HEALTH ▶▶▶
of contamination from animal and/or human pathogens and can produce novel and complex molecules that cannot yet be produced with animal cell cultures. Novel plant-based phar- maceuticals follow the same regulatory approval processes as other biologic (large molecule) protein drugs.
How plants are used to make drugs Dr Stewart explains that there are two main ways to geneti- cally modify plants to turn them into “mini-factories” for drug production: through a process called transient expres- sion or by developing lines of stable transgenic plants. “With transient expression methods, plant leaf material is infiltrated with an Agrobacterium suspension that contains the genetic material for the target therapeutic protein or antibody,” Dr Stewart explains. “This involves immersing fully grown plants in the sus- pension under vacuum pressure, which enables the Agro- bacterium to penetrate the plant cells to introduce the genes of interest [see Figure 1]. The plant’s DNA is changed so that the desired protein is produced. The plants continue to grow for another week or so, then they are harvest- ed and the protein is extracted and purified to make a biopharmaceutical drug.” PlantForm’s vivoXpress system is a transient expression method. It was developed by Dr J Christopher Hall, retired founder of PlantForm and former Canada research chair in recombinant antibody technology at the University of Guelph in Ontario. PlantForm was established in 2008 using a strain of tobacco.
Stable transgenic plant lines The other method is stable transgenic plant lines, developed by stably altering the DNA of a plant’s nuclear or chloroplast genomes. Seed lines are then developed for continual propa- gation of plant biomass using traditional agricultural tech- niques and equipment. However, it takes time to generate and select for the desired seed lines. Furthermore, stable transgenic (nuclear-transformed) plants typically produce lower yields of recombinant proteins compared to transient expression systems.
CSF: A contagious viral disease As those in the pig industry are well aware, CSF is a highly contagious viral disease that affects both domestic pigs and wild boar, causing severe illness and death in millions of swine each year around the world. In 2019, Bioapp in South Korea developed the world’s first plant-based CSF vaccine, called Herbavac CSF Green Marker. It was originally developed at Pohang University (Postech) in South Korea by a team led by Dr Eun Ju Sohn, whom Dr Stew- art calls the world’s leading specialist in plant-based vaccines for animal health. Bioapp also has a large state-of-the-art manufacturing facility in South Korea.
14 ▶ PIG PROGRESS | Volume 38, No. 3, 2022
Bringing the vaccine to the Americas In October 2021, Posco (a large commodities trading compa- ny and a major investor in Bioapp) signed an agreement with PlantForm to bring Herbavac to markets in North America, Brazil and Argentina. Registration is expected to be complete in the US and Canada within about a year, says Stewart, and in South America in one to two years. There are several CSF vaccines already available in different world markets. They are all live vaccines, which use a weak- ened (or attenuated) form of a pathogen like a virus. Because these vaccines are so similar to the infectious agent they help prevent, they create a strong and long-lasting immune response.
Easy differentiation of field infection In comparison, Herbavac provides strong immunity but also, says Dr Stewart, provides the capacity for easy differentiation of field infection from vaccinated animals. That is a unique characteristic of this vaccine, he explains, which allows veteri- narians, scientists and others to determine whether an anti- body reaction in a pig is from natural sources (including a live vaccine) or from vaccination with Herbavac. Storage require- ments (2–8°C) and expiry (18–24 months) are at least as good as competing products. Plant-based CSF vaccines are also allowed to be used in CSF- free countries such as the US, Canada and some European countries.
Tobacco plants being grown in a greenhouse for use in plant- based vaccines.
PHOTO: PLANTFORM
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