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Antibody injections in pregnancy might shield fetus from Zika

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By Dennis Thompson
HealthDay Reporter

(HealthDay News) -- A new antibody "cocktail" promises to provide effective, if temporary, protection against the Zika virus, a new study reports.

A blend of three potent antibodies completely prevented Zika infection in a group of four lab monkeys, said senior researcher David Watkins, a professor of pathology with the University of Miami Miller School of Medicine.

Regular injections of these antibodies potentially could provide vital protection to pregnant women either living in or traveling to areas where Zika is widespread, Watkins said.

Zika can cause devastating neurological birth defects, including microcephaly, a condition in which the brain and skull are underdeveloped.

"I would say if you were to give a woman in the first trimester an injection and then another injection at the middle of the second trimester, that would suffice" to protect her unborn child from Zika throughout the pregnancy, Watkins said.

The new study "provides important evidence that an antibody-based therapy for Zika is potentially feasible," said Dr. Amesh Adalja, a senior associate at the Johns Hopkins Center for Health Security.

"If further studies -- including ones done in humans -- replicate these findings, a preventative antibody cocktail could be constructed and used to temporarily protect those traveling to Zika-prone areas," Adalja said.

This is not a Zika vaccine, Watkins noted. Vaccines teach the immune system to produce its own antibody protection against a pathogen.

Instead, this approach belongs to a new wave of immunology called "passive immunotherapy," in which people are injected with pre-made antibodies that provide immediate and direct protection against viruses.

"What we're doing here is simply short-cutting the vaccination," Watkins said.

Unfortunately, these antibodies have a short half-life, living only weeks or months in the bloodstream before they wear out. People must receive regular injections of the antibodies to maintain their immunity, since their own immune system never learns how to make the antibodies.

The same approach has shown promise in protecting against HIV infection. Two research teams successfully used cloned antibodies to shield monkeys from HIV, according to findings published in the journals Science and Science Translational Medicine in September.

Antibodies work against Zika and other viruses by blocking their entry into human cells, Watkins said.

"These proteins will stick to a virus and prevent it from entering into the cells of that person," he said. "That's critical because a virus can't make copies of itself outside of a cell. It needs to get inside a cell to replicate and spread."

For this experiment, Watkins and his colleagues collected 91 different antibodies produced by a Zika-infected patient from Colombia.

They then selected three specific antibodies that seemed most potent against Zika, and cloned enough copies of the antibodies for use in injections.

Researchers injected the antibody trio into four lab monkeys, and a day later they were exposed to the Zika virus. None of the monkeys developed Zika infection during three weeks of observation, but four control monkeys exposed to the same strain of Zika did become infected with the virus.

Further testing in pregnant primates will be needed before human testing can occur, the researchers said. And animal findings frequently don't produce similar results in humans.

However, Watkins said he is "cautiously optimistic" that the antibody cocktail will be safe to both mother and unborn child.

"Mothers are full of antibodies already, and we know antibodies cross the placenta to provide protection to the fetus," Watkins said.

The researchers are currently seeking funding to grow large quantities of the antibodies for further primate and human testing, he said.

This approach to immune protection is easier than developing a vaccine and potentially more effective, since individual responses to vaccination can vary, Watkins said.

"I think the future of much of medicine will be administration of antibodies for infectious diseases," Watkins said.

The study appears Oct. 4 in the journal Science Translational Medicine.

More information

For more information on Zika, visit the U.S. Centers for Disease Control and Prevention.

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