SARS-CoV-2 infection protects against rechallenge in rhesus macaques

Abstract

Immunity from reinfection
One of the many open questions about severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is whether an individual who has cleared the virus can be infected a second time and get sick. Chandrashekar et al. and Deng et al. generated rhesus macaque models of SARS-CoV-2 infection and tested whether natural SARS-CoV-2 infection could result in immunity to viral rechallenge. They found that animals indeed developed immune responses that protected against a second infection. Although there are differences between SARS-CoV-2 infection in macaques and in humans, these findings have key implications for public health and economic initiatives if validated in human studies.
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Cite as: A. Chandrashekar et al., Science
10.1126/science.abc4776 (2020).
RESEARCH ARTICLES
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The explosive spread of the COVID-19 pandemic has made
the development of countermeasures an urgent global prior-
ity (1–8). However, our understanding of the immunopatho-
genesis of SARS-CoV-2 is currently very limited. In
particular, it is currently not known whether SARS-CoV-2
infection induces natural immunity that protects against re-
exposure in humans. Such information is critical for vaccine
strategies, epidemiologic modeling, and public health ap-
proaches. To explore this question, we developed a rhesus
macaque model of SARS-CoV-2 infection, and we assessed
virologic, immunologic, and pathologic features of infection
as well as protective immunity against rechallenge.
Virology and immunology of SARS-CoV-2 infection in
rhesus macaques
We inoculated 9 adult rhesus macaques (6-12 years old) with
a total of 1.1 × 106 PFU (Group 1; N = 3), 1.1 × 105 PFU
(Group 2; N = 3), or 1.1 × 104 PFU (Group 3; N = 3) SARS-
CoV-2, administered as 1 ml by the intranasal (IN) route and
1 ml by the intratracheal (IT) route. Following viral chal-
lenge, we assessed viral RNA levels by RT-PCR in multiple
anatomic compartments. We observed high levels of viral
RNA in bronchoalveolar lavage (BAL) (Fig. 1A) and nasal
swabs (NS) (Fig. 1B), with a median peak of 6.56 (range 5.32-
8.97) log10 RNA copies/ml in BAL and a median peak of 7.00
SARS-CoV-2 infection protects against rechallenge in
rhesus macaques
Abishek Chandrashekar1*, Jinyan Liu1*, Amanda J. Martinot1,2*, Katherine McMahan1*,
Noe B. Mercado1*, Lauren Peter1*, Lisa H. Tostanoski1*, Jingyou Yu1*, Zoltan Maliga3,
Michael Nekorchuk4, Kathleen Busman-Sahay4, Margaret Terry4, Linda M. Wrijil2, Sarah Ducat2,
David R. Martinez5, Caroline Atyeo3,6, Stephanie Fischinger6, John S. Burke6, Matthew D. Slein6,
Laurent Pessaint7, Alex Van Ry7, Jack Greenhouse7, Tammy Taylor7, Kelvin Blade7, Anthony Cook7,
Brad Finneyfrock7, Renita Brown7, Elyse Teow7, Jason Velasco7, Roland Zahn8, Frank Wegmann8,
Peter Abbink1, Esther A. Bondzie1, Gabriel Dagotto1,3, Makda S. Gebre1,3, Xuan He1,
Catherine Jacob-Dolan1,3, Nicole Kordana1, Zhenfeng Li1, Michelle A. Lifton1, Shant H. Mahrokhian1,
Lori F. Maxfield1, Ramya Nityanandam1, Joseph P. Nkolola1, Aaron G. Schmidt6,9, Andrew D. Miller10,
Ralph S. Baric5, Galit Alter6,9, Peter K. Sorger3, Jacob D. Estes4, Hanne Andersen7, Mark G. Lewis7,
Dan H. Barouch1,6,9†
1Center for Virology and Vaccine Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA. 2Tufts University Cummings
School of Veterinary Medicine, North Grafton, MA 01536, USA. 3Harvard Medical School, Boston, MA 02115, USA. 4Oregon Health & Sciences University, Beaverton,
OR 97006, USA. 5University of North Carolina, Chapel Hill, NC 27599, USA. 6Ragon Institute of MGH, MIT, and Harvard, Cambridge, MA 02139, USA. 7Bioqual,
Rockville, MD 20852, USA. 8Janssen Vaccines & Prevention BV, Leiden, Netherlands. 9Massachusetts Consortium on Pathogen Readiness, Boston, MA 02215, USA.
10Cornell University College of Veterinary Medicine, Ithaca, NY 14853, USA.
*These authors contributed equally to this work.
†Corresponding author. Email: dbarouch@bidmc.harvard.edu
An understanding of protective immunity to SARS-CoV-2 is critical for vaccine and public health strategies
aimed at ending the global COVID-19 pandemic. A key unanswered question is whether infection with
SARS-CoV-2 results in protective immunity against re-exposure. We developed a rhesus macaque model of
SARS-CoV-2 infection and observed that macaques had high viral loads in the upper and lower respiratory
tract, humoral and cellular immune responses, and pathologic evidence of viral pneumonia. Following
initial viral clearance, animals were rechallenged with SARS-CoV-2 and showed 5 log10 reductions in
median viral loads in bronchoalveolar lavage and nasal mucosa compared with primary infection.
Anamnestic immune responses following rechallenge suggested that protection was mediated by
immunologic control. These data show that SARS-CoV-2 infection induced protective immunity against re-
exposure in nonhuman primates.
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(range 5.06-8.55) log10 RNA copies/swab in NS. Viral RNA in
NS increased in all animals from day 1 to day 2, suggesting
viral replication. Viral RNA peaked on day 2 and typically
resolved by day 10-14 in BAL and by day 21-28 in NS. Fol-
lowing day 2, viral loads in BAL and NS appeared compara-
ble in all groups regardless of dose. Viral RNA was
undetectable in plasma (fig. S1). Animals exhibited modestly
decreased appetite and responsiveness suggestive of mild
clinical disease (fig. S2) as well as mild transient neutro-
penia and lymphopenia in the high dose group (fig. S3), but
fever, weight loss, respiratory distress, and mortality were
not observed.
To help differentiate input challenge virus from newly
replicating virus, we developed an RT-PCR assay to assess E
gene subgenomic mRNA (sgmRNA). E gene sgmRNA re-
flects viral replication cellular intermediates that are not
packaged into virions and thus represent putative replicat-
ing virus in cells (9). Compared with total viral RNA (Fig.
1B), sgmRNA levels were lower in NS on day 1 with a medi-
an of 5.11 (range <1.70-5.94) log10 sgmRNA copies/swab, but
then increased by day 2 to a median of 6.50 (range 4.16-7.81)
log10 sgmRNA copies/swab (Fig. 1C).
We next evaluated SARS-CoV-2-specific humoral and
cellular immune responses in these animals. All 9 macaques
developed binding antibody responses to the SARS-CoV-2
Spike (S) protein by ELISA (Fig. 2A) and neutralizing anti-
body (NAb) responses using both a pseudovirus neutraliza-
tion assay (10) (Fig. 2B) and a live virus neutralization assay
(11, 12) (Fig. 2C). NAb titers of approximately 100 were ob-
served in all animals on day 35 regardless of dose group
(range 83-197 by the pseudovirus neutralization assay and
35-326 by the live virus neutralization assay). Antibody re-
sponses of multiple subclasses were observed against the
receptor binding domain (RBD), the prefusion S ectodomain
(S), and the nucleocapsid (N), and antibodies exhibited di-
verse effector functions, including antibody-dependent
complement deposition (ADCD), antibody-dependent cellu-
lar phagocytosis (ADCP), antibody-dependent neutrophil
phagocytosis (ADNP), and antibody-dependent NK cell
degranulation (NK CD107a) and cytokine secretion (NK
MIP1β, NK IFNγ) (13) (Fig. 2D). Cellular immune responses
to pooled S peptides were observed in the majority of ani-
mals by IFN-γ ELISPOT assays on day 35, with a trend to-
ward lower responses in the lower dose groups (Fig. 2E).
Intracellular cytokine staining assays demonstrated induc-
tion of both S-specific CD8+ and CD4+ T cell responses (Fig.
2F).
SARS CoV-2 infection induces acute viral interstitial
pneumonia in rhesus macaques
Only limited pathology data from SARS-CoV-2 infected hu-
mans are currently available. To assess the pathologic char-
acteristics of SARS-CoV-2 infection in rhesus macaques, we
inoculated 4 animals with 1.1 × 105 PFU virus by the IN and
IT routes as above and necropsied them on day 2 (N = 2)
and day 4 (N = 2) following challenge. Multiple regions of
the upper respiratory tract, lower respiratory tract, gastroin-
testinal tract, lymph nodes, and other organs were harvest-
ed for virologic and pathologic analyses. High levels of viral
RNA were observed in all nasal mucosa, pharynx, trachea,
and lung tissues, and lower levels of virus were found in the
gastrointestinal tract, liver, and kidney (fig. S4). Viral RNA
was readily detected in paratracheal lymph nodes but was
only sporadically found in distal lymph nodes and spleen
(fig. S4).
Upper airway mucosae, trachea, and lungs were para-
formaldehyde fixed, paraffin embeded, and evaluated by
histopathology. On day 2 following challenge, both necrop-
sied animals demonstrated multifocal regions of inflamma-
tion and evidence of viral pneumonia, including expansion
of alveolar septae with mononuclear cell infiltrates, consoli-
dation, and edema (Fig. 3, A and B). Regions with edema
also contained numerous polymorphonuclear cells, predom-
inantly neutrophils. Terminal bronchiolar epithelium was
necrotic and sloughed with clumps of epithelial cells detect-
ed within airways and distally within alveolar spaces (Fig. 3,
C and D) with formation of occasional bronchiolar epithelial
syncytial cells (Fig. 3E). Hyaline membranes were occasion-
ally observed within alveolar septa, consistent with damage
to type I and type II pneumocytes (Fig. 3F). Diffusely reac-
tive alveolar macrophages filled alveoli, and some were mul-
tinucleated and labeled positive for nucleocapsid by
immunohistochemistry (Fig. 3G). Alveolar lining cells
(pneumocytes) also prominently labeled positive for nucle-
ocapsid (Fig. 3H).
Multifocal clusters of virus infected cells were present
throughout the lung parenchyma, as detected by immuno-
histochemistry and in situ RNA hybridization (RNAscope)
(14, 15) (Fig. 3I). Both positive-sense and negative-sense viral
RNA was observed by RNAscope (fig. S5), suggesting viral
replication in lung tissue. The dense inflammatory infil-
trates included polymorphonuclear cells detected by endog-
enous myeloperoxidase staining (MPO), CD68 and CD163
positive macrophages, CD4+ and CD8+ T lymphocytes, and
diffuse up-regulation of the type 1 interferon gene MX1 (fig.
S6). SARS-CoV-2 infection led to a significant increase in
polymorphonuclear cell infiltration of lung alveoli compared
with uninfected animals (P = 0.0286) as well as extensive
MX1 staining in approximately 30% of total lung tissue (P =
0.0286) (fig. S7). Inflammatory infiltrates were also detected
in the respiratory epithelial submucosa of larger airways
with transmigration of inflammatory cells into bronchiole
lumen (Fig. 3J). Ciliated epithelial cells also stained positive
for both SARS CoV-2 RNA (Fig. 3K) and SARS nucleocapsid
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(Fig. 3L). By day 4 following infection, the extent of inflam-
mation and viral pneumonia had diminished, but virus was
still detected in lung parenchyma and neutrophil infiltra-
tion and type 1 interferon responses persisted (fig. S7).
To further characterize infected tissues, we performed
cyclic immunofluorescence (CyCIF) imaging, a method for
multiplex immunophenotyping of paraformaldehyde fixed
tissue specimens (16). Tissues were stained for nucleocapsid
(SARS-N), pan-cytokeratin (to identify epithelial cells), Iba-1
(ionized calcium binding adaptor as a pan-macrophage
marker), CD68 (monocyte/macrophage marker), and CD206
(macrophage marker), in addition to a panel of markers to
identify other immune cells and anatomical structures (ta-
ble S1), and counterstaining for DNA to label all nuclei. Foci
of virus infected cells were randomly dispersed throughout
the lung and were variably associated with inflammatory
infiltrates (Fig. 4, A to D). Some areas of parenchymal con-
solidation and inflammation contained little to no virus
(Fig. 4A, arrows, and fig. S8). Virus infected cells frequently
co-stained with pan-cytokeratin (Fig. 4, E to H), suggesting
that they were alveolar epithelial cells (pneumocytes). Unin-
fected Iba-1+ CD68+ CD206+ activated macrophages were
also frequently detected adjacent to virally infected epitheli-
al cells (Fig. 4, E and I to K). These data demonstrate that
SARS-CoV-2 induced multifocal areas of acute inflammation
and viral pneumonia involving infected pneumocytes, ciliat-
ed bronchial epithelial cells, and likely other cell types.
Protective efficacy against rechallenge with SARS-CoV-
2 in rhesus macaques
On day 35 following initial viral infection (Figs. 1 and 2), we
rechallenged all 9 rhesus macaques with the same doses of
SARS-CoV-2 that were utilized for the primary infection,
namely 1.1 × 106 PFU (Group 1; N = 3), 1.1 × 105 PFU (Group
2; N = 3), or 1.1 × 104 PFU (Group 3; N = 3). We included 3
naïve animals as positive controls in the rechallenge exper-
iment. Very limited viral RNA was observed in BAL on day 1
following rechallenge in two Group 1 animals and in one
Group 2 animal, with no viral RNA detected at subsequent
timepoints (Fig. 5A). In contrast, high levels of viral RNA
were observed in the concurrently challenged naïve animals
(Fig. 5A), as expected. Median peak viral loads in BAL were
>5.1 log10 lower following rechallenge as compared with the
primary challenge (P < 0.0001, two-sided Mann-Whitney
test; Fig. 5B). Viral RNA following rechallenge was higher in
NS compared with BAL, but exhibited dose dependence and
rapid decline (Fig. 5C), and median peak viral loads in NS
were still >1.7 log10 lower following rechallenge as compared
with the primary challenge (P = 0.0011, two-sided Mann-
Whitney test; Fig. 5D).
We speculated that the majority of virus detected in NS
following rechallenge was input challenge virus, and we
therefore assessed sgmRNA levels in NS following rechal-
lenge. Low but detectable levels of sgmRNA were still ob-
served in 4 of 9 animals in NS on day 1 following
rechallenge, but sgmRNA levels declined quickly (Fig. 5E),
and median peak sgmRNA levels in NS were >4.8 log10 lower
following rechallenge as compared with the primary chal-
lenge (P = 0.0003, two-sided Mann-Whitney test; Fig. 5F).
Consistent with these data, plaque assays in BAL and NS
samples following rechallenge showed no recoverable virus
and were lower than following primary infection (P = 0.009
and 0.002, respectively, two-sided Mann-Whitney tests; fig.
S9). Moreover, little or no clinical disease was observed in
the animals following rechallenge (fig. S10).
Following SARS-CoV-2 rechallenge, animals exhibited
rapid anamnestic immune responses, including increased
virus-specific ELISA titers (P = 0.0034, two-sided Mann-
Whitney test), pseudovirus NAb titers (P = 0.0003), and live
virus NAb titers (P = 0.0003) as well as a trend toward in-
creased IFN-γ ELISPOT responses (P = 0.1837) by day 7 after
rechallenge (Fig. 6). In particular, NAb titers were markedly
higher on day 14 following rechallenge compared with day
14 following primary challenge (P < 0.0001, two-sided
Mann-Whitney test) (fig. S11). All animals developed anam-
nestic antibody responses following rechallenge, regardless
of the presence or absence of residual viral RNA or sgmRNA
in BAL or NS, and thus we speculate that the protective effi-
cacy against rechallenge was mediated by rapid immunolog-
ic control.
Discussion
Individuals who recover from certain viral infections typi-
cally develop virus-specific antibody responses that provide
robust protective immunity against re-exposure, but some
viruses do not generate protective natural immunity, such
as HIV-1 (17). Human challenge studies for the common cold
coronavirus 229E have suggested that there may be partial
natural immunity (18). However, there is currently no data
whether humans who have recovered from SARS-CoV-2 in-
fection are protected from re-exposure (World Health Or-
ganization, Scientific Brief, April 24, 2020; https://
www.who.int/news-room/commentaries/detail/immunity-
passports-in-the-context-of-covid-19). This is a critical issue
with profound implications for vaccine development, public
health strategies, antibody-based therapeutics, and epide-
miologic modeling of herd immunity. In this study, we
demonstrate that SARS-CoV-2 infection in rhesus macaques
provided protective efficacy against SARS-CoV-2 rechal-
lenge.
We developed a rhesus macaque model of SARS-CoV-2
infection that recapitulates many aspects of human SARS-
CoV-2 infection, including high levels of viral replication in
the upper and lower respiratory tract (Fig. 1) and clear
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pathologic evidence of viral pneumonia (Figs. 3 and 4). His-
topathology, immunohistochemistry, RNAscope, and CyCIF
imaging demonstrated multifocal clusters of virus infected
cells in areas of acute inflammation, with evidence for virus
infection of alveolar pneumocytes and ciliated bronchial
epithelial cells. These data suggest the utility of rhesus ma-
caques as a model for SARS-CoV-2 infection for testing vac-
cines and therapeutics and for studying
immunopathogenesis, and our findings complement and
extend recently published data in cynomolgus macaques
(19). However, neither nonhuman primate model led to res-
piratory failure or mortality, and thus further research will
be required to develop a nonhuman primate model of severe
COVID-19 disease.
SARS-CoV-2 infection in rhesus macaques led to hu-
moral and cellular immune responses (Fig. 2) and provided
protection against rechallenge (Fig. 5). Residual low levels of
subgenomic mRNA in nasal swabs in a subset of animals
(Fig. 5) and anamnestic immune responses in all animals
(Fig. 6) following SARS-CoV-2 rechallenge suggest that pro-
tection was mediated by immunologic control and likely
was not sterilizing.
Given the near-complete protection in all animals fol-
lowing SARS-CoV-2 rechallenge, we were unable to deter-
mine immune correlates of protection in this study. SARS-
CoV-2 infection in rhesus monkeys resulted in the induction
of neutralizing antibody titers of approximately 100 by both
a pseudovirus neutralization assay and a live virus neutrali-
zation assay, but the relative importance of neutralizing an-
tibodies, other functional antibodies, cellular immunity, and
innate immunity to protective efficacy against SARS-CoV-2
remains to be determined. Moreover, additional research
will be required to define the durability of natural immuni-
ty.
In summary, SARS-CoV-2 infection in rhesus macaques
induced humoral and cellular immune responses and pro-
vided protective efficacy against SARS-CoV-2 rechallenge.
These data raise the possibility that immunologic approach-
es to the prevention and treatment of SARS-CoV-2 infection
may in fact be possible. However, it is critical to emphasize
that there are important differences between SARS-CoV-2
infection in macaques and humans, with many parameters
still yet to be defined in both species, and thus our data
should be interpreted cautiously. Rigorous clinical studies
will be required to determine whether SARS-CoV-2 infection
effectively protects against SARS-CoV-2 re-exposure in hu-
mans.
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ACKNOWLEDGMENTS
We thank B. Walker, A. Chakraborty, K. Reeves, B. Chen, J. Feldman, B. Hauser, T.
Caradonna, S. Bondoc, C. Starke, C. Jacobson, D. O’Connor, S. O’Connor, N. Thorn-
burg, E. Borducchi, M. Silva, A. Richardson, C. Caron, and J. Cwiak for generous
advice, assistance, and reagents. Funding: We acknowledge support from the Ragon
Institute of MGH, MIT, and Harvard, Mark and Lisa Schwartz Foundation, Beth Israel
Deaconess Medical Center, Massachusetts Consortium on Pathogen Readiness
(MassCPR), Bill & Melinda Gates Foundation (INV-006131), Janssen Vaccines &
Prevention BV, and the National Institutes of Health (OD024917, AI129797,
AI124377, AI128751, AI126603 to D.H.B.; AI135098 to A.J.M.; AI007387 to L.H.T.;
AI007151 to D.R.M.; AI146779 to A.G.S.; 272201700036I-0-759301900131-1,
AI100625, AI110700, AI132178, AI149644, AI108197 to R.S.B.; CA225088 to P.K.S.;
and OD011092, OD025002 to J.D.E.). We also acknowledge a Fast Grant, Emergent
Ventures, Mercatus Center at George Mason University to A.J.M. and a Burroughs
Wellcome Fund Postdoctoral Enrichment Program Award to D.R.M. Author contri-
butions: D.H.B., H.A., and M.G.L. designed the study. A.C., J.L., K.M., N.B.M., L.P.,
L.H.T., J.Y., P.A., E.A.B., G.D., M.S.G., X.H., C.J.D., N.K., Z.L., M.A.L., L.F.M., and J.P.N.
performed the immunologic and virologic assays. A.J.M., Z.M., M.N., K.B.S., M.T.
L.M.W., S.D., A.D.M., P.K.S., and J.D.E. performed the pathology studies. D.R.M. and
R.S.B. performed the live virus neutralization assays. C.A., S.F., J.S.B., M.D.S., and
G.A. performed the antibody phenotyping. L.P., A.V.R., J.G., T.T., K.B., A.C., B.F.,
R.B., E.T., J.V., H.A., and M.G.L. led the clinical care of the animals and performed the
virologic assays. R.Z. and F.W. participated in study design and interpretation of
data. A.G.S. and B.C. provided purified proteins. D.H.B. wrote the paper with all co-
authors. Competing interests: The authors declare no competing financial interests.
G.A. is an inventor on patent application WO 2017/184733 A1 submitted by Massa-
chusetts General Hospital that covers systems serology. R.Z. and F.W. are employ-
ees of Janssen Vaccines & Prevention BV. Data and materials availability: All data
are available in the manuscript or the supplementary material. Virus stocks are
available from D.H.B. under a material transfer agreement with Beth Israel Deacon-
ess Medical Center. This work is licensed under a Creative Commons Attribution 4.0
International (CC BY 4.0) license, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited. To view a
copy of this license, visit https://creativecommons.org/licenses/by/4.0/. This
license does not apply to figures/photos/artwork or other content included in the
article that is credited to a third party; obtain authorization from the rights holder
before using such material.
SUPPLEMENTARY MATERIALS
science.sciencemag.org/cgi/content/full/science.abc4776/DC1
Materials and Methods
Table S1
Figs. S1 to S11
26 April 2020; accepted 16 May 2020
Published online 20 May 2020
10.1126/science.abc4776
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Fig. 1. Viral loads in SARS-CoV-2 challenged rhesus macaques.
Rhesus macaques were inoculated by the
intranasal and intratracheal route with 1.1 × 106 PFU (Group 1; N = 3), 1.1 × 105 PFU (Group 2; N = 3), or 1.1 × 104
PFU (Group 3; N = 3) SARS-CoV-2. (
A
) Log10 viral RNA copies/ml (limit 50 copies/ml) were assessed in
bronchoalveolar lavage (BAL) at multiple timepoints following challenge. (
B
and
C
) Log10 viral RNA copies/swab
(B) and log10 sgmRNA copies/swab (limit 50 copies/swab) (C) were assessed in nasal swabs (NS) at multiple
timepoints following challenge. Red horizontal bars reflect median viral loads.
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First release: 20 May 2020 www.sciencemag.org (Page numbers not final at time of first release) 7
Fig. 2. Immune responses in SARS-CoV-2
challenged rhesus macaques.
(
A
to
D
)
Humoral immune responses were assessed
following challenge by binding antibody
ELISA (A), pseudovirus neutralization assays
(B), live virus neutralization assays (C), and
systems serology profiles (D) including
antibody subclasses and effector functions
to receptor binding domain (RBD), soluble
spike (S) ectodomain, and nucleocapsid (N)
proteins on day 35. Antibody-dependent
complement deposition (ADCD), antibody-
dependent cellular phagocytosis (ADCP),
antibody-dependent neutrophil phagocytosis
(ADNP), and antibody-
dependent NK cell
degranulation (NK CD107a) and cytokine
secretion (NK MIP1β, NK IFNγ) are shown. (
E
and
F
) Cellular immune responses were also
assessed following challenge by IFN-γ
ELISPOT assays (E) and multiparameter
intracellular cytokine staining assays (F) in
response to pooled S peptides. Red and
horizontal bars reflect mean responses.
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Fig. 3. SARS-CoV-2 induces acute viral interstitial pneumonia.
(
A
to
F
) H&E sections of fixed lung tissue from
SARS-CoV-2 infected rhesus macaques 2 days following challenge showing interstitial edema and regional lung
consolidation (A), intra-alveolar edema and infiltrates of neutrophils (B), bronchiolar epithelial sloughing and
necrosis [(C) and (D)], bronchiolar epithelial syncytial cell formation (E), and hyaline membranes within alveolar
septa (F). (
G
and
H
) IHC for SARS nucleocapsid showing virus infected cells within interstitial spaces including a
viral syncytial cell within the lumen (G) and virus infected alveolar lining cells (H). (
I
) Inflammatory infiltrate
showing multiple cells containing SARS-CoV-2 RNA by RNAscope in situ hybridization. (
J
to
L
) bronchial
respiratory epithelium showing inflammation within the submucosa and transmigration of inflammatory cells into
the ciliated columnar respiratory epithelium of a bronchus (J), SARS-CoV-2 RNA (K), and SARS nucleocapsid (L).
Scale bars (A) = 200 microns; (C, I, K-L) = 100 micron; (G) = 50 micron; (B, D-F, J) = 20 microns, and (H) = 10
microns. H&E = hematoxylin and eosin; IHC = immunohistochemistry; RNAscope = SARS-CoV-2 RNA staining.
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Fig. 4. SARS-CoV-2 infects alveolar epithelial cells in rhesus macaques.
Cyclic immunofluorescence (CyCIF)
staining of fixed lung tissue from SARS-CoV-2 infected rhesus macaques 2 days following challenge. (
A
) Whole
slide image of a lung stained with Hoechst 33342 to visualize cell nuclei (greyscale); regions of nuclear
consolidation (arrows), and foci of viral replication (box) are highlighted. (
B
) Higher magnification image of inset
box in (A) showing staining for SARS nucleocapsid protein (SARS-N; green) and cell nuclei (grey scale). (
C
) Higher
magnification image of inset box in (B) showing SARS-N (green) and cell nuclei (blue). (
D
) Bright-field IHC for
SARS-N from corresponding lung region depicted in (C). (
E
to
K
) CyCIF staining for DNA (blue; all panels) and
SARS-N [(E), (F), and (H-K); green], CD206 [(E) and (K); magenta], pan-cytokeratin (pan-CK) [(G) and (H); red],
CD68 (I; yellow), or Iba-1 (J; greyscale) showing virus infected epithelial cells and macrophages near an infected
epithelial cell. Scale bars (F-K) = 50 microns.
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Fig. 5.
Viral loads following SARS-
CoV-
2 rechallenge in rhesus
macaques. On day 35 following
initial infection (Fig. 1), rhesus
macaques were rechallenged with
SARS-CoV-2 by the intranasal and
intratracheal route with 1.1 × 106
PFU (Group 1; N = 3), 1.1 × 105 PFU
(Group 2; N = 3), or 1.1 × 104 PFU
(Group 3; N = 3). Three naïve
animals were included as a positive
control in the rechallenge experi-
ment. (
A
) Log10 viral RNA copies/
ml (limit 50 copies/ml) were
assessed in bronchoalveolar lavage
(BAL) at multiple timepoints
following rechallenge. One of the
naïve animals could not be lavaged.
(
B
) Comparison of viral RNA in BAL
following primary challenge and
rechallenge. (
C
and
E
) Log10 viral
RNA copies/ml (C) and log10
sgmRNA copies/swab (limit 50
copies/ml) (E) were assessed in
nasal swabs (NS) at multiple
timepoints following rechallenge.
(
D
and
F
) Comparison of viral RNA
(D) and sgmRNA (F) in NS following
primary challenge and rechallenge.
Red horizontal bars reflect median
viral loads. P-values reflect two-
sided Mann-Whitney tests.
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Fig. 6. Anamnestic immune responses following SARS-CoV-2 rechallenge in rhesus
macaques.
Binding antibody ELISAs, pseudovirus neutralization assays, live virus neutralization
assays, and IFN-γ ELISPOT assays are depicted prior to and 7 days following SARS-CoV-2
rechallenge. Red lines reflect mean responses. P-values reflect two-sided Mann-Whitney tests.
on May 20, 2020 http://science.sciencemag.org/Downloaded from

SARS-CoV-2 infection protects against rechallenge in rhesus macaques
and Dan H. Barouch
Aaron G. Schmidt, Andrew D. Miller, Ralph S. Baric, Galit Alter, Peter K. Sorger, Jacob D. Estes, Hanne Andersen, Mark G. Lewis
Nicole Kordana, Zhenfeng Li, Michelle A. Lifton, Shant H. Mahrokhian, Lori F. Maxfield, Ramya Nityanandam, Joseph P. Nkolola,
Zahn, Frank Wegmann, Peter Abbink, Esther A. Bondzie, Gabriel Dagotto, Makda S. Gebre, Xuan He, Catherine Jacob-Dolan,
Greenhouse, Tammy Taylor, Kelvin Blade, Anthony Cook, Brad Finneyfrock, Renita Brown, Elyse Teow, Jason Velasco, Roland
Martinez, Caroline Atyeo, Stephanie Fischinger, John S. Burke, Matthew D. Slein, Laurent Pessaint, Alex Van Ry, Jack
Jingyou Yu, Zoltan Maliga, Michael Nekorchuk, Kathleen Busman-Sahay, Margaret Terry, Linda M. Wrijil, Sarah Ducat, David R.
Abishek Chandrashekar, Jinyan Liu, Amanda J. Martinot, Katherine McMahan, Noe B. Mercado, Lauren Peter, Lisa H. Tostanoski,
published online May 20, 2020
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REFERENCES http://science.sciencemag.org/content/early/2020/05/19/science.abc4776#BIBL
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