How the Experimental Ebola Serum Is Being Grown Inside Tobacco Plants

For years, scientists have been looking for cheaper and faster ways to make vaccines, including tinkering with what sounds like an unlikely source: Tobacco plants. In fact, the highly experimental serum given to the two American Ebola patients was created using this novel technique. Here's how it works.

Whether for vaccines or serums, the basic idea is to turn tobacco plants into protein factories. Tobacco plants aren't naturally inclined to make human-like proteins, of course, so it takes some clever genetic engineering. The experimental Ebola serum, ZMapp, was developed at small startup called Mapp Biopharmaceutical and manufactured at a Kentucky facility owned by Reynolds American—yes, the same tobacco giant that makes Camels. Presumably, they do know a thing or two about growing tobacco.

The serum itself is a mixture of three antibodies, or proteins that our immune systems make to bind to and neutralize invading pathogens. To obtain antibodies for the Ebola virus, scientists infected mice and harvested their antibodies. The mice antibodies have to then be "humanized" by swapping out mouse-specific parts for their human equivalents. This isn't easy work, but it's a pretty well-established technique.

Where we get into unfamiliar territory is mass producing these antibodies that have been painstakingly harvested and modified. That's where tobacco plants come in. The genes for the antibodies were slipped into a virus that specifically infects tobacco plants. As viruses do, they take over the plant's cells, forcing them to start making the antibodies. The last step is just harvesting the tobacco leaves and extracting the proteins.

But "mass producing" enough protein for a dose of serum is not the same as mass producing enough serum for a whole population. Reynolds tells The New York Times it'll take several months to scale up operations.

That's all assuming that ZMapp even works and is safe. In a highly unusual turn of events, the American patients got the serum before it was even tested for safety in large animal studies. And while they do seem to be doing better, there's no telling yet whether it was due to ZMapp. We're in uncharted territory here. [New York Times, Reuters]

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