Scientists at Harvard University recently announced a much anticipated milestone in regenerative medicine: the creation of stem cells from patients with a variety of diseases. The cells, which can be encouraged to develop into cell types damaged by disease, such as the insulin-producing cells in diabetes or neurons in Parkinson's, are poised to give scientists an unprecedented view of disease.

Scientists have hoped to create such cells for more than a decade, initially attempting the feat through human cloning. But cloning proved more challenging than expected, and it wasn't until the introduction of a novel technique, developed recently in Japan, that they succeeded. By exposing a patient's skin cells to four genetic factors found in the developing embryo, scientists can turn back the clock, triggering the cells to look and behave like embryonic stem cells. Known as induced pluripotent stem cells (iPS), they eliminate the need for human eggs or the creation or destruction of embryos, thus bypassing major ethical and technical hurdles that have plagued the field of embryonic stem-cell research.

The scientists who created the cells at the Harvard Stem Cell Institute, including George Daley and Kevin Eggan, now plan to distribute them to colleagues around the world. Doug Melton, codirector of the institute and a longtime champion of stem-cell research, talks with Technology Review about the future of the field.

Technology Review: Why are disease-specific cell lines so important?

Doug Melton: If a patient has Parkinson's disease, their dopamine-producing cells are gone. We don't understand anything about what makes those cells go away--the field is kind of stuck because you can't watch the progression of the disease.

Stem cells can make neurons in a dish. Imagine you have iPS cells from a healthy person and from a Parkinson's patient. If you make dopamine neurons from both sets of cells in separate dishes, you can look at what went wrong with the diseased stem cell. The same approach will work with different degenerative diseases, such as diabetes or ALS [amyotrophic lateral sclerosis, a motor-neuron disease].

TR: How long will it take to get insight into these diseases?

DM: For ALS, Kevin Eggan published a paper on mice showing he could see a defect in cell survival in motor neurons [made from cells derived from an animal model of the disease]. He is now looking for that defect in human cells. The next step would be to determine if that defect is the same in all patients.