Cost-effective production of a vaginal protein microbicide to prevent HIV transmission

Production of Plant-Derived Japanese Encephalitis Virus Multi-Epitope Peptide in Nicotiana benthamiana and Immunological Response in Mice

The current production of the Japanese encephalitis virus (JEV) vaccine is based on animal cells, where various risk factors for human health should be resolved. This study used a transient expression system to express the chimeric protein composed of antigenic epitopes from the JEV envelope (E) protein in Nicotiana benthamiana. JEV multi-epitope peptide (MEP) sequences fused with FLAG-tag or 6× His-tag at the C- or N-terminus for the purification were introduced into plant expression vectors and used for transient expression. Among the constructs, vector pSK480, which expresses MEP fused with a FLAG-tag at the C-terminus, showed the highest level of expression and yield in purification. Optimization of transient expression procedures further improved the target protein yield. The purified MEP protein was applied to an ICR mouse and successfully induced an antibody against JEV, which demonstrates the potential of the plant-produced JEV MEP as an alternative vaccine candidate.

Development of a facile genetic transformation system for the Spanish elite rice paella genotype Bomba

We report the development of an efficient and reproducible genetic transformation system for the recalcitrant Spanish elite rice paella genotype, Bomba. Preconditioned embryos derived from dry seeds were bombarded with gold particles carrying a plasmid containing a screenable and a selectable marker. We confirmed integration and expression of hpt and gusA in the rice genome. Transformation frequency was ca: 10% in several independent experiments. We show Mendelian inheritance of the input transgenes and zygosity determination of the transgenic lines in the T1 generation. A unique and critical step for the regeneration of plants from transformed tissue was shading during the early stages of regeneration, combined with a specific cytokinin:auxin ration at the onset of shifting callus to regeneration media.

Nicotiana spp. for the Expression and Purification of Functional IgG3 Antibodies Directed Against the Staphylococcus aureus Alpha Toxin

Immunoglobulin subclass IgG1 is bound and neutralized effectively by Staphylococcus aureus protein A, allowing the bacterium to evade the host’s adaptive immune response. In contrast, the IgG3 subclass is not bound by protein A and can be used to treat S. aureus infections, including drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA). However, the yields of recombinant IgG3 are generally low because this subclass is prone to degradation, and recovery is hindered by the inability to use protein A as an affinity ligand for antibody purification. Here, we investigated plants (Nicotiana spp.) as an alternative to microbes and mammalian cell cultures for the production of an IgG3 antibody specific for the S. aureus alpha toxin. We targeted recombinant IgG3 to different subcellular compartments and tested different chromatography conditions to improve recovery and purification. Finally, we tested the antigen-binding capacity of the purified antibodies. The highest IgG3 levels in planta (>130 mg kg−1 wet biomass) were achieved by targeting the endoplasmic reticulum or apoplast. Although the purity of IgG3 exceeded 95% following protein G chromatography, product recovery requires further improvement. Importantly, the binding affinity of the purified antibodies was in the nanomolar range and thus comparable to previous studies using murine hybridoma cells as the production system.

Affordable oral health care: dental biofilm disruption using chloroplast made enzymes with chewing gum delivery

Current approaches for oral health care rely on procedures that are unaffordable to impoverished populations, whereas aerosolized droplets in the dental clinic and poor oral hygiene may contribute to spread of several infectious diseases including COVID-19, requiring new solutions for dental biofilm/plaque treatment at home. Plant cells have been used to produce monoclonal antibodies or antimicrobial peptides for topical applications to decrease colonization of pathogenic microbes on dental surface. Therefore, we investigated an affordable method for dental biofilm disruption by expressing lipase, dextranase or mutanase in plant cells via the chloroplast genome. Antibiotic resistance gene used to engineer foreign genes into the chloroplast genome were subsequently removed using direct repeats flanking the aadA gene and enzymes were successfully expressed in marker-free lettuce transplastomic lines. Equivalent enzyme units of plant-derived lipase performed better than purified commercial enzymes against biofilms, specifically targeting fungal hyphae formation. Combination of lipase with dextranase and mutanase suppressed biofilm development by degrading the biofilm matrix, with concomitant reduction of bacterial and fungal accumulation. In chewing gum tablets formulated with freeze-dried plant cells, expressed protein was stable up to 3 years at ambient temperature and was efficiently released in a time-dependent manner using a mechanical chewing simulator device. Development of edible plant cells expressing enzymes eliminates the need for purification and cold-chain transportation, providing a potential translatable therapeutic approach. Biofilm disruption through plant enzymes and chewing gum-based delivery offers an effective and affordable dental biofilm control at home particularly for populations with minimal oral care access.

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.

Combating Human Viral Diseases: Will Plant-Based Vaccines Be the Answer?

Molecular pharming or the technology of application of plants and plant cell culture to manufacture high-value recombinant proteins has progressed a long way over the last three decades. Whether generated in transgenic plants by stable expression or in plant virus-based transient expression systems, biopharmaceuticals have been produced to combat several human viral diseases that have impacted the world in pandemic proportions. Plants have been variously employed in expressing a host of viral antigens as well as monoclonal antibodies. Many of these biopharmaceuticals have shown great promise in animal models and several of them have performed successfully in clinical trials. The current review elaborates the strategies and successes achieved in generating plant-derived vaccines to target several virus-induced health concerns including highly communicable infectious viral diseases. Importantly, plant-made biopharmaceuticals against hepatitis B virus (HBV), hepatitis C virus (HCV), the cancer-causing virus human papillomavirus (HPV), human immunodeficiency virus (HIV), influenza virus, zika virus, and the emerging respiratory virus, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) have been discussed. The use of plant virus-derived nanoparticles (VNPs) and virus-like particles (VLPs) in generating plant-based vaccines are extensively addressed. The review closes with a critical look at the caveats of plant-based molecular pharming and future prospects towards further advancements in this technology. The use of biopharmed viral vaccines in human medicine and as part of emergency response vaccines and therapeutics in humans looks promising for the near future.

COVID-19 Crisis: How Can Plant Biotechnology Help?

The emergence of the COVID-19 pandemic has led to significant public health crisis all over the world. The rapid spreading nature and high mortality rate of COVID-19 places a huge pressure on scientists to develop effective diagnostics and therapeutics to control the pandemic. Some scientists working on plant biotechnology together with commercial enterprises for the emergency manufacturing of diagnostics and therapeutics have aimed to fulfill the rapid demand for SARS-CoV-2 protein antigen and antibody through a rapid, scalable technology known as transient/stable expression in plants. Plant biotechnology using transient/stable expression offers a rapid solution to address this crisis through the production of low-cost diagnostics, antiviral drugs, immunotherapy, and vaccines. Transient/stable expression technology for manufacturing plant-based biopharmaceuticals is already established at commercial scale. Here, current opinions regarding how plant biotechnology can help fight against COVID-19 through the production of low-cost diagnostics and therapeutics are discussed.

Isolation and light chain shuffling of a Plasmodium falciparum AMA1-specific human monoclonal antibody with growth inhibitory activity

Background

Plasmodium falciparum, the parasite causing malaria, affects populations in many endemic countries threatening mainly individuals with low malaria immunity, especially children. Despite the approval of the first malaria vaccine Mosquirix™ and very promising data using cryopreserved P. falciparum sporozoites (PfSPZ), further research is needed to elucidate the mechanisms of humoral immunity for the development of next-generation vaccines and alternative malaria therapies including antibody therapy. A high prevalence of antibodies against AMA1 in immune individuals has made this antigen one of the major blood-stage vaccine candidates.

Material and methods

Using antibody phage display, an AMA1-specific growth inhibitory human monoclonal antibody from a malaria-immune Fab library using a set of three AMA1 diversity covering variants (DiCo 1–3), which represents a wide range of AMA1 antigen sequences, was selected. The functionality of the selected clone was tested in vitro using a growth inhibition assay with P. falciparum strain 3D7. To potentially improve affinity and functional activity of the isolated antibody, a phage display mediated light chain shuffling was employed. The parental light chain was replaced with a light chain repertoire derived from the same population of human V genes, these selected antibodies were tested in binding tests and in functionality assays.

Results

The selected parental antibody achieved a 50% effective concentration (EC₅₀) of 1.25 mg/mL. The subsequent light chain shuffling led to the generation of four derivatives of the parental clone with higher expression levels, similar or increased affinity and improved EC₅₀ against 3D7 of 0.29 mg/mL. Pairwise epitope mapping gave evidence for binding to AMA1 domain II without competing with RON2.

Conclusion

We have thus shown that a compact immune human phage display library is sufficient for the isolation of potent inhibitory monoclonal antibodies and that minor sequence mutations dramatically increase expression levels in Nicotiana benthamiana. Interestingly, the antibody blocks parasite inhibition independently of binding to RON2, thus having a yet undescribed mode of action.

Potential Applications of Plant Biotechnology against SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus responsible for an ongoing human pandemic (COVID-19). There is a massive international effort underway to develop diagnostic reagents, vaccines, and antiviral drugs in a bid to slow down the spread of the disease and save lives. One part of that international effort involves the research community working with plants, bringing researchers from all over the world together with commercial enterprises to achieve the rapid supply of protein antigens and antibodies for diagnostic kits, and scalable production systems for the emergency manufacturing of vaccines and antiviral drugs. Here, we look at some of the ways in which plants can and are being used in the fight against COVID-19.

Steric Accessibility of the Cleavage Sites Dictates the Proteolytic Vulnerability of the Anti-HIV-1 Antibodies 2F5, 2G12, and PG9 in Plants

Broadly neutralizing antibodies (bNAbs) to human immunodeficiency virus type 1 (HIV-1) hold great promise for immunoprophylaxis and the suppression of viremia in HIV-positive individuals. Several studies have demonstrated that plants as Nicotiana benthamiana are suitable hosts for the generation of protective anti-HIV-1 antibodies. However, the production of the anti-HIV-1 bNAbs 2F5 and PG9 in N. benthamiana is associated with their processing by apoplastic proteases in the complementarity-determining-region (CDR) H3 loops of the heavy chains. Here, it is shown that apoplastic proteases can also cleave the CDR H3 loop of the bNAb 2G12 when the unusual domain exchange between its heavy chains is prevented by the replacement of Ile19 with Arg. It is demonstrated that CDR H3 proteolysis leads to a strong reduction of the antigen-binding potencies of 2F5, PG9, and 2G12-I19R. Inhibitor profiling experiments indicate that different subtilisin-like serine proteases account for bNAb fragmentation in the apoplast. Differential scanning calorimetry experiments corroborate that the antigen-binding domains of wild-type 2G12 and 4E10 are more compact than those of proteolysis-sensitive antibodies, thus shielding their CDR H3 regions from proteolytic attack. This suggests that the extent of proteolytic inactivation of bNAbs in plants is primarily dictated by the steric accessibility of their CDR H3 loops.

Molecular farming - The slope of enlightenment

Molecular farming can be defined as the use of plants to produce recombinant protein products. The technology is now >30 years old. The early promise of molecular farming was based on three perceived advantages: the low costs of growing plants, the immense scalability of agricultural production, and the inherent safety of plants as hosts for the production of pharmaceuticals. This resulted in a glut of research publications in which diverse proteins were expressed in equally diverse plant-based systems, and numerous companies were founded hoping to commercialize the new technology. There was a moderate degree of success for companies producing non-pharmaceutical proteins, but in the pharmaceutical sector the anticipation raised by promising early research was soon met by the cold hard reality of industrial pragmatism. Plants did not have a track record of success in pharmaceutical protein manufacturing, lacked a regulatory framework, and did not perform as well as established industry platforms. Negative attitudes towards genetically modified plants added to the mix. By the early 2000s, major industry players started to lose interest and pharmaceutical molecular farming fell from a peak of expectation into a trough of disillusionment, just as predicted by the Gartner hype cycle. But many of the pioneers of molecular farming have refocused their activities and have worked to address the limitations that hampered the first generation of technologies. The field has now consolidated around a smaller number of better-characterized platforms and has started to develop standardized methods and best practices, mirroring the evolution of more mature industry sectors. Likewise, attention has turned from proof-of-principle studies to realistic techno-economic modeling to capture significant niche markets, replicating the success of the industrial molecular farming sector. Here we argue that these recent developments signify that pharmaceutical molecular farming is now climbing the slope of enlightenment and will soon emerge as a mature technology.

Unexpected synergistic HIV neutralization by a triple microbicide produced in rice endosperm

Our paper provides an approach for the durable deployment of anti-HIV agents in the developing world. We developed a transgenic rice line expressing three microbicidal proteins (the HIV-neutralizing antibody 2G12 and the lectins griffithsin and cyanovirin-N). Simultaneous expression in the same plant allows the crude seed extract to be used directly as a topical microbicide cocktail, avoiding the costs of multiple downstream processes. This groundbreaking strategy is realistically the only way that microbicidal cocktails can be manufactured at a cost low enough for the developing world, where HIV prophylaxis is most in demand.

The transmission of HIV can be prevented by the application of neutralizing monoclonal antibodies and lectins. Traditional recombinant protein manufacturing platforms lack sufficient capacity and are too expensive for developing countries, which suffer the greatest disease burden. Plants offer an inexpensive and scalable alternative manufacturing platform that can produce multiple components in a single plant, which is important because multiple components are required to avoid the rapid emergence of HIV-1 strains resistant to single microbicides. Furthermore, crude extracts can be used directly for prophylaxis to avoid the massive costs of downstream processing and purification. We investigated whether rice could simultaneously produce three functional HIV-neutralizing proteins (the monoclonal antibody 2G12, and the lectins griffithsin and cyanovirin-N). Preliminary in vitro tests showed that the cocktail of three proteins bound to gp120 and achieved HIV-1 neutralization. Remarkably, when we mixed the components with crude extracts of wild-type rice endosperm, we observed enhanced binding to gp120 in vitro and synergistic neutralization when all three components were present. Extracts of transgenic plants expressing all three proteins also showed enhanced in vitro binding to gp120 and synergistic HIV-1 neutralization. Fractionation of the rice extracts suggested that the enhanced gp120 binding was dependent on rice proteins, primarily the globulin fraction. Therefore, the production of HIV-1 microbicides in rice may not only reduce costs compared to traditional platforms but may also provide functional benefits in terms of microbicidal potency.

Platforms for Plant-Based Protein Production

Plant molecular farming depends on a diversity of plant systems for production of useful recombinant proteins. These proteins include protein biopolymers, industrial proteins and enzymes, and therapeutic proteins. Plant production systems include microalgae, cells, hairy roots, moss, and whole plants with both stable and transient expression. Production processes involve a narrowing diversity of bioreactors for cell, hairy root, microalgae, and moss cultivation. For whole plants, both field and automated greenhouse cultivation methods are used with products expressed and produced either in leaves or seeds. Many successful expression systems now exist for a variety of different products with a list of increasingly successful commercialized products. This chapter provides an overview and examples of the current state of plant-based production systems for different types of recombinant proteins.

Glyco-Engineering of Plant-Based Expression Systems

Most secreted proteins in eukaryotes are glycosylated, and after a number of common biosynthesis steps the glycan structures mature in a species-dependent manner. Therefore, human therapeutic proteins produced in plants often carry plant-like rather than human-like glycans, which can affect protein stability, biological function, and immunogenicity. The glyco-engineering of plant-based expression systems began as a strategy to eliminate plant-like glycans and produce human proteins with authentic or at least compatible glycan structures. The precise replication of human glycans is challenging, owing to the absence of a pathway in plants for the synthesis of sialylated proteins and the necessary precursors, but this can now be achieved by the coordinated expression of multiple human enzymes. Although the research community has focused on the removal of plant glycans and their replacement with human counterparts, the presence of plant glycans on proteins can also provide benefits, such as boosting the immunogenicity of some vaccines, facilitating the interaction between therapeutic proteins and their receptors, and increasing the efficacy of antibody effector functions. Graphical Abstract Typical structures of native mammalian and plant glycans with symbols indicating sugar residues identified by their short form and single-letter codes. Both glycans contain fucose, albeit with different linkages.

A Brief History of Promoter Development for Use in Transgenic Maize Applications

Promoters regulate gene expression, and are essential biotechnology tools. Since its introduction in the mid-1990s, biotechnology has greatly enhanced maize productivity primarily through the development of insect control and herbicide tolerance traits. Additional biotechnology applications include improving seed nutrient composition, industrial protein production, therapeutic production, disease resistance, abiotic stress resistance, and yield enhancement. Biotechnology has also greatly expanded basic research into important mechanisms that govern plant growth and reproduction. Many novel promoters have been developed to facilitate this work, but only a few are widely used. Transgene optimization includes a variety of strategies some of which effect promoter structure. Recent reviews examine the state of the art with respect to transgene design for biotechnology applications. This chapter examines the use of transgene technology in maize, focusing on the way promoters are selected and used. The impact of new developments in genomic technology on promoter structure is also discussed.

Pharmacokinetics and Preliminary Safety of Pod-Intravaginal Rings Delivering the Monoclonal Antibody VRC01-N for HIV Prophylaxis in a Macaque Model

The broadly neutralizing antibody (bNAb) VRC01, capable of neutralizing 91% of known human immunodeficiency virus type 1 (HIV-1) isolates in vitro, is a promising candidate microbicide for preventing sexual HIV infection when administered topically to the vagina; however, accessibility to antibody-based prophylactic treatment by target populations in sub-Saharan Africa and other underdeveloped regions may be limited by the high cost of conventionally produced antibodies and the limited capacity to manufacture such antibodies. Intravaginal rings of the pod design (pod-IVRs) delivering Nicotiana-manufactured VRC01 (VRC01-N) over a range of release rates have been developed. The pharmacokinetics and preliminary safety of VRC01-N pod-IVRs were evaluated in a rhesus macaque model. The devices sustained VRC01-N release for up to 21 days at controlled rates, with mean steady-state VRC01-N levels in vaginal fluids in the range of 10² to 10³ μg g^-1 being correlated with in vitro release rates. No adverse safety indications were observed. These findings indicate that pod-IVRs are promising devices for the delivery of the candidate topical microbicide VRC01-N against HIV-1 infection and merit further preclinical evaluation.

Fluorescence based real time monitoring of fouling in process chromatography

A real time monitoring of fouling in liquid chromatography has been presented. The versatility of the approach has been proven by successful implementation in three case studies with an error <1%. The first application demonstrates the monitoring of protein A ligand density and foulant concentration for assessing performance of protein A chromatography resin during purification of monoclonal antibodies. The observations have been supported from LC-MS/MS studies that were independently performed. The second application involves monitoring of foulant deposition during multimode cation exchange chromatography based purification of human serum albumin. Finally, in the third application, monitoring of foulants during multimodal hydrophobic interaction chromatography of recombinant human granulocyte colony stimulating factor is demonstrated. In all three cases, it is observed that the fluorescence intensity consistently increases with resin reuse as more foulants are deposited over time. The proposed approach can be readily used for real time monitoring of fouling and process control.

Affinity chromatography: A versatile technique for antibody purification

Antibodies continue to be extremely utilized entities in myriad applications including basic research, imaging, targeted delivery, chromatography, diagnostics, and therapeutics. At production stage, antibodies are generally present in complex matrices and most of their intended applications necessitate purification. Antibody purification has always been a major bottleneck in downstream processing of antibodies, due to the need of high quality products and associated high costs. Over the years, extensive research has focused on finding better purification methodologies to overcome this holdup. Among a plethora of different techniques, affinity chromatography is one of the most selective, rapid and easy method for antibody purification. This review aims to provide a detailed overview on affinity chromatography and the components involved in purification. An array of support matrices along with various classes of affinity ligands detailing their underlying working principles, together with the advantages and limitations of each system in purifying different types of antibodies, accompanying recent developments and important practical methodological considerations to optimize purification procedure are discussed.

Development of peptide inhibitors of HIV transmission

Treatment of HIV has long faced the challenge of high mutation rates leading to rapid development of resistance, with ongoing need to develop new methods to effectively fight the infection. Traditionally, early HIV medications were designed to inhibit RNA replication and protein production through small molecular drugs. Peptide based therapeutics are a versatile, promising field in HIV therapy, which continues to develop as we expand our understanding of key protein-protein interactions that occur in HIV replication and infection. This review begins with an introduction to HIV, followed by the biological basis of disease, current clinical management of the disease, therapeutics on the market, and finally potential avenues for improved drug development.

Biomanufacturing of protective antibodies and other therapeutics in edible plant tissues for oral applications

Although plant expression systems used for production of therapeutic proteins have the advantage of being scalable at a low price, the downstream processing necessary to obtain pure therapeutic molecules is as expensive as for the traditional Chinese hamster ovary (CHO) platforms. However, when edible plant tissues (EPTs) are used, there is no need for exhaustive purification, because they can be delivered orally as partially purified formulations that are safe for consumption. This economic benefit is especially interesting when high doses of recombinant proteins are required throughout the treatment/prophylaxis period, as is the case for antibodies used for oral passive immunization (OPI). The secretory IgA (SIgA) antibodies, which are highly abundant in the digestive tract and mucosal secretions, and thus the first choice for OPI, have only been successfully produced in plant expression systems. Here, we cover most of the up-to-date examples of EPT-produced pharmaceuticals, including two examples of SIgA aimed at oral delivery. We describe the benefits and drawbacks of delivering partially purified formulations and discuss a number of practical considerations and criteria to take into account when using plant expression systems, such as subcellular targeting, protein degradation, glycosylation patterns and downstream strategies, all crucial for improved yield, high quality and low cost of the final product.

Progress and Perspectives on HIV-1 microbicide development

The majority of HIV-1 infections occur via sexual intercourse. Women are the most affected by the epidemic, particularly in developing countries, due to their socio-economic dependence on men and the fact that they are often victims of gender based sexual violence. Despite significant efforts that resulted in the reduction of infection rates in some countries, there is still need for effective prevention methods against the virus. One of these methods for preventing sexual transmission in women is the use of microbicides. In this review we provide a summary of the progress made toward the discovery of affordable and effective HIV-1 microbicides and suggest future directions. We show that there is a wide range of compounds that have been proposed as potential microbicides. Although most of them have so far failed to show protection in humans, there are many promising ones currently in pre-clinical studies and in clinical trials.

Rice endosperm is cost-effective for the production of recombinant griffithsin with potent activity against HIV

Protein microbicides containing neutralizing antibodies and antiviral lectins may help to reduce the rate of infection with human immunodeficiency virus (HIV) if it is possible to manufacture the components in large quantities at a cost affordable in HIV-endemic regions such as sub-Saharan Africa. We expressed the antiviral lectin griffithsin (GRFT), which shows potent neutralizing activity against HIV, in the endosperm of transgenic rice plants (Oryza sativa), to determine whether rice can be used to produce inexpensive GRFT as a microbicide ingredient. The yield of (OS) GRFT in the best-performing plants was 223 μg/g dry seed weight. We also established a one-step purification protocol, achieving a recovery of 74% and a purity of 80%, which potentially could be developed into a larger-scale process to facilitate inexpensive downstream processing. (OS) GRFT bound to HIV glycans with similar efficiency to GRFT produced in Escherichia coli. Whole-cell assays using purified (OS) GRFT and infectivity assays using crude extracts of transgenic rice endosperm confirmed that both crude and pure (OS) GRFT showed potent activity against HIV and the crude extracts were not toxic towards human cell lines, suggesting they could be administered as a microbicide with only minimal processing. A freedom-to-operate analysis confirmed that GRFT produced in rice is suitable for commercial development, and an economic evaluation suggested that 1.8 kg/ha of pure GRFT could be produced from rice seeds. Our data therefore indicate that rice could be developed as an inexpensive production platform for GRFT as a microbicide component.

Antibody Production in Plants and Green Algae

Monoclonal antibodies (mAbs) have a wide range of modern applications, including research, diagnostic, therapeutic, and industrial uses. Market demand for mAbs is high and continues to grow. Although mammalian systems, which currently dominate the biomanufacturing industry, produce effective and safe recombinant mAbs, they have a limited manufacturing capacity and high costs. Bacteria, yeast, and insect cell systems are highly scalable and cost effective but vary in their ability to produce appropriate posttranslationally modified mAbs. Plants and green algae are emerging as promising production platforms because of their time and cost efficiencies, scalability, lack of mammalian pathogens, and eukaryotic posttranslational protein modification machinery. So far, plant- and algae-derived mAbs have been produced predominantly as candidate therapeutics for infectious diseases and cancer. These candidates have been extensively evaluated in animal models, and some have shown efficacy in clinical trials. Here, we review ongoing efforts to advance the production of mAbs in plants and algae.

Single-Step Purification and Characterization of A Recombinant Serine Proteinase Inhibitor from Transgenic Plants

Expression of recombinant therapeutic proteins in transgenic plants has a tremendous impact on safe and economical production of biomolecules for biopharmaceutical industry. The major limitation in their production is downstream processing of recombinant protein to obtain higher yield and purity of the final product. In this study, a simple and rapid process has been developed for purification of therapeutic recombinant α1-proteinase inhibitor (rα1-PI) from transgenic tomato plants, which is an abundant serine protease inhibitor in human serum and chiefly inhibits the activity of neutrophil elastase in lungs. We have expressed rα1-PI with modified synthetic gene in transgenic tomato plants at a very high level (≃3.2 % of total soluble protein). The heterologous protein was extracted with (NH4)2SO4 precipitation, followed by chromatographic separation on different matrices. However, only immunoaffinity chromatography resulted into homogenous preparation of rα1-PI with 54 % recovery. The plant-purified rα1-PI showed molecular mass and structural conformation comparable to native serum α1-PI, as shown by mass spectrometry and optical spectroscopy. The results of elastase inhibition assay revealed biological activity of the purified rα1-PI protein. This work demonstrates a simple and efficient one-step purification of rα1-PI from transgenic plants, which is an essential prerequisite for further therapeutic development.

Using Computational Modeling To Optimize the Design of Antibodies That Trap Viruses in Mucus

Immunoglobulin G (IgG) antibodies that trap viruses in cervicovaginal mucus (CVM) via adhesive interactions between IgG-Fc and mucins have recently emerged as a promising strategy to block vaginally transmitted infections. The array of IgG bound to a virus particle appears to trap the virus by making multiple weak affinity bonds to the fibrous mucins that form the mucus gel. However, the antibody characteristics that maximize virus trapping and minimize viral infectivity remain poorly understood. Toward this goal, we developed a mathematical model that takes into account physiologically relevant spatial dimensions and time scales, binding, and unbinding rates between IgG and virions and between IgG and mucins, as well as the respective diffusivities of virions and IgG in semen and CVM. We then systematically explored the IgG-antigen and IgG-mucin binding and unbinding rates that minimize the flux of infectious HIV arriving at the vaginal epithelium. Surprisingly, contrary to common intuition that infectivity would drop monotonically with increasing affinities between IgG and HIV, and between IgG and mucins, our model suggests maximal trapping of HIV and minimal flux of HIV to the epithelium are achieved with IgG molecules that exhibit (i) rapid antigen binding (high k_on) rather than very slow unbinding (low k_off), that is, high-affinity binding to the virion, and (ii) relatively weak affinity with mucins. These results provide important insights into the design of more potent "mucotrapping" IgG for enhanced protection against vaginally transmitted infections. The model is adaptable to other pathogens, mucosal barriers, geometries, and kinetic and diffusional effects, providing a tool for hypothesis testing and producing quantitative insights into the dynamics of immune-mediated protection.

Rice endosperm produces an underglycosylated and potent form of the HIV-neutralizing monoclonal antibody 2G12

Protein microbicides against HIV can help to prevent infection but they are required in large, repetitive doses. This makes current fermenter-based production systems prohibitively expensive. Plants are advantageous as production platforms because they offer a safe, economical and scalable alternative, and cereals such as rice are particularly attractive because they could allow pharmaceutical proteins to be produced economically and on a large scale in developing countries. Pharmaceutical proteins can also be stored as unprocessed seed, circumventing the need for a cold chain. Here, we report the development of transgenic rice plants expressing the HIV-neutralizing antibody 2G12 in the endosperm. Surprisingly for an antibody expressed in plants, the heavy chain was predominantly aglycosylated. Nevertheless, the heavy and light chains assembled into functional antibodies with more potent HIV-neutralizing activity than other plant-derived forms of 2G12 bearing typical high-mannose or plant complex-type glycans. Immunolocalization experiments showed that the assembled antibody accumulated predominantly in protein storage vacuoles but also induced the formation of novel, spherical storage compartments surrounded by ribosomes indicating that they originated from the endoplasmic reticulum. The comparison of wild-type and transgenic plants at the transcriptomic and proteomic levels indicated that endogenous genes related to starch biosynthesis were down-regulated in the endosperm of the transgenic plants, whereas genes encoding prolamin and glutaredoxin-C8 were up-regulated. Our data provide insight into factors that affect the functional efficacy of neutralizing antibodies in plants and the impact of recombinant proteins on endogenous gene expression.

Plant-Derived Monoclonal Antibodies for Prevention and Treatment of Infectious Disease

Numerous monoclonal antibodies (MAbs) that recognize and neutralize infectious pathogens have been isolated and developed over the years. The fact that infectious diseases can involve large populations of infected individuals is an important factor that has motivated the search for both cost-effective and scalable methods of antibody production. The current technologies for production of antibodies in plants allow for very rapid expression and evaluation that can also be readily scaled for multikilogram production runs. In addition, recent progress in manipulating glycosylation in plant production systems has allowed for the evaluation of antibodies containing glycans that are nearly homogeneous, are mammalian in structure, and have enhanced neutralizing capabilities. Among the anti-infectious disease antibodies that have been produced in plants are included those intended for prevention or treatment of anthrax, Clostridium perfringens, Ebola virus, human immunodeficiency virus, herpes simplex virus, rabies, respiratory syncytial virus, staphylococcal enterotoxin, West Nile virus, and tooth decay. Animal and human efficacy data for these MAbs are discussed.

Regulatory approval and a first-in-human phase I clinical trial of a monoclonal antibody produced in transgenic tobacco plants

Although plant biotechnology has been widely investigated for the production of clinical-grade monoclonal antibodies, no antibody products derived from transgenic plants have yet been approved by pharmaceutical regulators for clinical testing. In the Pharma-Planta project, the HIV-neutralizing human monoclonal antibody 2G12 was expressed in transgenic tobacco (Nicotiana tabacum). The scientific, technical and regulatory demands of good manufacturing practice (GMP) were addressed by comprehensive molecular characterization of the transgene locus, confirmation of genetic and phenotypic stability over several generations of transgenic plants, and by establishing standard operating procedures for the creation of a master seed bank, plant cultivation, harvest, initial processing, downstream processing and purification. The project developed specifications for the plant-derived antibody (P2G12) as an active pharmaceutical ingredient (API) based on (i) the guidelines for the manufacture of monoclonal antibodies in cell culture systems; (ii) the draft European Medicines Agency Points to Consider document on quality requirements for APIs produced in transgenic plants; and (iii) de novo guidelines developed with European national regulators. From the resulting process, a GMP manufacturing authorization was issued by the competent authority in Germany for transgenic plant-derived monoclonal antibodies for use in a phase I clinical evaluation. Following preclinical evaluation and ethical approval, a clinical trial application was accepted by the UK national pharmaceutical regulator. A first-in-human, double-blind, placebo-controlled, randomized, dose-escalation phase I safety study of a single vaginal administration of P2G12 was carried out in healthy female subjects. The successful completion of the clinical trial marks a significant milestone in the commercial development of plant-derived pharmaceutical proteins.

Antibody proteolysis: a common picture emerging from plants

We have recently characterized the degradation profiles of 2 human IgG1 monoclonal antibodies, the tumor-targeting mAb H10 and the anti-HIV mAb 2G12. Both mAbs were produced in plants either as stable transgenics or using a transient expression system based on leaf agroinfiltration. The purified antibodies were separated by 1DE and protein bands were characterized by N-terminal sequencing. The proteolytic cleavage sites identified in the heavy chain (HC) of both antibodies were localized in 3 inter-domain regions, suggesting that the number of proteolytic cleavage events taking place in plants is limited. One of the cleavage sites, close to the hinge region, was common to both antibodies.

Biodegradable Film for the Targeted Delivery of siRNA-Loaded Nanoparticles to Vaginal Immune Cells

The goal of this study was to develop and characterize a novel intravaginal film platform for targeted delivery of small interfering RNA (siRNA)-loaded nanoparticles (NP) to dendritic cells as a potential gene therapy for the prevention of sexually transmitted human immunodeficiency virus (HIV) infection. Poly(ethylene glycol) (PEG)-functionalized poly(D, L-lactic-co-glycolic acid) (PLGA)/polyethylenimine (PEI)/siRNA NP (siRNA-NP) were fabricated using a modified emulsion-solvent evaporation method and characterized for particle size, zeta potential, encapsulation efficiency (EE), and siRNA release. siRNA-NP were decorated with anti-HLA-DR antibody (siRNA-NP-Ab) for targeting delivery to HLA-DR+ dendritic cells (DCs) and homogeneously dispersed in a biodegradable film consisting of poly vinyl alcohol (PVA) and λ-carrageenan. The siRNA-NP-Ab-loaded film (siRNA-NP-Ab-film) was transparent, displayed suitable physicomechanical properties, and was noncytotoxic. Targeting activity was evaluated in a mucosal coculture model consisting of a vaginal epithelial monolayer (VK2/E6E7 cells) and differentiated KG-1 cells (HLA-DR+ DCs). siRNA-NP-Ab were rapidly released from the film and were able to penetrate the epithelial layer to be taken up by differentiated KG-1 cells. siRNA-NP-Ab demonstrated higher targeting activity and significantly higher knockdown of synaptosome-associated 23-kDa protein (SNAP-23) mRNA and protein when compared to siRNA-NP without antibody conjugation. Overall, these data suggest that our novel siRNA-NP-Ab-film may be a promising platform for preventing HIV infection within the female genital tract.

Expression of bioactive anti-CD20 antibody fragments and induction of ER stress response in Arabidopsis seeds

Seed-based expression system is an attractive platform for the production of recombinant proteins in molecular farming. Despite the many advantages of molecular farming, little is known about the effect of the different subcellular accumulation of recombinant proteins on the endoplasmic reticulum (ER) quality control system in host plants. In this study, we analyzed the expression of anti-CD20 antibody fragments in seeds of Arabidopsis thaliana (ecotype Columbia) and corresponding glycosylation mutants, and evaluated the influence of three different signal sequences on the expression levels of scFv-Fc of C2B8. The highest protein accumulation level, with a maximum of 6.12 % total soluble proteins, was observed upon fusing proteins to the signal peptide of Arabidopsis seed storage albumin 2. The ER stress responses in developing seeds at 13 days post-anthesis were also compared across different transgenic lines under normal and heat shock conditions. Based on the gene expression profiles of ER stress transducers, our results suggest that accumulation of antibody fragments in the ER exerts more stress on ER homeostasis. In addition, quantitative PCR results also implicate enhanced activation of ER-associated degradation in transgenic lines. Last but not the least, we also demonstrate the anti-tumor potency of plant-derived proteins by showing the anti-tumor activity of purified scFv-Fc proteins against Daudi cells. Together, our data implies that better understanding of the interaction between exogenous protein production and the cellular quality control system of the host plant is necessary for the development of an optimal expression strategy that will be especially beneficial to commercial protein manufacturing.

Extraction and downstream processing of plant-derived recombinant proteins

Plants offer the tantalizing prospect of low-cost automated manufacturing processes for biopharmaceutical proteins, but several challenges must be addressed before such goals are realized and the most significant hurdles are found during downstream processing (DSP). In contrast to the standardized microbial and mammalian cell platforms embraced by the biopharmaceutical industry, there are many different plant-based expression systems vying for attention, and those with the greatest potential to provide inexpensive biopharmaceuticals are also the ones with the most significant drawbacks in terms of DSP. This is because the most scalable plant systems are based on the expression of intracellular proteins in whole plants. The plant tissue must therefore be disrupted to extract the product, challenging the initial DSP steps with an unusually high load of both particulate and soluble contaminants. DSP platform technologies can accelerate and simplify process development, including centrifugation, filtration, flocculation, and integrated methods that combine solid-liquid separation, purification and concentration, such as aqueous two-phase separation systems. Protein tags can also facilitate these DSP steps, but they are difficult to transfer to a commercial environment and more generic, flexible and scalable strategies to separate target and host cell proteins are preferable, such as membrane technologies and heat/pH precipitation. In this context, clarified plant extracts behave similarly to the feed stream from microbes or mammalian cells and the corresponding purification methods can be applied, as long as they are adapted for plant-specific soluble contaminants such as the superabundant protein RuBisCO. Plant-derived pharmaceutical proteins cannot yet compete directly with established platforms but they are beginning to penetrate niche markets that allow the beneficial properties of plants to be exploited, such as the ability to produce 'biobetters' with tailored glycans, the ability to scale up production rapidly for emergency responses and the ability to produce commodity recombinant proteins on an agricultural scale.

Pharmacokinetics and immunogenicity of broadly neutralizing HIV monoclonal antibodies in macaques

The identification of highly potent broadly neutralizing antibodies (bnAbs) against HIV-1, and success in preventing SHIV infection following their passive administration, have increased the likelihood that immunotherapeutic strategies can be adopted to prevent and treat HIV-1 infection. However, while broad and potent neutralizing activity is an essential prerequisite, in vivo properties such as good circulatory stability and non-immunogenicity are equally critical for developing a human treatment. In the present study, glycoforms of the bnAbs 10-1074, NIH45-46G54W, 10E8, PGT121, PGT128, PGT145, PGT135, PG9, PG16, VRC01 and b12 were produced by Agrobacterium-mediated transient transfection of Nicotiana benthamiana and assessed following administration in rhesus macaques. The results indicate that (i) N-glycans within the VL domain impair plasma stability of plant-derived bnAbs and (ii) while PGT121 and b12 exhibit no immunogenicity in rhesus macaques after multiple injections, VRC01, 10-1074 and NIH45-46G54W elicit high titer anti-idiotypic antibodies following a second injection. These anti-idiotypic antibodies specifically bind the administered bnAb or a close family member, and inhibit the bnAb in neutralization assays. These findings suggest that specific mutations in certain bnAbs contribute to their immunogenicity and call attention to the prospect that these mutated bnAbs will be immunogenic in humans, potentially compromising their value for prophylaxis and therapy of HIV-1.

Site-specific proteolytic degradation of IgG monoclonal antibodies expressed in tobacco plants

Plants are promising hosts for the production of monoclonal antibodies (mAbs). However, proteolytic degradation of antibodies produced both in stable transgenic plants and using transient expression systems is still a major issue for efficient high-yield recombinant protein accumulation. In this work, we have performed a detailed study of the degradation profiles of two human IgG1 mAbs produced in plants: an anti-HIV mAb 2G12 and a tumour-targeting mAb H10. Even though they use different light chains (κ and λ, respectively), the fragmentation pattern of both antibodies was similar. The majority of Ig fragments result from proteolytic degradation, but there are only a limited number of plant proteolytic cleavage events in the immunoglobulin light and heavy chains. All of the cleavage sites identified were in the proximity of interdomain regions and occurred at each interdomain site, with the exception of the VL /CL interface in mAb H10 λ light chain. Cleavage site sequences were analysed, and residue patterns characteristic of proteolytic enzymes substrates were identified. The results of this work help to define common degradation events in plant-produced mAbs and raise the possibility of predicting antibody degradation patterns 'a priori' and designing novel stabilization strategies by site-specific mutagenesis.

Passive Immunization

Whereas active immunity refers to the process of exposing the individual to an antigen to generate an adaptive immune response, passive immunity refers to the transfer of antibodies from one individual to another. Passive immunity provides immediate but short-lived protection, lasting several weeks up to 3 or 4 months. Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta or from breast milk to the gut of the infant. It can also be produced artificially, when antibody preparations derived from sera or secretions of immunized donors or, more recently, different antibody producing platforms are transferred via systemic or mucosal route to nonimmune individuals. Passive immunization has recently become an attractive approach because of the emergence of new and drug-resistant microorganisms, diseases that are unresponsive to drug therapy and individuals with an impaired immune system who are unable to respond to conventional vaccines. This chapter addresses the contributions of natural and artificial acquired passive immunity in understanding the concept of passive immunization. We will mainly focus on administration of antibodies for protection against various infectious agents entering through mucosal surfaces.

The human anti-HIV antibodies 2F5, 2G12, and PG9 differ in their susceptibility to proteolytic degradation: down-regulation of endogenous serine and cysteine proteinase activities could improve antibody production in plant-based expression platforms

The tobacco-related species Nicotiana benthamiana has recently emerged as a promising host for the manufacturing of protein therapeutics. However, the production of recombinant proteins in N. benthamiana is frequently hampered by undesired proteolysis. Here, we show that the expression of the human anti-HIV antibodies 2F5, 2G12, and PG9 in N. benthamiana leaves leads to the accumulation of discrete heavy chain-derived degradation products of 30-40 kDa. Incubation of purified 2F5 with N. benthamiana intercellular fluid resulted in rapid conversion into the 40-kDa fragment, whereas 2G12 proved largely resistant to degradation. Such a differential susceptibility to proteolytic attack was also observed when these two antibodies were exposed to various types of proteinases in vitro. While serine and cysteine proteinases are both capable of generating the 40-kDa 2F5 fragment, the 30-kDa polypeptide is most readily obtained by treatment with the latter class of enzymes. The principal cleavage sites reside within the antigen-binding domain, the VH -CH 1 linker segment and the hinge region of the antibodies. Collectively, these results indicate that down-regulation of endogenous serine and cysteine proteinase activities could be used to improve the performance of plant-based expression platforms destined for the production of biopharmaceuticals.

Comparative evaluation of recombinant protein production in different biofactories: the green perspective

In recent years, the production of recombinant pharmaceutical proteins in heterologous systems has increased significantly. Most applications involve complex proteins and glycoproteins that are difficult to produce, thus promoting the development and improvement of a wide range of production platforms. No individual system is optimal for the production of all recombinant proteins, so the diversity of platforms based on plants offers a significant advantage. Here, we discuss the production of four recombinant pharmaceutical proteins using different platforms, highlighting from these examples the unique advantages of plant-based systems over traditional fermenter-based expression platforms.

Can plant biotechnology help break the HIV-malaria link?

The population of sub-Saharan Africa is at risk from multiple, poverty-related endemic diseases. HIV and malaria are the most prevalent, but they disproportionately affect different groups of people, i.e. HIV predominantly affects sexually-active adults whereas malaria has a greater impact on children and pregnant women. Nevertheless, there is a significant geographical and epidemiological overlap which results in bidirectional and synergistic interactions with important consequences for public health. The immunosuppressive effects of HIV increase the risk of infection when individuals are exposed to malaria parasites and also the severity of malaria symptoms. Similarly, acute malaria can induce a temporary increase in the HIV viral load. HIV is associated with a wide range of opportunistic infections that can be misdiagnosed as malaria, resulting in the wasteful misuse of antimalarial drugs and a failure to address the genuine cause of the disease. There is also a cumulative risk of toxicity when antiretroviral and antimalarial drugs are given to the same patients. Synergistic approaches involving the control of malaria as a strategy to fight HIV/AIDS and vice versa are therefore needed in co-endemic areas. Plant biotechnology has emerged as a promising approach to tackle poverty-related diseases because plant-derived drugs and vaccines can be produced inexpensively in developing countries and may be distributed using agricultural infrastructure without the need for a cold chain. Here we explore some of the potential contributions of plant biotechnology and its integration into broader multidisciplinary public health programs to combat the two diseases in developing countries.

Characterization of a plant-produced recombinant human secretory IgA with broad neutralizing activity against HIV

Recombinant Secretory IgA (SIgA) complexes have the potential to improve antibody-based passive immunotherapeutic approaches to combat many mucosal pathogens. In this report, we describe the expression, purification and characterization of a human SIgA format of the broadly neutralizing anti-HIV monoclonal antibody (mAb) 2G12, using both transgenic tobacco plants and transient expression in Nicotiana benthamiana as expression hosts (P2G12 SIgA). The resulting heterodecameric complexes accumulated in intracellular compartments in leaf tissue, including the vacuole. SIgA complexes could not be detected in the apoplast. Maximum yields of antibody were 15.2 μg/g leaf fresh mass (LFM) in transgenic tobacco and 25 μg/g LFM after transient expression, and assembly of SIgA complexes was superior in transgenic tobacco. Protein L purified antibody specifically bound HIV gp140 and neutralised tier 2 and tier 3 HIV isolates. Glycoanalysis revealed predominantly high mannose structures present on most N-glycosylation sites, with limited evidence for complex glycosylation or processing to paucimannosidic forms. O-glycan structures were not identified. Functionally, P2G12 SIgA, but not IgG, effectively aggregated HIV virions. Binding of P2G12 SIgA was observed to CD209 / DC-SIGN, but not to CD89 / FcalphaR on a monocyte cell line. Furthermore, P2G12 SIgA demonstrated enhanced stability in mucosal secretions in comparison to P2G12 IgG mAb.

The dynamic behavior of storage organelles in developing cereal seeds and its impact on the production of recombinant proteins

Cereal endosperm is a highly differentiated tissue containing specialized organelles for the accumulation of storage proteins, which are ultimately deposited either within protein bodies derived from the endoplasmic reticulum, or in protein storage vacuoles (PSVs). During seed maturation endosperm cells undergo a rapid sequence of developmental changes, including extensive reorganization and rearrangement of the endomembrane system and protein transport via several developmentally regulated trafficking routes. Storage organelles have been characterized in great detail by the histochemical analysis of fixed immature tissue samples. More recently, in vivo imaging and the use of tonoplast markers and fluorescent organelle tracers have provided further insight into the dynamic morphology of PSVs in different cell layers of the developing endosperm. This is relevant for biotechnological applications in the area of molecular farming because seed storage organelles in different cereal crops offer alternative subcellular destinations for the deposition of recombinant proteins that can reduce proteolytic degradation, allow control over glycan structures and increase the efficacy of oral delivery. We discuss how the specialized architecture and developmental changes of the endomembrane system in endosperm cells may influence the subcellular fate and post-translational modification of recombinant glycoproteins in different cereal species.

Plant molecular pharming for the treatment of chronic and infectious diseases

Plant molecular pharming has emerged as a niche technology for the manufacture of pharmaceutical products indicated for chronic and infectious diseases, particularly for products that do not fit into the current industry-favored model of fermenter-based production campaigns. In this review, we explore the areas where molecular pharming can make the greatest impact, including the production of pharmaceuticals that have novel glycan structures or that cannot be produced efficiently in microbes or mammalian cells because they are insoluble or toxic. We also explore the market dynamics that encourage the use of molecular pharming, particularly for pharmaceuticals that are required in small amounts (such as personalized medicines) or large amounts (on a multi-ton scale, such as blood products and microbicides) and those that are needed in response to emergency situations (pandemics and bioterrorism). The impact of molecular pharming will increase as the platforms become standardized and optimized through adoption of good manufacturing practice (GMP) standards for clinical development, offering a new opportunity to produce inexpensive medicines in regional markets that are typically excluded under current business models.

Efficient recovery of recombinant proteins from cereal endosperm is affected by interaction with endogenous storage proteins

Cereal seeds are versatile platforms for the production of recombinant proteins because they provide a stable environment for protein accumulation. Endogenous seed storage proteins, however, include several prolamin-type polypeptides that aggregate and crosslink via intermolecular disulfide bridges, which could potentially interact with multimeric recombinant proteins such as antibodies, which assemble in the same manner. We investigated this possibility by sequentially extracting a human antibody expressed in maize endosperm, followed by precipitation in vitro with zein. We provide evidence that a significant proportion of the antibody pool interacts with zein and therefore cannot be extracted using non-reducing buffers. Immunolocalization experiments demonstrated that antibodies targeted for secretion were instead retained within zein bodies because of such covalent interactions. Our findings suggest that the production of soluble recombinant antibodies in maize could be enhanced by eliminating or minimizing interactions with endogenous storage proteins.

Plant species and organ influence the structure and subcellular localization of recombinant glycoproteins

Many plant-based systems have been developed as bioreactors to produce recombinant proteins. The choice of system for large-scale production depends on its intrinsic expression efficiency and its propensity for scale-up, post-harvest storage and downstream processing. Factors that must be considered include the anticipated production scale, the value and intended use of the product, the geographical production area, the proximity of processing facilities, intellectual property, safety and economics. It is also necessary to consider whether different species and organs affect the subcellular trafficking, structure and qualitative properties of recombinant proteins. In this article we discuss the subcellular localization and N-glycosylation of two commercially-relevant recombinant glycoproteins (Aspergillus niger phytase and anti-HIV antibody 2G12) produced in different plant species and organs. We augment existing data with novel results based on the expression of the same recombinant proteins in Arabidopsis and tobacco seeds, focusing on similarities and subtle differences in N-glycosylation that often reflect the subcellular trafficking route and final destination, as well as differences generated by unique enzyme activities in different species and tissues. We discuss the potential consequences of such modifications on the stability and activity of the recombinant glycoproteins.