Hydrophobin-Protein A Fusion Protein Produced in Plants Efficiently Purified an Anti-West Nile Virus Monoclonal Antibody from Plant Extracts via Aqueous Two-Phase Separation

The development of monoclonal antibodies (mAbs) has provided vast opportunities to treat a wide range of diseases from cancer to viral infections. While plant-based production of mAbs has effectively lowered the upstream cost of mAb production compared to mammalian cell cultures, further optimization of downstream processing, especially in extending the longevity of Protein A resin by an effective bulk separation step, will further reduce the overall prohibitive cost of mAb production. In this study, we explored the feasibility of using aqueous two-phase separation (ATPS) in capturing and separating plant-made mAbs from host proteins. Our results demonstrated that an anti-West Nile virus mAb (E16) was efficiently separated from most plant host proteins by a single ATPS step, comprising the mixing of plant extracts containing Hydrophobin-Protein A fusion protein (HPA) and E16 and the subsequent incubation with an inexpensive detergent. This simple ATPS step yielded a highly enriched E16 mAb preparation with a recovery rate comparable to that of Protein A chromatography. The ATPS-enriched E16 retained its structural integrity and was fully functional in binding its target antigen. Notably, HPA-based ATPS was also effective in enriching E16 from plant host proteins when both HPA and E16 were produced in the same leaves, supporting the potential of further streamlining the downstream purification process. Thus, ATPS based on plant-produced HPA in unpurified extract is a cost-effective yet efficient initial capture step for purifying plant-made mAbs, which may significantly impact the approach of mAb purification.

Novel Hydrophobin Fusion Tags for Plant-Produced Fusion Proteins

Hydrophobin fusion technology has been applied in the expression of several recombinant proteins in plants. Until now, the technology has relied exclusively on the Trichoderma reesei hydrophobin HFBI. We screened eight novel hydrophobin tags, T. reesei HFBII, HFBIII, HFBIV, HFBV, HFBVI and Fusarium verticillioides derived HYD3, HYD4 and HYD5, for production of fusion proteins in plants and purification by two-phase separation. To study the properties of the hydrophobins, we used N-terminal and C-terminal GFP as a fusion partner. Transient expression of the hydrophobin fusions in Nicotiana benthamiana revealed large variability in accumulation levels, which was also reflected in formation of protein bodies. In two-phase separations, only HFBII and HFBIV were able to concentrate GFP into the surfactant phase from a plant extract. The separation efficiency of both tags was comparable to HFBI. When the accumulation was tested side by side, HFBII-GFP gave a better yield than HFBI-GFP, while the yield of HFBIV-GFP remained lower. Thus we present here two alternatives for HFBI as functional fusion tags for plant-based protein production and first step purification.

Plant-based solutions for veterinary immunotherapeutics and prophylactics

An alarming increase in emergence of antibiotic resistance among pathogens worldwide has become a serious threat to our ability to treat infectious diseases according to the World Health Organization. Extensive use of antibiotics by livestock producers promotes the spread of new resistant strains, some of zoonotic concern, which increases food-borne illness in humans and causes significant economic burden on healthcare systems. Furthermore, consumer preferences for meat/poultry/fish produced without the use of antibiotics shape today's market demand. So, it is viewed as inevitable by the One Health Initiative that humans need to reduce the use of antibiotics and turn to alternative, improved means to control disease: vaccination and prophylactics. Besides the intense research focused on novel therapeutic molecules, both these strategies rely heavily on the availability of cost-effective, efficient and scalable production platforms which will allow large-volume manufacturing for vaccines, antibodies and other biopharmaceuticals. Within this context, plant-based platforms for production of recombinant therapeutic proteins offer significant advantages over conventional expression systems, including lack of animal pathogens, low production costs, fast turnaround and response times and rapid, nearly-unlimited scalability. Also, because dried leaves and seeds can be stored at room temperature for lengthy periods without loss of recombinant proteins, plant expression systems have the potential to offer lucrative benefits from the development of edible vaccines and prophylactics, as these would not require "cold chain" storage and transportation, and could be administered in mass volumes with minimal processing. Several biotechnology companies currently have developed and adopted plant-based platforms for commercial production of recombinant protein therapeutics. In this manuscript, we outline the challenges in the process of livestock immunization as well as the current plant biotechnology developments aimed to address these challenges.

Influence of elastin-like polypeptide and hydrophobin on recombinant hemagglutinin accumulations in transgenic tobacco plants

Fusion protein strategies are useful tools to enhance expression and to support the development of purification technologies. The capacity of fusion protein strategies to enhance expression was explored in tobacco leaves and seeds. C-terminal fusion of elastin-like polypeptides (ELP) to influenza hemagglutinin under the control of either the constitutive CaMV 35S or the seed-specific USP promoter resulted in increased accumulation in both leaves and seeds compared to the unfused hemagglutinin. The addition of a hydrophobin to the C-terminal end of hemagglutinin did not significantly increase the expression level. We show here that, depending on the target protein, both hydrophobin fusion and ELPylation combined with endoplasmic reticulum (ER) targeting induced protein bodies in leaves as well as in seeds. The N-glycosylation pattern indicated that KDEL sequence-mediated retention of leaf-derived hemagglutinins and hemagglutinin-hydrophobin fusions were not completely retained in the ER. In contrast, hemagglutinin-ELP from leaves contained only the oligomannose form, suggesting complete ER retention. In seeds, ER retention seems to be nearly complete for all three constructs. An easy and scalable purification method for ELPylated proteins using membrane-based inverse transition cycling could be applied to both leaf- and seed-expressed hemagglutinins.

Production of a subunit vaccine candidate against porcine post-weaning diarrhea in high-biomass transplastomic tobacco

Post-weaning diarrhea (PWD) in piglets is a major problem in piggeries worldwide and results in severe economic losses. Infection with Enterotoxigenic Escherichia coli (ETEC) is the key culprit for the PWD disease. F4 fimbriae of ETEC are highly stable proteinaceous polymers, mainly composed of the major structural subunit FaeG, with a capacity to evoke mucosal immune responses, thus demonstrating a potential to act as an oral vaccine against ETEC-induced porcine PWD. In this study we used a transplastomic approach in tobacco to produce a recombinant variant of the FaeG protein, rFaeG(ntd/dsc), engineered for expression as a stable monomer by N-terminal deletion and donor strand-complementation (ntd/dsc). The generated transplastomic tobacco plants accumulated up to 2.0 g rFaeG(ntd/dsc) per 1 kg fresh leaf tissue (more than 1% of dry leaf tissue) and showed normal phenotype indistinguishable from wild type untransformed plants. We determined that chloroplast-produced rFaeG(ntd/dsc) protein retained the key properties of an oral vaccine, i.e. binding to porcine intestinal F4 receptors (F4R), and inhibition of the F4-possessing (F4+) ETEC attachment to F4R. Additionally, the plant biomass matrix was shown to delay degradation of the chloroplast-produced rFaeG(ntd/dsc) in gastrointestinal conditions, demonstrating a potential to function as a shelter-vehicle for vaccine delivery. These results suggest that transplastomic plants expressing the rFaeG(ntd/dsc) protein could be used for production and, possibly, delivery of an oral vaccine against porcine F4+ ETEC infections. Our findings therefore present a feasible approach for developing an oral vaccination strategy against porcine PWD.

Anti-clarin-1 AAV-delivered ribozyme induced apoptosis in the mouse cochlea

Usher syndrome type 3 is caused by mutations in the USH3A gene, which encodes the protein clarin-1. Clarin-1 is a member of the tetraspanin superfamily (TM4SF) of transmembrane proteins, expressed in the organ of Corti and spiral ganglion cells of the mouse ear. We have examined whether the AAV-mediated anti-clarin ribozyme delivery causes apoptotic cell death in vivo in the organ of Corti. We used an AAV-2 vector delivered hammerhead ribozyme, AAV-CBA-Rz, which specifically recognizes and cleaves wild type mouse clarin-1 mRNA. Cochleae of CD-1 mice were injected either with 1mul of the AAV-CBA-Rz, or control AAV vectors containing the green fluorescent protein (GFP) marker gene (AAV-CBA-GFP). Additional controls were performed with saline only. At one-week and one-month post-injection, the animals were sacrificed and the cochleae were studied by histology and fluorescence imaging. Mice injected with AAV-CBA-GFP displayed GFP reporter expression of varying fluorescence intensity throughout the length of the cochlea in the outer and inner hair cells and stria vascularis, and to a lesser extent, in vestibular epithelial cells. GFP expression was not detectable in the spiral ganglion. The pro-apoptotic effect of AAV-CBA-delivered anti-clarin-1 ribozymes was evaluated by TUNEL-staining. We observed in the AAV-CBA-Rz, AAV-CBA-GFP and saline control groups apoptotic nuclei in the outer and inner hair cells and in the stria vascularis one week after the microinjection. The vestibular epithelium was also observed to contain apoptotic cells. No TUNEL-positive spiral ganglion neurons were detected. After one-month post-injection, the AAV-CBA-Rz-injected group had significantly more apoptotic outer and inner hair cells and cells of the stria vascularis than the AAV-CBA-GFP group. In this study, we demonstrate that AAV-CBA mediated clarin-1 ribozyme may induce apoptosis of the cochlear hair cells and cells of the stria vascularis. Surprisingly, we did not observe apoptosis in spiral ganglion cells, which should also be susceptible to clarin-1 mRNA cleavage. This result may be due to the injection technique, the promoter used, or tropism of the AAV serotype 2 viral vector. These results suggest the role of apoptosis in the progression of USH3A hearing loss warrants further evaluation.

Conserved regions in the sequence of the F4 (K88) fimbrial adhesin FaeG suggest a donor strand mechanism in F4 assembly

Oral immunization of newly weaned piglets with recombinant F4 (K88) fimbrial adhesin FaeG induces a F4-specific immune response, significantly reducing F4+ Escherichia coli excretion following challenge. In order to use FaeG subunits in an oral vaccine against F4+ enterotoxigenic E. coli, it is necessary to determine the conservation of the adhesin subunit. Hereto, the faeG sequence was determined of 21 F4ac+ E. coli field isolates from piglets with diarrhoea and subsequently compared with these of the reference strain GIS26 and previously reported FaeG sequences from F4ab, F4ac and F4ad antigenic variant strains. The FaeG amino acid sequence was 96-100% homologous within each F4 serotype, but only 92 and 88% when the F4ab and F4ad antigenic variants were compared with the F4ac antigenic variant. Furthermore, the conserved regions of the adhesin suggest a donor strand mechanism in F4 fimbriae assembly as reported for type 1 and P pili. In conclusion, the results of the reported experiments support the usefulness FaeG in an oral subunit vaccine against F4+ E. coli infections or as a mucosal carrier since the adhesin is conserved among F4+ E. coli field isolates.

Rotaviruses detected by reverse transcription polymerase chain reaction in acute gastroenteritis during a trial of rhesus-human reassortant rotavirus tetravalent vaccine: implications for vaccine efficacy analysis

BACKGROUND

Rotaviruses are routinely diagnosed by detection of rotavirus antigen in stools using an enzyme immunoassay (EIA). A sensitive method, like reverse transcription polymerase chain reaction (RT-PCR), may reveal more rotaviruses, but the clinical significance of such findings is not well established.

OBJECTIVES

To study whether RT-PCR can detect more episodes of rotavirus-associated gastroenteritis than EIA and to determine how rotavirus RT-PCR findings might change efficacy analysis of a rotavirus vaccine trial, in which the outcome measure was rotavirus gastroenteritis diagnosis with EIA.

STUDY DESIGN

We applied RT-PCR for detection of rotaviruses in gastroenteritis episodes encountered in an efficacy trial of rhesus-human reassortant rotavirus tetravalent (RRV-TV) vaccine, in a total of 2398 infants. During a follow-up, covering two rotavirus epidemic seasons, 256 cases of rotavirus associated gastroenteritis were detected by EIA; 226 were in the primary efficacy analysis period that included children who had received three doses of vaccine or placebo.

RESULTS

With RT-PCR, 84 (33%) more cases of rotavirus gastroenteritis were diagnosed than with EIA, 65 of these were in the primary efficacy analysis period. Clinically, cases of rotavirus gastroenteritis diagnosed by RT-PCR were much milder (median severity score 6 on a 20-point scale) than those diagnosed by EIA (median score 11), P < 0.0001. RT-PCR revealed proportionally more G2 and G4 rotaviruses than EIA. G1 rotaviruses detected by RT-PCR were almost equally divided between RRV-TV (25) vaccine and placebo (28) groups, whereas an apparent vaccine protective effect was seen in the distribution of G2 (one in the RRV-TV and eight in the placebo group) and G4 rotaviruses (six in the RRV-TV and 14 in the placebo group).

CONCLUSION

RT-PCR is a useful tool in the diagnosis of rotavirus gastroenteritis, particularly for cases associated with other than the epidemiologically dominant G-type. Application of RT-PCR contributes to the overall appraisal of performance of rotavirus vaccine.

Human calicivirus-associated sporadic gastroenteritis in Finnish children less than two years of age followed prospectively during a rotavirus vaccine trial

BACKGROUND

Human caliciviruses (HuCV) cause outbreaks of gastroenteritis, but their role in sporadic diarrhea in young children is not well-established.

METHODS

Children (n = 2398) participating in a trial of oral rhesus-human reassortant rotavirus tetravalent (RRV-TV) vaccine were evaluated from 2 months to 2 years of age. Stool specimens from 1477 episodes of acute gastroenteritis (788 in a placebo and 689 in a RRV-TV vaccine recipient group) were tested for human calicivirus (HuCV) by reverse transcriptase-PCR with the use of broadly reactive primers, and positive results were confirmed by Southern hybridization with probes specific for main genetic clusters of Genogroups I and II of HuCV.

RESULTS

HuCV were detected in 158 (20%) and 155 (22%) cases of gastroenteritis in the placebo and RRV-TV vaccine groups, respectively. According to hybridization results, 8% of HuCV were of Genogroup I and 92% were of Genogroup II. The peak season of HuCV gastroenteritis was from November to February. Of the 148 patients with pure HuCV infection in the placebo group, 89% had vomiting, 79% had watery diarrhea, 21% had fever, 28% needed oral rehydration and 1.4% were hospitalized. The diarrhea in HuCV gastroenteritis was much less severe than that in rotavirus gastroenteritis, but vomiting was equally severe. There was no effect of RRV-TV vaccine on the frequency or clinical severity of HuCV gastroenteritis.

CONCLUSION

HuCVs are second in frequency to rotaviruses as causative agents in acute gastroenteritis in young children in the community.

Concurrent administration of rhesus rotavirus tetravalent (RRV-TV) vaccine with pentavalent diphtheria-pertussis-tetanus-Haemophilus influenzae beta-inactivated polio and hepatitis B vaccines

To investigate the incorporation of oral rhesus-human reassortant rotavirus tetravalent (RRV-TV) vaccine into a routine immunization programme, RRV-TV or oral placebo was coadministered with a pentavalent diphtheria-tetanus-whole-cell pertussis-Haemophilus influenzae b (Hib)-inactivated polio vaccine and hepatitis B vaccine following a 3-4-5-mo schedule in a double-blind trial involving 249 infants. Seroconversion rates after 3 doses of rotavirus vaccine were 80% for rotavirus immunoglobulin A (IgA) and 93% for RRV neutralizing antibodies. Rotavirus vaccine did not interfere with the immune responses to diphtheria, tetanus, pertussis, Hib, poliovirus 1, 2 and 3, or hepatitis B. Following the first, second and third doses of vaccine, fever >38 degrees C on the day of vaccination was seen in 31%, 24% and 24%, respectively, with no difference between RRV-TV- and placebo-vaccinated children. This fever was presumably due to the whole-cell pertussis vaccine. Those vaccinees who received concomitant RRV-TV vaccine had another peak of fever around d 4 after the first dose, when 25% of them had fever >38 degrees C and 3% >39 degrees C. It is concluded that RRV-TV rotavirus vaccine can be given concurrently with other childhood immunizations following a 3-4-5-mo vaccination schedule. However, febrile reactions to RRV-TV rotavirus vaccine are common when the first dose is given at the age of 3 mo.

Economic evaluation of rotavirus vaccinations in Finland: randomized, double-blind, placebo-controlled trial of tetravalent rhesus rotavirus vaccine

The cost-benefit ratio of tetravalent rhesus rotavirus vaccine (RRV-TV) in Finland for prevention of rotavirus gastroenteritis was assessed in a randomized, double-blind, placebo-controlled trial. Costs related to vaccination, side effects, and gastroenteritis were identified. Children received RRV-TV (n = 1,191) or placebo (n = 1,207) at 2, 3, and 5 months of age with other infant vaccinations. Prospective follow-up averaged 1.0 years per child. An intention-to-treat analysis was performed from the perspective of society. Nine cases of severe rotavirus gastroenteritis occurred in the RRV-TV group, versus 100 in the placebo group (P < .0001); mean cost per vaccinated child was 4 Finnish marks (FIM) in the RRV-TV group, versus 203 FIM in the placebo group. Side effects with related costs occurred after 11% and 7% of doses in the RRV-TV group and placebo group, respectively (P < .001); mean cost per child was 89 FIM vs. 75 FIM. The break-even cost (i.e., net benefit, excluding cost of vaccine) of RRV-TV in prevention of severe rotavirus gastroenteritis was 109 FIM (U.S. $19.60) per child.

Symptoms associated with rhesus-human reassortant rotavirus vaccine in infants

BACKGROUND

Severe rotavirus gastroenteritis is potentially preventable by oral rhesus-human reassortant tetravalent (RRV-TV) vaccine, which may soon be licensed in the US and Europe. The objective of this study was to evaluate symptoms associated with the high titer RRV-TV vaccine given concurrently with routine childhood immunizations.

METHODS

In a randomized placebo-controlled double blind trial of RRV-TV vaccine titer 4 x 10(5) plaque-forming units vs. placebo, 2282 children received all 3 doses of study vaccine between ages 2 and 7 months. Symptoms were followed by parents who also took daily rectal temperatures.

RESULTS

On Days 3 to 5 after the first dose of vaccine fever 38.0 degrees C or greater was detected in 387 of 1182 (33%) infants in the RRV-TV vaccine group vs. 27 of 1194 (2.3%) infants in the placebo group (P < 0.001) and fever 39.0 degrees C or greater was detected in 40 (3.4%) and 3 (0.2%) infants in the vaccine and placebo groups, respectively (P < 0.001). Irritability, decreased appetite and abdominal cramping on Days 3 to 5 postvaccination were also more common in the RRV-TV vaccine recipients than in the placebo recipients. One child in the RRV-TV group was hospitalized and 2 more infants seen in the clinic, vs. none in the placebo group, within the 5-day period after the first dose for a reason probably related to the RRV-TV vaccine. After the second and third doses of RRV-TV vaccine, there were only minor differences between the vaccine and placebo recipients in fever on Days 3 to 5 postvaccination.

CONCLUSIONS

The first dose of RRV-TV vaccine is associated with a relatively high rate of febrile and other reactions, which may require a physician visit and, rarely, hospitalization.

Randomised placebo-controlled trial of rhesus-human reassortant rotavirus vaccine for prevention of severe rotavirus gastroenteritis

BACKGROUND

Rotavirus is the most common cause of acute childhood gastroenteritis. Vaccination with live oral heterologous rotavirus vaccines may prevent rotavirus gastroenteritis. We assessed the efficacy of rhesus-human reassortant rotavirus tetravalent vaccine (RRV-TV) against severe rotavirus gastroenteritis in Finnish children in a randomised placebo-controlled double-blind trial.

METHODS

Placebo or RRV-TV (titre 4x10(5) plaque-forming units) was given to infants at ages 2, 3, and 5 months. The children were followed up for one or two rotavirus epidemic seasons. The main outcome measure was protection against severe rotavirus gastroenteritis (score > or =11 on a 20-point severity scale). 2398 children were enrolled and received at least one dose of RRV-TV (n=1191) or placebo (n=1207). The primary efficacy analysis was based on children who received three doses of RRV-TV (n=1128) or placebo (n=1145).

FINDINGS

256 episodes of rotavirus gastroenteritis occurred at any time during the study; 65 were among 1191 RRV-TV recipients, and 191 among 1207 placebo recipients (vaccine efficacy 66% [95% CI 55-74]; intention-to-treat analysis). 226 episodes were included in the primary efficacy analysis of fully vaccinated children (54 among 1128 RRV-TV recipients, 172 among 1145 placebo recipients; vaccine efficacy 68% [57-76]). 100 episodes were severe, eight in RRV-TV recipients and 92 in placebo recipients (vaccine efficacy 91% [82-96]).

INTERPRETATION

RRV-TV vaccine was highly effective against severe rotavirus gastroenteritis in young children. Incorporation of this vaccine into routine immunisation schedules of infants could reduce severe rotavirus gastroenteritis by 90% and severe gastroenteritis of all causes in young children by 60%.

Review of rotavirus vaccine trials in Finland

Oral rotavirus vaccines, including bovine rotavirus strains RIT 4237 and RIT 4256, rhesus rotavirus (RRV) vaccine, rhesus-human rotavirus vaccine reassortants (D x RRV, DS-1 x RRV, and tetravalent RRV), and human nursery rotavirus strain M37, have been evaluated in 5353 Finnish infants for safety, immunogenicity, and efficacy against rotavirus gastroenteritis. Bovine rotavirus vaccines were nonreactogenic in infants, whereas RRV-based and M37 vaccines were occasionally associated with febrile reactions 2-5 days after vaccination. All vaccines showed dose-dependent immunogenicity. Vaccine efficacy correlated with overall immunogenicity but not with the vaccine virus G serotype. For each vaccine, protective efficacy was better against severe rotavirus disease than against any rotavirus-associated gastroenteritis. Maximal protective efficacy against any rotavirus gastroenteritis in subjects with demonstrable vaccine immunogenicity was approximately 75%. To achieve similar protection in all vaccinees, efforts should be focused on enhancing the immunogenicity of oral rotavirus vaccines.

Improved immunogenicity of oral D x RRV reassortant rotavirus vaccine by Lactobacillus casei GG

In a search for new strategies to improve oral vaccination, the effect of orally administered Lactobacillus casei strain GG (LGG) in conjunction with D x RRV rhesus-human reassortant live oral rotavirus vaccine was tested in 2-5-month-old infants. Infants who received LGG showed an increased response with regard to rotavirus-specific IgM secreting cells, measured using an ELISPOT technique, on day 8 after vaccination. In infants receiving LGG or placebo, respectively, a rotavirus IgM seroconversion was detected in 26/27 (96%), versus 23/27 (85%) cases (p = 0.15) and rotavirus IgA seroconversion was detected in 26/28 (93%) versus 20/27 (74%) cases (p = 0.05). These findings suggest that LGG has an immunostimulating effect on oral rotavirus vaccination. The clinical significance of LGG-enhanced immune responses to oral vaccines should be further evaluated.