Overexpression of hepatitis B virus surface antigens including the preS1 region in a serum-free Chinese hamster ovary cell line

Integration of size-exclusion chromatography and ultracentrifugation for purification of recombinant hepatitis B surface antigen: An alternative method for immunoaffinity chromatography

In purification process of recombinant hepatitis B surface antigen (rHBsAg), immunoaffinity chromatography (IAF) is one of the most important and effective steps in rHBsAg purification. However, the buffer composition and the interaction of ligands-rHBsAg often lead to disassembly, deformation, and clumping of a portion of these virus-like particles (VLPs). Besides, the expensive media, variable biospecific ligand density and the possibility of product contamination are other reported drawbacks of using IAF which makes the production process of rHBsAg more challenging. This study investigated the possibility of substituting IAF with purification methods of size-exclusion chromatography (SEC) and ultracentrifugation. In the SEC, the efficacy of rHBsAg purification was examined by four different media in which Toyopearl HW 65S resin demonstrated the best results. By integrating Toyopearl HW 65S resin - with a bed height of 51 cm - and ultracentrifugation process at 47,000 rpm for 48 hr, 95% of protein impurities were removed. Compared to the IAF in rHBsAg production, the purified sample contained a higher percentage of multimeric rHBsAg particles without any noticeable monomer and aggregate forms. The result of this study indicates that the proposed integrated system could be an efficient mild purification alternative for conventional IAF.

Production of virus-like particles for vaccines

Virus-like particles (VLPs) are nanostructures that resemble the structures of viruses. They are composed of one or more structural proteins that can be arranged in several layers and can also contain a lipid outer envelope. VLPs trigger a high humoral and cellular immune response due to their repetitive structures. A key factor regarding VLP safety is the lack of viral genomic material, which enhances safety during both manufacture and administration. Contemporary VLP production may take advantage of several systems, including bacterial, yeast, insect and mammalian cells. The choice of production platform depends on several factors, including cost and the need for post-translational modifications (PTMs), which can be essential in generating an optimal immune response. Some VLP-based vaccines designed to prevent several infectious diseases are already approved and on the market, with many others at the clinical trial or research stage. Interest in this technology has recently increased due to its advantages over classical vaccines. This paper reviews the state-of-the-art of VLP production systems and the newest generation of VLP-based vaccines now available.

Virus-like particles in vaccine development

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome, potentially yielding safer and cheaper vaccine candidates. A handful of prophylactic VLP-based vaccines is currently commercialized worldwide: GlaxoSmithKline's Engerix (hepatitis B virus) and Cervarix (human papillomavirus), and Merck and Co., Inc.'s Recombivax HB (hepatitis B virus) and Gardasil (human papillomavirus) are some examples. Other VLP-based vaccine candidates are in clinical trials or undergoing preclinical evaluation, such as, influenza virus, parvovirus, Norwalk and various chimeric VLPs. Many others are still restricted to small-scale fundamental research, despite their success in preclinical tests. This article focuses on the essential role of VLP technology in new-generation vaccines against prevalent and emergent diseases. The implications of large-scale VLP production are discussed in the context of process control, monitorization and optimization. The main up- and down-stream technical challenges are identified and discussed accordingly. Successful VLP-based vaccine blockbusters are briefly presented concomitantly with the latest results from clinical trials and the recent developments in chimeric VLP-based technology for either therapeutic or prophylactic vaccination.

A highly efficient integrated chromatographic procedure for the purification of recombinant hepatitis B surface antigen from Hansenula polymorpha

The high expression level of recombinant hepatitis B surface antigen obtained from Hansenula polymorpha yeast cell (Hans-HBsAg) made it possible to produce HBsAg vaccine in a large scale and by cost-effective process. However, the present available purification process was somewhat tedious, time-consuming and difficult to scale up. To improve the purification efficiency and simplify the purification process, an integrated chromatographic process was developed and optimized. The downstream process included ion-exchange chromatography (IEC), hydrophobic interaction chromatography (HIC) and gel filtration chromatography (GFC). A series of chromatographic adsorbents were evaluated for their performances on the purification of Hans-HBsAg, and then the suitable adsorbents for IEC and HIC were screened out, respectively. After clarification by centrifugation, the supernatant of cell disruption (SCD) was purified by standard chromatographic steps, IEC on DEAE Sepharose FF, HIC on Butyl-S-QZT and GFC on Sepharose 4FF. Furthermore, HBsAg recovery, purification factor (PF) and purity during the downstream process were evaluated with enzyme-linked immunosorption assay (ELISA), sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and high-performance size-exclusion chromatography (HPSEC). The results demonstrated that in the scale of 550ml SCD, the total HBsAg recovery and PF of the whole procedure were about 21.0+/-0.9% and 80.7+/-8.4 (n=3) respectively, with the purity of above 99%. This new downstream process was efficient, reproducible and relatively easy to be scaled up.

Expression of hepatitis B surface antigen major subtypes in Pichia pastoris and purification for in vitro diagnosis

This study describes the expression in Pichia pastoris of hepatitis B surface antigens (HBsAg) corresponding to the S region of the four major subtypes: adr, adw2, ayr and ayw3 and to the preS2-S region of the two subtypes adr and adw2. The recombinant yeast strains have been selected amongst methanol utilization positive (Mut+) or sensitive strains (Mut s) and cultivated to high cell density in bioreactor using a short protocol. Our results prove the efficiency of P. pastoris to produce all the major HBsAg subtypes and confirm the ability of the methanol regulated promoter of alcohol oxidase I gene (AOX) to express heterologous protein through phenotype Mut+ or Mut s strains. All these recombinant HBsAg proteins, including subtype ayr, whose production has never been presented, have been highly purified using a short original sequence of steps which includes high-pressure cell disruption associated with detergent treatment, ultrafiltration and immunopurification chromatography using a mAb anti-HBs. The whole process avoids possible alterations of antigenic properties and allows to obtain with high yield, high quality reagents for in vitro diagnosis.

A novel RNA silencing vector to improve antigen expression and stability in Chinese hamster ovary cells

Chinese hamster ovary (CHO) cells and dihydrofolate reductase (dhfr)/methotrexate (MTX) gene amplification system are routinely used to generate stable producer CHO cell clones in biopharmaceutical industries. The present study proposes a novel method by the co-amplification of the silencing vector targeted to dhfr gene for improvements of selecting high-producing clones in dhfr-deficient and wild-type CHO cells. Using the silencing vector also resulted in improving the stability of the recombinant protein expression in the absence of MTX in the CHO/dhFr(-) and wild-type CHO cells. This new method is proposed to generate highly expressed stable cell clones of both dhfr-deficient and wild-type CHO cells for recombinant antigen production. Utilization of the silencing vector designed in this study can improve antigen expression through dhfr-directed gene amplification in other dhfr-competent cell lines for vaccine development.

Expression, purification and characterization of the Hepatitis B virus entire envelope large protein in Pichia pastoris

The current HBsAg vaccine has performed a vital role in preventing the transmission of HBV during the past 20 years. However, a number of individuals still show no response or a low response to the vaccine. In the present study, the HBV envelope large protein gene was cloned into the eukaryotic expression vector pPIC9k and was subsequently expressed in the yeast Pichia pastoris. The HBV large protein (L protein) was produced and secreted into the medium, where some of the L protein formed particles. The soluble L protein and particles were purified by column chromatography and sucrose density gradient centrifugation. Western blot analysis demonstrated that the particle was composed of both HBV L and S protein. To compare the antigenicity of the L protein and HBsAg, rabbits were immunized with the soluble L protein and the commercially available HBV vaccine and the increasing level of antibodies was determined by ELISA. The results showed that the anti-HBsAg antibody, from rabbits injected with the L protein at a dose of 2 and 10microg, was detected on day 14, whereas rabbits vaccinated with 10 and 2microg HBsAg did not develop antibodies until day 21 and 28, respectively. The antibody level in groups inoculated with the L protein was approximately 50% higher than in the group injected with HBsAg using the same dose. Furthermore, 2microg L protein induced a significant and rapid anti-HBsAg antibody response than 10microg HBsAg. Therefore, we suggest that the L protein is an ideal candidate for a new generation HB vaccine to protect people from HBV infection.

Secretory production system of bionanocapsules using a stably transfected insect cell line

Bionanocapsules (BNCs) are hollow nanoscale particles composed of L protein of the hepatitis B virus surface antigen that represent specific affinity for human hepatocytes. BNCs can transfer genes and drugs into human hepatocytes efficiently and specifically. BNC can be expressed in yeast cells. In this study, we developed a new L particle production system using a stably transfected insect cell line. For this purpose, we established a host-vector system using the Trichoplusia ni insect cell line. L particles were efficiently secreted by the overexpression of the L protein, which was fused to the secretion signal peptide. The concentration of L particles was reached approximately 1.7 microg/ml in 5 days during cultivation in a serum-free medium without antibiotic selective pressure. The production of L particles was maintained for at least 75 days. The secretory production of L particles facilitated their easy purification by chromatography. Furthermore, it was demonstrated that purified L particles can transfect only human hepatocytes. Therefore, an insect cell expression system is an attractive tool for the production of BNC.

Ion-exchange chromatography of hepatitis B virus surface antigen from a recombinant Chinese hamster ovary cell line

About 10% of the Chinese population are chronic carriers of hepatitis B virus (HBV). Thus, the development of a highly efficient process for the preparation of a vaccine based on a recombinant hepatitis B surface antigen (HBsAg) is very important to the Chinese national immunization program. To this end, the ion exchange chromatography recovery of CHO-HBsAg from a recombinant Chinese hamster ovary cell line was shown to increase from about 55 to 80% by the addition of 1% poly(ethylene glycol) (PEG 10,000) to the mobile phase. Furthermore, based on analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), the intact glycoprotein form of CHO-HBsAg was completely preserved by the addition of PEG. In the absence of PEG the glycoprotein form of CHO-HBsAg was also spread out into the high salt elution fraction. High-performance size-exclusion chromatography with on-line multiangle-laser-light scattering (HPSEC-MALLS) analysis was performed to monitor the status of the CHO-HBsAg aggregate structure assembly, particle size and molecular weight distribution after each purification step, and the results showed further that the presence of PEG facilitated the separation and recovery of intact glycoprotein form of CHO-HBsAg and promoted their assembly to proper virus-like particles, which are both important features and prerequisites of their immunogenicity.

Identification of the immunogenic domains in HBsAg preS1 region using overlapping preS1 fragment fusion proteins

AIM: The incorporation of hepatitis B virus (HBV) preS1 region into epitope-based vaccines against HBV has been accepted widely, but the incorporate site and size of preS1 sequence is controversial. Therefore our purpose was to further investigate its immunogenic domains for the epitope-based hepatitis B vaccine design.

METHODS: Eight GST fusion proteins containing overlapping preS1 fragments in preS1 (21-119) region were expressed in E.coli. Using these purified fusion proteins, the immunogenic domains in preS1 region were identified in detail in mice and humans by Western blot analysis and ELISA.

RESULTS: The results in mice showed that the immu-nogenic domains mainly existed in preS1 (21-59) and preS1 (95-109). Similarly, these fragments had strong immunogenicity in humans; whereas the other parts except for preS1 (60-70) also had some immunogenicity. More importantly, a major immunogenic domain, preS1 (34-59), which has much stronger immunogenicity, was identified. Additionally, the antibodies against some preS1 fragments, especially preS1 (34-59), were speculated to be virus-neutralizing.

CONCLUSION: Eight GST fusion proteins containing overlapping preS1 fragments were prepared successfully. They were used for the study on the immunogenic dom-ains in preS1 (21-119) region. The preS1 (34-59) fragm-ents were the major immunogenic domains in the preS1 region, and the antibodies against these fragments were speculated to be virus-neutralizing. Therefore, the incorporation of preS1 (34-59) fragments into epitope-based HBV vaccines may be efficient for enhancement of immune response. Additionally, the results also imply that there are more complex immune responses to preS1 region and more abundant immunogenic domains in humans.

The comparison of antibody response to different hepatitis b vaccines with and without pre-S2 antigen in children with cancer

Children with cancer are at an increased risk of hepatitis B infection and chronic liver disease. Since hepatitis B vaccines containing pre-S2 antigen has been recently reported as being more efficient in providing immunization in healthy individuals, the authors compared antibody response to pre-S2-containing vaccine with no-pre-S2-containing hepatitis B vaccine, when given in double doses to 100 children receiving chemotherapy. Patients, aged 1 to 16 years with negative HBV serology, were vaccinated with 2 different types of HBV vaccines between 1997 and 1999. Group 1 received Gen Hevac B containing pre-S2 (n = 41) in a dose of 20 microg for patients younger than 10 years old and 40 microg for older patients. Group 2 was vaccinated at the same dose with hepatitis B vaccines not containing pre-S2 antigen. All vaccinations were repeated at 0, 1, and 6 months. Serum samples were drawn for determination of anti-HBs titers at 1, 3, 6, and 8 months. After the third dose of vaccine, the seroconversion rate was 72% in group 1 and 62% in group 2. The anti-HBs levels were higher in the group receiving pre-S2-containing hepatitis B vaccine. However, the difference between groups was not statistically significant (p > .05). The administration of pre-S2-containing hepatitis B vaccines may give a better seroconversion and higher antibody response to vaccination in children with cancer. But a further large-scale study is needed to confirm this finding.