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

Expanding Possibilities for Foreign Gene Expression by Cucumber Green Mottle Mosaic Virus Genome-Based Bipartite Vector System

Expanding possibilities for foreign gene expression in cucurbits, we present a novel approach utilising a bipartite vector system based on the cucumber green mottle mosaic virus (CGMMV) genome. Traditional full-length CGMMV vectors face limitations such as a restricted cargo capacity and unstable foreign gene expression. To address these challenges, we developed two 'deconstructed' CGMMV genomes, DG-1 and DG-2. DG-1 features a major internal deletion, resulting in the loss of crucial replicase enzyme domains, rendering it incapable of self-replication. However, a staggered infiltration of DG-1 in CGMMV-infected plants enabled successful replication and movement, facilitating gene-silencing experiments. Conversely, DG-2 was engineered to enhance replication rates and provide multiple cloning sites. Although it exhibited higher replication rates, DG-2 remained localised within infiltrated tissue, displaying trans-replication and restricted movement. Notably, DG-2 demonstrated utility in expressing GFP, with a peak expression observed between 6 and 10 days post-infiltration. Overall, our bipartite system represents a significant advancement in functional genomics, offering a robust tool for foreign gene expression in Nicotiana benthamiana.

Development of tobacco rattle virus-based platform for dual heterologous gene expression and CRISPR/Cas reagent delivery

A large number of viral delivery systems have been developed for characterizing functional genes and producing heterologous recombinant proteins in plants, and but most of them are unable to co-express two fusion-free foreign proteins in the whole plant for extended periods of time. In this study, we modified tobacco rattle virus (TRV) as a TRVe dual delivery vector, using the strategy of gene substitution. The reconstructed TRVe had the capability to simultaneously produce two fusion-free foreign proteins at the whole level of Nicotiana benthamiana, and maintained the genetic stability for the insert of double foreign genes. Moreover, TRVe allowed systemic expression of two foreign proteins with the total lengths up to ∼900 aa residues. In addition, Cas12a protein and crRNA were delivered by the TRVe expression system for site-directed editing of genomic DNA in N. benthamiana 16c line constitutively expressing green fluorescent protein (GFP). Taker together, the TRV-based delivery system will be a simple and powerful means to rapidly co-express two non-fused foreign proteins at the whole level and facilitate functional genomics studies in plants.

Multiple gene expression in plants using MIDAS-P, a versatile type II restriction-based modular expression vector

MIDAS-P is a plant expression vector with blue/white screening for iterative cloning of multiple, tandemly arranged transcription units (TUs). We have used the MIDAS-P system to investigate the expression of up to five genes encoding three anti-HIV proteins and the reporter gene DsRed in Nicotiana benthamiana plants. The anti-HIV cocktail was made up of a broadly neutralizing monoclonal antibody (VRC01), a lectin (Griffithsin), and a single-chain camelid nanobody (J3-VHH). Constructs containing different combinations of 3, 4, or 5 TUs encoding different components of the anti-HIV cocktail were assembled. Messenger RNA (mRNA) levels of the genes of interest decreased beyond two TUs. Coexpression of the RNA silencing suppressor P19 dramatically increased the overall mRNA and protein expression levels of each component. The position of individual TUs in 3 TU constructs did not affect mRNA or protein expression levels. However, their expression dropped to non-detectable levels in constructs with four or more TUs each containing the same promoter and terminator elements, with the exception of DsRed at the first or last position in 5 TU constructs. This drop was alleviated by co-expression of P19. In short, the MIDAS-P system is suitable for the simultaneous expression of multiple proteins in one construct.

Efficient Protein Expression and Virus-Induced Gene Silencing in Plants Using a Crinivirus-Derived Vector

Plant virus-based vectors are valuable tools for recombinant gene expression and functional genomics for both basic and applied research. In this study, Lettuce infectious yellows virus (LIYV) of the genus Crinivirus was engineered into a virus vector that is applicable for efficient protein expression and virus-induced gene silencing (VIGS) in plants. We examined gene replacement and “add a gene” strategies to develop LIYV-derived vectors for transient expression of the green fluorescent protein (GFP) reporter in Nicotiana benthamiana plants. The latter yielded higher GFP expression and was further examined by testing the effects of heterologous controller elements (CEs). A series of five vector constructs with progressively extended LIYV CP sgRNA CEs were tested, the longest CE gave the highest GFP expression but lower virus accumulation. The whitefly transmissibility of the optimized vector construct to other host plants, and the capability to accommodate and express a larger gene, a 1.8 kb β-glucuronidase (GUS) gene, were confirmed. Furthermore, the LIYV vector was also validated VIGS by silencing the endogenous gene, phytoene desaturase (PDS) in N. benthamiana plants, and the transgene GFP in N. benthamiana line 16c plants. Therefore, LIYV-derived vectors could provide a technical reference for developing vectors of other economically important criniviruses.

A CGMMV genome-replicon vector with partial sequences of coat protein gene efficiently expresses GFP in Nicotiana benthamiana

A highly infectious clone of Cucumber green mottle mosaic virus (CGMMV), a cucurbit-infecting tobamovirus was utilized for designing of gene expression vectors. Two versions of vector were examined for their efficacy in expressing the green fluorescent protein (GFP) in Nicotiana benthamiana. When the GFP gene was inserted at the stop codon of coat protein (CP) gene of the CGMMV genome without any read-through codon, systemic expression of GFP, as well as virion formation and systemic symptoms expression were obtained in N. benthamiana. The qRT-PCR analysis showed 23 fold increase of GFP over actin at 10days post inoculation (dpi), which increased to 45 fold at 14dpi and thereafter the GFP expression was significantly declined. Further, we show that when the most of the CP sequence is deleted retaining only the first 105 nucleotides, the shortened vector containing GFP in frame of original CP open reading frame (ORF) resulted in 234 fold increase of GFP expression over actin at 5dpi in N. benthamiana without the formation of virions and disease symptoms. Our study demonstrated that a simple manipulation of CP gene in the CGMMV genome while preserving the translational frame of CP resulted in developing a virus-free, rapid and efficient foreign protein expression system in the plant. The CGMMV based vectors developed in this study may be potentially useful for the production of edible vaccines in cucurbits.

Techno-economic analysis of a transient plant-based platform for monoclonal antibody production

Plant-based biomanufacturing of therapeutic proteins is a relatively new platform with a small number of commercial-scale facilities, but offers advantages of linear scalability, reduced upstream complexity, reduced time to market, and potentially lower capital and operating costs. In this study we present a detailed process simulation model for a large-scale new "greenfield" biomanufacturing facility that uses transient agroinfiltration of Nicotiana benthamiana plants grown hydroponically indoors under light-emitting diode lighting for the production of a monoclonal antibody. The model was used to evaluate the total capital investment, annual operating cost, and cost of goods sold as a function of mAb expression level in the plant (g mAb/kg fresh weight of the plant) and production capacity (kg mAb/year). For the Base Case design scenario (300 kg mAb/year, 1 g mAb/kg fresh weight, and 65% recovery in downstream processing), the model predicts a total capital investment of $122 million dollars and cost of goods sold of $121/g including depreciation. Compared with traditional biomanufacturing platforms that use mammalian cells grown in bioreactors, the model predicts significant reductions in capital investment and >50% reduction in cost of goods compared with published values at similar production scales. The simulation model can be modified or adapted by others to assess the profitability of alternative designs, implement different process assumptions, and help guide process development and optimization.

When plant virology met Agrobacterium: the rise of the deconstructed clones

In the early days of molecular farming, Agrobacterium-mediated stable genetic transformation and the use of plant virus-based vectors were considered separate and competing technologies with complementary strengths and weaknesses. The demonstration that 'agroinfection' was the most efficient way of delivering virus-based vectors to their target plants blurred the distinction between the two technologies and permitted the development of 'deconstructed' vectors based on a number of plant viruses. The tobamoviruses, potexviruses, tobraviruses, geminiviruses and comoviruses have all been shown to be particularly well suited to the development of such vectors in dicotyledonous plants, while the development of equivalent vectors for use in monocotyledonous plants has lagged behind. Deconstructed viral vectors have proved extremely effective at the rapid, high-level production of a number of pharmaceutical proteins, some of which are currently undergoing clinical evaluation.

Commercial-scale biotherapeutics manufacturing facility for plant-made pharmaceuticals

Rapid, large-scale manufacture of medical countermeasures can be uniquely met by the plant-made-pharmaceutical platform technology. As a participant in the Defense Advanced Research Projects Agency (DARPA) Blue Angel project, the Caliber Biotherapeutics facility was designed, constructed, commissioned and released a therapeutic target (H1N1 influenza subunit vaccine) in <18 months from groundbreaking. As of 2015, this facility was one of the world's largest plant-based manufacturing facilities, with the capacity to process over 3500 kg of plant biomass per week in an automated multilevel growing environment using proprietary LED lighting. The facility can commission additional plant grow rooms that are already built to double this capacity. In addition to the commercial-scale manufacturing facility, a pilot production facility was designed based on the large-scale manufacturing specifications as a way to integrate product development and technology transfer. The primary research, development and manufacturing system employs vacuum-infiltrated Nicotiana benthamiana plants grown in a fully contained, hydroponic system for transient expression of recombinant proteins. This expression platform has been linked to a downstream process system, analytical characterization, and assessment of biological activity. This integrated approach has demonstrated rapid, high-quality production of therapeutic monoclonal antibody targets, including a panel of rituximab biosimilar/biobetter molecules and antiviral antibodies against influenza and dengue fever.

Development of a single-replicon miniBYV vector for co-expression of heterologous proteins

In planta production of recombinant proteins, including vaccine antigens and monoclonal antibodies, continues gaining acceptance. With the broadening range of target proteins, the need for vectors with higher performance is increasing. Here, we have developed a single-replicon vector based on beet yellows virus (BYV) that enables co-delivery of two target genes into the same host cell, resulting in transient expression of each target. This BYV vector maintained genetic stability during systemic spread throughout the host plant, Nicotiana benthamiana. Furthermore, we have engineered a miniBYV vector carrying the sequences encoding heavy and light chains of a monoclonal antibody (mAb) against protective antigen (PA) of Bacillius anthracis, and achieved the expression of the full-length functional anti-PA mAb at ~300 mg/kg of fresh leaf tissue. To demonstrate co-expression and functionality of two independent proteins, we cloned the sequences of the Pfs48/45 protein of Plasmodium falciparum and endoglycosidase F (PNGase F) from Flavobacterium meningosepticum into the miniBYV vector under the control of two subgenomic RNA promoters. Agroinfiltration of N. benthamiana with this miniBYV vector resulted in accumulation of biologically active Pfs48/45 that was devoid of N-linked glycosylation and had correct conformation and epitope display. Overall, our findings demonstrate that the new BYV-based vector is capable of co-expressing two functionally active recombinant proteins within the same host cell.

State of research in the field of the creation of plant vaccines for veterinary use

Transgenic plants as an alternative of costly systems of recombinant immunogenic protein expression are the source for the production of cheap and highly efficient biotherapeuticals of new generation, including plant vaccines. In the present review, possibilities of plant system application for the production of recombinant proteins for veterinary use are considered, the history of the "edible vaccine" concept is briefly summarized, advantages and disadvantages of various plant systems for the expression of recombinant immunogenic proteins are discussed. The list of recombinant plant vaccines for veterinary use, which are at different stages of clinical trials, is presented.

Synthetic immunosurveillance systems: nanodevices to monitor physiological events

The field of nanotechnology has recently seen vast advancements in its applications for therapeutic strategy. This technological revolution has led way to nanomedicine, which spurred the development of clever drug delivery designs and ingenious nanovehicles for the monitoring of cellular events in vivo. The clinical implementations of this technology are innumerable and have demonstrated utility as diagnostic tools and fortifying machineries for the mammalian immune system. Recently engineered viral vectors and multi-subunit packaging RNAs have verified stable enough for long-term existence in the physiological environment and therefore reveal unique potential as artificial immunosurveillance devices. Physiological and pathological events recorded by nanodevices could help develop "biocatalogs" of patients' infection history, frequency of disease, and much more. In this article, we introduce a novel design concept for a multilayer synthetic immune network parallel to the natural immune system; an artificial network of continuously patrolling nanodevices incorporated in the blood and lymphatic systems, and adapted for molecular event recording, anomaly detection, drug delivery, and gene silencing. We also aim to discuss the approaches and advances recently reported in nanomedicine, especially as it pertains to promising viral and RNA-based nanovehicles and their prospective applications for the development of a synthetic immunosurveillance system (SIS). Alternative suggestions and limitations of these technologies are also discussed.

Potato virus X-based expression vectors are stabilized for long-term production of proteins and larger inserts

Plus-strand RNA viruses such as Potato virus X (PVX) are often used as high-yielding expression vectors in plants, because they tolerate extra transgene insertion and expression without disrupting normal virus functions. However, sequence redundancy due to promoter duplication often leads to genetic instability. Although heterologous subgenomic promoter-like sequences (SGPs) have been successfully used in Tobacco mosaic virus vectors, only homologous SGP duplications have been used in PVX vectors. We stabilized PVX-based vectors by combining heterologous SGPs from related potexviruses with an N-terminal coat protein (CP) deletion. We selected two SGPs with core sequences homologous to PVX, from Bamboo mosaic virus (BaMV) and Cassava common mosaic virus, as well as a SGP with a heterologous core sequence from Foxtail mosaic virus (FoMV). We found that only the BaMV and CsCMV SGPs were utilized by the PVX replicase. However, the transgene remained unstable, due to the presence of an additional region with strong sequence similarity at the 5' end of the cp gene. The BaMV SGP combined with an N-terminal CP deletion achieved high PVX vector stability. This new expression vector is particularly useful for long-term production of proteins and for larger inserts. The improved PVX-based vectors are suitable for the systemic expression of any gene of interest in PVX host plants. The PVX-based vector can be advantageous for the overexpression of proteins, to analyze protein functions in planta or as a system for virus-induced gene silencing.

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

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

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

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

An efficient Foxtail mosaic virus vector system with reduced environmental risk

BACKGROUND

Plant viral vectors offer high-yield expression of pharmaceutical and commercially important proteins with a minimum of cost and preparation time. The use of Agrobacterium tumefaciens has been introduced to deliver the viral vector as a transgene to each plant cell via a simple, nonsterile infiltration technique called "agroinoculation". With agroinoculation, a full length, systemically moving virus is no longer necessary for excellent protein yield, since the viral transgene is transcribed and replicates in every infiltrated cell. Viral genes may therefore be deleted to decrease the potential for accidental spread and persistence of the viral vector in the environment.

RESULTS

In this study, both the coat protein (CP) and triple gene block (TGB) genetic segments were eliminated from Foxtail mosaic virus to create the "FECT" vector series, comprising a deletion of 29% of the genome. This viral vector is highly crippled and expresses little or no marker gene within the inoculated leaf. However, when co-agroinoculated with a silencing suppressor (p19 or HcPro), FECT expressed GFP at 40% total soluble protein in the tobacco host, Nicotiana benthamiana. The modified FoMV vector retained the full-length replicase ORF, the TGB1 subgenomic RNA leader sequence and either 0, 22 or 40 bases of TGB1 ORF (in vectors FECT0, FECT22 and FECT40, respectively). As well as N. benthamiana, infection of legumes was demonstrated. Despite many attempts, expression of GFP via syringe agroinoculation of various grass species was very low, reflecting the low Agrobacterium-mediated transformation rate of monocots.

CONCLUSIONS

The FECT/40 vector expresses foreign genes at a very high level, and yet has a greatly reduced biohazard potential. It can form no virions and can effectively replicate only in a plant with suppressed silencing.