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For your own good >. A gene-based vaccine protects rainbow trout against a fish virus.

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A new type of vaccine provides a blueprint to build antibodies, bypassing some of the steps traditional vaccines require. So far the technique has only been applied to protecting fish, but it might someday be adapted for human gene-based vaccines as well.

Traditional vaccines are made of inactivated pathogens. Even though they're harmless, the body reacts by developing antibodies that then guard against a real infection. But these vaccines pose a small risk of an adverse reaction. Newer DNA vaccines deliver genes that code for proteins normally found on an infective agent. The body builds up antibodies to these proteins, antibodies that later defend against an attack by the pathogen carrying the proteins. DNA vaccines, however, often don't stimulate the production of as many antibodies as conventional vaccines.

Looking for a better way to fend off invaders, Niels Lorenzen of the Danish Veterinary Laboratory in Århus, Denmark, speculated that genes for the antibodies themselves could be delivered directly. His team tested this idea by isolating a gene for an antibody that protects rainbow trout against a virus called VHSV. They injected the gene into the muscle of young trout that had never been exposed to VHSV.

After 12 days, the researchers found the antibody circulating in the fish's bloodstream. After another 6 days, they exposed the fish to the virus. More than 90% of the treated fish fought off the infection. Of the untreated trout, 80% died, the researchers report in the November issue of Nature Biotechnology. The gene vaccine didn't protect the fish indefinitely, though; 39 days after injection, the fish showed signs of inflammation at the site of the injection, and the muscle cells that had produced the antibody started dying off.

The study is a "significant step" toward using antibody genes to create temporary immunity against pathogens, says Scott LaPartra of the Clear Springs Trout Company in Idaho. Fish farms are particularly vulnerable to contagious diseases, because the fish are in such close quarters. An antibody gene vaccine might provide quick immunity once an outbreak starts. And Lorenzen hopes the research on protecting fish will be useful for human applications as well, particularly in people whose deficient immune systems don't respond strongly to standard vaccines.

Related sites

The Danish Veterinary Laboratory

For more on DNA vaccines