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The real promise of stem cells

by jerome a. zack

Recently, Californians overwhelmingly passed Proposition 71, the California Stem Cell Research and Cures Initiative, making available some $3 billion over a 10-year period for research on stem cells in California. Although still in its infancy, stem cell research may hold the key to new treatments or cures for many different diseases, including HIV/AIDS.

But what are stem cells and what can they do? Stem cells are primitive cells that have two major properties: First, they can develop into several types of more specialized cells with discrete functions; second, they are able to “self-renew,” meaning that as the cells replicate, some of them continue to remain stem cells while others develop into more mature cells.

There are several “flavors” of stem cells. Every organ system in our body has a set of stem cells that can develop into cells related to that organ and its function. For example, so-called hematopoietic stem cells can form all of the various cell types present in blood, and neural stem cells can form brain or nerve tissue. Collectively, these are called “adult stem cells,” and they are thought to be limited in the types of cells they can become. In contrast, embryonic stem cells, derived from a days-old embryo, can develop into any cell type found in the body.

More than 40 million people worldwide are infected by the AIDS virus, and since there is no cure or vaccine for this disease, it is imperative that new treatments be developed. AIDS, caused by the human immunodeficiency virus (HIV), is largely but not exclusively a disease affecting certain blood cells. Therefore, there is a huge potential to utilize hematopoietic stem cells to combat AIDS. HIV is known to impair the function of hematopoietic stem cells, so it is possible that stem cells can be used to replace the impaired cells.

In addition, several investigators at UCLA and elsewhere have put genes that hinder virus replication into hematopoietic stem cells. The idea is that as these cells develop into the more mature blood-cell types that could be infected with HIV, they will be protected from infection. Our group was involved in a recent phase I clinical trial where an anti-viral gene was inserted into hematopoietic stem cells from adults infected with HIV. When these cells were re-infused back into the patients, they gave rise to mature blood cells that carried the anti-viral gene. Although further studies along these lines are necessary to determine if these approaches will be clinically beneficial, they hold promise for patients with drug-resistant virus.

HIV can also infect cell types not derived from hematopoietic stem cells, such as neurons in the brain, or cells that line the intestine. These cells are from different organ systems. However, if scientists are able to decipher the signals needed to influence the proper development of embryonic stem cells, they may be able to generate both neurons and intestinal cells resistant to infection. While these proposed approaches are not a reality today, future research may make them feasible. With the recent advent of substantial state funding for embryonic stem cell research, the therapeutic potential of these cells might soon be realized.

Zack is associate director of the UCLA AIDS Institute.