Stanford scientists have developed a technique to genetically engineer certain immune cells and make them resistant to HIV - a technique that, if proved successful in human subjects, could provide an alternative to the lifetime of medication that people with HIV infections now face.

HIV is so harmful because of the virus' ability to break into and ultimately kill T-cells, eventually leading to AIDS and the collapse of the immune system. HIV often gains entry into T-cells via two genes - called CCR5 and CXCR4 - that are known to be receptive to the virus.

Some of the newest drugs used to fight HIV target both of those receptor genes. But if the genes could be altered in such a way to make them naturally invulnerable to HIV, the daily drug regimens wouldn't be necessary.

Scientists already have been studying a gene that hones in on CCR5 and breaks up a section of its DNA so that it is no longer receptive to HIV. The Stanford team added even more protection by creating another break in the DNA, then inserting two more genes known to provide protection from HIV.

That technique - placing multiple genes at one site - is known as stacking.

In lab tests, the Stanford team found that applying the single-gene protection provided some resistance against the virus via the CCR5 receptor. But stacking all three protective measures offered even stronger resistance, via both the CCR5 and CXCR4 receptors.

The study results were published in Tuesday's issue of the journal Molecular Therapy.

The stacking technique will need to be tested much more thoroughly now, first in T-cells taken directly from an AIDS patient, then in animals. The scientists hope to start human clinical trials in about five years.