Science - USA (2021-11-05)

NEWS | IN DEPTH

668 5 NOVEMBER 2021 • VOL 374 ISSUE 6568 science.org SCIENCE

PHOTO: JOE CARROTTA/NYU LANGONE HEALTH

But the technologies face many chal-
lenges. For starters, methane only exists at
levels of 2 parts per million, whereas CO 2
has now surpassed levels of 400 ppm. To
make a difference, methane removal tech-
nologies would have to be deployed on a
mammoth scale. “It’s like pulling a needle
from a haystack over and over again,”
Jackson says. The dream might be to remove
the 2 billion to 3 billion tons that would
restore preindustrial levels, Jackson says,
but a more modest goal might be removing
100 million tons per year to offset persistent
agricultural emissions, or new emissions
produced by a warming Arctic.
Funding is also lacking, says Daphne
Wysham, CEO of Methane Action. Although
technologies to remove carbon from the
atmosphere have received billions of dol-
lars in subsidies and incentives, methane
removal has gotten next to nothing, she
says. “Right now, it is so unknown in policy
circles.” The group hopes to persuade dip-
lomats at the summit to approve a declara-
tion that calls on governments to commit
resources to methane removal.
And some researchers and environmental-
ists are wary of monkeying with global atmo-
spheric chemistry. Lofting vast amounts of
iron-salt particles above the ocean is remi-
niscent of long-standing schemes for cooling
Earth by creating a reflective haze in the strato-
sphere, an idea some have derided as a po-
tentially dangerous form of “geoengineering.”
But Jackson rejects that label. Unlike solar
geoengineering, the iron-salt method would
just speed up a chemical reaction that occurs
naturally, he says. And the particles are short-
lived, so the scheme could be easily halted.
The group is planning an independent safety
study before going ahead.
Methane removal is “a fascinating idea,”
says University of Washington, Seattle, at-
mospheric chemist Alex Turner, “as long as
those methods don’t lead to destruction of
ecosystems or harm to the environment.”
But he would prefer to target the small
number of actors in agriculture and the fos-
sil fuel industry that are responsible for a
hefty portion of methane emissions.
Euan Nisbet, an earth scientist at Royal
Holloway University of London, says meth-
ane removal efforts ought to focus on sites
where the gas is already concentrated, like
“monster” landfills, which could be capped
with a layer of soil packed with methane-
guzzling microbes. Cow barns and coal
mine shafts could also be suitable targets
for removal technologies, he says.
Jackson says methane removal would
be futile if carbon and methane emissions
aren’t curtailed. But removal is urgent, too,
he says. “It has to be deployed in the next
20 to 30 years to really make a difference.” j

T

hough the study leader heralded an

operation as providing “new hope

for an unlimited supply of organs,”

last month’s much-publicized trans-

plant of a kidney from a genetically

modified pig to a brain-dead hu-

man recipient did little to usher in cross-

species organ swaps, others say. Still, the

engineered pigs could find less flashy uses

today: as donors for skin and nerve grafts,

providers of long-lasting heart valves, and

sources of allergy-free meat.

The transplant study, performed at New

York University (NYU), showed the human

immune system doesn’t immediately reject

an organ from a pig engineered to lack alpha-

gal, a sugar molecule that provokes a frenzied

immune response in people. The porcine kid-

ney filtered waste from the blood and pro-

duced urine for at least 54 hours. After that,

doctors shut off the recipient’s ventilator and

ended the experiment.

But those findings are “seriously not a sur-

prise,” says Wayne Hawthorne, a transplant

scientist at Australia’s Westmead Institute for

Medical Research and president of the Inter-

national Xenotransplantation Association, a

society for researchers who study using ani-

mal organs and cells to treat human disease.

Monkey experiments had already shown

that pig kidneys like the one the brain-dead

woman received usually last up to 1 week

with no problems. Science could not reach

NYU surgeon Robert Montgomery, but at a

press conference last month , he defended the

study, noting “many other examples of pre-

clinical primate studies that have not trans-

lated well into what happens in humans.”

Lacking just one sugar gene, the organs

aren’t a viable option for xenotransplants,

which need to last for years. Other sugar

molecules on porcine cells have similar

immune-triggering effects, and experts say

they, too, should be genetically purged.

Plus, several human genes may need to get

added to the pig genome to further tem-

per the body’s immune reaction. But the

pigs, engineered at a biotech company now

called Revivicor, do have promise for other

medical applications with less chance of im-

mune rejection. “Just taking out one sugar,

you can make a big difference,” says Thomas

Platts-Mills, a clinical immunologist at the

University of Virginia.

Pig kidney transplant obscures

value of engineered animals

Skin and nerves from pigs lacking immune-provoking

sugar could help patients today

BIOMEDICINE

By Elie Dolgin

An engineered pig’s kidney was attached last month to the circulation of a brain-dead person.