Researchers are reporting the world is one step closer to a future where disease therapies are grown on farms like spinach or lettuce is today. After more than a decade of work, scientists in Austria and Germany have coaxed plants to produce protein antibodies identical to those made by humans.
These antibodies, called immunoglobulin M (IgM), are being produced in the leaves of genetically modified plants. The advance is a feat of applied science because human IgM is a complex protein molecule—the largest antibody present in the circulatory system—that is released by the immune system to fight infection when it is first detected. The European team’s work caused plants to grow a specific variety of IgM that kills tumor cells and is a potential anti-cancer drug.
“This work happened in several steps. First we saw one thing, and then another small piece came together,” Herta Steinkellner, a molecular biologist and engineer at Vienna’s University of Natural Resources and Life Sciences, tells Txchnologist. “When I think back now, I’m so surprised. This was high-risk research that we didn’t expect to work, and then it worked. Amazing.”
Big potential for plant-made biopharmaceuticals
In recent years, many drug researchers have turned their investigations away from therapies based on chemicals to those built out of proteins. The effectiveness of this form of pharmaceutical, according to a 2012 paper in the journal Methods in Molecular Biology, has led to the development of more than 100 therapeutic proteins. In 2010, sales of these drugs amounted to $108 billion.
Proteins are being used as therapies in five categories: replacing a deficiency or abnormality that causes the patient to not produce enough of the protein; altering an existing metabolic pathway; making a new function or activity in the body; interfering with the action of other molecules or microbes; and delivering other drugs to specific locations.
But there’s currently a problem in manufacturing these therapeutic proteins. The process takes a long time, a lot of labor, and the end product is expensive. A common technique to mass-produce the molecules is to alter the DNA in living animal, bacteria or fungi cells so that they become molecular factories.
Even with genetic modification, many bacteria can’t form molecules that exactly mimic the human versions. That means that a patient’s immune system would attack this slightly different protein if it were introduced into the body. Animal cells are better at making proteins that a patient’s body would recognize, but using this approach is slow and expensive.
“So we were looking for a better way,” Steinkellner says. “It turns out that plants can do it—humans and plants have a lot of similarities at the molecular level. The human body can’t distinguish these plant-based antibodies.”
Because both plant and human cells are eukaryotic and evolutionarily not that far removed, their research found that an unmodified plant could already accomplish most of the steps to produce human molecules. They added human genes to the plant’s cells to alter some of the protein-construction steps to make the final product identical to ours. “The plant does most of the work natively and, what they can’t do, we add,” she says. “It was quite surprising, actually, that the plant could do that.”
Their work, published April 29 in the journal PNAS, modified a close relative of the smoking tobacco plant called Nicotiana benthamiana. This plant is an Australian indigenous species that contains nicotine and other alkaloids, albeit at lower levels than its commercial cousin. It is being used in many different studies of genetic modification and protein expression because it grows and makes the protein product rapidly within weeks. While the European team’s research developed just one antitumor version of IgM, Steinkellner says there are many options to customize molecule production in plants.
“This opens a new door in generating a very efficient, new class of drugs that hasn’t been available before,” she says. “With this method, we can systematically and specifically engineer the antibody to target any number of foreign bodies in a human—drug-resistant bacteria, cancer, and others.”
In a comment published alongside the team’s PNAS paper, biopharmaceutical researcher Andrew Hiatt, who was not involved in the research, said their effort holds promise. While it will allow investigators to probe the functional consequences of manipulating plant-produced IgM, it also “has the potential to jump start research into the structures of IgM that are most appropriate for high level production and ultimately for clinical development.”
Now that they’ve demonstrated their work, the next step to enlist altered N. benthamiana for pharmaceuticals is to work with companies to figure out how to scale up production. Most of the companies actively working on this, she says, are in the U.S. Then they will need to go through the regulatory process of testing the protein in animal models and then clinical trials. “Once we bring it out of the lab, we could use this technology for all types of complex protein-based drugs, not just antibodies,” she says. “If someone has anemia or those who can’t coagulate their blood because of a genetic defect—they’re all missing one enzyme. And if they get it, they’re cured. This process can make that enzyme.”
Multiple studies on tobacco molecule factories underway
The research effort is just one of several around the globe pressing N. benthamiana into service as living bioreactors to produce protein-based pharmaceuticals. The work floats a tantalizing question into the world. Could it be that a close cousin of the tobacco plant, which has sickened and killed millions around the world, might cure us of a host of diseases one day?
Last week, Modern Farmer reported on a project by biopharmaceutical company Medicago to produce flu vaccines using N. benthamiana. The company, which is jointly owned by Mitsubishi and cigarette maker Philip Morris, grows the plants in a 97,000-square-foot facility in The Research Triangle Park, North Carolina.
Their work to produce plant-made vaccines received $21 million in funding from the Department of Defense, which is looking to replace the current method of incubating vaccine doses in chicken eggs with a more quickly produced and more stable supply. Medicago says their North Carolina facility has the capacity to produce 30 million doses of seasonal flu and 120 million doses of pandemic flu vaccine a year.
Their technique starts with synthesizing genes from the genetic material of an influenza strain. Then N. benthamiana plants are grown from seed to maturity. A vacuum is applied to their roots, which causes negative pressure to build in their leaves. The plants are turned upside down and dunked into a solution containing the flu’s genetic material, which infiltrate the leaves’ cells due to negative pressure from the vacuum. The plants are incubated for several days in a greenhouse while their cells produce particles that are like the flu virus. The leaves are harvested and the vaccine’s active ingredients are extracted and purified.
“We think this is going to forever change how vaccines are produced,” Dave Henry, Medicago’s manufacturing director, told Modern Farmer.
Txchnologist reported on another sprouting of the potential tobacco-plant technology in March. In that bit of news, Swedish and American scientists reported that they had forced N. benthamiana to produce proteins normally made by female insects to attract mates. The result is a plant that produces insect sex pheromones to attract other insects. If safe and scalable, the modified plant could be part of a pest management system that lures problem insects away from valuable crops.
Top Image: A model of the complex mammalian antitumor immunoglobulin M antibody molecule that was successfully reproduced in a type of tobacco plant. Courtesy Loos et al./PNAS.