The recent Ebola virus outbreak in the Democratic Republic of Congo has refocused attention on the vaccine and treatment prospects for the highly contagious and deadly disease. As of late May, more than 7,500 doses of an experimental vaccine made by Merck Pharmaceuticals had been shipped to the beleaguered African nation, according to a World Health Organization press release.
Meanwhile, Ebola treatments were also sent. One of these, ZMapp, was successfully used to treat two American missionaries in Liberia in 2014. Charles Arntzen, who helped develop the treatment, calls that moment the highlight of his career: “It started in a lab as a fanciful idea that needed to be validated. In ten years, it was being used and people went from almost dead to almost recovered.”
His initial research was focused on the production of antibodies and vaccines in a novel manufacturing system. That system was the tobacco plant—not the smoking variety, or nicotiana tabacum. But rather, a distant cousin called nicotiana benthamiana, which is native to Australia, where it grows abundantly.
ZMapp is made from the plant, as are other therapeutics and vaccines. Indeed, the once-maligned plant family has turned its image upside down in the public health world, now holding promise to prevent and treat many conditions.
Cheap, easy and plentiful
Research on the tobacco plant’s medicinal potential goes back a few decades. In the early 1990s, research on plants as vaccine production platforms was just beginning. “We wanted to make a lower-cost vaccine manufacturing system to be used in developing countries to broaden our manufacturing base in the developing world,” said Arntzen, who is the founding director of the Biodesign Center for Immunotherapy, Vaccines and Virotherapy at Arizona State University. “There was and still is a shortage of vaccines in the poorest countries.”
Initially, research focused on food plants: bananas, tomatoes, and potatoes. While these efforts were successful, they were stymied by the “anti-GMO food establishment,” Arntzen said. “I didn’t want to spend my time fighting.” So, they switched to the tobacco plant.
“I’ve got a list of about fifty vaccines that should be made in tobacco,” said Denis Murphy, professor of biotechnology at the University of South Wales. “We know a lot about how to express genes in tobacco and get it made.”
Unlike egg-based vaccines, which require a clean, sterile laboratory to make, and can therefore be an expensive process, Murphy said, tobacco-based vaccines are relatively cheap to make. The process is simple: Three weeks after being planted, the plants are dipped into a liquid containing proteins from the given virus. The plants grow the proteins for another week and then are harvested and chopped up. The green liquid that results is the vaccine, which is purified and then bottled up in precise doses.
“The tobacco plant doesn’t seem to mind making all this foreign protein,” Murphy added. “The plants will stay alive and look okay, and they will be full of vaccine protein. If you did this with an animal, you’d probably kill it.”
Still, there are certain challenges to producing tobacco-based vaccines, particularly in the developing world, said Murphy, who is also a biotech consultant for the Food and Agricultural Organization of the United Nations.
“The purification process of the vaccine protein from leaves is still something for which you need a specialized lab. You couldn’t have that in the Congo,” he said. Security is another concern. “Someone could steal the plant and grow it themselves as a pirate version.”
Even birds could be the culprit for tobacco plant theft. “What if a bird came and started eating the leaves? You might want netting or greenhouse growing. That can be much more problematic in a developing country.”
While the ZMapp treatment for Ebola is produced from tobacco, efforts to develop a vaccine this way have not proved fruitful so far. (Merck’s Ebola vaccine is made from livestock.) “Our tobacco-based vaccine would require three doses for a full effect, while the vaccine made by Merck may only require a single dose,” Arntzen said. “Having to give three doses, over about a month, makes the tobacco-made vaccine much more cumbersome and expensive to deliver.” Yet a tobacco-derived vaccine for another newsworthy illness is in the works.
On the frontier of a flu vaccine
Quebec City-based biopharmaceutical company Medicago is using a novel technique to make a flu vaccine with tobacco. This offers several advantages over the current method of developing the vaccine from eggs.
First of all, the production is quicker: five to six weeks, versus four to six months, which means that researchers can wait to identify the circulating flu strain for the upcoming season, rather than guess and risk being wrong.
Also, with tobacco, developers can use something called virus-like particles, instead of the actual flu virus.
“They have the structure of the flu virus, but not its full genetic code, so the virus doesn’t replicate,” said Anne Shiraishi, Medicago’s communications manager. That’s a big deal because the flu is a rapidly mutating virus, and traditional egg-based vaccines encourage those mutations – which wind up making the vaccines less effective.
This problem happens because the flu virus mutates a key protein to better attach to receptors in bird cells, but in humans, this mutation won’t trigger an effective immune response, according to a Medicago fact sheet. That’s why some people who have been vaccinated still get the flu. Indeed, the 2017 flu season had the lowest vaccine effectiveness record ever for H3N2 at 10 percent in the Southern Hemisphere, and 0 percent effective in the EU and UK in people over age 65. At least theoretically, their tobacco-derived flu vaccine could be far more successful, since no such mutations occur with the virus-like particles.
Last year, Medicago, which is 40 percent owned by cigarette company Philip Morris, began a phase 3 trial of the flu vaccine with 10,000 subjects in five countries: half are getting the vaccine, and half are getting a placebo. “We hope to announce really good results this fall,” Shiraishi said. “We hope to be on the market by the 2020/21 flu season.”
They’re also preparing phase I trials for vaccines for the rotavirus and norovirus, two intractable gastro-intestinal viruses. They hope to roll those trials out in the next year or two.
Meanwhile, other research on antibodies is in their pipeline—all of it using tobacco, Shiraishi said. “We’ve taken something bad for public health and made it our mini factories.”