Aggregation and antigenicity of virus like particle in salt solution—A case study with hepatitis B surface antigen

The role of asymmetric flow field-flow fractionation in drug development - From size separation to advanced characterization

Drug development is a complex multi-stage process that aims to deliver therapeutic products to the market. This process employs different analytical methods to separate and characterise compounds, monitor manufacturing, and validate the final drug products to ensure their safety, quality, and efficacy. However, advancements in modern drug development and discovery have led to new types of the therapeutical products of increasing complexity. As such, the capabilities of some traditional analytical techniques have become limited, and the demand for using advanced analytical techniques like field-flow fractionation (FFF) has been increasing. A special feature offered by the FFF family is a unique way of separation based on the analytes' specific physicochemical properties. As such, FFF is a powerful tool for analysing diverse analytes and complex mixtures. Herein, asymmetric flow field-flow fractionation (AF4) is the most frequently used technique within the FFF family in drug development. Therefore, this review aims to provide a general overview of the usage of AF4 technology in the drug development field.

Highly stable Saccharomyces cerevisiae L-BC capsids with versatile packing potential

Virus-like particles (VLPs) are promising nanoscaffolds in development of vaccines and nanodelivery systems. Along with efficient production in various expression systems, they also offer extensive functionalization options. Nevertheless, the ultimate integrity of VLPs is an important burden for the applicability in nanobiotechnology. In this study, we characterize the Saccharomyces cerevisiae L-BC VLPs synthesized and purified from Escherichia coli and Saccharomyces cerevisiae cells. The particles exhibited prominent size stability in buffers within a range of ionic strength conditions, pH environment and presence of magnesium ions during the long-term storage at temperatures up to 37°C. Bacteria-derived particles exhibited alleviated stability in acidic pH values, higher ionic strength and temperature compared to yeast-derived particles. Taking advantage of gene engineering, 120 copies of red fluorescent protein mCherry were successfully encapsulated into both preparations of L-BC VLPs, while passive diffusion enabled encapsulation of antimicrobial peptide nisin into the yeast-derived unmodified VLPs. Our findings indicate that L-BC VLPs generally exhibit high long-term stability under various conditions, while yeast-derived L-BC VLPs are more stable under the elevated temperatures than bacteria-derived particles. Stability studies and encapsulation of particles by different molecules involving alternative strategies delineate the L-BC VLP potential to be developed into versatile nanodelivery system.

Risedronate-functionalized manganese-hydroxyapatite amorphous particles: A potent adjuvant for subunit vaccines and cancer immunotherapy

The cGAS-STING pathway and the Mevalonate Pathway are druggable targets for vaccine adjuvant discovery. Manganese (Mn) and bisphosphonates are known to exert adjuvant effects by targeting these two pathways, respectively. This study found the synergistic potential of the two pathways in enhancing immune response. Risedronate (Ris) significantly amplified the Mn adjuvant early antibody response by 166-fold and fortified its cellular immunity. However, direct combination of Mn2+ and Ris resulted in increased adjuvant toxicity (40% mouse mortality). By the combination of doping property of hydroxyapatite (HA) and its high affinity for Ris, we designed Ris-functionalized Mn-HA micro-nanoparticles as an organic-inorganic hybrid adjuvant, named MnHARis. MnHARis alleviated adjuvant toxicity (100% vs. 60% survival rate) and exhibited good long-term stability. When formulated with the varicella-zoster virus glycoprotein E (gE) antigen, MnHARis triggered a 274.3-fold increase in IgG titers and a 61.3-fold surge in neutralization titers while maintaining a better long-term humoral immunity compared to the aluminum adjuvant. Its efficacy spanned other antigens, including ovalbumin, HPV18 VLP, and SARS-CoV-2 spike protein. Notably, the cellular immunity elicited by the group of gE + MnHARis was comparable to the renowned Shingrix®. Moreover, intratumoral co-administration with an anti-trophoblast cell surface antigen 2 nanobody revealed synergistic antitumor capabilities. These findings underscore the potential of MnHARis as a potent adjuvant for augmenting vaccine immune responses and improving cancer immunotherapy outcomes.

[Modulation of Aggregation and Immunogenicity of a Protein: Based on the Study of Hen Lysozyme]

This study focuses on the modulation of protein aggregation and immunogenicity. As a starting point for investigating long-range interactions within a non-native protein, the effects of perturbing denatured protein states on their aggregation, including the formation of amyloid fibrils, were evaluated. The effects of adducts, sugar modifications, and stabilization on protein aggregation were then examined. We also investigated how protein immunogenicity was affected by enhancing protein conformational stability and other factors.

Field-flow fractionation - an excellent tool for fractionation, isolation and/or purification of biomacromolecules

Field-flow fractionation (FFF) with its several variants, has developed into a mature methodology. The scope of the FFF investigations has expanded, covering both a wide range of basic studies and especially a wide range of analytical applications. Special attention of this review is given to the achievements of FFF with reference to recent applications in the fractionation, isolation, and purification of biomacromolecules, and from which especially those of (in alphabetical order) bacteria, cells, extracellular vesicles, liposomes, lipoproteins, nucleic acids, and viruses and virus-like particles. In evaluating the major approaches and trends demonstrated since 2012, the most significant biomacromolecule applications are compiled in tables. It is also evident that asymmetrical flow field-flow fractionation is by far the most dominant technique in the studies. The industry has also shown current interest in FFF and adopted it in some sophisticated fields. FFF, in combination with appropriate detectors, handles biomacromolecules in open channel in a gentle way due to the lack of shear forces and unwanted interactions caused by the stationary phase present in chromatography. In addition, in isolation and purification of biomacromolecules quite high yields can be achieved under optimal conditions.

Yeast-Based Virus-like Particles as an Emerging Platform for Vaccine Development and Delivery

Virus-like particles (VLPs) are empty, nanoscale structures morphologically resembling viruses. Internal cavity, noninfectious, and particulate nature with a high density of repeating epitopes, make them an ideal platform for vaccine development and drug delivery. Commercial use of Gardasil-9 and Cervarix showed the usefulness of VLPs in vaccine formulation. Further, chimeric VLPs allow the raising of an immune response against different immunogens and thereby can help reduce the generation of medical or clinical waste. The economically viable production of VLPs significantly impacts their usage, application, and availability. To this end, several hosts have been used and tested. The present review will discuss VLPs produced using different yeasts as fermentation hosts. We also compile a list of studies highlighting the expression and purification of VLPs using a yeast-based platform. We also discuss the advantages of using yeast to generate VLPs over other available systems. Further, the issues or limitations of yeasts for producing VLPs are also summarized. The review also compiles a list of yeast-derived VLP-based vaccines that are presently in public use or in different phases of clinical trials.

Particles in Biopharmaceutical Formulations, Part 2: An Update on Analytical Techniques and Applications for Therapeutic Proteins, Viruses, Vaccines and Cells

Particles in biopharmaceutical formulations remain a hot topic in drug product development. With new product classes emerging it is crucial to discriminate particulate active pharmaceutical ingredients from particulate impurities. Technical improvements, new analytical developments and emerging tools (e.g., machine learning tools) increase the amount of information generated for particles. For a proper interpretation and judgment of the generated data a thorough understanding of the measurement principle, suitable application fields and potential limitations and pitfalls is required. Our review provides a comprehensive overview of novel particle analysis techniques emerging in the last decade for particulate impurities in therapeutic protein formulations (protein-related, excipient-related and primary packaging material-related), as well as particulate biopharmaceutical formulations (virus particles, virus-like particles, lipid nanoparticles and cell-based medicinal products). In addition, we review the literature on applications, describe specific analytical approaches and illustrate advantages and drawbacks of currently available techniques for particulate biopharmaceutical formulations.

Inactivation of SARS-CoV-2 by β-propiolactone causes aggregation of viral particles and loss of antigenic potential

Inactivated viral preparations are important resources in vaccine and antisera industry. Of the many vaccines that are being developed against COVID-19, inactivated whole-virus vaccines are also considered effective. β-propiolactone (BPL) is a widely used chemical inactivator of several viruses. Here, we analyze various concentrations of BPL to effectively inactivate SARS-CoV-2 and their effects on the biochemical properties of the virion particles. BPL at 1:2000 (v/v) concentrations effectively inactivated SARS-CoV-2. However, higher BPL concentrations resulted in the loss of both protein content as well as the antigenic integrity of the structural proteins. Higher concentrations also caused substantial aggregation of the virion particles possibly resulting in insufficient inactivation, and a loss in antigenic potential. We also identify that the viral RNA content in the culture supernatants can be a direct indicator of their antigenic content. Our findings may have important implications in the vaccine and antisera industry during COVID-19 pandemic.

Impact of hydrological factors on the dynamic of COVID-19 epidemic: A multi-region study in China

Considering the live SARS-CoV-2 was detected and isolated from the excrement and urine of infected patients, the potential public health risk of its waterborne transmission should be paid broad and close attention. The purpose of the current study is to investigate the associations between COVID-19 incidences and hydrological factors such as lake area, river length, precipitation and volume of water resources in 30 regions of China. All confirmed cases for each areas were divided into two clusters including first cases cluster driven by imported cases during the period of January 20th to January 29th, 2020 and second cases cluster driven by local cases during the period of January 30th to March 1st, 2020. Based on the results of descriptive analysis and nonlinear regression analysis, positive associations with COVID-19 confirmed numbers were observed for migration scale index (MSI), river length, precipitation and volume of water resources, but negative associations for population density. The correlation coefficient in the second stage cases cluster is apparently higher than that in the first stage cases cluster. Then, the negative binomial-generalized linear model (NB-GLM) was fitted to estimate area-specific effects of hydrological variables on relative risk (RR) with the incorporation of additional variables (e.g., MSI) and the effects of exposure-lag-response. The statistically significant associations between RR and river length, the volume of water resources, precipitation were obtained by meta-analysis as 1.24 (95% CI: 1.22, 1.27), 2.56 (95% CI: 2.50, 2.61) and 1.59 (95% CI: 1.56, 1.62), respectively. The possible water transmission routes of SARS-CoV-2 and the potential capacity of long-distance transmission of SARS-CoV-2 in water environment was also discussed. Our results could provide a better guidance for local and global authorities to broaden the mind for understanding the natural-social system or intervening measures for COVID-19 control at the current or futural stage.

Cost-effective purification process development for chimeric hepatitis B core (HBc) virus-like particles assisted by molecular dynamic simulation

Inserting foreign epitopes to hepatitis B core (HBc) virus-like particles (VLPs) could influence the molecular conformation and therefore vary the purification process. In this study, a cost-effective purification process was developed for two chimeric HBc VLPs displaying Epstein-Barr nuclear antigens 1 (EBNA1), and hepatitis C virus (HCV) core. Both chimeric VLPs were expressed in soluble form with high production yields in Escherichia coli. Molecular dynamic (MD) simulation was employed to predict the stability of chimeric VLPs. HCV core-HBc was found to be less stable in water environment compared with EBNA1-HBc, indicating its higher hydrophobicity. Assisting with MD simulation, ammonium sulfate precipitation was optimized to remove host cell proteins with high target protein recovery yields. Moreover, 99% DNA impurities were removed using POROS 50 HQ chromatography. In characterization measurement, we found that inserting HCV core epitope would reduce the ratio of α-helix of HCV core-HBc. This could be another reason on the top of its higher hydrophobicity predicted by MD simulation, causing its less stability. Tertiary structure, transmission electron microscopy, and immunogenicity results indicate that two chimeric VLPs maintained correct VLP structure ensuring its bioactivity after being processed by the developed cost-effective purification approach.

Abolition of aggregation of CH2 domain of human IgG1 when combining glycosylation and protein stabilization

The CH₂ domain is a critical element of the human Immunoglobulin G (IgG) constant region. Although the CH₂ domain is the least stable domain in IgG, it is also a promising scaffold candidate for developing novel therapeutic approaches. Recently, we succeeded in preparing glycosylated and non-glycosylated CH₂ domain in the host organism Pichia pastoris. Herein, we verified that glycosylation of the CH₂ domain decreased both, its tendency to aggregate and its immunogenicity in mice, suggesting that aggregation and immunogenicity are related. In addition, we have produced in P. pastoris a stabilized version of the CH₂ domain with and without glycan, and their propensity to aggregate evaluated. We found that stabilization alone significantly decreased the aggregation of the CH₂ domain. Moreover, the combination of glycosylation and stabilization completely suppressed its aggregation behavior. Since protein aggregation is related to immunogenicity, the combination of glycosylation and stabilization to eliminate the aggregation behavior of a protein could be a fruitful strategy to generate promising immunoglobulin scaffolds.

Characterization and stabilization in process development and product formulation for super large proteinaceous particles

Super large proteinaceous particles (SLPPs) such as virus, virus like particles, and extracellular vesicles have successful and promising applications in vaccination, gene therapy, and cancer treatment. The unstable nature, the complex particulate structure and composition are challenges for their manufacturing and applications. Rational design of the processing should be built on the basis of fully understanding the characteristics of these bio-particles. This review highlights useful analytical techniques for characterization and stabilization of SLPPs in the process development and product formulations, including high performance size exclusion chromatography, multi-angle laser light scattering, asymmetrical flow field-flow fractionation, nanoparticle tracking analysis, CZE, differential scanning calorimetry, differential scanning fluorescence, isothermal titration calorimetry , and dual polarization interferometry. These advanced analytical techniques will be helpful in obtaining deep insight into the mechanism related to denaturation of SLPPs, and more importantly, in seeking solutions to preserve their biological functions against deactivation or denaturation. Combination of different physicochemical techniques, and correlation with in vitro or in vivo biological activity analyses, are considered to be the future trend of development in order to guarantee a high quality, safety, and efficacy of SLPPs.

Stability Studies of the Vaccine Adjuvant U-Omp19

Unlipidated outer membrane protein 19 (U-Omp19) is a novel mucosal adjuvant in preclinical development to be used in vaccine formulations. U-Omp19 holds two main properties, it is capable of inhibiting gastrointestinal and lysosomal peptidases, increasing the amount of co-administered antigen that reaches the immune inductive sites and its half-life inside cells, and it is able to stimulate antigen presenting cells in vivo. These activities enable U-Omp19 to enhance the adaptive immune response to co-administrated antigens.

To characterize the stability of U-Omp19 we have performed an extensive analysis of its physicochemical and biological properties in a 3-year long-term stability study, and under potentially damaging freeze-thawing and lyophilization stress processes. Results revealed that U-Omp19 retains its full protease inhibitor activity, its monomeric state and its secondary structure even when stored in solution for 36 months or after multiple freeze-thawing cycles. Non-enzymatic hydrolysis resulted the major degradation pathway for storage in solution at 4 °C or room temperature which can be abrogated by lyophilization yet increasing protein tendency to form aggregates.

This information will play a key role in the development of a stable formulation of U-Omp19, allowing an extended shelf-life during manufacturing, storage, and shipping of a future vaccine containing this pioneering adjuvant.

Self-assembly into virus-like particles of the recombinant capsid protein of porcine circovirus type 3 and its application on antibodies detection

PCV3 capsid protein (Cap) is an important antigen for diagnosis and vaccine development. To achieve high-level expression of recombinant PCV3 Cap in Escherichia coli (E. coli), the gene of wild-type entire Cap (wt-eCap) was amplified from clinical samples, and three optimized entire Cap (opti-eCap) and one optimized Cap deleted nuclear location signal (NLS) (opti-dCap) gene fragments encoding the same amino acid sequence with wt-eCap were synthesized based on the codon bias of E. coli. Those gene fragments were inserted into the pET30a expression vector. One recombinant strain with the highest expressed soluble eCap from four entire Cap (one wt-eCap and three opti-eCap) and one recombinant strain expressed opti-dCap were selected for further purification. The purified eCap and dCap were identified by transmission electron microscopy (TEM), a large number of round hollow particles with a diameter of 10 nm virus-like particles (VLPs) were observed in eCap, whereas irregular aggregation of proteins observed in dCap. After formation the VLPs were applied as a coating antigen to establish an indirect ELISA (I-ELISA) for detection of PCV3-specific antibody in swine serum. 373 clinical swine serum samples from China collected in 2019 were tested utilizing the VLP-based I-ELISA method under optimized conditions. To the best of our knowledge, this is the first report of self-assembly into VLPs of PCV3 recombinant Cap. Our results demonstrated that the VLP-based I-ELISA will be a valuable tool for detecting the presence of PCV3 antibodies in serum samples and will facilitate screening of large numbers of swine serum for clinical purposes.

A method to induce hen egg lysozyme-specific humoral immune tolerance in mice by pre-exposition with the protein's oligomers

During treatment with protein therapeutics, such as monoclonal antibodies, the development of anti-drug antibodies is a serious side-effect of modern pharmacology. Anti-drug antibodies are produced as the number and exposure to therapeutic proteins increase. In this context, less immunogenic responses could diminish these noxious effects. Biophysical characterization of antigens, that is size, chemical composition, physical form, and degrability, are known to influence the outcome of immune responses. Here, using chemical modification, we have prepared oligomers of hen egg lysozyme (HEL), 3- to 5-mer, as a typical antigen in immunology and evaluated the efficacy as a tolerogen in HEL-specific antibody responses. Our results clearly demonstrated that pre-exposed the HEL-oligomers into mice effectively suppressed HEL-specific IgG responses regardless of the cross-linking mode. Therefore, the oligomerization is a method to induce tolerogenicity of proteins and may emerge as a promising strategy to control the production of undesirable anti-protein drug antibodies.

Asymmetrical Flow Field-Flow Fractionation on Virus and Virus-Like Particle Applications

Asymmetrical flow field-flow fractionation (AF4) separates sample components based on their sizes in the absence of a stationary phase. It is well suited for high molecular weight samples such as virus-sized particles. The AF4 experiment can potentially separate molecules within a broad size range (~10³−10⁹ Da; particle diameter from 2 nm to 0.5−1 μm). When coupled to light scattering detectors, it enables rapid assays on the size, size distribution, degradation, and aggregation of the studied particle populations. Thus, it can be used to study the quality of purified viruses and virus-like particles. In addition to being an advanced analytical characterization technique, AF4 can be used in a semi-preparative mode. Here, we summarize and provide examples on the steps that need optimization for obtaining good separation with the focus on virus-sized particles.

Assessing virus like particles formation and r-HBsAg aggregation during large scale production of recombinant hepatitis B surface antigen from Pichia pastoris

The aggregation of recombinant proteins in the different stages of purification leads to the loss of a considerable portion of target protein and reduction in the process efficiency. As the active HBsAg used in Hepatitis B vaccine production is in the form of virus-like particle (VLP), therefore the time and stages at which the VLP assembling happened through the process would be important. The aim of this study was to explore the product aggregation during different stages of large scale production of rHBsAg in Pichia pastoris at production unit of the Pasteur Institute of Iran. Dynamic light scattering (DLS) and transmission electron microscopy (TEM), and also size exclusion-high-performance liquid chromatography (SE-HPLC) were carried out on samples taken from each downstream processes steps to determine the rate of VLPs formation as the desired product and the aggregated form at each stage of the purification. Based on the results, it was found that VLPs formation started at the acid precipitation stage and reached up to 80% at the thermal treatment stage. The ultrafiltration, ion exchange chromatography and immunoaffinity chromatography stages were disclosed to have the highest contribution in the formation of VLP (virus like particle) 22 nm.

Purification of flavivirus VLPs by a two-step chomatographic process

Flaviviruses are enveloped viruses with positive-sense, single-stranded RNA, which are most commonly transmitted by infected mosquitoes. Zika virus (ZIKV) and yellow fever virus (YFV) are flaviviruses that have caused significant outbreaks in the last few years. Since there is no approved vaccine against ZIKV, and since the existing YF attenuated vaccine presents disadvantages related to limited supply and to rare, but fatal adverse effects, there is an urgent need for new vaccines to control these diseases. Virus-like particles (VLPs) represent a recombinant platform to produce safe and immunogenic vaccines. Thus, based on our experience of expressing in recombinant mammalian cells VLPs of most flaviviruses circulating in the Americas, this work focused on the evaluation of chromatographic purification processes for zika and yellow-fever VLPs. The clarified cell culture supernatant was processed by a membrane-based anion-exchange chromatography and then a multimodal chromatographic step. With this process, it was possible to obtain the purified VLPs with a yield (including the clarification step) of 66.4% for zika and 68.1% for yellow fever. DNA clearance was in the range of 99.8-99.9%, providing VLP preparations that meet the WHO limit for this critical contaminant. Correct size and morphology of the purified VLPs were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The promising results obtained for both zika and yellow fever VLPs indicate that this process could be potentially applied also to VLPs of other flaviviruses.

3D visualisation of hepatitis B vaccine in the oral delivery vehicle SBA-15

Developing a technology that enables oral vaccines to work efficiently remains a considerable effort since a number of difficulties must be addressed. The key objective being to ensure the safe passage through the harsh conditions within the gastrointestinal tract, promoting delivery that induces enhanced immune response. In the particular case of hepatitis B, the oral formulation in the nanostructured silica SBA-15 is a viable approach. As a result of its porous structure, low toxicity and structural stability, SBA-15 is capable to protect and release the hepatitis B surface antigen (HBsAg), used in the vaccination scheme, at the desired destination. Furthermore, when compared to the currently used injection based delivery method, better or similar antibody response has been observed. However, information about the organisation of the antigen protein remains unknown. For instance, HBsAg is too large to enter the 10 nm ordered mesopores of SBA-15 and has a tendency to agglomerate when protected by the delivery system. Here we report on the pH dependence of HBsAg aggregation in saline solution investigated using small angle X-rays scattering that resulted in an optimisation of the encapsulation conditions. Additionally, X-ray microscopy combined with neutron and X-ray tomography provided full 3D information of the HBsAg clustering (i.e. agglomeration) inside the SBA-15 macropores. This method enables the visualisation of the organisation of the antigen in the interior of the delivery system, where agglomerated HBsAg coexists with its immunological effective uniformly distributed counterpart. This new approach, to be taken into account while preparing the formulation, can greatly help in the understanding of clinical studies and advance new formulations.

Mannitol-induced gold nanoparticle aggregation for the ligand-free detection of viral particles

Addition of osmolytes causes viruses-coated AuNPs to aggregate and not protein-coated AuNPs. Ligand-free detection of virus was developed without the need for prior knowledge of the specific virus target.

Efficient production of porcine circovirus virus-like particles using the nonconventional yeast Kluyveromyces marxianus

Porcine circovirus type 2 (PCV2) is a ubiquitous virus with high pathogenicity closely associated with the postweaning multisystemic wasting syndrome (PMWS) and porcine circovirus diseases (PCVDs), which caused significant economic losses in the swine industry worldwide every year. The PCV2 virus-like particles (VLPs) are a powerful subunit vaccine that can elicit high immune response due to its native PCV2 virus morphology. The baculovirus expression system is the widely used platform for producing commercial PCV2 VLP vaccines, but its yield and cost limited the development of low-cost vaccines for veterinary applications. Here, we applied a nonconventional yeast Kluyveromyces marxianus to enhance the production of PCV2 VLPs. After codon optimization, the PCV2 Cap protein was expressed in K. marxianus and assemble spontaneously into VLPs. Using a chemically defined medium, we achieved approximately 1.91 g/L of PCV2 VLP antigen in a 5-L bioreactor after high cell density fermentation for 72 h. That yield greatly exceeded to recently reported PCV2 VLPs obtained by baculovirus-insect cell, Escherichia coli and Pichia pastoris. By the means of two-step chromatography, 652.8 mg of PCV2 VLP antigen was obtained from 1 L of the recombinant K. marxianus cell culture. The PCV2 VLPs induced high level of anti-PCV2 IgG antibody in mice serums and decreased the virus titers in both livers and spleens of the challenged mice. These results illustrated that K. marxianus is a powerful yeast for cost-effective production of PCV2 VLP vaccines.

Halophilic viruses with varying biochemical and biophysical properties are amenable to purification with asymmetrical flow field-flow fractionation

Viruses come in various shapes and sizes, and a number of viruses originate from extremities, e.g. high salinity or elevated temperature. One challenge for studying extreme viruses is to find efficient purification conditions where viruses maintain their infectivity. Asymmetrical flow field-flow fractionation (AF4) is a gentle native chromatography-like technique for size-based separation. It does not have solid stationary phase and the mobile phase composition is readily adjustable according to the sample needs. Due to the high separation power of specimens up to 50 µm, AF4 is suitable for virus purification. Here, we applied AF4 for extremophilic viruses representing four morphotypes: lemon-shaped, tailed and tailless icosahedral, as well as pleomorphic enveloped. AF4 was applied to input samples of different purity: crude supernatants of infected cultures, polyethylene glycol-precipitated viruses and viruses purified by ultracentrifugation. All four virus morphotypes were successfully purified by AF4. AF4 purification of culture supernatants or polyethylene glycol-precipitated viruses yielded high recoveries, and the purities were comparable to those obtained by the multistep ultracentrifugation purification methods. In addition, we also demonstrate that AF4 is a rapid monitoring tool for virus production in slowly growing host cells living in extreme conditions.

Structural Characterization and Physicochemical Stability Profile of a Double Mutant Heat Labile Toxin Protein Based Adjuvant

A novel protein adjuvant double-mutant Escherichia coli heat-labile toxin, LT (R192G/L211A) or dmLT, is in preclinical and early clinical development with various vaccine candidates. Structural characterization and formulation development of dmLT will play a key role in its successful process development, scale-up/transfer, and commercial manufacturing. This work describes extensive analytical characterization of structural integrity and physicochemical stability profile of dmLT from a lyophilized clinical formulation. Reconstituted dmLT contained a heterogeneous mixture of intact holotoxin (AB₅, ∼75%) and free B₅ subunit (∼25%) as assessed by analytical ultracentrifugation and hydrophobic interaction chromatography. Intact mass spectrometry (MS) analysis revealed presence of Lys⁸⁴ glycation near the native sugar-binding site in dmLT, and forced degradation studies using liquid chromatography-MS peptide mapping demonstrated specific Asn deamidation and Met oxidation sites. Using multiple biophysical measurements, dmLT was found most stable between pH 6.5 and 7.5 and at temperatures ≤50°C. In addition, soluble aggregates and particle formation were observed upon shaking stress. By identifying the physicochemical degradation pathways of dmLT using newly developed stability-indicating analytical methods from this study, we aim at developing more stable candidate formulations of dmLT that will minimize the formation of degradants and improve storage stability, as both a frozen bulk substance and eventually as a liquid final dosage form.

Viral Aggregation: Impact on Virus Behavior in the Environment

Aggregates of viruses can have a significant impact on quantification and behavior of viruses in the environment. Viral aggregates may be formed in numerous ways. Viruses may form crystal like structures and aggregates in the host cell during replication or may form due to changes in environmental conditions after virus particles are released from the host cells. Aggregates tend to form near the isoelectric point of the virus, under the influence of certain salts and salt concentrations in solution, cationic polymers, and suspended organic matter. The given conditions under which aggregates form in the environment are highly dependent on the type of virus, type of salts in solution (cation, anion. monovalent, divalent) and pH. However, virus type greatly influences the conditions when aggregation/disaggregation will occur, making predictions difficult under any given set of water quality conditions. Most studies have shown that viral aggregates increase the survival of viruses in the environment and resistance to disinfectants, especially with more reactive disinfectants. The presence of viral aggregates may also result in overestimation of removal by filtration processes. Virus aggregation-disaggregation is a complex process and predicting the behavior of any individual virus is difficult under a given set of environmental circumstances without actual experimental data.

Challenges and opportunities of using liquid chromatography and mass spectrometry methods to develop complex vaccine antigens as pharmaceutical dosage forms

Liquid chromatographic methods, combined with mass spectrometry, offer exciting and important opportunities to better characterize complex vaccine antigens including recombinant proteins, virus-like particles, inactivated viruses, polysaccharides, and protein-polysaccharide conjugates. The current abilities and limitations of these physicochemical methods to complement traditional in vitro and in vivo vaccine potency assays are explored in this review through the use of illustrative case studies. Various applications of these state-of-the art techniques are illustrated that include the analysis of influenza vaccines (inactivated whole virus and recombinant hemagglutinin), virus-like particle vaccines (human papillomavirus and hepatitis B), and polysaccharide linked to protein carrier vaccines (pneumococcal). Examples of utilizing these analytical methods to characterize vaccine antigens in the presence of adjuvants, which are often included to boost immune responses as part of the final vaccine dosage form, are also presented. Some of the challenges of using chromatographic and LC-MS as physicochemical assays to routinely test complex vaccine antigens are also discussed.

Biochemical and biophysical characterization of maize-derived HBsAg for the development of an oral vaccine

Although a vaccine against hepatitis B virus (HBV) has been available since 1982, it is estimated that 600,000 people die every year due to HBV. An affordable oral vaccine could help alleviate the disease burden and to this end the hepatitis B surface antigen (HBsAg) was expressed in maize. Orally delivered maize material induced the strongest immune response in mice when lipid was extracted by CO2 supercritical fluid extraction (SFE), compared to full fat and hexane-extracted material. The present study provides a biochemical and biophysical basis for these immunological differences by comparing the active ingredient in the differently treated maize material. Purified maize-derived HBsAg underwent biophysical characterization by gel filtration, transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-CD, and fluorescence. Gel filtration showed that HBsAg forms higher-order oligomers and TEM demonstrated virus-like particle (VLP) formation. The VLPs obtained from SFE were more regular in shape and size compared to hexane or full fat material. In addition, SFE-derived HBsAg showed the greatest extent of α-helical structure by far UV-CD spectrum. Fluorescence experiments also revealed differences in protein conformation. This work establishes SFE-treated maize material as a viable oral vaccine candidate and advances the development of the first oral subunit vaccine.