Feb. 17, 1999 A team of researchers, including grantees of the National Institute of Allergy and Infectious Diseases (NIAID), today reported positive results of research on a new, broad-based malaria vaccine. A paper describing their findings appears in the February 16 issue of the Proceedings of the National Academy of Sciences USA.
Health officials have long sought a vaccine to prevent malaria, a disease that affects 300 to 500 million people and kills up to 3 million people worldwide each year. "Improving international health is a high priority of the NIAID, and malaria research is a major area of interest," comments Anthony S. Fauci, M.D., director of the institute. "Although these results are preliminary and the candidate vaccine has yet to be tested in people, its effectiveness in laboratory tests makes it an interesting candidate for further study."
The most severe form of malaria is caused by a microscopic parasite, Plasmodium falciparum, that is transmitted to humans by mosquitoes. The parasite has a complex life cycle. Following injection into the bloodstream, it rapidly travels to the liver where it multiplies. New forms of the parasite are then released into the bloodstream where they invade red blood cells, ultimately destroying them. In their recent paper, a research team directed by Altaf A. Lal, Ph.D., of the U.S. Centers for Disease Control and Prevention (CDC), describes a new candidate vaccine that targets the malaria parasite at several stages of its life cycle.
The scientists combined segments of 21 different P. falciparum proteins to form a single recombinant protein, which they used to immunize rabbits. Each of the 21 segments, or peptides, was selected because it was recognized by the immune systems of people with malaria, as shown in earlier studies. Furthermore, the peptides targeted different branches of the immune system: B cells, helper T cells and cytotoxic T lymphocytes (CTLs).
Laboratory tests showed that the vaccine induced a high level of antibodies that recognized the parasite at different stages of development. The antibodies also blocked P. falciparum invasion into the rabbits' liver cells and inhibited growth of the organism in their blood. Although the researchers have not yet looked at the T-cell responses in vaccinated animals, these studies are under way.
"Multicomponent vaccines may offer an advantage over single-component vaccines because they may provide multiple levels of protection against different parasite stages," says Lee Hall, M.D., Ph.D., program officer for parasite vaccine development at NIAID. "Such vaccines may also reduce the spread of vaccine-resistant strains, which can arise when a pathogen changes a surface protein to avoid detection by the immune system."
NIAID is a component of the National Institutes of Health (NIH). NIAID conducts and supports research to prevent, diagnose and treat illnesses such as HIV disease and other sexually transmitted diseases, tuberculosis, malaria, asthma and allergies. NIH is an agency of the U.S. Department of Health and Human Services.
Reference: Y Ping Shi, et al. Immunogenicity and in vitro protective efficacy of a recombinant multistage Plasmodium falciparum candidate vaccine. Proc Natl Acad Sci USA 96:1615-20 (1999).
Press releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at http://www.niaid.nih.gov.
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