Experimental therapy prevents Zika in monkeys. But will it work in humans?
There is no vaccine or medicine for Zika, but the virus does have a natural enemy — antibodies created by the immune system’s response to infection.
Scientists long have known about the power of antibodies to neutralize viruses. But they faced a conundrum with Zika: A person has to be infected first before their immune system kicks in.
For pregnant women, who are at greatest risk from Zika because the virus can cause birth defects and neurological problems in the fetus, the key is to avoid infection in the first place.
On Wednesday, a team of scientists led by the University of Miami’s Miller School of Medicine reported a breakthrough. They stopped Zika from spreading to macaque monkeys by first injecting the primates with a mix of antibodies that had been cloned from the blood of an infected person.
It’s a promising step in the race to develop a therapy that will prevent and treat Zika, said David Watkins, a UM researcher who collaborated on the study, which was reported in the journal Science Translational Medicine.
“When there’s an outbreak of Zika,” Watkins said, “we need to protect the pregnant women, and this is the route we chose.”
For now, the best way to prevent Zika is to avoid bites from an infected Aedes aegypti species of mosquito. The virus also can be contracted from having sex with an infected person.
But if the research team can find a funder for a clinical trial of its experimental therapy, the findings reported Wednesday could lead to a treatment that would protect against Zika infection, said Diogo Magnani, a UM scientist who was the lead author of Wednesday’s article.
“Let’s say there’s an outbreak in Miami,” Magnani said. “We know that some populations might be more at risk than others, so you might want to prevent this…. Or you’re going to travel to an area that has an epidemic, you might want to take one of these shots before you travel there.”
The experimental therapy is not a vaccine, though, which typically works by injecting a weakened virus into a person to induce a natural immune response. Rather, the therapy uses a so-called cocktail of three antibodies that are especially effective at neutralizing Zika.
“Instead of each person having to create their own response, we now go and deliver the best response we can find,” Magnani said.
The cocktail of antibodies would create a temporary immunity that can last as long as 60 days, after which the person who received the therapy would be susceptible to Zika again, the researchers believe.
Scientists Dennis Burton and Thomas Rogers with the Scripps Research Institute in La Jolla, California, isolated the three antibodies out of dozens extracted from the blood an infected person in Colombia.
The antibodies were then purified and injected into four macaque monkeys at the Yerkes National Primate Research Center at Emory University near Atlanta. Another four monkeys were given a placebo.
One day later, all eight monkeys were infected with a Zika virus extracted from the urine of an infected pregnant woman at the Fiocruz Institute in Brazil, where a 2016 outbreak caused about 40 percent of pregnant women to have fetal problems, Watkins said, including birth defects such as microcephaly, where a baby’s head is smaller than expected because the brain did not develop properly in the womb.
“It’s really a pretty nasty virus,” Watkins said of the Zika virus used to infect the monkeys. “We wanted to test our antibodies against a real virus that was reflective of the virus that caused problems in South America.”
Scientists tested the monkeys for three days after infecting them.The four macaques that had received the cocktail of antibodies had no trace of virus in their blood, Watkins said, while the four that received the placebo were infected.
Though Zika has waned in the Caribbean and Central and South America this year, the disease is likely to become endemic to the regions, according to the Centers for Disease Control and Prevention. And that means it’s probably only a matter of time before Zika re-emerges in South Florida, where the warm, humid climate is inviting to both international travelers and the Aedes aegypti mosquitoes that spread the virus.
“Zika virus will likely be back,” Watkins said.
Watkins, who spent much of his career studying HIV, likened the experimental Zika therapy to drugs now used to prevent HIV infection, called Pre-Exposure Prophylaxis or PrEP.
But while the therapy given prior to exposure prevented Zika in monkeys, Magnani said more research is needed before scientists know if the treatment will work after infection.
Watkins, who began working on Zika therapies with colleagues in Brazil even before a local outbreak in Miami in June 2016, said a benefit of the therapy is that the antibodies are safe for people and can cross the placenta barrier, meaning it would like be effective for pregnant women and their fetuses.