706-C 5 NOVEMBER 2021 • VOL 374 ISSUE 6568 science.org SCIENCE
catalysis by palladium and
norbornene adds nitrogen to the
neighboring carbon while dis-
placing the triflate with hydride.
Hydrolysis then produces the
desired shifted ketone. The pro-
tocol is well suited to late-stage
variation of complex molecules
during drug optimization. —JSY
Science, abl7854, this issue p. 734
AIR POLLUTION
Little things matter
Particulate air pollution 2.5
micrometers or smaller in size
(PM2.5) is a major cause of
human mortality, and control-
ling its production is a health
policy priority. Nitrogen oxides
are an important precursor of
PM2.5 and have been a focus
of pollution control programs.
H oweve r, G u et al. now show that
abating ammonia emissions is
also an important component
of PM2.5 reduction, and the
societal benefits of abatement
greatly outweigh the costs (see
the Perspective by Erisman).
Reducing ammonia emissions
thus would be a cost-effective
complement to nitrogen oxides
and sulfur dioxide controls.
—HJS
Science, abf8623, this issue p. 758;
see also abm3492, p. 685
TUMOR IMMUNOLOGY
A unique T cell subset
in lung cancer
Although some non-small-cell
lung cancers (NSCLCs) are
sensitive to immune checkpoint
blockade (ICB), many patients
with NSCLC do not respond to
ICB, and this may be related to
the lack of infiltration of CD8+ T
cells. Horton et al. used mouse
models of flank and lung tumors
to show that CD8+ T cells from
lung tumors, but not flank
tumors, had a dysfunctional
phenotype distinct from con-
ventional T cell exhaustion that
was established in the draining
lymph node and correlated to
ICB resistance. Interleukin-2
and -12 treatment rescued this
phenotype, leading to control of
lung tumors. These data suggest
that cytokine therapy might be
able to rescue a specific subset
of dysfunctional T cells found in
lung tumors. —DAE
Sci. Immunol. 6 , eabi8800 (2021).PHYSIOLOGY
Modulating macrophages
to heal muscles
Pro-inflammatory macrophages
infiltrate injured skeletal muscle
and become anti-inflammatory.
Both macrophage phenotypes
are required for skeletal muscle
regeneration and are determined
by metabolism, which in turn
is shaped by mitochondrial
calcium ions. Feno et al. found
that the inhibitory subunit of the
mitochondrial calcium uniporter
MCUb promoted the acquisi-
tion of an anti-inflammatory
phenotype in macrophages and
the repair of damaged skeletal
muscle in mice. Thus, MCUb
activity is linked to a phenotypic
switch in macrophages that is
critical for skeletal muscle regen-
eration. —WW
Sci. Signal. 14 , eabf3838 (2021).MARTIAN GEOLOGY
Perseverance images
of a delta on Mars
The Perseverance rover landed
in Jezero crater on Mars in
February 2021. Earlier orbital
images showed that the crater
contains an ancient river delta
that was deposited by water
flowing into a lake billions of
years ago. Mangold et al. ana-
lyzed rover images taken shortly
after landing that show distant
cliff faces at the edge of the
delta. The exposed stratigraphy
and sizes of the boulders allowed
them to determine the past lake
level and water discharge rates.
An initially steady flow transi-
tioned into intermittent floods
as the planet dried out. This
history of the delta’s geology
provides context for the rest of
the mission and improves our
understanding of Mars’ ancient
climate. —KTS
Science, abl4051, this issue p. 711RESEARCH