Biotech executive C. Randal Mills flies a lot, and he's learned what to expect. Almost as likely as getting those tiny bags of peanuts or pretzels, someone in a neighboring seat will ask, "So what do you do for a living?"
Mills says his answer -- that he's chief executive of a stem-cell research company -- is met with comebacks that fluctuate between "you must be having a really hard time" to "you must really hate President Bush."
Mills's company, Osiris Therapeutics Inc. of Baltimore, is one of about a dozen firms developing therapies using adult cells, not cells from embryos. That puts Osiris both outside and inside the national debate over stem-cell research.
It isn't directly affected by the limits placed on federal funding of embryonic-cell research by the Bush administration. But in another sense it is in the thick of the scientific and political controversy: If life-saving treatments can be developed with adult cells, it would probably ease pressure on the administration to reverse its stand.
Three years ago, Bush limited federal spending for research using embryonic stem cells to a number of cell "lines" already derived from 5-day-old human embryos. Some conservatives liken research on embryos to abortion, while critics of Bush's policy say he has hobbled studies that could lead to cures of a broad range of diseases.
Stem cells differ from other cells because they can divide and regenerate. Embryonic stem cells, which were first isolated in 1998, are prized by scientists for their "plasticity," the potential to grow into many other cells or tissues. Scientists have for many years theorized that adult stem cells can regenerate only as cells of the tissue from which they are drawn.
But many of the companies working with adult stem cells are staking their efforts on a series of provocative and controversial scientific studies they claim show that adult stem cells can convert into other cell types -- that cells drawn from bone marrow can grow into cardiac muscle cells, for example.
None of the companies working with adult stem cells has yet brought a drug to market, but several have treatments in clinical trials. Some struggle for funding; a few are publicly traded. Others keep going with investments from biotech giants such as Amgen Inc. and Boston Scientific Corp. Like other biotech start-ups, all face skepticism as they try to show that their research can work as medicine and as a business.
The debate over adult stem cells, including among patients and investors, concerns whether they will ever approach the potential of embryonic stem cells, whose proponents predict revolutionary therapies to cure diseases such as Parkinson's. That question prompts impassioned disagreements between those who favor and those who oppose expanded research on embryonic cells.
"Adult stem cells are really where the real progress is being made," said Jay P. Lefkowitz, a former adviser to Bush on stem-cell policy.