Dengue virus sero-cross-reactivity drives antibody-dependent enhancement of infection with zika virus

Antibody-dependent enhancement of ORFV uptake into host cells

Orf virus (ORFV) has been demonstrated to infect both goat non-immune cells, specifically goat epithelial cells, and goat blood immune cells. Our previous studies have indicated that ORFV gains entry into goat epithelial cells via clathrin-mediated endocytosis and macropinocytosis pathways. However, the pathway by which ORFV enters goat blood immune cells has not yet been elucidated. Our findings revealed a differential viral internalization pathway in ORFV-infects goat immune cells contrasting the internalization pathways in goat epithelial cells, potentially involving an antibody-related mechanism. Therefore, our hypothesis posits that ORFV gains entry into goat immune cells via the antibody-dependent enhancement (ADE) pathway. Our experimental findings confirm the presence of the ADE effect in ORFV-infected goat immune cells, mediated by Fc receptors (FcRs) as demonstrated in antibody-blocking experiments. Furthermore, the ADE effect was also observed in goat epithelial cells. Nevertheless, the ADE effect observed in goat epithelial cells was not found to be dependent on the interaction between the virus-antibody complex and Fc receptors, as demonstrated by antibody-blocking experiments. Instead, it is suggested that an alternative mechanism involving the complement factor and complement receptors (CRs) may be responsible. Overall, this research offers insights into the unique ADE pathway of ORFV infection in different cell types, offering a novel perspective on the infection and pathogenic mechanisms of ORFV.

Role of non-human primate models in accelerating research and developing countermeasures against Zika virus infection

Zika virus, a mosquito-transmitted orthoflavivirus, has become a pathogen of global health concern ever since the virus caused an epidemic in Brazil in 2015 associated with approximately 700 000 laboratory-confirmed cases of congenital microcephaly. The subsequent spread of the epidemic in 2016 resulted in a wide spectrum of congenital neurological, ophthalmological, and developmental abnormalities across the Americas, Africa, and Asia. In this context, non-human primate models have become essential tools for Zika virus research to understand the pathogenesis of congenital brain injury and perinatal complications and for developing and testing medical countermeasures such as vaccines, diagnostics, and therapeutics. Fetal brain injury has been observed across various non-human primate species and is influenced by factors such as the Zika virus strain, gestational age at inoculation, and inoculation dose and route. Miscarriages are also seen as common outcomes of first trimester Zika virus infections. This Series paper reviews the diverse non-human primate models currently used for Zika virus research to mitigate the public health effects of future Zika virus epidemics.

Toward a deeper understanding of dengue: novel method for quantification and isolation of envelope protein epitope-specific antibodies

The dengue viruses (DENV) envelope (E) protein is the main target of the antibody (Ab) response. Abs target different epitopes on the E-protein, including sE-dimer, E domain III (EDIII), and fusion loop (FL). Anti-EDIII Abs are mainly serotype-specific, whereas anti-FL Abs can induce antibody-dependent enhancement (ADE) in vitro. Abs targeting sE-dimer epitopes can cross-neutralize different DENV serotypes. However, the involvement of each Ab subset in disease pathogenicity and/or protection remains unclear. We aimed to optimize the quantification and purification of DENV E-protein epitope-specific Abs from human samples. C-terminal biotinylated DENV2 E recombinant proteins (EDIII, soluble E [sE], and sE-dimer) were coupled to color-coded magnetic microspheres for a multiplex immunoassay (MIA), testing different antigen concentrations. Assay performance was evaluated using well-characterized anti-DENV monoclonal antibodies (mAbs) and total IgG from DENV seronegative and seropositive human plasma. Specific FL epitopes were blocked with mouse mAb clone 4G2 to quantify anti-FL- and sE-dimer-specific Abs, measuring antigen-antibody reactions as median fluorescence intensity (MFI). For isolation of E-protein epitope-specific antibodies, sE-proteins were conjugated to streptavidin resin beads. Total IgG from human plasma was incubated with immobilized EDIII to elute anti-EDIII Abs. The flow-through was incubated with sE-dimer resin beads to elute sE-dimer specific Ab enriched fraction, and the flow-through was applied to immobilized sE to elute anti-FL Abs. In conclusion, we have developed a serological assay to detect E-protein epitope-specific Abs in DENV-infected humans. Additionally, we successfully isolated anti-EDIII, anti-FL, and an enriched fraction of sE-dimer specific Abs from human samples.IMPORTANCEThe development of effective dengue virus (DENV) vaccines has been hampered by limited insights into the immunological mechanisms of protection. Our study addresses this gap by introducing a refined multiplex microsphere-based immunoassay (MIA) to quantify and isolate antibodies (Abs) targeting specific E-protein epitopes, such as E domain III (EDIII), the fusion loop (FL), and the sE-dimer specific Abs. This method provides detailed epitope-specific Ab profiling with high sensitivity and requires minimal sample volumes. The ability to isolate specific Ab subsets from human plasma also enables detailed investigations into their roles in protection or pathogenesis, paving the way for more effective dengue interventions.

Dengue Dilemma: Navigating Cross-Reactivity and Immune Challenges

This chapter examines the immunological mechanisms underlying the cross-reactivity and immune enhancement in dengue and how they influence the clinical outcomes. The four DENV serotypes (DENV-1 to DENV-4) share high genetic and antigenic similarity, leading to antibodies and T cells that can recognize multiple serotypes. While this cross-reactive immunity can confer partial or transient protection, it can also result in antibody-dependent enhancement (ADE), wherein non-neutralizing antibodies facilitate viral entry into immune cells, increasing the likelihood of severe disease in secondary infections and in infants carrying maternal anti-DENV antibodies. Furthermore, cross-reactivity with other flaviviruses, such as ZIKV, complicates serological diagnosis by producing false-positive results and uncertain prior exposure histories. These complexities extend to vaccine design, which must induce effective immunity against all four DENV serotypes while minimizing ADE risk. Epidemiological studies confirm that secondary infections, especially when antibody levels have waned, carry an elevated risk of severe clinical manifestations. However, the timing between infections and the specific serotype involved can modulate these outcomes. A thorough understanding of cross-reactivity and immune enhancement is therefore pivotal for advancing diagnostic accuracy, guiding patient care, and informing vaccine strategies and public health policies to better control dengue globally.

A novel immunogen comprising a bc loop and mutant fusion loop epitopes generates potent neutralization and protective abilities against flaviviruses without risk of disease enhancement

Flaviviruses, including Dengue virus (DENV), Zika virus (ZIKV) and Japanese encephalitis virus (JEV), remain major global health threats, and currently, there are no widely available vaccines for humans. The fusion loop region of the flavivirus envelope protein plays a crucial role in eliciting neutralizing antibodies and providing protection against secondary DENV infections. However, these antibodies often exhibit dual functionalities, with both neutralizing and enhancing activities, posing a challenge for vaccine development. In this study, we focused on optimizing the fusion loop epitope as the primary immunogen and incorporated the adjacent bc loop which we had reported previously as a complementary element, aiming to enhance the immunogen capable of robust neutralization and protection without inducing the risk of antibody-dependent enhancement (ADE). This newly designed immunogen was named as muBCFL which comprises sequences spanning from amino acid 69 to 116 primarily on DENV-2 envelope protein, along with four specific mutations (T76A, W101A, G106Q, and L107D). The synthesized muBCFL peptide elicited neutralizing antibodies against all four DENV serotypes, ZIKV, and JEV, with particularly strong neutralization activity against DENV-2, ZIKV, and JEV. Besides, compared to pre-immune sera, muBCFL-immune sera significantly reduced viremia levels in DENV- or ZIKV-infected AG129 mice and increased the survival rates of JEV-challenged ICR mice. Furthermore, in vitro and in vivo ADE assays validated that muBCFL-immune sera did not induce ADE compared with the control 4G2 monoclonal antibody. These findings indicated that the muBCFL sequence holds great potential as a safe and effective immunogen for developing a flavivirus vaccine in the future.

Heterologous prime-boost Zika virus vaccination induces comprehensive humoral and cellular immunity in mouse models

Zika virus (ZIKV) remained poorly studied until an outbreak in 2015 linked the virus to severe neurological disorders and congenital malformations. Currently, there are no antiviral drugs or vaccines available. We have previously demonstrated that a simian adenovirus vector vaccine (ChAdOx1 prMEΔTM) and a virus-like particle-based vaccine bearing E proteins locked in covalent dimers (VLP-cvD) are effective against ZIKV infection in animal challenge models. In this study, we further explored the efficacy of these vaccines, either individually or in combination, using a heterologous prime and boost vaccination strategy in mouse challenge models. Although the individual vaccines provided good protection levels, the heterologous prime-boost vaccination regimen (ChAdOx1 prMEΔTM followed by VLP-cvD) offered the most effective protection. This regimen elicited a strong cellular response and high levels of neutralising antibodies, which were attributed to ChAdOx1 prMEΔTM and VLP-cvD, respectively. Our findings support the use of combined vaccine technologies and offer valuable insights into the multifactorial protection achievable through heterologous vaccination. These results have important implications for the development of effective vaccination strategies against ZIKV and other emerging viruses.

From Antibodies to Immunity: Assessing Correlates of Flavivirus Protection and Cross-Reactivity

Flaviviruses are arthropod-borne RNA viruses that can cause a wide range of human diseases, from mild symptoms to severe illness with multiorgan failure and death. Effective prevention of these diseases relies on identifying reliable vaccine targets, typically measured by correlates of protection (CoPs), which help indicate host immunity after vaccination. Current vaccines primarily focus on neutralizing antibodies (nAbs) against the viral envelope E protein, though emerging evidence suggests other potential targets may also be effective in disease prevention. Additionally, there is growing evidence of cross-protection between different flaviviruses when immunity to one virus is achieved, although this can be limited by antibody-dependent enhancement. This review examines the current understanding of flavivirus immunity, CoPs, and the potential for cross-protection in the context of existing vaccine strategies.

mRNA vaccine platforms: linking infectious disease prevention and cancer immunotherapy

The advent of mRNA vaccines, accelerated by the global response to the COVID-19 pandemic, marks a transformative shift in vaccine technology. In this article, we discuss the development, current applications, and prospects of mRNA vaccines for both the prevention and treatment of infectious diseases and oncology. By leveraging the capacity to encode antigens within host cells directly, mRNA vaccines provide a versatile and scalable platform suitable for addressing a broad spectrum of pathogens and tumor-specific antigens. We highlight recent advancements in mRNA vaccine design, innovative delivery mechanisms, and ongoing clinical trials, with particular emphasis on their efficacy in combating infectious diseases, such as COVID-19, Zika, and influenza, as well as their emerging potential in cancer immunotherapy. We also address critical challenges, including vaccine stability, optimization of immune responses, and the broader issue of global accessibility. Finally, we review potential strategies for advancing next-generation mRNA vaccines, with the aim of overcoming current limitations in vaccine technology and enhancing both preventive and therapeutic approaches for infectious and oncological diseases.

Differential Serotype Specificity in the IgG Subclass Profile of the Anti-Domain III Response Elicited by Dengue Virus Infection

Dengue is a potentially fatal disease caused by any of the four serotypes of dengue virus complex (DENV1-4). Domain III (DIII) of the envelope protein mediates early virus:cell interactions and is target of potent neutralizing antibodies. Little data is available on the dynamic of IgG subclasses in anti-DIII response elicited during viral infection. Fifty-eight human sera were used to characterize the IgG subclass profile of the anti-DIII antibody response in terms of abundance and serotype-specificity. Immunodominant epitopes were also determined using 70 Ala-mutants of a recombinant DIII protein that spans residues with more than 15% of the exposed area in the virion. IgG1 and IgG3 were found as the subclasses that react to control primary infections while a significant response was detected for all IgG subclasses in response to secondary infections. Anti-DIII IgG1 exhibits a distinctive pattern of serotype-specificity with respect to the other IgG subclasses in the recognition of recombinant DIII proteins corresponding to the four DENV serotypes. The dominant epitope of IgG1 is located in the FG-loop, which is characterized by high variability in its amino acid sequence. In contrast, the dominant epitopes of IgG2, IgG3, and IgG4 were defined as regions enriched in complex- and subcomplex conserved residues such as the A-strand and the AB-loop of DIII. IgG1 plays a prominent role in neutralizing circulating DENV during infection. A balanced and timely response of the different IgG subclasses is critical in the evolution of dengue disease.

The SARS-CoV-2 antibody-dependent enhancement façade

Antibody-dependent enhancement (ADE) is an immunological paradox whereby sensitization following a primary viral infection results in the subsequent enhancement of a similar secondary infection. This idiosyncratic immune response has been established in dengue virus infections, driven by four antigenically related serotypes co-circulating in endemic regions. Several coronaviruses exhibit antibody-mediated mechanisms of viral entry, which has led to speculation of an ADE capacity for SARS-CoV-2, though in vivo and epidemiological evidence do not currently support this phenomenon. Three distinct antibody-dependent mechanisms for SARS-CoV-2 entry have recently been demonstrated: 1. FcR-dependent, 2. ACE2-FcR-interdependent, and 3. FcR-independent. These mechanisms of viral entry may be dependent on SARS-CoV-2 antibody specificity; antibodies targeting the receptor binding domain (RBD) typically result in Fc-dependent and ACE2-FcR-interdependent entry, whereas antibodies targeting the N-terminal domain can induce a conformational change to the RBD that optimizes ACE2-receptor binding domain interactions independent of Fc receptors. Whether these antibody-dependent entry mechanisms of SARS-CoV-2 result in the generation of infectious progenies and enhancement of infection has not been robustly demonstrated. Furthermore, ADE of SARS-CoV-2 mediated by antigenic seniority remains a theoretical concern, as no evidence suggests that SARS-CoV-2 imprinting blunts a subsequent immune response, contributing to severe COVID-19 disease.

Antibody-dependent enhancement of coronaviruses

The COVID-19 pandemic presents a significant challenge to the global health and the world economy, with humanity engaged in an extended struggle against the virus. Notable advancements have been achieved in the development of vaccines and therapeutic interventions, including the application of neutralizing antibodies (NAbs) and convalescent plasma (CP). While antibody-dependent enhancement (ADE) has not been observed in human clinical studies related to SARS-CoV-2, the potential for ADE remains a critical concern and challenge in addressing SARS-CoV-2 infections. Moreover, the causal relationship between ADE and viral characteristics remains to be clearly elucidated. Viruses that present with severe clinical manifestations of ADE have demonstrated the capacity to replicate in macrophages or other immune cells, or to alter the immunological status of these cells, which induces abortive infections characterized by systemic inflammation. In this review, we summarize experimental observations and clinical evidence concerning the ADE effect associated with coronaviruses. We critically examine the potential mechanisms through which coronaviruses mediate ADE, and propose strategies to mitigate this phenomenon in the context of viral infection treatment. Our aim is to offer informed recommendations for the containment of the COVID-19 pandemic and to strengthen the response to SARS-CoV-2, as well as to prepare for potential future coronavirus threats.

Zika and Dengue Virus Autoimmunity: An Overview of Related Disorders and Their Potential Mechanisms

Zika virus (ZIKV) and dengue virus (DENV) are two major mosquito-borne flaviviruses that pose a significant threat to the global public health system, particularly in tropical regions. The clinical outcomes related to these viral pathogens can vary from self-limiting asymptomatic infections to various forms of life-threatening pathological conditions such as haemorrhagic disorders. In addition to the direct effects of the viral pathogens, immune processes play also a significant function in the development of diseases mediated by ZIKV and DENV. Studing these processes is important for developing safer vaccines and targeted therapeutic strategies. These viruses have been reported to trigger various autoimmune disorders affecting different parts of human organ systems. It also has been shown that preexisting immunity to ZIKV or DENV can impact the outcome of subsequent infections caused by another virus. ZIKV and DENV infection can promote the development of autoimmune disorders by different mechanisms, such as molecular mimicry and autoantibody formation. The present review provides an overview of various autoimmune disorders associated with ZIKV and DENV infection and their potential underlying mechanisms.

Susceptible-infected-recovered-susceptible processes competing on simplicial complexes

Contagions do not exist in isolation but in the presence of other propagating quantities, with which they may compete. Furthermore, higher-order interactions (interactions involving more than two nodes) are widely represented in real-world systems. We propose a stochastic model for susceptible-infected-recovered-susceptible (SIRS) processes competing in a simplicial complex that accommodates higher-order interactions. We also propose deterministic microscopic Markov chain (MMC) and mean-field (MF) forms of this model, which we analyze to reveal conditions for the persistence of each infection. We verify our analysis via numerical simulations, which also unveil critical mass effects, discontinuous phase transitions, and bistability. The stochastic model exhibits eight distinct classes of dependence of final state on initial conditions. All eight of these classes can be approximately reproduced with MMC, but only seven are seen under MF. The class observed in MMC and approximated in the stochastic model, but missing from MF, involves three distinct steady states for a single set of parameter values. However, in the absence of higher-order interactions MF exhibits an additional class, not observed in MMC or the stochastic model, corresponding to an infinite spectrum of steady states, in which the ratio of infection levels remains at its initial level. Both MMC and MF models can exhibit sustained oscillations in which one contagion disappears while the other tends to a limit cycle.

Published by the American Physical Society 2024

Zika virus infection and acute transverse myelitis: a comprehensive systematic review

The Zika virus (ZIKV) has been associated with several complications, including acute transverse myelitis (ATM), an acute inflammation of the spinal cord, with rapid development of motor, sensory and dysautonomic symptoms. It is a rare disease, and its clinical features, as well as differences in relation to idiopathic ATMs, are still not completely known. The objective of this paper is to review the literature in search of clinical features and complementary exams of ATM post-ZIKV infection, alone or in association with other neurological conditions (mixed diseases), as well as its treatments and prognoses. The search was made on 5 databases, using the PRISMA methodology (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). Nine articles were selected (total of 20 subjects), which were divided between isolated ATM and mixed neurological syndromes with ATM. The study found a predominance of individuals aged 20 to 30. Among the six subjects in the mixed group, three were over 50 years old. The median prodromal period was 2 days for the mixed diseases group and 7 days for the isolated ATM group. Some individuals in the isolated ATM group exhibited signs of dysautonomia, such as syncope, postural lability, and arrhythmia. The mixed group had a higher incidence of coinfections, with 4 cases compared to 1 case in the isolated ATM group. Over 50% of the individuals had moderate to moderately severe disability. These findings suggest that severe conditions may progress to significant sequelae, highlighting the need for prompt diagnosis and treatment, particularly during endemic periods.

C1q modulation of antibody-dependent enhancement of dengue virus infection in human myeloid cell lines is dependent on cell type and antibody specificity

Antibody-dependent enhancement (ADE) of dengue virus (DENV) infection is one of the mechanisms contributing to increased severity during heterotypic, secondary infection. The complement protein C1q has been shown to reduce the magnitude of ADE in vitro. Therefore, we investigated the mechanisms of C1q modulation of ADE, focusing on processes of viral entry. Using a model of ADE of DENV-1 infection in human myeloid cell lines in the presence of monoclonal antibodies, 4G2 and 2H2, we found that C1q produced nearly a 40-fold reduction of ADE of DENV-1 in K562 cells, but had no effect in U937 cells. In K562 cells, C1q reduced adsorption of DENV-1/4G2 and exerted a dual inhibitory effect on adsorption and internalization of DENV-1/2H2. Distinct endocytic pathways in the presence of antibody corresponded to conditions where C1q produced a differential action. Also, C1q did not affect the intrinsic cell response mediated by FcγR in human myeloid cells. The modulation of ADE of DENV-1 by C1q is dependent on the FcγR expressed on immune cells and the specificity of the antibody comprising the immune complex. Understanding protective and pathogenic mechanisms in the humoral response to DENV infections is crucial for the successful design of antivirals and vaccines.

The Low-Density Lipoprotein Receptor-Related Protein-1 Is Essential for Dengue Virus Infection

Dengue virus (DENV) causes the most prevalent and rapidly spreading arboviral disease of humans. It enters human cells by receptor-mediated endocytosis. Numerous cell-surface proteins were proposed as DENV entry factors. Among these, the phosphatidylserine receptor TIM-1 is the only one known to mediate virus internalization. However, several cellular models lacking TIM-1 are permissive to DENV infection, suggesting that other receptors exist. Here, we show that the low-density lipoprotein receptor-related protein-1 (LRP1) binds DENV virions by interacting with the DIII of the viral envelope glycoprotein. DENV infection is effectively inhibited by the purified receptor at 5 × 10-8 mol/L, and the interaction of the envelope protein with LRP1 is also blocked by a natural ligand of LRP1. The depletion of LRP1 causes 100-fold lower production of infectious virus than controls. Our results indicate that LRP1 is another DENV receptor, thus becoming an attractive target to evaluate for the development of effective antiviral drugs against DENV.

The role of immunoglobulin transport receptor, neonatal Fc receptor in mucosal infection and immunity and therapeutic intervention

The neonatal Fc receptor (FcRn) can transport IgG and antigen-antibody complexes participating in mucosal immune responses that protect the host from most pathogens' invasion via the respiratory, digestive, and urogenital tracts. FcRn expression can be triggered upon stimulation with pathogenic invasion on mucosal surfaces, which may significantly modulate the innate immune response of the host. As an immunoglobulin transport receptor, FcRn is implicated in the pathophysiology of immune-related diseases such as infection and autoimmune disorders. In this review, we thoroughly summarize the recent advancement of FcRn in mucosal immunity and its therapeutic strategy. This includes insights into its regulation mechanisms of FcRn expression influenced by pathogens, its emerging role in mucosal immunity and its potential probability as a therapeutic target in infection and autoimmune diseases.

Efficacy and immunogenicity following dengue virus-1 human challenge after a tetravalent prime-boost dengue vaccine regimen: an open-label, phase 1 trial

BACKGROUND

Dengue human infection models (DHIMs) are important tools to down-select dengue vaccine candidates and establish tetravalent efficacy before advanced clinical field trials. We aimed to provide data for the safety and immunogenicity of DHIM and evaluate dengue vaccine efficacy.

METHODS

We performed an open-label, phase 1 trial at the University of Maryland (Baltimore, MD, USA). Eligible participants were healthy individuals aged 18-50 years who either previously received a tetravalent dengue purified inactivated vaccine prime followed by a live-attenuated vaccine boost (ie, the vaccinee group), or were unvaccinated flavivirus-naive participants (ie, the control group). Participants in the vaccinee group with detectable pre-challenge dengue virus-1 neutralising antibody titres and flavivirus-naive participants in the control group were inoculated with dengue virus-1 strain 45AZ5 in the deltoid region, 27-65 months following booster dosing. These participants were followed-up from days 4-16 following dengue virus-1 live virus human challenge, with daily real-time quantitative PCR specific to dengue virus-1 RNA detection, and dengue virus-1 solicited local and systemic adverse events were recorded. The primary outcomes were safety (ie, solicited local and systemic adverse events) and vaccine efficacy (ie, dengue virus-1 RNAaemia) following dengue challenge. This study is registered with ClinicalTrials.gov, number NCT04786457.

FINDINGS

In January 2021, ten eligible participants were enrolled; of whom, six (60%) were in the vaccinee group and four (40%) were in the control group. Daily quantitative PCR detected dengue virus-1 RNA in nine (90%) of ten participants (five [83%] of six in the vaccinee group and all four [100%] in the control group). The mean onset of RNAaemia occurred on day 5 (SD 1·0) in the vaccinee group versus day 8 (1·5) in the control group (95% CI 1·1-4·9; p=0·007), with a trend towards reduced RNAaemia duration in the vaccinee group compared with the control group (8·2 days vs 10·5 days; 95% CI -0·08 to 4·68; p=0·056). Mild-to-moderate symptoms (nine [90%] of ten), leukopenia (eight [89%] of nine), and elevated aminotransferases (seven [78%] of nine) were commonly observed. Severe adverse events were detected only in the vaccinee group (fever ≥38·9°C in three [50%] of six, headache in one [17%], and transient grade 4 aspartate aminotransferase elevation in one [17%]). No deaths were reported.

INTERPRETATION

Participants who had tetravalent dengue purified inactivated vaccine prime and live-attenuated vaccine boost were unprotected against dengue virus-1 infection and further showed increased clinical, immunological, and transcriptomic evidence for inflammation potentially mediated by pre-existing infection-enhancing antibodies. This study highlights the impact of small cohort, human challenge models studying dengue pathogenesis and downstream vaccine development.

FUNDING

Military Infectious Disease Research Program and Medical Technology Enterprise Consortium and Advanced Technology International.

Serological Evidence of Zika Virus Infections in Sudan

Little is known about the frequency of Zika virus (ZIKV) infections in Sudan. The aim of this study was to obtain data on the prevalence of ZIKV infections and the immunity of the population in the country. To this end, 198 sera obtained between December 2012 and January 2013 in different regions in Sudan were examined for neutralizing antibodies against ZIKV, dengue virus (DENV), and yellow fever virus (YFV). The sera were non-randomly selected. The neutralization titers were compared with each other and with the WHO 1st International Standard for anti-Asian lineage Zika virus antibody. Twenty-six sera neutralized ZIKV. One-third of these sera had higher neutralization titers against ZIKV than against DENV-2 and -3. Two sera showed higher neutralization titers than the WHO standard for ZIKV antibodies. These data suggest occasional ZIKV infections in Sudan. The low percentage of sera in this cohort that neutralized ZIKV indicates that, in the study period, the population was susceptible to ZIKV infection.

Rational design and production of a chimeric antigen targeting Zika virus that induces neutralizing antibodies in mice

The Zika virus (ZIKV) is considered a public health problem worldwide due to its association with the development of microcephaly and the Guillain-Barré syndrome. Currently, there is no specific treatment or vaccine approved to combat this disease, and thus, developing safe and effective vaccines is a relevant goal. In this study, a multi-epitope protein called rpZDIII was designed based on a series of ZIKV antigenic sequences, a bacterial carrier, and linkers. The analysis of the predicted 3D structure of the rpZDIII chimeric antigen was performed on the AlphaFold 2 server, and it was produced in E. coli and purified from inclusion bodies, followed by solubilization and refolding processes. The yield achieved for rpZDIII was 11 mg/L in terms of pure soluble recombinant protein per liter of fermentation. rpZDIII was deemed immunogenic since it induced serum IgG and IgM responses in mice upon subcutaneous immunization in a three-dose scheme. Moreover, sera from mice immunized with rpZDIII showed neutralizing activity against ZIKV. Therefore, this study reveals rpZDIII as a promising immunogen for the development of a rationally designed multi-epitope vaccine against ZIKV, and completion of its preclinical evaluation is guaranteed.

Mechanisms of Flavivirus Cross-Protection against Yellow Fever in a Mouse Model

The complete lack of yellow fever virus (YFV) in Asia, and the lack of urban YFV transmission in South America, despite the abundance of the peridomestic mosquito vector Aedes (Stegomyia.) aegypti is an enigma. An immunologically naïve population of over 2 billion resides in Asia, with most regions infested with the urban YF vector. One hypothesis for the lack of Asian YF, and absence of urban YF in the Americas for over 80 years, is that prior immunity to related flaviviruses like dengue (DENV) or Zika virus (ZIKV) modulates YFV infection and transmission dynamics. Here we utilized an interferon α/β receptor knock-out mouse model to determine the role of pre-existing dengue-2 (DENV-2) and Zika virus (ZIKV) immunity in YF virus infection, and to determine mechanisms of cross-protection. We utilized African and Brazilian YF strains and found that DENV-2 and ZIKV immunity significantly suppresses YFV viremia in mice, but may or may not protect relative to disease outcomes. Cross-protection appears to be mediated mainly by humoral immune responses. These studies underscore the importance of re-assessing the risks associated with YF outbreak while accounting for prior immunity from flaviviruses that are endemic.

A tetravalent dengue virus-like particle vaccine induces high levels of neutralizing antibodies and reduces dengue replication in non-human primates

Dengue virus (DENV) represents a significant global health burden, with 50% of the world's population at risk of infection, and there is an urgent need for next-generation vaccines. Virus-like particle (VLP)-based vaccines, which mimic the antigenic structure of the virus but lack the viral genome, are an attractive approach. Here, we describe a dengue VLP (DENVLP) vaccine which generates a neutralizing antibody response against all four DENV serotypes in 100% of immunized non-human primates for up to 1 year. Additionally, DENVLP vaccination produced no ADE response against any of four DENV serotypes in vitro. DENVLP vaccination reduces viral replication in a non-human primate challenge model. We also show that transfer of purified IgG from immunized monkeys into immunodeficient mice protects against subsequent lethal DENV challenge, indicating a humoral mechanism of protection. These results indicate that this DENVLP vaccine is immunogenic and can be considered for clinical evaluation. Immunization of non-human primates with a tetravalent DENVLP vaccine induces high levels of neutralizing antibodies and reduces the severity of infection for all four dengue serotypes.IMPORTANCEDengue is a viral disease that infects nearly 400 million people worldwide and causes dengue hemorrhagic fever, which is responsible for 10,000 deaths each year. Currently, there is no therapeutic drug licensed to treat dengue infection, which makes the development of an effective vaccine essential. Virus-like particles (VLPs) are a safe and highly immunogenic platform that can be used in young children, immunocompromised individuals, as well as healthy adults. In this study, we describe the development of a dengue VLP vaccine and demonstrate that it induces a robust immune response against the dengue virus for over 1 year in monkeys. The immunity induced by this vaccine reduced live dengue infection in both murine and non-human primate models. These results indicate that our dengue VLP vaccine is a promising vaccine candidate.

Envelope-dimer epitope-like broadly protective antibodies against dengue in children following natural infection and vaccination

Cross-reactive antibodies (Abs) to epitopes that span envelope proteins on the virion surface are hypothesized to protect against dengue. Here, we measured Abs targeting the quaternary envelope dimer epitope (EDE) as well as neutralizing and binding Abs and evaluate their association with dengue virus (DENV) infection, vaccine response, and disease outcome in dengue vaccinated and unvaccinated children (n=252) within a longitudinal cohort in Cebu, Philippines (n=2,996). Abs targeting EDE were prevalent and strongly associated with broad neutralization of DENV1-4 in those with baseline multitypic immunity. Subsequent natural infection and vaccination boosted EDE-like, neutralizing, and binding Abs. EDE-like Abs were associated with reduced dengue risk and mediated the protective effect of binding and neutralizing Abs on symptomatic and severe dengue. Thus, Abs targeting quaternary epitopes help explain broad cross protection in those with multiple prior DENV exposures, making them useful for evaluation and development of future vaccines and therapeutics.

Characteristics, risk factors, and outcomes related to Zika virus infection during pregnancy in Northeastern Thailand: A prospective pregnancy cohort study, 2018-2020

BACKGROUND

In response to the 2015-2016 Zika virus (ZIKV) outbreak and the causal relationship established between maternal ZIKV infection and adverse infant outcomes, we conducted a cohort study to estimate the incidence of ZIKV infection in pregnancy and assess its impacts in women and infants.

METHODOLOGY/PRINCIPAL FINDINGS

From May 2018-January 2020, we prospectively followed pregnant women recruited from 134 participating hospitals in two non-adjacent provinces in northeastern Thailand. We collected demographic, clinical, and epidemiologic data and blood and urine at routine antenatal care visits until delivery. ZIKV infections were confirmed by real-time reverse transcriptase polymerase chain reaction (rRT-PCR). Specimens with confirmed ZIKV underwent whole genome sequencing. Among 3,312 women enrolled, 12 (0.36%) had ZIKV infections, of which two (17%) were detected at enrollment. Ten (83%, 3 in 2nd and 7 in 3rd trimester) ZIKV infections were detected during study follow-up, resulting in an infection rate of 0.15 per 1,000 person-weeks (95% CI: 0.07-0.28). The majority (11/12, 91.7%) of infections occurred in one province. Persistent ZIKV viremia (42 days) was found in only one woman. Six women with confirmed ZIKV infections were asymptomatic until delivery. Sequencing of 8 ZIKV isolates revealed all were of Asian lineage. All 12 ZIKV infected women gave birth to live, full-term infants; the only observed adverse birth outcome was low birth weight in one (8%) infant. Pregnancies in 3,300 ZIKV-rRT-PCR-negative women were complicated by 101 (3%) fetal deaths, of which 67 (66%) had miscarriages and 34 (34%) had stillbirths. There were no differences between adverse fetal or birth outcomes of live infants born to ZIKV-rRT-PCR-positive mothers compared to live infants born to ZIKV-rRT-PCR-negative mothers.

CONCLUSIONS/SIGNIFICANCE

Confirmed ZIKV infections occurred infrequently in this large pregnancy cohort and observed adverse maternal and birth outcomes did not differ between mothers with and without confirmed infections.

Beyond bNAbs: Uses, Risks, and Opportunities for Therapeutic Application of Non-Neutralising Antibodies in Viral Infection

The vast majority of antibodies generated against a virus will be non-neutralising. However, this does not denote an absence of protective capacity. Yet, within the field, there is typically a large focus on antibodies capable of directly blocking infection (neutralising antibodies, NAbs) of either specific viral strains or multiple viral strains (broadly-neutralising antibodies, bNAbs). More recently, a focus on non-neutralising antibodies (nNAbs), or neutralisation-independent effects of NAbs, has emerged. These can have additive effects on protection or, in some cases, be a major correlate of protection. As their name suggests, nNAbs do not directly neutralise infection but instead, through their Fc domains, may mediate interaction with other immune effectors to induce clearance of viral particles or virally infected cells. nNAbs may also interrupt viral replication within infected cells. Developing technologies of antibody modification and functionalisation may lead to innovative biologics that harness the activities of nNAbs for antiviral prophylaxis and therapeutics. In this review, we discuss specific examples of nNAb actions in viral infections where they have known importance. We also discuss the potential detrimental effects of such responses. Finally, we explore new technologies for nNAb functionalisation to increase efficacy or introduce favourable characteristics for their therapeutic applications.

Biased virus transmission following sequential coinfection of Aedes aegypti with dengue and Zika viruses

BACKGROUND

Mosquito-borne arboviruses are expanding their territory and elevating their infection prevalence due to the rapid climate change, urbanization, and increased international travel and global trade. Various significant arboviruses, including the dengue virus, Zika virus, Chikungunya virus, and yellow fever virus, are all reliant on the same primary vector, Aedes aegypti. Consequently, the occurrence of arbovirus coinfection in mosquitoes is anticipated. Arbovirus coinfection in mosquitoes has two patterns: simultaneous and sequential. Numerous studies have demonstrated that simultaneous coinfection of arboviruses in mosquitoes is unlikely to exert mutual developmental influence on these viruses. However, the viruses' interplay within a mosquito after the sequential coinfection seems intricated and not well understood.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted experiments aimed at examining the phenomenon of arbovirus sequential coinfection in both mosquito cell line (C6/36) and A. aegypti, specifically focusing on dengue virus (DENV, serotype 2) and Zika virus (ZIKV). We firstly observed that DENV and ZIKV can sequentially infect mosquito C6/36 cell line, but the replication level of the subsequently infected ZIKV was significantly suppressed. Similarly, A. aegypti mosquitoes can be sequentially coinfected by these two arboviruses, regardless of the order of virus exposure. However, the replication, dissemination, and the transmission potential of the secondary virus were significantly inhibited. We preliminarily explored the underlying mechanisms, revealing that arbovirus-infected mosquitoes exhibited activated innate immunity, disrupted lipid metabolism, and enhanced RNAi pathway, leading to reduced susceptibility to the secondary arbovirus infections.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that, in contrast to simultaneous arbovirus coinfection in mosquitoes that can promote the transmission and co-circulation of these viruses, sequential coinfection appears to have limited influence on arbovirus transmission dynamics. However, it is important to note that more experimental investigations are needed to refine and expand upon this conclusion.

Engineered mRNA Delivery Systems for Biomedical Applications

Messenger RNA (mRNA)-based therapeutic strategies have shown remarkable promise in preventing and treating a staggering range of diseases. Optimizing the structure and delivery system of engineered mRNA has greatly improved its stability, immunogenicity, and protein expression levels, which has led to a wider range of uses for mRNA therapeutics. Herein, a thorough analysis of the optimization strategies used in the structure of mRNA is first provided and delivery systems are described in great detail. Furthermore, the latest advancements in biomedical engineering for mRNA technology, including its applications in combatting infectious diseases, treating cancer, providing protein replacement therapy, conducting gene editing, and more, are summarized. Lastly, a perspective on forthcoming challenges and prospects concerning the advancement of mRNA therapeutics is offered. Despite these challenges, mRNA-based therapeutics remain promising, with the potential to revolutionize disease treatment and contribute to significant advancements in the biomedical field.

Prior flavivirus immunity skews the yellow fever vaccine response to cross-reactive antibodies with potential to enhance dengue virus infection

The yellow fever 17D vaccine (YF17D) is highly effective but is frequently administered to individuals with pre-existing cross-reactive immunity, potentially impacting their immune responses. Here, we investigate the impact of pre-existing flavivirus immunity induced by the tick-borne encephalitis virus (TBEV) vaccine on the response to YF17D vaccination in 250 individuals up to 28 days post-vaccination (pv) and 22 individuals sampled one-year pv. Our findings indicate that previous TBEV vaccination does not affect the early IgM-driven neutralizing response to YF17D. However, pre-vaccination sera enhance YF17D virus infection in vitro via antibody-dependent enhancement (ADE). Following YF17D vaccination, TBEV-pre-vaccinated individuals develop high amounts of cross-reactive IgG antibodies with poor neutralizing capacity. In contrast, TBEV-unvaccinated individuals elicit a non-cross-reacting neutralizing response. Using YF17D envelope protein mutants displaying different epitopes, we identify quaternary dimeric epitopes as the primary target of neutralizing antibodies. Additionally, TBEV-pre-vaccination skews the IgG response towards the pan-flavivirus fusion loop epitope (FLE), capable of mediating ADE of dengue and Zika virus infections in vitro. Together, we propose that YF17D vaccination conceals the FLE in individuals without prior flavivirus exposure but favors a cross-reactive IgG response in TBEV-pre-vaccinated recipients directed to the FLE with potential to enhance dengue virus infection.

A Non-Active-Site Inhibitor with Selectivity for Zika Virus NS2B-NS3 Protease

Flavivirus infection usually results in fever accompanied by headache, arthralgia, and, in some cases, rash. Although the symptoms are mild, full recovery can take several months. Flaviviruses encode seven nonstructural proteins that represent potential drug targets for this viral family. Focusing on the Zika virus NS2B-NS3 protease, we uncovered a unique inhibitor, MH1, composed of aminothiazolopyridine and benzofuran moieties. MH1 inhibits ZVP with a biochemical IC50 of 440 nM and effectively blocks cleavage of ZVP substrates in cells. Surprisingly, MH1 inhibits the other flaviviral proteases at least 18-fold more weakly. This same phenomenon was observed in assays of the viral cytopathic effect, where only Zika virus showed sensitivity to MH1. This selectivity was unexpected since flaviviral proteases have high similarity in sequence and protein structure. MH1 binds at an allosteric site, as demonstrated by its ability to stabilize ZVP synergistically with an active site inhibitor. To understand its selectivity, we constructed a series of hybrid proteases composed of select segments of ZVP, which is sensitive to MH1, and dengue virus protease, which is essentially insensitive to MH1. Our results suggest that MH1 binds to the NS3 protease domain, disrupting its interaction with NS2B. These interactions are essential for substrate binding and cleavage. In particular, the unique dynamic properties of NS2B from Zika seem to be required for the function of MH1. Insights into the mechanism of MH1 function will aid us in developing non-active-site-directed, pan-flaviviral inhibitors, by highlighting the importance of evaluating and considering the dynamics of the NS2B regions.

Preexisting inter-serotype immunity drives antigenic evolution of dengue virus serotype 2

Dengue virus (DENV) infects roughly 400 million people annually, causing febrile and hemorrhagic disease. While preexisting inter-serotype immunity (PISI) provides transient protection, it may drive severe disease over time. PISI's impact on virus evolution, however, is less understood. Retrospective epidemiological analyses suggest that PISI may drive DENV evolution. Using in vitro directed evolution, we explored how DENV2 evolves in the presence of DENV3/4 convalescent serum. Two post-passaging mutations (E-I6M and E-N203D) were then studied for fitness effects in mammalian and insect hosts and immune escape. E-I6M resisted neutralization, altered fitness in mammalian cell culture models, and had no effect in Aedes albopictus mosquitoes. E-N203D showed no change in neutralization sensitivity, reduced fitness in a DENV-naïve epithelial model, and no effects in the other models. These results align with surveillance data, where E-I6M emerged and disappeared, while E-203D and E-203 N cocirculate, thus suggesting that PISI can drive DENV evolution.

Antibodies from dengue patients with prior exposure to Japanese encephalitis virus are broadly neutralizing against Zika virus

Exposure to multiple mosquito-borne flaviviruses within a lifetime is not uncommon; however, how sequential exposures to different flaviviruses shape the cross-reactive humoral response against an antigen from a different serocomplex has yet to be explored. Here, we report that dengue-infected individuals initially primed with the Japanese encephalitis virus (JEV) showed broad, highly neutralizing potencies against Zika virus (ZIKV). We also identified a rare class of ZIKV-cross-reactive human monoclonal antibodies with increased somatic hypermutation and broad neutralization against multiple flaviviruses. One huMAb, K8b, binds quaternary epitopes with heavy and light chains separately interacting with overlapping envelope protein dimer units spanning domains I, II, and III through cryo-electron microscopy and structure-based mutagenesis. JEV virus-like particle immunization in mice further confirmed that such cross-reactive antibodies, mainly IgG3 isotype, can be induced and proliferate through heterologous dengue virus (DENV) serotype 2 virus-like particle stimulation. Our findings highlight the role of prior immunity in JEV and DENV in shaping the breadth of humoral response and provide insights for future vaccination strategies in flavivirus-endemic countries.

Roles of NS1 Protein in Flavivirus Pathogenesis

Flaviviruses such as dengue, Zika, and West Nile viruses are highly concerning pathogens that pose significant risks to public health. The NS1 protein is conserved among flaviviruses and is synthesized as a part of the flavivirus polyprotein. It plays a critical role in viral replication, disease progression, and immune evasion. Post-translational modifications influence NS1's stability, secretion, antigenicity, and interactions with host factors. NS1 protein forms extensive interactions with host cellular proteins allowing it to affect vital processes such as RNA processing, gene expression regulation, and cellular homeostasis, which in turn influence viral replication, disease pathogenesis, and immune responses. NS1 acts as an immune evasion factor by delaying complement-dependent lysis of infected cells and contributes to disease pathogenesis by inducing endothelial cell damage and vascular leakage and triggering autoimmune responses. Anti-NS1 antibodies have been shown to cross-react with host endothelial cells and platelets, causing autoimmune destruction that is hypothesized to contribute to disease pathogenesis. However, in contrast, immunization of animal models with the NS1 protein confers protection against lethal challenges from flaviviruses such as dengue and Zika viruses. Understanding the multifaceted roles of NS1 in flavivirus pathogenesis is crucial for effective disease management and control. Therefore, further research into NS1 biology, including its host protein interactions and additional roles in disease pathology, is imperative for the development of strategies and therapeutics to combat flavivirus infections successfully. This Review provides an in-depth exploration of the current available knowledge on the multifaceted roles of the NS1 protein in the pathogenesis of flaviviruses.

West Nile virus in Mexico: Why vectors matter for explaining the current absence of epidemics

Since 2002, West Nile Virus (WNV) has been reported in 18 states in Mexico, either by PCR or serological testing. However, it is believed that the virus is present in more states. Only four states (out of 32) have reported confirmed human cases, and one state has serological evidence. In the country, WNV is present in mainly horses and birds, but its presence extends to crocodiles, felines, canines, swines, donkeys, caprines, antilopes, cattle, bats, and camelids. Positive mosquito species include Aedes and Culex spp. Different hypotheses have been proposed to explain the absence of WNV epidemics in Latin America. Since some regions of Mexico and the United States share ecological and climatic conditions, these hypotheses may not be sufficient to account for the absence of WNV outbreaks or epidemics. This paper discusses the proposed ideas and attempts to contextualize them for Mexico, particularly for the U.S.-Mexico border, where WNV infections have been reported in humans, horses, and mosquitoes. We propose that integration of urban ecology and entomology knowledge is needed to better understand the absence of WN cases in Mexico.

Identification of a critical role for ZIKV capsid α3 in virus assembly and its genetic interaction with M protein

Flaviviruses such as Zika and dengue viruses are persistent health concerns in endemic regions worldwide. Efforts to combat the spread of flaviviruses have been challenging, as no antivirals or optimal vaccines are available. Prevention and treatment of flavivirus-induced diseases require a comprehensive understanding of their life cycle. However, several aspects of flavivirus biogenesis, including genome packaging and virion assembly, are not well characterized. In this study, we focused on flavivirus capsid protein (C) using Zika virus (ZIKV) as a model to investigate the role of the externally oriented α3 helix (C α3) without a known or predicted function. Alanine scanning mutagenesis of surface-exposed amino acids on C α3 revealed a critical CN67 residue essential for ZIKV virion production. The CN67A mutation did not affect dimerization or RNA binding of purified C protein in vitro. The virus assembly is severely affected in cells transfected with an infectious cDNA clone of ZIKV with CN67A mutation, resulting in a highly attenuated phenotype. We isolated a revertant virus with a partially restored phenotype by continuous passage of the CN67A mutant virus in Vero E6 cells. Sequence analysis of the revertant revealed a second site mutation in the viral membrane (M) protein MF37L, indicating a genetic interaction between the C and M proteins of ZIKV. Introducing the MF37L mutation on the mutant ZIKV CN67A generated a double-mutant virus phenotypically consistent with the isolated genetic revertant. Similar results were obtained with analogous mutations on C and M proteins of dengue virus, suggesting the critical nature of C α3 and possible C and M residues contributing to virus assembly in other Aedes-transmitted flaviviruses. This study provides the first experimental evidence of a genetic interaction between the C protein and the viral envelope protein M, providing a mechanistic understanding of the molecular interactions involved in the assembly and budding of Aedes-transmitted flaviviruses.

Plant-expressed Zika virus envelope protein elicited protective immunity against the Zika virus in immunocompetent mice

Zika virus infection causes multiple clinical issues, including Guillain-Barré syndrome and neonatal malformation. Vaccination is considered as the only strategy for the prevention of ZIKV-induced clinical issues. This study developed a plant-based recombinant vaccine that transiently expressed the ZIKV envelope protein (ZikaEnv:aghFc) in Nicotiana benthamiana and evaluated the protective immunity afforded by it in immunocompetent mice. ZikaEnv:aghFc induced both humoral and cellular immunity at a low dose (1-5 μg). This immune-inducing potential was enhanced further when adjuvanted CIA09A. In addition, antigen-specific antibodies and neutralizing antibodies were vertically transferred from immunized females to their progeny and afforded both protective immunity to ZIKV and cross-protection to Dengue virus infection. These results suggest that our plant-based ZIKV vaccine provides a safe and efficient protective strategy with a competitive edge.

Superior efficacy of a skin-applied microprojection device for delivering a novel Zika DNA vaccine

Zika virus (ZIKV) infections are spreading silently with limited global surveillance in at least 89 countries and territories. There is a pressing need to develop an effective vaccine suitable for equitable distribution globally. Consequently, we previously developed a proprietary DNA vaccine encoding secreted non-structural protein 1 of ZIKV (pVAX-tpaNS1) to elicit rapid protection in a T cell-dependent manner in mice. In the current study, we evaluated the stability, efficacy, and immunogenicity of delivering this DNA vaccine into the skin using a clinically effective and proprietary high-density microarray patch (HD-MAP). Dry-coating of pVAX-tpaNS1 on the HD-MAP device resulted in no loss of vaccine stability at 40°C storage over the course of 28 days. Vaccination of mice (BALB/c) with the HD-MAP-coated pVAX-tpaNS1 elicited a robust anti-NS1 IgG response in both the cervicovaginal mucosa and systemically and afforded protection against live ZIKV challenge. Furthermore, the vaccination elicited a significantly higher magnitude and broader NS1-specific T helper and cytotoxic T cell response in vivo compared with traditional needle and syringe intradermal vaccination. Overall, the study highlights distinctive immunological advantages coupled with an excellent thermostability profile of using the HD-MAP device to deliver a novel ZIKV DNA vaccine.

Did COVID-19 or COVID-19 Vaccines Influence the Patterns of Dengue in 2021? An Exploratory Analysis of Two Observational Studies from North India

Dengue experienced a rise in disease burden in 2021 in specific regions of India. We aimed to explore the risk factors of dengue occurrence and severity in the post-COVID-19 and post-COVID-19 vaccination era and performed an exploratory analysis involving participants from two prior observational studies conducted from February 2021 to April 2022 in a tertiary hospital in North India. Health care workers constituted the majority of the study participants. Individuals were stratified into five groups based on COVID-19 infection and timing of vaccination: COVID-No Vaccine, Vaccine-No COVID (VNC), COVID After Vaccine (CAV), Vaccine After COVID (VAC), and No Vaccine-No COVID (NVNC) groups. The occurrence of laboratory-confirmed dengue and severe forms of dengue were the main outcomes of interest. A total of 1,701 participants (1,520 vaccinated, 181 unvaccinated) were included. Of these, symptomatic dengue occurred in 133 (7.8%) and was "severe" in 42 (31.6%) cases. Individuals with a history of COVID-19 in 2020 had a 2-times-higher odds of developing symptomatic dengue (P = 0.002). The VAC group had 3.6 (P = 0.019)-, 2 (P = 0.002)-, and 1.9 (P = 0.01)-times-higher odds of developing symptomatic dengue than the NVNC, VNC, and CAV groups, respectively. The severity of dengue was not affected by COVID-19 vaccination but with marginal statistical significance, a 2-times-higher risk of severe dengue was observed with any COVID-19 of the past (P = 0.08). We conclude that COVID-19 may enhance the risk of developing symptomatic dengue. Future research should explore the predisposition of COVID-19-recovered patients toward other viral illnesses. Individuals receiving COVID-19 vaccines after recovering from COVID-19 particularly seem to be at greater risk of symptomatic dengue and need long-term watchfulness. Possible mechanisms, such as antibody-dependent enhancement or T-cell dysfunction, should be investigated in COVID-19-recovered and vaccinated individuals.

Development and biochemical characteristics of a monoclonal antibody against prM protein of Tembusu virus

Tembusu virus (TMUV), a pathogenic member of the Flavivirus family, is an infectious diseases that seriously jeopardize duck health in 2010 in China. TMUV disease causes significant economic losses to the duck industry. This study aimed to prepare monoclonal antibodies against TMUV prM protein and to identify their epitopes. The 501bp prM gene was amplified to the pET-32a prokaryotic expression vector and expressed as a recombinant protein of size 38 KD in Escherichia coli. The purified recombinant proteins were inoculated into BALB/c mice to generate splenic lymphocytes capable of secreting anti-prM antibodies, and hybridoma cells were obtained after fusion with SP2/0 cells. A new hybridoma cell line named B27, which stably secreted IgG1-antibody against TMUV prM with high antibody titers up to 1:1:3,276,800 was screened. This monoclonal antibody (mAb) is well specific and can be used for ELISA/Western-blot (WB)/indirect fluorescence assay (IFA) etc. The mAb B27 has poor neutralization ability and concentration dependence, with a maximum neutralization degree of 23.87% at antibody dilution 10-6. Next, we truncated prM gene and expressed the truncated protein to screen antigen epitopes. The mAb's linear antigen epitope of the TMUV prM protein was first identified and was accurate to 6 consecutive amino acids 59GYEPED64, which located in the pr protein. Bioinformatic analysis showed that this antigenic epitope was located on the surface of the antigen, which was conducive to the direct contact of antigen antibody and conformed to the properties of antigenic epitopes. In addition, its 6 amino acids are highly homologous among 27 published TMUV strains, indicating that its epitope is stable. This study will help to further understand the protein structure and the function of prM, and lay the foundation for establishing specific prM detection methods and the mechanistic study of TMUV prM protein.

The Therapeutic Monoclonal Antibody Bamlanivimab Does Not Enhance SARS-CoV-2 Infection by FcR-Mediated Mechanisms

As part of the non-clinical safety package characterizing bamlanivimab (SARS-CoV-2 neutralizing monoclonal antibody), the risk profile for antibody-dependent enhancement of infection (ADE) was evaluated in vitro and in an African green monkey (AGM) model of COVID-19. In vitro ADE assays in primary human macrophage, Raji, or THP-1 cells were used to evaluate enhancement of viral infection. Bamlanivimab binding to C1q, FcR, and cell-based effector activity was also assessed. In AGMs, the impact of bamlanivimab pretreatment on viral loads and clinical and histological pathology was assessed to evaluate enhanced SARS-CoV-2 replication or pathology. Bamlanivimab did not increase viral replication in vitro, despite a demonstrated effector function. In vivo, no significant differences were found among the AGM groups for weight, temperature, or food intake. Treatment with bamlanivimab reduced viral loads in nasal and oral swabs and BAL fluid relative to control groups. Viral antigen was not detected in lung tissue from animals treated with the highest dose of bamlanivimab. Bamlanivimab did not induce ADE of SARS-CoV-2 infection in vitro or in an AGM model of infection at any dose evaluated. The findings suggest that high-affinity monoclonal antibodies pose a low risk of mediating ADE in patients and support their safety profile as a treatment of COVID-19 disease.

EDIII-Fc induces protective immune responses against the Zika virus in mice and rhesus macaque

Zika virus can infect the fetus through the placental barrier, causing ZIKV congenital syndrome and even miscarriage, which can cause great harm to pregnant women and infants. Currently, there is no vaccine and drug available to combat the Zika virus. In this study, we designed a fusion protein named EDIII-Fc, including the EDIII region of Zika E protein and human IgG Fc fragment, and obtained 293T cells that stably secreted EDIII-Fc protein using the lentiviral expression system. Mice were immunized with the EDIII-Fc protein, and it was observed that viral replication was significantly inhibited in the immunized mice compared to non-immunized mice. In rhesus macaques, we found that EDIII-Fc effectively induce the secretion of neutralizing antibodies and T cell immunity. These experimental data provide valid data for further use of Zika virus E protein to prepare an effective, safe, affordable Zika vaccine.

Priming with Japanese encephalitis virus or yellow fever virus vaccination led to the recognition of multiple flaviviruses without boosting antibody responses induced by an inactivated Zika virus vaccine

BACKGROUND

Complex patterns of cross-reactivity exist between flaviviruses, yet there is no precise understanding of how sequential exposures due to flavivirus infections or vaccinations impact subsequent antibody responses.

METHODS

We investigated whether B cell priming from Japanese encephalitis virus (JEV) or yellow fever virus (YFV) vaccination impacted binding and functional antibody responses to flaviviruses following vaccination with a Zika virus (ZIKV) purified inactivated virus (ZPIV) vaccine. Binding antibody responses and Fc gamma receptor engagement against 23 flavivirus antigens were characterized along with neutralization titres and Fc effector responses in 75 participants at six time points.

FINDINGS

We found no evidence that priming with JEV or YFV vaccines improved the magnitude of ZPIV induced antibody responses to ZIKV. Binding antibodies and Fc gamma receptor engagement to ZIKV antigens did not differ significantly across groups, while antibody-dependent cellular phagocytosis (ADCP) and neutralizing responses were higher in the naïve group than in the JEV and YFV primed groups following the second ZPIV immunization (p ≤ 0.02). After a third dose of ZPIV, ADCP responses remained higher in the naïve group than in the primed groups. However, priming affected the quality of the response following ZPIV vaccination, as primed individuals recognized a broader array of flavivirus antigens than individuals in the naïve group.

INTERPRETATION

While a priming vaccination to either JEV or YFV did not boost ZIKV-specific responses upon ZIKV vaccination, the qualitatively different responses elicited in the primed groups highlight the complexity in the cross-reactive antibody responses to flaviviruses.

FUNDING

This work was supported by a cooperative agreement between The Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., and the U.S. Department of the Army [W81XWH-18-2-0040]. The work was also funded in part by the National Institute of Allergy and Infectious Diseases (NIAID) R01AI155983 to SJK and KM.

Influence of previous Zika virus infection on acute dengue episode

BACKGROUND

The co-circulation of flaviviruses in tropical regions has led to the hypothesis that immunity generated by a previous dengue infection could promote severe disease outcomes in subsequent infections by heterologous serotypes. This study investigated the influence of antibodies generated by previous Zika infection on the clinical outcomes of dengue infection.

METHODOLOGY/PRINCIPAL FINDINGS

We enrolled 1,043 laboratory confirmed dengue patients and investigated their prior infection to Zika or dengue. Severe forms of dengue disease were more frequent in patients with previous Zika infection, but not in those previously exposed to dengue.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that previous Zika infection may represent a risk factor for subsequent severe dengue disease, but we did not find evidence of antibody-dependent enhancement (higher viral titer or pro-inflammatory cytokine overexpression) contributing to exacerbation of the subsequent dengue infection.

Development of Therapeutic Monoclonal Antibodies for Emerging Arbovirus Infections

Antibody-based passive immunotherapy has been used effectively in the treatment and prophylaxis of infectious diseases. Outbreaks of emerging viral infections from arthropod-borne viruses (arboviruses) represent a global public health problem due to their rapid spread, urging measures and the treatment of infected individuals to combat them. Preparedness in advances in developing antivirals and relevant epidemiological studies protect us from damage and losses. Immunotherapy based on monoclonal antibodies (mAbs) has been shown to be very specific in combating infectious diseases and various other illnesses. Recent advances in mAb discovery techniques have allowed the development and approval of a wide number of therapeutic mAbs. This review focuses on the technological approaches available to select neutralizing mAbs for emerging arbovirus infections and the next-generation strategies to obtain highly effective and potent mAbs. The characteristics of mAbs developed as prophylactic and therapeutic antiviral agents for dengue, Zika, chikungunya, West Nile and tick-borne encephalitis virus are presented, as well as the protective effect demonstrated in animal model studies.

Exacerbated Zika virus-induced neuropathology and microcephaly in fetuses of dengue-immune nonhuman primates

Zika virus (ZIKV) is a mosquito-borne flavivirus that can vertically transmit from mother to fetus, potentially causing congenital defects, including microcephaly. It is not fully understood why some fetuses experience severe complications after in utero exposure to ZIKV, whereas others do not. Given the antigenic similarity between ZIKV and the closely related virus dengue (DENV) and the potential of DENV-specific antibodies to enhance ZIKV disease severity in mice, we questioned whether maternal DENV immunity could influence fetal outcomes in a nonhuman primate model of ZIKV vertical transmission. We found significantly increased severity of congenital Zika syndrome (CZS) in fetuses of DENV-immune cynomolgus macaques infected with ZIKV in early pregnancy compared with naïve controls, which occurred despite no effect on maternal ZIKV infection or antibody responses. Ultrasound measurements of head circumference and biparietal diameter measurements taken sequentially throughout pregnancy demonstrated CZS in fetuses of DENV-immune pregnant macaques. Furthermore, severe CZS enhanced by DENV immunity was typified by reduced cortical thickness and increased frequency of neuronal death, hemorrhaging, cellular infiltrations, calcifications, and lissencephaly in fetal brains. This study shows that maternal immunity to DENV can worsen ZIKV neurological outcomes in fetal primates, and it provides an animal model of vertical transmission closely approximating human developmental timelines that could be used to investigate severe ZIKV disease outcomes and interventions in fetuses.

Zika, chikungunya and co-occurrence in Brazil: space-time clusters and associated environmental-socioeconomic factors

Chikungunya and Zika have been neglected as emerging diseases. This study aimed to analyze the space-time patterns of their occurrence and co-occurrence and their associated environmental and socioeconomic factors. Univariate (individually) and multivariate (co-occurrence) scans were analyzed for 608,388 and 162,992 cases of chikungunya and Zika, respectively. These occurred more frequently in the summer and autumn. The clusters with the highest risk were initially located in the northeast, dispersed to the central-west and coastal areas of São Paulo and Rio de Janeiro (2018-2021), and then increased in the northeast (2019-2021). Chikungunya and Zika demonstrated decreasing trends of 13% and 40%, respectively, whereas clusters showed an increasing trend of 85% and 57%, respectively. Clusters with a high co-occurrence risk have been identified in some regions of Brazil. High temperatures are associated with areas at a greater risk of these diseases. Chikungunya was associated with low precipitation levels, more urbanized environments, and places with greater social inequalities, whereas Zika was associated with high precipitation levels and low sewage network coverage. In conclusion, to optimize the surveillance and control of chikungunya and Zika, this study's results revealed high-risk areas with increasing trends and priority months and the role of socioeconomic and environmental factors.

Recombinant protein based on domain III and capsid regions of zika virus induces humoral and cellular immune response in immunocompetent BALB/c mice

Zika virus infection continues to be a global concern for human health due to the high-risk association of the disease with neurological disorders and microcephaly in newborn. Nowadays, no vaccine or specific antiviral treatment is available, and the development of safe and effective vaccines is yet a challenge. In this study, we obtained a novel subunit vaccine that combines two regions of zika genome, domain III of the envelope and the capsid, in a chimeric protein in E. coli bacteria. The recombinant protein was characterized with polyclonal anti-ZIKV and anti-DENV antibodies that corroborate the specificity of the molecule. In addition, the PBMC from zika-immune donors stimulated with the ZEC recombinant antigen showed the capacity to recall the memory T cell response previously generated by the natural infection. The chimeric protein ZEC was able to self-assemble after combination with an immunomodulatory specific oligonucleotide to form aggregates. The inoculation of BALB/c mice with ZEC aggregated and not aggregated form of the protein showed a similar humoral immune response, although the aggregated variant induced more cell-mediated immunity evaluated by in vitro IFNγ secretion. In this study, we propose a novel vaccine candidate against the zika disease based on a recombinant protein that can stimulate both arms of the immune system.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Mimotope discovery as a tool to design a vaccine against Zika and dengue viruses

Vaccine development against dengue virus is challenging because of the antibody-dependent enhancement of infection (ADE), which causes severe disease. Consecutive infections by Zika (ZIKV) and/or dengue viruses (DENV), or vaccination can predispose to ADE. Current vaccines and vaccine candidates contain the complete envelope viral protein, with epitopes that can raise antibodies causing ADE. We used the envelope dimer epitope (EDE), which induces neutralizing antibodies that do not elicit ADE, to design a vaccine against both flaviviruses. However, EDE is a discontinuous quaternary epitope that cannot be isolated from the E protein without other epitopes. Utilizing phage display, we selected three peptides that mimic the EDE. Free mimotopes were disordered and did not elicit an immune response. After their display on adeno-associated virus (AAV) capsids (VLP), they recovered their structure and were recognized by an EDE-specific antibody. Characterization by cryo-EM and enzyme-linked immunosorbent assay confirmed the correct display of a mimotope on the surface of the AAV VLP and its recognition by the specific antibody. Immunization with the AAV VLP displaying one of the mimotopes induced antibodies that recognized ZIKV and DENV. This work provides the basis for developing a Zika and dengue virus vaccine candidate that will not induce ADE.

The increasing complexity of arbovirus serology: An in-depth systematic review on cross-reactivity

Diagnosis of arbovirus infection or exposure by antibody testing is becoming increasingly difficult due to global expansion of arboviruses, which induce antibodies that may (cross-)react in serological assays. We provide a systematic review of the current knowledge and knowledge gaps in differential arbovirus serology. The search included Medline, Embase and Web of Science databases and identified 911 publications which were reduced to 102 after exclusion of studies not providing data on possible cross-reactivity or studies that did not meet the inclusion criteria regarding confirmation of virus exposure of reference population sets. Using a scoring system to further assess quality of studies, we show that the majority of the selected papers (N = 102) provides insufficient detail to support conclusions on specificity of serological outcomes with regards to elucidating antibody cross-reactivity. Along with the lack of standardization of assays, metadata such as time of illness onset, vaccination, infection and travel history, age and specificity of serological methods were most frequently missing. Given the critical role of serology for diagnosis and surveillance of arbovirus infections, better standards for reporting, as well as the development of more (standardized) specific serological assays that allow discrimination between exposures to multiple different arboviruses, are a large global unmet need.