Expression of hepatitis B surface antigen in tobacco cell suspension cultures

Tobacco-Based Vaccines, Hopes, and Concerns: A Systematic Review

Emerging infectious diseases have vigorously devastated the global economy and health sector; cost-effective plant-based vaccines (PBV) can be the potential solution to withstand the current health economic crisis. The prominent role of tobacco as an efficient expression system for PBV has been well-established for decades, through this review we highlight the importance of tobacco-based vaccines (TBV) against evolving infectious diseases in humans. Studies focusing on the use of TBV for human infectious diseases were searched in PubMed, Google Scholar, and science direct from 1995 to 2021 using the keywords Tobacco-based vaccines OR transgenic tobacco OR Nicotiana benthamiana vaccines AND Infectious diseases or communicable diseases. We carried out a critical review of the articles and studies that fulfilled the eligibility criteria and were included in this review. Of 976 studies identified, only 63 studies fulfilling the eligibility criteria were included, which focused on either the in vitro, in vivo, or clinical studies on TBV for human infectious diseases. Around 43 in vitro studies of 23 different infectious pathogens expressed in tobacco-based systems were identified and 23 in vivo analysis studies were recognized to check the immunogenicity of vaccine candidates while only 10 of these were subjected to clinical trials. Viral infectious pathogens were studied more than bacterial pathogens. From our review, it was evident that TBV can be an effective health strategy to combat the emerging viral infectious diseases which are very difficult to manage with the current health facilities. The timely administration of cost-effective TBV can prevent the outburst of viral infections, thereby can protect the global healthcare system to a greater extent.

Current Strategies to Improve Yield of Recombinant Protein Production in Rice Suspension Cells

A plant cell-based recombinant glucocerebrosidase was approved by the FDA in 2012 for the treatment of human inherited Gaucher disease, indicating that plant suspension cells have advantages in biosafety and a low production cost as a commercial pharmaceutical recombinant protein expression system. A low allergenic rice suspension cell-based recombinant protein expression system controlled by the αAmy3/RAmy3D promoter has been shown to result in relatively high protein yields in plant cell-based systems. Although several recombinant proteins have been produced in rice suspension cell-based systems, yields must be improved to compete with the current commercial protein expression systems. Different strategies were performed and showed successful improvements in recombinant protein yields in this rice system. The review updates and highlights strategies for potential improvements of the αAmy3-based rice suspension cell-based system.

Isolation, cloning and transgenic expression of hepatitis B surface antigen (HBsAg) in Solanum lycopersicum L

The Hepatitis B virus (HBV) infection is one of the most widespread viral infections of humans. HBV causes acute and chronic hepatitis. Chronic hepatitis leads to hepatocellular carcinoma, which is a significant cause of death. DNA-based immunization programs to control the spread of Hepatitis B in developing countries are costly and require special storage and transportation. The alternative way is to express Hepatitis B surface antigen (HBsAg) in plants to develop oral vaccines. In this study, HBsAg gene was isolated, cloned, and then transformed in tomato plants. The transgenic tomato plants were confirmed through RT-qPCR. HBsAg expression was analysed in mature green and red stages of tomato fruit through quantitative real-time PCR. It was observed that expression of HBsAg was high in matured red tomato as compared to mature green. The present study is the first step to developing Solanum lycopersicum as an edible vaccine production system in this world region.

Gold nanoparticle biosensors, a novel application in gene transformation and expression

The conventional techniques of PCR, Southern blot, northern blot, in situ hybridization, and RNase protection assay have long been used to investigate transformation and expression of genes, but most of them are time-consuming and have relatively low sensitivity. In recent years, applying biosensors for molecular identification of biomolecules has been expanding significantly. Hence in this study, Zabol melon was used as a model plant to introduce new DNA and RNA-based biosensors for confirming gene transformation and expression. First, the melon seeds were grown in vivo and Agrobacterium tumefaciens LBA4404 was used to introduce GUS reporter gene to the plant. In order to analyze GUS gene transformation and expression, probes were designed based on DNA, RNA, and cDNA of GUS gene sequence. Then, the analysis was performed using probes attached to gold nanoparticles to observe color change of the solution in presence of the target biomolecules. Hybridization of the probes with target molecules was evaluated at a wavelength of 400-700 nm and maximum change was observed in the wavelength range of 550-650 nm. In addition, lower detection limit of the assay was 0.25 ng/μL and linear regression showed the relationship between different concentrations of the genomic DNA and absorbance. Consequently, results showed that application of detectors attached to gold nanoparticles for investigation on gene transformation and expression is more rapid, specific and economic compared to the biochemical and molecular techniques. These tests can be carried out with initial optimization at research centers using the least facilities; hence there will be no need for special equipment.

Simultaneous Expression of GUS and Actin Genes by Using the Multiplex RT-PCR and Multiplex Gold Nanoparticle Probes

Gene expression analysis is considered to be extremely important in many different biological researches. DNA-based diagnostic test, which contributes to DNA identification, has higher specificity, cost, and speed than some biochemical and molecular methods. In this study, we try to use the novel nano technology approach with Multiplex RT-PCR and Gold nano particular probes (GNPs-probes) in order to get gene expression in Curcumas melons. We used Agrobacterium tumefactions for gene transfer and GUS reporter gene as a reporter. After cDNA synthesis, Multiplex PCR and Multiplex RT-PCR techniques were used. Finally, probes were designed for RNA of GUS and Actin genes, and then the analysis of the gene expression using the probes attached to GNPs was carried out and the color changes in the GNPs were applied. In the following, probes hybridization was checked with DNA between 400 to 700 nm wavelengths and the highest rate was observed in the 550 to 650 nm. The results show that the simultaneous use of GNP-attached detectors and Multiplex RT-PCRcan reduce time and costmore considerably than somelaboratory methods for gene expiration investigation. Additionally, it can be seen thatthere is an increase in sensitivity and specificity of our investigation. Based on our findings, this can bea novel study doneusingMultiplex RT-PCRand unmodified AuNPs for gene transfer and expression detection to plants. We can claim that this assay has a remarkable advantage including rapid, cost-effectiveness, specificity and accuracy to detect transfer and expression genes in plants. Also,we can use this technique from other gene expressionsin many different biology samples.

New perspectives on dietary-derived treatments and food safety-antinomy in a new era

Despite the advances in science and technology and wide use of chemical drugs, dietary intervention (or food therapy) remains useful in preventing or treating many human diseases. A huge body of evidence shows that the dietary pattern or habit is also an important contributing factor to the development of chronic diseases such as hypertension, type 2 diabetes, hyperlipidemia, and cancers. In recent years, over-the-counter health foods, nutraceuticals, and plant-derived medicinal products have been gaining popularity all over the world, particularly in developed countries. Unfortunately, owing to the contamination with various harmful substances in foods and the presence of toxic food components, food-borne diseases have also become increasingly problematic. Incidents of food poisonings or tainted food have been increasing worldwide, particularly in China and other developing countries. Therefore, the government should put in a greater effort in enforcing food safety by improving the surveillance mechanism and exerting highest standards of quality control for foods.

Immunodiagnostic Properties of Wucheraria bancrofti SXP-1, a Potential Filarial Diagnostic Candidate Expressed in Tobacco Plant, Nicotiana tabacum

Transgenic tobacco plants were developed expressing WbSXP-1, a diagnostic antigen isolated from the cDNA library of L3 stage larvae of Wucheraria bancrofti. This antigen produced by recombinant Escherichia coli has been demonstrated by to be successful as potential diagnostic candidate against lymphatic filariasis. A rapid format simple and qualitative flow through immune-filtration diagnostic kit has been developed for the identification of IgG antibodies to the recombinant WbSXP-1 and is being marketed by M/S Span Diagnostics Ltd in India and Africa. Here, we present the results of experiments on the transformation and expression of the same filarial antigen, WbSXP-1, in tobacco plant, Nicotiana tabacum, to produce plant-based diagnostic antigen. It was possible to successfully transform the tobacco plant with WbSXP-1, the integration of the parasite-specific gene in plants was confirmed by PCR amplification and the expression of the filarial protein by Western blotting. The immunoreactivity of the plant-produced WbSXP-1 was assessed based on its reaction with the monoclonal antibodies developed against the E. coli-produced protein. Immunological screening using clinical sera from patients indicates that the plant-produced protein is comparable to E. coli-produced diagnostic antigen. The result demonstrated that plants can be used as suitable expression systems for the production of diagnostic proteins against lymphatic filariasis, a neglected tropical infectious disease which has a negative impact on socioeconomic development. This is the first report of the integration, expression and efficacy of a diagnostic candidate of lymphatic filariasis in plants.Key MessageTransgenic tobacco plants with WbSXP-1, a filarial diagnostic candidate, were developed. The plant-produced protein showed immunoreactivity on par with the E. coli product.

Plant–derived vaccines: a look back at the highlights and a view to the challenges on the road ahead

The sobering reality is that each year, 33 million children remain unvaccinated for vaccine-preventable diseases. Universal childhood vaccination would have profound effects on leveling the health inequities in many parts of the world. As an alternative to administration of vaccines by needle and syringe, oral vaccines offer significant logistical advantages, as the polio eradication campaign has demonstrated. Over the past decade, the expression of subunit vaccine antigens in plants has emerged as a convenient, safe and potentially economical platform technology, with the potential to provide a novel biotechnological solution to vaccine production and delivery. As this technology has come of age, many improvements have been made on several fronts, as a growing number of research groups worldwide have extensively investigated plants as factories for vaccine production. This review attempts to highlight some of the achievements over the past 15 years, identify some of the potential problems and discuss the promises that this technology could fulfill.

Immunogenicity of Brugia malayi Abundant Larval Transcript-2, a potential filarial vaccine candidate expressed in tobacco

KEY MESSAGE

Transgenic tobacco plants with Bm ALT-2, a filarial vaccine candidate, were developed. The plant-produced antigen showed immunogenicity on par with the E.coli product. Transgenic tobacco plants were developed using Brugia malayi Abundant Larval Transcript-2 (Bm ALT-2), a major antigen produced from recombinant E.coli found to be experimentally successful as potential vaccine candidate against lymphatic filariasis. Results of experiments on the transformation and expression of the Bm ALT-2 in tobacco plant to produce plant-based vaccine are presented here. We have successfully transformed the tobacco plant with Bm ALT-2 and confirmed that the plants expressed the filarial protein by PCR analysis and Western blotting. The level of expression varied from 50 to 90 ng/μg of total soluble protein for ALT-2. Immunization of mice with plant-extracted protein indicated that the plant-produced protein had immunological characteristics similar to the E.coli-produced protein. Antibody titres produced by plant-produced recombinant ALT 2-immunized mice were on par with those immunized with recombinant protein produced by E.coli. Antibody isotype assay showed that plant-produced recombinant ALT-2 induced significant IgG1, whereas E.coli-produced recombinant ALT-2 induced IgG3. This result is a step forward towards the development of a model eukaryotic system for the production of recombinant filarial proteins, which can be utilized to produce therapeutic and diagnostic molecules against lymphatic filariasis, a neglected tropical infectious disease which has a negative impact on socioeconomic development. In addition, this is the first report of the immunogenicity of a plant-derived filarial antigen.

The twenty-year story of a plant-based vaccine against hepatitis B: stagnation or promising prospects?

Hepatitis B persists as a common human disease despite effective vaccines having been employed for almost 30 years. Plants were considered as alternative sources of vaccines, to be mainly orally administered. Despite 20-year attempts, no real anti-HBV plant-based vaccine has been developed. Immunization trials, based on ingestion of raw plant tissue and conjugated with injection or exclusively oral administration of lyophilized tissue, were either impractical or insufficient due to oral tolerance acquisition. Plant-produced purified HBV antigens were highly immunogenic when injected, but their yields were initially insufficient for practical purposes. However, knowledge and technology have progressed, hence new plant-derived anti-HBV vaccines can be proposed today. All HBV antigens can be efficiently produced in stable or transient expression systems. Processing of injection vaccines has been developed and needs only to be successfully completed. Purified antigens can be used for injection in an equivalent manner to the present commercial vaccines. Although oral vaccines require improvement, plant tissue, lyophilized or extracted and converted into tablets, etc., may serve as a boosting vaccine. Preliminary data indicate also that both vaccines can be combined in an effective parenteral-oral immunization procedure. A partial substitution of injection vaccines with oral formulations still offers good prospects for economically viable and efficacious anti-HBV plant-based vaccines.

Enhanced cell disruption strategy in the release of recombinant hepatitis B surface antigen from Pichia pastoris using response surface methodology

BACKGROUND

Cell disruption strategies by high pressure homogenizer for the release of recombinant Hepatitis B surface antigen (HBsAg) from Pichia pastoris expression cells were optimized using response surface methodology (RSM) based on the central composite design (CCD). The factors studied include number of passes, biomass concentration and pulse pressure. Polynomial models were used to correlate the above mentioned factors to project the cell disruption capability and specific protein release of HBsAg from P. pastoris cells.

RESULTS

The proposed cell disruption strategy consisted of a number of passes set at 20 times, biomass concentration of 7.70 g/L of dry cell weight (DCW) and pulse pressure at 1,029 bar. The optimized cell disruption strategy was shown to increase cell disruption efficiency by 2-fold and 4-fold for specific protein release of HBsAg when compared to glass bead method yielding 75.68% cell disruption rate (CDR) and HBsAg concentration of 29.20 mg/L respectively.

CONCLUSIONS

The model equation generated from RSM on cell disruption of P. pastoris was found adequate to determine the significant factors and its interactions among the process variables and the optimum conditions in releasing HBsAg when validated against a glass bead cell disruption method. The findings from the study can open up a promising strategy for better recovery of HBsAg recombinant protein during downstream processing.

Overview of expression of hepatitis B surface antigen in transgenic plants

Hepatitis B virus (HBV), a pathogen for chronic liver infection, afflicts more than 350 million people world-wide. The effective way to control the virus is to take HBV vaccine. Hepatitis B surface antigen (HBsAg) is an effective protective antigen suitable for vaccine development. At present, "edible" vaccine based on transgenic plants is one of the most promising directions in novel types of vaccines. HBsAg production from transgenic plants has been carried out, and the transgenic plant expression systems have developed from model plants (such as tobacco, potato and tomato) to other various plant platforms. Crude or purified extracts of transformed plants have been found to conduct immunological responses and clinical trials for hepatitis B, which gave the researches of plant-based HBsAg production a big boost. The aim of this review was to summarize the recent data about plant-based HBsAg development including molecular biology of HBsAg gene, selection of expression vector, the expression of HBsAg gene in plants, as well as corresponding immunological responses in animal models or human.

Production of recombinant proteins in suspension-cultured plant cells

Plants have emerged in the past decade as a suitable alternative to the current production systems for recombinant pharmaceutical proteins and, today their potential for low-cost production of high quality, much safer and biologically active mammalian proteins is largely documented. Among various plant expression systems being explored, genetically modified suspension-cultured plant cells offer a promising system for production of biopharmaceuticals. Indeed, when compared to other plant-based production platforms that have been explored, suspension-cultured plant cells have the advantage of being totally devoid of problems associated with the vagaries of weather, pest, soil and gene flow in the environment. Because of short growth cycles, the timescale needed for the production of recombinant proteins in plant cell culture can be counted in days or weeks after transformation compared to months needed for the production in transgenic plants. Moreover, recovery and purification of recombinant proteins from plant biomass is an expensive and technically challenging business that may amount to 80-94% of the final product cost. One additional advantage of plant cell culture is that the recombinant protein fused with a signal sequence can be expressed and secreted into the culture medium, and therefore recovered and purified in the absence of large quantities of contaminating proteins. Consequently, the downstream processing of proteins extracted from plant cell culture medium is less expensive, which may/does balance the higher costs of fermentation. When needed for clinical use, recombinant proteins are easily produced in suspension-cultured plant cells under certified, controllable and sterile conditions that offer improved safety and provide advantages for good manufacturing practices and regulatory compliance. In this chapter, we present basic protocols for rapid generation of transgenic suspension-cultured cells of Nicotiana tabacum, Oriza sativa and Arabidopis thaliana. These systems are powerful tools for plant-made pharmaceuticals production in highly controlled conditions.

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.

Expression of HIV-1 antigens in plants as potential subunit vaccines

BACKGROUND

Human immunodeficiency virus type 1 (HIV-1) has infected more than 40 million people worldwide, mainly in sub-Saharan Africa. The high prevalence of HIV-1 subtype C in southern Africa necessitates the development of cheap, effective vaccines. One means of production is the use of plants, for which a number of different techniques have been successfully developed. HIV-1 Pr55Gag is a promising HIV-1 vaccine candidate: we compared the expression of this and a truncated Gag (p17/p24) and the p24 capsid subunit in Nicotiana spp. using transgenic plants and transient expression via Agrobacterium tumefaciens and recombinant tobamovirus vectors. We also investigated the influence of subcellular localisation of recombinant protein to the chloroplast and the endoplasmic reticulum (ER) on protein yield. We partially purified a selected vaccine candidate and tested its stimulation of a humoral and cellular immune response in mice.

RESULTS

Both transient and transgenic expression of the HIV antigens were successful, although expression of Pr55Gag was low in all systems; however, the Agrobacterium-mediated transient expression of p24 and p17/p24 yielded best, to more than 1 mg p24/kg fresh weight. Chloroplast targeted protein levels were highest in transient and transgenic expression of p24 and p17/p24. The transiently-expressed p17/p24 was not immunogenic in mice as a homologous vaccine, but it significantly boosted a humoral and T cell immune response primed by a gag DNA vaccine, pTHGagC.

CONCLUSION

Transient agroinfiltration was best for expression of all of the recombinant proteins tested, and p24 and p17/p24 were expressed at much higher levels than Pr55Gag. Our results highlight the usefulness of plastid signal peptides in enhancing the production of recombinant proteins meant for use as vaccines. The p17/p24 protein effectively boosted T cell and humoral responses in mice primed by the DNA vaccine pTHGagC, showing that this plant-produced protein has potential for use as a vaccine.

Analysis of the limitations of hepatitis B surface antigen expression in soybean cell suspension cultures

Soybean cell suspension cultures were transformed using Agrobacterium tumefaciens harboring pHBS/pHER constructs to express hepatitis B surface antigen (HBsAg). The transformed colonies were selected and analyzed for the expression of HBsAg by PCR, reverse transcription (RT) PCR, Western blot and ELISA analysis. The maximum expression of 700 ng/g F.W. was noted in pHER transformed cells. The highest expressing colonies were used to initiate the cell suspension cultures and the expression of HBsAg was estimated periodically. The expression levels were reduced drastically in cell suspension cultures compared to the colonies maintained on semi-solid medium. Various parameters were studied to maximize the cell growth and to retain the expression levels. The supplementation of culture medium with a protease inhibitor, leupeptin hemisulfate could restore up to 50% of HBsAg expression in cell suspension cultures. This is the first report to investigate the possible cause and solution to the loss of recombinant protein expression levels in plant cell suspension cultures.

Improving containment strategies in biopharming

This review examines the challenges of segregating biopharmed crops expressing pharmaceutical or veterinary agents from mainstream crops, particularly those destined for food or feed use. The strategy of using major food crops as production vehicles for the expression of pharmaceutical or veterinary agents is critically analysed in the light of several recent episodes of contamination of the human food chain by non-approved crop varieties. Commercially viable strategies to limit or avoid biopharming intrusion into the human food chain require the more rigorous segregation of food and non-food varieties of the same crop species via a range of either physical or biological methods. Even more secure segregation is possible by the use of non-food crops, non-crop plants or in vitro plant cultures as production platforms for biopharming. Such platforms already under development range from outdoor-grown Nicotiana spp. to glasshouse-grown Arabidopsis, lotus and moss. Amongst the more effective methods for biocontainment are the plastid expression of transgenes, inducible and transient expression systems, and physical containment of plants or cell cultures. In the current atmosphere of heightened concerns over food safety and biosecurity, the future of biopharming may be largely determined by the extent to which the sector is able to maintain public confidence via a more considered approach to containment and security of its plant production systems.

Virus-like particles production in green plants

Viruses-like particles (VLPs), assembled from capsid structural subunits of several different viruses, have found a number of biomedical applications such as vaccines and novel delivery systems for nucleic acids and small molecules. Production of recombinant proteins in different plant systems has been intensely investigated and improved upon in the last two decades. Plant-derived antibodies, vaccines, and microbicides have received great attention and shown immense promise. In the case of mucosal vaccines, orally delivered plant-produced VLPs require minimal processing of the plant tissue, thus offering an inexpensive and safe alternative to more conventional live attenuated and killed virus vaccines. For other applications which require higher level of purification, recent progress in expression levels using plant viral vectors have shown that plants can compete with traditional fermentation systems. In this review, the different methods used in the production of VLPs in green plants are described. Specific examples of expression, assembly, and immunogenicity of several plant-derived VLPs are presented.

Expression and characterization of a recombinant single-domain monoclonal antibody against MUC1 mucin in tobacco plants

A promising alternative to conventional antibodies is the single-domain antibody fragment of the Camelidae (V(HH)), which (because of features such as small length, high expression, solubility, and stability) is preferred to other antibody derivatives. In this report, a recombinant single-domain antibody (V(HH)) against MUC1 mucin in the tobacco plant, which may be considered as a suitable and economical alternative expression system, was produced. This antibody was expressed under the control of a strong constitutive promoter, CaMV35S, and NOS terminator. A plant high-expression sequence (Kozak sequence) was linked at the 5' end for overexpression of the V(HH) gene. The constructed cassette (pBIV(HH)) was transferred to agrobacterium, and the VHH gene was inserted into the plant genome by agrobacterium-mediated transformation. Transgenic lines were selected on kanamycin (100 mg/L) and maintained in soil, and subsequent generations were obtained. The presence and expression of the transgene was confirmed in the transformants by polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and Western blot. Tobacco transgenic lines leave expressed V(HH) at levels varying from 1.12% to 1.63% of the total soluble protein. This report examines the transformation and expression of recombinant single-domain antibody (V(HH)) against antigen-associated tumor in tobacco plants.

Genetic transformation of tobacco NT1 cells with Agrobacterium tumefaciens

This protocol is used to produce stably transformed tobacco (Nicotiana tabacum) NT1 cell lines, using Agrobacterium tumefaciens-mediated DNA delivery of a binary vector containing a gene encoding hepatitis B surface antigen and a gene encoding the kanamycin selection marker. The NT1 cultures, at the appropriate stage of growth, are inoculated with A. tumefaciens containing the binary vector. A 3-day cocultivation period follows, after which the cultures are rinsed and placed on solid selective medium. Transformed colonies ('calli') appear in approximately 4 weeks; they are subcultured until adequate material is obtained for analysis of antigen production. 'Elite' lines are selected based on antigen expression and growth characteristics. The time required for the procedure from preparation of the plant cell materials to callus development is approximately 5 weeks. Growth of selected calli to sufficient quantities for antigen screening may require 4-6 weeks beyond the initial selection. Creation of the plasmid constructs, transformation of the A. tumefaciens line, and ELISA and Bradford assays to assess protein production require additional time.

Production of human serum albumin by sugar starvation induced promoter and rice cell culture

Human serum albumin (HSA) is the most widely used clinical serum protein. Currently, commercial HSA can only be obtained from human plasma, due to lack of commercially feasible recombinant protein expression systems. In this study, inducible expression and secretion of HSA by transformed rice suspension cell culture was established. Mature form of HSA was expressed under the control of the sucrose starvation-inducible rice alpha Amy3 promoter, and secretion of HSA into the culture medium was achieved by using the alpha Amy3 signal sequence. High concentrations of HSA were secreted into culture medium in a short time (2-4 days) by sucrose depletion after cell concentrations had reached a peak density in culture medium containing sucrose. The recombinant HSA had the same electrophoretic mobility as commercial HSA and was stable and free from apparent proteolysis in the culture medium. In a flask scale culture with repeated sucrose provision-depletion cycles, HSA was stably produced with yields up to 11.5% of total medium proteins or 15 mg/L per cycle after each sucrose provision-depletion cycle. A bubble column type bioreactor was designed for production of HSA. In the bioreactor scale culture, HSA was produced with yields up to 76.4 mg/L 4 days after sucrose depletion. HSA was purified from the culture medium to high purity by a simple purification scheme. Enrichment of HSA in culture medium simplifies downstream purification, minimizes protease degradation, and may reduce production cost. The combination of a DNA construct containing the alpha Amy3 promoter and signal sequence, and the use of a rice suspension cell culture can provide an effective system for the production of recombinant pharmaceutical proteins.

Expression of hepatitis B surface antigen in transgenic banana plants

Embryogenic cells of bananan cv. Rasthali (AAB) have been transformed with the 's' gene of hepatitis B surface antigen (HBsAg) using Agrobacterium mediated transformation. Four different expression cassettes (pHBS, pHER, pEFEHBS and pEFEHER) were utilized to optimize the expression of HBsAg in banana. The transgenic nature of the plants and expression of the antigen was confirmed by PCR, Southern hybridization and reverse transcription (RT)-PCR. The expression levels of the antigen in the plants grown under in vitro conditions as well as the green house hardened plants were estimated by ELISA for all the four constructs. Maximum expression level of 38 ng/g F.W. of leaves was noted in plants transformed with pEFEHBS grown under in vitro conditions, whereas pHER transformed plants grown in the green house showed the maximum expression level of 19.92 ng/g F.W. of leaves. Higher monoclonal antibody binding of 67.87% of the antigen was observed when it was expressed with a C-terminal ER retention signal. The buoyant density in CsCl of HBsAg derived from transgenic banana leaves was determined and found to be 1.146 g/ml. HBsAg obtained from transgenic banana plants is similar to human serum derived one in buoyant density properties. The transgenic plants were grown up to maturity in the green house and the expression of HBsAg in the fruits was confirmed by RT-PCR. These transgenic plants were multiplied under in vitro using floral apex cultures. Attempts were also made to enhance the expression of HBsAg in the leaves of transgenic banana plants by wounding and/or treatment with plant growth regulators. This is the first report on the expression of HBsAg in transgenic banana fruits.

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 microg 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 microM: increased secretion of HBsAg by six fold.

Oral hepatitis B vaccine candidates produced and delivered in plant material

Hepatitis B is a major global health problem; approximately two billion people are infected with the virus worldwide, despite the fact that safe and efficacious vaccines have been developed and used for nearly 20 years. Prohibitive costs for vaccine purchase and administration restrict uptake in many developing nations. Agencies such as the Global Alliance for Vaccination and Immunization are helping to make current vaccines more available, but reduced costs would greatly aid this effort. Oral delivery is an option to reduce the expense of administering hepatitis B vaccines. It may also improve compliance, and orally delivered vaccines may be more efficacious among poor responders to current vaccines. However, to induce protective efficacy, oral administration may require encapsulation of antigen and delivery of large doses. Plant-based expression systems offer an oral delivery alternative with low production costs, and they also encapsulate the antigen. Some plant-based systems also stabilize antigen and therefore reduce storage and distribution costs. The hepatitis B major surface antigen has been expressed in several plant systems. A variety of regulatory sequences and subcellular targets have been used to achieve expression suitable for early stage clinical trials. However, further increase in expression will be necessary for practical and efficacious products. Appropriate processing can yield palatable products with uniform antigen concentration. The antigen expressed in plant systems shows extensive disulphide cross-linking and oligomerization and forms virus-like particles. Oral delivery of the antigen in plant material can induce a serum antibody response, prime the immune system for a subsequent injection of antigen and give a boosted response to a prior injection. Small scale clinical trials in which the antigen has been delivered orally in edible plant material indicate safety and immunogenicity.

Plant cell cultures for the production of recombinant proteins

The use of whole plants for the synthesis of recombinant proteins has received a great deal of attention recently because of advantages in economy, scalability and safety compared with traditional microbial and mammalian production systems. However, production systems that use whole plants lack several of the intrinsic benefits of cultured cells, including the precise control over growth conditions, batch-to-batch product consistency, a high level of containment and the ability to produce recombinant proteins in compliance with good manufacturing practice. Plant cell cultures combine the merits of whole-plant systems with those of microbial and animal cell cultures, and already have an established track record for the production of valuable therapeutic secondary metabolites. Although no recombinant proteins have yet been produced commercially using plant cell cultures, there have been many proof-of-principle studies and several companies are investigating the commercial feasibility of such production systems.