Plant-derived hemagglutinin protects ferrets against challenge infection with the A/Indonesia/05/05 strain of avian influenza

Production of non-glycosylated recombinant proteins in Nicotiana benthamiana plants by co-expressing bacterial PNGase F

Application of tools of molecular biology and genomics is increasingly leading towards the development of recombinant protein-based biologics. As such, it is leading to an increased diversity of targets that have important health applications and require more flexible approaches for expression because of complex post-translational modifications. For example, Plasmodium parasites may have complex post-translationally modified proteins such as Pfs48/45 that do not carry N-linked glycans (Exp. Parasitol. 1998; 90, 165.) but contain potential N-linked glycosylation sites that can be aberrantly glycosylated during expression in mammalian and plant systems. Therefore, it is important to develop strategies for producing non-glycosylated forms of these targets to preserve biological activity and native conformation. In this study, we are describing in vivo deglycosylation of recombinant N-glycosylated proteins as a result of their transient co-expression with bacterial PNGase F (Peptide: N-glycosidase F). In addition, we show that the recognition of an in vivo deglycosylated plant-produced malaria vaccine candidate, Pfs48F1, by monoclonal antibodies I, III and V raised against various epitopes (I, III and V) of native Pfs48/45 of Plasmodium falciparum, was significantly stronger compared to that of the glycosylated form of plant-produced Pfs48F1. To our knowledge, neither in vivo enzymatic protein deglycosylation has been previously achieved in any eukaryotic system, including plants, nor has bacterial PNGase F been expressed in the plant system. Thus, here, we report for the first time the expression in plants of an active bacterial enzyme PNGase F and the production of recombinant proteins of interest in a non-glycosylated form.

The human potential of a recombinant pandemic influenza vaccine produced in tobacco plants

Rapid production of influenza vaccine antigen is an important challenge when a new pandemic occurs. Production of recombinant antigens in plants is a quick, cost effective and up scalable new strategy for influenza vaccine production. In this study, we have characterized a recombinant influenza haemagglutinin antigen (HAC1) that was derived from the 2009 pandemic H1N1 (pdmH1N1) virus and expressed in tobacco plants. Volunteers vaccinated with the 2009 pdmH1N1 oil-in-water adjuvanted vaccine provided serum and lymphocyte samples that were used to study the immunogenic properties of the HAC1 antigen in vitro. By 7 d post vaccination, the vaccine fulfilled the licensing criteria for antibody responses to the HA detected by haemagglutination inhibition and single radial hemolysis. By ELISA and ELISPOT analysis we showed that HAC1 was recognized by specific serum antibodies and antibody secreting cells, respectively. We conducted a kinetic analysis and found a peak of serum HAC1 specific antibody response between day 14 and 21 post vaccination by ELISA. We also detected elevated production of IL-2 and IFNγ and low frequencies of CD4(+) T cells producing single or multiple Th1 cytokines after stimulating PBMCs (peripheral blood mononuclear cells) with the HAC1 antigen in vitro. This indicates that the antigen can interact with T cells, although confirming an effective adjuvant would be required to improve the T-cell stimulation of plant based vaccines. We conclude that the tobacco derived recombinant HAC1 antigen is a promising vaccine candidate recognized by both B- and T cells.

A plant-based system for rapid production of influenza vaccine antigens

BACKGROUND

Influenza virus is a globally important respiratory pathogen that causes a high degree of annual morbidity and mortality. Significant antigenic drift results in emergence of new, potentially pandemic, virus variants. The best prophylactic option for controlling emerging virus strains is to manufacture and administer pandemic vaccines in sufficient quantities and to do so in a timely manner without impacting the regular seasonal influenza vaccine capacity. Current, egg-based, influenza vaccine production is well established and provides an effective product, but has limited capacity and speed.

OBJECTIVES

To satisfy the additional global demand for emerging influenza vaccines, high-performance cost-effective technologies need to be developed. Plants have a potential as an economic and efficient large-scale production platform for vaccine antigens.

METHODS

In this study, a plant virus-based transient expression system was used to produce hemagglutinin (HA) proteins from the three vaccine strains used during the 2008-2009 influenza season, A/Brisbane/59/07 (H1N1), A/Brisbane/10/07 (H3N2), and B/Florida/4/06, as well as from the recently emerged novel H1N1 influenza A virus, A/California/04/09.

RESULTS

The recombinant plant-based HA proteins were engineered and produced in Nicotiana benthamiana plants within 2 months of obtaining the genetic sequences specific to each virus strain. These antigens expressed at the rate of 400-1300 mg/kg of fresh leaf tissue, with >70% solubility. Immunization of mice with these HA antigens induced serum anti-HA IgG and hemagglutination inhibition antibody responses at the levels considered protective against these virus infections.

CONCLUSIONS

These results demonstrate the feasibility of our transient plant expression system for the rapid production of influenza vaccine antigens.

Setting up a platform for plant-based influenza virus vaccine production in South Africa

Background

During a global influenza pandemic, the vaccine requirements of developing countries can surpass their supply capabilities, if these exist at all, compelling them to rely on developed countries for stocks that may not be available in time. There is thus a need for developing countries in general to produce their own pandemic and possibly seasonal influenza vaccines. Here we describe the development of a plant-based platform for producing influenza vaccines locally, in South Africa. Plant-produced influenza vaccine candidates are quicker to develop and potentially cheaper than egg-produced influenza vaccines, and their production can be rapidly upscaled. In this study, we investigated the feasibility of producing a vaccine to the highly pathogenic avian influenza A subtype H5N1 virus, the most generally virulent influenza virus identified to date. Two variants of the haemagglutinin (HA) surface glycoprotein gene were synthesised for optimum expression in plants: these were the full-length HA gene (H5) and a truncated form lacking the transmembrane domain (H5tr). The genes were cloned into a panel of Agrobacterium tumefaciens binary plant expression vectors in order to test HA accumulation in different cell compartments. The constructs were transiently expressed in tobacco by means of agroinfiltration. Stable transgenic tobacco plants were also generated to provide seed for stable storage of the material as a pre-pandemic strategy.

Results

For both transient and transgenic expression systems the highest accumulation of full-length H5 protein occurred in the apoplastic spaces, while the highest accumulation of H5tr was in the endoplasmic reticulum. The H5 proteins were produced at relatively high concentrations in both systems. Following partial purification, haemagglutination and haemagglutination inhibition tests indicated that the conformation of the plant-produced HA variants was correct and the proteins were functional. The immunisation of chickens and mice with the candidate vaccines elicited HA-specific antibody responses.

Conclusions

We managed, after synthesis of two versions of a single gene, to produce by transient and transgenic expression in plants, two variants of a highly pathogenic avian influenza virus HA protein which could have vaccine potential. This is a proof of principle of the potential of plant-produced influenza vaccines as a feasible pandemic response strategy for South Africa and other developing countries.

An interspecific Nicotiana hybrid as a useful and cost-effective platform for production of animal vaccines

The use of transgenic plants to produce novel products has great biotechnological potential as the relatively inexpensive inputs of light, water, and nutrients are utilised in return for potentially valuable bioactive metabolites, diagnostic proteins and vaccines. Extensive research is ongoing in this area internationally with the aim of producing plant-made vaccines of importance for both animals and humans. Vaccine purification is generally regarded as being integral to the preparation of safe and effective vaccines for use in humans. However, the use of crude plant extracts for animal immunisation may enable plant-made vaccines to become a cost-effective and efficacious approach to safely immunise large numbers of farm animals against diseases such as avian influenza. Since the technology associated with genetic transformation and large-scale propagation is very well established in Nicotiana, the genus has attributes well-suited for the production of plant-made vaccines. However the presence of potentially toxic alkaloids in Nicotiana extracts impedes their use as crude vaccine preparations. In the current study we describe a Nicotiana tabacum and N. glauca hybrid that expresses the HA glycoprotein of influenza A in its leaves but does not synthesize alkaloids. We demonstrate that injection with crude leaf extracts from these interspecific hybrid plants is a safe and effective approach for immunising mice. Moreover, this antigen-producing alkaloid-free, transgenic interspecific hybrid is vigorous, with a high capacity for vegetative shoot regeneration after harvesting. These plants are easily propagated by vegetative cuttings and have the added benefit of not producing viable pollen, thus reducing potential problems associated with bio-containment. Hence, these Nicotiana hybrids provide an advantageous production platform for partially purified, plant-made vaccines which may be particularly well suited for use in veterinary immunization programs.

Transient expression of hemagglutinin antigen from low pathogenic avian influenza A (H7N7) in Nicotiana benthamiana

The influenza A virus is of global concern for the poultry industry, especially the H5 and H7 subtypes as they have the potential to become highly pathogenic for poultry. In this study, the hemagglutinin (HA) of a low pathogenic avian influenza virus of the H7N7 subtype isolated from a Swedish mallard Anas platyrhynchos was sequenced, characterized and transiently expressed in Nicotiana benthamiana. Recently, plant expression systems have gained interest as an alternative for the production of vaccine antigens. To examine the possibility of expressing the HA protein in N. benthamiana, a cDNA fragment encoding the HA gene was synthesized de novo, modified with a Kozak sequence, a PR1a signal peptide, a C-terminal hexahistidine (6×His) tag, and an endoplasmic retention signal (SEKDEL). The construct was cloned into a Cowpea mosaic virus (CPMV)-based vector (pEAQ-HT) and the resulting pEAQ-HT-HA plasmid, along with a vector (pJL3:p19) containing the viral gene-silencing suppressor p19 from Tomato bushy stunt virus, was agro-infiltrated into N. benthamiana. The highest gene expression of recombinant plant-produced, uncleaved HA (rHA0), as measured by quantitative real-time PCR was detected at 6 days post infiltration (dpi). Guided by the gene expression profile, rHA0 protein was extracted at 6 dpi and subsequently purified utilizing the 6×His tag and immobilized metal ion adsorption chromatography. The yield was 0.2 g purified protein per kg fresh weight of leaves. Further molecular characterizations showed that the purified rHA0 protein was N-glycosylated and its identity confirmed by liquid chromatography-tandem mass spectrometry. In addition, the purified rHA0 exhibited hemagglutination and hemagglutination inhibition activity indicating that the rHA0 shares structural and functional properties with native HA protein of H7 influenza virus. Our results indicate that rHA0 maintained its native antigenicity and specificity, providing a good source of vaccine antigen to induce immune response in poultry species.

Co-expression of multiple target proteins in plants from a tobacco mosaic virus vector using a combination of homologous and heterologous subgenomic promoters

To co-express multiple target proteins, we engineered a single-component chimeric tobacco mosaic virus (TMV)-based vector containing homologous and heterologous capsid protein subgenomic RNA promoters. Delivery of this vector into Nicotiana benthamiana plants via agroinfiltration resulted in co-expression of two reporter genes within a single cell. Furthermore, co-expression of a host-specific antisense RNA or a silencing suppressor protein from this vector augmented the accumulation of green fluorescent protein or a vaccine antigen, hemagglutinin from avian influenza virus A/Vietnam/1194/04. These findings suggest that this chimeric vector utilizing the homologous and heterologous subgenomic TMV promoters has a potential for high-level production of multiple therapeutic proteins including monoclonal antibodies.

GMP issues for recombinant plant-derived pharmaceutical proteins

Recombinant proteins can be produced in a diverse array of plant-based systems, ranging from whole plants growing in the soil to plant suspension cells growing in a fully-defined synthetic medium in a bioreactor. When the recombinant proteins are intended for medical use (plant-derived pharmaceutical proteins, PDPs) they fall under the same regulatory guidelines for manufacturing that cover drugs from all other sources, and when such proteins enter clinical development this includes the requirement for production according to good manufacturing practice (GMP). In principle, the well-characterized GMP regulations that apply to pharmaceutical proteins produced in bacteria and mammalian cells are directly transferrable to plants. In practice, the cell-specific terminology and the requirement for a contained, sterile environment mean that only plant cells in a bioreactor fully meet the original GMP criteria. Significant changes are required to adapt these regulations for proteins produced in whole-plant systems and it is only recently that the first GMP-compliant production processes using plants have been delivered.

Strategies for the plant-based expression of dengue subunit vaccines

Despite significant efforts in many countries, there is still no commercially viable dengue vaccine. Currently, attention is focused on the development of either live attenuated vaccines or live attenuated chimaeric vaccines using a variety of backbones. Alternate vaccine approaches, such as whole inactivated virus and subunit vaccines are in the early stages of development, and are each associated with different problems. Subunit vaccines offer the advantage of providing a uniform antigen of well-defined nature, without the added risk of introducing any genetic material into the person being inoculated. Preliminary trials of subunit vaccines (using dengue E protein) in rhesus monkeys have shown promising results. However, the primary disadvantages of dengue subunit vaccines are the low levels of expression of dengue proteins in mammalian or insect cells, as well as the added unknown risks of antigens produced from mammalian cells containing other potential sources of contamination. In the past two decades, plants have emerged as an alternative platform for expression of biopharmaceutical products, including antigens of bacterial, fungal or viral origin. In the present minireview, we highlight the current plant expression technologies used for expression of biopharmaceutical products, with an emphasis on plants as a production system for dengue subunit vaccines.

A plant-produced Pfs230 vaccine candidate blocks transmission of Plasmodium falciparum

Plasmodium falciparum is transmitted to a new host after completing its sexual cycle within a mosquito. Developing vaccines against the parasite sexual stages is a critical component in the fight against malaria. We are targeting multiple proteins of P. falciparum which are found only on the surfaces of the sexual forms of the parasite and where antibodies against these proteins have been shown to block the progression of the parasite's life cycle in the mosquito and thus block transmission to the next human host. We have successfully produced a region of the Pfs230 antigen in our plant-based transient-expression system and evaluated this vaccine candidate in an animal model. This plant-produced protein, 230CMB, is expressed at approximately 800 mg/kg in fresh whole leaf tissue and is 100% soluble. Administration of 230CMB with >90% purity induces strong immune responses in rabbits with high titers of transmission-blocking antibodies, resulting in a greater than 99% reduction in oocyst counts in the presence of complement, as determined by a standard membrane feeding assay. Our data provide a clear perspective on the clinical development of a Pfs230-based transmission-blocking malaria vaccine.

Recombinant trimeric HA protein immunogenicity of H5N1 avian influenza viruses and their combined use with inactivated or adenovirus vaccines

BACKGROUND

The highly pathogenic avian influenza (HPAI) H5N1 virus continues to cause disease in poultry and humans. The hemagglutinin (HA) envelope protein is the primary target for subunit vaccine development.

METHODOLOGY/PRINCIPAL FINDINGS

We used baculovirus-insect cell expression to obtain trimeric recombinant HA (rHA) proteins from two HPAI H5N1 viruses. We investigated trimeric rHA protein immunogenicity in mice via immunizations, and found that the highest levels of neutralizing antibodies resulted from coupling with a PELC/CpG adjuvant. We also found that the combined use of trimeric rHA proteins with (a) an inactivated H5N1 vaccine virus, or (b) a recombinant adenovirus encoding full-length HA sequences for prime-boost immunization, further improved antibody responses against homologous and heterologous H5N1 virus strains. Data from cross-clade prime-boost immunization regimens indicate that sequential immunization with different clade HA antigens increased antibody responses in terms of total IgG level and neutralizing antibody titers.

CONCLUSION/SIGNIFICANCE

Our findings suggest that the use of trimeric rHA in prime-boost vaccine regimens represents an alternative strategy for recombinant H5N1 vaccine development.

Intranasal c-di-GMP-adjuvanted plant-derived H5 influenza vaccine induces multifunctional Th1 CD4+ cells and strong mucosal and systemic antibody responses in mice

Vaccination is the best available measure of limiting the impact of the next influenza pandemic. Ideally, a candidate pandemic influenza vaccine should be easy to administer and should elicit strong mucosal and systemic immune responses. Production of influenza subunit antigen in transient plant expression systems is an alternative to overcome the bottleneck in vaccine supply during influenza pandemic. Furthermore, a needle-free intranasal influenza vaccine is an attractive approach, which may provide immunity at the portal of virus entry. The present study investigated the detailed humoral and cellular immune responses in mice vaccinated intranasally or intramuscularly with plant-derived influenza H5N1 (A/Anhui/1/05) antigen alone or formulated with bis-(3',5')-cyclic dimeric guanosine monophosphate (c-di-GMP) as adjuvant. The use of c-di-GMP as intramuscular adjuvant did not enhance the immune response to plant-derived influenza H5 antigen. However, intranasal c-di-GMP-adjuvanted vaccine induced strong mucosal and systemic humoral immune responses. Additionally, the intranasal vaccine elicited a balanced Th1/Th2 profile and, most importantly, high frequencies of multifunctional Th1 CD4(+) cells. Our results highlight that c-di-GMP is a promising mucosal adjuvant for pandemic influenza vaccine development.

Membrane-based inverse transition cycling: an improved means for purifying plant-derived recombinant protein-elastin-like polypeptide fusions

Elastin-like peptide (ELP) was fused to two different avian flu H5N1 antigens and expressed in transgenic tobacco plants. The presence of the ELP tag enhanced the accumulation of the heterologous proteins in the tobacco leaves. An effective membrane-based Inverse Transition Cycling was developed to recover the ELPylated antigens and antibodies from plant material. The functionality of both the ELPylated neuraminidase and an ELPylated nanobody was demonstrated.

A recombinant vaccine of H5N1 HA1 fused with foldon and human IgG Fc induced complete cross-clade protection against divergent H5N1 viruses

Development of effective vaccines to prevent influenza, particularly highly pathogenic avian influenza (HPAI) caused by influenza A virus (IAV) subtype H5N1, is a challenging goal. In this study, we designed and constructed two recombinant influenza vaccine candidates by fusing hemagglutinin 1 (HA1) fragment of A/Anhui/1/2005(H5N1) to either Fc of human IgG (HA1-Fc) or foldon plus Fc (HA1-Fdc), and evaluated their immune responses and cross-protection against divergent strains of H5N1 virus. Results showed that these two recombinant vaccines induced strong immune responses in the vaccinated mice, which specifically reacted with HA1 proteins and an inactivated heterologous H5N1 virus. Both proteins were able to cross-neutralize infections by one homologous strain (clade 2.3) and four heterologous strains belonging to clades 0, 1, and 2.2 of H5N1 pseudoviruses as well as three heterologous strains (clades 0, 1, and 2.3.4) of H5N1 live virus. Importantly, immunization with these two vaccine candidates, especially HA1-Fdc, provided complete cross-clade protection against high-dose lethal challenge of different strains of H5N1 virus covering clade 0, 1, and 2.3.4 in the tested mouse model. This study suggests that the recombinant fusion proteins, particularly HA1-Fdc, could be developed into an efficacious universal H5N1 influenza vaccine, providing cross-protection against infections by divergent strains of highly pathogenic H5N1 virus.

Transient expression systems for plant-derived biopharmaceuticals

In the molecular farming area, transient expression approaches for pharmaceutical proteins production, mainly recombinant monoclonal antibodies and vaccines, were developed almost two decades ago and, to date, these systems basically depend on Agrobacterium-mediated delivery and virus expression machinery. We survey here the current state-of-the-art of this research field. Several vectors have been designed on the basis of DNA- and RNA-based plant virus genomes and viral vectors are used both as single- and multicomponent expression systems in different combinations depending on the protein of interest. The obvious advantages of these systems are ease of manipulation, speed, low cost and high yield of proteins. In addition, Agrobacterium-mediated expression also allows the production in plants of complex proteins assembled from subunits. Currently, the transient expression methods are preferential over any other transgenic system for the exploitation of large and unrestricted numbers of plants in a contained environment. By designing optimal constructs and related means of delivery into plant cells, the overall technology plan considers scenarios that envisage high yield of bioproducts and ease in monitoring the whole spectrum of upstream production, before entering good manufacturing practice facilities. In this way, plant-derived bioproducts show promise of high competitiveness towards classical eukaryotic cell factory systems.

Immunization with plant-expressed hemagglutinin protects chickens from lethal highly pathogenic avian influenza virus H5N1 challenge infection

Highly pathogenic avian influenza (HPAI) is a striking disease in susceptible poultry, which leads to severe economic losses. Inactivated vaccines are the most widely used vaccines in avian influenza virus (AIV) vaccination programs. However, these vaccines interfere with the serological detection of wild-type AIV infections in immunized populations. The use of vaccines that allow differentiation between infected and vaccinated animals (DIVA strategy) would stop current stamping-out policies. Therefore, novel vaccination strategies are needed to allow improved protection of animals and humans against HPAI virus (HPAIV) infection. The presented study analyzed for the first time the immunogenic capacity of plant-expressed full-length hemagglutinin (rHA0) of HPAIV H5N1 in several vaccine formulations within the highly relevant host species chicken. We were able to express plant-expressed rHA0 at high levels and could show that, when administered with potent adjuvants, it is highly immunogenic and can fully protect chicken against lethal challenge infection. Real-time reverse transcription (RT)-PCR and serological tests demonstrated only marginally increased virus replication in animals vaccinated with plant-derived rHA0 compared to animals immunized with an inactivated reference vaccine. In addition, the use of plant-expressed rHA0 also allowed an easy serological differentiation of vaccinated from AIV-infected animals based on antibodies against the influenza virus NP protein.

A novel two-component Tobacco mosaic virus-based vector system for high-level expression of multiple therapeutic proteins including a human monoclonal antibody in plants

Expression of multiple therapeutic proteins from Tobacco mosaic virus (TMV)-based vectors was not successful when plants were coinoculated with a mixture of two TMV vectors engineered to express two foreign genes individually. Here, we have engineered and developed a defective RNA (dRNA)-based TMV vector (dRT-V) that utilizes two components of the same virus, with the dRNA component depending on the helper virus for replication. Agrobacterium-mediated coinoculation of Nicotiana benthamiana plants with both components of the dRT-V resulted in high-level expression of a human growth hormone and a lichenase-fused lethal factor protein of Bacillus anthracis. Furthermore, both heavy and light chains were expressed and assembled into a monoclonal antibody (mAb) specific to the protective antigen of B. anthracis, and the average yield of the purified antibody obtained was 120 mg/kg of fresh tissue. Our data suggest that dRT-V has a potential for rapid, cost-effective, large-scale manufacturing of multiple therapeutic proteins including mAbs in response to any biological emergencies.

Report of the fourth meeting on 'Influenza vaccines that induce broad spectrum and long-lasting immune responses', World Health Organization and Wellcome Trust, London, United Kingdom, 9-10 November 2009

Current influenza vaccines are limited by the need for annual immunisation, frequent antigenic updating to match the evolution of circulating influenza virus strains, and reduced efficacy in elderly persons. On 9-10 November 2009, the Initiative for Vaccine Research of the World Health Organization convened jointly with the Wellcome Trust in London, United Kingdom, the fourth meeting on 'Influenza vaccines that induce broad spectrum and long-lasting immune responses'. Presentations were made by representatives from industry, academia, governmental and non-governmental organisations. The objectives of the meeting were to update the progress of research in the field of influenza vaccine strategies able to generate cross protection against divergent influenza virus strains. Improvements in existing strategies including live attenuated influenza vaccines and adjuvantation of inactivated vaccines were summarised. Developments in novel antigen production methods, new routes of vaccine delivery and administration, and vaccine approaches based on conserved virus antigens were explored. In addition, correlates of immune protection and regulatory issues for the evaluation and approval of future novel vaccine strategies were discussed.

Plant-made vaccine antigens and biopharmaceuticals

Plant cells are ideal bioreactors for the production and oral delivery of vaccines and biopharmaceuticals, eliminating the need for expensive fermentation, purification, cold storage, transportation and sterile delivery. Plant-made vaccines have been developed for two decades but none has advanced beyond Phase I. However, two plant-made biopharmaceuticals are now advancing through Phase II and Phase III human clinical trials. In this review, we evaluate the advantages and disadvantages of different plant expression systems (stable nuclear and chloroplast or transient viral) and their current limitations or challenges. We provide suggestions for advancing this valuable concept for clinical applications and conclude that greater research emphasis is needed on large-scale production, purification, functional characterization, oral delivery and preclinical evaluation.

Vaccines: the fourth century

Vaccine development, which began with Edward Jenner's observations in the late 18th century, has entered its 4th century. From its beginnings, with the use of whole organisms that had been weakened or inactivated, to the modern-day use of genetic engineering, it has taken advantage of the tools discovered in other branches of microbiology. Numerous successful vaccines are in use, but the list of diseases for which vaccines do not exist is long. However, the multiplicity of strategies now available, discussed in this article, portends even more successful development of vaccines.