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Various types of stem-cell research exist. Embryonic, fetal, induced pluripotent (adult stem cells regressed to an embryonic state) and adult are the main types, each with its own limitations.

“This is not a one-size-fits-all,” Mr. Lanza said. “There will be a combination of approaches depending on the disease.”

Public debate specifically targets embryonic stem-cell research. These stem cells are primitive and potent, thus offering the greatest promise because they are able to become virtually any cell in the human body.

But the usual process of harvesting the stem cells destroys the human embryo (or human clones), a practice condemned as immoral by many religious and conservative groups. In 2001, President Bush prohibited federal funding for research into new embryonic stem-cell lines, though he did not ban funding for the existing 21 lines.

The funding ban was seen as a profound setback in U.S. stem-cell research by many scientists. Several states, including Massachusetts, responded by passing laws to permit human embryonic stem-cell research using state funds.

In March, President Obama lifted restrictions on federal funding for research on new stem-cell lines.

The National Institutes of Health has issued guidelines that allow federally funded research on stem cells derived from embryos specifically donated for that purpose by fertility clinic patients. The NIH received $10.4 billion in stimulus funds and intends to fund additional embryonic research under its new guidelines.

Opposition to embryonic stem-cell work remains, but most groups distinguish it from other stem-cell work.

“We enthusiastically support all avenues of stem-cell research that do not require the destruction of human life and that do not require the creation of new human life by cloning to produce embryos to be destroyed in research,” said Gene Tarne, spokesman for Do No Harm, the Coalition of Americans for Research Ethics, based in Washington.

Embryonic stem cells have specific-use drawbacks as well. They have not yet yielded treatments approved for the market, and they can also produce genetic abnormality.

“Embryonic stem cells occasionally form tumors when they grow,” said Ms. Torchilin, from Biocell Center. “Data from our company shows that amniotic-fluid stem cells remain healthy.”

Research on non-controversial stem cells is producing dramatic results that are virtually unknown to the public, said Jean Peduzzi-Nelson, associate professor at Michigan’s Wayne State University, who is involved with stem cell work on spinal-cord injury.

She described a recent European trial of adult stem-cell therapy combined with intense rehabilitation that allowed a quadriplegic patient to walk using a walker.

“These are fantastic results that most people don’t know about,” Ms. Peduzzi-Nelson said. “It’s a silent explosion in the medical field.”