University of Cape Town scientists, who spent two decades researching plant-made vaccines before turning their attention to COVID-19 when the pandemic hit, have successfully reported the expression of the near-full length SARS-CoV-2 spike vaccine in plants.
This work leverages recent advances in the Biopharming Research Unit (BRU) to produce viral surface glycoproteins in plants, by providing elements of the human intracellular folding machinery. This strategy forms part of a new research initiative to develop novel approaches to producing vaccines against emerging viruses in plants.
Their recent work, shared as a preprint entitled Calreticulin co-expression supports high level production of a recombinant SARS-CoV-2 spike mimetic in Nicotiana benthamiana, is proof-of-concept that their technology platform can be applied to producing a vaccine for an emerging virus, like SARS-CoV-2. This builds on previous success in expressing HIV-1 Env protein, and several other viral glycoproteins.
“With sufficient investment and development we could have a vaccine platform to service the needs not only of South Africa, but also of the continent.”
Cheaper, faster, safer, scalable
However, without the critical investment necessary for further development and to move their research beyond the laboratory, its potential is unlikely to be realised.
“With sufficient investment and development we could actually have a vaccine platform to service the needs not only of South Africa, but also of the continent,” says UCT postdoctoral scientist and lead author on the paper, Emmanuel Margolin, stressing that plants offer a potentially cheaper, faster, safer and highly scalable means of producing pharmaceutically-relevant proteins.
Typically, modern virus vaccines are produced in mammalian cells, which is highly expensive and requires the kind of infrastructure that is mostly absent in developing countries. This makes plant-based vaccine manufacturing an increasingly attractive alternative, Margolin points out, as both the infrastructure and the costs to scale up production are potentially lower.
Margolin and his co-authors released the paper on the preprint server bioRxiv in June last year, due to the potential impact of their findings on what was by that time a global race to produce a COVID-19 vaccine.
For the study, he and his co-authors - Matthew Verbeek, Dr Ann Meyers, Dr Rosamund Chapman, Professor Anna-Lise Williamson and Professor Edward Rybicki - studied the production of a SARS-CoV-2 spike mimetic in Nicotiana benthamiana, an Australian tobacco-related species widely used in the field of plant virology.
Explaining their motivation, Margolin says that plant-based subunit vaccine production has long been viewed as a cheaper alternative. However, when compared to mammalian cells, low expression yields and differences along the secretory pathway have impeded the production of certain viral glycoproteins which have potential as vaccines.
Important proof-of-concept may develop platform for emerging viruses
While their recent work has dramatically improved the production of many viral surface proteins in plants, they are also developing approaches to modify glycosylation and support processing events which may not otherwise occur adequately in plants, he adds.
“Our ongoing research is examining why it is so difficult to produce surface proteins of virus in plants. In many cases, the level of viral glycoproteins accumulation is too low for it to be feasible, and in some cases protein folding may not be optimal.
The work has already yielded four patent applications, all contributing to fine-tuning the underlying technology to produce vaccines to fight COVID-19 and other future emerging viruses.
“Our approach has been to identify bottlenecks in the plant system, and then to systematically fix them by introducing human folding machinery into the plant,” Margolin explains.
What they found was that “the co-expression of human calreticulin (a protein critical to protein folding) dramatically improved the accumulation of the viral spike, which was (otherwise) barely detectable”.
Put simply, the cells in which these viral proteins are dependent on the host machinery to support their folding. Margolin’s work has shown that some of the folding proteins in plants are different, and that calreticulin is often a significant bottleneck to high level expression of many viral surface proteins in the system.
“We observed that when we expressed the calreticulin at the same time as the viral glycoprotein, we elevated the levels of production by, in some cases, as much as 10-to 20-fold,” he reveals.
In short, they demonstrated the potential of molecular engineering to boost the production of viral glycoproteins in plants, while supporting the feasibility of plant-based production of SARS-CoV-2 spike-based vaccines.
“This was an important proof-of-concept because our work was ultimately trying to develop a platform that we can use for emerging viruses,” Margolin says.
It’s a lucrative investment opportunity, with one estimate predicting that the plant-based vaccine market will rise from $40 million to $600 million over the next seven years.
Lucrative plant-based vaccine market
His work straddles the Division of Medical Virology in UCT’s Department of Pathology, the university’s Institute of Infectious Disease and Molecular Medicine, the Biopharming Research Unit in the Department of Molecular and Cell Biology, and the Department of Integrative Biomedical Sciences.
This study was one of several being conducted at UCT around plant-based vaccine production, specifically in the BRU. Recently, Margolin was co-lead author on another paper, Site-Specific Glycosylation of Recombinant Viral Glycoproteins Produced in Nicotiana benthamiana, published in Frontiers in Plant Science. The result of a collaboration between BRU and the University of Southampton’s Glycoprotein Therapeutics Laboratory, it also examined how vaccine production in plants is impacted by the host plant machinery.
Both studies contribute to the growing body of work driven by Margolin and the BRU, which aims to accelerate plant-based vaccine production. This work has already yielded four patent applications, says Margolin, all contributing to the task of fine-tuning the underlying technology to produce vaccines to fight not only COVID-19, but other future emerging viruses too.
In July this year, National Geographic reported that several plant-based vaccines are in the pipeline, although none are yet available for human use. A Canadian biotechnology company has developed a plant-based COVID-19 vaccine that is currently in Phase 3 trials, while their plant-based ‘flu vaccine has completed clinical trials and is awaiting final approval from that government.
In October 2020, a Japanese company launched Phase 1 clinical trials for its plant-derived norovirus vaccine, while two months later, a United States bioprocessing company announced its plant-based COVID-19 vaccine was entering Phase 1 clinical trials.
Margolin says UCT’s approach is slightly different from the work being conducted in Canada and the US: “We’re trying to support production in plants by engineering the folding machinery, which makes our work unique.”
It’s a lucrative investment opportunity, considering that one estimate predicts that the plant-based vaccine market will rise from $40 million to $600 million over the next seven years.
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