Scientists have been experimenting with an Ebola vaccine in animals for the past few years, but they've been stymied. There's no easy way to test its effectiveness in people.
Immunologists at the Public Health Agency of Canada in Winnipeg have found a way to crack the problem. They've discovered a molecule that predicts whether one kind of Ebola vaccine will work in monkeys — and the prediction appears quite good, up to 99 percent accurate.
The findings, just published in Science Translational Medicine, could help move an Ebola vaccine into human tests.
Unlike HIV or the flu, Ebola infections are rare and sporadic. So researchers have been stuck testing the vaccine on animals. What scientists have needed is a way to measure the shot's potency without exposing people to the deadly virus.
That's where Gary Kobinger and his research team come in. They gave 74 macaques an experimental Ebola vaccine, either 28 days before or immediately after they infected the monkeys with the virus.
The scientists then carefully watched how the monkeys' immune systems coped with the virus and the vaccine. One response jumped out. They saw a big increase in a specific antibody that appears to neutralize the virus.
Animals that survived the Ebola infection produced about 8 times more of the antibody, on average, than those who died. And, the antibody levels accurately predicted whether an animal could successfully fight off Ebola.
"We can now predict protection against Ebola," Kobinger tells Shots. "It is quite helpful for moving the vaccine to the clinic."
These results don't prove for sure that the antibodies are responsible for clearing out the virus, Kobinger says. But recent studies from his team and other groups demonstrate that these molecules can protect monkeys from Ebola, even when given after an infection.
Thus, scientists seem to be zeroing on the immune system's first line of defense against Ebola. These antibodies stick to the virus's surface, and they may help the immune system catch up with Ebola. "They buy time. Or keep a lid on the virus until the [full] immune response comes up," Kobinger says.
Fighting off Ebola is a complex process, and "you need every arm of the immune system to win the battle," Kobinger says. But he thinks these antibodies are the most critical artillery the immune system has against infection. "They seem to be responsible for about 70 percent of viral clearance, while T cells contribute about 20 percent."
Now immunologists can start tweaking the vaccine to boost production of the antibodies.
But Nancy Sullivan, an immunologist at the National Institute of Allergy and Infectious Disease, warns that these antibodies might not be important for all types of Ebola vaccines.
She tells Shots, "the study supports the notion that for some gene-based vaccines, the antibodies are correlative of protection." But, she says, we still have a fair way to go before we know how that relates, exactly, to fighting off Ebola.