Navy Medicine Reaches Milestone in Malaria Vaccine Development

Story Number: NNS100504-21Release Date: 5/4/2010 8:13:00 PM
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By Doris Ryan, Naval Medical Research Center Public Affairs

SILVER SPRING, Md. (NNS) -- Navy Medicine researchers announced a milestone April 28 in the decades-long effort to develop a highly effective malaria vaccine to protect military personnel.

The research findings were described at two major scientific meetings, one held in Copper Mountain, Colo., and the second in Bethesda, Md.

Findings from the small clinical trial were detailed by principal investigator Cmdr. Ilin Chuang in a poster presentation in Colorado and an oral presentation in Maryland. While more research is needed to improve the vaccine, initial results are promising, she said.

"This is the first time our gene-based vaccine approach has paid off," said Chuang, an investigator in the joint service U.S. Military Malaria Vaccine Program (USMMVP), at the Naval Medical Research Center (NMRC) and Walter Reed Army Institute of Research (WRAIR). "We must develop new weapons in our arsenal. An effective vaccine would be the best weapon of all. Vaccines offer a 'fire and forget' preventative strategy that provides much less burden to deployed military personnel than the current prevention methods, which consist of drug prophylaxis and the use of insecticides and repellents to deter the mosquito vector."

The importance of malaria to the U.S. military was illustrated by the mission-altering evacuation of 43 Marines from the West African country of Liberia in 2003. Five of these Marines required intensive care before recovering, and in December 2009, a Seabee also deployed to Liberia died of malaria.

The research team announced they had induced complete protection against malaria in four volunteers immunized with a novel gene-based candidate vaccine designed to prevent infection with the deadly malaria parasite Plasmodium falciparum.

If a single malaria parasite enters an individual's blood stream and invades a liver cell, the parasite can multiply, producing 30,000-40,000 progeny parasites (merozoites) in five days. These can then be released into the blood in the event the liver cell ruptures, with each parasite invading a red blood cell and growing, producing 8-24 copies of itself in five days, continuing a cycle which over the course of one or two weeks, could lead to as many as 1 trillion parasites circulating in the blood stream.

This cycle could cause coma and death, but vaccines are designed to interrupt this destructive life cycle - and do so during the early stages of infection in the liver, before the damaging blood stages even start.

"In our trial, four of 15 volunteers were completely protected - by far the best result to date for a gene-based vaccine," said Chuang.

In the current trial, USMMVP investigators combined two adenovirus vectors, each containing the genes for a different malaria protein. The adenovirus vectors are designed to carry the malaria genes (DNA) into the muscle cells of the body, where the malaria genes are used as templates to express the malaria proteins, which in turn induce a strong immune response.

"One of the interesting things about our vaccine is that antibodies do not seem to be involved in protection, unlike most other vaccines," said Capt. Tom Richie, the director of the Navy Component of the USMMVP, who leads the adenovirus vaccine development effort. "The adenovirus-vectored, gene-based approach rather induces killer T cells. These killer T cells detect the infected liver cells, and destroy these cells as well as the parasite harbored within. The next step will be to increase the number of malaria genes in the vaccine. We hope that adding genes will increase the level of protection to 80% or more of immunized volunteers, from the current level of 27 percent. Our goal is to develop a vaccine against malaria that protects 80 percent of vaccinated Sailors and Marines against infection for a minimum of six months."

A warfighter with malaria can be incapacitated for one to three weeks and some malaria infections can rapidly become life threatening if not promptly diagnosed and treated. In addition, warfighters can be exposed to more than one malaria species in today's complex military operations.

"People who get malaria are typically very sick with high fevers, shaking chills, and flu-like illness," said Richie. "Although malaria can be a deadly disease, severe illness and death from malaria can be prevented if protective measures are taken, such as drugs and insect repellents."

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