Stem cells derived from "adult" tissues, such as skin or umbilical cord blood, have not been controversial. They've shown some promise and are eligible for federal funds.
But the derivation of stem cells from very young human embryos has drawn objections from many who believe the resulting destruction of the embryos is immoral. For some, it makes no difference that the embryos - created during in vitro reproduction purposes but no longer needed - were to be thrown away.
Those concerns led to the restrictions on federal funding that Obama has pledged to ease while retaining what his campaign described as "high ethical standards" for such research.
Until the NIH develops its own ethical rules, all work with embryos must comply with professional and institutional guidelines ensuring, among other things, that embryo donors gave informed consent and received no financial incentives.
Despite its promise, human embryonic stem cell research has received relatively modest federal funding. Of $698 million approved by NIH for all stem cell research this year, only $41 million has gone to work with human embryonic stem cells, limited to just 21 approved cell lines.
By comparison, research using nonembryonic human stem cells received $203 million in NIH funding this year. The balance goes to nonhuman and cord blood stem cell research.
"The greatest scientific engine in the history of man is the NIH, with a $28 billion yearly budget. And for eight years it has been largely on the sidelines in one of the most promising areas" of medical research, said Bernard Siegel of the Florida-based Genetics Policy Institute, an advocacy organization promoting stem cell research.
A number of states, among them New Jersey, Wisconsin, Massachusetts, Illinois and New York, have moved into the breach with their own tax dollars. The largest has been California, approving $3 billion over 10 years. Maryland's Stem Cell Initiative plans to spend $219 million over 10 years.
Some critics of embryonic stem cell research argue that successes with adult stem cells have curbed the need for work with embryonic cells. But scientists say it's too soon to reach that conclusion.
"I think we're going to see different forms of stem cells used for different clinical purposes," Fishman said. "It's scientifically naive to think we'll end up with one strategy and one type of cell."
