Allergy vaccine may take fear out of nuts.

An experimental vaccine mitigates the worst effects of peanut allergies, at least in mice. The DNA-based oral vaccine immunizes the animals against a peanut protein that otherwise can kill them.

Food allergies are becoming more common and more dangerous (SN: 9/7/96, p. 150). Between 100 and 125 people in the United States die each year of allergic reactions to peanuts or true nuts, says Wesley Burks of the Arkansas Children's Hospital in Little Rock.

A further price of a peanut allergy is eternal vigilance. Peanuts pop up in many unexpected places, such as egg roll wrappers, chili fillers, and protein extenders in cake mixes. Once sensitized by exposure to peanut proteins, someone with a severe allergy may react the next time with hives or a swollen mouth and throat. In the most serious response, respiratory distress called anaphylactic shock, the person may die unless immediately given a shot of epinephrine.

Kam W. Leong and his colleagues at Johns Hopkins Medical Institutions in Baltimore successfully vaccinated mice against peanut allergens, they report in the April NATURE MEDICINE. The mice had been bred to develop peanut allergies. Once sensitized, the mice react to the same peanut proteins that allergic humans do, one of which is called Arah2.

To make the vaccine, the re searchers created balls of two molecules: the peanut DNA that encodes Arah2 and a compound called chitosan, which is found in crustacean shells. The chitosan protects the DNA and delivers it to cells in the intestines. Those cells then produce Arah2.

This result provides "a testament to the extraordinary ability of DNA to make itself at home wherever it can find the machinery for [making proteins]," comment Miriam F. Moffatt and William O.C. Cookson of John Radcliffe Hospital in Oxford, England, in an article accompanying the report.

Rather than triggering an allergic sensitivity, the vaccine protects the mice against a violent reaction. Vaccinated animals produce fewer of the antibodies, including immunoglobulin E, that fuel allergic reactions.

When subsequently exposed to peanut extracts, the vaccinated mice reacted more mildly than unprotected mice, which had been given either naked Arah2 DNA or chitosan alone.

"This is the first time that an oral vaccine against peanut allergens works," says Leong. The mice were vaccinated before they had their first allergic reaction to peanuts, when their immune systems were presumably more adaptable than those in mice that had already gone through an allergic response, he says.

Even if researchers develop a human version of this vaccine, Burks says, "people [with allergies] would not be able to go out and eat peanuts." A vaccine that weakens allergic reactions, however, could save lives.