In labs from Boston to San Diego, scientists labor toward a dream deferred: to launch a medical revolution in which the diseases of aging are treated--not with intrusive surgeries, cobalt-chrome joints and pacemakers--but with healthy, homegrown tissues.

This new era of regenerative medicine promises to use our own stem cells to cure and prevent diseases. In a scientific milestone, President Obama lifted the restrictions on embryonic research, creating federal funding for this controversial science.

But not everyone is convinced the divisive new funding guidelines are a necessary ingredient for success. In fact, some researchers believe adult stem cells, which are taken from the skin and bone marrow, will be able to do everything embryonic stem cells can do--without posing the obvious ethical dilemmas.

Either way, scientists in the realms of both adult stem cell and embryonic stem cell research continue to move steps closer to an as yet unrealized dream: using one's own cells to replace worn-out organs or vessels damaged by stroke, heart attack and diabetes.

Promise and Potential
The essential building blocks for life, embryonic stem cells have the remarkable ability to transform into any of the body's 220 tissues. This ability--known as pluripotency--means doctors one day could inject stem cells into diseased tissue so it could repair itself. It also opens the possibility patients could receive transplants of tissues derived from their own cells, wiping out the risk of rejection.

Additionally, by studying life at its origin, scientists hope to understand the development and progression of disease. This understanding, scientists say, will help them develop drugs or create gene therapies that would repair glitches in the cellular machinery before it breaks down--well before cancer tumors or Alzheimer's plaques take hold.

The funding guidelines, although punctuated with some strong limitations, are a welcome reprieve for many researchers who believe embryos will help regenerative medicine reach its full potential.

"A dark cloud over much of the research has been lifted," said Jonathan Moreno, PhD, professor of medical ethics at the University of Pennsylvania in Philadelphia. "There will be lots of exciting new science coming down the road in the next few years," he said.

After nearly a decade of controversy and restrictions surrounding embryonic stem cell research, the first clinical trials are under way. In January 2009, the FDA approved the first-ever human trial of a therapy derived from embryonic stem cells. Biotech firm Geron, Menlo Park, CA, will run the phase 1 trial, which will inject embryonic stem cell-derived neural cells into the spinal cord 7 days after spinal cord injuries.

Researchers hope the neural cells, called oligodendrocytes, will repair the myelin around the nerve cells, restoring the ability of the nerve cells to carry signals. The ultimate hope seems a far-off possibility--that patients in wheelchairs may be able to walk again.

International strides in embryonic stem cell research are being made, as well. For example, British regulators gave the biotech firm ReNeuron, Guildford, UK, the green light to proceed with a phase 1 clinical trial using embryonic stem cells to regenerate brain cells in stroke victims. The cell therapy will be injected directly into the damaged regions of patients' brains 6 to 24 months after their strokes. Successful treatment could allow stroke patients to regenerate tissue as well as restore function.

Future Therapeutic Applications
This focus on embryonic stem cell research is a welcome new chapter for Kevin Eggan, PhD, who has spent the last decade working to surmount the technical hurdles involved with turning embryonic stem cells into viable human tissues.

Dr. Eggan, an assistant professor in Harvard's department of stem cell and regenerative biology, has focused on replicating amyotrophic lateral sclerosis (ALS) disease in a laboratory dish using spinal motor neurons derived from human embryonic stem cells.

Without embryonic stem cells, Dr. Eggan said, scientists have never been able to culture motor neurons with ALS in the laboratory because the cells die over time as the disease progresses.

After deriving the ALS-like motor neurons, Dr. Eggan is able to study the neurons' molecular structures to understand how ALS develops. This knowledge, he hopes, will enable drug makers to develop therapies to restore muscle control and strength in patients with the disease. This could potentially improve patients' abilities to speak, breathe and walk.

Dr. Eggan has developed a process to derive disease-specific cell lines with embryonic stem cells, which could also help drug makers screen new medications for a variety of diseases. Scientists could derive tissues with a genetic predisposition for, say, asthma or diabetes, and test the toxicity levels and side effects of a new drug right in the laboratory dish. This would allow researchers to rule out dangerous drugs from the start before rolling it out to humans with large and expensive trials.

Additionally, drug makers could test their drugs in a wider patient population without enlisting the help of thousands of study participants. Pharmaceutical researchers could test their therapies in stem cell-derived panels of cells that could be engineered to reflect diverse ethnic backgrounds and genetic makeups, according to Leo T. Furcht, MD, chairman of the department of laboratory medicine and pathology at the University of Minnesota in Minneapolis.

Beyond drug testing, embryonic stem cells could also be used to derive precursors for cardiac muscle, predicted Dr. Furcht, coauthor of the book, The Stem Cell Dilemma (Arcade Publishing). Physicians could then inject the cells into the heart to repair tissue damaged just hours after an attack.

Restrictions Remain
Despite these possibilities, the new guidelines do have some limitations. As drafted by the National Institutes of Health, the federal government will only bankroll research on stem cells taken from embryos left over from fertility clinics. Under federal law, the guidelines do not fund any steps in the research process that creates or destroys embryos.

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