With a closely divided House poised to vote today on whether to expand federal funding of human embryonic stem cell research, opponents are offering fence-sitters what they say is an embryo-friendly alternative: a bill that would foster the use of stem cells from umbilical cords discarded after birth.
The Stem Cell Therapeutic and Research Act — introduced by Rep. Christopher H. Smith (R-N.J.), chairman of the House Pro-Life Caucus — would establish a network of blood banks to help make cord blood cells readily available for patients and research. The bill is set for a House vote this morning in advance of a vote on the hotly contested Stem Cell Research Enhancement Act. That bill would boost federal research spending on cells taken from live human embryos slated for disposal at fertility clinics.
As good as the real thing?
The pairing of the votes raises a scientific question: Are stem cells from umbilical cords reasonable substitutes for embryonic stem cells, which can give rise to all of the body's 200 or so cell types, including nerve, liver, skin, bone, heart muscle and the pancreas, the organ that goes awry in diabetes?
Opponents of embryonic stem cell research have strongly implied the answer is yes.
"Published studies have shown that cord blood stem cells have the capacity to change into other cell types, which give them the potential to treat . . . debilitating conditions such as spinal cord injury, Parkinson's, diabetes and heart disease," Smith said in a recent statement.
But several researchers said that statement stretches the truth of what is known about umbilical cord cells. For while scientists do dream of coaxing umbilical cells to produce a wide array of other cells, the only thing they can reliably give rise to today are the components of blood — red cells, white cells and platelets.
Umbilical and embryonic stem cells "are not in any way interchangeable," said David Scadden, co-director of the Harvard Stem Cell Institute and chief of the Massachusetts General Hospital Center for Regenerative Medicine and Technology.
Umbilical cord cells, squeezed harmlessly from discarded umbilical cords and frozen for later use, are clearly of great medical value. Since 1988, doctors have transplanted them into thousands of patients whose bone marrow had succumbed to disease or been obliterated by chemotherapy. After being transfused into a patient's vein, cord cells work their way into the marrow, where they produce a constant supply of fresh blood for the rest of the patient's life.
Branching out from blood
Opponents of embryo cell research often correctly note that dozens of diseases have been cured with umbilical cord cells. What is not often emphasized is that all are diseases of the blood.
Still, there are some hints that umbilical cord cells may have the potential to do more. Some blood disease patients treated with the cells have shown improvements in other organs — perhaps just from having healthier blood but perhaps because the umbilical cord cells helped regenerate those organs.
A few laboratory experiments have also suggested that cord blood may contain very rare cells that can make more than just blood. At least three teams have published preliminary evidence that cord blood may contain a kind of stem cell that can give rise to bone and fat cells and nerve-nurturing cells called microglia. But at best these stem cells are extremely rare, difficult to isolate and almost impossible to keep alive in culture dishes. Moreover, it is still not clear whether the cells they gave rise to are really bone, fat and microglia or simply have some of the cellular markers of those kinds of cells.
"The bottom line as far as I'm concerned is we just don't know at this point what each can do, and we ought to be investigating both," said Joanne Kurtzberg, director of the pediatric blood and marrow transplant program at Duke University Medical Center.
The cord blood bill "is not an alternative bill. It's an additional bill," said Elizabeth Wenk, spokeswoman for Rep. Michael N. Castle (R-Del.), who introduced the embryonic stem cell bill with Diana DeGette (D-Colo.). "It's something we'd encourage all members to support because all avenues of stem cell research need to be explored."