U.S. scientists have developed a new vaccine against the deadly ebola virus which has the potential to remain potent after years of storage.
Ebola is one of the deadliest viruses known. It kills about nine out of every 10 people it infects. Fortunately, outbreaks have been rare. But concern about more widespread infection, and the possibility of ebola being used as a biological weapon, have spurred research of a vaccine.
Several experimental vaccines were developed based on the ebola virus itself. But because the virus degrades over time, virus-based vaccines have to be stored at very cold temperatures, which can be expensive. And because they use the actual ebola virus, there are safety concerns as well.
So researchers in Arizona are trying something different. Their idea is, in effect, to trick the body's immune system into mounting a defense against ebola by making a vaccine based on material that's on the surface of the virus.
"We take the proteins that stick out and form spikes on the virus," explained University of Arizona scientist Melissa Herbst-Kralovetz. "They're called glycoproteins. And we fuse that to an antibody backbone."
Co-researcher Charles Arntzen of Arizona State University says the protein-antibody particles attach to each other to form an "ebola immune complex" - or, as he put it, sort of a "glob."
"Turns out, whenever you have a complex of identical proteins like this, it's really a nice signal to our body to say, 'oh, this is unusual, it looks like a virus, what we need to do is mount an immune response against this complex,'" he says.
To make the glycoprotein-antibody material, the scientists used an unusual manufacturing process. They started with the DNA that contains the instructions for the spiky ebola surface protein, inserted it into a bacteria, and then dipped tobacco plants into a solution with the bacteria.
Arntzen says that reprograms the tobacco leaf cells. "And after about 10 days to 12 days, the tobacco plant starts to get looking very sick because it's diverting all of its energy into making our vaccine."
Herbst-Kralovetz says the experimental vaccine was tested on laboratory mice, who were exposed to live ebola virus. Combined with an adjuvant - a substance often added to make vaccines work better - she says four out of five mice were protected against the virus.
"So, 80 percent protection correlated with the best level of protection from another candidate vaccine. And so we were very happy with that."
And her colleague, Arntzen, says the vaccine can be dried to a powder, so it should survive long-term storage.
The next step, before beginning human trials, is testing the vaccine in non-human primates.
The research is reported in the Proceedings of the National Academy of Sciences.