Yield Optimisation of Hepatitis B Virus Core Particles in E. coli Expression System for Drug Delivery Applications

Synthesis of the full-length hepatitis B virus core protein and its capsid formation

Chronic infection with hepatitis B virus (HBV) is a major cause of cirrhosis and liver cancer. Capsid assembly modulators can induce error-prone assembly of HBV core proteins to prevent the formation of infectious virions, representing promising candidates for treating chronic HBV infections. To explore novel capsid assembly modulators from unexplored mirror-image libraries of natural products, we have investigated the synthetic process of the HBV core protein for preparing the mirror-image target protein. In this report, the chemical synthesis of full-length HBV core protein (Cp183) containing an arginine-rich nucleic acid-binding domain at the C-terminus is presented. Sequential ligations using four peptide segments enabled the synthesis of Cp183 via convergent and C-to-N direction approaches. After refolding under appropriate conditions, followed by the addition of nucleic acid, the synthetic Cp183 assembled into capsid-like particles.

Cross-Reactivity of HBe Antigen-Specific Polyclonal Antibody with HBc Antigen

Hepatitis B virus (HBV) infection is a major health problem worldwide and causes almost one million deaths annually. The HBV core gene codes for two related antigens, known as core antigen (HBcAg) and e-antigen (HBeAg), sharing 149 residues but having different amino- and carboxy-terminals. HBeAg is a soluble variant of HBcAg and a clinical marker for determining the disease severity and patients' screening. Currently available HBeAg assays have a shortcoming of showing cross-reactivity with HBcAg. In this study, for the first time, we evaluated whether HBcAg-adsorbed anti-HBe polyclonal antibodies could specifically recognize HBeAg or still show cross-reactivity with HBcAg. Recombinant HBeAg was cloned in pCold1 vector and successfully expressed in Escherichia coli and after purification by Ni-NTA resin was used to generate polyclonal anti-HBe antibodies in rabbit. Purified HBeAg was further characterized by assessing its reactivity with anti-HBe in the sera of chronically infected patients and HBeAg-immunized rabbit. Sera from patients with chronic HBV infection, containing anti-HBe, specifically reacted with recombinant HBeAg, implying antigenic similarity between the prokaryotic and native HBeAg in the serum of HBV-infected patients. In addition, the designed enzyme-linked immunosorbent assay (ELISA) with rabbit anti-HBe polyclonal antibodies could detect recombinant HBeAg with high sensitivity, while high cross-reactivity with HBcAg was observed. It is noteworthy that HBcAg-adsorbed anti-HBe polyclonal antibodies still showed high cross-reactivity with HBcAg, implying that due to the presence of highly similar epitopes in both antigens, HBcAg-adsorbed polyclonal antibodies cannot differentiate between the two antigens.

Size-selective downstream processing of virus particles and non-enveloped virus-like particles

Non-enveloped virus-like particles (VLPs) are versatile protein nanoparticles with great potential for biopharmaceutical applications. However, conventional protein downstream processing (DSP) and platform processes are often not easily applicable due to the large size of VLPs and virus particles (VPs) in general. The application of size-selective separation techniques offers to exploit the size difference between VPs and common host-cell impurities. Moreover, size-selective separation techniques offer the potential for wide applicability across different VPs. In this work, basic principles and applications of size-selective separation techniques are reviewed to highlight their potential in DSP of VPs. Finally, specific DSP steps for non-enveloped VLPs and their subunits are reviewed as well as the potential applications and benefits of size-selective separation techniques are shown.

Chimeric Hepatitis B core virus-like particles harboring SARS-CoV2 epitope elicit a humoral immune response in mice

BACKGROUND

Virus-like particles are an interesting vector platform for vaccine development. Particularly, Hepatitis B virus core antigen has been used as a promising VLP platform. It is highly expressed in different recombinant expression systems, such as E. coli, and self-assembled in vitro. It effectively improves the immunogenicity of foreign antigenic epitopes on its surface. Various foreign antigens from bacteria, viruses, and protozoa can be genetically inserted into such nanoparticles. The effective immunogenicity due to VLP vaccines has been reported. However, no research has been performed on the SARS-CoV2 vaccine within this unique platform through genetic engineering. Considering the high yield of target proteins, low cost of production, and feasibility of scaling up, E. coli is an outstanding expression platform to develop such vaccines. Therefore, in this investigation, we planned to study and develop a unique HBc VLP-based vaccine against SARS-Cov2 utilizing the E. coli expression system due to its importance.

RESULTS

Insertion of the selected epitope was done into the major immunodominant region (MIR) of truncated (149 residues) hepatitis B core capsid protein. The chimeric protein was constructed in PET28a⁺ and expressed through the bacterial E. coli BL21 expression system. However, the protein was expressed in inclusion body forms and extracted following urea denaturation from the insoluble phase. Following the extraction, the vaccine protein was purified using Ni2 + iminodiacetic acid (IDA) affinity chromatography. SDS-PAGE and western blotting were used to confirm the protein expression. Regarding the denaturation step, the unavoidable refolding process was carried out, so that the chimeric VLP reassembled in native conformation. Based on the transmission electron microscopy (TEM) analysis, the HBC VLP was successfully assembled. Confirming the assembled chimeric VLP, we explored the immunogenic effectivity of the vaccine through mice immunization with two-dose vaccination with and without adjuvant. The utilization of adjuvant was suggested to assess the effect of adjuvant on improving the immune elicitation of chimeric VLP-based vaccine. Immunization analysis based on anti-spike specific IgG antibody showed a significant increase in antibody production in harvested serum from immunized mice with HBc-VLP harboring antigenic epitope compared to HBc-VLP- and PBS-injected mice.

CONCLUSIONS

The results approved the successful production and the effectiveness of the vaccine in terms of humoral IgG antibody production. Therefore, this platform can be considered a promising strategy for developing safe and reasonable vaccines; however, more complementary immunological evaluations are needed.

Rapid screening and scaled manufacture of immunogenic virus-like particles in a tobacco BY-2 cell-free protein synthesis system

Several vaccine platforms have been developed to fight pathogenic threats, with Virus-Like Particles (VLPs) representing a very promising alternative to traditional platforms. VLPs trigger strong and lasting humoral and cellular immune responses with fewer safety concerns and higher stability than other platforms. The use of extensively characterized carrier VLPs modified with heterologous antigens was proposed to circumvent the viral complexity of specific viruses that could lead to poor VLP assembly and yields. Although carrier VLPs have been successfully produced in a wide variety of cell-based systems, these are limited by low protein yields and protracted clone selection and optimization workflows that limit VLP screening approaches. In response, we have demonstrated the cell-free protein synthesis (CFPS) of several variants of the hepatitis B core (HBc) carrier VLP using a high-yielding tobacco BY-2 lysate (BYL). High VLP yields in the BYL system allowed in-depth characterization of HBc variants. Insertion of heterologous sequences at the spike region of the HBc monomer proved more structurally demanding than at the N-terminus but removal of the C-terminal domain allowed higher particle flexibility and insert acceptance, albeit at the expense of thermal and chemical stability. We also proved the possibility to scale the CFPS reaction up to 1L in batch mode to produce 0.45 grams of the native HBc VLP within a 48-hour reaction window. A maximum yield of 820 µg/ml of assembled VLP particles was observed at the 100µl scale and most remarkably the CFPS reaction was successfully scaled from 50µl to 1L without any reduction in protein yield across this 20,000-fold difference in reaction volumes. We subsequently proved the immunogenicity of BYL-derived VLPs, as flow cytometry and microscopy clearly showed prompt recognition and endocytosis of fluorescently labelled VLPs by human dendritic cells. Triggering of inflammatory cytokine production in human peripheral blood mononuclear cells was also quantitated using a multiplex assay. This research establishes BYL as a tool for rapid production and microscale screening of VLP variants with subsequent manufacturing possibilities across scales, thus accelerating discovery and implementation of new vaccine candidates using carrier VLPs.

Effects of Different Lengths of a Nucleic Acid Binding Region and Bound Nucleic Acids on the Phase Behavior and Purification Process of HBcAg Virus-Like Particles

Virus-like particles (VLPs) are macromolecular structures with great potential as vehicles for the targeted administration of functional molecules. Loaded with nucleic acids, VLPs are a promising approach for nanocarriers needed for gene therapy. There is broad knowledge of the manufacturing of the truncated wild-type lacking a nucleic acid binding region, which is mainly being investigated for vaccine applications. Whereas for their potential application as a nanocarrier for gene therapy, hepatitis B core antigen (HBcAg) VLPs with a nucleic acid binding region for efficient cargo-loading are being investigated. VLP structure, loading, and phase behavior are of central importance to their therapeutic efficacy and thereby considerably affecting the production process. Therefore, HBcAg VLPs with different lengths of the nucleic acid binding region were produced in E. coli. VLP attributes such as size, zeta potential, and loading with host cell-derived nucleic acids were evaluated. Capsid’s size and zeta potential of the VLP constructs did not differ remarkably, whereas the analysis of the loading with host cell-derived nucleic acids revealed strong differences in the binding of host cell-derived nucleic acids dependent on the length of the binding region of the constructs, with a non-linear correlation but a two-zone behavior. Moreover, the phase behavior and purification process of the HBcAg VLPs as a function of the liquid phase conditions and the presence of host cell-derived nucleic acids were investigated. Selective VLP precipitation using ammonium sulfate was scarcely affected by the encapsulated nucleic acids. However, the disassembly reaction, which is crucial for structure homogeneity, separation of encapsulated impurities, and effective loading of the VLPs with therapeutic nucleic acids, was affected both by the studied liquid phase conditions, varying pH and concentration of reducing agents, and the different VLP constructs and amount of bound nucleic acids, respectively. Thereby, capsid-stabilizing effects of the bound nucleic acids and capsid-destabilizing effects of the nucleic acid binding region were observed, following the two-zone behavior of the construct’s loading, and a resulting correlation between the capsid stability and disassembly yields could be derived.

Bioengineering of virus-like particles as dynamic nanocarriers for in vivo delivery and targeting to solid tumours

Virus-like particles (VLPs) are known as self-assembled, non-replicative and non-infectious protein particles, which imitate the formation and structure of original wild type viruses, however, lack the viral genome and/or their fragments. The capacity of VLPs to encompass small molecules like nucleic acids and others has made them as novel vessels of nanocarriers for drug delivery applications. In addition, VLPs surface have the capacity to achieve variation of the surface display via several modification strategies including genetic modification, chemical modification, and non-covalent modification. Among the VLPs nanocarriers, Hepatitis B virus core (HBc) particles have been the most encouraging candidate. HBc particles are hollow nanoparticles in the range of 30-34 nm in diameter and 7 nm thick envelopes, consisting of 180 or 240 copies of identical polypeptide monomer. They also employ a distinctive position among the VLPs carriers due to the high-level synthesis, which serves as a strong protective capsid shell and efficient self-assembly properties. This review highlights on the bioengineering of HBc particles as dynamic nanocarriers for in vivo delivery and specific targeting to solid tumours.

Process development for cross-flow diafiltration-based VLP disassembly: A novel high-throughput screening approach

Virus-like particles (VLPs) are particulate structures, which are applied as vaccines or delivery vehicles. VLPs assemble from subunits, named capsomeres, composed of recombinantly expressed viral structural proteins. During downstream processing, in vivo-assembled VLPs are typically dis- and reassembled to remove encapsulated impurities and to improve particle morphology. Disassembly is achieved in a high-pH solution and by the addition of a denaturant or reducing agent. The optimal disassembly conditions depend on the VLP amino acid sequence and structure, thus requiring material-consuming disassembly experiments. To this end, we developed a low-volume and high-resolution disassembly screening that provides time-resolved insight into the VLP disassembly progress. In this study, two variants of C-terminally truncated hepatitis B core antigen were investigated showing different disassembly behaviors. For both VLPs, the best capsomere yield was achieved at moderately high urea concentration and pH. Nonetheless, their disassembly behaviors differed particularly with respect to disassembly rate and aggregation. Based on the high-throughput screening results, a diafiltration-based disassembly process step was developed. Compared with mixing-based disassembly, it resulted in higher yields of up to 0.84 and allowed for integrated purification. This process step was embedded in a filtration-based process sequence of disassembly, capsomere separation, and reassembly, considerably reducing high-molecular-weight species.

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.

In Vitro Assembly of Virus-Like Particles and Their Applications

Virus-like particles (VLPs) are increasingly used for vaccine development and drug delivery. Assembly of VLPs from purified monomers in a chemically defined reaction is advantageous compared to in vivo assembly, because it avoids encapsidation of host-derived components and enables loading with added cargoes. This review provides an overview of ex cella VLP production methods focusing on capsid protein production, factors that impact the in vitro assembly, and approaches to characterize in vitro VLPs. The uses of in vitro produced VLPs as vaccines and for therapeutic delivery are also reported.

In vitro preparation of uniform and nucleic acid free hepatitis B core particles through an optimized disassembly-purification-reassembly process

Structure heterogeneity and host nucleic acids contamination are two major problems for virus-like particles (VLPs) produced by various host cells. In this study, an in vitro optimized disassembly-purification-reassembly process was developed to obtain uniform and nucleic acid free hepatitis B core (HBc) based VLPs from E. coli fermentation. The process started with ammonium sulfate precipitation of all heterogeneous HBc structures after cell disintegration. Then, dissolution and disassembly of pellets into basic subunits were carried out under the optimized disassembly condition. All contaminants, including host nucleic acids and proteins, were efficiently removed with affinity chromatography. The purified subunits reassembled into VLPs by final removal of the chaotropic agent. Two uniform and nucleic acid free HBc-based VLPs, truncated HBc₁₄₉ and chimeric HBc₁₈₃-MAGE3 I, were successfully prepared. It was found that disassembly degree of HBc-based VLPs had a great influence on the protein yield, nucleic acid removal and reassembly efficiency. 4 M urea was optimal because lower concentration would not disassemble the particles completely while higher concentration would further denature the subunits into disordered aggregate and could not be purified and reassembled efficiently. For removal of strong binding nucleic acids such as in the case of HBc₁₈₃-MAGE3 I, benzonase nuclease was added to the disassembly buffer before affinity purification. Through the optimized downstream process, uniform and nucleic acid free HBc₁₄₉ VLPs and HBc₁₈₃-MAGE3 I VLPs were obtained with purities above 90% and yields of 55.2 and 43.0 mg/L, respectively. This study would be a reference for efficient preparation of other VLPs.

Human Serum Albumin in the Presence of AGuIX Nanoagents: Structure Stabilisation without Direct Interaction

The gadolinium-based nanoagent named AGuIX^® is a unique radiosensitizer and contrast agent which improves the performance of radiotherapy and medical imaging. Currently tested in clinical trials, AGuIX^® is administrated to patients via intravenous injection. The presence of nanoparticles in the blood stream may induce harmful effects due to undesired interactions with blood components. Thus, there is an emerging need to understand the impact of these nanoagents when meeting blood proteins. In this work, the influence of nanoagents on the structure and stability of the most abundant blood protein, human serum albumin, is presented. Synchrotron radiation circular dichroism showed that AGuIX^® does not bind to the protein, even at the high ratio of 45 nanoparticles per protein at 3 mg/L. However, it increases the stability of the albumin. Isothermal thermodynamic calorimetry and fluorescence emission spectroscopy demonstrated that the effect is due to preferential hydration processes. Thus, this study confirms that intravenous injection of AGuIX^® presents limited risks of perturbing the blood stream. In a wider view, the methodology developed in this work may be applied to rapidly evaluate the impact and risk of other nano-products that could come into contact with the bloodstream.

Theranostic Quercetin Nanoparticle for Treatment of Hepatic Fibrosis

The progression of hepatic fibrosis can lead to cirrhosis and hepatic failure, but the development of antifibrotic drugs have faced the challenges of poor effectiveness and targeted specificity. Herein, a theranostic strategy was carried to encapsulate a natural medicine (Quercetin, QR) into hepatitis B core (HBc) protein nanocages (NCs) for imaging and targeted treatment of hepatic fibrosis. It was noted that nanoparticles (RGD-HBc/QR) with surface-displayed RGD targeting ligand exhibit a rather high selectivity toward activated HSCs via the binding affinity with integrin α_vβ₃, and an efficient inhibition of proliferation and activation of hepatic stellate cells (HSCs) in vitro and in vivo. Once encapsulated in quercetin-gadolinium complex and/or labeled with the NIR fluorescent probes (Cy5.5), the resulting nanoparticles (RGD-HBc/QGd) show great potential as NIR fluorescent and magnetic resonance imaging contrast agents for hepatic fibrosis in vivo. Therefore, the multifunctional integrin-targeted nanoparticles could selectively deliver QR to the activated HSCs, and may provide an effective antifibrotic theranostic strategy.

Immunogenicity of a Virus-Like-Particle Vaccine Containing Multiple Antigenic Epitopes of Toxoplasma gondii Against Acute and Chronic Toxoplasmosis in Mice

There is no effective protective vaccine against human toxoplasmosis, which is a potential threat to nearly a third of the world population. Vaccines based on virus-like particles (VLPs) have been highly successful in humans for many years, but have rarely been applied against Toxoplasma gondii infection. In this study, we inserted a B cell epitope (SAG1₈₂₋₁₀₂ or SAG1_301−320), a CD8⁺ cell epitope (HF10 or ROP7), and a CD4⁺ cell epitope (AS15) of T. gondii into a truncated HBc_Δ(amino acids1–149) particle to construct four chimeric VLP vaccine formulations, i.e., HBc_ΔH82, HBc_ΔH301, HBc_{Δ R82}, and HBc_{Δ R301}. When these chimeric HBc particles were expressed in Escherichia coli, they showed icosahedral morphology similar to that of the original VLPs and were evaluated as vaccine formulations against acute and chronic toxoplasmosis in a mouse model (BALB/c mice (H-2^d). All these chimeric HBc VLPs induced strong humoral and cellular immune responses with high IgG antibody titers and interferon(IFN)-γ production. Only the mice immunized with HBc_ΔH82 showed prolonged survival time (15.6 ± 3.8 vs. 5.6 ± 0.8 days) against acute infection with RH tachyzoites and decrease in brain parasite load (1,454 ± 239 vs. 2,091 ± 263) against chronic infection with Prugniuad cysts, as compared to the findings for the control group. These findings suggest that HBc VLPs would act as an effective carrier for delivering effective multiple antigenic epitopes and would be beneficial for developing a safe and long-acting vaccine against toxoplasmosis.

Miranda B, Lodoso-Torrecilla I, van Nisselroy CAJ, Hoogenberg BJ, Dantuma S, Hollmann F, de Vries JW, Warszawik EM, Fischer R, Commandeur U, van Rijn P. Biocatalytically induced surface modification of the tobacco mosaic virus and the bacteriophage M13

A one-step laccase induced free radical oxidation of the tobacco mosaic virus and bacteriophage M13 led to acrylate-functionalized viruses with customizable properties.