The first official attempt at gene therapy appears to be bolstering the immune defenses of a 4-year-old girl who began the historic treatment in September, scientists said Friday.

"I am delighted at the way things are going," said Dr. Michael Blaese of the National Cancer Institute, who led the research with Dr. W. French Anderson of the National Heart, Lung and Blood Institute.In a presentation to a National Institutes of Health panel, Blaese said preliminary results indicate the trailblazing procedure appears to be "a partially successful strategy."

While it may take another two months or more to see if the therapy fully reconstitutes the child's immune system, preliminary data indicates "the patient's immune function seems to be improving," Blaese said.

"We have seen positive benefits so far, but we still have a long way to go. We want to make sure it doesn't have a down side as well," he said. A third patient may begin the therapy in the next few months, he said.

Tests found that the girl, whose name has not been released, had a striking increase in her ability to make certain disease-fighting antibodies after her treatment. In addition, the child's level of key immune cells called T-lymphocytes tripled, rising to normal for the first time in her life.

Tests also showed the child's genetically corrected cells are producing a vital missing enzyme up to 40 days after each treatment.

Although the experiment involves a rare disease, Anderson said if it works, genetic techniques might usher in a "major revolution in medicine," providing cures for everything from cancer to AIDS to heart disease.