Some people think of tobacco as a drug, whereas others think of it as a therapy — or both. But for the most part, it's hard to find people who think of the tobacco plant in terms of its medical applications. Qiang Chen, an infectious disease researcher at Arizona State University, is one such person. His team of scientists conducted an experiment, published today in PLOS ONE, that demonstrates how a drug produced in tobacco plants can be used to prevent death in mice infected with a lethal dose of West Nile virus. The study represents an important first step in the development of a treatment for the mosquito-borne disease that has killed 400 people in the US within the last two years.
The mice evaded death
In the study, scientists introduced a gene that produces monoclonal antibodies (MAbs) — proteins derived from cloned immune cells that fight off disease — into a "deconstructed" plant virus vector. Then, they introduced the vector into the tobacco plants. "The vector is in the plant transiently for about 10 days," Chen said in an email to The Verge. During this period, the virus vector produces a large amount of MAbs that the researchers can then extract, after harvesting the plants.
Once extracted, the scientists injected the MAbs into mice that had already been infected with West Nile virus. The results of the study show that in 90 percent of cases, the mice evaded death — and eventually made a full recovery.
Preventing the virus from entering brain cells
The reason MAbs can neutralize the virus is because they are able to target and bind to proteins located on its surface. This binding action is what prevents the virus from entering the mouse's brain cells and causing lethal neurological damage. And because West Nile virus can take a few days to settle into its host's cells, the treatment was effective even four days after the viral injection.
This isn't the first MAb-based treatment that scientists have been able to use against West Nile virus. But previous attempts to produce MAbs involved making them in animal cells. That approach is not only expensive, but is also carries a risk for the transmission of human or animal pathogens, the researchers wrote in the study. Here, the scientists used tobacco plants because they are capable of producing a large amount of proteins and seeds — properties that make them ideal candidates for scaling-up production, Chen explained. So, thanks to these plants, the researchers were able to develop a therapeutic candidate that is "more efficacious and cheaper to make" than previous attempts, Chen said — an advancement that could make a big difference for healthcare providers and patients in developing countries.
These tobacco-derived MAbs have not been tested on humans, however, so the results of this study are a far cry from a cure for West Nile virus. "The next step will be to enhance the ability of MAbs to penetrate into the brain, where the virus does most of the damage," Chen said. Yet, should the drug prove effective in future trials, the tobacco plant might one day be associated with more than smoke-related cancer, as it could also help prevent thousands of people from suffering serious neurological complications, and even death.