For the past 80 years, eggs have been a main ingredient in vaccines for measles, mumps, rubella, chicken pox, the flu, and others. Typically, modified genetic material from a virus is inserted into an egg’s proteins, and those proteins are then introduced into the human body to “teach” it an immune response. But since each egg must be modified individually, the lag time for egg-based vaccines can literally be a killer. In the U.S., for example, the CDC must predict in January what strains of the flu will erupt nearly a year later, to give drugmakers time to manufacture enough inoculations. A handful of companies, however, are pioneering vaccines developed in plants, which can be grown and treated in bulk. Using a cousin of the tobacco plant (nicotiana benthamiana), biomedical companies Kentucky Bioprocessing (KBP) and Medicago have been pursuing plant-based flu vaccines for years, and are currently working on COVID-19 immunizations. The companies also both began human trials of vaccines over the summer. Here’s how they turn plants into lifesaving weapons against illness.
Preparing the virus
The companies’ scientists identify an antigen—a version of the virus that will elicit an immune response without triggering symptoms in a patient. These must be specifically formulated to work in plant carriers.
Infecting the plants
Once a safe and effective antigen is determined, the companies submerge the nicotiana benthamiana plants into an antigen-infused solution and force the viral particles into the leaves via a vacuum.
Incubation and growth
The antigens rapidly replicate inside the plant, taking one to two weeks to fully infiltrate the host cells and transform them into antigen-carrying proteins. Because plants can be grown quickly and affordably, KBP estimates that it could make 3 million doses of a vaccine in five weeks, compared to three to six months for traditional vaccines.
Harvest and transformation
Plants are harvested and go through a purification process that turns them into a medical-grade solution that, combined with other ingredients, can be injected directly into the human body.
Medicago medical officer Brian Ward says that because they’re cheaper to grow and incubate, plant vaccines have the potential to “democratize vaccine production.” Medicago estimates that its large-scale facility opening in 2023 could produce 1 billion vaccine doses per year.