A new vaccine spurs people to produce a strong immune response against human papillomavirus (HPV), a virus that can infect both men and women and causes cervical cancer in women. The research bodes well for scientists aiming to develop a vaccine that prevents this disease.

Researchers injected 55 men and women with the vaccine. Half got a large dose and half a small dose. Eleven other volunteers received a placebo shot. The volunteers, six of whom were already infected with HPV, received three injections over 4 months. Researchers and volunteers didn't know which shots contained the vaccine. None of the volunteers showed any lasting side effect.

One month after the final injections, uninfected people getting a large vaccine dose had blood concentrations of antibodies against HPV that were 40 times as high as concentrations found in the infected volunteers at the start of the study. Uninfected people getting a smaller vaccine dose had a more modest response but still had produced higher concentrations of HPV antibodies than the infected people had. People getting the placebo didn't produce a significant amount of antibodies. The report appears in the Feb. 21 Journal of the National Cancer Institute.

The results mirror animals' immune response to HPV vaccines in earlier studies, says coauthor John T. Schiller, a virologist at the National Cancer Institute (NCI) in Bethesda, Md.

"The prospects for this vaccination are remarkably promising," Harald zur Hausen of the German Cancer Research Center in Heidelberg says in the same journal. Several other research groups and drug companies are also working on HPV vaccines, he says.

There are nearly 100 types of HPV, Schiller says. The vaccine in the new study is made up of a harmless copy of a protein found on HPV-16, which is responsible for roughly half of all cervical cancers. The protein induced vigorous antibody production.

"This is a very well-done study," says Darron R. Brown, a physician at Indiana University School of Medicine in Indianapolis. He cautions, however, that HPV acquired by sexual intercourse hides from a woman's immune system in the mucus lining the vagina. Since little blood circulates to this lining, he says, the virus remains largely free of immune attention, which may explain the dearth of anti-HPV antibodies in infected people.

Based on the new results, Schiller is optimistic that an HPV vaccine will elicit such high concentrations of antibodies that some will reach the lining of the female genital tract and prevent infections there.

Some HPV types cause genital warts, and others are harmless. At least 15 types--including HPV-16--cause abnormal cell growth, says Schiller. Even if further research confirms the new vaccine's effect against HPV-16, the vaccine probably won't work against other virus types.

For that reason, drug companies will probably pack vaccines with proteins from several cancer-causing HPV types, along with some from types causing genital warts, Schiller predicts. First, NCI is planning a 5-year study of the HPV-16 vaccine in thousands of women to see whether it does in fact prevent infections, he says.

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