03:32 AM ET 02/22/99
Pigs Grown With Human Genes
Pigs Grown With Human Genes
By PAT EATON-ROBB=
Associated Press Writer=
NEW HAVEN, Conn. (AP) _ At a top-secret farm hidden in the
Northeast, scientists are growing pigs whose DNA has been altered
with human genes.
It sounds like the stuff of science fiction, yet officials at
Alexion Pharmaceuticals Inc. say they are close to figuring out how
these pigs can figure in the treatment of human organ failures,
spinal cord injuries and illnesses such as Parkinson's disease.
The idea of transplanting animal parts to humans, called
xenotransplantation, isn't new. But, until recently, nobody knew
how to keep the human body from rejecting the organs.
About 18,000 organ transplants are performed in the United
States each year and more than 40,000 patients are waiting for
donor organs, according to the United Network for Organ Sharing.
About 10 Americans die each day waiting for transplants, network
officials say.
Alexion's first altered pigs, created with the help of
researchers at Virginia Tech in the early 1990s, contained a human
gene called CD-59. Scientists hoped the grafted gene would trick
the human body's immune system into believing that the pig parts
were human.
While transplanted organs from those pigs were able to survive
for a couple of days in their new host, the body eventually
rejected the parts.
A major breakthrough came last year when the small biotechnology
firm, working with scientists in Australia, figured out a way to
alter a sugar-like molecule in pig cells so that human antibodies
would not recognize it as foreign.
The molecule had been acting as a magnet for human antibodies,
betraying the fact that the transplanted tissue was not human.
Alexion quickly patented the process.
''If you now take cells from those animals and challenge them
with human serum, they are almost indestructible in the lab,'' said
Stephen P. Squinto, the chief technology officer at Alexion.
Scientists at Alexion have already transplanted brain cells from
their transgenic pigs into rodents with a syndrome similar to
Parkinson's, a degenerative nerve condition that affects motor
function.
The transplanted cells not only survived, they became
neurotransmitters in the animals' brains and helped correct the
tremors, Squinto said.
The same experiments are now being conducted in baboons. If
those experiments work, Alexion hopes to begin human trials by the
end of the year. Researchers hope that within 15 years humans will
be able to receive permanent organ transplants from swine.
The company also has seen remarkable results by transplanting
cells from a pig's snout into the damaged spinal columns of
rodents, Squinto said. The cells replace the damaged protective
sheath around the spine and allow nerve cells to regenerate.
''Would we expect that we will be able to take a person who is a
paraplegic and have them walking or running in the Olympics?''
Squinto said. ''No, I don't think that's the case. But restoring
some function to that person is certainly a goal.''
Xenotransplantation faces stiff opposition from some in the
medical community and from animal-rights activists. Alexion was
unwilling to allow a reporter or photographer to visit their
facilities, in part because they could be targeted by animal rights
protesters.
Among the medical concerns: the fear that transplanted organs
could bring with them new diseases caused by viruses now living
only in pigs. A virus originally transmitted from chimpanzees to
humans is believed to have caused AIDS.
Because a transplant patient's immune system is suppressed with
drugs, xenotransplantation provides an ideal environment for pig
viruses to mutate, said Dr. Thomas Murray, director of the Center
for Biomedical Ethics at Case Western Reserve University.
''There are risks to third parties here,'' he said. ''If you get
an organ from a cadaver, you decide whether to accept that risk for
yourself. But if you get an organ from a pig, many more people are
put at an unknown risk.''
The FDA had temporarily banned animal-to-human transplant
experiments because of pig viruses, but dropped the ban late in
1997. Scientists now believe they have identified all the so-called
retroviruses that are unique to pigs and can screen for them,
Squinto said.
Dr. David Hull, director of the clinical transplant program at
Hartford Hospital, is excited by the idea of farms filled with
transplantable organs.
The technology could dramatically improve the lives of thousands
of people, many of whom can no longer even get out of bed because
their own hearts or livers are failing, he said.
''You'd be able to meet the needs of everybody,'' he said. ''You
would save a tremendous amount of money and lives.''
But animal rights activists say they whole process is
unnecessary. Rather than killing animals for organs, they suggest
everyone be considered an organ donor unless they specifically
request an exemption, the opposite of the current policy.
''That is the way to save a lot of money, and it would save a
lot of suffering,'' said Sandra Larson, with the New England
Anti-Vivisection Society. |
