Immunogenicity of a Live-Attenuated Dengue Vaccine Using a Heterologous Prime-Boost Strategy in a Phase 1 Randomized Clinical Trial

Advancements in dengue vaccines: A historical overview and pro-spects for following next-generation candidates

Dengue, caused by four serotypes of dengue viruses (DENV-1 to DENV-4), is the most prevalent and widely mosquito-borne viral disease affecting humans. Dengue virus (DENV) infection has been reported in over 100 countries, and approximately half of the world's population is now at risk. The paucity of universally licensed DENV vaccines highlights the urgent need to address this public health concern. Action and atten-tion to antibody-dependent enhancement increase the difficulty of vaccine development. With the worsen-ing dengue fever epidemic, Dengvaxia® (CYD-TDV) and Qdenga® (TAK-003) have been approved for use in specific populations in affected areas. However, these vaccines do not provide a balanced immune response to all four DENV serotypes and the vaccination cannot cover all populations. There is still a need to develop a safe, broad-spectrum, and effective vaccine to address the increasing number of dengue cases worldwide. This review provides an overview of the existing DENV vaccines, as well as potential candidates for future studies on DENV vaccine development, and discusses the challenges and possible solutions in the field.

Current Dengue Virus Vaccine Developments and Future Directions

Dengue fever (DF), a leading arboviral disease globally, is caused by the Dengue virus (DENV) and represents a significant public health concern, with an estimated 390 million cases reported annually. Due to the complexity of the various dengue variants and the severity of the disease, vaccination emerges as the essential strategy for combating this widespread infectious disease. The absence of specific antiviral medications underscores the critical need for developing a Dengue vaccine. This review aims to present the current status and future prospects of Dengue vaccine development. Further, this review elaborates on the various strategies employed in vaccine development, including attenuated, inactivated, subunit, and viral vector vaccines. Each approach is evaluated based on its immunogenicity, safety, and efficacy, drawing on data from preclinical and clinical studies to highlight the strengths and limitations of each candidate vaccine. The current study sheds light on future directions and research priorities in developing Dengue vaccines. In conclusion, the development of a Dengue vaccine holds significant potential for reducing the global burden of DF. However, challenges remain in terms of vaccine safety, efficacy, delivery, and availability. Overcoming these challenges, coupled with advancements in vaccine technology, could lead to better control and prevention of Dengue, thereby enhancing public health and quality of life.

Unlocking Hope: Paving the Way for a Cutting-Edge Multi-Epitope Dengue Virus Vaccine

Dengue fever is a significant health issue in Pakistan, demanding a vaccine effective against all the viral strains. This study employs reverse vaccinology to develop potential dengue vaccine candidates (DVAX I-III). The study thoroughly examined conserved areas of dengue virus serotypes 1-4's structural and non-structural proteins. Key viral proteins were analyzed to find antigenic peptides, which were incorporated into vaccine candidates and potentiated with adjuvants. Computational methods predicted peptide structures and evaluated their binding to immune receptors TLR 2, TLR 4, HLA *A1101, and DRB*401. A molecular dynamics simulation lasting 100 ns of the DVAX II-TLR4 complex at different time intervals clearly indicated that the ligand is attached to the receptor. Normal mode analysis assessed the stability and flexibility of these interactions. Encouragingly, all three vaccine candidates demonstrated favorable interactions with these immune receptors and the potential to induce a robust immune response. These findings suggest their safety and warrant further in vivo studies to evaluate their efficacy for clinical development.

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.

Development of Vaccines against Emerging Mosquito-Vectored Arbovirus Infections

Among emergent climate-sensitive infectious diseases, some mosquito-vectored arbovirus infections have epidemiological, social, and economic effects. Dengue virus (DENV), West Nile virus (WNV), and Chikungunya virus (CHIKV) disease, previously common only in the tropics, currently pose a major risk to global health and are expected to expand dramatically in the near future if adequate containment measures are not implemented. The lack of safe and effective vaccines is critical as it seems likely that emerging mosquito-vectored arbovirus infections will be con-trolled only when effective and safe vaccines against each of these infections become available. This paper discusses the clinical characteristics of DENV, WNV, and CHIKV infections and the state of development of vaccines against these viruses. An ideal vaccine should be able to evoke with a single administration a prompt activation of B and T cells, adequate concentrations of protecting/neutralizing antibodies, and the creation of a strong immune memory capable of triggering an effective secondary antibody response after new infection with a wild-type and/or mutated infectious agent. Moreover, the vaccine should be well tolerated, safe, easily administrated, cost-effective, and widely available throughout the world. However, the development of vaccines against emerging mosquito-vectored arbovirus diseases is far from being satisfactory, and it seems likely that it will take many years before effective and safe vaccines for all these infections are made available worldwide.

Dengue hemorrhagic fever: a growing global menace

Dengue virus is an arthropod-borne virus, transmitted by Aedes aegypti among humans. In this review, we discussed the epidemiology of dengue hemorrhagic fever (DHF) as well as the disease's natural history, cycles of transmission, clinical diagnosis, aetiology, prevention, therapy, and management. A systematic literature search was done by databases such as PubMed and Google Scholar using search terms, 'dengue fever', 'symptoms and causes of dengue fever', 'dengue virus transmission', and 'strategies to control dengue'. We reviewed relevant literature to identify hazards related to DHF and the most recent recommendations for its management and prevention. Clinical signs and symptoms of dengue infection range from mild dengue fever (DF) to potentially lethal conditions like DHF or dengue shock syndrome (DSS). Acute-onset high fever, muscle and joint pain, myalgia, a rash on the skin, hemorrhagic episodes, and circulatory shock are among the most common symptoms. An early diagnosis is vital to lower mortality. As dengue virus infections are self-limiting, but in tropical and subtropical areas, dengue infection has become a public health concern. Hence, developing and executing long-term control policies that can reduce the global burden of DHF is a major issue for public health specialists everywhere.

Dengue Vaccination: Towards a New Dawn of Curbing Dengue Infection

Dengue is an infectious disease caused by dengue virus (DENV) and is a serious global burden. Antibody-dependent enhancement and the ability of DENV to infect immune cells, along with other factors, lead to fatal Dengue Haemorrhagic Fever and Dengue Shock Syndrome. This necessitates the development of a robust and efficient vaccine but vaccine development faces a number of hurdles. In this review, we look at the epidemiology, genome structure and cellular targets of DENV and elaborate upon the immune responses generated by human immune system against DENV infection. The review further sheds light on various challenges in development of a potent vaccine against DENV which is followed by presenting a current account of different vaccines which are being developed or have been licensed.

Biologics for dengue prevention: up-to-date

INTRODUCTION

Dengue is a worsening global public health problem. The vector-viral-host interactions driving the pathogenesis of dengue are multi-dimensional. Sequential dengue virus (DENV) infections with different DENV types significantly increase the risk of severe disease. Treatment is supportive in nature as there are no licensed anti-DENV antivirals or immuno-therapeutics. A single dengue vaccine has widely been licensed with two others in advanced clinical development. Dengvaxia® has been licensed in numerous countries but uptake has been slow as a result of safety signals noted in the youngest recipients and those who were dengue naïve at the time of vaccination.

AREAS COVERED

In this review, the current state of dengue vaccine and antiviral drug development will be discussed as well as new developments in controlled human infection models to support product development.

EXPERT OPINION

The world needs a safe and efficacious tetravalent dengue vaccine capable of protecting multiple different populations across a broad age range and different flavivirus immunologic backgrounds. Safe and effective antivirals are also needed to prevent or attenuate dengue disease in the unvaccinated, in cases of vaccine failure, or in high-risk populations.

Preparedness for the Dengue Epidemic: Vaccine as a Viable Approach

Dengue fever is one of the significant fatal mosquito-borne viral diseases and is considered to be a worldwide problem. Aedes mosquito is responsible for transmitting various serotypes of dengue viruses to humans. Dengue incidence has developed prominently throughout the world in the last ten years. The exact number of dengue cases is underestimated, whereas plenty of cases are misdiagnosed as alternative febrile sicknesses. There is an estimation that about 390 million dengue cases occur annually. Dengue fever encompasses a wide range of clinical presentations, usually with undefinable clinical progression and outcome. The diagnosis of dengue depends on serology tests, molecular diagnostic methods, and antigen detection tests. The therapeutic approach relies completely on supplemental drugs, which is far from the real approach. Vaccines for dengue disease are in various stages of development. The commercial formulation Dengvaxia (CYD-TDV) is accessible and developed by Sanofi Pasteur. The vaccine candidate Dengvaxia was inefficient in liberating a stabilized immune reaction toward different serotypes (1-4) of dengue fever. Numerous promising vaccine candidates are now being developed in preclinical and clinical stages even though different serotypes of DENV exist that worsen the situation for a vaccine to be equally effective for all serotypes. Thus, the development of an efficient dengue fever vaccine candidate requires time. Effective dengue fever management can be a multidisciplinary challenge, involving international cooperation from diverse perspectives and expertise to resolve this global concern.

'Mix and Match' vaccination: Is dengue next?

The severity of the COVID-19 pandemic and the development of multiple SARS-CoV-2 vaccines expedited vaccine 'mix and match' trials in humans and demonstrated the benefits of mixing vaccines that vary in formulation, strength, and immunogenicity. Heterologous sequential vaccination may be an effective approach for protecting against dengue, as this strategy would mimic the natural route to broad dengue protection and may overcome the imbalances in efficacy of the individual leading live attenuated dengue vaccines. Here we review 'mix and match' vaccination trials against SARS-CoV-2, HIV, and dengue virus and discuss the possible advantages and concerns of future heterologous immunization with the leading dengue vaccines. COVID-19 trials suggest that priming with a vaccine that induces strong cellular responses, such as an adenoviral vectored product, followed by heterologous boost may optimize T cell immunity. Moreover, heterologous vaccination may induce superior humoral immunity compared to homologous vaccination when the priming vaccine induces a narrower response than the boost. The HIV trials reported that heterologous vaccination was associated with broadened antigen responses and that the sequence of the vaccines significantly impacts the regimen's immunogenicity and efficacy. In heterologous dengue immunization trials, where at least one dose was with a live attenuated vaccine, all reported equivalent or increased immunogenicity compared to homologous boost, although one study reported increased reactogenicity. The three leading dengue vaccines have been evaluated for safety and efficacy in thousands of study participants but not in combination in heterologous dengue vaccine trials. Various heterologous regimens including different combinations and sequences should be trialed to optimize cellular and humoral immunity and the breadth of the response while limiting reactogenicity. A blossoming field dedicated to more accurate correlates of protection and enhancement will help confirm the safety and efficacy of these strategies.

Controlled Human Infection Models To Accelerate Vaccine Development

The timelines for developing vaccines against infectious diseases are lengthy, and often vaccines that reach the stage of large phase 3 field trials fail to provide the desired level of protective efficacy. The application of controlled human challenge models of infection and disease at the appropriate stages of development could accelerate development of candidate vaccines and, in fact, has done so successfully in some limited cases. Human challenge models could potentially be used to gather critical information on pathogenesis, inform strain selection for vaccines, explore cross-protective immunity, identify immune correlates of protection and mechanisms of protection induced by infection or evoked by candidate vaccines, guide decisions on appropriate trial endpoints, and evaluate vaccine efficacy. We prepared this report to motivate fellow scientists to exploit the potential capacity of controlled human challenge experiments to advance vaccine development. In this review, we considered available challenge models for 17 infectious diseases in the context of the public health importance of each disease, the diversity and pathogenesis of the causative organisms, the vaccine candidates under development, and each model's capacity to evaluate them and identify correlates of protective immunity. Our broad assessment indicated that human challenge models have not yet reached their full potential to support the development of vaccines against infectious diseases. On the basis of our review, however, we believe that describing an ideal challenge model is possible, as is further developing existing and future challenge models.

Dengue Vaccines: An Update

Dengue is one of the most prevalent mosquito-borne diseases in the world, affecting an estimated 390 million people each year, according to models. For the last two decades, efforts to develop safe and effective vaccines to prevent dengue virus (DENV) infections have faced several challenges, mostly related to the complexity of conducting long-term studies to evaluate vaccine efficacy and safety to rule out the risk of vaccine-induced DHS/DSS, particularly in children. At least seven DENV vaccines have undergone different phases of clinical trials; however, only three of them (Dengvaxia^®, TV003, and TAK-003) have showed promising results, and are addressed in detail in this review in terms of their molecular design, efficacy, and immunogenicity. Safety-related challenges during DENV vaccine development are also discussed.

Current status and perspectives on vaccine development against dengue virus infection

Dengue virus (DENV) consists of four serotypes in the family Flaviviridae and is a causative agent of dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. DENV is transmitted by mosquitoes, Aedes aegypti and A. albopictus, and is mainly observed in areas where vector mosquitoes live. The number of dengue cases reported by the World Health Organization increased more than 8-fold over the last two decades from 505,430 in 2000 to over 2.4 million in 2010 to 5.2 million in 2019. Although vaccine is the most effective method against DENV, only one commercialized vaccine exists, and it cannot be administered to children under 9 years of age. Currently, many researchers are working to resolve the various problems hindering the development of effective dengue vaccines; understanding of the viral antigen configuration would provide insight into the development of effective vaccines against DENV infection. In this review, the current status and perspectives on effective vaccine development for DENV are examined. In addition, a plausible direction for effective vaccine development against DENV is suggested.

Revival of the heterologous prime-boost technique in COVID-19: An outlook from the history of outbreaks

BACKGROUND

The heterologous prime-boost vaccination technique is not novel as it has a history of deployment in previous outbreaks.

AIM

Hence, this narrative review aims to provide critical insight for reviving the heterologous prime-boost immunization strategy for SARS-CoV-2 vaccination relative to a brief positive outlook on the mix-dose approach deployed in previous and existing outbreaks (ie, Ebola virus disease (EVD), malaria, tuberculosis, hepatitis B, HIV and influenza virus).

METHODOLOGY AND MATERIALS

A Boolean search was carried out to find the literature in MEDLINE-PubMed, Clinicaltrials, and Cochrane Central Register of Controlled Trials databases up till December 22, 2021, using the specific keywords that include "SARS-CoV2", "COVID-19", "Ebola," "Malaria," "Tuberculosis," "Human Immunodeficiency Virus," "Hepatitis B," "Influenza," "Mix and match," "Heterologous prime-boost," with interposition of "OR" and "AND." Full text of all the related articles in English language with supplementary appendix was retrieved. In addition, the full text of relevant cross-references was also retrieved.

RESULTS

Therefore, as generally evident by the primary outcomes, that is, safety, reactogenicity, and immunogenicity reported and updated by preclinical and clinical studies for addressing previous and existing outbreaks so far, including COVID-19, it is understood that heterologous prime-boost immunization has been proven successful for eliciting a more efficacious immune response as of yet in comparison to the traditional homologous prime-boost immunization regimen.

DISCUSSION

Accordingly, with increasing cases of COVID-19, many countries such as Germany, Pakistan, Canada, Thailand, and the United Kingdom have started administering the heterologous vaccination as the technique aids to rationalize the usage of the available vaccines to aid in the global race to vaccinate majority to curb the spread of COVID-19 efficiently. However, the article emphasizes the need for more large controlled trials considering demographic details of vaccine recipients, which would play an essential role in clearing the mistrust about safety concerns to pace up the acceptance of the technique across the globe.

CONCLUSION

Consequently, by combatting the back-to-back waves of COVID-19 and other challenging variants of concerns, including Omicron, the discussed approach can also help in addressing the expected evolution of priority outbreaks as coined by WHO, that is, "Disease X" in 2018 with competency, which according to WHO can turn into the "next pandemic" or the "next public health emergency," thus would eventually lead to eradicating the risk of "population crisis."

Enhanced dengue vaccine virus replication and neutralizing antibody responses in immune primed rhesus macaques

Antibody-dependent enhancement (ADE) is suspected to influence dengue virus (DENV) infection, but the role ADE plays in vaccination strategies incorporating live attenuated virus components is less clear. Using a heterologous prime-boost strategy in rhesus macaques, we examine the effect of priming with DENV purified inactivated vaccines (PIVs) on a tetravalent live attenuated vaccine (LAV). Sera exhibited low-level neutralizing antibodies (NAb) post PIV priming, yet moderate to high in vitro ADE activity. Following LAV administration, the PIV primed groups exhibited DENV-2 LAV peak viremias up to 1,176-fold higher than the mock primed group, and peak viremia correlated with in vitro ADE. Furthermore, PIV primed groups had more balanced and higher DENV-1–4 NAb seroconversion and titers than the mock primed group following LAV administration. These results have implications for the development of effective DENV vaccine prime-boost strategies and for our understanding of the role played by ADE in modulating DENV replication.

Dengue Virus and Vaccines: How Can DNA Immunization Contribute to This Challenge?

Dengue infections still have a tremendous impact on public health systems in most countries in tropical and subtropical regions. The disease is systemic and dynamic with broad range of manifestations, varying from mild symptoms to severe dengue (Dengue Hemorrhagic Fever and Dengue Shock Syndrome). The only licensed tetravalent dengue vaccine, Dengvaxia, is a chimeric yellow fever virus with prM and E genes from the different dengue serotypes. However, recent results indicated that seronegative individuals became more susceptible to develop severe dengue when infected after vaccination, and now WHO recommends vaccination only to dengue seropositive people. One possibility to explain these data is the lack of robust T-cell responses and antibody-dependent enhancement of virus replication in vaccinated people. On the other hand, DNA vaccines are excellent inducers of T-cell responses in experimental animals and it can also elicit antibody production. Clinical trials with DNA vaccines have improved and shown promising results regarding the use of this approach for human vaccination. Therefore, in this paper we review preclinical and clinical tests with DNA vaccines against the dengue virus. Most of the studies are based on the E protein since this antigen is the main target for neutralizing antibody production. Yet, there are other reports with DNA vaccines based on non-structural dengue proteins with protective results, as well. Combining structural and non-structural genes may be a solution for inducing immune responses aging in different infection moments. Furthermore, DNA immunizations are also a very good approach in combining strategies for vaccines against dengue, in heterologous prime/boost regimen or even administering different vaccines at the same time, in order to induce efficient humoral and cellular immune responses.

Short or Long Interval between Priming and Boosting: Does It Impact on the Vaccine Immunogenicity?

Characterizing the impact of the vaccination schedule on the induction of B and T cell immune responses is critical for improving vaccine immunogenicity. Here we compare the effect of a short (4 weeks) or a long (18 weeks) interval between priming and boosting in mice, using a model vaccine formulation based on the chimeric tuberculosis vaccine antigen H56 combined with alum. While no significant difference was observed in serum antigen-specific IgG response and the induction of antigen-specific T follicular helper cells into draining lymph nodes after the two immunization schedules, a longer interval between priming and boosting elicited a higher number of germinal center-B cells and H56-specific antibody-secreting cells and modulated the effector function of reactivated CD4+ T cells. These data show that the scheduling of the booster immunization could affect the immune response elicited by vaccination modulating and improving the immunogenicity of the vaccine.