BALTIMORE, September 14, 2011 /PRNewswire/ --

- Blood-Stage Vaccine Would Prevent Illness and Transmission of Deadly Disease

Scientists have identified the first effective blood-stage malaria vaccine, according to a New England Journal of Medicine study from University of Maryland School of Medicine researchers, in collaboration with the University of Bamako in Mali, West Africa, and other partners. Development of a blood-stage vaccine has been a major goal of malaria prevention research. Such a vaccine would kill the malaria parasite as it emerges from the liver into the bloodstream, where it causes fevers and other symptoms that can lead to coma and even death. There are more than 300 million cases of malaria each year worldwide, and the disease kills more than 800,000 people annually.

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In a Phase II trial of an experimental blood-stage vaccine in Mali, the scientists found that the vaccine produced a high level of strain-specific protection. That is, people who received the vaccine were well protected against parasites that had a similar genetic make-up to the malaria strain used in the vaccine. The study was published Sept. 15.

"This trial is the first good news that we have had in a long while for blood-stage vaccines," says senior author Christopher Plowe, M.D., professor of medicine, epidemiology and public health and microbiology and immunology and leader of the Malaria Group at the University of Maryland School of Medicine's Center for Vaccine Development. "The fact that we saw this partial protection against malaria has reinvigorated the entire field. This gives us hope that we could create an effective blood-stage vaccine by using a precise combination of just the right strains to protect against most types of malaria."

A successful blood-stage malaria vaccine could resemble the polio vaccine, which was created by choosing three specific strains of polio to create broad immunity against the disease, explains Dr. Plowe, who is also a Doris Duke Distinguished Clinical Scientist and Howard Hughes Medical Institute investigator.

The vaccine described in the NEJM study, called FMP2.1/AS02A, is based on a single strain of the Plasmodium falciparum malaria parasite - the most common and deadliest form of the parasite found in Africa. The vaccine consists of a malaria protein from the blood stages of the parasite, and was invented and manufactured by Walter Reed Army Institute of Research. The protein, known as AMA1, is combined with an adjuvant developed and manufactured by GlaxoSmithKline Biologicals. The adjuvant is a compound that boosts the immune response to the vaccine.

For the study, the University of Maryland School of Medicine's CVD team collaborated with scientists from Walter Reed and GlaxoSmithKline and the National Institute of Allergy and Infectious Diseases, as well as with a group of Malian researchers from the Malaria Research and Training Center at the University of Bamako in Mali. The group included lead author Mahamadou Thera, M.D., Ph.D., and Ogobara Doumbo M.D., Ph.D., both professors of parasitology at the University of Bamako. The study was supported by the National Institute of Allergy and Infectious Diseases and the U.S. Agency for International Development.

During the summer of 2007, 200 Malian children received the vaccine, and 200 received a control - a rabies vaccine. Researchers then tracked the children's rate of malaria illness over the next six months. The scientists initially found that children who got the malaria vaccine had almost as many cases of malaria as those who got the rabies vaccine - the vaccine was only 17 percent protective against all strains of malaria.

The scientists decided to take a closer look. Using blood samples collected from children during bouts of malaria, the scientists sequenced the parasite gene for the vaccine protein, AMA1. They were excited to find that the vaccine was highly protective against parasites with a similar genetic make-up to the malaria used in the vaccine.

"If children were infected with a parasite with similar AMA1 to that of the parasite used in the vaccine, we saw that it was 64 percent protective," says Dr. Plowe. "No other blood-stage vaccine has shown any detectable efficacy against clinical malaria. This is the first good news that we have had in a long while for blood-stage vaccines."

The key to an effective blood-stage vaccine will be to find a precise combination of malaria strains to create the broadest protection, Dr. Plowe adds. The research group is already working on possibilities.

SOURCE University of Maryland School of Medicine