History's first patient to be treated by gene-replacement therapy appears to be improving from a severe immune disorder, a National Institutes of Health researcher reports.

Dr. R. Michael Blaese, co-researcher in the experimental gene therapy, said a 4-year-old girl being treated for an immune deficiency is showing signs that a replacement gene first injected last September is doing its job."We're starting to see improved immune function," Blaese said Monday at a meeting of the American Association for the Advancement of Science.

Blaese said he and his co-researcher, Dr. W. French Anderson of NIH, are now treating a second child for the same genetic deficiency.

Both children were born without a gene that produces an enzyme called adenosine deaminase, or ADA, which is essential for a healthy immune system. Most children born with ADA deficiency die of infection by the age of 2.

The NIH researchers developed a technique in which the missing ADA gene is inserted into the patient's blood cells and the blood is then returned to the patient.

Blaese said the first child has now received three infusions of the treated cells, and her ADA levels are now about 20 percent of normal.