Development and characterization of a plant-derived norovirus-like particle vaccine

BACKGROUND

Norovirus (NoV) is the most common cause of diarrheal episodes globally. Issues with in vitro cultivation systems, genetic variation, and animal models have hindered vaccine development. Plant-derived virus-like particles (VLPs) may address some of these concerns because they are highly immunogenic, can be administered by different routes, and can be rapidly produced to accommodate emerging viral strains.

METHODS

NoV VLPs (NoVLP) composed of the surface viral protein (VP) 1 of the GI and GII genogroups were produced in Nicotiana benthamiana using an Agrobacterium tumefaciens-based recombinant transient expression system. Leaves from infiltrated plants were harvested and NoVLPs were extracted and purified. The safety and immunogenicity of the GII.4 NoVLP, the genotype currently causing most human disease, were subsequently examined in rabbits and mice.

RESULTS

Fifteen GI and GII NoVLPs were successfully expressed in N. benthamiana and were structurally similar to NoV virions, as determined by cryogenic transmission electron microscopy. The NoVLP was well-tolerated, with no local or systemic signs of toxicity in rabbits. Three intramuscular doses of the GII.4 NoVLP adjuvanted with aluminum hydroxide induced robust IgG titers, IgG-secreting cells, histo-blood group antigen blocking titers, and IFNγ-secreting T cells in mice. In addition to circulating antibodies, oral administration of the NoVLP in mice induced significant IgA levels in feces, indicative of a mucosal response.

CONCLUSIONS

The plant-made NoVLP vaccine was safe and immunogenic in mice and rabbits. Multi-modal vaccination, combining oral and intramuscular administration could be considered for future clinical development to maximize systemic and mucosal immune responses.

Durability and cross-reactivity of immune responses induced by a plant-based virus-like particle vaccine for COVID-19

As the SARS-CoV-2 pandemic evolves, vaccine evaluation needs to include consideration of both durability and cross-reactivity. This report expands on previously reported results from a Phase 1 trial of an AS03-adjuvanted, plant-based coronavirus-like particle (CoVLP) displaying the spike (S) glycoprotein of the ancestral SARS-CoV-2 virus in healthy adults (NCT04450004). Humoral and cellular responses against the ancestral strain were evaluated 6 months post-second dose (D201) as secondary outcomes. Independent of dose, all vaccinated individuals retain binding antibodies, and ~95% retain neutralizing antibodies (NAb). Interferon gamma and interleukin-4 responses remain detectable in ~94% and ~92% of vaccinees respectively. In post-hoc analyses, variant-specific (Alpha, Beta, Delta, Gamma and Omicron) NAb were assessed at D42 and D201. Using a live virus neutralization assay, broad cross-reactivity is detectable against all variants at D42. At D201, cross-reactive antibodies are detectable in almost all participants against Alpha, Gamma and Delta variants (94%) and the Beta variant (83%) and in a smaller proportion against Omicron (44%). Results are similar with the pseudovirion assay. These data suggest that two doses of 3.75 µg CoVLP+AS03 elicit a durable and cross-reactive response that persists for at least 6 months post-vaccination.

Efficacy and Safety of a Recombinant Plant-Based Adjuvanted Covid-19 Vaccine

BACKGROUND

Coronavirus-like particles (CoVLP) that are produced in plants and display the prefusion spike glycoprotein of the original strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are combined with an adjuvant (Adjuvant System 03 [AS03]) to form the candidate vaccine.

METHODS

In this phase 3, multinational, randomized, placebo-controlled trial conducted at 85 centers, we assigned adults (≥18 years of age) in a 1:1 ratio to receive two intramuscular injections of the CoVLP+AS03 vaccine or placebo 21 days apart. The primary objective of the trial was to determine the efficacy of the CoVLP+AS03 vaccine in preventing symptomatic coronavirus disease 2019 (Covid-19) beginning at least 7 days after the second injection, with the analysis performed after the detection of at least 160 cases.

RESULTS

A total of 24,141 volunteers participated in the trial; the median age of the participants was 29 years. Covid-19 was confirmed by polymerase-chain-reaction assay in 165 participants in the intention-to-treat population; all viral samples that could be sequenced contained variants of the original strain. Vaccine efficacy was 69.5% (95% confidence interval [CI], 56.7 to 78.8) against any symptomatic Covid-19 caused by five variants that were identified by sequencing. In a post hoc analysis, vaccine efficacy was 78.8% (95% CI, 55.8 to 90.8) against moderate-to-severe disease and 74.0% (95% CI, 62.1 to 82.5) among the participants who were seronegative at baseline. No severe cases of Covid-19 occurred in the vaccine group, in which the median viral load for breakthrough cases was lower than that in the placebo group by a factor of more than 100. Solicited adverse events were mostly mild or moderate and transient and were more frequent in the vaccine group than in the placebo group; local adverse events occurred in 92.3% and 45.5% of participants, respectively, and systemic adverse events in 87.3% and 65.0%. The incidence of unsolicited adverse events was similar in the two groups up to 21 days after each dose (22.7% and 20.4%) and from day 43 through day 201 (4.2% and 4.0%).

CONCLUSIONS

The CoVLP+AS03 vaccine was effective in preventing Covid-19 caused by a spectrum of variants, with efficacy ranging from 69.5% against symptomatic infection to 78.8% against moderate-to-severe disease. (Funded by Medicago; ClinicalTrials.gov number, NCT04636697.).

Elimination of receptor binding by influenza hemagglutinin improves vaccine-induced immunity

The binding of influenza hemagglutinin (HA) to sialic acid (SA) receptors plays a well-defined role in shaping infection but the impact of such binding on vaccine responses has not yet been explored. We generated a virus-like particle (VLP) vaccine bearing the HA of H1N1 A/California/07/09 that is unable to bind to its α(2,6)-linked SA receptor (H1_Y98F-VLP) and compared its immunogenicity and efficacy to a wild-type H1-VLP (H1_WT-VLP) in mice. The H1_Y98F-VLP elicited significantly stronger and more durable antibody responses (hemagglutination inhibition and microneutralization titers) and greater avidity maturation, likely attributable to improved germinal center formation. H1_Y98F-VLP also resulted in a robust population of IL-2⁺TNFα⁺IFNγ⁻ CD4⁺ T cells that correlated with antibody responses. Compared to H1_WT-VLP vaccination, mice immunized with H1_Y98F-VLP had 2.3-log lower lung viral loads and significantly lower pulmonary inflammatory cytokine levels 5 days post-challenge. These findings suggest that abrogation of HA-SA interactions may be a promising strategy to improve the quality and durability of influenza vaccine-induced humoral responses.

Safety, immunogenicity, and protection provided by unadjuvanted and adjuvanted formulations of a recombinant plant-derived virus-like particle vaccine candidate for COVID-19 in nonhuman primates

Although antivirals are important tools to control severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, effective vaccines are essential to control the current coronavirus disease 2019 (COVID-19) pandemic. Plant-derived virus-like particle (VLP) vaccine candidates have previously demonstrated immunogenicity and efficacy against influenza. Here, we report the immunogenicity and protection induced in rhesus macaques by intramuscular injections of a VLP bearing a SARS-CoV-2 spike protein (CoVLP) vaccine candidate formulated with or without Adjuvant System 03 (AS03) or cytidine-phospho-guanosine (CpG) 1018. Although a single dose of the unadjuvanted CoVLP vaccine candidate stimulated humoral and cell-mediated immune responses, booster immunization (at 28 days after priming) and adjuvant administration significantly improved both responses, with higher immunogenicity and protection provided by the AS03-adjuvanted CoVLP. Fifteen micrograms of CoVLP adjuvanted with AS03 induced a polyfunctional interleukin-2 (IL-2)-driven response and IL-4 expression in CD4 T cells. Animals were challenged by multiple routes (i.e., intratracheal, intranasal, and ocular) with a total viral dose of 106 plaque-forming units of SARS-CoV-2. Lower viral replication in nasal swabs and bronchoalveolar lavage fluid (BALF) as well as fewer SARS-CoV-2-infected cells and immune cell infiltrates in the lungs concomitant with reduced levels of proinflammatory cytokines and chemotactic factors in the BALF were observed in animals immunized with the CoVLP adjuvanted with AS03. No clinical, pathologic, or virologic evidence of vaccine-associated enhanced disease was observed in vaccinated animals. The CoVLP adjuvanted with AS03 was therefore selected for vaccine development and clinical trials.

Lack of effects on female fertility or pre- and postnatal development of offspring in rats after exposure to AS03-adjuvanted recombinant plant-derived virus-like particle vaccine candidate for COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection resulting in the coronavirus disease 2019 (COVID-19) has afflicted tens of millions of people in a worldwide pandemic. A recently developed recombinant Plant-Derived Virus-Like Particle Vaccine candidate for COVID-19 (CoVLP) formulated with AS03 has been shown to be well-tolerated and highly immunogenic in healthy adults. Since the target population for the vaccine includes women of childbearing potential, the objective of the study was to evaluate any untoward prenatal and postnatal effects of AS03-adjuvanted CoVLP administered intramuscularly to Sprague-Dawley female rats before cohabitation for mating (22 and 8 days prior) and during gestation (Gestation Days [GD] 6 and 19). The embryo-fetal development (EFD) cohort was subjected to cesarean on GD 21 and the pre/post-natal (PPN) cohort was allowed to naturally deliver. Effects of AS03-adjuvanted CoVLP was evaluated on pregnant rats, embryo-fetal development (EFD), during parturition, lactation and the development of the F1 offspring up to weaning Vaccination with AS03-adjuvanted CoVLP induced an antibody response in F0 females and anti-SARS-CoV-2 spike-specific maternal antibodies were detected in the offspring at the end of the gestation and lactation periods. Overall, there was no evidence of untoward effects of AS03-adjuvanted CoVLP on the fertility or reproductive performance of the vaccinated F0 females. There was no evidence of untoward effects on embryo-fetal development (including teratogenicity), or early (pre-weaning) development of the F1 offspring. These results support the acceptable safety profile of the AS03-adjuvanted CoVLP vaccine for administration to women of childbearing potential.

Phase 1 randomized trial of a plant-derived virus-like particle vaccine for COVID-19

Several severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are being deployed, but the global need greatly exceeds the supply, and different formulations might be required for specific populations. Here we report Day 42 interim safety and immunogenicity data from an observer-blinded, dose escalation, randomized controlled study of a virus-like particle vaccine candidate produced in plants that displays the SARS-CoV-2 spike glycoprotein (CoVLP: NCT04450004). The co-primary outcomes were the short-term tolerability/safety and immunogenicity of CoVLP formulations assessed by neutralizing antibody (NAb) and cellular responses. Secondary outcomes in this ongoing study include safety and immunogenicity assessments up to 12 months after vaccination. Adults (18–55 years, n = 180) were randomized at two sites in Quebec, Canada, to receive two intramuscular doses of CoVLP (3.75 μg, 7.5 μg, and 15 μg) 21 d apart, alone or adjuvanted with AS03 or CpG1018. All formulations were well tolerated, and adverse events after vaccination were generally mild to moderate, transient and highest in the adjuvanted groups. There was no CoVLP dose effect on serum NAbs, but titers increased significantly with both adjuvants. After the second dose, NAbs in the CoVLP + AS03 groups were more than tenfold higher than titers in Coronavirus 2019 convalescent sera. Both spike protein-specific interferon-γ and interleukin-4 cellular responses were also induced. This pre-specified interim analysis supports further evaluation of the CoVLP vaccine candidate.

Safety and immunogenicity results in humans of a two-dose SARS-CoV-2 vaccine made from plants support further assessment of potential efficacy.

Phase III: Randomized observer-blind trial to evaluate lot-to-lot consistency of a new plant-derived quadrivalent virus like particle influenza vaccine in adults 18-49 years of age

BACKGROUND

The global reliance on eggs to produce most influenza vaccines has several limitations and new approaches to influenza vaccine production are needed. Herein we describe a phase 3, lot-to-lot consistency trial (NCT03321968) of a quadrivalent, recombinant, virus-like particle (VLP) influenza vaccine produced in plants. This platform is based on transient expression of proteins in Nicotiana benthamiana and yields VLPs bearing hemagglutinin (HA) protein trimers that are combined in a quadrivalent vaccine (QVLP).

METHODS

The HAs targeted in this study were A/California/07/2009 H1N1, A/Hong Kong/4801/2014 H3N2, B/Brisbane/60/08 and B/Phuket/3073/2013: recommended for the 2016-2017 Northern Hemisphere season. Healthy adults 18-49 years of age (n = 1200) were randomized 1:1:1 to receive a 0.5 mL intramuscular injection of QVLP (30 μg HA/strain) from three sequential lots. Local and systemic reactions were monitored for 21 days post-vaccination and blood was collected pre-vaccination and at day 21 (D21) after vaccination to measure hemagglutination inhibition (HI) antibodies.

RESULTS

Subject demographics were similar between groups and compliance with study procedures was 96.3%. The study population was 54.8% female, the mean age (±SD) was 29.9 ± 9.01 and the racial distribution was 77.8% Caucasian, 15.6% Asian, 5.8% Black/African American and 0.8% other. The HI responses met the Center for Biologics Evaluation and Research criteria for seroconversion (SCR ≥ 40%) and seroprotection rates (SPR ≥ 70%). The geometric mean fold rise in HI titers was ≥ 2.5 for all 4 strains for each lot. Lot-to-lot consistency was met with the 95% confidence intervals of the D21 mean geometric titre ratios falling between 0.67 and 1.5 for all four strains. No safety concerns were identified. Solicited adverse events were generally mild and transient: typical for what is reported after inactivated influenza vaccines.

CONCLUSIONS

This study supported earlier findings of the safety profile and immunogenicity of the plant-derived QVLP and demonstrated the consistency with which it can be produced.

Efficacy, immunogenicity, and safety of a plant-derived, quadrivalent, virus-like particle influenza vaccine in adults (18-64 years) and older adults (≥65 years): two multicentre, randomised phase 3 trials

BACKGROUND

Seasonal influenza remains a substantial public health threat despite the availability of egg-derived and other vaccines. Plant-based manufacturing might address some of the limitations of current vaccines. We describe two phase 3 efficacy studies of a recombinant quadrivalent virus-like particle (QVLP) influenza vaccine manufactured in plants, one in adults aged 18-64 years (the 18-64 study) and one in older people aged 65 years and older (the 65-plus study).

METHODS

We did two randomised, observer-blind, multinational studies in the northern hemisphere in the 2017-18 (the 18-64 study) and 2018-19 (the 65-plus study) influenza seasons. The 18-64 study was done at 73 sites and the 65-plus study was done at 104 sites, both across Asia, Europe, and North America. In the 18-64 study, inclusion criteria were body-mass index less than 40 kg/m²; age 18-64 years at screening visit; and good health. In the 65-plus study, inclusion criteria were body-mass index of maximum 35 kg/m²; aged 65 years or older at screening visit; not living in a rehabilitation centre or care home; and no acute or evolving medical problems. Participants in the 18-64 study were randomly assigned (1:1) to receive either QVLP vaccine (30 μg haemagglutinin per strain) or placebo. Participants in the 65-plus study were randomly assigned (1:1) to receive QVLP vaccine (30 μg haemagglutinin per strain) or quadrivalent inactivated vaccine (QIV; 15 μg haemagglutinin per strain). The primary outcome in the 18-64 study was absolute vaccine efficacy to prevent laboratory-confirmed, respiratory illness caused by antigenically matched influenza strains. The primary outcome in the 65-plus study was relative vaccine efficacy to prevent laboratory-confirmed influenza-like illness caused by any influenza strain. The primary analyses were done in the per-protocol population and safety was assessed in all participants who received the assigned treatment. These studies are registered with ClinicalTrials.gov (18-64 study NCT03301051; 65-plus study NCT03739112).

FINDINGS

In the 18-64 study, between Aug 30, 2017, and Jan 15, 2018, 10 160 participants were randomly assigned to receive either QVLP vaccine (5077 participants) or placebo (5083 participants). The per-protocol population consisted of 4814 participants in the QVLP group and 4812 in the placebo group. The study did not meet its primary endpoint of 70% absolute vaccine efficacy for the QVLP vaccine (35·1% [95% CI 17·9 to 48·7]) against respiratory illness caused by matched strains. 55 (1·1%) of 5064 participants in the QVLP group versus 51 (1·0%) of 5072 in the placebo group had a serious adverse event. Four (0·1%) and six [0·1%] participants had severe treatment-related treatment-emergent adverse events. In the 65-plus study, between Sept 18, 2018, and Feb 22, 2019, 12 794 participants were randomly assigned to receive either QVLP vaccine (6396 participants) or QIV (6398 participants). The per-protocol population consisted of 5996 participants in the QVLP group and 6026 in the QIV group. The study met its primary non-inferiority endpoint with a relative vaccine efficacy of the QVLP vaccine for the prevention of influenza-like illness caused by any strain of 8·8% (-16·7 to 28·7). 263 (4·1%) of 6352 participants in the QVLP group versus 266 (4·2%) of 6366 in the QIV group had serious adverse events (one [<0·1%] vs two [<0·1%] were considered treatment-related); one (<0·1%) versus three (<0·1%) participants had severe treatment-related treatment-emergent adverse events.

INTERPRETATION

These efficacy studies are the first large-scale studies of any plant-derived human vaccine. Together, they show that the plant-derived QVLP vaccine can provide substantial protection against respiratory illness and influenza-like illness caused by influenza viruses in adults. QVLP vaccine was well tolerated and no major safety signal arose in participants who received QVLP vaccine across the two studies.

FUNDING

Medicago.

Prime-pull vaccination with a plant-derived virus-like particle influenza vaccine elicits a broad immune response and protects aged mice from death and frailty after challenge

Background

Administered intramuscularly (IM), plant-derived, virus-like-particle (VLP) vaccines based on the influenza hemagglutinin (HA) protein elicit both humoral and cellular responses that can protect aged mice from lethal challenge. Unlike split virus vaccines, VLPs can be administered by different routes including intranasally (IN). We evaluated novel vaccine strategies such as prime-pull (IM boosted by IN) and multi-modality vaccination (IM and IN given simultaneously). We wished to determine if these approaches would provide better quality protection in old mice after less severe (borderline-lethal) challenge (ie: immunogenicity, frailty and survival).

Results

Survival rates were similar in all vaccinated groups. Antibody responses were modest in all groups but tended to be higher in VLP groups compared to inactivated influenza vaccine (IIV) recipients. All VLP groups had higher splenocyte T cell responses than the split virus group. Lung homogenate chemokine/cytokine levels and virus loads were lower in the VLP groups compared to IIV recipients 3 days after challenge (p < 0.05 for viral load vs all VLP groups combined). The VLP-vaccinated groups also had less weight loss and recovered more rapidly than the IIV recipients. There was limited evidence of an immunologic or survival advantage with IN delivery of the VLP vaccine.

Conclusion

Compared to IIV, the plant-derived VLP vaccine induced a broader immune response in aged mice (cellular and humoral) using either traditional (IM/IM) or novel schedules (multi-modality, prime-pull).

A plant-derived VLP influenza vaccine elicits a balanced immune response even in very old mice with co-morbidities

BACKGROUND

The elderly are at high risk from influenza, in part because immunity wanes with age and through the accumulation of comorbidities. A novel plant-derived virus-like-particle (VLP) vaccine bearing influenza hemagglutinin can induce a balanced humoral and cellular response in old mice (16-18 months) while split virion vaccines elicit mostly antibodies. Because mice also collect comorbidities and lose immune competence as they age, we wished to determine how the plant-derived VLP vaccine would perform in animals approaching the end of their life-span.

MATERIALS AND METHODS

Old (24-26 months) female BALB/c mice received two intramuscular doses of H1-VLP vaccine, an inactivated H1N1 vaccine (IIV) (both based on A/H1N1/California/07/09) (3μg each) or PBS. Serum was collected on day 42 and humoral responses were measured by enzyme-linked immunosorbent assay (ELISA), microneutralization (MN) and hemagglutination inhibition (HI) assays. Influenza-specific splenocyte CD4+ & CD8+ T cell responses were measured by flow cytometry. Full body computed tomography (CT) and structured necropsies were performed on day 42. Comorbidities including reduced lung volume (kyphosis), masses, abscesses, etc. were assessed using a standard scoring system (1-21) and mice with scores ≥5 were considered to have important comorbidities.

RESULTS

Overall, 53.3% of the animals had significant comorbidities. Three weeks post-boost, HI and MN titres were mostly undetectable but ELISA titres were significantly higher in the H1-VLP animals compared to the IIV group (GMT (95% CI): 961 (427, 2163) vs 425 (200, 903): p = 0.03). Both CD4+(TNFα, IFNγ) and CD8+ (IFNγ) T cell responses were also greater in the H1-VLP group than the IIV.

CONCLUSIONS

Even in very old mice with comorbidities, the plant-made H1-VLP vaccine elicited a stronger and more balanced immune response than IIV. Animals with fewer comorbidities tended to have the better composite (humoral and cellular) responses. These novel vaccines have the potential to address some of the limitations of current vaccines in the elderly.

The adjuvant GLA-AF enhances human intradermal vaccine responses

Adjuvants are key to shaping the immune response to vaccination, but to date, no adjuvant suitable for human use has been developed for intradermal vaccines. These vaccines could be self-administered and sent through the mail as they do not require long needles or technical expertise in immunization. In the event of a pandemic outbreak, this approach could alleviate the congregation of patients in health centers and thus reduce the potential of these centers to enhance the spread of lethal infection. A reliable and potent vaccine system for self-administration would provide an effective countermeasure for delivery through existing product distribution infrastructure. We report results from preclinical and clinical trials that demonstrate the feasibility of an adjuvanted, intradermal vaccine that induced single shot protection in ferrets and seroprotection in humans against one of the more lethal strains of pandemic flu, Indonesia H5N1. In the human trial, the vaccine was safe and clinical responses were above approvable endpoints for a protective flu vaccine. Inclusion of a modern TLR4 (Toll-like receptor 4) agonist-based adjuvant was critical to the development of the response in the intradermal groups. In humans, this is the first report of a safe and effective intradermal adjuvant, GLA-AF (aqueous formulation of glucopyranosyl lipid adjuvant), and provides a future path for developing a vaccine-device combination for distribution by mail and self-administration in case of a pandemic.

Humoral and cell-mediated immune responses to H5N1 plant-made virus-like particle vaccine are differentially impacted by alum and GLA-SE adjuvants in a Phase 2 clinical trial

The hemagglutinination inhibition (HI) response remains the gold standard used for the licensure of influenza vaccines. However, cell-mediated immunity (CMI) deserves more attention, especially when evaluating H5N1 influenza vaccines that tend to induce poor HI response. In this study, we measured the humoral response (HI) and CMI (flow cytometry) during a Phase II dose-ranging clinical trial (NCT01991561). Subjects received two intramuscular doses, 21 days apart, of plant-derived virus-like particles (VLP) presenting the A/Indonesia/05/2005 H5N1 influenza hemagglutinin protein (H5) at the surface of the VLP (H5VLP). The vaccine was co-administrated with Alhydrogel^® or with a glucopyranosyl lipid adjuvant-stable emulsion (GLA-SE). We demonstrated that low doses (3.75 or 7.5 μg H5VLP) of GLA-SE-adjuvanted vaccines induced HI responses that met criteria for licensure at both antigen doses tested. Alhydrogel adjuvanted vaccines induced readily detectable HI response that however failed to meet licensure criteria at any of three doses (10, 15 and 20 μg) tested. The H5VLP also induced a sustained (up to 6 months) polyfunctional and cross-reactive HA-specific CD4⁺ T cell response in all vaccinated groups. Interestingly, the frequency of central memory Th1-primed precursor cells before the boost significantly correlated with HI titers 21 days after the boost. The ability of the low dose GLA-SE-adjuvanted H5VLP to elicit both humoral response and a sustained cross-reactive CMI in healthy adults is very attractive and could result in significant dose-sparing in a pandemic situation.

The establishment of surrogates and correlates of protection: Useful tools for the licensure of effective influenza vaccines?

The search for a test that can predict vaccine efficacy is an important part of any vaccine development program. Although regulators hesitate to acknowledge any test as a true ‘correlate of protection’, there are many precedents for defining ‘surrogate’ assays. Surrogates can be powerful tools for vaccine optimization, licensure, comparisons between products and development of improved products. When such tests achieve ‘reference’ status however, they can inadvertently become barriers to new technologies that do not work the same way as existing vaccines. This is particularly true when these tests are based upon circularly-defined ‘reference’ or, even worse, proprietary reagents. The situation with inactivated influenza vaccines is a good example of this phenomenon. The most frequently used tests to define vaccine-induced immunity are all serologic assays: hemagglutination inhibition (HI), single radial hemolysis (SRH) and microneutralization (MN). The first two, and particularly the HI assay, have achieved reference status and criteria have been established in many jurisdictions for their use in licensing new vaccines and to compare the performance of different vaccines. However, all of these assays are based on biological reagents that are notoriously difficult to standardize and can vary substantially by geography, by chance (i.e. developing reagents in eggs that may not antigenitically match wild-type viruses) and by intention (ie: choosing reagents that yield the most favorable results). This review describes attempts to standardize these assays to improve their performance as surrogates, the dangers of over-reliance on ‘reference’ serologic assays, the ways that manufacturers can exploit the existing regulatory framework to make their products ‘look good’ and the implications of this long-established system for the introduction of novel influenza vaccines.

A plant-derived quadrivalent virus like particle influenza vaccine induces cross-reactive antibody and T cell response in healthy adults

Recent issues regarding efficacy of influenza vaccines have re-emphasized the need of new approaches to face this major public health issue. In a phase 1-2 clinical trial, healthy adults received one intramuscular dose of a seasonal influenza plant-based quadrivalent virus-like particle (QVLP) vaccine or placebo. The hemagglutination inhibition (HI) titers met all the European licensure criteria for the type A influenza strains at the 3μg/strain dose and for all four strains at the higher dosages 21days after immunization. High HI titers were maintained for most of the strains 6months after vaccination. QVLP vaccine induced a substantial and sustained increase of hemagglutinin-specific polyfunctional CD4 T cells, mainly transitional memory and TEMRA effector IFN-γ(+) CD4 T cells. A T cells cross-reactive response was also observed against A/Hong-Kong/1/1968 H3N2 and B/Massachusetts/2/2012. Plant-based QVLP offers an attractive alternative manufacturing method for producing effective and HA-strain matching seasonal influenza vaccines.

Plant-derived H7 VLP vaccine elicits protective immune response against H7N9 influenza virus in mice and ferrets

In March 2013, the Chinese Centre for Disease Control and Prevention confirmed the first reported case of human infection with an avian influenza A H7N9 virus. Infection with this virus often caused severe pneumonia and acute respiratory distress syndrome resulting in a case fatality rate >35%. The risk of pandemic highlighted, once again, the need for a more rapid and scalable vaccine response capability. Here, we describe the rapid (19 days) development of a plant-derived VLP vaccine based on the hemagglutinin sequence of influenza H7N9 A/Hangzhou/1/2013. The immunogenicity of the H7 VLP vaccine was assessed in mice and ferrets after one or two intramuscular dose(s) with and without adjuvant (alum or GLA-SE™). In ferrets, we also measured H7-specific cell-mediated immunity. The mice and ferrets were then challenged with H7N9 A/Anhui/1/2013 influenza virus. A single immunization with the adjuvanted vaccine elicited a strong humoral response and protected mice against an otherwise lethal challenge. Two doses of unadjuvanted vaccine significantly increased humoral response and resulted in 100% protection with significant reduction of clinical signs leading to nearly asymptomatic infections. In ferrets, a single immunization with the alum-adjuvanted H7 VLP vaccine induced strong humoral and CMI responses with antigen-specific activation of CD3(+) T cells. Compared to animals injected with placebo, ferrets vaccinated with alum-adjuvanted vaccine displayed no weight loss during the challenge. Moreover, the vaccination significantly reduced the viral load in lungs and nasal washes 3 days after the infection. This candidate plant-made H7 vaccine therefore induced protective responses after either one adjuvanted or two unadjuvanted doses. Studies are currently ongoing to better characterize the immune response elicited by the plant-derived VLP vaccines. Regardless, these data are very promising for the rapid production of an immunogenic and protective vaccine against this potentially pandemic virus.

Generation and characterization of a trackable plant-made influenza H5 virus-like particle (VLP) containing enhanced green fluorescent protein (eGFP)

Medicago, Inc. has developed an efficient virus-like particle (VLP) vaccine production platform using the Nicotiana benthamiana expression system, and currently has influenza-based products targeting seasonal/pandemic hemagglutinin (HA) proteins in advanced clinical trials. We wished to generate a trackable HA-based VLP that would allow us to study both particle assembly in plants and VLP interactions within the mammalian immune system. To this end, a fusion protein was designed, composed of H5 (from influenza A/Indonesia/05/2005 [H5N1]) with enhanced green fluorescent protein (eGFP). Expression of H5-eGFP in N. benthamiana produced brightly fluorescent ∼160 nm particles resembling H5-VLPs. H5-eGFP-VLPs elicited anti-H5 serologic responses in mice comparable to those elicited by H5-VLPs in almost all assays tested (hemagglutination inhibition/IgG(total)/IgG1/IgG2b/IgG2a:IgG1 ratio), as well as a superior anti-GFP IgG response (mean optical density = 2.52 ± 0.16 sem) to that elicited by soluble GFP (mean optical density = 0.12 ± 0.06 sem). Confocal imaging of N. benthamiana cells expressing H5-eGFP displayed large fluorescent accumulations at the cell periphery, and draining lymph nodes from mice given H5-eGFP-VLPs via footpad injection demonstrated bright fluorescence shortly after administration (10 min), providing proof of concept that the H5-eGFP-protein/VLPs could be used to monitor both VLP assembly and immune trafficking. Given these findings, this novel fluorescent reagent will be a powerful tool to gain further fundamental insight into the biology of influenza VLP vaccines.

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.

Human antibody response to N-glycans present on plant-made influenza virus-like particle (VLP) vaccines

BACKGROUND

Plant-made biotherapeutics are gathering momentum and some plant glycoproteins are allergens. Glycans with core β1-2xylose and α1,3fucose motifs and antennae terminated by mannose residues (e.g.: MMXF) are found on several plant allergens and can cross-react with glyco-epitopes from other sources. To date, reactivity to these cross-reactive determinants has not been associated with clinical symptoms.

OBJECTIVE

We produced VLP vaccines bearing the hemagglutinin(HA) of H5(A/Indonesia/5/05) or H1(A/California/07/09) influenza viruses by transfection of Nicotiana benthamiana. Subjects enrolled in Phase I/II trials were followed for evidence of allergy/hypersensitivity and development of antibodies against plant glyco-epitopes.

METHODS

A total of 280/349 subjects received either one (H1) or 2 doses (H5) of vaccine (5-45 μg of HA/dose) intramuscularly including 40 with pre-existing plant allergies. Subjects were monitored for 6 months. IgG and IgE to plant glyco-epitopes were measured by ELISA using corn-/egg-derived avidin and bromelain as target antigens.

RESULTS

No subject developed allergic/hypersensitivity symptoms. Some (34%) developed transient IgG and, in some cases IgE, to plant glyco-epitopes but no subject mounted an IgE response to the MMXF motif. Antibodies returned to baseline by 6 months in most subjects.

CONCLUSION

VLP vaccines bearing influenza HA glycoproteins can elicit transient IgG and, in some cases, IgE responses that are not associated with either the development or worsening of allergic/hypersensitivity symptoms.

Influenza virus-like particle vaccines made in Nicotiana benthamiana elicit durable, poly-functional and cross-reactive T cell responses to influenza HA antigens

Cell-mediated immunity plays a major role in long-lived, cross-reactive protection against influenza virus. We measured long-term poly-functional and cross-reactive T cell responses to influenza hemagglutinin (HA) elicited by a new plant-made Virus-Like Particle (VLP) vaccine targeting either H1N1 A/California/7/09 (H1) or H5N1 A/Indonesia/5/05 (H5). In two independent clinical trials, we characterized the CD4(+) and CD8(+) T cell homotypic and heterotypic responses 6 months after different vaccination regimens. Responses of VLP-vaccinated subjects were compared with placebo and/or a commercial trivalent inactivated vaccine (TIV:Fluzone™) recipients. Both H1 and H5 VLP vaccines elicited significantly greater poly-functional CD4(+) T cell responses than placebo and TIV. Poly-functional CD8(+) T cell responses were also observed after H1 VLP vaccination. Our results show that plant-made HA VLP vaccines elicit both strong antibody responses and poly-functional, cross-reactive memory T cells that persist for at least 6 months after vaccination.

Preclinical and clinical development of plant-made virus-like particle vaccine against avian H5N1 influenza

The recent swine H1N1 influenza outbreak demonstrated that egg-based vaccine manufacturing has an Achille's heel: its inability to provide a large number of doses quickly. Using a novel manufacturing platform based on transient expression of influenza surface glycoproteins in Nicotiana benthamiana, we have recently demonstrated that a candidate Virus-Like Particle (VLP) vaccine can be generated within 3 weeks of release of sequence information. Herein we report that alum-adjuvanted plant-made VLPs containing the hemagglutinin (HA) protein of H5N1 influenza (A/Indonesia/5/05) can induce cross-reactive antibodies in ferrets. Even low doses of this vaccine prevented pathology and reduced viral loads following heterotypic lethal challenge. We further report on safety and immunogenicity from a Phase I clinical study of the plant-made H5 VLP vaccine in healthy adults 18-60 years of age who received 2 doses 21 days apart of 5, 10 or 20 µg of alum-adjuvanted H5 VLP vaccine or placebo (alum). The vaccine was well tolerated at all doses. Adverse events (AE) were mild-to-moderate and self-limited. Pain at the injection site was the most frequent AE, reported in 70% of vaccinated subjects versus 50% of the placebo recipients. No allergic reactions were reported and the plant-made vaccine did not significantly increase the level of naturally occurring serum antibodies to plant-specific sugar moieties. The immunogenicity of the H5 VLP vaccine was evaluated by Hemagglutination-Inhibition (HI), Single Radial Hemolysis (SRH) and MicroNeutralisation (MN). Results from these three assays were highly correlated and showed similar trends across doses. There was a clear dose-response in all measures of immunogenicity and almost 96% of those in the higher dose groups (2 × 10 or 20 µg) mounted detectable MN responses. Evidence of striking cross-protection in ferrets combined with a good safety profile and promising immunogenicity in humans suggest that plant-based VLP vaccines should be further evaluated for use in pre-pandemic or pandemic situations.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00984945.

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 microg of purified influenza H5-VLPs triggered a strong immune response against the homologous virus, whereas two doses of 0.5 microg 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.

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 microg of purified influenza H5-VLPs triggered a strong immune response against the homologous virus, whereas two doses of 0.5 microg 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.

A radioimmunoassay for the measurement of paclitaxel and taxanes in biological specimens using commercially available reagents

We have developed a rapid and sensitive radioimmunoassay for the measurement of paclitaxel and related taxanes in biological specimens using commercially available reagents. The presence of paclitaxel competitively inhibited the binding of radioactive paclitaxel to polyclonal anti-taxane antibody or anti-taxane monoclonal antibody. When using polyclonal antibody, this method detected paclitaxel in concentrations as low as 0.87 nM and was also effective in 20% methanol. This radioimmunoassay is useful for the measurement of paclitaxel and taxanes in biological specimens like culture medium of paclitaxel-producing microorganisms and may be useful for the measurement of paclitaxel and related compounds in other potential natural sources.