embryo developed into a mouse with a random
mixture of traits from the two species. A few
years later, the method was used to
crossbreed a goat and a sheep.
Chimera research took a major step in the
right direction in 2010, when Japanese
scientists managed to create mice with rat
pancreases. Instead of a random mix of the
two animal species, scientists were able to
pick the traits they wanted from the two
animals. The successful experiments promised
well for scientists being able to create human
organs in pigs.
GENE EDITING TOOL DELETES PIG HEART
Juan Carlos Belmonte and his colleagues are
the first in the world to have seriously included
humans in chimera research, aiming to grow
donor organs in pigs using the patient’s own
cells. In this way, the organ would always fit the
patient, who avoids that the organ is rejected
by his immune system. So, Belmonte’s team
used human skin cells as their starting point,
reprogramming them by means of specific
substances to become stem cells, which could
potentially develop into any human organ.
The scientists injected the human cells into
early pig embryos and made the embryos
develop for four weeks in a surrogate mother.
When the embryos were removed, the
scientists could identify the human cells,
which had been marked by a green, fluorescent
protein. The green cells were located
throughout the embryo, forming part of
several organs. So, the experiment showed
that human cells can survive in animal embryos
and even produce organs.
The next step in Belmonte’s plan is to
create pig embryos with organs which almost
only consist of human cells. To do this, the
scientists use a method which they have
already successfully used to grow rat
organs in mice. The trick is to allow the pig’s
own cells to produce the organ. Using one
of the major biotech discoveries of the
decade, the CRISPR-Cas9 gene editing tool,
scientists can delete genes in the pig’s
cells. The tool includes RNA sequences,
which recognize a specific gene – such as
one which is necessary for the formation of
the heart. Subsequently, the other part of
the tool, the Cas9 enzyme, makes sure to
cut through the gene. When the pig can no
longer form a heart itself, the embryo will
recruit the human cells to do the job
instead. If the method works, the pig will
develop a human heart. Belmonte and his
team have already set to work.HUGE ORGAN FARMS
The scientists emphasize that human
organs grown in pigs are still well into the
future, but ground-breaking technologies
such as CRISPR-Cas9 have already led to a
series of minor advances, which could soon
benefit patients with weak organs. By
editing genes in pig cells, scientists can
prevent the pig organs from forming the
proteins which trigger the worst immune
reactions in the patient. This very method
has made the American biotech company
Rivivicor invest millions of dollars, buying a
large strip of land in North Carolina, where it
plans to build a huge donor farm, which
will be able to deliver 1,000
genetically engineered pig organs
directly to American hospitals and
patients annually.BREAKTHROUGH
ENCOUNTERS
OPPOSITIONA human being trapped inside a
pig body. Opponents fear that the
new scientific method will cause
nightmarish scenarios.When scientists insert cells from a
human being into a pig embryo,
they risk that the cells develop into
more than just the organ, which the
patient needs. Opponents of the
method particularly fear that the
human cells will form part of the
pig's brain, making it think like a
human being. The human cells
could also develop into egg or
sperm cells, and though the cells
could probably not produce a viable
embryo, the opponents fear that
the pigs could become the parents
of a new generation of even more
bizarre animals. So, future research
must ensure much more monitoring
of human cell development.Human organs from pigs could be mass-
producered and delivered, when they are
needed for transplants.Pig embryos with human cells could
become the parents of hybrid
animals with partly human brains.Cultured organs will be well-
functioning,unlike the often weak organs
from braindead people, which are used today.Organs from pigs could include
virus, and scientists do not yet know if
they might be dangerous to humans.Organ development could stop the
transplant organ black market, where
healthy people sell their organs.Pigs live shorter lives than humans,
and so, organs from pigs might have
limited life cycles.PROS CONS
OPPONENTS
FEAR THAT PIGS WILL
BECOME JUST AS
SMART AS HUMANS.Artistic interpretation
of a hybrid animal.
RICARDO BOTELHO/BRAZIL PHOTO PRESS/GETTY IMAGES