Oral Delivery of Protein Drugs Bioencapsulated in Plant Cells

Delivery of biologics: Topical administration

Biologics are unaffordable to a large majority of the global population because of prohibitively expensive fermentation systems, purification and the requirement for cold chain for storage and transportation. Limitations of current production and delivery systems of biologics were evident during the recent pandemic when <2.5% of vaccines produced were available to low-income countries and ∼19 million doses were discarded in Africa due to lack of cold-chain infrastructure. Among FDA-approved biologics since 2015, >90% are delivered using invasive methods. While oral or topical drugs are highly preferred by patients because of their affordability and convenience, only two oral drugs have been approved by FDA since 2015. A newly launched oral biologic costs only ∼3% of the average cost of injectable biologics because of the simplified regulatory approval process by elimination of prohibitively expensive fermentation, purification, cold storage/transportation. In addition, the cost of developing a new biologic injectable product (∼$2.5 billion) has been dramatically reduced through oral or topical delivery. Topical delivery has the unique advantage of targeted delivery of high concentration protein drugs, without getting diluted in circulating blood. However, only very few topical drugs have been approved by the FDA. Therefore, this review highlights recent advances in oral or topical delivery of proteins at early or advanced stages of human clinical trials using chewing gums, patches or sprays, or nucleic acid drugs directly, or in combination with, nanoparticles and offers future directions.

Development of a plant-based oral vaccine candidate against the bovine respiratory pathogen Mannheimia haemolytica

Bovine respiratory disease (BRD) affects feedlot cattle across North America, resulting in economic losses due to animal treatment and reduced performance. In an effort to develop a vaccine candidate targeting a primary bacterial agent contributing to BRD, we produced a tripartite antigen consisting of segments of the virulence factor Leukotoxin A (LktA) and lipoprotein PlpE from Mannheimia haemolytica, fused to a cholera toxin mucosal adjuvant (CTB). This recombinant subunit vaccine candidate was expressed in the leaves of Nicotiana benthamiana plants, with accumulation tested in five subcellular compartments. The recombinant protein was found to accumulate highest in the endoplasmic reticulum, but targeting to the chloroplast was employed for scaling up production due the absence of post-translational modification while still producing feasible levels. Leaves were freeze dried, then orally administered to mice to determine its immunogenicity. Sera from mice immunized with leaf tissue expressing the recombinant antigen contained IgG antibodies, specifically recognizing both LktA and PlpE. These mice also had a mucosal immune response to the CTB+LktA+PlpE protein as measured by the presence of LktA- and PlpE-specific IgA antibodies in lung and fecal material. Moreover, the antigen remained stable at room temperature with limited deterioration for up to one year when stored as lyophilized plant material. This study demonstrated that a recombinant antigen expressed in plant tissue elicited both humoral and mucosal immune responses when fed to mice, and warrants evaluation in cattle.

Affordable oral proinsulin bioencapsulated in plant cells regulates blood sugar levels similar to natural insulin

Diabetes Mellitus is a silent epidemic affecting >500 million, which claimed 6.7 million lives in 2021, a projected increase of >670% in <20 years old in the next two decades but insulin is unaffordable for the large majority of the globe. Therefore, we engineered proinsulin in plant cells to facilitate oral delivery. Stability of the proinsulin gene and expression in subsequent generations, after removal of the antibiotic-resistance gene, was confirmed using PCR, Southern and western blots. Proinsulin expression was high (up to 12 mg/g DW or 47.5% of total leaf protein), stable up to one year after storage of freeze-dried plant cells at ambient temperature and met FDA regulatory requirements of uniformity, moisture content and bioburden. GM1 receptor binding, required for uptake via gut epithelial cells was confirmed by pentameric assembly of CTB-Proinsulin. IP insulin injections (without C peptide) in STZ mice rapidly decreased blood glucose level leading to transient hypoglycemia, followed by hepatic glucose compensation. On the other hand, other than the 15-min lag period of oral proinsulin (transit time required to reach the gut), the kinetics of blood sugar regulation of oral CTB-Proinsulin in STZ mice was very similar to naturally secreted insulin in healthy mice (both contain C-peptide), without rapid decrease or hypoglycemia. Elimination of expensive fermentation, purification and cold storage/transportation should reduce cost and increase other health benefits of plant fibers. The recent approval of plant cell delivery of therapeutic proteins by FDA and approval of CTB-ACE2 for phase I/II human clinical studies augur well for advancing oral proinsulin to the clinic.

Immunogenicity and contraceptive efficacy of plant-produced putative mouse-specific contraceptive peptides

Rodent population control through contraception requires species-specific oral contraceptive vaccines. Therefore, in this study, we produced putative mouse-specific contraceptive peptides, mZP2 (from oocyte) and mIzumo1 (from sperm), in plants using Agrobacterium-mediated transient expression. Peptides were produced separately in Nicotiana benthamiana using constructs encoding antigens containing three copies of each peptide. We also determined the immunogenicity and contraceptive effects of the plant-produced antigens in female BALB/c mice. Mice immunized subcutaneously with a relatively low amount of antigen (5 µg/dose of each peptide in a mixture) showed systemic immune responses against mZP2-3 and mIzumo1-3 antigens. Moreover, the mean litter size of mice treated with the plant-produced antigens was reduced by 39% compared to that of the control mice. Notably, there was a significant negative correlation between the number of pups born and individual antibody levels against both antigens. Immunofluorescence assays demonstrated the binding of induced antibodies to the oocytes of BALB/c and wild-type mice in vivo and in vitro, respectively. Our study demonstrate the feasibility of producing small contraceptive peptides in plants that can be further used to develop oral contraceptive vaccines against mouse populations.

Multidimensional futuristic approaches to address the pandemics beyond COVID-19

Globally, the impact of the coronavirus disease 2019 (COVID-19) pandemic has been enormous and unrelenting with ∼6.9 million deaths and ∼765 million infections. This review mainly focuses on the recent advances and potentially novel molecular tools for viral diagnostics and therapeutics with far-reaching implications in managing the future pandemics. In addition to briefly highlighting the existing and recent methods of viral diagnostics, we propose a couple of potentially novel non-PCR-based methods for rapid, cost-effective, and single-step detection of nucleic acids of viruses using RNA mimics of green fluorescent protein (GFP) and nuclease-based approaches. We also highlight key innovations in miniaturized Lab-on-Chip (LoC) devices, which in combination with cyber-physical systems, could serve as ideal futuristic platforms for viral diagnosis and disease management. We also discuss underexplored and underutilized antiviral strategies, including ribozyme-mediated RNA-cleaving tools for targeting viral RNA, and recent advances in plant-based platforms for rapid, low-cost, and large-scale production and oral delivery of antiviral agents/vaccines. Lastly, we propose repurposing of the existing vaccines for newer applications with a major emphasis on Bacillus Calmette-Guérin (BCG)-based vaccine engineering.

Antimicrobial Peptides: Challenging Journey to the Pharmaceutical, Biomedical, and Cosmeceutical Use

Antimicrobial peptides (AMPs), or host defence peptides, are short proteins in various life forms. Here we discuss AMPs, which may become a promising substitute or adjuvant in pharmaceutical, biomedical, and cosmeceutical uses. Their pharmacological potential has been investigated intensively, especially as antibacterial and antifungal drugs and as promising antiviral and anticancer agents. AMPs exhibit many properties, and some of these have attracted the attention of the cosmetic industry. AMPs are being developed as novel antibiotics to combat multidrug-resistant pathogens and as potential treatments for various diseases, including cancer, inflammatory disorders, and viral infections. In biomedicine, AMPs are being developed as wound-healing agents because they promote cell growth and tissue repair. The immunomodulatory effects of AMPs could be helpful in the treatment of autoimmune diseases. In the cosmeceutical industry, AMPs are being investigated as potential ingredients in skincare products due to their antioxidant properties (anti-ageing effects) and antibacterial activity, which allows the killing of bacteria that contribute to acne and other skin conditions. The promising benefits of AMPs make them a thrilling area of research, and studies are underway to overcome obstacles and fully harness their therapeutic potential. This review presents the structure, mechanisms of action, possible applications, production methods, and market for AMPs.

Suppression of anti-drug antibody formation against coagulation factor VIII by oral delivery of anti-CD3 monoclonal antibody in hemophilia A mice

Active tolerance to ingested dietary antigens forms the basis for oral immunotherapy to food allergens or autoimmune self-antigens. Alternatively, oral administration of anti-CD3 monoclonal antibody can be effective in modulating systemic immune responses without T cell depletion. Here we assessed the efficacy of full length and the F(ab')2 fragment of oral anti-CD3 to prevent anti-drug antibody (ADA) formation to clotting factor VIII (FVIII) protein replacement therapy in hemophilia A mice. A short course of low dose oral anti-CD3 F(ab')2 reduced the production of neutralizing ADAs, and suppression was significantly enhanced when oral anti-CD3 was timed concurrently with FVIII administration. Tolerance was accompanied by the early induction of FoxP3+LAP-, FoxP3+LAP+, and FoxP3-LAP+ populations of CD4+ T cells in the spleen and mesenteric lymph nodes. FoxP3+LAP+ Tregs expressing CD69, CTLA-4, and PD1 persisted in spleens of treated mice, but did not produce IL-10. Finally, we attempted to combine the anti-CD3 approach with oral intake of FVIII antigen (using our previously established method of using lettuce plant cells transgenic for FVIII antigen fused to cholera toxin B (CTB) subunit, which suppresses ADAs in part through induction of IL-10 producing FoxP3-LAP+ Treg). However, combining these two approaches failed to improve suppression of ADAs. We conclude that oral anti-CD3 treatment is a promising approach to prevention of ADA formation in systemic protein replacement therapy, albeit via mechanisms distinct from and not synergistic with oral intake of bioencapsulated antigen.

Recent Advances in Oral and Transdermal Protein Delivery Systems

Protein and peptide drugs are predominantly administered by injection to achieve high bioavailability, but this greatly compromises patient compliance. Oral and transdermal drug delivery with minimal invasiveness and high adherence represent attractive alternatives to injection administration. However, oral and transdermal administration of bioactive proteins must overcome biological barriers, namely the gastrointestinal and skin barriers, respectively. The rapid development of new materials and technologies promises to address these physiological obstacles. This review provides an overview of the latest advances in oral and transdermal protein delivery, including chemical strategies, synthetic nanoparticles, medical microdevices, and biomimetic systems for oral administration, as well as chemical enhancers, physical approaches, and microneedles in transdermal delivery. We also discuss challenges and future perspectives of the field with a focus on innovation and translation.

Oral tolerance to prevent anti-drug antibody formation in protein replacement therapies

Protein based therapeutics have successfully improved the quality of life for patients of monogenic disorders like hemophilia, Pompe and Fabry disease. However, a significant proportion of patients develop immune responses towards intravenously infused therapeutic protein, which can complicate or neutralize treatment and compromise patient safety. Strategies aimed at circumventing immune responses following therapeutic protein infusion can greatly improve therapeutic efficacy. In recent years, antigen-based oral tolerance induction has shown promising results in the prevention and treatment of autoimmune diseases, food allergies and can prevent anti-drug antibody formation to protein replacement therapies. Oral tolerance exploits regulatory mechanisms that are initiated in the gut associated lymphoid tissue (GALT) to promote active suppression of orally ingested antigen. In this review, we outline general perceptions and current knowledge about the mechanisms of oral tolerance, including tissue specific sites of tolerance induction and the cells involved, with emphasis on antigen presenting cells and regulatory T cells. We define several factors, such as cytokines and metabolites that impact the stability and expansion potential of these immune modulatory cells. We highlight preclinical studies that have been performed to induce oral tolerance to therapeutic proteins or enzymes for single gene disorders, such as hemophilia or Pompe disease. These studies mainly utilize a transgenic plant-based system for oral delivery of antigen in conjugation with fusion protein technology that favors the prevention of antigen degradation in the stomach while enhancing uptake in the small intestine by antigen presenting cells and regulatory T cell induction, thereby promoting antigen specific systemic tolerance.

Recent Progress on Vaccines Produced in Transgenic Plants

The development of vaccines from plants has been going on for over two decades now. Vaccine production in plants requires time and a lot of effort. Despite global efforts in plant-made vaccine development, there are still challenges that hinder the realization of the final objective of manufacturing approved and safe products. Despite delays in the commercialization of plant-made vaccines, there are some human vaccines that are in clinical trials. The novel coronavirus (SARS-CoV-2) and its resultant disease, coronavirus disease 2019 (COVID-19), have reminded the global scientific community of the importance of vaccines. Plant-made vaccines could not be more important in tackling such unexpected pandemics as COVID-19. In this review, we explore current progress in the development of vaccines manufactured in transgenic plants for different human diseases over the past 5 years. However, we first explore the different host species and plant expression systems during recombinant protein production, including their shortcomings and benefits. Lastly, we address the optimization of existing plant-dependent vaccine production protocols that are aimed at improving the recovery and purification of these recombinant proteins.

Debulking different Corona (SARS-COV-2 delta, omicron, OC43) and influenza (H1N1, H3N2) virus strains by plant viral trap proteins in chewing gums to decrease infection and transmission

Because oral transmission of SARS-CoV-2 is 3–5 orders of magnitude higher than nasal transmission, we investigated debulking of oral viruses using viral trap proteins (CTB-ACE2, FRIL) expressed in plant cells, delivered through the chewing gum. In omicron nasopharyngeal (NP) samples, the microbubble count (based on N-antigen) was significantly reduced by 20 μg of FRIL (p < 0.0001) and 0.925 μg of CTB-ACE2 (p = 0.0001). Among 20 delta or omicron NP samples, 17 had virus load reduced below the detection level of spike protein in the RAPID assay, after incubation with the CTB-ACE2 gum powder. A dose-dependent 50% plaque reduction with 50–100 ng FRIL or 600–800 μg FRIL gum against Influenza strains H1N1, H3N2, and Coronavirus HCoV-OC43 was observed with both purified FRIL, lablab bean powder or gum. In electron micrographs, large/densely packed clumps of overlapping influenza particles and FRIL protein were observed. Chewing simulator studies revealed that CTB-ACE2 release was time/dose-dependent and release was linear up to 20 min chewing. Phase I/II placebo-controlled, double-blinded clinical trial (IND 154897) is in progress to evaluate viral load in saliva before or after chewing CTB-ACE2/placebo gum. Collectively, this study advances the concept of chewing gum to deliver proteins to debulk oral viruses and decrease infection/transmission.

Debulking SARS-CoV-2 in saliva using angiotensin converting enzyme 2 in chewing gum to decrease oral virus transmission and infection

To advance a novel concept of debulking virus in the oral cavity, the primary site of viral replication, virus-trapping proteins CTB-ACE2 were expressed in chloroplasts and clinical-grade plant material was developed to meet FDA requirements. Chewing gum (2 g) containing plant cells expressed CTB-ACE2 up to 17.2 mg ACE2/g dry weight (11.7% leaf protein), have physical characteristics and taste/flavor like conventional gums, and no protein was lost during gum compression. CTB-ACE2 gum efficiently (>95%) inhibited entry of lentivirus spike or VSV-spike pseudovirus into Vero/CHO cells when quantified by luciferase or red fluorescence. Incubation of CTB-ACE2 microparticles reduced SARS-CoV-2 virus count in COVID-19 swab/saliva samples by >95% when evaluated by microbubbles (femtomolar concentration) or qPCR, demonstrating both virus trapping and blocking of cellular entry. COVID-19 saliva samples showed low or undetectable ACE2 activity when compared with healthy individuals (2,582 versus 50,126 ΔRFU; 27 versus 225 enzyme units), confirming greater susceptibility of infected patients for viral entry. CTB-ACE2 activity was completely inhibited by pre-incubation with SARS-CoV-2 receptor-binding domain, offering an explanation for reduced saliva ACE2 activity among COVID-19 patients. Chewing gum with virus-trapping proteins offers a general affordable strategy to protect patients from most oral virus re-infections through debulking or minimizing transmission to others.

Advances and Applications of Metal-Organic Framework Nanomaterials as Oral Delivery Carriers: A Review

Oral administration is a commonly used, safe, and patient-compliant method of drug delivery. However, due to the multiple absorption barriers in the gastrointestinal tract (GIT), the oral bioavailability of many drugs is low, resulting in a limited range of applications for oral drug delivery. Nanodrug delivery systems have unique advantages in overcoming the multiple barriers to oral absorption and improving the oral bioavailability of encapsulated drugs. Metal-organic frameworks (MOFs) are composed of metal ions and organic linkers assembled by coordination chemistry. Unlike other nanomaterials, nanoscale metal-organic frameworks (nano-MOFs, NMOFs) are increasingly popular for drug delivery systems (DDSs) due to their tunable pore size and easily modified surfaces. This paper summarizes the literature on MOFs in pharmaceutics included in SCI for the past ten years. Then, the GIT structure and oral drug delivery systems are reviewed, and the advantages, challenges, and solution strategies possessed by oral drug delivery systems are discussed. Importantly, two major classes of MOFs suitable for oral drug delivery systems are summarized, and various representative MOFs as oral drug carriers are evaluated in the context of oral drug delivery systems. Finally, the challenges faced by DDSs in the development of MOFs, such as biostability, biosafety, and toxicity, are examined.

Biofunctionalization of Endolysins with Oligosacharides: Formulation of Therapeutic Agents to Combat Multi-Resistant Bacteria and Potential Strategies for Their Application

In the aquaculture sector, the biofunctionalization of biomaterials is discussed using materials from algae and analyzed as a possible potential strategy to overcome the challenges that hinder the future development of the application of endolysins in this field. Derived from years of analysis, endolysins have recently been considered as potential alternative therapeutic antibacterial agents, due to their attributes and ability to combat multi-resistant bacterial cells when applied externally. On the other hand, although the aquaculture sector has been characterized by its high production rates, serious infectious diseases have led to significant economic losses that persist to this day. Although there are currently interesting data from studies under in vitro conditions on the application of endolysins in this sector, there is little or no information on in vivo studies. This lack of analysis can be attributed to the relatively low stability of endolysins in marine conditions and to the complex gastrointestinal conditions of the organisms. This review provides updated information regarding the application of endolysins against multi-resistant bacteria of clinical and nutritional interest, previously addressing their important characteristics (structure, properties and stability). In addition, regarding the aquaculture sector, the biofunctionalization of biomaterials is discussed using materials from algae and analyzed as a possible potential strategy to overcome the challenges that hinder the future development of the application of endolysins in this field.

A Pair of "ACEs"

The emergence of the COVID-19 viral pandemic has generated a renewed interest in pharmacologic agents that target the renin angiotensin system (RAS). Angiotensin-converting enzyme 1 (ACE1) inhibitors decrease the synthesis of angiotensin II (Ang II) from its precursor angiotensin I and inhibit the breakdown of bradykinin, while Ang II receptor blockers antagonize the action of Ang II at the receptor level downstream. The actions of both classes of drugs lead to vasodilation, a blunting of sympathetic drive and a reduction in aldosterone release, all beneficial effects in hypertension and congestive heart failure. ACE2 cleaves the vasoconstrictor Ang II to produce the anti-inflammatory cytoprotective angiotensin 1-7 (Ang 1-7) peptide, which functions through the G protein-coupled receptor MAS to counteract the pathophysiologic effects induced by Ang II via its receptors, including vasoconstriction, inflammation, hypercoagulation, and fibrosis. SARS-CoV-2 enters human cells by binding ACE2 on the cell surface, decreases ACE2 activity, competes for ACE2 receptor-binding sites, and shifts the RAS toward an overexpression of Ang II, accounting for many of the deleterious effects of the virus. Thus, there is great interest in developing recombinant ACE2 as a therapeutic for prevention or treatment of COVID-19. Notably, ACE2 is highly expressed in the oral cavity, and saliva and dorsum of the tongue are major reservoirs of SARS-CoV-2. Cost-effective methods to debulk the virus in the oral cavity may aid in the prevention of viral spread. Here we review the pharmacology of targeted small molecule inhibitors of the RAS and discuss novel approaches to employing ACE2 as a therapeutic for COVID-19.

Insight of oral vaccines as an alternative approach to health and disease management: An innovative intuition and challenges

Vaccination is the most suitable and persuasive healthcare program for the prohibition of various deadly diseases. However, the higher production cost and purification strategies are out of reach for the developing nations. In this scenario, development of edible vaccine turns out to be the most promising alternative for remodeling the pharmaceutical industry with reduced production and purification costs. Generally, oral route of vaccination is mostly preferred due to its safety, compliance, low manufacturing cost and most importantly the ability to induce immunity in both systemic and mucosal sites. Genetically modified microorganisms and plants could efficiently be used as vehicles for edible vaccines. Edible vaccines are supposed to reduce the risk associated with traditional vaccines. Currently, oral vaccines are available in the market for several viral and bacterial diseases like cholera, hepatitis B, malaria, rabies etc. Herein, the review focuses on the breakthrough events in the area of edible vaccines associated with dietary microbes and plants for better control over diseases.

Preclinical development of plant-based oral immune modulatory therapy for haemophilia B

Anti-drug antibody (ADA) formation is a major complication in treatment of the X-linked bleeding disorder haemophilia B (deficiency in coagulation factor IX, FIX). Current clinical immune tolerance protocols are often not effective due to complications such as anaphylactic reactions against FIX. Plant-based oral tolerance induction may address this problem, as illustrated by the recent first regulatory approval of orally delivered plant cells to treat peanut allergy. Our previous studies showed that oral delivery of plant cells expressing FIX fused to the transmucosal carrier CTB (cholera toxin subunit B) in chloroplasts suppressed ADA in animals with haemophilia B. We report here creation of the first lettuce transplastomic lines expressing a coagulation factor, in the absence of antibiotic resistance gene. Stable integration of the CTB-FIX gene and homoplasmy (transformation of ˜10 000 copies in each cell) were maintained in both T1 and T2 generation marker-free plants. CTB-FIX expression in lyophilized leaves of T1 and T2 marker-free plants was 1.0-1.5 mg/g dry weight, confirming that the marker excision did not affect antigen levels. Oral administration of CTB-FIX to Sprague Dawley rats at 0.25, 1 or 2.5 mg/kg did not produce overt adverse effects or toxicity. The no-observed-adverse-effect level (NOAEL) is at least 2.5 mg/kg for a single oral administration in rats. Oral administration of CTB-FIX at 0.3 or 1.47 mg/kg either mixed in food or as an oral suspension to Beagle dogs did not produce any observable toxicity. These toxicology studies should facilitate filing of regulatory approval documents and evaluation in haemophilia B patients.

Ma J, McDonald KA, Murad A, Nandi S, O’Keef B, Parthiban S, Paul MJ, Ponndorf D, Rech E, Rodrigues JC, Ruf S, Schillberg S, Schwestka J, Shah PS, Singh R, Stoger E, Twyman RM, Varghese IP, Vianna GR, Webster G, Wilbers RHP, Christou P, Oksman‐Caldentey K, Capell T. Contributions of the international plant science community to the fight against infectious diseases in humans-part 2: Affordable drugs in edible plants for endemic and re-emerging diseases

The fight against infectious diseases often focuses on epidemics and pandemics, which demand urgent resources and command attention from the health authorities and media. However, the vast majority of deaths caused by infectious diseases occur in endemic zones, particularly in developing countries, placing a disproportionate burden on underfunded health systems and often requiring international interventions. The provision of vaccines and other biologics is hampered not only by the high cost and limited scalability of traditional manufacturing platforms based on microbial and animal cells, but also by challenges caused by distribution and storage, particularly in regions without a complete cold chain. In this review article, we consider the potential of molecular farming to address the challenges of endemic and re-emerging diseases, focusing on edible plants for the development of oral drugs. Key recent developments in this field include successful clinical trials based on orally delivered dried leaves of Artemisia annua against malarial parasite strains resistant to artemisinin combination therapy, the ability to produce clinical-grade protein drugs in leaves to treat infectious diseases and the long-term storage of protein drugs in dried leaves at ambient temperatures. Recent FDA approval of the first orally delivered protein drug encapsulated in plant cells to treat peanut allergy has opened the door for the development of affordable oral drugs that can be manufactured and distributed in remote areas without cold storage infrastructure and that eliminate the need for expensive purification steps and sterile delivery by injection.

Antibodies induced by oral immunization of mice with a recombinant protein produced in tobacco plants harboring Bordetella pertussis epitopes

Bordetella pertusis causes whooping cough or pertussis, disease that has not been eradicated and is reemerging despite the availability and massive application for decades of vaccines, such as Boostrix® which is an acellular vaccine harboring two regions of S1 subunit of the pertussis toxin, one region of filamentous hemagglutinin and one region of pertactin. In 2008, the World Health Organization estimated 16 million new cases and 95% occurred in developing countries with 195,000 children's deaths. We attempt to improve the vaccine against whooping cough and reduce its production costs by obtaining plants and bacteria expressing a heterologous protein harboring pertactin, pertussis toxin, and filamentous hemagglutinin epitopes from B. pertussis and assessing its immunogenicity after oral administration to mice. First, we designed a synthetic gene that encodes a multiepitope, then it was cloned into a vector for transient transformation by infiltration of tobacco plants with low amounts of nicotine; the codon bias-optimized construct was also cloned into an Escherichia coli expression vector. Recombinant proteins from E. coli cells (PTF) and tobacco leaves (PTF-M3') were purified by nickel affinity with a yield of 0.740 mg of recombinant protein per g dry weight. Purified recombinant proteins were administered orally to groups of Balb/c mice using the Boostrix® vaccine and vehicle (PBS) as positive and negative controls, respectively. A higher mucosal and systemic antibody responses were obtained in mice receiving the PTF and PTF-M3' proteins than Boostrix® or PBS. These findings prove the concept that oral administration of multiepitope recombinant proteins expressed in plants may be a potential edible vaccine.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11240-021-02107-1.

Expression of Antimicrobial Peptide (AMP), Cecropin B, in a Fused Form to SUMO Tag With or Without Three-Glycine Linker in Escherichia coli and Evaluation of Bacteriolytic Activity of the Purified AMP

Current antibiotics have limited action mode, which makes it difficult for the antibiotics dealing with the emergence of bacteria resisting the existing antibiotics. As a need for new bacteriolytic agents alternative to the antibiotics, AMPs have long been considered substitutes for the antibiotics. Cecropin B was expressed in a fusion form to six-histidine and SUMO tags in Escherichia coli. Six-histidine tag attached to SUMO was for purification of SUMO-cecropin B fusion proteins and removal of the SUMO tag from cecropin B. Chimeric gene was constructed into pKSEC1 vector that was designed to be functional in both Escherichia coli and chloroplast. To maximize translation of the fusion protein, sequences were codon-optimized. Four different constructs were tested for the level of expression and solubility, and the construct with a linker, 6xHisSUMO3xGly-cecropin B, showed the highest expression. In addition, cleavage of the SUMO tag by SUMOase in the three fusion constructs which have no linker sequence (3xGly, three glycines) was not as efficient as the construct with the linker between SUMO and cecropin B. The cleaved cecropin B showed bacteriolytic activity against Bacillus subtilis at a concentration of 0.0625 μg/μL, while cecropin B fused to SUMO had no activity at a higher concentration, 0.125 μg/μL. As an expression system for AMPs in prokaryotic hosts, the use of tag proteins and appropriate codon-optimization strategy can be employed and further genetic modification of the fusion construct should help the complete removal of the tag proteins from the AMP in the final step of purification.

Plant-based vaccines and cancer therapy: Where are we now and where are we going?

Therapeutic vaccines are an effective approach in cancer therapy for treating the disease at later stages. The Food and Drug Administration (FDA) recently approved the first therapeutic cancer vaccine, and further studies are ongoing in clinical trials. These are expected to result in the future development of vaccines with relatively improved efficacy. Several vaccination approaches are being studied in pre-clinical and clinical trials, including the generation of anti-cancer vaccines by plant expression systems.This approach has advantages, such as high safety and low costs, especially for the synthesis of recombinant proteins. Nevertheless, the development of anti-cancer vaccines in plants is faced with some technical obstacles.Herein, we summarize some vaccines that have been used in cancer therapy, with an emphasis on plant-based vaccines.

Microparticles and Nanoparticles from Plants-The Benefits of Bioencapsulation

The efficacy of drugs and vaccines depends on their stability and ability to interact with their targets in vivo. Many drugs benefit from encapsulation, which protects them from harsh conditions and allows targeted delivery and controlled release. Although many encapsulation methods are inexpensive, such as the formulation of tablets for oral delivery, others require complex procedures that add significantly to production costs and require low-temperature transport and storage, making them inaccessible in developing countries. In this review we consider the benefits of encapsulation technologies based on plants. Plant-derived biopolymers such as starch and the maize storage protein zein are already used as protective coatings, but plant cells used as production host provide natural in vivo bioencapsulation that survives passage through the stomach and releases drugs in the intestine, due to the presence of microbes that can digest the cell wall. Proteins can also be encapsulated in subcellular compartments such as protein bodies, which ensure stability and activity while often conferring additional immunomodulatory effects. Finally, we consider the incorporation of drugs and vaccines into plant-derived nanoparticles assembled from the components of viruses. These are extremely versatile, allowing the display of epitopes and targeting peptides as well as carrying cargoes of drugs and imaging molecules.

Oral delivery of therapeutic proteins bioencapsulated in plant cells: preclinical and clinical advances

Oral delivery of protein drugs (PDs) made in plant cells could revolutionize current approaches of their production and delivery. Expression of PDs reduces their production cost by elimination of prohibitively expensive fermentation, purification, cold transportation/storage, and sterile injections and increases their shelf life for several years. Ability of plant cell wall to protect PDs from digestive acids/enzymes, commensal bacteria to release PDs in gut lumen after lysis of plant cell wall and role of GALT in inducing tolerance facilitate prevention or treatment allergic, autoimmune diseases or anti-drug antibody responses. Delivery of functional proteins facilitate treatment of inherited or metabolic disorders. Recent advances in making PDs free of antibiotic resistance genes in edible plant cells, long-term storage at ambient temperature maintaining their efficacy, production in cGMP facilities, IND enabling studies for clinical advancement and FDA approval of orally delivered PDs augur well for advancing this novel drug delivery platform technology.

Molecular pharming to support human life on the moon, mars, and beyond

Space missions have always assumed that the risk of spacecraft malfunction far outweighs the risk of human system failure. This assumption breaks down for longer duration exploration missions and exposes vulnerabilities in space medical systems. Space agencies can no longer reduce the majority of the human health and performance risks through crew members selection process and emergency re-supply or evacuation. No mature medical solutions exist to address this risk. With recent advances in biotechnology, there is promise for lessening this risk by augmenting a space pharmacy with a biologically-based space foundry for the on-demand manufacturing of high-value medical products. Here we review the challenges and opportunities of molecular pharming, the production of pharmaceuticals in plants, as the basis of a space medical foundry to close the risk gap in current space medical systems. Plants have long been considered to be an important life support object in space and can now also be viewed as programmable factories in space. Advances in molecular pharming-based space foundries will have widespread applications in promoting simple and accessible pharmaceutical manufacturing on Earth.

Plant-made vaccines against parasites: bioinspired perspectives to fight against Chagas disease

Introduction: Three decades of evidence have demonstrated that plants are an affordable platform for biopharmaceutical production and delivery. For instance, several plant-made recombinant proteins have been approved for commercialization under good manufacturing practice (GMP). Thus far, plant-based vaccine prototypes have been evaluated at pre- and clinical levels. Particularly, plant-made vaccines against parasitic diseases, such as malaria, cysticercosis, and toxoplasmosis have been successfully produced and orally delivered with promising outcomes in terms of immunogenicity and protection. The experience on several approaches and technical strategies over 30 years accounts for their potential low-cost, high scalability, and easy administration.Areas covered: This platform is an open technology to fight against Chagas disease, one of the most important neglected tropical diseases worldwide.Expert opinion: This review provides a perspective for the potential use of plants as a production platform and delivery system of Trypanosoma cruzi recombinant antigens, analyzing the advantages and limitations with respect to plant-made vaccines produced for other parasitic diseases. Plant-made vaccines are envisioned to fight against Chagas disease and other neglected tropical diseases in those countries suffering endemic prevalence.

A cross talk between the immunization and edible vaccine: Current challenges and future prospects

INTRODUCTION

It is well known that immune system is highly specific to protect the body against various environmental pathogens. The concept of conventional vaccination has overcome the pandemic situation of several infectious diseases outbreak.

AREA COVERED

The recent idea of immunization through oral route (edible vaccine) is vital alternatives over conventional vaccines. Edible vaccines are composed of antigenic protein introduced into the plant cells which induce these altered plants to produce the encoded protein. Edible vaccine has no way of forming infection and safety is assured as it only composed of antigenic protein and is devoid of pathogenic genes. Edible vaccines have significant role in stimulating mucosal immunity as they come in contact with digestive tract lining. They are safe, cost-effective, easy-to-administer and have reduced manufacturing cost hence have a dramatic impact on health care in developing countries.

EXPERT OPINION

The edible vaccine might be the solution for the potential hazard associated with the parenteral vaccines. In this review we discuss the detailed study of pros, cons, mechanism of immune stimulation, various outbreaks that might be controlled by edible vaccines with the possible future research and applied application of edible vaccine.

Review of recently used techniques and materials to improve the efficiency of orally administered proteins/peptides

OBJECTIVES

The main objective of present review is to explore and evaluate the effectiveness of recently developed methods to improve the bioavailability of orally administered biopharmaceutical drugs.

METHODS

A systematic search of sciencedirect, tandfonline and Google Scholar databases based on various sets of keywords was performed. All results were evaluated based on their abstracts, and irrelevant studies were neglected during further evaluation.

RESULTS

At present, biopharmaceuticals are used as injectable therapies as they are not absorbed adequately from the different routes of drug administration, particularly the oral one. Their insufficient absorption is attributed to their high molecular weight, degradation by proteolytic enzymes, high hydrophilicity and rigidity of the absorptive tissues. From industrial aspect incorporation of enzyme inhibitors (EIs) and permeation enhancers (PEs) and mucoadhesive polymers into conventional dosage forms may be the easiest way of formulation of orally administered macromolecular drugs, but the effectiveness of protection and absorption enhancement here is the most questionable. Conjugation may be problematic from regulatory aspect. Encapsulation into lipid-based vesicles sufficiently protects the incorporated macromolecule and improves intestinal uptake but have considerable stability issues. In contrast, polymeric nanocarriers may provide good stability but provides lower internalization efficacy in comparison with the lipid-based carriers.

CONCLUSION

It can be concluded that the combination of the advantages of mucoadhesive polymeric and lid-based carriers in hybrid lipid/polymer nanoparticles may result in improved absorption and might represent a potential means for the oral administration of therapeutic proteins in the near future. Graphical abstract Delivery systems for oral protein daministration.

Role of Small Intestine and Gut Microbiome in Plant-Based Oral Tolerance for Hemophilia

Fusion proteins, which consist of factor VIII or factor IX and the transmucosal carrier cholera toxin subunit B, expressed in chloroplasts and bioencapsulated within plant cells, initiate tolerogenic immune responses in the intestine when administered orally. This approach induces regulatory T cells (Treg), which suppress inhibitory antibody formation directed at hemophilia proteins induced by intravenous replacement therapy in hemophilia A and B mice. Further analyses of Treg CD4+ lymphocyte sub-populations in hemophilia B mice reveal a marked increase in the frequency of CD4+CD25-FoxP3-LAP+ T cells (but not of CD4+CD25+FoxP3+ T cells) in the lamina propria of the small but not large intestine. The adoptive transfer of very small numbers of CD4+CD25-LAP+ Treg isolated from the spleen of tolerized mice was superior in suppression of antibodies directed against FIX when compared to CD4+CD25+ T cells. Thus, tolerance induction by oral delivery of antigens bioencapsulated in plant cells occurs via the unique immune system of the small intestine, and suppression of antibody formation is primarily carried out by induced latency-associated peptide (LAP) expressing Treg that likely migrate to the spleen. Tolerogenic antigen presentation in the small intestine requires partial enzymatic degradation of plant cell wall by commensal bacteria in order to release the antigen. Microbiome analysis of hemophilia B mice showed marked differences between small and large intestine. Remarkably, bacterial species known to produce a broad spectrum of enzymes involved in degradation of plant cell wall components were found in the small intestine, in particular in the duodenum. These were highly distinct from populations of cell wall degrading bacteria found in the large intestine. Therefore, FIX antigen presentation and Treg induction by the immune system of the small intestine relies on activity of a distinct microbiome that can potentially be augmented to further enhance this approach.

Investigational new drug enabling angiotensin oral-delivery studies to attenuate pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a deadly and uncurable disease characterized by remodeling of the pulmonary vasculature and increased pulmonary artery pressure. Angiotensin Converting Enzyme 2 (ACE2) and its product, angiotensin-(1-7) [ANG-(1-7)] were expressed in lettuce chloroplasts to facilitate affordable oral drug delivery. Lyophilized lettuce cells were stable up to 28 months at ambient temperature with proper folding, assembly of CTB-ACE2/ANG-(1-7) and functionality. When the antibiotic resistance gene was removed, Ang1-7 expression was stable in subsequent generations in marker-free transplastomic lines. Oral gavage of monocrotaline-induced PAH rats resulted in dose-dependent delivery of ANG-(1-7) and ACE2 in plasma/tissues and PAH development was attenuated with decreases in right ventricular (RV) hypertrophy, RV systolic pressure, total pulmonary resistance and pulmonary artery remodeling. Such attenuation correlated well with alterations in the transcription of Ang-(1-7) receptor MAS and angiotensin II receptor AGTRI as well as IL-1β and TGF-β1. Toxicology studies showed that both male and female rats tolerated ~10-fold ACE2/ANG-(1-7) higher than efficacy dose. Plant cell wall degrading enzymes enhanced plasma levels of orally delivered protein drug bioencapsulated within plant cells. Efficient attenuation of PAH with no toxicity augurs well for clinical advancement of the first oral protein therapy to prevent/treat underlying pathology for this disease.

Oral delivery of novel human IGF-1 bioencapsulated in lettuce cells promotes musculoskeletal cell proliferation, differentiation and diabetic fracture healing

Human insulin-like growth factor-1 (IGF-1) plays important roles in development and regeneration of skeletal muscles and bones but requires daily injections or surgical implantation. Current clinical IGF-1 lacks e-peptide and is glycosylated, reducing functional efficacy. In this study, codon-optimized Pro-IGF-1 with e-peptide (fused to GM1 receptor binding protein CTB or cell penetrating peptide PTD) was expressed in lettuce chloroplasts to facilitate oral delivery. Pro-IGF-1 was expressed at high levels in the absence of the antibiotic resistance gene in lettuce chloroplasts and was maintained in subsequent generations. In lyophilized plant cells, Pro-IGF-1 maintained folding, assembly, stability and functionality up to 31 months, when stored at ambient temperature. CTB-Pro-IGF-1 stimulated proliferation of human oral keratinocytes, gingiva-derived mesenchymal stromal cells and mouse osteoblasts in a dose-dependent manner and promoted osteoblast differentiation through upregulation of ALP, OSX and RUNX2 genes. Mice orally gavaged with the lyophilized plant cells significantly increased IGF-1 levels in sera, skeletal muscles and was stable for several hours. When bioencapsulated CTB-Pro-IGF-1 was gavaged to femoral fractured diabetic mice, bone regeneration was significantly promoted with increase in bone volume, density and area. This novel delivery system should increase affordability and patient compliance, especially for treatment of musculoskeletal diseases.

Expression of a Functional Recombinant Human Glycogen Debranching Enzyme (hGDE) in N. benthamiana Plants and in Hairy Root Cultures

BACKGROUND

Glycogen storage disease type III (GSDIII, Cori/Forbes disease) is a metabolic disorder due to the deficiency of the Glycogen Debranching Enzyme (GDE), a large monomeric protein (about 176 kDa) with two distinct enzymatic activities: 4-α-glucantransferase and amylo-α-1,6-glucosidase. Several mutations along the amylo-alpha-1,6-glucosidase,4-alphaglucanotransferase (Agl) gene are associated with loss of enzymatic activity. The unique treatment for GSDIII, at the moment, is based on diet. The potential of plants to manufacture exogenous engineered compounds for pharmaceutical purposes, from small to complex protein molecules such as vaccines, antibodies and other therapeutic/prophylactic entities, was shown by modern biotechnology through "Plant Molecular Farming".

OBJECTIVE AND METHODS

In an attempt to develop novel protein-based therapeutics for GSDIII, the Agl gene, encoding for the human GDE (hGDE) was engineered for expression as a histidinetagged GDE protein both in Nicotiana benthamiana plants by a transient expression approach, and in axenic hairy root in vitro cultures (HR) from Lycopersicum esculentum and Beta vulgaris.

RESULTS

In both plant-based expression formats, the hGDE protein accumulated in the soluble fraction of extracts. The plant-derived protein was purified by affinity chromatography in native conditions showing glycogen debranching activity.

CONCLUSION

These investigations will be useful for the design of a new generation of biopharmaceuticals based on recombinant GDE protein that might represent, in the future, a possible therapeutic option for GSDIII.

Biomimetic and bioinspired strategies for oral drug delivery

Oral drug delivery remains the most preferred approach due to its multiple advantages. Recently there has been increasing interest in the development of advanced vehicles for oral delivery of different therapeutics. Among them, biomimetic and bioinspired strategies are emerging as novel approaches that are promising for addressing biological barriers encountered by traditional drug delivery systems. Herein we provide a state-of-the-art review on the current progress of biomimetic particulate oral delivery systems. Different biomimetic nanoparticles used for oral drug delivery are first discussed, mainly including ligand/antibody-functionalized nanoparticles, transporter-mediated nanoplatforms, and nanoscale extracellular vesicles. Then we describe bacteria-derived biomimetic systems, with respect to oral delivery of therapeutic proteins or antigens. Subsequently, yeast-derived oral delivery systems, based on either chemical engineering or bioengineering approaches are discussed, with emphasis on the treatment of inflammatory diseases and cancer as well as oral vaccination. Finally, bioengineered plant cells are introduced for oral delivery of biological agents. A future perspective is also provided to highlight the existing challenges and possible resolution toward clinical translation of currently developed biomimetic oral therapies.

Cold chain and virus-free oral polio booster vaccine made in lettuce chloroplasts confers protection against all three poliovirus serotypes

To prevent vaccine-associated paralytic poliomyelitis, WHO recommended withdrawal of Oral Polio Vaccine (Serotype-2) and a single dose of Inactivated Poliovirus Vaccine (IPV). IPV however is expensive, requires cold chain, injections and offers limited intestinal mucosal immunity, essential to prevent polio reinfection in countries with open sewer system. To date, there is no virus-free and cold chain-free polio vaccine capable of inducing robust mucosal immunity. We report here a novel low-cost, cold chain/poliovirus-free, booster vaccine using poliovirus capsid protein (VP1, conserved in all serotypes) fused with cholera non-toxic B subunit (CTB) expressed in lettuce chloroplasts. PCR using unique primer sets confirmed site-specific integration of CTB-VP1 transgene cassettes. Absence of the native chloroplast genome in Southern blots confirmed homoplasmy. Codon optimization of the VP1 coding sequence enhanced its expression 9-15-fold in chloroplasts. GM1-ganglioside receptor-binding ELISA confirmed pentamer assembly of CTB-VP1 fusion protein, fulfilling a key requirement for oral antigen delivery through gut epithelium. Transmission Electron Microscope images and hydrodynamic radius analysis confirmed VP1-VLPs of 22.3 nm size. Mice primed with IPV and boosted three times with lyophilized plant cells expressing CTB-VP1co, formulated with plant-derived oral adjuvants, enhanced VP1-specific IgG1, VP1-IgA titres and neutralization (80%-100% seropositivity of Sabin-1, 2, 3). In contrast, IPV single dose resulted in <50% VP1-IgG1 and negligible VP1-IgA titres, poor neutralization and seropositivity (<20%, <40% Sabin 1,2). Mice orally boosted with CTB-VP1co, without IPV priming, failed to produce any protective neutralizing antibody. Because global population is receiving IPV single dose, booster vaccine free of poliovirus or cold chain offers a timely low-cost solution to eradicate polio.

Production of tetravalent dengue virus envelope protein domain III based antigens in lettuce chloroplasts and immunologic analysis for future oral vaccine development

Dengue fever is a mosquito (Aedes aegypti) -transmitted viral disease that is endemic in more than 125 countries around the world. There are four serotypes of the dengue virus (DENV 1-4) and a safe and effective dengue vaccine must provide protection against all four serotypes. To date, the first vaccine, Dengvaxia (CYD-TDV), is available after many decades' efforts, but only has moderate efficacy. More effective and affordable vaccines are hence required. Plants offer promising vaccine production platforms and food crops offer additional advantages for the production of edible human and animal vaccines, thus eliminating the need for expensive fermentation, purification, cold storage and sterile delivery. Oral vaccines can elicit humoural and cellular immunity via both the mucosal and humoral immune systems. Here, we report the production of tetravalent EDIII antigen (EDIII-1-4) in stably transformed lettuce chloroplasts. Transplastomic EDIII-1-4-expressing lettuce lines were obtained and homoplasmy was verified by Southern blot analysis. Expression of EDIII-1-4 antigens was demonstrated by immunoblotting, with the EDIII-1-4 antigen accumulating to 3.45% of the total protein content. Immunological assays in rabbits showed immunogenicity of EDIII-1-4. Our in vitro gastrointestinal digestion analysis revealed that EDIII-1-4 antigens are well protected when passing through the oral and gastric digestion phases but underwent degradation during the intestinal phase. Our results demonstrate that lettuce chloroplast engineering is a promising approach for future production of an affordable oral dengue vaccine.

Plant cell-made protein antigens for induction of Oral tolerance

The gut associated lymphoid tissue has effective mechanisms in place to maintain tolerance to food antigens. These can be exploited to induce antigen-specific tolerance for the prevention and treatment of autoimmune diseases and severe allergies and to prevent serious immune responses in protein replacement therapies for genetic diseases. An oral tolerance approach for the prevention of peanut allergy in infants proved highly efficacious and advances in treatment of peanut allergy have brought forth an oral immunotherapy drug that is currently awaiting FDA approval. Several other protein antigens made in plant cells are in clinical development. Plant cell-made proteins are protected in the stomach from acids and enzymes after their oral delivery because of bioencapsulation within plant cell wall, but are released to the immune system upon digestion by gut microbes. Utilization of fusion protein technologies facilitates their delivery to the immune system, oral tolerance induction at low antigen doses, resulting in efficient induction of FoxP3⁺ and latency-associated peptide (LAP)⁺ regulatory T cells that express immune suppressive cytokines such as IL-10. LAP and IL-10 expression represent potential biomarkers for plant-based oral tolerance. Efficacy studies in hemophilia dogs support clinical development of oral delivery of bioencapsulated antigens to prevent anti-drug antibody formation. Production of clinical grade materials in cGMP facilities, stability of antigens in lyophilized plant cells for several years when stored at ambient temperature, efficacy of oral delivery of human doses in large animal models and lack of toxicity augur well for clinical advancement of this novel drug delivery concept.

Nanoparticles: Oral Delivery for Protein and Peptide Drugs

Protein and peptide drugs have many advantages, such as high bioactivity and specificity, strong solubility, and low toxicity. Therefore, the strategies for improving the bioavailability of protein peptides are reviewed, including chemical modification of nanocarriers, absorption enhancers, and mucous adhesion systems. The status, advantages, and disadvantages of various strategies are systematically analyzed. The systematic and personalized design of various factors affecting the release and absorption of drugs based on nanoparticles is pointed out. It is expected to design a protein peptide oral delivery system that can be applied in the clinic.

An evaluation of microalgae as a recombinant protein oral delivery platform for fish using green fluorescent protein (GFP)

Recombinant proteins produced by biological systems such as bacteria, yeasts, mammalian and insect cell cultures are widely used for clinical or industrial purposes. Most therapeutic protein drugs require purification, cold chain, and injection, which make them prohibitively expensive and hinders their widespread use. Here, we describe a new economical oral vaccination platform using algae and evaluated its potential for the delivery of recombinant drugs using GFP expressed in the chloroplast of algal cells. The transplastomic algae expressing recombinant GFPs were freeze-dried for long-term storage at ambient temperature and for easy handling in feeding. GFPs bioencapsulated by lyophilized Chlamydomonas reinhardtii were found intact without degradation for several months at ambient temperature. The expression level of GFP in the lyophilized algae was estimated at 0.47 μg/mg dry weight. The GFPs bioencapsulated and orally delivered to Danio rerio were immunostained and observed in the intestinal tissues using a confocal microscope. Furthermore, the uptaken GFPs in the intestine were detected in the blood using ELISA and the detected level was 5.4 ng of GFP/μl of serum. These results demonstrate that microalgae can be a viable protein production and oral delivery system to vaccinate fish. The results give greater justification to continue exploring the concept of microalgal-based oral vaccines. The potential of the technology would greatly benefit aquaculture farmers by providing them with affordable, environmentally sustainable, and user-friendly vaccines.

Challenges and Recent Progress in Oral Drug Delivery Systems for Biopharmaceuticals

Routes of drug administration and the corresponding physicochemical characteristics of a given route play significant roles in therapeutic efficacy and short term/long term biological effects. Each delivery method has favorable aspects and limitations, each requiring a specific delivery vehicles design. Among various routes, oral delivery has been recognized as the most attractive method, mainly due to its potential for solid formulations with long shelf life, sustained delivery, ease of administration and intensified immune response. At the same time, a few challenges exist in oral delivery, which have been the main research focus in the field in the past few years. The present work concisely reviews different administration routes as well as the advantages and disadvantages of each method, highlighting why oral delivery is currently the most promising approach. Subsequently, the present work discusses the main obstacles for oral systems and explains the most recent solutions proposed to deal with each issue.

A new prokaryotic expression vector for the expression of antimicrobial peptide abaecin using SUMO fusion tag

Background

Despite the growing demand for antimicrobial peptides (AMPs) for clinical use as an alternative approach against antibiotic-resistant bacteria, the manufacture of AMPs relies on expensive, small-scale chemical methods. The small ubiquitin-related modifier (SUMO) tag is industrially practical for increasing the yield of recombinant proteins by increasing solubility and preventing degradation in expression systems.

Results

A new vector system, pKSEC1, was designed to produce AMPs, which can work in prokaryotic systems such as Escherichia coli and plant chloroplasts. 6xHis was tagged to SUMO for purification of SUMO-fused AMPs. Abaecin, a 34-aa-long antimicrobial peptide from honeybees, was expressed in a fusion form to 6xHis-SUMO in a new vector system to evaluate the prokaryotic expression platform of the antimicrobial peptides. The fusion sequences were codon-optimized in three different combinations and expressed in E. coli. The combination of the native SUMO sequence with codon-optimized abaecin showed the highest expression level among the three combinations, and most of the expressed fusion proteins were detected in soluble fractions. Cleavage of the SUMO tag by sumoase produced a 29-aa-long abaecin derivative with a C-terminal deletion. However, this abaecin derivative still retained the binding sequence for its target protein, DnaK. Antibacterial activity of the 29-aa long abaecin was tested against Bacillus subtilis alone or in combination with cecropin B. The combined treatment of the abaecin derivative and cecropin B showed bacteriolytic activity 2 to 3 times greater than that of abaecin alone.

Conclusions

Using a SUMO-tag with an appropriate codon-optimization strategy could be an approach for the production of antimicrobial peptides in E.coli without affecting the viability of the host cell.

Electronic supplementary material

The online version of this article (10.1186/s12896-019-0506-x) contains supplementary material, which is available to authorized users.

Research, diagnosis and education in inborn errors of metabolism in Colombia: 20 years' experience from a reference center

The use of specialized centers has been the main alternative for an appropriate diagnosis, management and follow up of patients affected by inborn errors of metabolism (IEM). These centers facilitate the training of different professionals, as well as the research at basic, translational and clinical levels. Nevertheless, few reports have described the experience of these centers and their local and/or global impact in the study of IEM. In this paper, we describe the experience of a Colombian reference center for the research, diagnosis, training and education on IEM. During the last 20 years, important advances have been achieved in the clinical knowledge of these disorders, as well as in the local availability of several diagnosis tests. Organic acidurias have been the most frequently detected diseases, followed by aminoacidopathies and peroxisomal disorders. Research efforts have been focused in the production of recombinant proteins in microorganisms towards the development of new enzyme replacement therapies, the design of gene therapy vectors and the use of bioinformatics tools for the understanding of IEM. In addition, this center has participated in the education and training of a large number professionals at different levels, which has contributed to increase the knowledge and divulgation of these disorders along the country. Noteworthy, in close collaboration with patient advocacy groups, we have participated in the discussion and construction of initiatives for the inclusion of diagnosis tests and treatments in the health system.

Expression and assembly of largest foreign protein in chloroplasts: oral delivery of human FVIII made in lettuce chloroplasts robustly suppresses inhibitor formation in haemophilia A mice

Inhibitor formation is a serious complication of factor VIII (FVIII) replacement therapy for the X-linked bleeding disorder haemophilia A and occurs in 20%-30% of patients. No prophylactic tolerance protocol currently exists. Although we reported oral tolerance induction using FVIII domains expressed in tobacco chloroplasts, significant challenges in clinical advancement include expression of the full-length CTB-FVIII sequence to cover the entire patient population, regardless of individual CD4+ T-cell epitope responses. Codon optimization of FVIII heavy chain (HC) and light chain (LC) increased expression 15- to 42-fold higher than the native human genes. Homoplasmic lettuce lines expressed CTB fusion proteins of FVIII-HC (99.3 kDa), LC (91.8 kDa), C2 (31 kDa) or single chain (SC, 178.2 kDa) up to 3622, 263, 3321 and 852 μg/g in lyophilized plant cells, when grown in a cGMP hydroponic facility (Fraunhofer). CTB-FVIII-SC is the largest foreign protein expressed in chloroplasts; despite a large pentamer size (891 kDa), assembly, folding and disulphide bonds were maintained upon lyophilization and long-term storage as revealed by GM1-ganglioside receptor binding assays. Repeated oral gavages (twice/week for 2 months) of CTB-FVIII-HC/CTB-FVIII-LC reduced inhibitor titres ~10-fold (average 44 BU/mL to 4.7 BU/mL) in haemophilia A mice. Most importantly, increase in the frequency of circulating LAP-expressing CD4+ CD25+ FoxP3+ Treg in tolerized mice could be used as an important cellular biomarker in human clinical trials for plant-based oral tolerance induction. In conclusion, this study reports the first clinical candidate for oral tolerance induction that is urgently needed to protect haemophilia A patients receiving FVIII injections.

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.

Enhanced transport of plant-produced rabies single-chain antibody-RVG peptide fusion protein across an in cellulo blood-brain barrier device

The biomedical applications of antibody engineering are developing rapidly and have been expanded to plant expression platforms. In this study, we have generated a novel antibody molecule in planta for targeted delivery across the blood-brain barrier (BBB). Rabies virus (RABV) is a neurotropic virus for which there is no effective treatment after entry into the central nervous system. This study investigated the use of a RABV glycoprotein peptide sequence to assist delivery of a rabies neutralizing single-chain antibody (ScFv) across an in cellulo model of human BBB. The 29 amino acid rabies virus peptide (RVG) recognizes the nicotinic acetylcholine receptor (nAchR) at neuromuscular junctions and the BBB. ScFv and ScFv-RVG fusion proteins were produced in Nicotiana benthamiana by transient expression. Both molecules were successfully expressed and purified, but the ScFv expression level was significantly higher than that of ScFv-RVG fusion. Both ScFv and ScFv-RVG fusion molecules had potent neutralization activity against RABVin cellulo. The ScFv-RVG fusion demonstrated increased binding to nAchR and entry into neuronal cells, compared to ScFv alone. Additionally, a human brain endothelial cell line BBB model was used to demonstrate that plant-produced ScFv-RVGP fusion could translocate across the cells. This study indicates that the plant-produced ScFv-RVGP fusion protein was able to cross the in celluloBBB and neutralize RABV.

LTB-Syn: a recombinant immunogen for the development of plant-made vaccines against synucleinopathies

A recombinant antigen targeting α-synuclein was produced in the plant cell rendering an immunogenic protein capable to induce humoral responses in mice upon oral administration. Synucleinopathies are neurodegenerative diseases characterized by the abnormal accumulation of α-synuclein (α-Syn, a 140 amino acid protein that normally plays various neurophysiologic roles) aggregates. Parkinson's disease (PD) is the synucleinopathy with the highest epidemiologic impact and although its etiology remains unknown, α-Syn aggregation during disease progression pointed out α-Syn as target in the development of immunotherapies. Herein a chimeric protein, comprising the B subunit of the enterotoxin from enterotoxigenic Escherichia coli and α-Syn epitopes, was expressed in the plant cell having the potential to induce humoral responses following oral immunization. This approach will serve as the basis for the development of oral plant-based vaccines against PD with several potential advantages such as low cost, easy scale-up during production, and easy administration.

Investigating Engineered Ribonucleoprotein Particles to Improve Oral RNAi Delivery in Crop Insect Pests

Genetically modified (GM) crops producing double-stranded RNAs (dsRNAs) are being investigated largely as an RNA interference (RNAi)-based resistance strategy against crop insect pests. However, limitations of this strategy include the sensitivity of dsRNA to insect gut nucleases and its poor insect cell membrane penetration. Working with the insect pest cotton boll weevil (Anthonomus grandis), we showed that the chimeric protein PTD-DRBD (peptide transduction domain—dsRNA binding domain) combined with dsRNA forms a ribonucleoprotein particle (RNP) that improves the effectiveness of the RNAi mechanism in the insect. The RNP slows down nuclease activity, probably by masking the dsRNA. Furthermore, PTD-mediated internalization in insect gut cells is achieved within minutes after plasma membrane contact, limiting the exposure time of the RNPs to gut nucleases. Therefore, the RNP provides an approximately 2-fold increase in the efficiency of insect gene silencing upon oral delivery when compared to naked dsRNA. Taken together, these data demonstrate the role of engineered RNPs in improving dsRNA stability and cellular entry, representing a path toward the design of enhanced RNAi strategies in GM plants against crop insect pests.