Production and Purification of Filovirus Glycoproteins in Insect and Mammalian Cell Lines

Broad antibody and T cell responses to Ebola, Sudan, and Bundibugyo ebolaviruses using mono- and multi-valent adjuvanted glycoprotein vaccines

Currently, there are two approved vaccine regimens designed to prevent Ebola virus (EBOV) disease (EVD). Both are virus-vectored, and concerns about cold-chain storage and pre-existing immunity to the vectors warrant investigating additional vaccine strategies. Here, we have explored the utility of adjuvanted recombinant glycoproteins (GPs) from ebolaviruses Zaire (EBOV), Sudan (SUDV), and Bundibugyo (BDBV) for inducing antibody (Ab) and T cell cross-reactivity. Glycoproteins expressed in insect cells were administered to C57BL/6 mice as free protein or bound to the surface of liposomes, and formulated with toll-like receptor agonists CpG and MPLA (agonists for TLR 9 and 4, respectively), with or without the emulsions AddaVax or TiterMax. The magnitude of Ab cross-reactivity in binding and neutralization assays, and T cell cross-reactivity in antigen recall assays, correlated with phylogenetic relatedness. While most adjuvants screened induced IgG responses, a combination of CpG, MPLA and AddaVax emulsion ("IVAX-1") was the most potent and polarized in an IgG2c (Th1) direction. Breadth was also achieved by combining GPs into a trivalent (Tri-GP) cocktail with IVAX-1, which did not compromise antibody responses to individual components in binding and neutralizing assays. Th1 signature cytokines in T cell recall assays were undetectable after Tri-GP/IVAX-1 administration, despite a robust IgG2c response, although administration of Tri-GP on lipid nanoparticles in IVAX-1 elevated Th1 cytokines to detectable levels. Overall, the data indicate an adjuvanted trivalent recombinant GP approach may represent a path toward a broadly reactive, deployable vaccine against EVD.

Recombinant SpTransformer proteins are functionally diverse for binding and phagocytosis by three subtypes of sea urchin phagocytes

Introduction

The California purple sea urchin, Strongylocentrotus purpuratus, relies solely on an innate immune system to combat the many pathogens in the marine environment. One aspect of their molecular defenses is the SpTransformer (SpTrf) gene family that is upregulated in response to immune challenge. The gene sequences are highly variable both within and among animals and likely encode thousands of SpTrf isoforms within the sea urchin population. The native SpTrf proteins bind foreign targets and augment phagocytosis of a marine Vibrio. A recombinant (r)SpTrf-E1-Ec protein produced by E. coli also binds Vibrio but does not augment phagocytosis.

Methods

To address the question of whether other rSpTrf isoforms function as opsonins and augment phagocytosis, six rSpTrf proteins were expressed in insect cells.

Results

The rSpTrf proteins are larger than expected, are glycosylated, and one dimerized irreversibly. Each rSpTrf protein cross-linked to inert magnetic beads (rSpTrf::beads) results in different levels of surface binding and phagocytosis by phagocytes. Initial analysis shows that significantly more rSpTrf::beads associate with cells compared to control BSA::beads. Binding specificity was verified by pre-incubating the rSpTrf::beads with antibodies, which reduces the association with phagocytes. The different rSpTrf::beads show significant differences for cell surface binding and phagocytosis by phagocytes. Furthermore, there are differences among the three distinct types of phagocytes that show specific vs. constitutive binding and phagocytosis.

Conclusion

These findings illustrate the complexity and effectiveness of the sea urchin innate immune system driven by the natSpTrf proteins and the phagocyte cell populations that act to neutralize a wide range of foreign pathogens.

Considerations for Glycoprotein Production

This chapter is intended to provide insights for researchers aiming to choose an appropriate expression system for the production of recombinant glycoproteins. Producing glycoproteins is complex, as glycosylation patterns are determined by the availability and abundance of specific enzymes rather than a direct genetic blueprint. Furthermore, the cell systems often employed for protein production are evolutionarily distinct, leading to significantly different glycosylation when utilized for glycoprotein production. The selection of an appropriate production system depends on the intended applications and desired characteristics of the protein. Whether the goal is to produce glycoproteins mimicking native conditions or to intentionally alter glycan structures for specific purposes, such as enhancing immunogenicity in vaccines, understanding glycosylation present in the different systems and in different growth conditions is essential. This chapter will cover Escherichia coli, baculovirus/insect cell systems, Pichia pastoris, as well as different mammalian cell culture systems including Chinese hamster ovary (CHO) cells, human endothelial kidney (HEK) cell lines, and baby hamster kidney (BHK) cells.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Immunoinformatic screening of Marburgvirus epitopes and computational investigations of epitope-allele complexes

Marburgvirus (MARV), a member of the Filovirus family, causes severe hemorrhagic fever in humans. Currently, there are no approved vaccines or post exposure treatment methods available against MARV. With the aim of identifying vaccine candidates against MARV, we employ different sequence-based computational methods to predict the MHC-I and MHC-II T-cell epitopes as well as B-cell epitopes for the complete MARV genome. We analyzed the variations in the predicted epitopes among four MARV variants, the Lake Victoria, Angola, Musoke, and Ravn. We used a consensus approach to identify several epitopes, including novel epitopes, and narrowed down the selection based on different parameters such as antigenicity and IC₅₀ values. The selected epitopes can be used in various vaccine constructs that give effective antibody responses. The MHC-I epitope-allele complexes for GP and NP with favorably low IC₅₀ values were investigated using molecular dynamics computations to determine the molecular details of the epitope-allele complexes. This study provides information for further experimental validation of the potential epitopes and the design and development of MARV vaccines.

IgY antibodies against Ebola virus possess post-exposure protection in a murine pseudovirus challenge model and excellent thermostability

Ebola virus (EBOV) is one of the most virulent pathogens that causes hemorrhagic fever and displays high mortality rates and low prognosis rates in both humans and nonhuman primates. The post-exposure antibody therapies to prevent EBOV infection are considered effective as of yet. However, owing to the poor thermal stability of mammalian antibodies, their application in the tropics has remained limited. Therefore, a thermostable therapeutic antibody against EBOV was developed modelled on the poultry(chicken) immunoglobulin Y (IgY). The IgY antibodies retaining their neutralising activity at 25°C for one year, displayed excellent thermal stability, opposed to conventional polyclonal antibodies (pAbs) or monoclonal antibodies (mAbs). Laying hens were immunised with a variety of EBOV vaccine candidates and it was confirmed that VSVΔG/EBOVGP encoding the EBOV glycoprotein could induce high titer neutralising antibodies against EBOV. The therapeutic efficacy of immune IgY antibodies in vivo was evaluated in the newborn Balb/c mice who have been challenged with the VSVΔG/EBOVGP model. Mice that have been challenged with a lethal dose of the pseudovirus were treated 2 or 24 h post-infection with different doses of anti-EBOV IgY. The group receiving a high dose of 10⁶ NAU/kg (neutralising antibody units/kilogram) showed complete protection with no symptoms of a disease, while the low-dose group was only partially protected. Conversely, all mice receiving naive IgY died within 10 days. In conclusion, the anti-EBOV IgY exhibits excellent thermostability and protective efficacy. Anti-EBOV IgY shows a lot of promise in entering the realm of efficient Ebola virus treatment regimens.

Despite the amount of efficient Ebola virus therapeutic antibodies reported in recent years, their application in tropical endemic areas has remained limited due to the low thermal stability of mammalian antibodies. A highly thermostable therapeutic polyclonal antibody against EBOV was developed based on chicken immunoglobulin Y (IgY). The EBOV specific IgY antibodies displayed excellent thermal stability, retaining their neutralising activity at 25°C for one year. The newborn mice receiving the passive transfer of IgY achieved complete protection against a lethal dose of virus challenge proving that the anti-EBOV IgY provides a promising recourse to solve some of the current clinical application hindrances of Ebola antibody-based treatments in Africa due to thermal stability.

Mosaic Bovine Viral Diarrhea Virus Antigens Elicit Cross-Protective Immunity in Calves

Bovine Viral Diarrhea Virus (BVDV) is an important pathogen that plays a significant role in initiating Bovine Respiratory Disease Complex (BRDC) in cattle. The disease causes multi-billion dollar losses globally due to high calf mortality and increased morbidity leading to heavy use of antibiotics. Current commercial vaccines provide limited cross-protection with several drawbacks such as safety, immunosuppression, potential reversion to virulence, and induction of neonatal pancytopenia. This study evaluates two prototype vaccines containing multiple rationally designed recombinant mosaic BVDV antigens for their potential to confer cross-protection against diverse BVDV strains. Genes encoding three novel mosaic antigens, designated E2¹²³, NS2-3¹, and NS2-3², were designed in silico and expressed in mammalian cells for the formulation of a prototype protein-based vaccine. The mosaic antigens contain highly conserved protective epitopes from BVDV-1a, -1b, and -2, and included unique neutralizing epitopes from disparate strains to broaden coverage. We tested immunogenicity and protective efficacy of Expi293^TM-expressed mosaic antigens (293F-E2¹²³, 293F-NS2-3¹, and 293F-NS2-3²), and baculovirus-expressed E2¹²³ (Bac-E2¹²³) mosaic antigen in calves. The Expi293^TM-expressed antigen cocktail induced robust BVDV-specific cross-reactive IFN-γ responses, broadly neutralizing antibodies, and following challenge with a BVDV-1b strain, the calves had significantly (p < 0.05) reduced viremia and clinical BVD disease compared to the calves vaccinated with a commercial killed vaccine. The Bac-E2¹²³ antigen was not as effective as the Expi293^TM-expressed antigen cocktail, but it protected calves from BVD disease better than the commercial killed vaccine. The findings support feasibility for development of a broadly protective subunit BVDV vaccine for safe and effective management of BRD.

The expanding role of mass spectrometry in the field of vaccine development

Biological mass spectrometry has evolved as a core analytical technology in the last decade mainly because of its unparalleled ability to perform qualitative as well as quantitative profiling of enormously complex biological samples with high mass accuracy, sensitivity, selectivity and specificity. Mass spectrometry-based techniques are also routinely used to assess glycosylation and other post-translational modifications, disulfide bond linkage, and scrambling as well as for the detection of host cell protein contaminants in the field of biopharmaceuticals. The role of mass spectrometry in vaccine development has been very limited but is now expanding as the landscape of global vaccine development is shifting towards the development of recombinant vaccines. In this review, the role of mass spectrometry in vaccine development is presented, some of the ongoing efforts to develop vaccines for diseases with global unmet medical need are discussed and the regulatory challenges of implementing mass spectrometry techniques in a quality control laboratory setting are highlighted.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.

Generation of therapeutic antisera for emerging viral infections

The recent Ebola virus outbreak has highlighted the therapeutic potential of antisera and renewed interest in this treatment approach. While human convalescent sera may not be readily available in the early stages of an outbreak, antisera of animal origin can be produced in a short time frame. Here, we compared adjuvanted virus-like particles (VLP) with recombinant modified vaccinia virus Ankara and vesicular stomatitis virus (VSV), both expressing the Ebola virus antigens. The neutralizing antibody titers of rabbits immunized with adjuvanted VLPs were similar to those immunized with the replication-competent VSV, indicating that presentation of the antigen in its native conformation rather than de novo antigen expression is essential for production of functional antibodies. This approach also yielded high-titer antisera against Nipah virus glycoproteins, illustrating that it is transferable to other virus families. Multiple-step immunoglobulin G purification using a two-step 20–40% ammonium sulfate precipitation followed by protein A affinity chromatography resulted in 90% recovery of functionality and sustained in vivo stability. Adjuvanted VLP-based immunization strategies are thus a promising approach for the rapid generation of therapeutic antisera against emerging infections.

Passive immunity through the transfer of anti-serum represents the earliest clinical application of antibodies and is still widely used to this day in the form of anti-venoms. Veronika von Messling and colleagues at the Paul Ehrlich Institute investigate the potential of generating neutralizing anti-serum to the emerging viruses Ebola and Nipah. The authors compare different vaccination platforms in mice and rabbits and find that following multiple vaccine challenges, neutralizing antibody titers equivalent to that seen in convalescent patients could be obtained. Purification of the IgG fraction and processing into F(ab’)₂ fragments has the potential to significantly reduce xeno-responses yet the authors find that neutralizing capacity is largely retained albeit at the cost of a shorter in vivo half-life. These findings offer the hope of rapidly generating large quantities of neutralizing anti-serum that could be used in a viral outbreak scenario.

Immunogenicity of a Candidate Ebola Hemorrhagic Fever Vaccine in Mice Based on Controlled In Vitro Expression of Ebolavirus Glycoprotein

Ebolavirus (EBOV) is the etiology of Ebola hemorrhagic fever (EHF). A major EHF outbreak in 2014-2015 in West Africa claimed >11,000 lives. A licensed vaccine is not available for EHF, although several vaccines have undergone clinical trials. We developed a human adenovirus (Ad) serotype 5-based candidate EHF vaccine based on controlled expression of the EBOV (Makona strain) glycoprotein (GP) as the immunogen. Two clones, AdGP72 and AdGP75, and a control Ad515 vector, were generated and tested for protein expression in vitro and immunogenicity in mice. Eight groups of mice were immunized with three doses of buffer, Ad515, AdGP72, and AdGP75, by two different dose regimens. Three different antigens (AdGP75-infected Vero E6 cell extract and two baculovirus expressed EBOV GP antigens, namely, GP alone or GP with EBOV VP40) were used to evaluate the immune response. Expression studies indicated that full-length GP was cleaved into its component subunits when expressed in mammalian cells through the Ad vectors. Moreover, in coimmunoprecipitation studies, EBOV GP was found to be associated with VP40 when expressed in baculoviruses. The candidate vaccines were immunogenic in mice, as evaluated by enzyme-linked immunosorbent assay using mammalian- or baculovirus-derived antigens. Further characterization and development of the candidate vaccines are warranted.