Recombinant lipidated dengue-3 envelope protein domain III stimulates broad immune responses in mice

Approaches of dengue control: vaccine strategies and future aspects

Dengue, caused by the dengue virus (DENV), affects millions of people worldwide every year. This virus has two distinct life cycles, one in the human and another in the mosquito, and both cycles are crucial to be controlled. To control the vector of DENV, the mosquito Aedes aegypti, scientists employed many techniques, which were later proved ineffective and harmful in many ways. Consequently, the attention shifted to the development of a vaccine; researchers have targeted the E protein, a surface protein of the virus and the NS1 protein, an extracellular protein. There are several types of vaccines developed so far, such as live attenuated vaccines, recombinant subunit vaccines, inactivated virus vaccines, viral vectored vaccines, DNA vaccines, and mRNA vaccines. Along with these, scientists are exploring new strategies of developing improved version of the vaccine by employing recombinant DNA plasmid against NS1 and also aiming to prevent the infection by blocking the DENV life cycle inside the mosquitoes. Here, we discussed the aspects of research in the field of vaccines until now and identified some prospects for future vaccine developments.

Recombinant lipidated FLIPr effectively enhances mucosal and systemic immune responses for various vaccine types

Formyl peptide receptor-like 1 inhibitor protein (FLIPr) is an immune evasion protein produced by Staphylococcus aureus, and FLIPr is a potential vaccine candidate for reducing Staphylococcus aureus virulence and biofilm formation. We produced recombinant lipidated FLIPr (rLF) to increase the immunogenicity of FLIPr and showed that rLF alone elicited potent anti-FLIPr antibody responses to overcome the FLIPr-mediated inhibition of phagocytosis. In addition, rLF has potent immunostimulatory properties. We demonstrated that rLF is an effective adjuvant. When an antigen is formulated with rLF, it can induce long-lasting antigen-specific immune responses and enhance mucosal and systemic antibody responses as well as broad-spectrum T-cell responses in mice. These findings support further exploration of rLF in the clinic as an adjuvant for various vaccine types with extra benefits to abolish FLIPr-mediated immunosuppressive effects.

Targets and strategies for vaccine development against dengue viruses

Dengue virus (DENV) is a global health threat causing about half of the worldwide population to be at risk of infection, especially the people living in tropical and subtropical area. Although the dengue disease caused by dengue virus (DENV) is asymptomatic and self-limiting in most people with first infection, increased severe dengue symptoms may be observed in people with heterotypic secondary DENV infection. Since there is a lack of specific antiviral medication, the development of dengue vaccines is critical in the prevention and control this disease. Several targets and strategies in the development of dengue vaccine have been demonstrated. Currently, Dengvaxia, a live-attenuated chimeric yellow-fever/tetravalent dengue vaccine (CYD-TDV) developed by Sanofi Pasteur, has been licensed and approved for clinical use in some countries. However, this vaccine has demonstrated low efficacy in children and dengue-naïve individuals and also increases the risk of severe dengue in young vaccinated recipients. Accordingly, many novel strategies for the dengue vaccine are under investigation and development. Here, we conducted a systemic literature review according to PRISMA guidelines to give a concise overview of various aspects of the vaccine development process against DENVs, mainly targeting five potential strategies including live attenuated vaccine, inactivated virus vaccine, recombinant subunit vaccine, viral-vector vaccine, and DNA vaccine. This study offers the comprehensive view of updated information and current progression of immunogen selection as well as strategies of vaccine development against DENVs.

Dengue vaccine: an update

Introduction: Dengue virus is a global health threat, with approximately 390 million dengue infections annually. Efficient vaccines for dengue prevention are currently lacking. This review aims to summarize the current progress in dengue vaccine development.Area covered: This article discusses recent dengue vaccine developments based on the published literature and ClinicalTrials.gov website up to December 2020.Expert opinion: The first live-attenuated chimeric yellow-fever/tetravalent dengue vaccine (CYD-TDV), Dengvaxia, has been licensed in several countries. However, the low efficacy of this vaccine was observed in children and dengue-naïve individuals. It also increased the risk of severe dengue in people who had not been exposed to dengue. The heterologous prime-boost regimen of sequential immunization with DENVax and Dengvaxia covers four serotypes of immunogenicity, eliminating the effect of ADE. Moreover, a heterologous prime-boost regimen that combines inactivated vaccines with alum and live attenuated vaccines might increase the immunogenic response. The lack of an ideal animal model is an obstacle to the development of dengue vaccines, and the macaque model may be considered for similar immunologic responses in humans.

DENV-3 precursor membrane (prM) glycoprotein enhances E protein immunogenicity and confers protection against DENV-2 infections in a murine model

To improve a DNA vaccine containing the truncated dengue virus serotype 2 (DENV-2) envelope (E) protein and evaluate the influence of precursor membrane (prM) glycoprotein polymorphism on E protein immunogenicity, two vaccine candidates have been constructed by upstream insertion of the DENV-2 and DENV-3 prM genes into the DENV-2 E gene, named pCID2EtD2prM and pCID2EtD3prM, respectively. Both constructs were able to induce antibody production, which were neutralizing against DENV-2 in a murine model. Splenocytes of immunized groups, when challenged with virus, demonstrated Th1 cytokine pattern and proliferation, in addition to the increase of specific T cells. Vaccine candidates pCID2EtD2prM and pCID2EtD3prM confer 70% and 90% protection against DENV-2, respectively. The pCID2EtD3prM plasmid conferred only 40% protection in the lethal challenge with DENV-2. The results demonstrate that DENV-3 prM has a greater influence on the immunogenicity of the E protein and, probably due to its role as a chaperone, these results may be related to the correct folding and, consequently, an increase in the presentation efficiency of produced transcripts.

A Polypeptide of Tumor-Associated Antigen L6 with Intrinsic Adjuvant Activity Enhances Antitumor Immunity

Peptide vaccines are safe, and aim to elicit and expand tumor-specific immunity so as to eradicate tumors. However, achieving strong and long-lasting anti-tumor immunity with peptide vaccines for the antigen-specific treatment of cancer is challenging, in part because their efficacy depends on strong adjuvants or immunomodulators. We approached this problem by conjugating an epitope-based cancer vaccine with a lipidated sequence (an immunomodulator) to elicit a strong immune response. Lipidated and non-lipidated polyepitope proteins were generated that contained the universal T helper cell epitope (pan-DR), B cell epitopes, and the extended loop sequence of extracellular domain 2 of tumor-associated antigen L6 (TAL6). We show that the lipidated polyepitope cancer vaccine can activate bone marrow-derived dendritic cells, and trigger effective antigen-specific antibody and T helper cell responses, more effectively than the non-lipidated vaccine. Moreover, potent T cell immune responses were elicited in mice inoculated with the lipidated polyepitope cancer vaccine, providing protective antitumor immunity in mice bearing TAL6 tumors. Our study demonstrates that a lipidated polyepitope cancer vaccine could be employed to generate potent anti-tumor immune responses, including humoral and cellular immunity, which could be beneficial in the treatment of TAL6⁺ cancer.

Anti-Flavivirus Vaccines: Review of the Present Situation and Perspectives of Subunit Vaccines Produced in Escherichia coli

This article aims to review the present status of anti-flavivirus subunit vaccines, both those at the experimental stage and those already available for clinical use. Aspects regarding development of vaccines to Yellow Fever virus, (YFV), Dengue virus (DENV), West Nile virus (WNV), Zika virus (ZIKV), and Japanese encephalitis virus (JEV) are highlighted, with particular emphasis on purified recombinant proteins generated in bacterial cells. Currently licensed anti-flavivirus vaccines are based on inactivated, attenuated, or virus-vector vaccines. However, technological advances in the generation of recombinant antigens with preserved structural and immunological determinants reveal new possibilities for the development of recombinant protein-based vaccine formulations for clinical testing. Furthermore, novel proposals for multi-epitope vaccines and the discovery of new adjuvants and delivery systems that enhance and/or modulate immune responses can pave the way for the development of successful subunit vaccines. Nonetheless, advances in this field require high investments that will probably not raise interest from private pharmaceutical companies and, therefore, will require support by international philanthropic organizations and governments of the countries more severely stricken by these viruses.

Recombinant lipidated Zika virus envelope protein domain III elicits durable neutralizing antibody responses against Zika virus in mice

Background

The emergence of Zika virus (ZV) in tropical and subtropical areas of the world has created an urgent need for vaccines against ZV. However, approved vaccines that prevent ZV infection are not available. To develop an effective vaccine against ZV infection, a lipidated form of ZV envelope protein domain III that possesses an intrinsic adjuvant property was rationally designed. Our goal was to examine the immunogenicity of recombinant lipidated ZV envelope protein domain III (rLZE3) and evaluate its potential as a vaccine candidate against ZV.

Methods

Recombinant ZV envelope protein domain III (rZE3) and rLZE3 were prepared with an Escherichia coli-based system. Dendritic cell surface marker expression and cytokine production upon stimulation were analyzed to evaluate the function of rLZE3. Neutralizing antibody capacities were evaluated using focus reduction neutralization tests after immunization. To investigate the protective immunity in immunized mice, serum samples collected from immunized mice were adoptively transferred into AG129 mice, and then viremia levels and survival times were examined after ZV challenge.

Results

rLZE3 alone but not rZE3 alone efficiently activated dendritic cells in vitro and was taken up by dendritic cells in vivo. Immunization of C57BL/6 mice with rLZE3 alone (without exogenous adjuvant) could induce ZV-specific neutralizing antibody responses. Furthermore, serum samples obtained from rLZE3-immunized mice provided protection as indicated by a reduction in viremia levels and prolongation of survival times after ZV challenge.

Conclusion

These results indicate that rLZE3 is an excellent vaccine candidate and has great potential that should be evaluated in further preclinical studies.

Long-Term Protection Elicited by a DNA Vaccine Candidate Expressing the prM-E Antigen of Dengue Virus Serotype 3 in Mice

Dengue virus (DENV) is the causative agent of dengue, and its incidence has increased 30-fold in the past five decades. Among the four cocirculating serotypes, DENV3 is associated with an increased number of severe infections and has become widespread. Vaccination is the mainstay of prevention in reducing disease burden. Previously, the protective efficacy of DNA vaccine candidates toward DENV1, 2, and 4 was confirmed in mice. In this study, a DNA vaccine candidate (pVAX1-D3ME) expressing the prM and E proteins of DENV3 was constructed, and then the immunogenicity and protection were assessed in mice to further develop a tetravalent dengue vaccine. Moreover, the cross-reactive immune responses against the other three serotypes were investigated. The results showed that three doses of 50 μg of pVAX1-D3ME were sufficient to induce strong antigen-specific T cell responses and robust and consistent neutralizing antibodies. Additionally, immunization with pVAX1-D3ME offered protective immunity against not only DENV3 but also the other three serotypes, which could be observed even after 12 months. This study shows great promise for the further evaluation of a dengue tetravalent DNA vaccine candidate in large animal models, including non-human primates.

A Review on Dengue Vaccine Development

Dengue virus (DENV) has become a global health threat with about half of the world's population at risk of infection. Although the disease caused by DENV is self-limiting in the first infection, the antibody-dependent enhancement (ADE) effect increases the mortality in the second infection with a heterotypic virus. Since there is no specific efficient medicine in treatment, it is urgent to develop vaccines to prevent infection and disease progression. Currently, only a live attenuated vaccine, chimeric yellow fever 17D-tetravalent dengue vaccine (CYD-TDV), has been licensed for clinical use in some countries, and many candidate vaccines are still under research and development. This review discusses the progress, strengths, and weaknesses of the five types of vaccines including live attenuated vaccine, inactivated virus vaccine, recombinant subunit vaccine, viral vectored vaccine, and DNA vaccine.

Recent Developments in Recombinant Protein-Based Dengue Vaccines

Recombinant proteins are gaining enormous importance these days due to their wide application as biopharmaceutical products and proven safety record. Various recombinant proteins of therapeutic and prophylactic importance have been successfully produced in microbial and higher expression host systems. Since there is no specific antiviral therapy available against dengue, the prevention by vaccination is the mainstay in reducing the disease burden. Therefore, efficacious vaccines are needed to control the spread of dengue worldwide. Dengue is an emerging viral disease caused by any of dengue virus 1-4 serotypes that affects the human population around the globe. Dengue virus is a single stranded RNA virus encoding three structural proteins (capsid protein, pre-membrane protein, and envelope protein) and seven non-structural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, NS5). As the only licensed dengue vaccine (Dengvaxia) is unable to confer balanced protection against all the serotypes, therefore various approaches for development of dengue vaccines including tetravalent live attenuated, inactivated, plasmid DNA, virus-vectored, virus-like particles, and recombinant subunit vaccines are being explored. These candidates are at different stages of vaccine development and have their own merits and demerits. The promising subunit vaccines are mainly based on envelope or its domain and non-structural proteins of dengue virus. These proteins have been produced in different hosts and are being investigated for development of a successful dengue vaccine. Novel immunogens have been designed employing various strategies like protein engineering and fusion of antigen with various immunostimulatory motif to work as self-adjuvant. Moreover, recombinant proteins can be formulated with novel adjuvants to enhance the immunogenicity and thus conferring better protection to the vaccinees. With the advent of newer and safer host systems, these recombinant proteins can be produced in a cost effective manner at large scale for vaccine studies. In this review, we summarize recent developments in recombinant protein based dengue vaccines that could lead to a good number of efficacious vaccine candidates for future human use and ultimately alternative dengue vaccine candidates.

Efficient Uptake of Recombinant Lipidated Survivin by Antigen-Presenting Cells Initiates Antigen Cross-Presentation and Antitumor Immunity

Survivin is overexpressed in various types of human cancer, but rarely expressed in terminally differentiated adult tissues. Thus, survivin is a potential target antigen for a cancer vaccine. However, self-tumor-associated antigens are not highly immunogenic. Bacteria-derived lipoproteins can activate antigen-presenting cells through their toll-like receptors to enhance immune responses. In this context, lipidated survivin is an attractive candidate for cancer immunotherapy. In the present study, recombinant lipidated human survivin (LSur) was prepared from an Escherichia coli-based system. We investigated whether LSur is efficiently captured by antigen-presenting cells then facilitating effective induction of survivin cross-presentation and generation of immunity against cancer cells. Our results demonstrate that LSur, but not its non-lipidated counterpart, can activate mouse bone-marrow-derived-dendritic cells (BMDCs) to enhance cytokine (IL-6, TNF-α, and IL-12) secretion and costimulatory molecules (CD40, CD80, CD86, and MHC II) expression. However, the pathways involved in the capture of the recombinant lipidated antigen by antigen-presenting cells have not yet been elucidated. To this end, we employ various endocytosis inhibitors to study the effect on LSur internalization. We show that the internalization of LSur is suppressed by the inhibition of various routes of endocytosis. These results suggest that endocytosis of LSur by BMDCs can be mediated by multiple mechanisms. Furthermore, LSur is trafficked to the early endosome after internalization by BMDCs. These features of LSur are advantageous for cross-presentation and the induction of antitumor immunity. We demonstrate that immunization of C57BL/6 mice with LSur under treatment with exogenous adjuvant-free formulation induce survivin-specific CD8⁺ T-cell responses and suppress tumor growth. The antitumor responses are mediated by CD8⁺ cells. Our findings indicate that LSur is a potential candidate for stimulating protective antitumor immunity. This study suggests that lipidated tumor antigens may be a promising approach for raising a robust antitumor response in cancer immunotherapy.

EDIII-DENV3 nanospheres drive immature dendritic cells into a mature phenotype in an in vitro model

Domain III of E protein of dengue virus (DENV) is a target for vaccine development. Unfortunately, this protein based platform has low general immunogenicity. To circumvent this problem, the use of an adjuvant-nanoparticle delivery system to facilitate immunogenicity of soluble DENV-EDIII protein was investigated. One of the key features of this delivery system is its ability to simultaneously deliver antigens and exert adjuvanticity on specialized immune cells. In this study, N-trimethyl chitosan (TMC) nanoparticles (NPs) were generated to be used as adjuvant and carrier for soluble E-domain III of dengue virus serotype 3 (sEDIII-D3). Using ionotropic gelation, purified sEDIII-D3 was encapsulated into TMC NPs to form EDIII-D3 TMC NPs. After optimization, EDIII-D3 TMC particles exhibited a loading efficiency of 81% and a loading capacity of 41%. The immunogenicity of EDIII-D3 TMC NPs was tested using monocyte-derived dendritic cells (MoDCs). It was found that EDIII-D3 TMC NPs were well taken up by MoDCs. In addition, EDIII-D3 TMC NP treated MoDCs significantly upregulated maturation markers (CD80, CD83, CD86 and HLA-DR) and induced secretion of various cytokines and chemokines (IFN-α, IL-1β, IL-6, IL-2, IL-12p70, IFN-γ, IL-4, IL-10, IL-8, MCP-1, macrophage inflammatory protein-1β, granulocyte-colony stimulating factor, granulocyte-macrophage colony-stimulating factor and IL-7). These results indicate that EDIII-D3 TMC NPs are potent immunogens, at least in vitro, with the ability to induce maturation of DCs and highlight the potential use of TMC NPs for enhancing immunogenicity of a non-replicating dengue vaccine.

Dengue viruses and promising envelope protein domain III-based vaccines

Dengue viruses are emerging mosquito-borne pathogens belonging to Flaviviridae family which are transmitted to humans via the bites of infected mosquitoes Aedes aegypti and Aedes albopictus. Because of the wide distribution of these mosquito vectors, more than 2.5 billion people are approximately at risk of dengue infection. Dengue viruses cause dengue fever and severe life-threatening illnesses as well as dengue hemorrhagic fever and dengue shock syndrome. All four serotypes of dengue virus can cause dengue diseases, but the manifestations are nearly different depending on type of the virus in consequent infections. Infection by any serotype creates life-long immunity against the corresponding serotype and temporary immunity to the others. This transient immunity declines after a while (6 months to 2 years) and is not protective against other serotypes, even may enhance the severity of a secondary heterotypic infection with a different serotype through a phenomenon known as antibody-depended enhancement (ADE). Although, it can be one of the possible explanations for more severe dengue diseases in individuals infected with a different serotype after primary infection. The envelope protein (E protein) of dengue virus is responsible for a wide range of biological activities, including binding to host cell receptors and fusion to and entry into host cells. The E protein, and especially its domain III (EDIII), stimulates host immunity responses by inducing protective and neutralizing antibodies. Therefore, the dengue E protein is an important antigen for vaccine development and diagnostic purposes. Here, we have provided a comprehensive review of dengue disease, vaccine design challenges, and various approaches in dengue vaccine development with emphasizing on newly developed envelope domain III-based dengue vaccine candidates.

Structural and Functional Characterization of a Cross-Reactive Dengue Virus Neutralizing Antibody that Recognizes a Cryptic Epitope

Understanding the molecular basis of the neutralizing antibody response to dengue virus (DENV) is an essential component in the design and development of effective vaccines and immunotherapeutics. Here we present the structure of a cross-reactive, neutralizing antibody, 3E31, in complex with domain III (DIII) of the DENV envelope (E) protein and reveal a conserved, temperature-sensitive, cryptic epitope on DIII that is not available in any of the known conformations of E on the dengue virion. We observed that 3E31 inhibits E-mediated membrane fusion, suggesting that the antibody is able to neutralize virus through binding an as-yet uncharacterized intermediate conformation of DENV E and sterically block trimer formation. Finally, we show that, unlike cross-reactive fusion peptide-specific antibodies, 3E31 does not promote antibody-dependent enhancement of infection at sub-neutralizing concentrations. Our results highlight the 3E31 epitope on the E protein DIII as a promising target for immunotherapeutics or vaccine design.

Immunogenicity of a novel tetravalent vaccine formulation with four recombinant lipidated dengue envelope protein domain IIIs in mice

We developed a novel platform to express high levels of recombinant lipoproteins with intrinsic adjuvant properties. Based on this technology, our group developed recombinant lipidated dengue envelope protein domain IIIs as vaccine candidates against dengue virus. This work aims to evaluate the immune responses in mice to the tetravalent formulation. We demonstrate that 4 serotypes of recombinant lipidated dengue envelope protein domain III induced both humoral and cellular immunity against all 4 serotypes of dengue virus on the mixture that formed the tetravalent formulation. Importantly, the immune responses induced by the tetravalent formulation in the absence of the exogenous adjuvant were functional in clearing the 4 serotypes of dengue virus in vivo. We affirm that the tetravalent formulation of recombinant lipidated dengue envelope protein domain III is a potential vaccine candidate against dengue virus and suggest further detailed studies of this formulation in nonhuman primates.