Potential medical treatments from human stem cells are continuing to advance swiftly from laboratories to clinical trials, and some could be available sooner than researchers once hoped, several UC Davis scientists said.

In the latest of a series of "Stem Cell Dialogs," three researchers with the university's Institute for Regenerative Cures gave a quick primer this week on the versatile cells and how they might be harnessed to treat vision or hearing loss.

The updates from Jan Nolta, the institute's director; Dr. Susanna Park, a professor of ophthalmology; and Ebenezer Yamoah, a neuroscience researcher focused on hearing, are summarized in question-and-answer form, supplemented with other current information about stem cells:

>What are stem cells?

They are cells capable of developing into many different forms. Very early cells in a human embryo are called "pluripotent" because as they divide, they will give rise to every cell in the human body. Nerve cells, bone, muscle, and blood all are built from pluripotent stem cells. Early in human development, this versatility is damped down. Adults retain some "multipotent" stem cells, such as those in bone marrow, which can differentiate into various types of blood cells. Researchers are looking hard at bone marrow stem cells, which may turn out to be more versatile than originally thought.

>How do researchers get stem cells?

Multipotent stem cells can be harvested from umbilical cord blood, and from bone marrow, fat, the walls of blood vessels and many other areas of the body. Pluripotent stem cells can be harvested from discarded human embryos, a source that divided people both in and out of medical research and led former President George W. Bush to ban federal funding of new embryonic stem cell lines. However, researchers have found ways to turn the biological clock back on human skin cells, and make them behave very much like embryonic stem cells. These are called induced pluripotent stem cells, or IPS cells, and they are now the focus of much stem cell research.

>What diseases can be cured by stem cells right now?

A bone marrow transplant is essentially a stem cell treatment. Marrow transplants are risky, but they can cure some genetic diseases such as sickle cell anemia.

>What other diseases are being looked at for stem cell cures?

Almost everything, if the time horizon is long enough. In the short term, cancer and blood diseases remain the focus of most stem cell research. In California, close to 200 clinical trials are recruiting people for stem cell studies, almost all for various cancers or for diseases of the circulatory system, where bone marrow stem cells can have a big impact. But a handful of studies for other ailments are also recruiting. They include research into using stem cells after a heart attack to see if the cells help strengthen the heart wall; using stem cells in spinal fusion to see if they work better than existing approaches, and using stem cells to try to reduce the need for immunity-suppressing drugs after a kidney transplant.

>What about vision problems?

UC Davis researchers have asked the federal government's permission to become the first clinical center in the country to test a stem cell treatment for one of the most common causes of blindness in working-age adults: diabetic retinopathy. The center hopes to begin enrolling people next year in its study, which would involve extracting a person's own stem cells from his or her bone marrow and injecting the cells into the eye. If that clinical trial goes well, UC Davis could move on within a year or two to test the same procedure in people with macular degeneration, a leading cause of blindness among seniors. This approach has been tested at UC Davis in mice, and so far it appears to restore vision without dangerous side effects in the eye.

>What about hearing?

Clinical trials there are further off, but hope has been growing for years that researchers might find a way to regrow the delicate hair cells inside the inner ear. Humans are born with about 10,000 to 20,000 of these sensory cells, but we lose them as we age and they don't replenish themselves in people the way they do in birds. At UC Davis, tests have been done on lab rats to try to get stem cells to the right part of the ear for growing new hair cells, and to ensure that the new growth interacts properly with nerves. Researchers have restored hearing in about 80 percent of the rats they worked on, and they hope to try the procedure soon on nonhuman primates. If it's successful, it could be tested in humans in five to 10 years.

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