Infection with chikungunya virus confers heterotypic cross-neutralizing antibodies and memory B-cells against other arthritogenic alphaviruses predominantly through the B domain of the E2 glycoprotein

Cross-neutralizing activity of the chikungunya vaccine VLA1553 against three prevalent chikungunya lineages

Cross-neutralization is generally a prerequisite for cross-protection of vaccines against diseases caused by heterologous viruses. Using sera obtained from a randomized clinical phase 3 trial in adults, we investigated the cross-neutralization activity of VLA1553, a vaccine recently approved to prevent chikungunya disease. Analysed in a plaque reduction neutralization test, the three major chikungunya virus (CHIKV) lineages, namely the East Central South African, the West African, and the Asian lineage, were inhibited by CHIKV-specific neutralizing antibodies present in the sera from vaccinated humans. This effect was independent of the time elapsed since vaccination. Moreover, the magnitude of the immune response was similar to the antibody levels detected in sera from convalescent chikungunya patients. Thus, VLA1553 has the potential to diminish the burden of chikungunya disease on a global scale.Trial registration: ClinicalTrials.gov identifier: NCT04546724.

Development of a virulent O'nyong'nyong challenge model to determine heterologous protection mediated by a hydrogen peroxide-inactivated chikungunya virus vaccine

O'nyong-nyong virus (ONNV) is a mosquito-transmitted alphavirus identified in Uganda in 1959. The virus has potential for enzootic and urban transmission cycles, and in humans, ONNV infection manifests as fever, rash, and joint/muscle pain that can persist. There are currently no specific vaccines or antiviral treatments for ONNV. Since highly passaged alphaviruses often lose pathogenic features, we constructed an infectious clone for ONNV-UVRI0804 (ONNV0804), a 2017 isolate from a febrile patient in Uganda. Viral replication for ONNV0804 was compared to the highly passaged strain, ONNVUgMP30, and ONNVUgMP30 replicated to higher levels in human dermal fibroblasts and Vero cells, but both viruses replicated similarly in C6/36 and mouse embryonic fibroblast cells. We performed a head-to-head comparison of in vivo virulence in both immunocompetent C57BL/6 mice and interferon deficient AG129 mice. In both mouse strains, ONNV0804 was substantially more pathogenic than ONNVUgMP30. Unlike ONNVUgMP30, ONNV0804 caused significant footpad swelling and broader tissue distribution with higher vRNA loads at both 5- and 43-days post-infection (dpi) relative to ONNVUgMP30. This finding indicates that ONNV can persist in joint and muscle tissues for long periods of time, which has been associated with chronic arthritogenic human disease. In AG129 mice, ONNV0804 caused a more rapid onset of disease, higher viremia, and a >800-fold increase in virulence. Previous studies have shown that CHIKV infection or vaccination can provide cross-reactive immunity to ONNV. To determine if a CHIKV vaccine can protect against the more virulent ONNV0804 strain, we vaccinated mice with a hydrogen peroxide-inactivated CHIKV vaccine, HydroVax-CHIKV. Neutralizing antibody titers were determined against ONNV0804 and CHIKV and animals were challenged with ONNV0804. An optimized two-dose vaccination regimen of HydroVax-CHIKV protected against lethal infection and reduced virus-associated arthritogenic disease. These data indicate that we have developed new and robust models for studying severe ONNV disease and that HydroVax-CHIKV vaccination can protect against infection with a highly pathogenic contemporary strain of ONNV.

Exposure to non-endemic arboviruses (alphaviruses) in Costa Rica assessed from human samples collected in areas with contrasting levels of dengue endemicity

Arboviruses represent a global public health challenge. The lack of diagnostic protocols and the presence of asymptomatic infections complicate confirmatory diagnostics. Alphaviruses, such as the equine encephalitis viruses, can cause severe outbreaks and are usually misdiagnosed as dengue. Thus, evidence for their circulation was assessed here. Plaque reduction neutralization test (PRNT) was used to compare sera collected during 2022-2023 from an area with high dengue endemicity (Hone Creek) with another with low endemicity (Great Metropolitan Area, GMA) to elucidate the putative alphavirus circulation and determine whether there were differences between the two areas. The screening results of PRNT50% against the Venezuelan equine encephalitis virus (VEEV) and the Eastern equine encephalitis virus showed that 20.5% of sera collected from Hone Creek were positive for VEEV, with 15.4% (n = 40) showing real neutralizing titers. In the GMA, only 0.8% tested positive for VEEV during the screening, with only 0.3% (n = 1) showing a true neutralizing titer. No sample was positive for the Eastern equine encephalitis virus or Mayaro (MAYV) and one serum sample from Hone Creek was chikungunya positive. This study underscores the global health challenge posed by arboviruses with their similar clinical presentation and antibody cross-reactivity, particularly in tropical regions where flaviviruses and alphaviruses prevail and co-circulate. The comparison of PRNT results between high and low dengue-endemic areas in Costa Rica shed light on the potential circulation of the VEEV and the fact that there is no circulation of Eastern equine encephalitis virus or Mayaro yet. These findings indicate a higher prevalence of VEEV in the high-endemic area, emphasizing the importance of targeted surveillance, control measures, and better diagnostics.

Chikungunya virus E2 B domain nanoparticle immunogen elicits homotypic neutralizing antibody in mice

Alphaviruses are enveloped, positive-sense single-stranded RNA viruses that cause severe human and animal illness. Arthritogenic alphaviruses, such as Chikungunya virus (CHIKV) and Mayaro virus (MAYV), are globally distributed, transmitted by mosquitoes, and can cause rheumatic disease characterized by fever, rash, myalgia, and peripheral polyarthralgia that can persist for years post-infection. These infections can also result in more severe clinical manifestations such as hemorrhage, encephalopathy, and mortality. Several potent monoclonal antibodies (mAbs) with broad neutralizing activity have been shown to bind to the E2 B domain (E2-B) of the alphavirus glycoprotein, suggesting that E2-B epitopes are a site of susceptibility for multiple arthritogenic alphaviruses. However, it is unknown whether E2-B alone can elicit a broadly neutralizing humoral response. Here, we generate and characterize nanoparticle-based immunogens containing CHIKV and MAYV E2-B. Immunization with the CHIKV E2-B nanoparticle elicited sera that were cross-reactive toward CHIKV and MAYV E2-B, but had only homotypic neutralizing activity (serum titer of 1:512) against CHIKV vaccine strain 181/25. Furthermore, immunization with MAYV E2-B nanoparticles elicited non-neutralizing antibody, but sera were cross-reactive for both CHIKV and MAYV E2-B. Our findings suggest that the immunodominant epitopes within CHIKV and MAYV E2-B are bound by cross-reactive, but not cross-neutralizing antibody. Therefore, development of broad E2-B based vaccines that induce broadly neutralizing antibody responses will require engineering to alter the immunodominant landscape.

Pathogenicity and virulence of chikungunya virus

Chikungunya virus (CHIKV) is a mosquito-transmitted, RNA virus that causes an often-severe musculoskeletal illness characterized by fever, joint pain, and a range of debilitating symptoms. The virus has re-emerged as a global health threat in recent decades, spreading from its origin in Africa across Asia and the Americas, leading to widespread outbreaks impacting millions of people. Despite more than 50 years of research into the pathogenesis of CHIKV, there is still no curative treatment available. Current management of CHIKV infections primarily involves providing supportive care to alleviate symptoms and improve the patient's quality of life. Given the ongoing threat of CHIKV, there is an urgent need to better understand its pathogenesis. This understanding is crucial for deciphering the mechanisms underlying the disease and for developing effective strategies for both prevention and management. This review aims to provide a comprehensive overview of CHIKV and its pathogenesis, shedding light on the complex interactions of viral genetics, host factors, immune responses, and vector-related factors. By exploring these intricate connections, the review seeks to contribute to the knowledge base surrounding CHIKV, offering insights that may ultimately lead to more effective prevention and management strategies for this re-emerging global health threat.

Chikungunya Virus Vaccines: A Review of IXCHIQ and PXVX0317 from Pre-Clinical Evaluation to Licensure

Chikungunya virus is an emerging mosquito-borne alphavirus that causes febrile illness and arthritic disease. Chikungunya virus is endemic in 110 countries and the World Health Organization estimates that it has caused more than 2 million cases of crippling acute and chronic arthritis globally since it re-emerged in 2005. Chikungunya virus outbreaks have occurred in Africa, Asia, Indian Ocean islands, South Pacific islands, Europe, and the Americas. Until recently, no specific countermeasures to prevent or treat chikungunya disease were available. To address this need, multiple vaccines are in human trials. These vaccines use messenger RNA-lipid nanoparticles, inactivated virus, and viral vector approaches, with a live-attenuated vaccine VLA1553 and a virus-like particle PXVX0317 in phase III testing. In November 2023, the US Food and Drug Administration (FDA) approved the VLA1553 live-attenuated vaccine, which is marketed as IXCHIQ. In June 2024, Health Canada approved IXCHIQ, and in July 2024, IXCHIQ was approved by the European Commission. On August 13, 2024, the US FDA granted priority review for PXVX0317. The European Medicine Agency is considering accelerated assessment review of PXVX0317, with potential for approval by both agencies in 2025. In this review, we summarize published data from pre-clinical and clinical trials for the IXCHIQ and PXVX0317 vaccines. We also discuss unanswered questions including potential impacts of pre-existing chikungunya virus immunity on vaccine safety and immunogenicity, whether long-term immunity can be achieved, safety in children, pregnant, and immunocompromised individuals, and vaccine efficacy in people with previous exposure to other emerging alphaviruses in addition to chikungunya virus.

Generating prophylactic immunity against arboviruses in vertebrates and invertebrates

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

Nonreciprocity in CHIKV and MAYV Vaccine-Elicited Protection

Chikungunya virus (CHIKV) is a pathogenic arthritogenic alphavirus responsible for large-scale human epidemics for which a vaccine was recently approved for use. Mayaro virus (MAYV) is a related emerging alphavirus with epidemic potential with circulation overlap potential with CHIKV. We previously reported the ability of a non-replicating human adenovirus (AdV)-vectored vaccine expressing the MAYV structural polyprotein to protect against disease in mice following challenge with MAYV, CHIKV and UNAV. Herein, we evaluated mouse immunity and protective efficacy for an AdV-CHIKV full structural polyprotein vaccine in combination with heterologous AdV-MAYV prime/boost regimens versus vaccine coadministration. Heterologous prime/boost regimens skewed immunity toward the prime vaccine antigen but allowed for a boost of cross-neutralizing antibodies, while vaccine co-administration elicited robust, balanced responses capable of boosting. All immunization strategies protected against disease from homologous virus infection, but reciprocal protective immunity differences were revealed upon challenge with heterologous viruses. In vivo passive transfer experiments reproduced the inequity in reciprocal cross-protection after heterologous MAYV challenge. We detected in vitro antibody-dependent enhancement of MAYV replication, suggesting a potential mechanism for the lack of cross-protection. Our findings provide important insights into rational alphavirus vaccine design that may have important implications for the evolving alphavirus vaccine landscape.

The Approved Live-Attenuated Chikungunya Virus Vaccine (IXCHIQ®) Elicits Cross-Neutralizing Antibody Breadth Extending to Multiple Arthritogenic Alphaviruses Similar to the Antibody Breadth Following Natural Infection

The first vaccine against chikungunya virus (CHIKV) was recently licensed in the U.S., Europe, and Canada (brand IXCHIQ®, referred to as VLA1553). Other pathogenic alphaviruses co-circulate with CHIKV and major questions remain regarding the potential of IXCHIQ to confer cross-protection for populations that are exposed to them. Here, we characterized the cross-neutralizing antibody (nAb) responses against heterotypic CHIKV and additional arthritogenic alphaviruses in individuals at one month, six months, and one year post-IXCHIQ vaccination. We characterized nAbs against CHIKV strains LR2006, 181/25, and a 2021 isolate from Tocantins, Brazil, as well as O'nyong-nyong virus (ONNV), Mayaro virus (MAYV), and Ross River virus (RRV). IXCHIQ elicited 100% seroconversion to each virus, with the exception of RRV at 83.3% seroconversion of vaccinees, and cross-neutralizing antibody potency decreased with increasing genetic distance from CHIKV. We compared vaccinee responses to cross-nAbs elicited by natural CHIKV infection in individuals living in the endemic setting of Puerto Rico at 8-9 years post-infection. These data suggest that IXCHIQ efficiently and potently elicits cross-nAb breadth that extends to related alphaviruses in a manner similar to natural CHIKV infection, which may have important implications for individuals that are susceptible to alphavirus co-circulation in regions of potential vaccine rollout.

Potential Serological Misdiagnosis of Barmah Forest Virus and Ross River Virus Diseases as Chikungunya Virus Infections in Australia: Comparison of ELISA with Neutralization Assay Results

To evaluate the frequency of errors in the diagnosis of medical laboratory-diagnosed Chikungunya virus (CHIKV) infections in Australia, we studied 42 laboratory-diagnosed CHIKV serum samples from one Queensland medical laboratory by ELISA IgG/IgM and measured the specific neutralization antibodies (Nab) against Barmah Forest virus (BFV), CHIKV and Ross River virus (RRV). The sero-positivity rates for the sera were as follows: anti-BFV IgG+ 19% (8/42), IgM+ 2.4% (1/42) and Nab+ 16.7% (7/42); anti-CHIKV IgG+ 90.5% (38/42), IgM+ 21.4% (9/42) and Nab+ 90.5% (38/42); anti-RRV IgG+ 88.1% (37/42), IgM+ 28.6% (12/42) and Nab+ 83.2% (35/42), respectively. Among the samples with multiple antibody positivity, 2.4% (1/42) showed triple ELISA IgM+, and 14.3% (6/42) exhibited double IgM RRV+CHIKV+; 9.5% (4/42) showed triple IgG+, 76.2% (32/42) displayed double IgG RRV+CHIKV+, 4.8% (2/42) showed IgG BFV+RRV+ and 4.8% (2/42) showed IgG BFV++CHIKV+; and 9.5% (4/42) showed triple Nab+ and 69% (29/42) exhibited double Nab RRV+CHIKV+, respectively. Our analysis of the single-virus infection control Nab results suggested no cross-neutralization between RRV and BFV, and only mild cross-neutralization between CHIKV and RRV, BFV and CHIKV, all with a ≥4-fold Nab titre ratio difference between the true virus infection and cross-reactivity counterpart virus. Subsequently, we re-diagnosed these 42 patients as 1 BFV+, 8 CHIKV+ and 23 RRV+ single-virus infections, along with five RRV+/BFV+ and four RRV+/CHIKV+ double infections, and one possible RRV+/BFV+ or RRV+CHIKV+, respectively. These findings suggests that a substantial proportion of medically attended RRV and BFV infections were misdiagnosed as CHIKV infections, highlighting the imperative need for diagnostic laboratory tests capable of distinguishing between CHIKV infections and actively co-circulating RRV and BFV. For a correct diagnosis, it is crucial to consider reliable diagnostic methods such as the neutralization assay to exclude RRV and BFV.

Mayaro virus pathogenesis and immunity in rhesus macaques

Mayaro virus (MAYV) is a mosquito-transmitted alphavirus that causes debilitating and persistent arthritogenic disease. While MAYV was previously reported to infect non-human primates (NHP), characterization of MAYV pathogenesis is currently lacking. Therefore, in this study we characterized MAYV infection and immunity in rhesus macaques. To inform the selection of a viral strain for NHP experiments, we evaluated five MAYV strains in C57BL/6 mice and showed that MAYV strain BeAr505411 induced robust tissue dissemination and disease. Three male rhesus macaques were subcutaneously challenged with 105 plaque-forming units of this strain into the arms. Peak plasma viremia occurred at 2 days post-infection (dpi). NHPs were taken to necropsy at 10 dpi to assess viral dissemination, which included the muscles and joints, lymphoid tissues, major organs, male reproductive tissues, as well as peripheral and central nervous system tissues. Histological examination demonstrated that MAYV infection was associated with appendicular joint and muscle inflammation as well as presence of perivascular inflammation in a wide variety of tissues. One animal developed a maculopapular rash and two NHP had viral RNA detected in upper torso skin samples, which was associated with the presence of perivascular and perifollicular lymphocytic aggregation. Analysis of longitudinal peripheral blood samples indicated a robust innate and adaptive immune activation, including the presence of anti-MAYV neutralizing antibodies with activity against related Una virus and chikungunya virus. Inflammatory cytokines and monocyte activation also peaked coincident with viremia, which was well supported by our transcriptomic analysis highlighting enrichment of interferon signaling and other antiviral processes at 2 days post MAYV infection. The rhesus macaque model of MAYV infection recapitulates many of the aspects of human infection and is poised to facilitate the evaluation of novel therapies and vaccines targeting this re-emerging virus.