A molecular evaluation of dengue virus pathogenesis and its latest vaccine strategies

Development of a tetravalent subunit vaccine against dengue virus through a vaccinomics approach

Dengue virus infection (DVI) is a mosquito-borne disease that can lead to serious morbidity and mortality. Dengue fever (DF) is a major public health concern that affects approximately 3.9 billion people each year globally. However, there is no vaccine or drug available to deal with DVI. Dengue virus consists of four distinct serotypes (DENV1-4), each raising a different immunological response. In the present study, we designed a tetravalent subunit multi-epitope vaccine, targeting proteins including the structural protein envelope domain III (EDIII), precursor membrane proteins (prM), and a non-structural protein (NS1) from each serotype by employing an immunoinformatic approach. Only conserved sequences obtained through a multiple sequence alignment were used for epitope mapping to ensure efficacy against all serotypes. The epitopes were shortlisted based on an IC50 value <50, antigenicity, allergenicity, and a toxicity analysis. In the final vaccine construct, overall, 11 B-cell epitopes, 10 HTL epitopes, and 10 CTL epitopes from EDIII, prM, and NS1 proteins targeting all serotypes were selected and joined via KK, AAY, and GGGS linkers, respectively. We incorporated a 45-amino-acid-long B-defensins adjuvant in the final vaccine construct for a better immunogenic response. The vaccine construct has an antigenic score of 0.79 via VaxiJen and is non-toxic and non-allergenic. Our refined vaccine structure has a Ramachandran score of 96.4%. The vaccine has shown stable interaction with TLR3, which has been validated by 50 ns of molecular dynamics (MD) simulation. Our findings propose that a designed multi-epitope vaccine has substantial potential to elicit a strong immune response against all dengue serotypes without causing any adverse effects. Furthermore, the proposed vaccine can be experimentally validated as a probable vaccine, suggesting it may serve as an effective preventative measure against dengue virus infection.

Dengue overview: An updated systemic review

Dengue is caused by the dengue virus (DENVs) infection and clinical manifestations include dengue fever (DF), dengue hemorrhagic fever (DHF), or dengue shock syndrome (DSS). Due to a lack of antiviral drugs and effective vaccines, several therapeutic and control strategies have been proposed. A systemic literature review was conducted according to PRISMA guidelines to select proper references to give an overview of DENV infection. Results indicate that understanding the virus characteristics and epidemiology are essential to gain the basic and clinical knowledge as well as dengue disseminated pattern and status. Different factors and mechanisms are thought to be involved in the presentation of DHF and DSS, including antibody-dependent enhancement, immune dysregulation, viral virulence, host genetic susceptibility, and preexisting dengue antibodies. This study suggests that dissecting pathogenesis and risk factors as well as developing different types of therapeutic and control strategies against DENV infection are urgently needed.

Serological Diagnosis of Dengue

A reliable and specific diagnosis is imperative in viral diagnosis, both for clinical management and surveillance, and to ensure that early treatment and control measures are carried out. The number of days of illness is important to choose the most appropriate method to be used and for the correct interpretation of the results obtained. Specific IgM is elicited after that period, indicating an active infection and usually lasts up to 3 months. However, in DENV secondary infections, IgM levels may be significantly lower or undetectable. After 10-12 days, a lifetime specific IgG is produced. Routinely, the laboratory diagnosis of DENV infections can be performed by viral isolation and/or detection of viral nucleic acid, serological assays for the detection of specific antibodies (IgM/IgG), antigen (NS1) and the detection of viral antigens in tissues, which are suitable during certain phases of the disease. For serological diagnosis, serum, plasma, or cerebrospinal fluid (CSF) samples may be investigated. If the test is carried out a few days after collection, the specimens can be stored at 4 °C, since the immunoglobulins are stable in serum or plasma. If the storage period is extended, the material must be kept at -20 °C or -70 °C. In serology, several methods can be used to detect specific viral antigens and/or antibodies, produced by the host in response to DENV infection. Routinely, serological tests include the hemagglutination inhibition (HI) assay, the plaque reduction neutralizing test (PRNT), the gold standard assay for dengue immune response characterization, and ELISAs to detect IgM (MAC-ELISA) and IgG (IgG-ELISA).

An insight into dengue virus proteins as potential drug/vaccine targets

Dengue virus (DENV) is an arbovirus that belongs to family flaviviridae. Its genome is composed of a single stranded RNA molecule that encodes a single polyprotein. The polyprotein is processed by viral and cellular proteases to generate ten viral proteins. There are four antigenically distinct serotypes of DENV (DENV1, DENV2, DENV3 and DENV4), which are genetically related. Although protein variability is a major problem in dengue treatment, the functional and structural studies of individual proteins are equally important in treatment development. The data accumulated on dengue proteins are significant to provide detailed understanding of viral infection, replication, host-immune evasion and pathogenesis. In this review, we summarized the detailed current knowledge about DENV proteins.

Epitope Presentation of Dengue Viral Envelope Glycoprotein Domain III on Hepatitis B Core Protein Virus-Like Particles Produced in Nicotiana benthamiana

Dengue fever is currently ranked as the top emerging tropical disease, driven by increased global travel, urbanization, and poor hygiene conditions as well as global warming effects which facilitate the spread of Aedes mosquitoes beyond their current distribution. Today, more than 100 countries are affected most of which are tropical Asian and Latin American nations with limited access to medical care. Hence, the development of a dengue vaccine that is dually cost-effective and able to confer a comprehensive protection is ultimately needed. In this study, a consensus sequence of the antigenic dengue viral glycoprotein domain III (cEDIII) was used aiming to provide comprehensive coverage against all four circulating dengue viral serotypes and potential clade replacement event. Utilizing hepatitis B tandem core technology, the cEDIII sequence was inserted into the immunodominant c/e1 loop region so that it could be displayed on the spike structures of assembled particles. The tandem core particles displaying cEDIII epitopes (tHBcAg-cEDIII) were successfully produced in Nicotiana benthamiana via Agrobacterium-mediated transient expression strategy to give a protein of ∼54 kDa, detected in both soluble and insoluble fractions of plant extracts. The assembled tHBcAg-cEDIII virus-like particles (VLPs) were also visualized from transmission electron microscopy. These VLPs had diameters that range from 32 to 35 nm, presenting an apparent size increment as compared to tHBcAg control particles without cEDIII display (namely tEL). Mice immunized with tHBcAg-cEDIII VLPs showed a positive seroconversion to cEDIII antigen, thereby signifying that the assembled tHBcAg-cEDIII VLPs have successfully displayed cEDIII antigen to the immune system. If it is proven to be successful, tHBcAg-cEDIII has the potential to be developed as a cost-effective vaccine candidate that confers a simultaneous protection against all four infecting dengue viral serotypes.

Designing a polytope for use in a broad-spectrum dengue virus vaccine

OBJECTIVES

Dengue virus surface proteins are often used in the development of vaccines that protect against dengue virus infection. However, the surface proteins on the four serotypes of dengue virus display high variation, which increases the difficulty of developing a vaccine that can protect against all viral strains. In this study, a polytope that is recognized by broadly neutralizing antibodies (bnAbs) was designed using conserved epitopes from the four serotypes.

METHODS

We constructed a polytope using four conserved dengue virus epitopes such that two aligned epitopes were separated from the other two epitopes by a histidyl-tRNA synthetase spacer. The epitopes were selected based on our previous docking studies. We then performed molecular docking of the polytope with the four bnAbs.

RESULTS

The polytope bound precisely to the four bnAbs-B7, C8, A11, and C10. Moreover, the polytope had a higher affinity for the bnAbs compared to the DENV2 antigen. The polytope and A11 antibody complex had the lowest binding energy relative to complexes between the polytope and the other three antibodies assessed. The highest total number of hydrogen bonds was found in the polytope and B7 antibody complex. The hydrogen bond length in all the complexes ranged from 2.07 to 3.03 Å, implying that hydrogen bonds stabilized the complexes.

CONCLUSION

The developed polytope interacted with four different bnAbs that recognize the four serotypes of dengue virus. The results of this study suggest that this polytope warrants further development for use in a broad-spectrum vaccine against dengue virus.

Clinical Efficacy, Safety, and Immunogenicity of a Live Attenuated Tetravalent Dengue Vaccine (CYD-TDV) in Children: A Systematic Review with Meta-analysis

BACKGROUND

Dengue hemorrhagic fever is the leading cause of hospitalization and death in children living in Asia and Latin America. There is an urgent need for an effective and safe dengue vaccine to reduce morbidity and mortality in this high-risk population given the lack of dengue specific treatment at present. This review aims to determine the efficacy, safety, and immunogenicity of CYD-TDV vaccine in children.

METHODS

This is a systematic review including meta-analysis of randomized controlled clinical trial data from Embase, Medline, the Cochrane Library, Web of Science, and ClinicalTrials.gov. Studies that assessed CYD-TDV vaccine efficacy [(1 - RR)*100], safety (RR), and immunogenicity (weighted mean difference) in children were included in this study. Random effects model was employed to analyze patient-level data extracted from primary studies.

RESULTS

The overall efficacy of CYD-TDV vaccine was 54% (40-64), while serotype-specific efficacy was 77% (66-85) for DENV4, 75% (65-82) for DENV3, 50% (36-61) for DENV1, and 34% (14-49) for DENV2. 15% (-174-74) vaccine efficacy was obtained for the unknown serotype. Meta-analysis of included studies with longer follow-up time (25 months) revealed that CYD-TDV vaccine significantly increased the risk of injection site reactions (RR = 1.1: 1.04-1.17; p-value = 0.001). Immunogenicity (expressed as geometric mean titers) in descending order was 439.7 (331.7-547.7), 323 (247 - 398.7), 144.1 (117.9-170.2), and 105 (88.7-122.8) for DENV3, DENV2, DENV1, and DENV4, respectively.

CONCLUSION

CYD-TDV vaccine is effective and immunogenic in children overall. Reduced efficacy of CYD-TDV vaccine against DENV2 notoriously known for causing severe dengue infection and dengue outbreaks cause for serious concern. Post hoc meta-analysis of long-term follow-up data (≥25 months) from children previously vaccinated with CYD-TDV vaccine is needed to make a conclusion regarding CYD-TDV vaccine safety in children. However, CYD-TDV vaccine should be considered for use in regions where DENV2 is not endemic as currently there is no specific treatment for dengue infection.

Current perspectives on dengue episode in Malaysia

Prevalence of dengue transmission has been alarmed by an estimate of 390 million infections per annum. Urban encroachment, ecological disruption and poor sanitation are all contributory factors of increased epidemiology. Complication however arises from the fact that dengue virus inherently exists as four different serotypes. Secondary infection is often manifested in the more severe form, such that antibody-dependent enhancement (ADE) could aggravate ailment by allowing pre-existing antibodies to form complexes with infecting viruses as means of intrusion. Consequently, increased viraemic titter and suppression of antiviral response are observed. Deep concerns are thus expressed in regards to escalating trend of hospitalisation and mortality rates. In Malaysia, situation is exacerbated by improper clinical management and pending vector control operations. As a preparedness strategy against the potential deadly dengue pandemic, the call for development of a durable and cost-effective dengue vaccine against all infecting serotypes is intensified. Even though several vaccine candidates are currently being evaluated in clinical trials, uncertainties in regards to serotypes interference, incomplete protection and dose adequacy have been raised. Instead of sole reliance on outsourcing, production of local vaccine should be considered in coherent to government's efforts to combat against dengue.

Dengue virus RNA purification from human plasma: a comparison of two techniques

Dengue virus RNA purification from human plasma is useful for research and clinical purposes. Dengue is endemic in the Espirito Santo State, Brazil, and it is progressively becoming a hard-to-control public health problem. Dengue virus types 1, 2 and 3 are currently found in Brazilian territory, and recently Dengue virus type 4 has been reported to enter Brazilian borders. This virus spreads rapidly during epidemic outbreaks, and thousands of patients are infected annually, with an underestimated number of deaths in consequence of hemorrhagic Dengue. Because this disease affects mainly developing countries, it is imperative that a robust, rapid and low cost method for viral nucleic acid purification is found. In this manuscript we compare two RNA extraction methods from serum/plasma of patients with clinical diagnosis of dengue. The QIAamp(®) UltraSens Virus Kit (Qiagen Inc., Valencia, USA) and the less expensive Chomczynski-Sacchi method were used to analyze a total of 47 samples. After nucleic acid purification, reverse transcription and polymerase chain reaction amplification with dengue virus type 2 specific primers were performed. This subtype is the most prevalent in our geographical location. Thirty-four samples were positive when RNA was extracted by the Chomczynski-Sacchi technique, whereas only 27 of these were positive when the QIAamp(®) UltraSens Virus Kit was used. These results favor the utilization of the more affordable technique for the purification of viral RNA, which is especially important for developing countries.