Adjuvant-Mediated Epitope Specificity and Enhanced Neutralizing Activity of Antibodies Targeting Dengue Virus Envelope Protein

Highly heterogenous humoral immune response in Lyme disease patients revealed by broad machine learning-assisted antibody binding profiling with random peptide arrays

Introduction

Lyme disease (LD), a rapidly growing public health problem in the US, represents a formidable challenge due to the lack of detailed understanding about how the human immune system responds to its pathogen, the Borrelia burgdorferi bacterium. Despite significant advances in gaining deeper insight into mechanisms the pathogen uses to evade immune response, substantial gaps remain. As a result, molecular tools for the disease diagnosis are lacking with the currently available tests showing poor performance. High interpersonal variability in immune response combined with the ability of the pathogen to use a number of immune evasive tactics have been implicated as underlying factors for the limited test performance.

Methods

This study was designed to perform a broad profiling of the entire repertoire of circulating antibodies in human sera at the single-individual level using planar arrays of short linear peptides with random sequences. The peptides sample sparsely, but uniformly the entire combinatorial sequence space of the same length peptides for profiling the humoral immune response to a B.burg. infection and compare them with other diseases with etiology similar to LD and healthy controls.

Results

The study revealed substantial variability in antibody binding profiles between individual LD patients even to the same antigen (VlsE protein) and strong similarity between individuals diagnosed with Lyme disease and healthy controls from the areas endemic to LD suggesting a high prevalence of seropositivity in endemic healthy control.

Discussion

This work demonstrates the utility of the approach as a valuable analytical tool for agnostic profiling of humoral immune response to a pathogen.

An update on one-dose HPV vaccine studies, immunobridging and humoral immune responses - A meeting report

The 12th HPV Prevention and Control meeting was held on June 2-3, 2022, in Antwerp, Belgium. This technical meeting focused on several topics. This report summarises the discussions and lessons learned on two topics: an update on one-dose HPV vaccination studies and humoral immune responses upon HPV vaccination. Long-term follow-up studies from Costa Rica (eleven years) and India (ten years) report stable levels of antibodies after a single HPV vaccination. High vaccine effectiveness against incident persistent HPV 16/18 infection was seen in India (95.4%, 85.0-99.9) ten years postvaccination and in Kenya (97.5%, 81.7-99.7) eighteen months postvaccination, an important observation in a setting with a higher HPV prevalence. The potential impact of HPV vaccination using a one-dose schedule in India was modelled and showed that implementation of one-dose schedule can contribute towards achieving WHO Cervical Cancer elimination goals. These data support the WHO SAGE recommendations for adopting a one-dose schedule for females aged 9-20 years. Immunobridging studies were discussed during the meeting. General agreement was reached that when thoughtfully applied, they can support and accelerate the expanded use of HPV vaccine with new vaccine schedules, age cohorts, or vaccine formulations. Internationally standardised measurements of HPV immune responses important for the progress of HPV vaccinology field. Humoral immune responses upon HPV vaccination plateau at 24 months regardless of number of doses, therefore, data should be analysed after at least 24 months of follow-up to bridge studies accurately.

Adjuvanted Fusion Protein Vaccine Induces Durable Immunity to Onchocerca volvulus in Mice and Non-Human Primates

Onchocerciasis remains a debilitating neglected tropical disease. Due to the many challenges of current control methods, an effective vaccine against the causative agent Onchocerca volvulus is urgently needed. Mice and cynomolgus macaque non-human primates (NHPs) were immunized with a vaccine consisting of a fusion of two O. volvulus protein antigens, Ov-103 and Ov-RAL-2 (Ov-FUS-1), and three different adjuvants: Advax-CpG, alum, and AlT4. All vaccine formulations induced high antigen-specific IgG titers in both mice and NHPs. Challenging mice with O. volvulus L3 contained within subcutaneous diffusion chambers demonstrated that Ov-FUS-1/Advax-CpG-immunized animals developed protective immunity, durable for at least 11 weeks. Passive transfer of sera, collected at several time points, from both mice and NHPs immunized with Ov-FUS-1/Advax-CpG transferred protection to naïve mice. These results demonstrate that Ov-FUS-1 with the adjuvant Advax-CpG induces durable protective immunity against O. volvulus in mice and NHPs that is mediated by vaccine-induced humoral factors.

Modeling the sequence dependence of differential antibody binding in the immune response to infectious disease

Past studies have shown that incubation of human serum samples on high density peptide arrays followed by measurement of total antibody bound to each peptide sequence allows detection and discrimination of humoral immune responses to a variety of infectious diseases. This is true even though these arrays consist of peptides with near-random amino acid sequences that were not designed to mimic biological antigens. This "immunosignature" approach, is based on a statistical evaluation of the binding pattern for each sample but it ignores the information contained in the amino acid sequences that the antibodies are binding to. Here, similar array-based antibody profiles are instead used to train a neural network to model the sequence dependence of molecular recognition involved in the immune response of each sample. The binding profiles used resulted from incubating serum from 5 infectious disease cohorts (Hepatitis B and C, Dengue Fever, West Nile Virus and Chagas disease) and an uninfected cohort with 122,926 peptide sequences on an array. These sequences were selected quasi-randomly to represent an even but sparse sample of the entire possible combinatorial sequence space (~1012). This very sparse sampling of combinatorial sequence space was sufficient to capture a statistically accurate representation of the humoral immune response across the entire space. Processing array data using the neural network not only captures the disease-specific sequence-binding information but aggregates binding information with respect to sequence, removing sequence-independent noise and improving the accuracy of array-based classification of disease compared with the raw binding data. Because the neural network model is trained on all samples simultaneously, a highly condensed representation of the differential information between samples resides in the output layer of the model, and the column vectors from this layer can be used to represent each sample for classification or unsupervised clustering applications.

Polyclonal Antibodies Derived from Transchromosomic Bovines Vaccinated with the Recombinant F1-V Vaccine Increase Bacterial Opsonization In Vitro and Protect Mice from Pneumonic Plague

Plague is an ancient disease that continues to be of concern to both the public health and biodefense research communities. Pneumonic plague is caused by hematogenous spread of Yersinia pestis bacteria from a ruptured bubo to the lungs or by directly inhaling aerosolized bacteria. The fatality rate associated with pneumonic plague is significant unless effective antibiotic therapy is initiated soon after an early and accurate diagnosis is made. As with all bacterial pathogens, drug resistance is a primary concern when developing strategies to combat these Yersinia pestis infections in the future. While there has been significant progress in vaccine development, no FDA-approved vaccine strategy exists; thus, other medical countermeasures are needed. Antibody treatment has been shown to be effective in animal models of plague. We produced fully human polyclonal antibodies in transchromosomic bovines vaccinated with the recombinant F1-V plague vaccine. The resulting human antibodies opsonized Y. pestis bacteria in the presence of RAW264.7 cells and afforded significant protection to BALB/c mice after exposure to aerosolized Y. pestis. These data demonstrate the utility of this technology to produce large quantities of non-immunogenic anti-plague human antibodies to prevent or possibly treat pneumonic plague in human.

Diagnostic and vaccine potential of Zika virus envelope protein (E) derivates produced in bacterial and insect cells

Introduction

In the present study we evaluated the features of different recombinant forms of Zika virus (ZIKV) proteins produced in either bacterial (Eschericha coli) or insect cells (Drosophila melanogaster). The ZIKV-envelope glycoprotein (EZIKV) is responsible for virus entry into host cells, is the main target of neutralizing antibodies and has been used as a target antigen either for serological tests or for the development of subunit vaccines. The EZIKV is composed of three structural and functional domains (EDI, EDII, and EDIII), which share extensive sequence conservation with the corresponding counterparts expressed by other flaviviruses, particularly the different dengue virus (DENV) subtypes.

Methods

In this study, we carried out a systematic comparison of the antigenicity and immunogenicity of recombinant EZIKV, EDI/IIZIKV and EDIIIZIKV produced in E. coli BL21 and Drosophila S2 cells. For the antigenicity analysis we collected 88 serum samples from ZIKV-infected participants and 57 serum samples from DENV-infected. For immunogenicity, C57BL/6 mice were immunized with two doses of EZIKV, EDI/IIZIKV and EDIIIZIKV produced in E. coli BL21 and Drosophila S2 cells to evaluate humoral and cellular immune response. In addition, AG129 mice were immunized with EZIKV and then challenge with ZIKV.

Results

Testing of samples collected from ZIKV-infected and DENV-infected participants demonstrated that the EZIKV and EDIIIZIKV produced in BL21 cells presented better sensitivity and specificity compared to proteins produced in S2 cells. In vivo analyses were carried out with C57BL/6 mice and the results indicated that, despite similar immunogenicity, antigens produced in S2 cells, particularly EZIKV and EDIIIZIKV, induced higher ZIKV-neutralizing antibody levels in vaccinated mice. In addition, immunization with EZIKV expressed in S2 cells delayed the onset of symptoms and increased survival rates in immunocompromised mice. All recombinant antigens, either produced in bacteria or insect cells, induced antigen-specific CD4+ and CD8+ T cell responses.

Conclusion

In conclusion, the present study highlights the differences in antigenicity and immunogenicity of recombinant ZIKV antigens produced in two heterologous protein expression systems.

Differences in HPV-specific antibody Fc-effector functions following Gardasil® and Cervarix® vaccination

Gardasil® (Merck) and Cervarix® (GlaxoSmithKline) both provide protection against infection with Human Papillomavirus 16 (HPV16) and Human Papillomavirus 18 (HPV18), that account for around 70% of cervical cancers. Both vaccines have been shown to induce high levels of neutralizing antibodies and are known to protect against progression beyond cervical intraepithelial neoplasia grade 2 (CIN2+), although Cervarix® has been linked to enhanced protection from progression. However, beyond the transmission-blocking activity of neutralizing antibodies against HPV, no clear correlate of protection has been defined that may explain persistent control and clearance elicited by HPV vaccines. Beyond blocking, antibodies contribute to antiviral activity via the recruitment of the cytotoxic and opsonophagocytic power of the immune system. Thus, here, we used systems serology to comprehensively profile Gardasil®- and Cervarix®- induced antibody subclass, isotype, Fc-receptor binding, and Fc-effector functions against the HPV16 and HPV18 major capsid protein (L1). Overall, both vaccines induced robust functional humoral immune responses against both HPV16 and HPV18. However, Cervarix® elicited higher IgG3 and antibody-dependent complement activating responses, and an overall more coordinated response between HPV16 and 18 compared to Gardasil®, potentially related to the distinct adjuvants delivered with the vaccines. Thus, these data point to robust Fc-effector functions induced by both Gardasil® and Cervarix®, albeit with enhanced coordination observed with Cervarix®, potentially underlying immunological correlates of post-infection control of HPV.

Nano-multilamellar lipid vesicles promote the induction of SARS-CoV-2 immune responses by a protein-based vaccine formulation

The development of safe and effective vaccine formulations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents a hallmark in the history of vaccines. Here we report a COVID-19 subunit vaccine based on a SARS-CoV-2 Spike protein receptor binding domain (RBD) incorporated into nano-multilamellar vesicles (NMV) associated with monophosphoryl lipid A (MPLA). The results based on immunization of C57BL/6 mice demonstrated that recombinant antigen incorporation into NMVs improved antibody and T-cell responses without inducing toxic effects under both in vitro and in vivo conditions. Administration of RBD-NMV-MPLA formulations modulated antigen avidity and IgG subclass responses, whereas MPLA incorporation improved the activation of CD4⁺/CD8⁺ T-cell responses. In addition, immunization with the complete vaccine formulation reduced the number of doses required to achieve enhanced serum virus-neutralizing antibody titers. Overall, this study highlights NMV/MPLA technology, displaying the performance improvement of subunit vaccines against SARS-CoV-2, as well as other infectious diseases.

Preclinical Study of Formulated Recombinant Nucleocapsid protein, the Receptor Binding Domain of the Spike protein, and Truncated Spike (S1) Protein as Vaccine Candidates against COVID-19 in Animal Models

Background

Methods

Results

Conclusion

Execution and Design of an Anti HPIV-1 Vaccine with Multiple Epitopes Triggering Innate and Adaptive Immune Responses: An Immunoinformatic Approach

Human Parainfluenza Virus (HPIV) Type-1, which is an anti-sense ribonucleic acid (RNA) virus belonging to the paramyxoviridae family, induces upper and lower respiratory tract infections. The infections caused by the HPIV Type-1 virus are usually confined to northwestern regions of America. HPIV-1 causes infections through the virulence of the hemagglutinin-neuraminidase (HN) protein, which plays a key role in the attachment of the viral particle with the host’s receptor cells. To the best of our knowledge, there is no effective antiviral drugs or vaccines being developed to combat the infection caused by HPIV-1. In the current study, a multiple epitope-based vaccine was designed against HPIV-1 by taking the viral HN protein as a probable vaccine candidate. The multiple epitopes were selected in accordance with their allergenicity, antigenicity and toxicity scoring. The determined epitopes of the HN protein were connected simultaneously using specific conjugates along with an adjuvant to construct the subunit vaccine, with an antigenicity score of 0.6406. The constructed vaccine model was docked with various Toll-like Receptors (TLRs) and was computationally cloned in a pET28a (+) vector to analyze the expression of vaccine sequence in the biological system. Immune stimulations carried out by the C-ImmSim Server showed an excellent result of the body’s defense system against the constructed vaccine model. The AllerTop tool predicted that the construct was non-allergen with and without the adjuvant sequence, and the VaxiJen 2.0 with 0.4 threshold predicted that the construct was antigenic, while the Toxinpred predicted that the construct was non-toxic. Protparam results showed that the selected protein was stable with 36.48 instability index (II) scores. The Grand average of Hydropathicity or GRAVY score indicated that the constructed protein was hydrophilic in nature. Aliphatic index values (93.53) confirmed that the construct was thermostable. This integrated computational approach shows that the constructed vaccine model has a potential to combat laryngotracheobronchitis infections caused by HPIV-I.

Nano-multilamellar lipid vesicles loaded with a recombinant form of the chikungunya virus E2 protein improve the induction of virus-neutralizing antibodies

Chikungunya virus (CHIKV) is responsible for a self-limited illness that can evolve into long-lasting painful joint inflammation. In this study, we report a novel experimental CHIKV vaccine formulation of lipid nanoparticles loaded with a recombinant protein derived from the E2 structural protein. This antigen fragment, designated ∆E2.1, maintained the antigenicity of the native viral protein and was specifically recognized by antibodies induced in CHIKV-infected patients. The antigen has been formulated into nanoparticles consisting of nano-multilamellar vesicles (NMVs) combined with the adjuvant monophosphoryl lipid A (MPLA). The vaccine formulation demonstrated a depot effect, leading to controlled antigen release, and induced strong antibody responses significantly higher than in mice immunized with the purified protein combined with the adjuvant. More relevantly, E2-specific antibodies raised in mice immunized with ∆E2.1-loaded NMV-MPLA neutralized CHIKV under in vitro conditions. Taken together, the results demonstrated that the new nanoparticle-based vaccine formulation represents a promising approach for the development of effective anti-CHIKV vaccines.

Solubility Controlling Peptide Tags of Opposite Charges Generate a Bivalent Immune Response Against Dengue ED3 Serotypes 3 and 4

We previously demonstrated that a protein’s immunogenicity could be substantially increased by attaching a hydrophobic solubility controlling peptide tag (SCP-tag) producing small sub-visible aggregates. Here, we report the oligomerization of Dengue envelop protein domain 3 (ED3), and consequently, its immunogenicity increase by mixing ED3s attached with SCP-tags of opposite charges at equimolar concentration. We used ED3 of serotype 3 (D3ED3) and serotype 4 (D4ED3), which are, respectively, moderately and poorly immunogenic, and their SCP tagged variants constructed by attaching either a C-termini 5-Aspartic acid (C5D) or a 5-Lysine (C5K) tag. Light scattering indicated that the isolated tagged ED3s remained monomeric, but mixing the C5D and C5K tagged ED3s at equimolar concentration generated sub-visible aggregates or oligomers of ~500 nm through electrostatic interaction. In addition, the oligomerized ED3s remained in a native-like state, as assessed by fluorescence spectroscopy and circular dichroism. The in vivo immunogenicity of the D3ED3 and D4ED3 oligomers generated by the charged tags increased by 5 and 16 fold, respectively. Furthermore, injection of heterotypic ED3 oligomers (D3C5D+D4C5K) induced an immune response against both D3ED3 and D4ED3 in 3 of 4 responsive mice, and the IgG titer of the bivalent anti-D3C5D-D4C5K sera was over 100 times higher than that generated by co-injecting the untagged D3ED3 and D4ED3 (D3+D4). Altogether, these observations suggest that SCP-tags could be used as a platform for producing a long-sought tetravalent dengue vaccine.

Immunodominance of Epitopes and Protective Efficacy of HI Antigen Are Differentially Altered Using Different Adjuvants in a Mouse Model of Staphylococcus aureus Bacteremia

HI, a fusion protein that consists of the alpha-toxin (Hla) and the N2 domain of iron surface determinant B (IsdB), is one of the antigens in the previously reported S. aureus vaccine rFSAV and has already entered phase II clinical trials. Previous studies revealed that HI is highly immunogenic in both mice and healthy volunteers, and the humoral immune response plays key roles in HI-mediated protection. In this study, we further investigated the protective efficacy of immunization with HI plus four different adjuvants in a mouse bacteremia model. Results showed that HI-mediated protection was altered in response to different adjuvants. Using antisera from immunized mice, we identified seven B-cell immunodominant epitopes on Hla and IsdB, including 6 novel epitopes (Hla_1-18, Hla_84-101, Hla_186-203, IsdB_342-359, IsdB_366-383, and IsdB_384-401). The immunodominance of B-cell epitopes, total IgG titers and the levels of IFN-γ and IL-17A from mice immunized with HI plus different adjuvants were different from each other, which may explain the difference in protective immunity observed in each immunized group. Thus, our results indicate that adjuvants largely affected the immunodominance of epitopes and the protective efficacy of HI, which may guide further adjuvant screening for vaccine development and optimization.

Immunization with recombinant Erns-LTB fusion protein elicits protective immune responses against bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV), a major infectious pathogen and is associated with major economic losses and significant impact on animal welfare worldwide. Here, recombinant E^rns-LTB protein vaccine containing MF59 adjuvant was prepared and assessed using a mouse model. The recombinant plasmid (pET32a-E^rns-LTB) was constructed and transformed into BL21 (DE3) cells to produce E^rns-LTB protein. The E^rns-LTB protein was formulated with MF59 adjuvant, when delivered intraperitoneally in mice, exhibited higher immunogenic and induced superior levels of anti-BVDV IgG compared with the MF59 adjuvanted E^rns protein. Importantly, after challenged with different BVDV BJ175170 and BJ1305 isolate strains, mice inoculated with E^rns-LTB protein displayed alleviated pathological damage and decreased plasma virus shedding compared with mice inoculated with E^rns protein. The enhanced protection from E^rns-LTB protein is mediated by T cell immunity and primarily based on CD4⁺ T helper (Th) and CD8⁺ cytotoxic T lymphocyte (CTL), these results suggest that E^rns-LTB protein has potential to protect against a broad range of BVDV strains thereby providing a novel direction for developing broadly protective vaccines.

Glycosylation is required for the neutralizing activity of human IgG1 antibodies against human rabies induced by pre-exposure prophylaxis

Rabies lyssavirus (RABV) neutralizing IgG antibodies confer protection after rabies vaccination, although how the RABV-specific antibodies neutralize the virus is still unknown. As changes in the antibody's carbohydrate chain can interfere with its effector functions, we compared the glycosylation patterns of both neutralizing and non-neutralizing IgG1 induced by pre-exposure prophylaxis to human rabies and analyzed their influence on in vitro antibody neutralizing activities. Specific IgG1 were purified from human serum using affinity chromatography. Purity and avidity were analyzed by SDS-PAGE and indirect ELISA using NH₄SCN respectively. The N-linked oligosaccharide chain of the purified IgG antibody was evaluated using a lectin-based ELISA assay with a panel of seven lectins. The activity of purified IgG1 and neutralizing IgG1 deglycosylated by PNGase F enzyme were analyzed using the rapid fluorescent focus inhibition test. The purified IgG1 showed an electrophoretic pattern compatible with human IgG. All of the antibodies recognized RABV, although neutralizing IgG1 had a higher avidity (RAI = 80%) than non-neutralizing IgG1 (RAI = 30%). The neutralizing IgG1 also showed higher binding to WFA, ECA, WGA, and ConA lectins, indicating possible different N-acetylgalactosamine, galactose, N-acetylglucosamine, and mannose contents. Non-neutralizing IgG1, on the other hand, showed strong binding at UEA-1 and SNA, which bind to fucose and sialic acid residues respectively. Different glycosylation profiles were also observed in Fab and Fc fragments from neutralizing and non-neutralizing IgG1, although the deglycosylated IgG1 lost its neutralizing activity. Our results suggest that antibody glycosylation is important for neutralizing RABV in vitro, since neutralizing IgG1 has a different glycosylation profile than non-neutralizing IgG1. Further research will be needed to better evaluate the differential glycosylation patterns between IgG1 antibodies following vaccination.

Rapid Response to Pandemic Threats: Immunogenic Epitope Detection of Pandemic Pathogens for Diagnostics and Vaccine Development Using Peptide Microarrays

Emergence and re-emergence of pathogens bearing the risk of becoming a pandemic threat are on the rise. Increased travel and trade, growing population density, changes in urbanization, and climate have a critical impact on infectious disease spread. Currently, the world is confronted with the emergence of a novel coronavirus SARS-CoV-2, responsible for yet more than 800 000 deaths globally. Outbreaks caused by viruses, such as SARS-CoV-2, HIV, Ebola, influenza, and Zika, have increased over the past decade, underlining the need for a rapid development of diagnostics and vaccines. Hence, the rational identification of biomarkers for diagnostic measures on the one hand, and antigenic targets for vaccine development on the other, are of utmost importance. Peptide microarrays can display large numbers of putative target proteins translated into overlapping linear (and cyclic) peptides for a multiplexed, high-throughput antibody analysis. This enabled for example the identification of discriminant/diagnostic epitopes in Zika or influenza and mapping epitope evolution in natural infections versus vaccinations. In this review, we highlight synthesis platforms that facilitate fast and flexible generation of high-density peptide microarrays. We further outline the multifaceted applications of these peptide array platforms for the development of serological tests and vaccines to quickly encounter pandemic threats.

Co-Administration of Aluminium Hydroxide Nanoparticles and Protective Antigen Domain 4 Encapsulated Non-Ionic Surfactant Vesicles Show Enhanced Immune Response and Superior Protection against Anthrax

Aluminium salts have been the adjuvant of choice in more than 100 licensed vaccines. Here, we have studied the synergistic effect of aluminium hydroxide nanoparticles (AH np) and non-ionic surfactant-based vesicles (NISV) in modulating the immune response against protective antigen domain 4 (D4) of Bacillus anthracis. NISV was prepared from Span 60 and cholesterol, while AH np was prepared from aluminium chloride and sodium hydroxide. AH np was co-administered with NISV encapsulating D4 (NISV-D4) to formulate AHnp/NISV-D4. The antigen-specific immune response of AHnp/NISV-D4 was compared with that of commercial alhydrogel (alhy) co-administered with NISV-D4 (alhydrogel/NISV-D4), NISV-D4, AHnp/D4, and alhydrogel/D4. Co-administration of NISV-D4 with AH np greatly improved the D4-specific antibody titer as compared to the control groups. Based on IgG isotyping and ex vivo cytokine analysis, AHnp/NISV-D4 generated a balanced Th1/Th2 response. Furthermore, AH np/NISV-D4 showed superior protection against anthrax spore challenge in comparison to other groups. Thus, we demonstrate the possibility of developing a novel combinatorial nanoformulation capable of augmenting both humoral and cellular response, paving the way for adjuvant research.

Intradermal Delivery of Dendritic Cell-Targeting Chimeric mAbs Genetically Fused to Type 2 Dengue Virus Nonstructural Protein 1

Targeting dendritic cells (DCs) by means of monoclonal antibodies (mAbs) capable of binding their surface receptors (DEC205 and DCIR2) has previously been shown to enhance the immunogenicity of genetically fused antigens. This approach has been repeatedly demonstrated to enhance the induced immune responses to passenger antigens and thus represents a promising therapeutic and/or prophylactic strategy against different infectious diseases. Additionally, under experimental conditions, chimeric αDEC205 or αDCIR2 mAbs are usually administered via an intraperitoneal (i.p.) route, which is not reproducible in clinical settings. In this study, we characterized the delivery of chimeric αDEC205 or αDCIR2 mAbs via an intradermal (i.d.) route, compared the elicited humoral immune responses, and evaluated the safety of this potential immunization strategy under preclinical conditions. As a model antigen, we used type 2 dengue virus (DENV2) nonstructural protein 1 (NS1). The results show that the administration of chimeric DC-targeting mAbs via the i.d. route induced humoral immune responses to the passenger antigen equivalent or superior to those elicited by i.p. immunization with no toxic effects to the animals. Collectively, these results clearly indicate that i.d. administration of DC-targeting chimeric mAbs presents promising approaches for the development of subunit vaccines, particularly against DENV and other flaviviruses.

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.

Dimerization of Dengue Virus E Subunits Impacts Antibody Function and Domain Focus

Dengue virus (DENV) is responsible for the most prevalent and significant arthropod-borne viral infection of humans. The leading DENV vaccines are based on tetravalent live-attenuated virus platforms. In practice, it has been challenging to induce balanced and effective responses to each of the four DENV serotypes because of differences in the replication efficiency and immunogenicity of individual vaccine components. Unlike live vaccines, tetravalent DENV envelope (E) protein subunit vaccines are likely to stimulate balanced immune responses, because immunogenicity is replication independent. However, E protein subunit vaccines have historically performed poorly, in part because the antigens utilized were mainly monomers that did not display quaternary-structure epitopes found on E dimers and higher-order structures that form the viral envelope. In this study, we compared the immunogenicity of DENV2 E homodimers and DENV2 E monomers. The stabilized DENV2 homodimers, but not monomers, were efficiently recognized by virus-specific and flavivirus cross-reactive potently neutralizing antibodies that have been mapped to quaternary-structure epitopes displayed on the viral surface. In mice, the dimers stimulated 3-fold-higher levels of virus-specific neutralizing IgG that recognized epitopes different from those recognized by lower-level neutralizing antibodies induced by monomers. The dimer induced a stronger E domain I (EDI)- and EDII-targeted response, while the monomer antigens stimulated an EDIII epitope response and induced fusion loop epitope antibodies that are known to facilitate antibody-dependent enhancement (ADE). This study shows that DENV E subunit antigens that have been designed to mimic the structural organization of the viral surface are better vaccine antigens than E protein monomers.IMPORTANCE Dengue virus vaccine development is particularly challenging because vaccines have to provide protection against four different dengue virus stereotypes. The leading dengue virus vaccine candidates in clinical testing are all based on live-virus vaccine platforms and struggle to induce balanced immunity. Envelope subunit antigens have the potential to overcome these limitations but have historically performed poorly as vaccine antigens, because the versions tested previously were presented as monomers and not in their natural dimer configuration. This study shows that the authentic presentation of DENV2 E-based subunits has a strong impact on antibody responses, underscoring the importance of mimicking the complex protein structures that are found on DENV particle surfaces when designing subunit vaccines.

Development of biotinylated polyclonal anti-ribonucleoprotein IgG for detection of rabies virus antigen by direct rapid immunohistochemical test

The direct rapid immunohistochemical test (dRIT) has been recommended for laboratorial diagnosis of rabies, especially in developing countries. The absence of commercial primary antibodies, however, still represents a major limitation to its wider use in testing. We describe here the development of a biotinylated polyclonal antibody against Rabies lyssavirus (RABV) ribonucleoprotein (RNP) and its use as a primary reagent in dRIT. Anti-RNP polyclonal horse IgG was purified by ionic exchange chromatography followed by immunoaffinity column chromatography, and its affinity, diagnostic sensitivity, and specificity were evaluated. CNS samples (120) of suspected rabies cases in different animal species were tested by dRIT, with the positive (n = 14) and negative (n = 106) results confirmed by direct fluorescence antibody testing (dFAT). Comparing the results of dRIT and dFAT, we found that the biotinylated anti-RNP IgG delivered 100% diagnostic specificity and sensibility for rabies diagnosis. Our findings show that the biotinylated anti-RNP polyclonal IgG can be produced with the quality required for application in dRIT. This work represents an important step in efforts to diagnose rabies in developing countries.

Purification of IgG against ribonucleoprotein by a homemade immunoaffinity chromatography column for rabies diagnosis

Polyclonal or monoclonal antibodies against rabies virus ribonucleoprotein (RNP) conjugated to fluorescein isothiocyanate (FITC) have been employed for Rabies virus (RABV) antigen detection by the direct fluorescent antibody test (DFA). To date, these biomolecules have been purified by traditional methods such as precipitation by ammonium sulfate or ion exchange chromatography followed by ammonium sulfate precipitation, which allows only for partial detection of the protein of interest. In this study, we aimed to purify anti-RNP polyclonal horse IgG antibodies by cation-exchange chromatography in combination with a homemade immunoaffinity chromatography on RNP immobilized (RNP-IAC). Furthermore, to evaluate the accuracy of the prepared anti-RNP IgG fluorescent antibody in diagnostic purposes, DFA was applied for RABV antigen detection in suspected brain samples of different animal species. The combination of these two techniques made it possible to obtain antibodies with high selectivity and purity. Compared with the performance of the traditional method, anti-RNP IgG antibodies purified by RNP-IAC can be obtained from a smaller volume of hyperimmune serum and with greater avidity. Furthermore, the results obtained by DFA analyses revealed that the prepared anti-RNP IgG fluorescent antibody achieved 100% diagnostic specificity and sensitivity for RABV antigen detection. Thus, two-technique chromatographic, including RNP-IAC technology could be appropriate methods for the purification of polyclonal anti-RNP IgG for the use as a diagnostic reagent for rabies.

Dendritic Cell Targeting Using a DNA Vaccine Induces Specific Antibodies and CD4+ T Cells to the Dengue Virus Envelope Protein Domain III

Dengue fever has become a global threat, causing millions of infections every year. An effective vaccine against all four serotypes of dengue virus (DENV) has not been developed yet. Among the different vaccination strategies available today, DNA vaccines are safe and practical, but currently induce relatively weak immune responses in humans. In order to improve immunogenicity, antigens may be targeted to dendritic cells (DCs), the main antigen presenting cells and orchestrators of the adaptive immune response, inducing T and B cell activation. It was previously shown that a DNA vaccine encoding a fusion protein comprised of an antigen and a single-chain Fv antibody (scFv) specific for the DC endocytic receptor DEC205 induced strong immune responses to the targeted antigen. In this work, we evaluate this strategy to improve the immunogenicity of dengue virus (DENV) proteins. Plasmids encoding the scFv αDEC205, or an isotype control (scFv ISO), fused to the DENV2 envelope protein domain III (EDIII) were generated, and EDIII specific immune responses were evaluated in immunized mice. BALB/c mice were intramuscularly (i.m.) immunized three times with plasmid DNAs encoding either scDEC-EDIII or scISO-EDIII followed by electroporation. Analyses of the antibody responses indicated that EDIII fusion with scFv targeting the DEC205 receptor significantly enhanced serum anti-EDIII IgG titers that inhibited DENV2 infection. Similarly, mice immunized with the scDEC-EDIII plasmid developed a robust CD4⁺ T cell response to the targeted antigen, allowing the identification of two linear epitopes recognized by the BALB/c haplotype. Taken together, these results indicate that targeting DENV2 EDIII protein to DCs using a DNA vaccine encoding the scFv αDEC205 improves both antibody and CD4⁺ T cell responses. This strategy opens perspectives for the use of DNA vaccines that encode antigens targeted to DCs as a strategy to increase immunogenicity.

Nanoparticle delivery of a tetravalent E protein subunit vaccine induces balanced, type-specific neutralizing antibodies to each dengue virus serotype

Dengue virus (DENV) is the causative agent of dengue fever and dengue hemorrhagic shock syndrome. Dengue vaccine development is challenging because of the need to induce protection against four antigenically distinct DENV serotypes. Recent studies indicate that tetravalent DENV vaccines must induce balanced, serotype-specific neutralizing antibodies to achieve durable protective immunity against all 4 serotypes. With the leading live attenuated tetravalent DENV vaccines, it has been difficult to achieve balanced and type-specific responses to each serotype, most likely because of unbalanced replication of vaccine viral strains. Here we evaluate a tetravalent DENV protein subunit vaccine, based on recombinant envelope protein (rE) adsorbed to the surface of poly (lactic-co-glycolic acid) (PLGA) nanoparticles for immunogenicity in mice. In monovalent and tetravalent formulations, we show that particulate rE induced higher neutralizing antibody titers compared to the soluble rE antigen alone. Importantly, we show the trend that tetravalent rE adsorbed to nanoparticles stimulated a more balanced serotype specific antibody response to each DENV serotype compared to soluble antigens. Our results demonstrate that tetravalent DENV subunit vaccines displayed on nanoparticles have the potential to overcome unbalanced immunity observed for leading live-attenuated vaccine candidates.