OpenUCT :: Browsing by Author "Meyers, Ann"

Browsing by Author "Meyers, Ann"

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Open Access
Abrogation of contaminating RNA activity in HIV-1 Gag VLPs
(BioMed Central Ltd, 2011) Valley-Omar, Ziyaad; Meyers, Ann; Shephard, Enid; Williamson, Anna-Lise; Rybicki, Edward
BACKGROUND: HIV-1 Gag virus like particles (VLPs) used as candidate vaccines are regarded as inert particles as they contain no replicative nucleic acid, although they do encapsidate cellular RNAs. During HIV-1 Gag VLP production in baculovirus-based expression systems, VLPs incorporate the baculovirus Gp64 envelope glycoprotein, which facilitates their entry into mammalian cells. This suggests that HIV-1 Gag VLPs produced using this system facilitate uptake and subsequent expression of encapsidated RNA in mammalian cells - an unfavourable characteristic for a vaccine. METHODS: HIV-1 Gag VLPs encapsidating reporter chloramphenicol acetyl transferase (CAT) RNA, were made in insect cells using the baculovirus expression system. The presence of Gp64 on the VLPs was verified by western blotting and RT-PCR used to detect and quantitate encapsidated CAT RNA. VLP samples were heated to inactivate CAT RNA. Unheated and heated VLPs incubated with selected mammalian cell lines and cell lysates tested for the presence of CAT protein by ELISA. Mice were inoculated with heated and unheated VLPs using a DNA prime VLP boost regimen. RESULTS: HIV-1 Gag VLPs produced had significantly high levels of Gp64 (~1650 Gp64 molecules/VLP) on their surfaces. The amount of encapsidated CAT RNA/mug Gag VLPs ranged between 0.1 to 7 ng. CAT protein was detected in 3 of the 4 mammalian cell lines incubated with VLPs. Incubation with heated VLPs resulted in BHK-21 and HeLa cell lysates showing reduced CAT protein levels compared with unheated VLPs and HEK-293 cells. Mice inoculated with a DNA prime VLP boost regimen developed Gag CD8 and CD4 T cell responses to GagCAT VLPs which also boosted a primary DNA response. Heating VLPs did not abrogate these immune responses but enhanced the Gag CD4 T cell responses by two-fold. CONCLUSIONS: Baculovirus-produced HIV-1 Gag VLPs encapsidating CAT RNA were taken up by selected mammalian cell lines. The presence of CAT protein indicates that encapsidated RNA was expressed in the mammalian cells. Heat-treatment of the VLPs altered the ability of protein to be expressed in some cell lines tested but did not affect the ability of the VLPs to stimulate an immune response when inoculated into mice.
Open Access
Beak and feather disease virus candidate vaccine development
(2012) Duvenage, Lucian; Rybicki, Ed; Hitzeroth, Inga; Meyers, Ann
[Fix supervisors field.] Psittacine beak and feather disease, caused by a circovirus known as beak and feather disease virus (BFDV), is a threat to both wild and captive psittacine species. There is currently no vaccine against BFDV and safe and affordable vaccine candidates are needed to alleviate the disease burden caused by this virus. Production of the BFDV's major antigenic determinant, the capsid protein (CP), in the inexpensive and highly scalable plant expression system, could satisfy these requirements as a potential subunit vaccine. In this work, truncated CP (ÄN40 CP) was first expressed in E. coli to successfully generate anti-CP polyclonal antibodies. ÄN40 CP and full-length CP transient expression in tobacco (Nicotiana benthamiana) was optimised as fusions to elastin-like polypeptide (ELP). Fusion of CP or ÄN40 CP to ELPs of different lengths was shown to increase yield relative to unfused CP/ÄN40 CP. Free ELP and a GFP-ELP fusion could be purified by inverse transition cycling (ITC), using centrifugation and membrane filtration methods. A ÄN40 CP-ELP fusion expressed in plants could be partially purified and represents low-cost vaccine candidate against BFDV. A candidate DNA vaccine expressing ÄN40 CP was also evaluated for expression of the antigen in vitro and may prove useful in a prime-boost regimen together with one of the plant-produced vaccine candidates.
Restricted
Chimaeric HIV-1 subtype C Gag molecules with large in-frame C-terminal polypeptide fusions form virus-like particles.
(Elsevier, 2008) Halsey, Richard J; Tanzer, Fiona L; Meyers, Ann; Pillay, Sirika; Lynch, Alisson; Shephard, Enid; Williamson, Anna-Lise; Rybicki, Edward P
HIV-1 Pr55 Gag virus-like particles (VLPs) are strong immunogens with potential as candidate HIV vaccines. VLP immunogenicity can be broadened by making chimaeric Gag molecules: however, VLPs incorporating polypeptides longer than 200 aa fused in frame with Gag have not yet been reported. We constructed a range of gag-derived genes encoding in-frame C-terminal fusions of myristoylation-competent native Pr55Gag and p6-truncated Gag (Pr50Gag) to test the effects of polypeptide length and sequence on VLP formation and morphology, in an insect cell expression system. Fused sequences included a modified reverse transcriptase-Tat-Nef fusion polypeptide (RTTN, 778 aa), and truncated versions of RTTN ranging from 113 aa to 450 aa. Baculovirus-expressed chimaeric proteins were examined by western blot and electron microscopy. All chimaeras formed VLPs which could be purified by sucrose gradient centrifugation. VLP diameter increased with protein MW, from ∼100 nm for Pr55Gag to ∼250 nm for GagRTTN. The presence or absence of the Gag p6 region did not obviously affect VLP formation or appearance. GagRT chimaeric particles were successfully used in mice to boost T-cell responses to Gag and RT that were elicited by a DNA vaccine encoding a GagRTTN polypeptide, indicating the potential of such chimaeras to be used as candidate HIV vaccines.
Open Access
Development of a transformation protocol and cell culture system for the commercially important species of red macroalga, Gracilaria gracilis
(2011) Huddy, Suzanne Margaret; Coyne, Vernon; Meyers, Ann
A better understanding of how this commercially important seaweed responds at a genetic level to stresses faced in the aquaculture environment would not only be advantageous to the South African industry, but this knowledge is essential for selecting and/or engineering macroalgal strains that are either more tolerant or resistant to these stresses. This requires in vivo analysis of G. gracilis gene function and regulation in order to introduce new or improved genes into G. gracilis, and for this to be possible, a protocol for transformation of recombinant DNA into G. gracilis is required. In this study a transformation and tissue culture system for G. gracilis was developed. These tools provide the necessary groundwork for future genetic manipulation studies that are essential for improving our understanding of the role that various genes play in stress response and tolerance in G. gracilis.
Open Access
Development of plant-produced African horse sickness vaccines
(2019) Dennis, Susan Jennifer; Rybicki, Ed; Hitzeroth, Inga; Meyers, Ann
African horse sickness is a devastating disease that causes great suffering and many fatalities amongst horses in sub-Saharan Africa. It is caused by nine different serotypes of the orbivirus African horse sickness virus (AHSV) and it is spread by Culicoid midges. The disease has significant economic consequences for the equine industry both in southern Africa and increasingly further afield as the geographic distribution of the midge vector broadens with global warming and climate change. Live attenuated vaccines (LAV) have been used with relative success for many decades, but carry the risk of reversion to virulence and/or genetic re-assortment between outbreak and vaccine strains. Furthermore, the vaccines lack DIVA capacity, the ability to distinguish between vaccine-induced immunity and that induced by natural infection. These concerns have motivated interest in the development of new, more favourable recombinant vaccines, initially focusing on the use of insect and mammalian cell expression systems. More recently, several studies have demonstrated the potential for using plant expression systems for the production of virus-like particles (VLPs), which are excellent vaccine candidates, as they do not contain virus genetic material and are DIVA compliant. A vaccine alternative to the currently used live vaccine necessarily needs to provide protection against all nine serotypes of the virus. Cross-protection has been shown to exist between certain serotypes of the virus and as capsid protein VP2 is the protein responsible for AHSV serotype specificity, the idea of a plant-produced VLP vaccine containing a representative VP2 protein from each of the different serotype groups, was conceived. Such a vaccine would potentially provideprotection against all 9 serotypes of the virus and would have DIVA capability. Furthermore, it would address local concerns regarding the use of a live vaccine and would serve as a potentially acceptable prophylactic or rapid response antidote in the wider international context. This work describes two approaches in the development of VLP vaccines in plants. In the first part of this study, the ability of 2 different serotypes of plant-produced AHSV VLPs to safely stimulate an immune response in horses, was investigated. Co-infiltration of Nicotiana benthamiana plants with Agrobacterium constructs encoding the four AHSV serotype 5 structural proteins VP2, VP3, VP5 and VP7, was shown to result in assembly of complete VLPs. Furthermore, co-infiltration with the constructs, encoding VP3 and VP7, together with constructs encoding the two outer capsid proteins VP2 and VP5 of a second serotype, AHSV 4, resulted in assembly of complete AHSV 4 VLPs. Horses vaccinated with plant-produced AHSV 4 and 5 VLPs, all seroconverted after two doses of the vaccine and the virus neutralization titres indicated that the plant-produced VLP vaccines are likely to be at least as effective as the current LAV in protecting against AHSV 4 or AHSV 5. However, they have the added advantage of being free from any of the associated risks of a live vaccine, such as reversion to virulence or genetic re-assortment with field or vaccine strains. In the second part of the study, the use of the so-called SpyTag/SpyCatcher or bacterial “superglue” technology was investigated. This technology is based on the peptide SpyTag irreversibly coupling to the SpyCatcher protein, forming an isopeptide bond when the two are mixed together. The plant-based expression system was used to produce Spy VLPs consisting of either Acinetobacter phage (AP205) VLPs or tobacco mosaic virus (TMV) VLPs displaying a SpyTag or SpyCatcher peptide. In addition, AHSV 5 VP2 displaying SpyTag was expressed in plants and several coupling strategies were tested to determine whether AP205 particles displaying AHSV 5 VP2 could be formed as a result of binding between the SpyTag/SpyCatcher moieties of the recombinant proteins. Although it was not proven that coupling occurred, this research will pave the way towards developing a multivalent vaccine platform whereby VP2 of different AHSV serotypes can be displayed on the Spy VLP surface to allow optimal presentation of these proteins to the animal's immune system. Together, the results obtained in this study show that there is great potential for the production of novel, diverse, efficacious and economically viable AHSV VLP vaccines in plants.
Open Access
Development of plant-produced Bluetongue virus vaccines
(2014) van Zyl, Albertha R; Meyers, Ann; Rybicki, Edward P
Bluetongue is a disease of domestic and wild ruminants caused by Bluetongue virus (BTV). It has caused several serious outbreaks, the most recent occurring in Northern Europe in 2006 during which high mortality rates of livestock were reported. The only vaccines currently approved and commercially available for use are live-attenuated or inactivated virus strains and although these are effective, there is the risk of reversion in the case of live-attenuated strains to more virulent forms by recombination. Another drawback associated with the use of live-attenuated virus vaccines is that they are not DIVA (differentiate infected from vaccinated animals) compliant, this means that naturally infected animals cannot be distinguished from vaccinated animals. Recombinantly produced vaccines would be preferable to minimize the risks associated with live-attenuated virus vaccines and also enable the development of candidate vaccines that are DIVA-compliant. A number of recombinant vaccine candidates have been developed against BTV, with the most promising vaccine consisting of BTV virus-like particles (VLPs). BTV VLPs were successfully produced in insect cells by the co-expression of the four BTV capsid proteins (VP2, VP3, VP5 and VP7). Sheep vaccinated with insect cell-produced BTV VLPs were shown to be protected against challenge with wild type virus. However, the high costs associated with the production and scale-up of BTV VLPs in insect cells has possibly limited their widespread application. Plants – such as N. benthamiana – provides a safe, efficient and cost effective system for the production of recombinant proteins. In this study the best plant expression vector with which to co-express the four BTV serotype 8 (BTV-8) VPs – which direct formation of BTV-8 VLPs – was identified. Expression and purification of the BTV-8 VLPs was optimised with the aim of producing a VLP-based vaccine for BTV-8. It was further undertaken to develop two novel second generation plant-produced protein body (PB) vaccines that are DIVA compliant. Mice were immunised with the plantproduced VLP and PB vaccines in order to analyse their ability to elicit humoral immune responses.
Open Access
Development of Rift Valley fever virus candidate vaccines and reagents produced in Nicotiana benthamiana
(2017) Mbewana, Sandiswa; Rybicki, Edward P; Meyers, Ann
Rift Valley fever (RVF) is a haemorrhagic fever agent caused by an infection with an enveloped negative-stranded RNA Rift Valley fever virus (RVFV). It belongs to the genus Phlebovirus in the family Bunyaviridae. The virus is spread by infected mosquitoes and affects ruminants and humans, causing high numbers of neonatal fatalities in animals and occasional fatalities in humans. It is endemic to parts of Africa and the Arabian Peninsula, but is described as an emerging virus due to the wide range of mosquitoes that could spread the disease into non-endemic areas, posing serious health and agricultural problems. The disease can be prevented by vaccination, but there is currently no Food and Drug Administration-approved RVFV vaccine that can be used outside endemic areas, while there are two live attenuated vaccines available for use in endemic areas. These vaccines have the potential for reversion, and are therefore not recommended for use in countries where RVFV is not endemic. This indicates the need for more RVFV vaccine research and development. This work focused on the development of a RVFV vaccine candidate that would allow for differentiation between infected and vaccinated animals as well as humans.
Open Access
Development of West Nile virus candidate vaccines in Nicotiana benthamiana
(2021) Wayland, Jennifer; Meyers, Ann; Chabeda, Aleyo; Rybicki, Ed
West Nile virus (WNV) is a widely disseminated flavivirus, with a geographical range that now includes Africa, America, Europe, the Middle East, West Asia and Australia. The virus is vectored by Culex mosquitoes and is maintained in a bird-mosquito transmission cycle with hundreds of bird species acting as reservoir hosts. In humans, infections can develop into febrile illness and severe meningoencephalitis and to date, there is no treatment or vaccine available. In horses, approximately 20% of infections are symptomatic, of which 90% of cases involve neurological disease, with 30-40% fatality rates. Several veterinary vaccines specific to the lineage 1 WNV strains are commercially produced in America and Europe, however, these vaccines are not easily obtainable for low and middle-income countries (LMIC) due to their high cost and that associated with importation as well as the need for annual vaccination. Due to continuous global disease outbreaks in birds, humans and horse populations with no preventative measures for humans, WNV poses a major public health threat, especially in naïve populations. The development of a vaccine that contributes to the ‘One Health' Initiative could be the answer to prevent the spread of the virus and control the disease. Current veterinary vaccines are produced in expensive cell culture systems that require sterile conditions, high-level biosafety facilities and trained personnel for their preparation. Transient plant-based expression systems have proven to be a very cost-effective means of making complex proteins. Plants can produce and modify proteins in a similar manner to mammalian cells and production does not require sterile conditions or specialised facilities. We propose that plants could be a viable means of making feasible, low-cost reagents for WNV, specifically virus-like particles (VLPs) for use as vaccines in South Africa and other LMIC. In this study, we set out to develop two particulate candidate vaccines based on a virulent South African WNV strain using Nicotiana benthamiana as the expression platform. We aimed to develop the first candidate vaccine by exploiting the virus's ability to form noninfectious VLPs by expressing only the WNV membrane (prM – precursor, M – matured) and envelope (E) proteins. Infiltration of these recombinant plasmids into plants yielded no protein expression unless co-expressed with the human chaperone protein calnexin (CNX), upon which expression of both M and E proteins were observed. We investigated the assembly of prM and E into VLPs by transmission electron microscopy (TEM), however, purification of these particles proved difficult with poor reproducibility and VLP yield. This led to the development of an alternative candidate vaccine making use of the antigendisplay technology based on the SpyTag (ST) and SpyCatcher (SC) peptides. The immunodominant epitope of the WNV E protein, domain III (EdIII), was selected for antigen display. Two constructs of the EdIII gene were generated, one with the SC peptide on the 5'- (SC-EdIII) and the other on the 3' end (EdIII-SC). Both SC-EdIII and EdIII-SC proteins were successfully expressed in the presence of the human chaperone protein calreticulin, and purified with yields of 9 mg/kg and 69 mg/kg fresh leaf weight (FLW), respectively. The VLP core selected for the display of the SC-linked EdIII proteins comprised the coat protein of the bacteriophage AP205 with the ST peptide linked to its N-terminus (ST-AP205). Spytagged-VLPs were purified by density gradient ultracentrifugation at a yield of approximately 50 mg/kg FLW. The purified SC-linked EdIII proteins and ST-AP205 VLPs were coupled in vitro, but successful complex formation of AP205:EdIII was only observed between ST-AP205 and EdIII-SC and not when the SC peptide was located on the N-terminus of EdIII. We further demonstrated the successful complex formation of AP205:EdIII in vivo by coinfiltration of the EdIII-SC and ST-AP205 constructs, as well as by extracting leaves of plants infiltrated individually with either of the constructs. Due to the ease of purification and the high yields of AP205:EdIII achieved, the co-extraction process was optimised to obtain the best coupling yield possible by evaluating different FLW extraction ratios and the formation of VLPs was confirmed by TEM. The optimal co-extraction process was established at a FLW ratio of 1:2 ST-AP205 to EdIII-SC yielding approximately 23 mg/kg AP205:EdIII/FLW processed. In this study, we describe the successful production of two particulate candidate vaccines. The first is based on the expression of the WNV prM and E genes in the presence of human CNX and the second is based on the ST/SC antigen-display technology. These outcomes exhibit the potential plants have of being used as biofactories for making significant pharmaceutical products for the ‘One Health' Initiative and could be used to address the need for their local production in LMIC.
Open Access
Expression of HIV-1 antigens in plants as potential subunit vaccines
(BioMed Central Ltd, 2008) Meyers, Ann; Chakauya, Ereck; Shephard, Enid; Tanzer, Fiona; Maclean, James; Lynch, Alisson; Williamson, Anna-Lise; Rybicki, Edward
BACKGROUND: Human immunodeficiency virus type 1 (HIV-1) has infected more than 40 million people worldwide, mainly in sub-Saharan Africa. The high prevalence of HIV-1 subtype C in southern Africa necessitates the development of cheap, effective vaccines. One means of production is the use of plants, for which a number of different techniques have been successfully developed. HIV-1 Pr55Gag is a promising HIV-1 vaccine candidate: we compared the expression of this and a truncated Gag (p17/p24) and the p24 capsid subunit in Nicotiana spp. using transgenic plants and transient expression via Agrobacterium tumefaciens and recombinant tobamovirus vectors. We also investigated the influence of subcellular localisation of recombinant protein to the chloroplast and the endoplasmic reticulum (ER) on protein yield. We partially purified a selected vaccine candidate and tested its stimulation of a humoral and cellular immune response in mice. RESULTS: Both transient and transgenic expression of the HIV antigens were successful, although expression of Pr55Gag was low in all systems; however, the Agrobacterium-mediated transient expression of p24 and p17/p24 yielded best, to more than 1 mg p24/kg fresh weight. Chloroplast targeted protein levels were highest in transient and transgenic expression of p24 and p17/p24. The transiently-expressed p17/p24 was not immunogenic in mice as a homologous vaccine, but it significantly boosted a humoral and T cell immune response primed by a gag DNA vaccine, pTHGagC. CONCLUSION: Transient agroinfiltration was best for expression of all of the recombinant proteins tested, and p24 and p17/p24 were expressed at much higher levels than Pr55Gag. Our results highlight the usefulness of plastid signal peptides in enhancing the production of recombinant proteins meant for use as vaccines. The p17/p24 protein effectively boosted T cell and humoral responses in mice primed by the DNA vaccine pTHGagC, showing that this plant-produced protein has potential for use as a vaccine.
Open Access
HIV-1 sub-type C chimaeric VLPs boost cellular immune responses in mice
(BioMed Central Ltd, 2010) Pillay, Sirika; Shephard, Enid; Meyers, Ann; Williamson, Anna-Lise; Rybicki, Edward P
Several approaches have been explored to eradicate HIV; however, a multigene vaccine appears to be the best option, given their proven potential to elicit broad, effective responses in animal models. The Pr55Gag protein is an excellent vaccine candidate in its own right, given that it can assemble into large, enveloped, virus-like particles (VLPs) which are highly immunogenic, and can moreover be used as a scaffold for the presentation of other large non-structural HIV antigens. In this study, we evaluated the potential of two novel chimaeric HIV-1 Pr55Gag-based VLP constructs - C-terminal fusions with reverse transcriptase and a Tat::Nef fusion protein, designated GagRT and GagTN respectively - to enhance a cellular response in mice when used as boost components in two types of heterologous prime-boost vaccine strategies. A vaccine regimen consisting of a DNA prime and chimaeric HIV-1 VLP boosts in mice induced strong, broad cellular immune responses at an optimum dose of 100 ng VLPs. The enhanced cellular responses induced by the DNA prime-VLP boost were two- to three-fold greater than two DNA vaccinations. Moreover, a mixture of GagRT and GagTN VLPs also boosted antigen-specific CD8+ and CD4+ T-cell responses, while VLP vaccinations only induced predominantly robust Gag CD4+ T-cell responses. The results demonstrate the promising potential of these chimaeric VLPs as vaccine candidates against HIV-1.
Open Access
HPV pseudovirion production in plants
(2013) Kennedy, Paul; Rybicki, Ed; Hitzeroth, Inga; Meyers, Ann
Human papilloma virus (HPV) infection is the most common etiological agent of cervical cancer, the most common cancer in women in Africa. The lifecycle of HPV has historically made the virus difficult to culture in vitro, and this has hindered the study of the virus, as well as development of vaccines. The development of synthetic HPV particles, such as virus-like particles (VLPs) and more recently pseudovirions (PsVs), has allowed for unprecedented insights into the lifecycle and immunology of this virus. This has led to the development of two currently available vaccines, namely Cervarix™ and Gardasil®. Cervarix offers protection against high-risk HPV types 16 and 18, while Gardasil offers further protection against types 6 and 11. Both of these vaccines are based on major capsid protein L1 Virus-like particles (VLPs). While these vaccines show no loss of efficacy, further work is underway to develop a second generation HPV vaccine that is cheap, stable and displays cross-neutralising activity across a broader range of HPV types. The recent efficient methods for intracellular production of HPV PsVs encapsidating nonpapillomaviral DNA (pseudogenomes) has allowed for development of a robust and sensitive pseudovirion-based neutralisation assay (PBNA), which has become the gold standard neutralisation assay for the testing of candidate HPV vaccines. The currently accepted PsV production method utilises mammalian cell culture to produce HPV PsVs, encapsidating a SEAP reporter plasmid, at high titres. While this is an effective method of PsV production, mammalian cell culture is expensive and time-consuming. Transient recombinant protein expression in plants offers a rapid and cost-effective alternative to mammalian cell culture. Here, we developed a method of high-titre HPV PsV production in plants. The autonomously replicating plant vector, pRIC3, was modified to include mammalian reporter cassettes encoding luc or SEAP, for the production of reporter pseudogenomes DNA in plants by Agrobacterium-mediated transient expression. The SEAP and luc cassettes were introduced into pRIC3 upstream of the plant cassette, which was included only to increase the final pseudogenome size for efficient packaging into PsVs. The SEAP cassette was also introduced into pRIC3 in place of the plant cassette, to form a smaller pseudogenome. Thus three vectors were created, namely pRIC3-mSEAP+ (6.4Kbp pseudogenome), pRIC3-mluc+ (7.4Kbp pseudogenome), and pRIC3-mSEAP (4.8Kbp pseudogenome), which would produce pseudogenomes that covered the full range of plasmid sizes incorporated by assembling HPV capsid proteins in vivo. All three replicating vectors demonstrated the formation of a replicon, and autonomous replication, in Nicotiana benthamiana plants. Each of these vectors were co-infiltrated with the non-replicating transient plant expression constructs pTRAc-hL1 and pTRAc-hL2, which encode human-codon optimised forms of HPV-16 major and minor capsid proteins, respectively. It was expected that encapsidation of replicon DNA as a pseudogenome into assembling HPV particles would result in the production of HPV PsVs in planta. In addition, L1 and L2 were expressed in the absence of replicon DNA to form L1/L2 VLPs. Particles were extracted from plant material at four days post-infiltration, using a modified VLP extraction protocol. HPV particles were separated on the basis of isopycnic caesium chloride density gradient ultracentrifugation, dialysed against high-salt PBS and identified by fractionation and probing with an anti-L1 antibody. Particles corresponding to the buoyant density of pseudovirions were seen in samples with or without replicon DNA. Western blotting showed that all particles had incorporated both L1 and L2 proteins. Particles were digested with proteinase K to release encapsidated pseudogenome DNA and PCR confirmed the presence of replicon-specific DNA in each PsV. Electron microscopy confirmed the presence of HPV-16 PsVs in all samples. To test whether plant-produced HPV-16 PsVs could be used in pseudovirion-based neutralisation assays, mammalian cells were pseudoinfected with purified mSEAP, mSEAP+ or mluc+ PsVs. mSEAP and mluc+ PsVs elicited a reporter gene response in mammalian cells 72 hours post-infection using SEAP and luciferase assays, respectively, while mSEAP+ PsVs showed no reporter gene expression in mammalian cells. PsVs incubated with a known HPV-16 neutralising antibody showed partial neutralisation of mSEAP PsVs and complete neutralisation of mluc+ PsVs To our knowledge, this is the first demonstration of production of HPV PsVs in plants, and their use in a PBNA. Further, it is the first demonstration of production of HPV L1/L2 VLPs in plants. While much work remains to improve plant production and purification methods of PsVs, as well as mammalian expression following PsV pseudoinfection, this is an important step towards a new method of PsV production.
Open Access
Investigating the production of a particulate plant-produced vaccine candidate against African horse sickness
(2021) Luhanga, Gloria; Hitzeroth, Inga; Meyers, Ann; Dennis, Susan Jennifer
African horse sickness (AHS) is a non-communicable, infectious disease that affects equids and is mainly prevalent in sub-Saharan Africa. The disease has a major impact on the economy of the equine industry as well as an emotional impact on horse owners. There are nine known serotypes of African horse sickness virus (AHSV), which is spread by Culicoides midges. Currently, a multivalent live attenuated vaccine is the only vaccine licensed for use in South Africa. However, it has the inherent risk of reverting to virulence as well as the possibility of genome segment reassortment between vaccine and outbreak strains. Additionally, it is not DIVA compliant (cannot Differentiate between Infected and Vaccinated Animals). There is therefore a need for a safer and more cost-effective alternative vaccine to protect horses against AHSV. Virus-like particles (VLPs) that display antigens on their surface may be suitable vaccine platforms. One such display particle is the phage AP205 VLP, which is comprised of AP205 coat proteins. To aid antigen display, studies have utilized the SpyTag (ST) - SpyCatcher (SC) or “plug-and-display” system, a novel conjugation system used to display several antigens fused to AP205 VLPs. This study aimed at displaying the neutralizing epitope of AHSV serotype 5, known as the VP2 domain (dom) (873bp), on phage AP205 VLP particles using the SpyTag/SpyCatcher technology. The display particle vaccine candidates were produced in Nicotiana benthamiana plants. Firstly, AHSV 5 VP2dom was expressed by being linked to either the ST or SC peptide at its C-terminus. Recombinant pEAQ-AHSV 5-VP2dom ST and pEAQ-AHSV 5- VP2domSC plasmid constructs were constructed from the full-length pEAQ-AHSV 5-VP2- SpyTag and pEAQ-AHSV 5-VP2-SpyCatcher clones using in-fusion cloning. The ST/SC constructs were transformed into Stellar™ competent E. coli cells and thereafter into Agrobacterium tumefaciens AGL-1 cells. Expression time trials were conducted on plants infiltrated with the recombinant Agrobacterial strains to examine transient AHSV 5- VP2domST/SC small-scale expression. Expression was detected for AHSV 5 VP2domSC but not AHSV 5 VP2domST using guinea pig anti-AHSV 5 and rabbit antiST-AP205 sera. Secondly, the development of a particle display vaccine candidate was investigated by coupling AHSV 5 VP2domSC to plant-expressed ST-AP205 VLPs. Three coupling techniques, namely in vitro coupling of purified products, co-infiltration and co-purification, were deployed to determine the assembly of ST-AP205_AHSV 5 VP2domSC VLPs. In vitro coupling involved carrying out separate infiltrations and purification of pEAQ-STAP205 VLPs and pEAQ-AHSV 5 VP2domSC in plants and thereafter mixing the purified products. For co-infiltration, pEAQ-ST-AP205 VLPs and VP2domSC recombinant cultures were used together to infiltrate plants and the presence of complex formations was determined. During co-purification, the presence of coupled products was analysed following separate infiltration of plants with pEAQ-ST-AP205 and VP2domSC recombinant Agrobacterial strains; the homogenates were then incubated together at different VLP: antigen leaf:weight ratios. From the three coupling techniques, copurification at a 1:1 VLP: antigen ratio was identified as the best coupling approach based on the quality and quantity of particles visualised by electron microscopy. These findings indicate the potential of producing an AHSV vaccine candidate in plants, which is ultimately a safer and cheaper alternative to the currently-produced AHSV vaccine. Moreover, this preliminary data may pave the way for developing a vaccine that provides protection against all nine serotypes of AHSV by displaying VP2domSC for other serotypes on the ST-AP205 display particles.
Open Access
An investigation into improved HIV-1 subtype C envelope based vaccine design
(2014) Margolin, Emmanuel Aubrey; Williamson, Anna-Lise; Rybicki, Ed; Chapman, Ros; Meyers, Ann
Includes abstract. Includes bibliographical references.
Open Access
Investigation of particulate HIV-1 Env vaccine candidates using Zera® and SpyTag/SpyCatcher technologies
(2022) Ximba, Phindile Thobeka; Rybicki, Ed; Williamson, Anna-Lise; Meyers, Ann
The HIV-1 envelope glycoprotein (Env) is the primary focus of prophylactic HIV vaccine development. However, the unusually low density of Env spikes on the virion (≈14 spikes/virion) is unfavourable for eliciting high titre, long-lasting antibody responses. It is possible that increasing the Env spike density of particulate vaccine candidates generated by protein body formation or via the display of Env on nanoparticles could improve the induction of long-lasting neutralising antibodies (NAbs). For this thesis, two different nanoparticle approaches were therefore investigated. The HIV-1 Env sequence used for both approaches was derived from the superinfecting subtype C CAP256 virus. This was truncated to remove the transmembrane domain, and engineered to contain a flexible linker (FL) in place of the furin cleavage site and an I559P mutation to generate soluble, stable and cleavageindependent gp140 proteins. The first approach investigated the impact of genetically fusing a 27 kDa proline-cysteine-rich domain of the ɣ-zein maize seed storage protein - Zera® - to either the N- or C-terminus of CAP256 gp140. Fusion of Zera® to a protein of interest can promote the self-assembly of large protein bodies (PBs) containing the protein of interest, thereby improving yields of the recombinant protein and enabling easy isolation using gradient ultracentrifugation. The purification of Zera-induced Env PBs from infiltrated Nicotiana benthamiana plants was not optimal. Consequently, the generation of Zera®-induced gp140 protein bodies was evaluated in a mammalian expression system. Stable HEK293 cell lines expressing Zera®-gp140 or gp140-Zera® were generated. A mixture of small PB-like structures was observed in cells expressing gp140-Zera®. However, no PB-like structures were seen in cells expressing Zera®-gp140. The immunogenicity of Zera®-gp140 and gp140-Zera® was evaluated by in rabbits. Binding and Tier 1A neutralising serum titres were higher for gp140-Zera® than for Zera®-gp140. Neither gp140-Zera® nor Zera®-gp140-specific sera neutralised a Tier 1B pseudovirus or the autologous Tier 2 CAP256SU pseudovirus, suggesting that Zera® might have compromised the structure of the Zera®-tagged gp140 proteins. The second approach investigated the two-component SpyCatcher/SpyTag technology. The stable HEK293 cell line expressing CAP256 gp140-SpyTag (gp140-ST) was generated, and trimers were purified to homogeneity using gel filtration. SpyCatcher (SC)-AP205 VLPs were produced in E. coli and purified by ultracentrifugation. The gp140-ST trimers and the SCAP205 VLPs were mixed in varying molar ratios to generate VLPs displaying the glycoprotein (AP205-gp140-ST particles). SDS-PAGE, dynamic light scattering and negative stain electron microscopy indicated that gp140-ST was successfully bound to the VLPs, although not all potential binding sites were occupied. The immunogenicity of the coupled VLPs was evaluated in a pilot study in rabbits. One group was injected four times with coupled VLPs. The second group was primed with DNA vaccines expressing Env and a mosaic Gag, followed by modified vaccinia Ankara expressing the same antigens and then boosted twice with coupled VLPs. Encouragingly, gp140-ST displayed on SC-AP205 VLPs was an effective boost to heterologously primed rabbits, leading to induction of autologous Tier 2 neutralising antibodies in 2/5 rabbits. These results demonstrate that careful selection of a geometrically-suitable nanoparticle scaffold to achieve a high-density display of HIV-1 envelope trimers is an important consideration and that this could improve the effect of nanoparticle-displayed gp140.
Open Access
Novel expression and production of Foot-and-mouth disease virus vaccine candidates in Nicotiana benthamiana
(2017) Veerapen, Varusha Pillay; Meyers, Ann; Rybicki, Edward P
Foot-and-mouth disease, also known as FMD, is caused by the aphthovirus Foot-and-mouth disease virus (FMDV), which is a highly contagious disease of cloven-hoofed animals. It is endemic in Africa, parts of South America and southern Asia. In South Africa, the disease is controlled essentially through prophylactic vaccination. Current vaccines on the market are chemically inactivated virus strains. However, these are not considered ideal due to the possibly insufficient inactivation which could fail to render the virus harmless. Research on recombinant vaccines which obviate the need for high biosafety requirements for vaccine preparation has shown that recombinant FMDV virus-like particles (VLPs), devoid of viral genetic material, are an ideal vaccine candidate as they are as immunogenic as the virions themselves when administered to animals. These VLPs are formed by the assembly of the FMDV capsid proteins VP0, VP1 and VP3, which are generated upon the proteolytic cleavage of the capsid precursor protein P1-2A, by the FMDV 3C-protease. The expression platforms used to co-express and produce the component capsid proteins and the protease are usually mammalian, insect or E. coli cells. The use of these expression systems requires extensive bioreactor infrastructure and sterile conditions for vaccine preparation which are costly. In addition, some studies have shown how the co-expression of the 3C-protease can prove to be deleterious when expressed at a high concentration in expression systems. In order to circumvent this, and encourage more efficient production of the capsid proteins and subsequent VLP assembly, researchers have shown that the levels of the 3C-protease can be down-regulated by introducing mutations in the 3C gene or a ribosomal frameshift in the gene sequence which subsequently reduce its deleterious effect. Our laboratory has previously shown that similar FMDV VLPs can be assembled by the expression of FMDV P1-2A (referred to as oP1-2A, in this study), in the absence of the 3C-protease in the plant Nicotiana benthamiana, albeit in low amounts. This platform does not require high biocontainment facilities for the production of recombinant proteins and VLPs and the process is easily scalable. This study centers mainly on optimisation of the FMDV capsid protein expression in N. benthamiana in order to increase VLP yields. I first used codon-optimisation as an approach to improve expression of the capsid proteins and compared expression in the presence and absence of the 3C-protease, using mP1-2A-3C (a new codon-optimised construct), mP1-2A and oP1-2A. Electron microscopy (EM) showed that VLPs resulting from the expression of both mP1-2A-3C and mP1-2A were very low in yield, and irregular in shape and size compared to those produced using oP1-2A. The stability of the plant-produced VLPs was assessed by counting numbers of VLPs, when it was seen that expression of mP1-2A-3C compared to oP1-2A produced an average of 1 VLP per field of view versus 3 VLPs per view, for the same magnification. Furthermore, maturation trials at room temperature was performed on the oP1-2A VLPs, whereby a time-point between 30 to 45 minutes was considered ideal to produce stable VLPs. It is also known that FMDV, unlike the other members of the Picornaviridae family, is acid and heat-labile. The second aim of this study was to promote the stability, and hence encourage the amount of the VLPs produced, by engineering acid and heat-resistant mutants, namely, VP1 N17D, VP2 H93C and VP1 N17D/VP4 S73N using site-directed mutagenesis. A fourth mutant, VP3 A118V which is acid sensitive was used as a control in downstream experiments. The mutants were subjected to a lower than normal pH and a higher than normal temperature. Expression of oP1-2A from the pH and heat assays was assessed to be better than its mutants. The optimum VLP count of 3 VLPs per field of view, was achieved from expression of oP1-2A, after treatment at pH 6.2, compared to 2 VLPs or 1 VLP per field of view for the other mutants tested under all the different conditions. The final aim of this study was to test the immunogenicity of the VLPs from expression of oP1-2A in Balb/C mice. Due to the low yields of VLPs obtained from purification through a continuous gradient, a partial purification method was adopted. Two experimental groups of animals were either vaccinated with P1-2A VLPs or with adjuvanted P1-2A VLPs. A control group was administered with partially-purified plant extract, previously infiltrated with pEAQ-HT. The two experimental groups elicited a marginal increase in humoral immune response at 41 days post vaccination (dpv), which increased significantly at 58 dpv. To my knowledge, this is the first study showing that VLPs produced from expression of FMDV P1-2A only, in tobacco plants, can withstand otherwise degradative acidic and heat conditions. This characteristic has potential for extending the shelf-life of such a candidate vaccine. I also implemented maturation steps to further promote the stability of such VLPs. Finally, the partially purified VLPs showed that they stimulate a significant FMDV P1-2A-specific immune response, particularly in combination with the adjuvant Montanide suggesting that it has potential as a candidate FMDV vaccine.
Open Access
Optimization of chimaeric HIV-1 virus-like particle (VLP) production and immunogenicity testing of VLPs in mice
(2008) Pillay, Sirika; Rybicki, Ed; Meyers, Ann
The devastating effect the HIV pandemic has had on the human population in the last twenty five years has highlighted the great need to develop a prophylactic HIV vaccine. The manufacture of a vaccine has proven difficult though, with a number of successful designs in animal models having little success in humans. In view of this, there has been a need for novel vaccine approaches that are able to elicit effective cellular and humoral immune responses, both of which are believed to be important in the eradication of the virus. One such approach is the use of HIV-1 Gag VLPs as vaccine candidates. In this study, the production of two chimaeric (Gag VLP vaccine candidates (GagRT and GagTN) was optimized in insect cells, and their ability to enhance a murine immune response in a DNA prime-VLP boost vaccine strategy was evaluated.
Open Access
Plant-expressed diagnostic proteins and their use for the identification and differentiation of infected and vaccinated animals with foot-and-mouth disease virus
(2017) De Beer, Scott; Meyers, Ann; Rybicki, Edward P
The Foot-and-mouth disease virus (FMDV) affects cloven-hoofed animals and is endemic in most parts of Africa, South America and southern Asia. South Africa is considered a FMDV-free zone but the virus is maintained within the wildlife in the Kruger National Park (KNP), making mitigation of outbreaks a high priority. Diagnostic methods are usually costly due to the high production cost of the reagents used, meaning that regular monitoring and diagnosis of animals around the KNP for FMDV is expensive due to the large amounts of serum continuously being tested. I propose an alternative plant expression platform for the local production of more cost effective diagnostic reagents capable of distinguishing between infected and vaccinated animals (DIVA). I selected the non-structural 3ABC polyprotein of FMDV to express, as it is a suitable candidate as a coating antigen in a competitive enzyme linked immunosorbent assay (C-ELISA) for the detection of neutralizing antibodies in livestock sera. I also chose other variations of the full polyprotein (3AB, 3AB1 and 3B) for expression as they have previously been shown to be effective in FMDV diagnosis. I also selected a second reagent to be expressed: this was the CRAb-FM27 single chain variable fragment (scFv), which binds a 3B epitope on the 3ABC polyprotein and has previously shown to be effective as a competing antibody in a C-ELISA. The 3B antigen and the scFv were successfully expressed and purified from N. benthamiana, which to my knowledge is the first time either has been shown. The plant produced scFv successfully bound the 3B antigen in an I-ELISA. Separately, the plant produced 3B antigen could be used to successfully differentiate FMDV infected and vaccinated guinea pig serum in an I-ELISA. However, testing of these reagents in tandem within a C-ELISA to DIVA sera was inconclusive, and further research is required to optimise C-ELISA conditions.
Open Access
The production of a Crimean-Congo haemorrhagic fever virus diagnostic antigen in plants
(2016) Atkinson, Richard; Meyers, Ann; Rybicki, Edward P
Crimean-Congo Hemorrhagic Fever (CCHF) is a highly infectious, life threatening disease, caused by the Crimean-Congo Hemorrhagic Fever Virus (CCHFV), a nairovirus that forms part of the Bunyaviridae family. CCHFV has a case fatality rate of approximately 40%. Current diagnostic methods for CCHFV involve the use of live virus antigen, requiring biosafety level 4 (BSL4) conditions for safe handling. The development of a safer diagnostic reagent for detection of this disease is therefore desirable. This project involves the development of a recombinant CCHFV nucleocapsid protein (NP). The nucleocapsid (NP) protein was expressed in Nicotiana benthamiana and purified using a 6x histidine-tag. The protein was then reacted against serum samples collected from confirmed CCHFV patients to determine its ability to detect IgG antibodies against CCHFV in human sera.
Open Access
RNA transmission and expression from inert HIV candidate vaccine virus-like-particles
(2008) Valley-Omar, Ziyaad; Rybicki, Ed; Meyers, Ann; Shephard, Enid
HIV-1 Gag virus-like-particles (VLPs) produced in various expression systems are potent stimulators of both cellular and humoral immune responses in animal models. The encapsidation of large concentrations of random cellular RNA species is known to accompany the assembly of HIV virus particles. This RNA plays a crucial role by serving as a molecular scaffold for the assembly of Gag structural proteins into particles. Non-pseudotyped VLPs that do not present any HIV envelope glycoproteins are regarded as inert particles as they contain no replicative nucleic acid and are presumed to be unable to deliver encapsidated RNA for expression in inoculated individuals. Live virus cellular entry studies have shown that non-pseudotyped Gag particles are destined for degradation in acidified vesicles subsequent to receptor independent cellular entry. In addition to host cell RNA incorporation, Gag VLPs produced in insect cell-based, baculovirus expression systems have been observed to incorporate the baculovirus-derived Gp64 envelope glycoprotein. Gp64 has been shown to be efficient at enabling the delivery and expression of genes from recombinant baculoviruses and other Gp64 pseudotyped live viruses in mammalian cell lines both in vivo and in vitro. This study, therefore, set out to establish for the first time whether inert, baculovirus-derived (Gp64 pseudotyped) Gag VLPs could mediate delivery and expression of randomly encapsidated RNAs in mammalian cell lines.
Open Access
Stability studies of HIV-1 Pr55gag virus-like particles made in insect cells after storage in various formulation media
(BioMed Central Ltd, 2012) Lynch, Alisson; Meyers, Ann; Williamson, Anna-Lise; Rybicki, Edward
BACKGROUND:HIV-1 Pr55gag virus-like particles (VLPs) expressed by baculovirus in insect cells are considered to be a very promising HIV-1 vaccine candidate, as they have been shown to elicit broad cellular immune responses when tested in animals, particularly when used as a boost to DNA or BCG vaccines. However, it is important for the VLPs to retain their structure for them to be fully functional and effective. The medium in which the VLPs are formulated and the temperature at which they are stored are two important factors affecting their stability.FINDINGS:We describe the screening of 3 different readily available formulation media (sorbitol, sucrose and trehalose) for their ability to stabilise HIV-1 Pr55gag VLPs during prolonged storage. Transmission electron microscopy (TEM) was done on VLPs stored at two different concentrations of the media at three different temperatures (4degreesC, -20degreesC and 70degreesC) over different time periods, and the appearance of the VLPs was compared. VLPs stored in 15% trehalose at 70degreesC retained their original appearance the most effectively over a period of 12 months. VLPs stored in 5% trehalose, sorbitol or sucrose were not all intact even after 1 month storage at the temperatures tested. In addition, we showed that VLPs stored under these conditions were able to be frozen and re-thawed twice before showing changes in their appearance. CONCLUSIONS: Although the inclusion of other analytical tools are essential to validate these preliminary findings, storage in 15% trehalose at 70degreesC for 12 months is most effective in retaining VLP stability.