Washington,
DC (8/18/00)- Cloned pigs are the latest arrival in the biotech
barnyard. This could be a step towards creating a ready supply of genetically
engineered organs for rejection-free transplantation into humans. And, ethicists
warn, it could be a another step towards the cloning of humans.
The scientists used a slightly different approach than that used to produce
the famous Dolly sheep clone.Xena, a female piglet, was cloned by microinjecting
genetic material from fetal pig skin cells into eggs lacking their own genetic
material. A needle-like pipette used in the microinjection works like a tiny
gun or drill, firing into the egg in a controlled and rapid motion.
Right: Xena,
a healthy black piglet with her surrogate mother.
This method, sometimes known as the Honolulu
technique is based on one reported two years ago by Teruhiko Wakayama
and colleagues at the University of Honolulu to successfully clone mice. That
experiment produced the first male mammal clone.
The researchers believe that the quick and clean insertion technique used
in this case may be key to Xena's successful birth. The method transfers only
the genetic material from the fetal donor cell. By comparison, the method
used to clone Dolly fuses together the entire donor cell containing the genetic
material and the empty egg.
"With microinjection, you can be quite selective about the genetic transfer,"
says Anthony C.F. Perry of the Rockefeller University. "You can separate the
chromosomes out, and avoid contaminating the egg with the rest of the material
from the donor cell nucleus."
Xena cloned from the genetic material of a black pig may have come as a
surprise to he pink-white surrogate mother. Subsequent genetic testing confirmed
what appeared to be obvious, that Xena was indeed a clone, with no genetic
input from the host animal.
Organ Debate
Pigs have sometimes been considered the ideal animal for xenotransplnation
because their organs are very similar in size and function to human organs.
The cloning of Xena is being touted as a step towards producing organs for
xenotransplantation, that is, from one species to another. Researchers believe
it will be possible to modify the genome of cloned pigs so that they produce
organs that would not be rejected by the human immune system.
By making these alterations at the genetic level in the cells used to create
clones, "it may some day be possible to obtain a supply of pigs with organs
suitable for human transplant," says Akira Onishi of the National Institute
of Animal Industry in Japan.
However, the announcement of the new cloning achievement comes at a time
when many scientists are backing away from the idea of xenotransplnation of
any type, out of concern for the potential transmission of unknown viruses
from pigs and other animals to humans. In fact, a recent study in the journal
in Nature reported that mice receiving pig tissue transplants did become infected
with a swine virus
More likely perhaps, the new cloning technique could prove a boon to the
swine industry. The cloning approach would allow virtually unlimited production
of favorite breeds for meat production and breeding stock.
Ethical watchdogs note that the new development also appears to be another
step closer to human cloning, since the same technique may prove equally successful
in humans. Indeed, a group calling itself Clonaid:announced it is ready to
set up a laboratory and proceed toward the last steps to generate the first
human embryonic clone. Also, the same week the current research appeared,
the British government announced it was considering relaxing its strict prohibition
against human embryo stem cell research.
Chief Medical Officer Professor Liam Donaldson said: "Stem cell research
opens up a new medical frontier. It offers enormous potential for new treatments
of chronic diseases and injuries, and the relief of human suffering. Our
report offers a way to ensure that this potential can be fully explored,
whilst ensuring full and rigorous safeguards. In particular reproductive cloning
- the cloning of individuals - will remain banned in the UK."
Currently in the US, researchers can do human stem cell research, but only
if no federal funding is involved.
The pig clone research appears in the 18 August '00 issue of Science.
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