A fundamentally new treatment for people with acquired immune deficiency syndrome appears to boost the immune system with few side effects, offering the hope that some complications of AIDS can be prevented, researchers reported last week.

Sixteen AIDS patients were treated with a natural body protein that stimulates the production of certain white blood cells that protect the body from infections by bacteria and fungi. These growth factors also may be able to overcome the bone-marrow-suppressing side effects of the current anti-AIDS drug AZT.

"This was the first study ever done in humans with this particular substance," said Dr. Ronald T. Mitsuyasu of the University of California at Los Angeles School of Medicine and one of the study authors. "We were very encouraged by the initial results."

While the treatment is not a cure for AIDS and has no direct effect on the virus itself, researchers hope it will be useful in the prevention and treatment of so-called opportunistic infections, which arise when otherwise harmless bacteria and fungi take advantage of the body's crippled immune system.

The growth factor -- human granulocytic-macrophage colony-stimulating factor, or GM-CSF -- is produced through genetic engineering techniques. It stimulates the production of white blood cells, which recognize and kill invading organisms. It does not, however, stimulate T-4 cells, the antibody-producing cells most commonly attacked by the AIDS virus.

Patients received one of five different doses of the drug intravenously for two weeks. "The drug was very well tolerated in patients with AIDS," said Mitsuyasu, "and all patients had a response, a rise in their white blood counts." Side effects included fever, skin rashes and diarrhea.

After the drug was discontinued, however, their blood counts fell. "With prolonged treatment, we are hopeful that we will be able to maintain a sustained increase in white blood counts," said Mitsuyasu. "It is possible that they will need to take it for the rest of their lives."

A controversy exists about whether the increase in white blood cells will in turn cause the body to attack and kill the AIDS virus-infected cells, Mitsuyasu said. Some labs say yes; others say no.

One indirect measure of the viral activity -- the level of p24, a protein made by the AIDS virus -- was measured in some of the patients treated with GM-CSF. In five patients, the level of p24 declined during treatment, Mitsuyasu said.

While the study was not designed to determine effectiveness of the treatment, Mitsuyasu said, "the ability of the white blood cells to kill infectious organisms was enhanced with treatment."

The blood growth factors also may prove useful for treating diseases such as aplastic anemia and the complications of chemotherapy for cancer.