form. Currently, there are no FDA approved vaccines against these viruses.In this study, we used a novel approach to develop inactivated vaccines for VEEV and CHIKV by applying gamma-radiation together with a synthetic Mn-decapeptide-phosphate complex (MnDpPi), based on manganous-peptide-orthophosphate antioxidants accumulated in the extremely radiation-resistant bacterium Deinococcus radiodurans. Classical gamma-irradiated vaccine development approaches are limited by immunogenicity-loss due to oxidative damage to the surface proteins at the high doses of radiation required for complete virus-inactivation. However, addition of MnDpPi during irradiation process selectively protects proteins, but not the nucleic acids, from the radiation-induced oxidative damage, as required for safe and efficacious vaccine development. Previously, this approach was used to develop a bacterial vaccine. In the present study, we show that this approach can successfully be applied to protecting mice against viral infections.Irradiation of VEEV and CHIKV in the presence of MnDpPi resulted in substantial epitope preservation even at supra-lethal doses of gamma-rays (50,000 Gy). Irradiated viruses were found to be completely inactivated and safe in vivo (neonatal mice). Upon immunization, VEEV inactivated in the presence of MnDpPi resulted in drastically improved protective efficacy. Thus, the MnDpPi-based gamma-inactivation approach described here can readily be applied to developing vaccines against any pathogen of interest in a fast and cost-effective manner.     

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.     

Chimeric alphavirus vaccine candidates for chikungunya

Chikungunya virus (CHIKV) is an emerging alphavirus that has caused major epidemics in India and islands off the east coast of Africa since 2005. Importations into Europe and the Americas, including one that led to epidemic transmission in Italy during 2007, underscore the risk of endemic establishment elsewhere. Because there is no licensed human vaccine, and an attenuated Investigational New Drug product developed by the U.S. Army causes mild arthritis in some vaccinees, we developed chimeric alphavirus vaccine candidates using either Venezuelan equine encephalitis attenuated vaccine strain TC-83, a naturally attenuated strain of eastern equine encephalitis virus (EEEV), or Sindbis virus as a backbone and the structural protein genes of CHIKV. All vaccine candidates replicated efficiently in cell cultures, and were highly attenuated in mice. All of the chimeras also produced robust neutralizing antibody responses, although the TC-83 and EEEV backbones appeared to offer greater immunogenicity. Vaccinated mice were fully protected against disease and viremia after CHIKV challenge.     

Primary respiratory syncytial virus infection: pathology, immune response, and evaluation of vaccine challenge strains in a new mouse model

Respiratory syncytial virus (RSV) is the primary cause of lower respiratory tract illness in young children. Vaccine development has been hampered by the experience of the formalin-inactivated vaccine tested in the 1960's. Currently, several vaccine candidates are under development and immune response to these candidate vaccines must be evaluated closely. We introduce a novel low-dose murine model of RSV infection and a new pathologic scoring system for the resultant pulmonary disease. We have also developed new sensitive methods for measuring cytokine expression. We then used this new model to test vaccine challenge strains of RSV in order to determine their pathogenicity.     

A phase 1, randomized,placebo-controlled,dose-ranging study to evaluate the safety and immunogenicity of an mRNA-based chikungunya virus vaccine in healthy adults

BackgroundChikungunya, a mosquito-borne viral disease caused by the chikungunya virus (CHIKV), causes a significant global health burden, and there is currently no approved vaccine to prevent chikungunya disease. In this study, the safety and immunogenicity of a CHIKV mRNA vaccine candidate (mRNA-1388) were evaluated in healthy participants in a CHIKV-nonendemic region.MethodsThis phase 1, first-in-human, randomized, placebo-controlled, dose-ranging study enrolled healthy adults (ages 18–49 years) between July 2017 and March 2019 in the United States. Participants were randomly assigned (3:1) to receive 2 intramuscular injections 28 days apart with mRNA-1388 in 3 dose-level groups (25 μg, 50 μg, and 100 μg) or placebo and were followed for up to 1 year. Safety (unsolicited adverse events [AEs]), tolerability (local and systemic reactogenicity; solicited AEs), and immunogenicity (geometric mean titers [GMTs] of CHIKV neutralizing and binding antibodies) of mRNA-1388 versus placebo were evaluated.ResultsSixty participants were randomized and received ≥ 1 vaccination; 54 (90 %) completed the study. mRNA-1388 demonstrated favorable safety and reactogenicity profiles at all dose levels. Immunization with mRNA-1388 induced substantial and persistent humoral responses. Dose-dependent increases in neutralizing antibody titers were observed; GMTs (95 % confidence intervals [CIs]) at 28 days after dose 2 were 6.2 (5.1–7.6) for mRNA-1388 25 μg, 53.8 (26.8–108.1) for mRNA-1388 50 μg, 92.8 (43.6–197.6) for mRNA-1388 100 μg, and 5.0 (not estimable) for placebo. Persistent humoral responses were observed up to 1 year after vaccination and remained higher than placebo in the 2 higher mRNA-1388 dose groups. The development of CHIKV-binding antibodies followed a similar trend as that observed with neutralizing antibodies.ConclusionsmRNA-1388, the first mRNA vaccine against CHIKV, was well tolerated and elicited substantial and long-lasting neutralizing antibody responses in healthy adult participants in a nonendemic region.ClinicalTrials.gov: NCT03325075.     

Confronting the pneumococcus: a target shift or bullet change?

Pneumococcal disease remains a major killer, despite several years of biomedical research and vaccine technology. The striking efficacy of a seven-valent pneumococcal conjugate vaccine in the US brings hope for the potential conquest of pneumococcal disease but there are still several obstacles in completing this conquest. Although capsular specific antibodies have been shown to be highly protective, it remains unclear what concentration of these serotype-specific antibodies protect against disease and more recently it has become clear that opsonic activity and avidity of these antibodies are more critical determinants of protection than concentration. During the last decade the immunogenicity and protective capacity of several pneumococcal proteins have been described in animal models and these are now being explored for the development of species-common protein based vaccines. Protein conjugate vaccines are no doubt a great new addition to our amarmatorium in the battle against pneumococcal disease but for several epidemiologic reasons the results from Northern California will not be applicable to most other parts of the world. The vaccine contains a limited number of pneumococcal serotypes and given adequate ecological pressure, replacement disease by non-vaccine serotypes remains a real threat, particularly in areas with very high disease burden. The development of new non-serotype-specific vaccine candidates should be encouraged. Defining immune correlates of protection is crucial for the evaluation of these new generation vaccines. As currently available diagnostic methods are poorly sensitive, the true burden of pneumococcal disease may not be revealed until there is a highly efficacious vaccine in widespread use.     

Phylogeny of Dengue and Chikungunya viruses in Al Hudayda governorate,Yemen

Yemen, which is located in the southwestern end of the Arabian Peninsula, is one of countries most affected by recurrent epidemics caused by emerging vector-borne viruses. Dengue virus (DENV) outbreaks have been reported with increasing frequency in several governorates since the year 2000, and the Chikungunya virus (CHIKV) has been also responsible of large outbreaks and it is now a major public health problem in Yemen. We report the results of the phylogenetic analysis of DENV-2 and CHIKV isolates (NS1 and E1 genes, respectively) detected in an outbreak occurred in Al-Hudayda in 2012. Estimates of the introduction date of CHIKV and DENV-2, and the phylogeographic analysis of DENV-2 are also presented. Phylogenetic analysis showed that the Yemen isolates of DENV belonged to the lineage 2 Cosmopolitan subtype, whereas CHIKV isolates from Yemen belonged to the ECSA genotype. All the CHIKV isolates from Yemen were statistically supported and dated back to the year 2010 (95% HPD: 2009–2011); these sequences showed an alanine in the aminoacid position 226 of the E1 protein. Phylogeographic analysis of DENV-2 virus showed that cluster 1, which included Yemen isolates, dated back to 2003 Burkina Faso strains (95% HPD 1999–2007). The Yemen, cluster dated back to 2011 (95% HPD 2009–2012). Our study sheds light on the global spatiotemporal dynamics of DENV-2 and CHIKV in Yemen. This study reinforces both the need to monitor the spread of CHIKV and DENV, and to apply significant measures for vector control.     

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

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

A human challenge model for dengue infection reveals a possible protective role for sustained interferon gamma levels during the acute phase of illness

Dengue has recently been defined by the World Health Organization as a major international public health concern. Although several vaccine candidates are in various stages of development, there is no licensed vaccine available to assist in controlling the further spread of this mosquito borne disease. The need for a reliable animal model for dengue disease increases the risk to vaccine developers as they move their vaccine candidates into large-scale phase III testing. In this paper we describe the cellular immune responses observed in a human challenge model for dengue infection; a model that has the potential to provide efficacy data for potential vaccine candidates in a controlled setting. Serum levels of sIL-2Rα and sTNF-RII were increased in volunteers who developed illness. Supernatants from in vitro stimulated PBMC were tested for cytokines associated with a T_H1 or T_H2 T-cell response (IL-2, TNF-α, IFN-γ, IL-4, IL-10, IL-5) and only IFN-γ was associated with protection against fever and/or viremia. Interestingly, IFN-γ levels drop to 0 pg/mL for volunteers who develop illness after challenge suggesting that some mechanism of immunosuppression may play a role in dengue illness. The human challenge model provides an opportunity to test potential vaccine candidates for efficacy prior to large-scale phase III testing, and hints at a possible mechanism for immune suppression by dengue.