Monday, March 18, 2002
A scientist working with Geron Corp. said he plans to seek government approval to test whether embryonic stem cells can repair spinal injuries in paralyzed patients without cloning the cells to overcome immune system rejection.
Hans Keirstead, a researcher at the University of California at Irvine, said that when he seeks permission to conduct these human trials, he intends to propose using immune-suppression drugs to prevent rejection of the transplanted stem cells.
Keirstead's disclosure, made in response to a Chronicle reporter's questions, undercuts the notion that scientists must use cloning to turn versatile embryonic cells into replacement nerves, muscles or other tissues.
The concern has been that a patient's immune system would reject transplanted cells. In theory, by taking the nucleus from a patient's cell and inserting that nucleus into the stem cells, researchers hope to create genetically compatible transplants.
That argument was advanced earlier this month, when paralyzed actor Christopher Reeve was wheeled into a Senate hearing room to testify in favor of a bill by Sen. Dianne Feinstein. The California Democrat wants to ban the cloning of babies but to permit so-called therapeutic cloning to advance stem cell studies.
"Why do we need therapeutic cloning?" asked Reeve, who told senators that "implantation of human embryonic stem cells is not safe unless they contain the patient's own DNA."
Reeve testified against a competing proposal from Sen. Sam Brownback, R-Kan. , who wants the Senate to adopt the no-exceptions ban on human cloning that has passed the House of Representatives.
But in response to questions, Keirstead said scientists could use off-the- shelf medicines to prevent immune system rejection of certain stem cell transplants, without therapeutic cloning.
"That message has not gotten out," said Keirstead, who was among the scientists who testified against Brownback's ban at a recent public hearing at Stanford University.
At that hearing, Keirstead said he had spent six months treating rodents with Geron's human embryonic stem cells. He showed a video of two rats with spinal column injuries. The untreated rat dragged its rear. The other rat, which had been treated with human embryonic stem cells, regained partial use of its legs.
After the presentation, Keirstead, in answer to a reporter's question, said he had used immunosuppressants to prevent the rat from rejecting the transplanted human cells. He said that if the rat experiments continue to go well, he would ask university officials to seek the U.S. Food and Drug Administration's approval to test the human embryonic stem cells on human patients with spinal cord injuries.
Initially, Keirstead said he might be ready to take this step in about a year. But university officials later suggested that time line was unduly optimistic.
In a follow-up interview last week, Keirstead said he would propose
immunosuppressants to prevent rejection of the transplanted cells in those
NEED FOR CLONING OVERSTATED
Robert Lanza, chief scientist at Advanced Cell Technology in Worcester, Mass., an ardent advocate for both embryonic stem cell studies and therapeutic cloning, agreed that in the course of the political debate, the need for cloning to overcome immune system rejection has been overstated, especially in such conditions as paralysis, Parkinson's disease, multiple sclerosis and other conditions of the central nervous system.
"It's not all or nothing. You can move ahead," said Lanza, explaining that the central nervous system is what scientists call "immune privileged."
This means brain and nerve tissues have little or no immune system protection
and are less likely than other organs to reject transplants, he said.
IMMUNE SYSTEM HAZARDS
But Lanza said scientists probably couldn't use immune suppression drugs to test stem cell therapies on conditions like diabetes. Weakening the immune system leaves patients open to infection, and the negative effects of immune suppression would outweigh the benefits of stem cell therapy for diseases that are not life-threatening or debilitating, he said.
So while therapeutic cloning is not a prerequisite for all stem cell studies, Lanza said to deny scientists that option "would be like moving ahead with one hand tied behind your back."
In a telephone interview, Reeve said he was familiar with Keirstead's work - - the actor's foundation supports the research -- but played down the importance of the immunosuppressive strategy and restated the need for therapeutic cloning.
"For some patients, it may be possible to safely treat them with immunosuppressants, but for others we may have to have cloning," he said.
For instance, Reeve said many paralysis patients suffer from lung or bladder infections and could not afford to have their immune systems weakened. He believes scientists must be able to pursue nonreproductive cloning as an alternative.
"I believe that both approaches need to be tried: immunosuppressants and therapeutic cloning," Reeve said.
Oswald Steward, director of the Reeve-Irvine Research Center and Keirstead's boss, said "there is really a lot of divergent opinion" in the scientific community about differing strategies for controlling rejection. Steward said he believes therapeutic cloning is the safer, quicker way to advance stem cell medicines.
But whatever its internal disagreements, the scientific community has
put out the message that a ban on therapeutic cloning will prevent researchers
from solving the immune-system problem -- an argument that seems at best
a stretch, and at worst, a deception.
©2002 San Francisco Chronicle