New vaccine sneaks into body, then self-destructs

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - A new type of vaccine that sneaks into the body and then self-destructs -- all without needles -- may offer a new way to protect against a range of diseases, U.S. researchers reported on Monday.

The researchers genetically engineered a type of Salmonella bacteria to carry a little piece of Streptococcus and dripped it into the mouths of mice.

Reporting in the Proceedings of the National Academy of Sciences, they said the vaccine protected the mice, and the Salmonella carrier blew itself up.

"We have developed a technique of biological containment where the microorganism self-destructs," Roy Curtiss of the Biodesign Institute at Arizona State University, who led the study, said in a telephone interview.

"Not only does the bacteria lyse (break open) and die and have no survival, but it can be used with an antigen," Curtiss added.

An antigen is a protein that can be recognized and attacked by the immune system.

Curtiss and colleagues used an antigen found in Streptococcus pneumonia, which causes bacterial pneumonia. They put it into Salmonella, a bacteria that invades cells and then reproduces out of control until it bursts the cell.

The vaccine protected mice from infection, carrying the strep antigen into cells. Then, before the Salmonella could do any damage, it burst open.