Only one man seems to have ever been cured of AIDS, a patient who also had leukemia. To treat the leukemia, he received a bone marrow transplant in Berlin from a donor who, as luck would have it, was naturally immune to the AIDS virus.

If that natural mutation could be mimicked in human blood cells, patients could be endowed with immunity to the deadly virus. But there is no effective way of making precise alterations in human DNA.

That may be about to change, if a powerful new technique for editing the genetic text proves to be safe and effective. At the University of Pennsylvania, Dr. Carl June and colleagues have used the technique to disrupt a gene in patients’ T cells, the type attacked by the AIDS virus. They have then infused those cells back into the body. A clinical trial is now under way to see if the treated cells will reconstitute a patient’s immune system and defeat the virus.

The technique, which depends on natural agents called zinc fingers, may revive the lagging fortunes of gene therapy because it overcomes the inability to insert new genes at a chosen site. Other researchers plan to use the zinc finger technique to provide genetic treatments for diseases like bubble-boy disease, hemophilia and sickle-cell anemia.