Have A (Pig) Heart

In January the team that helped clone Dolly the sheep revealed another distortion in nature: five genetically modified cloned pigs.

PPL Therapeutics is betting that hearts and other organs from pigs can be transplanted into humans. About the same time, another group at the University of Missouri reported a similar cloning of swine.

About 16 Americans die every day waiting for a transplant donor. Scientists believe pigs are the most likely candidates for xenotransplantation because their organs are biologically similar to those of humans. The biggest obstacle has been rejection by the human immune system. In the new piglet clones, a gene that codes for a sugar on the surface of cells has been turned off.

“Blocking production of this sugar has been the Holy Grail of xenotransplantation, because the molecule causes a hyperacute rejection within the first two or three minutes of putting a pig organ or cell into a human or primate,” said PPL spokesperson David Ayares.

Knocking out one gene, however, doesn’t mean the body will accept a new organ. “We need to have strategies for T-cell-mediated, or chronic, rejection,” Ayares said, which usually occurs within a few days after transplantation. That will involve adding human genes to the DNA of a pig clone so its organs will look more familiar to a human immune system.

And researchers still have to worry about pig viruses that could be transplanted into humans along with the organs. PPL intends to begin trials in primates in the next six to 12 months.

Published in Discover’s Year in Science 2002

Copycat

In February scientists at Texas A&M reported cloning the first house pet: a gray tabby named CC. Researchers created CC in partnership with a biotech firm called Genetics Savings & Clone, which plans to offer cloning services to pet owners within a year.

After CC’s birth, the company received hundreds of calls, both for and against, says spokesperson Ben Carlson. “A lot of people alarmed about cloning believe cloning pets is really the most slippery slope toward cloning humans.”

After many attempts, CC was created by coaxing the nucleus of a cell from a calico cat into an enucleated egg; an electrical spark prompted the hybrid to divide, and the resulting embryo
was then transferred into a surrogate mother. The team performed 188 nuclear transfers to produce 87 cloned embryos. Eight of the embryos were implanted in surrogate mothers, and
one led to a live birth. The group has tried to clone dogs, but canine reproductive physiology has proved to be complex.

CC’s appearance shows that clones are not exact copies. With her gray fur, CC doesn’t even look like the calico cat that donated her genes. Coat color is determined by a poorly understood
process that randomly inactivates certain genes in the cells of a developing embryo. The process of gene inactivation is thought to be a phenomenon of all mammals, including humans.

Genetic Savings & Clone warns that pet owners may be expecting more than cloning can deliver. Carlson says: “We have gone to great pains to emphasize that a clone is a brand new animal,
without any of the memories of the old one. It’s not going to be a reincarnation of Fluffy.”

Published in Discover’s Year in Science 2002