Immunogenicity of plant‐produced African horse sickness virus‐like particles: implications for a novel vaccine

African horse sickness (AHS) is a debilitating and often fatal viral disease affecting horses in much of Africa, caused by the dsRNA orbivirus African horse sickness virus (AHSV). Vaccination remains the single most effective weapon in combatting AHS, as there is no treatment for the disease apart from good animal husbandry. However, the only commercially available vaccine is a live‐attenuated version of the virus (LAV). The threat of outbreaks of the disease outside its endemic region and the fact that the LAV is not licensed for use elsewhere in the world, have spurred attempts to develop an alternative safer, yet cost‐effective recombinant vaccine. Here, we report the plant‐based production of a virus‐like particle (VLP) AHSV serotype five candidate vaccine by Agrobacterium tumefaciens‐mediated transient expression of all four capsid proteins in Nicotiana benthamiana using the cowpea mosaic virus‐based HyperTrans (CPMV‐HT) and associated pEAQ plant expression vector system. The production process is fast and simple, scalable, economically viable, and most importantly, guinea pig antiserum raised against the vaccine was shown to neutralize live virus in cell‐based assays. To our knowledge, this is the first report of AHSV VLPs produced in plants, which has important implications for the containment of, and fight against the spread of, this deadly disease.     

A DNA replicon system for rapid high‐level production of virus‐like particles in plants

Recombinant virus‐like particles (VLPs) represent a safe and effective vaccine strategy. We previously described a stable transgenic plant system for inexpensive production and oral delivery of VLP vaccines. However, the relatively low‐level antigen accumulation and long‐time frame to produce transgenic plants are the two major roadblocks in the practical development of plant‐based VLP production. In this article, we describe the optimization of geminivirus‐derived DNA replicon vectors for rapid, high‐yield plant‐based production of VLPs. Co‐delivery of bean yellow dwarf virus (BeYDV)‐derived vector and Rep/RepA‐supplying vector by agroinfiltration of Nicotiana benthamiana leaves resulted in efficient replicon amplification and robust protein production within 5 days. Co‐expression of the P19 protein of tomato bush stunt virus, a gene silencing inhibitor, further enhanced VLP accumulation by stabilizing the mRNA. With this system, hepatitis B core antigen (HBc) and Norwalk virus capsid protein (NVCP) were produced at 0.80 and 0.34 mg/g leaf fresh weight, respectively. Sedimentation analysis and electron microscopy of transiently expressed antigens verified the efficient assembly of VLPs. Furthermore, a single replicon vector containing a built‐in Rep/RepA cassette without P19 drove protein expression at similar levels as the three‐component system. These results demonstrate the advantages of fast and high‐level production of VLP‐based vaccines using the BeYDV‐derived DNA replicon system for transient expression in plants. Biotechnol. Bioeng. 2009;103: 706–714. © 2009 Wiley Periodicals, Inc.     

Biochemical composition of haemagglutinin‐based influenza virus‐like particle vaccine produced by transient expression in tobacco plants

Influenza virus‐like particles (VLPs) are noninfectious particles resembling the influenza virus representing a promising vaccine alternative to inactivated influenza virions as antigens. Medicago inc. has developed a plant‐based VLP manufacturing platform allowing the large‐scale production of GMP‐grade influenza VLPs. In this article, we report on the biochemical compositions of these plant‐based influenza candidate vaccines, more particularly the characterization of the N‐glycan profiles of the viral haemagglutinins H1 and H5 proteins as well as the tobacco‐derived lipid content and residual impurities. Mass spectrometry analyses showed that all N‐glycosylation sites of the extracellular domain of the recombinant haemagglutinins carry plant‐specific complex‐type N‐glycans having core α(1,3)‐fucose, core β(1,2)‐xylose epitopes and Lewis^a extensions. Previous phases I and II clinical studies have demonstrated that no hypersensibility nor induction of IgG or IgE directed against these glycans was observed. In addition, this article showed that the plant‐made influenza vaccines are highly pure VLPs preparations while detecting no protein contaminants coming either from Agrobacterium or from the enzymes used for the enzyme‐assisted extraction process. In contrast, VLPs contain few host cell proteins and glucosylceramides associated with plant lipid rafts. Identification of such raft markers, together with the type of host cell impurity identified, confirmed that the mechanism of VLP formation in planta is similar to the natural process of influenza virus assembly in mammals.     

Escherichia coli‐based cell free production of flagellin and ordered flagellin display on virus‐like particles

Bacterial flagellin has been explored as a potential vaccine adjuvant for enhancing immune responses. In this article, we describe Escherichia coli‐based cell‐free protein synthesis (CFPS) as a method to rapidly produce soluble phase 1 flagellin (FliC) protein from Salmonella typhimurium. The yield was about 300 µg/mL and the product had much higher affinity for the TLR5 receptor (EC50 = 2.4 ± 1.4 pM) than previously reported. The flagellin coding sequence was first optimized for cell‐free expression. We then found that the D0 domain at the C‐terminus of flagellin was susceptible to proteolytic degradation in the CFPS system. Proteolysis was reduced by protease inhibitors, the use of protease‐deficient cell extracts or deletion of the flagellin D0 domain. A human Toll‐Like Receptor 5 (hTLR5)‐specific bioactivity analysis of purified flagellin demonstrated that, although the D0 domain is far from the TLR5 recognition region, it is important for flagellin bioactivity. We next incorporated a non‐natural amino acid displaying an alkyne moiety into flagellin using the CFPS system and attached flagellin to hepatitis B core virus‐like particles (VLPs) using bioorthogonal azide‐alkyne cycloaddition reactions. The ordered and oriented VLP display of flagellin increased its specific TLR5 stimulation activity by approximately 10‐fold. Biotechnol. Bioeng. 2013; 110: 2073–2085. © 2013 Wiley Periodicals, Inc.     

Cell wall biochemical alterations during Agrobacterium‐mediated expression of haemagglutinin‐based influenza virus‐like vaccine particles in tobacco

Influenza virus‐like particles (VLPs) have been shown to induce a safe and potent immune response through both humoral and cellular responses. They represent promising novel influenza vaccines. Plant‐based biotechnology allows for the large‐scale production of VLPs of biopharmaceutical interest using different model organisms, including Nicotiana benthamiana plants. Through this platform, influenza VLPs bud from the plasma membrane and accumulate between the membrane and the plant cell wall. To design and optimize efficient production processes, a better understanding of the plant cell wall composition of infiltrated tobacco leaves is a major interest for the plant biotechnology industry. In this study, we have investigated the alteration of the biochemical composition of the cell walls of N. benthamiana leaves subjected to abiotic and biotic stresses induced by the Agrobacterium‐mediated transient transformation and the resulting high expression levels of influenza VLPs. Results show that abiotic stress due to vacuum infiltration without Agrobacterium did not induce any detectable modification of the leaf cell wall when compared to non infiltrated leaves. In contrast, various chemical changes of the leaf cell wall were observed post‐Agrobacterium infiltration. Indeed, Agrobacterium infection induced deposition of callose and lignin, modified the pectin methylesterification and increased both arabinosylation of RG‐I side chains and the expression of arabinogalactan proteins. Moreover, these modifications were slightly greater in plants expressing haemagglutinin‐based VLP than in plants infiltrated with the Agrobacterium strain containing only the p19 suppressor of silencing.     

Effects of disinfectants against norovirus virus‐like particles predict norovirus inactivation

Human noroviruses (NoVs) are a major cause of epidemic and sporadic acute gastroenteritis worldwide. Public and personal hygiene is one of the most important countermeasures for preventing spread of NoV infection. However, no a practicable cell culture system for NoV had been developed, initial tests of the virucidal effectiveness of anti‐NoV disinfectants and sanitizers have been performed using surrogate viruses. In this study, NoV virus‐like particles (VLPs) were used as a new surrogate for NoVs and a method for evaluating NoV inactivation using them developed. This method is based on morphological changes in VLPs after treatment with sodium hypochlorite. VLP specimens were found to become deformed and degraded in a concentration‐dependent manner. Based on these results, the effects of sodium hypochlorite on VLPs were classified into four phases according to morphological changes and number of particles. Using the criteria thus established, the efficacy of ethanol, carbonates and alkali solutions against VLPs was evaluated. Deformation and aggregation of VLPs were observed after treatment with these disinfectants under specific conditions. To determine the degradation mechanism(s), VLPs were examined by SDS‐PAGE and immunoblotting after treatment with sodium hypochlorite and ethanol. The band corresponding to the major capsid protein, VP1, was not detected after treatment with sodium hypochlorite at concentrations greater than 500 ppm, but remained after treatment with ethanol. These results suggest that VLPs have excellent potential as a surrogate marker for NoVs and can be used in initial virucidal effectiveness tests to determine the mechanism(s) of chemical agents on NoVs.     

Modeling the competition between aggregation and self‐assembly during virus‐like particle processing

Understanding and controlling aggregation is an essential aspect in the development of pharmaceutical proteins to improve product yield, potency and quality consistency. Even a minute quantity of aggregates may be reactogenic and can render the final product unusable. Self‐assembly processing of virus‐like particles (VLPs) is an efficient method to quicken the delivery of safe and efficacious vaccines to the market at low cost. VLP production, as with the manufacture of many biotherapeutics, is susceptible to aggregation, which may be minimized through the use of accurate and practical mathematical models. However, existing models for virus assembly are idealized, and do not predict the non‐native aggregation behavior of self‐assembling viral subunits in a tractable nor useful way. Here we present a mechanistic mathematical model describing VLP self‐assembly that accounts for partitioning of reactive subunits between the correct and aggregation pathways. Our results show that unproductive aggregation causes up to 38% product loss by competing favorably with the productive nucleation of self‐assembling subunits, therefore limiting the availability of nuclei for subsequent capsid growth. The protein subunit aggregation reaction exhibits an apparent second‐order concentration dependence, suggesting a dimerization‐controlled agglomeration pathway. Despite the plethora of possible assembly intermediates and aggregation pathways, protein aggregation behavior may be predicted by a relatively simple yet realistic model. More importantly, we have shown that our bioengineering model is amenable to different reactor formats, thus opening the way to rational scale‐up strategies for products that comprise biomolecular assemblies. Biotechnol. Bioeng. 2010;107: 550–560. © 2010 Wiley Periodicals, Inc.     

A method for rapid production of heteromultimeric protein complexes in plants: assembly of protective bluetongue virus‐like particles

Plant expression systems based on nonreplicating virus‐based vectors can be used for the simultaneous expression of multiple genes within the same cell. They therefore have great potential for the production of heteromultimeric protein complexes. This work describes the efficient plant‐based production and assembly of Bluetongue virus‐like particles (VLPs), requiring the simultaneous expression of four distinct proteins in varying amounts. Such particles have the potential to serve as a safe and effective vaccine against Bluetongue virus (BTV), which causes high mortality rates in ruminants and thus has a severe effect on the livestock trade. Here, VLPs produced and assembled in Nicotiana benthamiana using the cowpea mosaic virus–based HyperTrans (CPMV‐HT) and associated pEAQ plant transient expression vector system were shown to elicit a strong antibody response in sheep. Furthermore, they provided protective immunity against a challenge with a South African BTV‐8 field isolate. The results show that transient expression can be used to produce immunologically relevant complex heteromultimeric structures in plants in a matter of days. The results have implications beyond the realm of veterinary vaccines and could be applied to the production of VLPs for human use or the coexpression of multiple enzymes for the manipulation of metabolic pathways.     

Influenza virus‐like particles produced by transient expression in Nicotiana benthamiana induce a protective immune response against a lethal viral challenge in mice

A strain‐specific vaccine represents the best possible response to the threat of an influenza pandemic. Rapid delivery of such a vaccine to the world's population before the peak of the first infection wave seems to be an unattainable goal with the current influenza vaccine manufacturing capacity. Plant‐based transient expression is one of the few production systems that can meet the anticipated surge requirement. To assess the capability of plant agroinfiltration to produce an influenza vaccine, we expressed haemagglutinin (HA) from strains A/Indonesia/5/05 (H5N1) and A/New Caledonia/20/99 (H1N1) by agroinfiltration of Nicotiana benthamiana plants. Size distribution analysis of protein content in infiltrated leaves revealed that HA was predominantly assembled into high‐molecular‐weight structures. H5‐containing structures were purified and examination by transmission electron microscopy confirmed virus‐like particle (VLP) assembly. High‐performance thin layer chromatography analysis of VLP lipid composition highlighted polar and neutral lipid contents comparable with those of purified plasma membranes from tobacco plants. Electron microscopy of VLP‐producing cells in N. benthamiana leaves confirmed that VLPs accumulated in apoplastic indentations of the plasma membrane. Finally, immunization of mice with two doses of as little as 0.1 µg of purified influenza H5‐VLPs triggered a strong immune response against the homologous virus, whereas two doses of 0.5 µg of H5‐VLPs conferred complete protection against a lethal challenge with the heterologous A/Vietnam/1194/04 (H5N1) strain. These results show, for the first time, that plants are capable of producing enveloped influenza VLPs budding from the plasma membrane; such VLPs represent very promising candidates for vaccination against influenza pandemic strains.     

Optimization of norovirus virus‐like particle production in Pichia pastoris using a real‐time near‐infrared bioprocess monitor

The production of norovirus virus‐like particles (NoV VLPs) displaying NY‐ESO‐1 cancer testis antigen in Pichia pastoris BG11 Mut⁺ has been enhanced through feed‐strategy optimization using a near‐infrared bioprocess monitor (RTBio^® Bioprocess Monitor, ASL Analytical, Inc.), capable of monitoring and controlling the concentrations of glycerol and methanol in real‐time. The production of NoV VLPs displaying NY‐ESO‐1 in P. pastoris has potential as a novel cancer vaccine platform. Optimization of the growth conditions resulted in an almost two‐fold increase in the expression levels in the fermentation supernatant of P. pastoris as compared to the starting conditions. We investigated the effect of methanol concentration, batch phase time, and batch to induction transition on NoV VLP‐NY‐ESO‐1 production. The optimized process included a glycerol transition phase during the first 2 h of induction and a methanol concentration set point of 4 g L^?1 during induction. Utilizing the bioprocess monitor to control the glycerol and methanol concentrations during induction resulted in a maximum NoV VP1‐NY‐ESO‐1 yield of 0.85 g L^?1. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:518–526, 2016     

Insert engineering and solubility screening improves recovery of virus‐like particle subunits displaying hydrophobic epitopes

The Polyomavirus coat protein, VP1 has been developed as an epitope presentation system able to provoke humoral immunity against a variety of pathogens, such as Influenza and Group A Streptococcus. The ability of the system to carry cytotoxic T cell epitopes on a surface‐exposed loop and the impact on protein solubility has not been examined. Four variations of three selected epitopes were cloned into surface‐exposed loops of VP1, and expressed in Escherichia coli. VP1 pentamers, also known as capsomeres, were purified via a glutathione‐S‐transferase tag. Size exclusion chromatography indicated severe aggregation of the recombinant VP1 during enzymatic tag removal resulting from the introduction the hydrophobic epitopes. Inserts were modified to possess double aspartic acid residues at each end of the hydrophobic epitopes and a high‐throughput buffer condition screen was implemented with protein aggregation monitored during tag removal by spectrophotometry and dynamic light scattering. These analyses showed that the insertion of charged residues at the extremities of epitopes could improve solubility of capsomeres and revealed multiple windows of opportunity for further condition optimization. A combination of epitope design, pH optimization, and the additive l ‐arginine permitted the recovery of soluble VP1 pentamers presenting hydrophobic epitopes and their subsequent assembly into virus‐like particles.     

Enhanced enterovirus 71 virus‐like particle yield from a new baculovirus design

Enterovirus 71 (EV71) is responsible for the outbreaks of hand‐foot‐and‐mouth disease in the Asia‐Pacific region. To produce the virus‐like particle (VLP) vaccine, we previously constructed recombinant baculoviruses to co‐express EV71 P1 polypeptide and 3CD protease using the Bac‐to‐Bac^® vector system. The recombinant baculoviruses resulted in P1 cleavage by 3CD and subsequent VLP assembly in infected insect cells, but caused either low VLP yield or excessive VLP degradation. To tackle the problems, here we explored various expression cassette designs and flashBAC GOLD? vector system which was deficient in v‐cath and chiA genes. We found that the recombinant baculovirus constructed using the flashBAC GOLD? system was insufficient to improve the EV71 VLP yield. Nonetheless, BacF‐P1‐C3CD, a recombinant baculovirus constructed using the flashBAC GOLD^TM system to express P1 under the polh promoter and 3CD under the CMV promoter, dramatically improved the VLP yield while alleviating the VLP degradation. Infection of High Five^TM cells with BacF‐P1‐C3CD enhanced the total and extracellular VLP yield to ≈268 and ≈171 mg/L, respectively, which enabled the release of abundant VLP into the supernatant and simplified the downstream purification. Intramuscular immunization of mice with 5 μg purified VLP induced cross‐protective humoral responses and conferred protection against lethal virus challenge. Given the significantly improved extracellular VLP yield (≈171 mg/L) and the potent immunogenicity conferred by 5 μg VLP, one liter High Five^TM culture produced ≈12,000 doses of purified vaccine, thus rendering the EV71 VLP vaccine economically viable and able to compete with inactivated virus vaccines. Biotechnol. Bioeng. 2015;112: 2005–2015. © 2015 Wiley Periodicals, Inc.

     

Production of the virus‐like particles of nipah virus matrix protein in Pichia pastoris as diagnostic reagents

The matrix (M) protein of Nipah virus (NiV) is a peripheral protein that plays a vital role in the envelopment of nucleocapsid protein and acts as a bridge between the viral surface and the nucleocapsid proteins. The M protein is also proven to play an important role in production of virus‐like particles (VLPs) and is essential for assembly and budding of NiV particles. The recombinant M protein produced in Escherichia coli assembled into VLPs in the absence of the viral surface proteins. However, the E. coli produced VLPs are smaller than the native virus particles. Therefore, the aims of this study were to produce NiV M protein in Pichia pastoris, to examine the structure of the VLPs formed, and to assess the potential of the VLPs as a diagnostic reagent. The M protein was successfully expressed in P. pastoris and was detected with anti‐myc antibody using Western blotting. The VLPs formed by the recombinant M protein were purified with sucrose density gradient ultracentrifugation, high‐performance liquid chromatography (HPLC), and Immobilized Metal Affinity Chromatography (IMAC). Immunogold staining and transmission electron microscopy confirmed that the M protein assembled into VLPs as large as 200 nm. ELISA revealed that the NiV M protein produced in P. pastoris reacted strongly with positive NiV sera demonstrating its potential as a diagnostic reagent. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1038–1045, 2016     

Protective efficacy of a DNA vaccine encoding capsid protein of porcine circovirus‐like virus P1 against porcine circovirus 2 in mice

The capsid protein is the major immunogenic protein of porcine circovirus 2 (PCV2). The nucleotide sequence of porcine circovirus‐like virus P1 shares high homology with open reading frame (ORF) 2 of PCV2, and ORF1 of P1 encodes its structural protein. Mice were vaccinated twice intramuscularly with a plasmid expressing the P1 ORF1 protein (pcDNA3.1(+)‐ORF1) at 2‐week intervals. All animals vaccinated with pcDNA3.1(+)‐ORF1 developed higher specific anti‐P1 antibody levels, and had less PCV2 viremia and milder histopathological changes than PCV2‐challenged mice in the control group. Our results show that the P1 DNA vaccine elicited immune responses against PCV2 infection in a mouse model.

     

The influence of innate and pre‐existing immunity on adenovirus therapy

Recombinant adenovirus serotype 5 (Ad5) vectors have been studied extensively in preclinical gene therapy models and in a range of clinical trials. However, innate immune responses to adenovirus vectors limit effectiveness of Ad5 based therapies. Moreover, extensive pre‐existing Ad5 immunity in human populations will likely limit the clinical utility of adenovirus vectors, unless methods to circumvent neutralizing antibodies that bind virus and block target cell transduction can be developed. Furthermore, memory T cell and humoral responses to Ad5 are associated with increased toxicity, raising safety concerns for therapeutic adenovirus vectors in immunized hosts. Most preclinical studies have been performed in naïve animals; although pre‐existing immunity is among the greatest hurdles for adenovirus therapies, it is also one of the most neglected experimentally. Here we summarize findings using adenovirus vectors in naïve animals, in Ad‐immunized animals and in clinical trials, and review strategies proposed to overcome innate immune responses and pre‐existing immunity. J. Cell. Biochem. 108: 778–790, 2009. © 2009 Wiley‐Liss, Inc.