Anti-cancer activity of plant-produced HPV16 E7 vaccine

A Therapeutic DNA Vaccine Targeting HPV16 E7 in Combination with Anti-PD-1/PD-L1 Enhanced Tumor Regression and Cytotoxic Immune Responses

Persistent infection of high-risk human papillomavirus (HPV) and the expression of E6 and E7 oncoproteins are the main causes of cervical cancer. Several prophylactic HPV vaccines are used in the clinic, but these vaccines have limited efficacy in patients already infected with HPV. Since HPV E7 is vital for tumor-specific immunity, developing a vaccine against HPV E7 is an attractive strategy for cervical cancer treatment. Here, we constructed an HPV16 E7 mutant that loses the ability to bind pRb while still eliciting a robust immune response. In order to build a therapeutic DNA vaccine, the E7 mutant was packaged in an adenovirus vector (Ad-E7) for efficient expression and enhanced immunogenicity of the vaccine. Our results showed that the Ad-E7 vaccine effectively inhibited tumor growth and increased the proportion of interferon-gamma (IFN-γ)-secreting CD8+ T cells in the spleen, and tumor-infiltrating lymphocytes in a mouse cervical cancer model was achieved by injecting with HPV16-E6/E7-expressing TC-1 cells subcutaneously. Combining the Ad-E7 vaccine with the PD-1/PD-L1 antibody blockade significantly improved the control of TC-1 tumors. Combination therapy elicited stronger cytotoxic T lymphocyte (CTL) responses, and IFN-γ secretion downregulated the proportion of Tregs and MDSCs significantly. The expressions of cancer-promoting factors, such as TNF-α, were also significantly down-regulated in the case of combination therapy. In addition, combination therapy inhibited the number of capillaries in tumor tissues and increased the thickness of the tumor capsule. Thus, Ad-E7 vaccination, in combination with an immune checkpoint blockade, may benefit patients with HPV16-associated cervical cancer.

Harnessing the Potential of Plant Expression System towards the Production of Vaccines for the Prevention of Human Papillomavirus and Cervical Cancer

Cervical cancer is the most common gynecological malignant tumor worldwide, and it remains a major health problem among women, especially in developing countries. Despite the significant research efforts employed for tumor prevention, cervical cancer ranks as the leading cause of cancer death. Human papillomavirus (HPV) is the most important risk factor for cervical cancer. Cervical cancer is a preventable disease, for which early detection could increase survival rates. Immunotherapies represent a promising approach in the treatment of cancer, and several potential candidates are in clinical trials, while some are available in the market. However, equal access to available HPV vaccines is limited due to their high cost, which remains a global challenge for cervical cancer prevention. The implementation of screening programs, disease control systems, and medical advancement in developed countries reduce the serious complications associated with the disease somewhat; however, the incidence and prevalence of cervical cancer in low-income and middle-income countries continues to gradually increase, making it the leading cause of mortality, largely due to the unaffordable and inaccessible anti-cancer therapeutic options. In recent years, plants have been considered as a cost-effective production system for the development of vaccines, therapeutics, and other biopharmaceuticals. Several proof-of-concept studies showed the possibility of producing recombinant biopharmaceuticals for cancer immunotherapy in a plant platform. This review summarizes the current knowledge and therapeutic options for the prevention of cervical cancer and discusses the potential of the plant expression platform to produce affordable HPV vaccines.

Emerging trends of edible vaccine therapy for combating human diseases especially COVID ‐19: Pros, cons, and future challenges

The researchers are still doing efforts to develop an effective, reliable, and easily accessible vaccine candidate to protect against COVID‐19. As of the August 2020, nearly 30 conventional vaccines have been emerged in clinical trials, and more than 200 vaccines are in various development stages. Nowadays, plants are also considered as a potential source for the production of monoclonal antibodies, vaccines, drugs, immunomodulatory proteins, as well as used as bioreactors or factories for their bulk production. The scientific evidences enlighten that plants are the rich source of oral vaccines, which can be given either by eating the edible parts of plants and/or by oral administration of highly refined proteins. The use of plant‐based edible vaccines is an emerging trend as it possesses minimum or no side effects compared with synthetic vaccines. This review article gives insights into different types of vaccines, the use of edible vaccines, advantages of edible vaccines over conventional vaccines, and mechanism of action of edible vaccines. This review article also focuses on the applications of edible vaccines in wide‐range of human diseases especially against COVID‐19 with emphasis on future perspectives of the use of edible vaccines.

Natural Bioactives: Back to the Future in the Fight against Human Papillomavirus? A Narrative Review

Human papillomavirus (HPV) still represents an important threat to health worldwide. Better therapy in terms of further improvement of outcomes and attenuation of related side-effects is desirable. The pharmaceutical industry has always targeted natural substances-phytochemicals in particular-to identify lead compounds to be clinically validated and industrially produced as antiviral and anticancer drugs. In the field of HPV, numerous naturally occurring bioactives and dietary phytochemicals have been investigated as potentially valuable in vitro and in vivo. Interference with several pathways and improvement of the efficacy of chemotherapeutic agents have been demonstrated. Notably, some clinical trials have been conducted. Despite being endowed with general safety, these natural substances are in urgent need of further assessment to foresee their clinical exploitation. This review summarizes the basic research efforts conducted so far in the study of anti-HPV properties of bio-actives with insights into their mechanisms of action and highlights the variety of their natural origin in order to provide comprehensive mapping throughout the different sources. The clinical studies available are reported, as well, to highlight the need of uniformity and consistency of studies in the future to select those natural compounds that may be suited to clinical application.

Transient expression of fusion and hemagglutinin-neuraminidase epitopes of Newcastle disease virus in maize as a potent candidate vaccine

Purpose

Newcastle disease (ND) represents a major viral disease across the world which imposes high costs to poultry producers for vaccination. Hemagglutinin-neuraminidase (HN) and fusion (F) proteins are the major immunogenic epitopes of Newcastle disease virus and hence, have been the main targets for development of anti-ND vaccines. This paper reports transient expression of a synthetic gene composing of four tandem repeats of HN and three tandem repeats of F epitopes in maize leaves as initial step toward production of recombinant vaccine against ND.

Materials and Methods

The synthetic gene was cloned in pBI121 plasmid to yield an expression vector. The vector was sophisticated by the addition of AUG codon, polyhistidine-tag, tobacco mosaic virus omega sequence, stop codon, and restriction sites. Leaf transformation was conducted by the agroinfiltration method. Molecular detection assays including polymerase chain reaction, reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) were carried out to evaluate transgene expression in infiltrated leaves of the corn plant.

Results

The result obtained in this research revealed that the transgene was transcribed and translated in maize leaves only 48 hours after infiltration. In the second phase of the experiment, the expressed protein was injected into rabbits. The result of the ELISA assay indicated induction of immune response in the rabbits after injection with the heterologous protein.

Conclusion

These results confirm the feasibility of agroinfiltration for transient gene expression of viral epitopes in monocot plants which naturally resist stable transformation by Agrobacterium tumefaciens. Practical implications of this finding are discussed in detail and some recommendations for future studies are proposed.

Contributions of the international plant science community to the fight against human infectious diseases - part 1: epidemic and pandemic diseases

Infectious diseases, also known as transmissible or communicable diseases, are caused by pathogens or parasites that spread in communities by direct contact with infected individuals or contaminated materials, through droplets and aerosols, or via vectors such as insects. Such diseases cause ˜17% of all human deaths and their management and control places an immense burden on healthcare systems worldwide. Traditional approaches for the prevention and control of infectious diseases include vaccination programmes, hygiene measures and drugs that suppress the pathogen, treat the disease symptoms or attenuate aggressive reactions of the host immune system. The provision of vaccines and biologic drugs such as antibodies is hampered by the high cost and limited scalability of traditional manufacturing platforms based on microbial and animal cells, particularly in developing countries where infectious diseases are prevalent and poorly controlled. Molecular farming, which uses plants for protein expression, is a promising strategy to address the drawbacks of current manufacturing platforms. In this review article, we consider the potential of molecular farming to address healthcare demands for the most prevalent and important epidemic and pandemic diseases, focussing on recent outbreaks of high-mortality coronavirus infections and diseases that disproportionately affect the developing world.

Plant-Based COVID-19 Vaccines: Current Status, Design, and Development Strategies of Candidate Vaccines

The prevalence of the coronavirus disease 2019 (COVID-19) pandemic in its second year has led to massive global human and economic losses. The high transmission rate and the emergence of diverse SARS-CoV-2 variants demand rapid and effective approaches to preventing the spread, diagnosing on time, and treating affected people. Several COVID-19 vaccines are being developed using different production systems, including plants, which promises the production of cheap, safe, stable, and effective vaccines. The potential of a plant-based system for rapid production at a commercial scale and for a quick response to an infectious disease outbreak has been demonstrated by the marketing of carrot-cell-produced taliglucerase alfa (Elelyso) for Gaucher disease and tobacco-produced monoclonal antibodies (ZMapp) for the 2014 Ebola outbreak. Currently, two plant-based COVID-19 vaccine candidates, coronavirus virus-like particle (CoVLP) and Kentucky Bioprocessing (KBP)-201, are in clinical trials, and many more are in the preclinical stage. Interim phase 2 clinical trial results have revealed the high safety and efficacy of the CoVLP vaccine, with 10 times more neutralizing antibody responses compared to those present in a convalescent patient's plasma. The clinical trial of the CoVLP vaccine could be concluded by the end of 2021, and the vaccine could be available for public immunization thereafter. This review encapsulates the efforts made in plant-based COVID-19 vaccine development, the strategies and technologies implemented, and the progress accomplished in clinical trials and preclinical studies so far.

Plant-Derived Natural Compounds in Genetic Vaccination and Therapy for HPV-Associated Cancers

Simple Summary

DNA vaccination represents a useful approach for human papillomavirus (HPV) cancer therapy. The therapeutic potential of plant-based natural compounds for control of HPV- associated cancers has been also widely explored. Genetic vaccines for HPV-associated tumors that include plant protein-encoding gene sequences, used alone or in combinations with plant metabolites, are being investigated but are still in their infancy. Main focus of this paper is to provide an overview of the current state of novel therapeutic strategies employing genetic vaccines along with plant-derived compounds and genes. We highlight the importance of multimodality treatment regimen such as combining immunotherapy with plant-derived agents.

Abstract

Antigen-specific immunotherapy and, in particular, DNA vaccination provides an established approach for tackling human papillomavirus (HPV) cancers at different stages. DNA vaccines are stable and have a cost-effective production. Their intrinsic low immunogenicity has been improved by several strategies with some success, including fusion of HPV antigens with plant gene sequences. Another approach for the control of HPV cancers is the use of natural immunomodulatory agents like those derived from plants, that are able to interfere in carcinogenesis by modulating many different cellular pathways and, in some instances, to reduce chemo- and radiotherapy resistance of tumors. Indeed, plant-derived compounds represent, in many cases, an abundantly available, cost-effective source of molecules that can be either harvested directly in nature or obtained from plant cell cultures. In this review, an overview of the most relevant data reported in literature on the use of plant natural compounds and genetic vaccines that include plant-derived sequences against HPV tumors is provided. The purpose is also to highlight the still under-explored potential of multimodal treatments implying DNA vaccination along with plant-derived agents.

Production of bioactive human IFN-γ protein by agroinfiltration in tobacco

In animals, interferon-γ (IFN-γ) is known as a cytokine involved in antiviral and anticancer activities with a higher biochemical activity in contrast to other IFNs. To produce recombinant human IFN-γ (hIFN-γ) protein in tobacco, factors influencing gene delivery were first evaluated for higher efficiency of transient expression by fluorometric measurement of GUS activity. Higher levels of transient expression were observed in leaves of Nicotiana tabacum cv. Samsun infiltrated with GV3101 strain (optical density equal to 1.0 at 600 nm) under treatment of 200 μM AS at 4 days post agroinfiltration (dpa). The Samsun cv. proved to be amenable with 1.4- and 1.5-fold higher levels of transient expression than Xanthi and N. benthamiana, respectively. In addition, the GV3101 remained the best strain for use in transient assays without any necrotic response in tobacco. The levels of transient hIFN-γ expression were also estimated in the Samsun cv. infiltrated with different Agrobacterium tumefaciens strains carrying various expression constructs. Higher levels of accumulation were obtained with targeting the hIFN-γ protein to endoplasmic reticulum (ER) or apoplastic space than those expressed into cytoplasm. Moreover, antiviral bioassay revealed that recombinant hIFN-γ protein produced in tobacco is biologically active and protects the Vero cells from infection generated by vesicular stomatitis virus (VSV).

Virus-based pharmaceutical production in plants: an opportunity to reduce health problems in Africa

BACKGROUND

Developing African countries face health problems that they struggle to solve. The major causes of this situation are high therapeutic and logistical costs. Plant-made therapeutics are easy to produce due to the lack of the safety considerations associated with traditional fermenter-based expression platforms, such as mammalian cells. Plant biosystems are easy to scale up and inexpensive, and they do not require refrigeration or a sophisticated medical infrastructure. These advantages provide an opportunity for plant-made pharmaceuticals to counteract diseases for which medicines were previously inaccessible to people in countries with few resources.

MAIN BODY

The techniques needed for plant-based therapeutic production are currently available. Viral expression vectors based on plant viruses have greatly enhanced plant-made therapeutic production and have been exploited to produce a variety of proteins of industrial, pharmaceutical and agribusiness interest. Some neglected tropical diseases occurring exclusively in the developing world have found solutions through plant bioreactor technology. Plant viral expression vectors have been reported in the production of therapeutics against these diseases occurring exclusively in the third world, and some virus-derived antigens produced in plants exhibit appropriate antigenicity and immunogenicity. However, all advances in the use of plants as bioreactors have been made by companies in Europe and America. The developing world is still far from acquiring this technology, although plant viral expression vectors may provide crucial help to overcome neglected diseases.

CONCLUSION

Today, interest in these tools is rising, and viral amplicons made in and for Africa are in progress. This review describes the biotechnological advances in the field of plant bioreactors, highlights factors restricting access to this technology by those who need it most and proposes a solution to overcome these limitations.

Different types of adjuvants in prophylactic and therapeutic human papillomavirus vaccines in laboratory animals: a systematic review

Human papillomavirus (HPV) causes cervical carcinoma, which and is the third most common cancer, accounting for 275,000 deaths annually worldwide. Adjuvants have a key role in promotion of vaccine efficacy; therefore, using prophylactic and therapeutic vaccines combined with adjuvant could be of great benefit in prevention and treatment of cervical cancer. There are different types of adjuvants, including MF59^TM adjuvants, RNA-based, JY (interleukin2/chitosan), cholera toxin (CT), heat-labile enterotoxin (LT), Freund's adjuvant, alum, SA-4-1BBL, λ-carrageenan (λ-CGN), heat shock proteins (HSPs), juzen-taiho-to (JTT) and hochu-ekki-to (HET), ISCOM and ISCOMATRIX™, very small size proteoliposomes (VSSPs), granulocyte macrophage colony-stimulating factor (GM-CSF), and Toll-like receptors (TLRs). Adjuvants have various functions, especially in therapeutic vaccines, and they lead to an increase in cytotoxic T lymphocytes (CTLs), so they are important in the design of vaccines. Here, we review the currently used adjuvants and their combinations with HPV protein vaccines in order to introduce an appropriate adjuvant for HPV vaccines.

Bioproduction of a Therapeutic Vaccine Against Human Papillomavirus in Tomato Hairy Root Cultures

Human papillomavirus (HPV) tumor disease is a critical public health problem worldwide, especially in the developing countries. The recognized pathogenic function of E5, E6, and E7 oncoproteins offers the opportunity to devise therapeutic vaccines based on engineered recombinant proteins. The potential of plants to manufacture engineered compounds for pharmaceutical purposes, from small to complex protein molecules, allows the expression of HPV antigens and, possibly, the regulation of immune functions to develop very specific therapies as a reinforcement to available nonspecific therapies and preventive vaccination also in developed countries. Among plant-based expression formats, hairy root cultures are a robust platform combining the benefits of eukaryotic plant-based bioreactors, with those typical of cell cultures. In this work, to devise an experimental therapeutic vaccine against HPV, hairy root cultures were used to express a harmless form of the HPV type 16 E7 protein (E7*) fused to SAPKQ, a noncytotoxic form of the saporin protein from Saponaria officinalis, that we had shown to improve E7-specific cell-mediated responses as a fusion E7*-SAPKQ DNA vaccine. Hairy root clones expressing the E7*-SAPKQ candidate vaccine were obtained upon infection of leaf explants of Solanum lycopersicum using a recombinant plant expression vector. Yield was approximately 35.5 μg/g of fresh weight. Mouse immunization with vaccine-containing crude extracts was performed together with immunological and biological tests to investigate immune responses and anticancer activity, respectively. Animals were primed with either E7*-SAPKQ DNA-based vaccine or E7*-SAPKQ root extract-based vaccine and boosted with the same (homologous schedule) or with the other vaccine preparation (heterologous schedule) in the context of TC-1 experimental mouse model of HPV-associated tumor. All the formulations exhibited an immunological response associated to anticancer activity. In particular, DNA as prime and hairy root extract as boost demonstrated the highest efficacy. This work, based on the development of low-cost technologies, highlights the suitability of hairy root cultures as possible biofactories of therapeutic HPV vaccines and underlines the importance of the synergic combination of treatment modalities for future developments in this field.

Engineering Plants for the Future: Farming with Value-Added Harvest

Plants and their rich variety of natural compounds are used to maintain and to improve health since the earliest stages of civilization. Despite great advances in synthetic organic chemistry, one fourth of present-day drugs have still a botanical origin, and we are currently living a revival of interest in new pharmaceuticals from plant sources.

Modern biotechnology has defined the potential of plants to be systems able to manufacture not only molecules naturally occurring in plants but also newly engineered compounds, from small to complex protein molecules, which may originate even from non-plant sources. Among these compounds, pharmaceuticals such as vaccines, antibodies and other therapeutic or prophylactic entities can be listed. For this technology, the term plant molecular farming has been coined with reference to agricultural applications due to the use of crops as biofactories for the production of high-added value molecules. In this perspective, edible plants have also been thought as a tool to deliver by the oral route recombinant compounds of medical significance for new therapeutic strategies. Despite many hurdles in establishing regulatory paths for this “novel” biotechnology, plants as bioreactors deserve more attention when considering their intrinsic advantages, such as the quality and safety of the recombinant molecules that can be produced and their potential for large-scale and low-cost production, despite worrying issues (e.g. amplification and diffusion of transgenes) that are mainly addressed by regulations, if not already tackled by the plant-made products already commercialized. The huge benefits generated by these valuable products, synthesized through one of the safest, cheapest and most efficient method, speak for themselves.

Milestone for plant-based recombinant protein production for human health use was the approval in 2012 by the US Food and Drug Administration of plant-made taliglucerase alfa, a therapeutic enzyme for the treatment of Gaucher’s disease, synthesized in carrot suspension cultures by Protalix BioTherapeutics.

In this review, we will go through the various approaches and results for plant-based production of proteins and recent progress in the development of plant-made pharmaceuticals (PMPs) for the prevention and treatment of human diseases. An analysis on acceptance of these products by public opinion is also tempted.

Therapeutic vaccines for high-risk HPV-associated diseases

Cancer is the second leading cause of death worldwide, and it is estimated that Human papillomavirus (HPV) related cancers account for 5% of all human cancers. Current HPV vaccines are extremely effective at preventing infection and neoplastic disease; however, they are prophylactic and do not clear established infections. Therapeutic vaccines which trigger cell-mediated immune responses for the treatment of established infections and malignancies are therefore required. The E6 and E7 early genes are ideal targets for vaccine therapy due to their role in disruption of the cell cycle and their constitutive expression in premalignant and malignant tissues. Several strategies have been investigated for the development of therapeutic vaccines, including live-vector, nucleic acid, peptide, protein-based and cell-based vaccines as well as combinatorial approaches, with several vaccine candidates progressing to clinical trials. With the current understanding of the HPV life cycle, molecular mechanisms of infection, carcinogenesis, tumour biology, the tumour microenvironment and immune response mechanisms, an approved HPV therapeutic vaccine seems to be a goal not far from being achieved. In this article, the status of therapeutic HPV vaccines in clinical trials are reviewed, and the potential for plant-based vaccine production platforms described.

Cross-reactivity of antigens and antibodies belonging to different pathogenic types of human papillomaviruses

The analysis of the properties of a quadrivalent peroral vaccine against the cervical cancer, which was created in a plant expression system on the base of transgenic tomato fruits, by immunoassay and Western blot hybridization showed that the antibodies against human papilloma virus 16 L1 (HPV16 L1) actively interacted not only with the antigenic proteins HPV18 L1, HPV31 L1, and HPV45 L1, but also with the antigenic protein HPV6 L1, which belongs to another HPV family. Thus, new data on the possibility of crossreactivity between antibodies and antigens belonging to remote HPV families were obtained.

Hydroponic Treatment of Nicotiana benthamiana with Kifunensine Modifies the N-glycans of Recombinant Glycoprotein Antigens to Predominantly Man9 High-Mannose Type upon Transient Overexpression

Nicotiana benthamiana transient overexpression systems offer unique advantages for rapid and scalable biopharmaceuticals production, including high scalability and eukaryotic post-translational modifications such as N-glycosylation. High-mannose-type glycans (HMGs) of glycoprotein antigens have been implicated in the effectiveness of some subunit vaccines. In particular, Man₉GlcNAc₂ (Man9) has high binding affinity to mannose-specific C-type lectin receptors such as the mannose receptor and dendritic cell-specific intracellular adhesion molecule 3-grabbing non-integrin (DC-SIGN). Here, we investigated the effect of kifunensine, an α-mannosidase I inhibitor, supplemented in a hydroponic culture of N. benthamiana for the production of Man9-rich HMG glycoproteins, using N-glycosylated cholera toxin B subunit (gCTB) and human immunodeficiency virus gp120 that are tagged with a H/KDEL endoplasmic reticulum retention signal as model vaccine antigens. Biochemical analysis using anti-fucose and anti-xylose antibodies as well as Endo H and PNGase F digestion showed that kifunensine treatment effectively reduced plant-specific glycoforms while increasing HMGs in the N-glycan compositions of gCTB. Detailed glycan profiling revealed that plant-produced gp120 had a glycan profile bearing mostly HMGs regardless of kifunensine treatment. However, the gp120 produced under kifunensine-treatment conditions showed Man9 being the most prominent glycoform (64.5%), while the protein produced without kifunensine had a substantially lower Man9 composition (20.3%). Our results open up possibilities for efficient production of highly mannosylated recombinant vaccine antigens in plants.

Rapid and Low-Cost Tools Derived from Plants to Face Emerging/Re-emerging Infectious Diseases and Bioterrorism Agents

Whether naturally occurring or man-made, biological threats pose a severe risk in an increasingly globalized world.

The dual-use nature of biological research, with its most recent advances in biotechnology (‘synthetic biology’, gene editing, nanotechnologies etc.) and the rapid diffusion of knowledge, raise proliferation concerns of biological weapons by non-state actors.

Thus, there is an urgent need to develop measures intended to enhance diagnostic, prophylactic and therapeutic capabilities and capacities to improve the ability of society to combat infectious diseases outbreaks, as well as to alleviate the effects of bioterrorism attacks.

We present here two examples of biotechnology usage for biodefence purposes: (i) plants as biofactories for the rapid production of improved biopharmaceuticals (‘Plant Molecular Farming’), and (ii) plant sequences as immune-modulating agents to enhance the efficacy of genetic vaccines.

These platforms represent two promising (and complementary) approaches for the rapid and low-cost production of countermeasures (diagnostics and vaccine candidates) against emerging, re-emerging and bioterrorism-related infections.

Expression optimization of a cell membrane-penetrating human papillomavirus type 16 therapeutic vaccine candidate in Nicotiana benthamiana

High-risk human papillomaviruses (hr-HPVs) cause cervical cancer, the fourth most common cancer in women worldwide. A HPV-16 candidate therapeutic vaccine, LALF32-51-E7, was developed by fusing a modified E7 protein to a bacterial cell-penetrating peptide (LALF): this elicited both tumour protection and regression in pre-clinical immunization studies. In the current study, we investigated the potential for producing LALF32-51-E7 in a plant expression system by evaluating the effect of subcellular localization and usage of different expression vectors and gene silencing suppressors. The highest expression levels of LALF32-51-E7 were obtained by using a self-replicating plant expression vector and chloroplast targeting, which increased its accumulation by 27-fold compared to cytoplasmic localization. The production and extraction of LALF32-51-E7 was scaled-up and purification optimized by affinity chromatography. If further developed, this platform could potentially allow for the production of a more affordable therapeutic vaccine for HPV-16. This would be extremely relevant in the context of developing countries, where cervical cancer and other HPV-related malignancies are most prevalent, and where the population have limited or no access to preventative vaccines due to their typical high costs.

Plant Virus Expression Vectors: A Powerhouse for Global Health

Plant-made biopharmaceuticals have long been considered a promising technology for providing inexpensive and efficacious medicines for developing countries, as well as for combating pandemic infectious diseases and for use in personalized medicine. Plant virus expression vectors produce high levels of pharmaceutical proteins within a very short time period. Recently, plant viruses have been employed as nanoparticles for novel forms of cancer treatment. This review provides a glimpse into the development of plant virus expression systems both for pharmaceutical production as well as for immunotherapy.

Reconceptualizing cancer immunotherapy based on plant production systems

Plants can be used as inexpensive and facile production platforms for vaccines and other biopharmaceuticals. More recently, plant-based biologics have expanded to include cancer immunotherapy agents. The following review describes the current state of the art for plant-derived strategies to prevent or reduce cancers. The review discusses avenues taken to prevent infection by oncogenic viruses, solid tumors and lymphomas. Strategies including cancer vaccines, monoclonal antibodies and virus nanoparticles are described, and examples are provided. The review ends with a discussion of the implications of plant-based cancer immunotherapy for developing countries.

Cancer immunotherapy has made great strides over recent years. This review describes the use of plants as production systems to produce biopharmaceuticals such as vaccines and antibodies to treat a wide variety of cancers. The use of nanoparticle technology based on plant viruses as a novel strategy to target and combat cancers is also included. The review concludes with a discussion of plant production platforms and their relevance for the generation of cheap and effective cancer immunotherapies for developing countries.

Production of Recombinant Anti-Cancer Vaccines in Plants

Plant expression systems have been developed to produce anti-cancer vaccines. Plants have several advantages as bioreactors for the production of subunit vaccines: they are considered safe, and may be used to produce recombinant proteins at low production cost. However, several technical issues hinder large-scale production of anti-cancer vaccines in plants. The present review covers design strategies to enhance the immunogenicity and therapeutic potency of anti-cancer vaccines, methods to increase vaccine-expressing plant biomass, and challenges facing the production of anti-cancer vaccines in plants. Specifically, the issues such as low expression levels and plant-specific glycosylation are described, along with their potential solutions.

A plant protein signal sequence improved humoral immune response to HPV prophylactic and therapeutic DNA vaccines

Signal sequences (ss) play a critical role in the sorting of nascent secretory and membrane proteins. This function has been conserved from bacteria through eukaryotes, although ss appear diverse in length and amino acid composition. Sorting of proteins is also critical to instruct antigens for a proper immunological response. Thus, a plant ss was used to drive Human Papillomavirus (HPV) model antigens into the human secretory pathway: the HPV16 E7 oncoprotein, its chimera with the coat protein (CP) of the Potato Virus X (PVX), the first 200 amino acids of the HPV16 minor capsid protein L2 (known to harbour cross-reacting epitopes) and its chimera with E7 gene. These genes were used to transfect HEK-293 cells and to immunize C57BL/6 mice. The ss-provided genes were expressed, and proteins detected by immunofluorescence and immunoblotting. Mouse immunization with DNA constructs carrying the ss elicited a strong humoral response against both E7 and L2 and a weak cell-mediated immunity. To our knowledge this is the first demonstration that a signal sequence derived from a plant can modulate the sorting of a heterologous protein in mammalian cells. This activity in mammalian cells may be responsible for the observed increased humoral response to DNA-based vaccines that are generally weak inducers of IgG response. This might open new perspectives in the design of DNA vaccines, especially to counteract infections where a strong humoral response is needed.

The Last Ten Years of Advancements in Plant-Derived Recombinant Vaccines against Hepatitis B

Disease prevention through vaccination is considered to be the greatest contribution to public health over the past century. Every year more than 100 million children are vaccinated with the standard World Health Organization (WHO)-recommended vaccines including hepatitis B (HepB). HepB is the most serious type of liver infection caused by the hepatitis B virus (HBV), however, it can be prevented by currently available recombinant vaccine, which has an excellent record of safety and effectiveness. To date, recombinant vaccines are produced in many systems of bacteria, yeast, insect, and mammalian and plant cells. Among these platforms, the use of plant cells has received considerable attention in terms of intrinsic safety, scalability, and appropriate modification of target proteins. Research groups worldwide have attempted to develop more efficacious plant-derived vaccines for over 30 diseases, most frequently HepB and influenza. More inspiring, approximately 12 plant-made antigens have already been tested in clinical trials, with successful outcomes. In this study, the latest information from the last 10 years on plant-derived antigens, especially hepatitis B surface antigen, approaches are reviewed and breakthroughs regarding the weak points are also discussed.

Plant virus nanoparticles: new applications and new benefits

For over two decades now, plants have been explored for their potential to act as production platforms for biopharmaceuticals, such as vaccines and monoclonal antibodies. More recently, plant viruses have been designed as nontoxic nanoparticles that can target a variety of cancers and thus empower the immune system to slow or even reverse tumor progression. The following paper describes the employment of plant virus expression vectors for the treatment of some of the most challenging diseases known today. The paper concludes with a projection of the multiple avenues by which virus nanoparticles could impact developing countries.

Immunotherapy of HPV-associated cancer: DNA/plant-derived vaccines and new orthotopic mouse models

Under the optimistic assumption of high-prophylactic HPV vaccine coverage, a significant reduction of cancer incidence can only be expected after decades. Thus, immune therapeutic strategies are needed for persistently infected individuals who do not benefit from the prophylactic vaccines. However, the therapeutic strategies inducing immunity to the E6 and/or E7 oncoprotein of HPV16 are more effective for curing HPV-expressing tumours in animal models than for treating human cancers. New strategies/technologies have been developed to improve these therapeutic vaccines. Our studies focussed on preparing therapeutic vaccines with low-cost technologies by DNA preparation fused to either plant-virus or plant-toxin genes, such as saporin, and by plant-produced antigens. In particular, plant-derived antigens possess an intrinsic adjuvant activity that makes these preparations especially attractive for future development. Additionally, discrepancy in vaccine effectiveness between animals and humans may be due to non-orthotopic localization of animal models. Orthotopic transplantation leads to tumours giving a more accurate representation of the parent tumour. Since HPV can cause cancer in two main localizations, anogenital and oropharynx area, we developed two orthotopic tumour mouse models in these two sites. Both models are bioluminescent in order to follow up the tumour growth by imaging and are induced by cell injection without the need to intervene surgically. These models were utilized for immunotherapies with genetic or plant-derived therapeutic vaccines. In particular, the head/neck orthotopic model appears to be very promising for studies combining chemo-radio-immune therapy that seems to be very effective in patients.

The potential of plants for the production and delivery of human papillomavirus vaccines

The available vaccines against human papillomavirus have some limitations such as low coverage due to their high cost, reduced immune coverage and the lack of therapeutic effects. Recombinant vaccines produced in plants (genetically engineered using stable or transient expression systems) offer the possibility to obtain low cost, efficacious and easy to administer vaccines. The status on the development of plant-based vaccines against human papillomavirus is analyzed and placed in perspective in this review. Some candidates have been characterized at a preclinical level with interesting outcomes. However, there is a need to perform the immunological characterization of several vaccine prototypes, especially through the oral administration route, as well as develop new candidates based on new chimeric designs intended to provide broader immunoprotection and therapeutic activity.

Transient plant transformation mediated by Agrobacterium tumefaciens: Principles, methods and applications

Agrobacterium tumefaciens is widely used as a versatile tool for development of stably transformed model plants and crops. However, the development of Agrobacterium based transient plant transformation methods attracted substantial attention in recent years. Transient transformation methods offer several applications advancing stable transformations such as rapid and scalable recombinant protein production and in planta functional genomics studies. Herein, we highlight Agrobacterium and plant genetics factors affecting transfer of T-DNA from Agrobacterium into the plant cell nucleus and subsequent transient transgene expression. We also review recent methods concerning Agrobacterium mediated transient transformation of model plants and crops and outline key physical, physiological and genetic factors leading to their successful establishment. Of interest are especially Agrobacterium based reverse genetics studies in economically important crops relying on use of RNA interference (RNAi) or virus-induced gene silencing (VIGS) technology. The applications of Agrobacterium based transient plant transformation technology in biotech industry are presented in thorough detail. These involve production of recombinant proteins (plantibodies, vaccines and therapeutics) and effectoromics-assisted breeding of late blight resistance in potato. In addition, we also discuss biotechnological potential of recombinant GFP technology and present own examples of successful Agrobacterium mediated transient plant transformations.

Current status of viral expression systems in plants and perspectives for oral vaccines development

During the last 25 years, the technology to produce recombinant vaccines in plant cells has evolved from modest proofs of the concept to viable technologies adopted by some companies due to significant improvements in the field. Viral-based expression strategies have importantly contributed to this success owing to high yields, short production time (which is in most cases free of tissue culture steps), and the implementation of confined processes for production under GMPs. Herein the distinct expression systems based on viral elements are analyzed. This review also presents the outlook on how these technologies have been successfully applied to the development of plant-based vaccines, some of them being in advanced stages of development. Perspectives on how viral expression systems could allow for the development of innovative oral vaccines constituted by minimally-processed plant biomass are discussed.

Plant-based vaccines against viruses

Plant-made or "biofarmed" viral vaccines are some of the earliest products of the technology of plant molecular farming, and remain some of the brightest prospects for the success of this field. Proofs of principle and of efficacy exist for many candidate viral veterinary vaccines; the use of plant-made viral antigens and of monoclonal antibodies for therapy of animal and even human viral disease is also well established. This review explores some of the more prominent recent advances in the biofarming of viral vaccines and therapies, including the recent use of ZMapp for Ebolavirus infection, and explores some possible future applications of the technology.

Anti-tumor effects of genetic vaccines against HPV major oncogenes

Expression of HPV E5, E6 and E7 oncogenes are likely to overcome the regulation of cell proliferation and to escape immunological control, allowing uncontrolled growth and providing the potential for malignant transformation. Thus, their three oncogenic products may represent ideal target antigens for immunotherapeutic strategies. In previous attempts, we demonstrated that genetic vaccines against recombinant HPV16 E7 antigen were able to affect the tumor growth in a pre-clinical mouse model. To improve this anti-HPV strategy we developed a novel approach in which we explored the effects of E5-based genetic immunization. We designed novel HPV16 E5 genetic vaccines based on two different gene versions: whole E5 gene and E5Multi. The last one is a long multi epitope gene designed as a harmless E5 version. Both E5 genes were codon optimized for mammalian expression. In addition, we demonstrated that HPV 16 E5 oncogene is expressed in C3 mouse cell line making it an elective model for the study of E5 based vaccine. In this mouse model the immunological and biological activity of the E5 vaccines were assessed in parallel with the activity of anti-E7 and anti-E6 vaccines already reported to be effective in an immunotherapeutic setting. These E7 and E6 vaccines were made with mutated oncogenes, the E7GGG mutant that does not bind pRb and the E6F47R mutant that is less effective in inhibiting p53, respectively. Results confirmed the immunological activity of genetic formulations based on attenuated HPV16 oncogenes and showed that E5-based genetic immunization provided notable anti-tumor effects.

Transgenic plants: a 5-year update on oral antipathogen vaccine development

The progressive interest in transgenic plants as advantageous platforms for the production and oral delivery of vaccines has led to extensive research and improvements in this technology over recent years. In this paper, the authors examine the most significant advances in this area, including novel approaches for higher yields and better containment, and the continued evaluation of new vaccine prototypes against several infectious diseases. The use of plants to deliver vaccine candidates against viruses, bacteria, and eukaryotic parasites within the last 5 years is discussed, focusing on innovative expression strategies and the immunogenic potential of new vaccines. A brief section on the state of the art in mucosal immunity is also included.

Human papillomavirus (HPV) type 16 E7 protein bodies cause tumour regression in mice

BACKGROUND

Human papillomaviruses (HPV) are the causative agents of cervical cancer in women, which results in over 250 000 deaths per year. Presently there are two prophylactic vaccines on the market, protecting against the two most common high-risk HPV types 16 and 18. These vaccines remain very expensive and are not generally affordable in developing countries where they are needed most. Additionally, there remains a need to treat women that are already infected with HPV, and who have high-grade lesions or cervical cancer.

METHODS

In this paper, we characterize the immunogenicity of a therapeutic vaccine that targets the E7 protein of the most prevalent high-risk HPV - type 16 - the gene which has previously been shown to be effective in DNA vaccine trials in mice. The synthetic shuffled HPV-16 E7 (16E7SH) has lost its transforming properties but retains all naturally-occurring CTL epitopes. This was genetically fused to Zera®, a self-assembly domain of the maize γ-zein able to induce the accumulation of recombinant proteins into protein bodies (PBs), within the endoplasmic reticulum in a number of expression systems.

RESULTS

High-level expression of the HPV 16E7SH protein fused to Zera® in plants was achieved, and the protein bodies could be easily and cost-effectively purified. Immune responses comparable to the 16E7SH DNA vaccine were demonstrated in the murine model, with the protein vaccine successfully inducing a specific humoral as well as cell mediated immune response, and mediating tumour regression.

CONCLUSIONS

The fusion of 16E7SH to the Zera® peptide was found to enhance the immune responses, presumably by means of a more efficient antigen presentation via the protein bodies. Interestingly, simply mixing the free PBs and 16E7SH also enhanced immune responses, indicating an adjuvant activity for the Zera® PBs.

Optimization and utilization of Agrobacterium-mediated transient protein production in Nicotiana

Agrobacterium-mediated transient protein production in plants is a promising approach to produce vaccine antigens and therapeutic proteins within a short period of time. However, this technology is only just beginning to be applied to large-scale production as many technological obstacles to scale up are now being overcome. Here, we demonstrate a simple and reproducible method for industrial-scale transient protein production based on vacuum infiltration of Nicotiana plants with Agrobacteria carrying launch vectors. Optimization of Agrobacterium cultivation in AB medium allows direct dilution of the bacterial culture in Milli-Q water, simplifying the infiltration process. Among three tested species of Nicotiana, N. excelsiana (N. benthamiana × N. excelsior) was selected as the most promising host due to the ease of infiltration, high level of reporter protein production, and about two-fold higher biomass production under controlled environmental conditions. Induction of Agrobacterium harboring pBID4-GFP (Tobacco mosaic virus-based) using chemicals such as acetosyringone and monosaccharide had no effect on the protein production level. Infiltrating plant under 50 to 100 mbar for 30 or 60 sec resulted in about 95% infiltration of plant leaf tissues. Infiltration with Agrobacterium laboratory strain GV3101 showed the highest protein production compared to Agrobacteria laboratory strains LBA4404 and C58C1 and wild-type Agrobacteria strains at6, at10, at77 and A4. Co-expression of a viral RNA silencing suppressor, p23 or p19, in N. benthamiana resulted in earlier accumulation and increased production (15-25%) of target protein (influenza virus hemagglutinin).

Immunologic treatments for precancerous lesions and uterine cervical cancer

Development of HPV-associated cancers not only depends on efficient negative regulation of cell cycle control that supports the accumulation of genetic damage, but also relies on immune evasion that enable the virus to go undetected for long periods of time. In this way, HPV-related tumors usually present MHC class I down-regulation, impaired antigen-processing ability, avoidance of T-cell mediated killing, increased immunosuppression due to Treg infiltration and secrete immunosuppressive cytokines. Thus, these are the main obstacles that immunotherapy has to face in the treatment of HPV-related pathologies where a number of different strategies have been developed to overcome them including new adjuvants. Although antigen-specific immunotherapy induced by therapeutic HPV vaccines was proved extremely efficacious in pre-clinical models, its progression through clinical trials suffered poor responses in the initial trials. Later attempts seem to have been more promising, particularly against the well-defined precursors of cervical, anal or vulvar cancer, where the local immunosuppressive milieu is less active. This review focuses on the advances made in these fields, highlighting several new technologies (such as mRNA vaccine, plant-derived vaccine). The most promising immunotherapies used in clinical trials are also summarized, along with integrated strategies, particularly promising in controlling tumor metastasis and in eliminating cancer cells altogether.

After the early promising clinical results, the development of therapeutic HPV vaccines need to be implemented and applied to the users in order to eradicate HPV-associated malignancies, eradicating existing perception (after the effectiveness of commercial preventive vaccines) that we have already solved the problem.

Plant-produced human recombinant erythropoietic growth factors support erythroid differentiation in vitro

Clinically available red blood cells (RBCs) for transfusions are at high demand, but in vitro generation of RBCs from hematopoietic stem cells requires significant quantities of growth factors. Here, we describe the production of four human growth factors: erythropoietin (EPO), stem cell factor (SCF), interleukin 3 (IL-3), and insulin-like growth factor-1 (IGF-1), either as non-fused proteins or as fusions with a carrier molecule (lichenase), in plants, using a Tobacco mosaic virus vector-based transient expression system. All growth factors were purified and their identity was confirmed by western blotting and peptide mapping. The potency of these plant-produced cytokines was assessed using TF1 cell (responsive to EPO, IL-3 and SCF) or MCF-7 cell (responsive to IGF-1) proliferation assays. The biological activity estimated here for the cytokines produced in plants was slightly lower or within the range cited in commercial sources and published literature. By comparing EC50 values of plant-produced cytokines with standards, we have demonstrated that all four plant-produced growth factors stimulated the expansion of umbilical cord blood-derived CD34+ cells and their differentiation toward erythropoietic precursors with the same potency as commercially available growth factors. To the best of our knowledge, this is the first report on the generation of all key bioactive cytokines required for the erythroid development in a cost-effective manner using a plant-based expression system.

A Chlamydomonas-derived Human Papillomavirus 16 E7 vaccine induces specific tumor protection

Background

The E7 protein of the Human Papillomavirus (HPV) type 16, being involved in malignant cellular transformation, represents a key antigen for developing therapeutic vaccines against HPV-related lesions and cancers. Recombinant production of this vaccine antigen in an active form and in compliance with good manufacturing practices (GMP) plays a crucial role for developing effective vaccines. E7-based therapeutic vaccines produced in plants have been shown to be active in tumor regression and protection in pre-clinical models. However, some drawbacks of in whole-plant vaccine production encouraged us to explore the production of the E7-based therapeutic vaccine in Chlamydomonas reinhardtii, an organism easy to grow and transform and fully amenable to GMP guidelines.

Methodology/Principal Findings

An expression cassette encoding E7GGG, a mutated, attenuated form of the E7 oncoprotein, alone or as a fusion with affinity tags (His6 or FLAG), under the control of the C. reinhardtii chloroplast psbD 5′ UTR and the psbA 3′ UTR, was introduced into the C. reinhardtii chloroplast genome by homologous recombination. The protein was mostly soluble and reached 0.12% of total soluble proteins. Affinity purification was optimized and performed for both tagged forms. Induction of specific anti-E7 IgGs and E7-specific T-cell proliferation were detected in C57BL/6 mice vaccinated with total Chlamydomonas extract and with affinity-purified protein. High levels of tumor protection were achieved after challenge with a tumor cell line expressing the E7 protein.

Conclusions

The C. reinhardtii chloroplast is a suitable expression system for the production of the E7GGG protein, in a soluble, immunogenic form. The production in contained and sterile conditions highlights the potential of microalgae as alternative platforms for the production of vaccines for human uses.

Immunotherapy in new pre-clinical models of HPV-associated oral cancers

Cervical, anal, penile and a sub-set of head and neck (HN) tumors are critical health problems caused by high risk Human Papilloma Viruses (HPVs), like HPV type 16. No specific/effective pharmacological treatments exist. A valid preventive vaccination as well as the immunotherapy of persistent infections, pre-cancerous lesions or early-stage cancers could drive the HPV disease burden down. These treatments might be featured through low-cost platforms like those based on DNA and plant biotechnologies to produce tailored and enhanced formulations taking profit from the use of plants as bio-factories and as a source of immune-stimulators. Finally, and regardless of the formulation type, pre-clinical tests and models are crucial to foresee efficacy of immunotherapy before clinical trials.   In this study, we created an orthotopic mouse model for HPV-related oral tumors, a subset of HN tumors for which no models have been generated before. The model was obtained by inducing the stable expression of the HPV16 E7 protein into the mouse oral squamous cell carcinoma (OSCC) AT-84 (AT-84 E7). The AT-84 E7 cells were injected into the mouth pavement of C3H mice via an extra-oral route to obtain orthotopic tumors. The model turned out to mimic the natural history of the human HPV oral cancer. From AT-84 E7, through engineering to express luciferase, the bioluminescent AT-84 E7-Luc cells were obtained for a fast and easy monitoring by imaging. The AT-84 E7 and the AT-84 E7-Luc tumors were used to test the efficacy of E7-based therapeutic vaccines that we had previously generated and that had been already proven to be active in mice against non-orthotopic E7-expressing tumors (TC-1 cells). In particular, we used genetic and plant-derived formulations based on attenuated HPV16 E7 variants either fused to plant virus genes with immunological activity or produced by tobacco plants. Mice were monitored by imaging allowing to test the size reduction of the mouth implanted experimental tumors in function of the different regimens used. The proposed tumor model is easy to handle and to reproduce and it is efficacious in monitoring immunotherapy. Furthermore, it is expected to be more predictive of clinical outcome of therapeutic vaccines than non-orthotopic models that are currently used. Finally, imaging offers unique opportunities to predict formulation efficacy through measuring tumor growth in vivo.

Plant virus expression vectors set the stage as production platforms for biopharmaceutical proteins

Transgenic plants present enormous potential as a cost-effective and safe platform for large-scale production of vaccines and other therapeutic proteins. A number of different technologies are under development for the production of pharmaceutical proteins from plant tissues. One method used to express high levels of protein in plants involves the employment of plant virus expression vectors. Plant virus vectors have been designed to carry vaccine epitopes as well as full therapeutic proteins such as monoclonal antibodies in plant tissue both safely and effectively. Biopharmaceuticals such as these offer enormous potential on many levels, from providing relief to those who have little access to modern medicine, to playing an active role in the battle against cancer. This review describes the current design and status of plant virus expression vectors used as production platforms for biopharmaceutical proteins.

Plant viral vectors for delivery by Agrobacterium

Plant viral vectors delivered by Agrobacterium are the basis of several manufacturing processes that are currently in use for producing a wide range of proteins for multiple applications, including vaccine antigens, antibodies, protein nanoparticles such as virus-like particles (VLPs), and other protein and protein-RNA scaffolds. Viral vectors delivered by agrobacterial T-DNA transfer (magnifection) have also become important tools in research. In recent years, essential advances have been made both in the development of second-generation vectors designed using the 'deconstructed virus' approach, as well as in the development of upstream manufacturing processes that are robust and fully scalable. The strategy relies on Agrobacterium as a vector to deliver DNA copies of one or more viral RNA/DNA replicons; the bacteria are delivered into leaves by vacuum infiltration, and the viral machinery takes over from the point of T-DNA transfer to the plant cell nucleus, driving massive RNA and protein production and, if required, cell-to-cell spread of the replicons. Among the most often used viral backbones are those of the RNA viruses Tobacco mosaic virus (TMV), Potato virus X (PVX) and Cowpea mosaic virus (CPMV), and the DNA geminivirus Bean yellow dwarf virus. Prototypes of industrial processes that provide for high yield, rapid scale up and fast manufacturing cycles have been designed, and several GMP-compliant and GMP-certified manufacturing facilities are in place. These efforts have been successful as evidenced by the fact that several antibodies and vaccine antigens produced by magnifection are currently in clinical development.

Efficient expression of Human papillomavirus 16 E7 oncoprotein fused to C-terminus of Tobacco mosaic virus (TMV) coat protein using molecular chaperones in Escherichia coli

The Human papillomavirus 16 (HPV16) E7 oncoprotein is a promising candidate for development of anti-cancer therapeutic vaccine. We have prepared the expression construct carrying mutagenized E7 oncoprotein fused to the C-terminus of Tobacco mosaic virus (TMV) coat protein via 15 amino acids β-sheet linker. The fusion protein was expressed in Escherichia coli MC 1061 cells. We have obtained high level expression, but most of the protein remained in insoluble inclusion bodies. To increase the ratio of soluble protein various molecular chaperones (TF, DnaK-DnaJ-GrpE, GroEL-GroES) were used. The immunological reactivity of expressed recombinant protein was evaluated with anti-E7 and anti-TMV antibodies. The distribution of expressed product during ultracentrifugation on sucrose gradient was studied.

Transient expression of Human papillomavirus type 16 L2 epitope fused to N- and C-terminus of coat protein of Potato virus X in plants

Transient expression of foreign genes based on plant viral vectors is a suitable system for the production of relevant immunogens that can be used for the development of a new generation of vaccines against a variety of infectious diseases. In the present study the epitope derived from HPV-16 L2 minor capsid protein (amino acids 108-120) was expressed from Potato virus X (PVX)-based vector pGR106 as N- or C-terminal fusion with the PVX coat protein (PVX CP) in transgenic Nicotiana benthamiana plants. The fusion protein L2 108-120-PVX CP was successfully expressed in plants at a level of 170 mg/kg of fresh leaf tissue. The C-terminal fusion protein PVX CP- L2 108-120 was expressed using mutated vector sequence to avoid homologous recombination at a level of 8 mg/kg of fresh leaf tissue. Immunogenicity of L2 108-120-PVX CP virus-like particles was tested after immunization of mice by subcutaneous injection or tattoo administration. In animal sera the antibodies against the PVX CP and the L2 108-120 epitope were found after both methods of vaccine delivery.

Extraction, purification and characterization of the plant-produced HPV16 subunit vaccine candidate E7 GGG

Several studies indicated that biopharmaceuticals based on the recombinant protein E7 of human papillomavirus (HPV) can serve as therapeutic vaccines preventing the development of cancer in women infected with high-risk types of HPV such as HPV16. Here, we report effective extraction and purification of a plant-produced E7GGG-lichenase fusion protein, an HPV16 subunit vaccine candidate, from Nicotiana benthamiana plants, to a high yield. The target contains the modified HPV16 E7 protein internally fused to the surface loop of a truncated, hexa-His- and KDEL-tagged variant of bacterial lichenase, and has been previously shown to possess anti-cancer activity in an animal model. We purified the protein using a combination of immobilized metal-ion affinity chromatography and gel filtration. The achieved purity of the final product was 99% as confirmed by Coomassie or SYPRO Ruby staining after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by analytical size exclusion chromatography coupled with multi-angle laser light scattering. The overall yield was 50% corresponding to 0.1g of protein per 1 kg plant biomass. Only slight changes in these parameters were observed during the process scale-up from 50 g to 1 kg of processed leaf biomass.

Two decades of plant-based candidate vaccines: a review of the chimeric protein approaches

Genetic engineering revolutionized the concept of traditional vaccines since subunit vaccines became reality. Additionally, over the past two decades plant-derived antigens have been studied as potential vaccines with several advantages, including low cost and convenient administration. More specifically, genetic fusions allowed the expression of fusion proteins carrying two or more components with the aim to elicit immune responses against different targets, including antigens from distinct pathogens or strains. This review aims to provide an update in the field of the production of plant-based vaccine, focusing on those approaches based on the production of chimeric proteins comprising antigens from human pathogens, emphasizing the case of cholera toxin/E. coli enterotoxin fusions, chimeric viruses like particles approaches as well as the possible use of adjuvant-producing plants as expression hosts. Challenges for the near future in this field are also discussed.

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.