The study, to be published the week of July 3 in the online edition of the Proceedings of the National Academy of Sciences, found that it is possible to convert human embryonic stem cells into blood-forming stem cells that in turn can differentiate into the helper T-cells that HIV specifically targets. T-cells are one of the body's main defenses against disease.

The results mark the first time that scientists have been able to derive T-cells out of human embryonic stem cells, said Zoran Galic, assistant research biologist, and lead researcher on the study.

"This tells you that you may be able to use human embryonic stem cells to treat T cell and other blood diseases. This could be a very important weapon in the fight against AIDS," Galic said.

In their study, the researchers cultured human embryonic stem cells, which were incubated on mouse bone marrow support cells, which in turn converted them into blood forming cells. Those cells were then injected into a human thymus gland that had been implanted in a mouse, and the thymus then changed those blood-forming cells into T-cells. Located just above the heart in humans, the thymus is the organ where T-cells develop. It gradually shrinks in adults, weakening the immune system over time.

These results indicate that it is possible to decipher the signals that control the development of embryonic stem cells into mature T-cells, said study co-author Jerome Zack, associate director of the UCLA AIDS Institute, and professor of medicine and of microbiology, immunology and molecular genetics at the David Geffen School of Medicine at UCLA.

"That way we can eventually repopulate the immune system in patients needing T-cells," Zack said.

This in turn could give rise to gene therapy approaches to treat other diseases involving T-cells. In addition to HIV, for instance, the technique could be used to treat severe combined immunodeficiency, or the "bubble boy disease," which leaves its victims without a working immune system, forcing them to a life in an antiseptic, germ-free environment.

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