In a bold new approach ultimately aimed at trying to cure AIDS, scientists used genetic engineering in six patients to develop blood cells that are resistant to HIV, the virus that causes the disease.

It's far too early to know if this scientific first will prove to be a cure, or even a new treatment. The research was only meant to show that, so far, it seems feasible and safe.

The concept was based on the astonishing case of an AIDS patient who seems to be cured after getting blood cells from a donor with natural immunity to HIV nearly four years ago in Berlin. Researchers are seeking a more practical way to achieve similar immunity using patients' own blood cells.

The results announced Monday at a conference in Boston left experts cautiously excited.

"For the first time, people are beginning to think about a cure" as a real possibility, said Dr. John Zaia, head of the government panel that oversees gene therapy experiments. Even if the new approach doesn't get rid of HIV completely, it may repair patients' immune systems enough that they can control the virus and not need AIDS medicines — "what is called a functional cure," he said.

Carl Dieffenbach, AIDS chief at the National Institute of Allergy and Infectious Diseases, agreed.

"We're hopeful that this is sufficient to give the level of immune reconstitution similar to what was seen with the patient from Germany," he said.

This is the first time researchers have permanently deleted a human gene and infused the altered cells back into patients. Other gene therapy attempts tried to add a gene or muffle the activity of one, and have not worked against HIV.

The virus can damage the immune system for years before people develop symptoms and are said to have AIDS — acquired immune deficiency syndrome. The virus targets special immune system soldiers called T-cells. It usually enters these cells through a protein receptor, or "docking station," called CCR5.