G. B. Sunil Kumar

Production of Hepatitis B Surface Antigen in Recombinant Plant Systems: An Update

There is a growing interest to develop oral vaccines for infectious diseases, as it is the most convenient and effective way to attain mucosal immunity. Hepatitis B continues to be a major infectious disease in many developing countries despite the availability of recombinant vaccine. On a global scenario, Hepatitis B Virus infection is probably the single most prevalent cause of persistent viraemia in humans. There are about 350 million chronic carriers of HBV, which is about 5% of the total world population. It is estimated that 75–100 million of them will die of liver cirrhosis and/or hepatocellular carcinoma. Progress in plant genetic engineering has enabled the transfer of useful genes for desirable traits. The recent trend is to use this technique to exploit plants as biofactories for the production of therapeutic proteins including vaccines. Rapid progress has been made in this area to develop plant‐based vaccines for hepatitis B. This review describes the expression, characterization, and immunogenicity studies of hepatitis B vaccines produced in recombinant plant systems and their implications for developing a plant‐based vaccine.

Secretion of hepatitis B surface antigen in transformed tobacco cell suspension cultures.

Six different expression cassettes of hepatitis B surface antigen (HBsAg) were used to transform tobacco cell suspension cultures. The transgenic nature of the cells was confirmed by PCR. The secreted HBsAg was assayed by ELISA and analyzed by Western blotting. A maximum of 31 μg antigen/l was obtained in the spent medium from the transformed cells. The use of an ethylene-forming enzyme promoter and incorporation of C-terminal endoplasmic-reticulum-retention signal enhanced the secretion of HBsAg. Salicylic or jasmonic acid at 10 μM increased secretion of HBsAg by six fold.

Plant Molecular Farming: Host Systems, Technology and Products

Plants have been used for various medicines by mankind over centuries and one quarter of prescription drugs are still of plant origin. The advances made in genomics and proteomics resulted in the isolation of several useful genes. These have been expressed in various expression systems including plants. The plant based production of pharmaceutically and industrially useful recombinant proteins is referred as molecular farming. Plants have been successfully genetically engineered using different methods. Stable nuclear transformation by Agrobacterium or biolistic methods, plastid engineering, use of viral based transient expression, agroinfiltration and magnifection techniques. In this review, an overview of plant molecular farming, host systems employed, vaccinogen production in plants with an emphasis on hepatitis B vaccine, technology perspective as well as the commercialized products are described

Hepatitis B surface antigen expression in NT-1 cells of tobacco using different expression cassettes

Nicotiana tabacum 1 (NT-1) cells were transformed with four different expression cassettes of hepatitis B surface antigen (HBsAg). The transformed nature of the cells was confirmed by polymerase chain reaction (PCR). The expression levels were assayed by enzyme linked immunosorbent assay (ELISA). The expressivities varied among the different cassettes and the maximum expression of 16.6 ng g−1(f.m.) of cells was noted in pEFEHER transformed cells. Salicylic acid (100 µM) treatment resulted in 1.8 fold increase of expression in pEFEHBS transformed cells. The effect of different concentrations of kanamycin and geneticin was studied on the growth of transformed cells and HBsAg expression. The cell growth was optimum at lower concentrations of the antibiotics, and the maximum expression was noted at 200 mg dm−3 of kanamycin.