Two steps forward, one step back. (Vaccines).

Just a few days after the National Institutes of Health announced it was canceling a large AIDS-vaccine trial, researchers at this meeting announced preliminary results from a new vaccine that appears safe. Although the vaccine probably won't keep people from getting infected, it could help them fight the infection.

Typically, when viruses enter the body, some of them are taken up by immune cells, chopped into bits, and presented to other cells in the immune system. Among this latter group are T cells, which trigger search-and-destroy missions after learning to recognize viral fragments. Two vaccines are now being tested by a drug company to boost this immune response, reports Emilio Emini of Merck Research Laboratories in West Point, Penn.

The pivotal component of one vaccine is a small ring of genetic material containing viral DNA; the other vaccine consists of a genetically engineered cold virus designed to carry HIV genes. Early studies of just over 100 people given the DNA-based vaccine or a placebo indicate that, within a month, T cells from one-quarter to one-half of those receiving the vaccine began to fight HIV. Studies of about 50 people given the cold-virus-based vaccine show that several injections prompt most people to exhibit responses against HIV observable after 30 weeks. Neither vaccine causes serious side effects, and the Merck team is already testing the vaccines in combination as a one-two punch.

HIV vaccines are also being examined as possible means for boosting the immune response of people who have had the disease for a long time. Julianna Lisziewicz and her colleagues at the Research Institute for Genetic and Human Therapy in Washington, D.C., developed a vaccine that combines HIV DNA and polymers. To the immune system, the combo resembles a bacterial infection. Repeated doses of the vaccine helped rhesus macaques with the simian version of AIDS control the amount of virus in their blood, even after other drugs were discontinued and long after untreated macaques died, Lisziewicz says.

"The approach is an intriguing one" and worth testing in people, says Alan Landay of the Rush-Presbyterian-St. Luke's Medical Center in Chicago. --D.C.