D.
Scientists have cleared a major barrier to transplanting organs from pigs into humans after removing threatening viruses
from the animals’ DNA. The new research opens up the possibility of breeding animals to harvest their organs to meet the
demand for new tissue. Some challenges, including major ethical objections still remain, but experts said the breakthrough is
a significant step towards pig-to-man transplants, also known as xenotransplantation. The shortage of organs for transplants is
one of the biggest challenges to modern medicine, and the current supply of tissue meets only a tiny amount of the total demand,
the authors said. But the ability to breed pigs specifically for that purpose would allow that to be easily addressed, since they
have similar organs to ours and can be bred in large numbers.
Until now, the use of pig organs in humans has been held back in large part by fears about retroviruses that are found in
pigs and could prove fatal to humans, if they made their way into the body, and could then cause an epidemic as they spread
from human to human. Porcine endogenous retroviruses, known as Pervs, are a permanent part of the gene and so appeared to
be impossible to remove. But the researchers have now successfully removed those Pervs from the pig genome, using the
CRISPR-Cas9 gene editing technique that allowed them to produce Perv-free, living pigs. That, __________, removes one of
the biggest barriers to organ transplantation from pigs to man.
“This represents a significant step forward towards the possibility of making xenotransplantation a reality,” said Darren
Griffin, a professor of genetics at the University of Kent. “The chance of transmitting PERV from the pig organ to the human
cells was a significant barrier and the study shows yet another application of the CRISPR-Cas9 system. By comprehensively
demonstrating that PERV is the problem that we suspected that it may be, then providing a solution, the authors present a very
elegant study. However, there are so many variables including ethical issues to resolve before xenotransplantation can take
place.”
Those ethical worries are significant, and include a consideration of the harm and benefit brought to the person receiving
the heart. Though scientists have eliminated the biggest barrier to safety in putting a pig’s heart into a human, there remain
risks–and those risks would have to be balanced by ethical committees. It would also be difficult to ensure that people could
give proper consent to the procedure, which could be used in the most dire of circumstances.
But those objections may fade if it becomes clear that the transplants will be useful. When human organ transplantation
was beginning, in the 1960s and 1970s, many opposed the idea – but those objections were put aside when it became clear
how effectively transplants could keep people alive.
【題組】49. Which of the following may best fill in the blank in paragraph 2?
(A) in turn
(B) by contrast
(C) however
(D) alternatively
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