Myeloid cell interferon responses correlate with clearance of SARS-CoV-2

The emergence of mutant SARS-CoV-2 strains associated with an increased risk of COVID-19-related death necessitates better understanding of the early viral dynamics, host responses and immunopathology. While studies have reported immune profiling using single cell RNA sequencing in terminal human COVID-19 patients, performing longitudinal immune cell dynamics in humans is challenging. Macaques are a suitable model of SARS-CoV-2 infection. We performed longitudinal single-cell RNA sequencing of bronchoalveolar lavage (BAL) cell suspensions from adult rhesus macaques infected with SARS-CoV-2 (n=6) to delineate the early dynamics of immune cells changes. The bronchoalveolar compartment exhibited dynamic changes in transcriptional landscape 3 days post-SARS-CoV-2-infection (3dpi) (peak viremia), relative to 14–17dpi (recovery phase) and pre-infection (baseline). We observed the accumulation of distinct populations of both macrophages and T-lymphocytes expressing strong interferon-driven inflammatory gene signature at 3dpi. Type I IFN response was highly induced in the plasmacytoid dendritic cells. The presence of a distinct HLADR+CD68+CD163+SIGLEC1+ macrophage population exhibiting higher angiotensin converting enzyme 2 (ACE2) expression was also observed. These macrophages were significantly recruited to the lungs of macaques at 3dpi and harbored SARS-CoV-2, while expressing a strong interferon-driven innate anti-viral gene signature. The accumulation of these responses correlated with decline in viremia and recovery. The recruitment of a myeloid cell-mediated Type I IFN response is associated with the rapid clearance of SARS-CoV-2 infection in macaques.


Introduction
The underlying immune mechanisms that drive disease versus protection during the Coronavirus disease 2019 (COVID- 19) are not well understood. Analysis of system-wide transcriptomic responses can be extremely useful in identifying features of protection and pinpoint the host immune processes involved in the control of infection and drivers of pathology 1,2

. Transcriptional changes in cells in the bronchoalveolar lavage (BAL) and peripheral blood mononuclear cells (PBMCs) of COVID-19 patients
show distinct host in ammatory cytokine pro les, suggesting that excessive cytokine release is associated with COVID-19 pathogenesis 3 . However, analyses were conducted using end-point samples in patients, and it is possible that the excessive cytokine storm at that time is a representation of an exacerbated viral infection and associated immune dysregulation. We recently developed a nonhuman primate (NHP) model of SARS-CoV-2 infection 4 , where NHPs develop signs of COVID-19 disease including characteristic ground glass opacities in lungs, coinciding with a cytokine storm and a myeloid cell in ux, followed by clearance of the virus and recovery 4 . Using RNAseq, we showed that Interferon (IFN) signaling, neutrophil degranulation and innate immune pathways were signi cantly induced in the SARS-CoV-2-infected lungs of NHPs, while pathways associated with collagen formation were downregulated 5 . Since these animals controlled infection naturally, our results point to the importance of early innate immune responses and cytokine signaling, particularly Type I IFN signaling, in protecting against COVID-19. One limitation of the above study was that it was conducted in terminal lung samples and thus may not represent the dynamic changes that occur immediately after infection. Furthermore, system-wide transcriptomics was studied using bulk-RNAseq, thus averaging the overall contributions of various cell types and pathways at play.
The use of single-cell technologies such as RNA-sequencing (scRNAseq) allows unbiased and signi cantly more in-depth pro ling of immune cell populations in animal models and humans in both healthy and diseased states. Because scRNAseq can de ne the transcriptomic heterogeneity of a complex community of cells and assign unbiased identity classi cations to cell populations, it is optimally suited for the study of complex in ammatory states such as the one engendered by SARS-CoV-2 infection. ScRNAseq has recently identi ed initial cellular targets of SARS-CoV-2 infection in model organisms [6][7][8] and patients [9][10][11][12][13] and characterized peripheral and local immune responses in severe COVID-19 14 , with severe disease being associated with a cytokine storm and increased neutrophil accumulation. However, the human studies have mostly been performed in peripheral blood samples 14 , BAL 9 and tissues 8,15 from a limited number of moderate or severe COVID-19 patients within limited age ranges. To overcome the limitations associated with longitudinal early immune pro ling in human subjects and to get more in-depth understanding of the early dynamics of transcriptional changes during COVID-19, we characterized the transcriptional signatures at the single cell level in the broncho-alveolar compartment of rhesus macaques at pre-infection collected 7 days before infection (-7dpi), at early stage of SARS-CoV-2 infection (3dpi) and at endpoint of the study (14-17dpi). Thus, the immune landscape in the broncho-alveolar compartment of SARS-CoV-2 infected adult rhesus macaques serves as a surrogate of early immune dynamics of protective immune responses in lungs after SARS-CoV-2 infection. We observed the appearance of distinct macrophage and T-lymphocyte populations exhibiting IFN-driven in ammatory gene signatures at 3dpi. The IFN responsive macrophage populations upregulated ACE2 expression and were infected by SARS-CoV-2. Further analysis of upregulated genes in the macrophages revealed IFN-driven innate antiviral defense and negative regulation of viral genome replication, suggesting a prominent role of macrophages driven innate immunity in resolution of SARS-CoV-2 infection.

Results
Landscape of immune cells in the BAL of rhesus macaques during SARS-CoV-2 infection and recovery.
To understand the early immune responses generated by SARS-CoV-2 in NHP model of COVID-19, we analyzed cryopreserved single cells isolated from BAL of young rhesus macaques infected by SARS-CoV-We subjected single cells isolated from BAL of the SARS-CoV-2 infected rhesus macaques to 3' 10x Genomics based scRNAseq processing and analysis pipeline with rigorous QC threshold (Fig S1) at -7dpi (n = 6), 3dpi (n = 6), and 14-17dpi (n = 6). Sequencing yielded a total of 170078 cells ranging from 1543-16608 cells per sample. The mean number of cells per sample in -7dpi was 8484, 3dpi was 9840 and 14-17dpi was 10021. Majority of the cells were immunocytes (Fig 1c) distributed across all time points (Fig   1d) and animals (Fig 1c, Fig S2). Consistent with the prior reports on cellular composition of BAL in rhesus macaques, myeloid were abundant comprising 77% of total cell than lymphoid compartment with 22% cells across all time points. The populations were homogenously distributed across all animals and across timepoints (Fig S2b). We identi ed 19 distinct cell clusters spanning varied cell types based on Although IFN-a and ACE2 transcripts were not abundantly present in the scRNAseq dataset, confocal analysis validated strong upregulation of IFN-a and ACE-2 in lungs of macaques on 3dpi compared to healthy or 14-17dpi (Fig 2c,d). Confocal analyses also validated higher expression IFN responsive transcripts like MX1 (Fig2e), MX2 (Fig2f) and ISG15 (Fig2g) in lung tissues isolated from rhesus macaques at 3dpi (Fig 2c) when compared to 14-17dpi and healthy macaques.
As described previously, in BAL, SARS-CoV-2 vRNA levels were detected in of 5/6 macaques at 3dpi by RT-qPCR. Virtually no BAL vRNA was detected at the endpoint suggesting that the rhesus macaques cleared the virus, from the BAL compartment 4 . vRNA in Nasal Swabs (NS) could be detected in only 4 animals at Day 3, while all animals recorded vRNA at Day 9, and only 3 at the endpoints. vRNA was detected in the lungs of 3 macaques at necropsy (14-17dpi) while no SARS CoV-2 subgenomic RNA (correlate for infectious/replicating virus) was detected in any rhesus macaque lungs at Endpoints 4 . No vRNA was detected in any plasma samples or in randomly selected urine samples. Based on vRNA persistence in the lungs of immunocompetent young macaques and the absence of replicative virus, it was concluded that that macaques e ciently control SARS-CoV-2 infection in a duration of two weeks 4 . In lieu of the absence of replicating virus in lungs at endpoint and peak viremia in 3dpi BAL, in vivo pathology was also found to peak around 3dpi and subsided thereafter as shown by chest x-ray scores. Furthermore, tissue pathologies were observed in lungs at endpoints suggesting viral antigen triggered immune response by persisting antigen. Along with the absence of replicating virus in lungs at endpoint pathological observations were found as shown by histological analyses endpoint 4 . Our previous immunological analyses of BAL cells by ow cytometry had revealed a massive in ltration of immunocytes mainly comprising of T cells, interstitial macrophages, neutrophils and plasmacytoid Dendritic Cells 4 . Appearance of these populations also correlated strongly with the viral loads 4 . When combined with these previously reported ndings, our new results clearly establish in ux of myeloid cells and induction of a fully functional IFN driven innate immune response in macrophages against SARS-CoV-2 in the lungs of rhesus macaques. Our scRNA-seq based deep cellular phenotyping analysis clearly establishes the induction of a robust and targeted innate immune response mainly driven by macrophages as opposed to dysregulated immune responses against SARS-CoV-2 in the early phase of infection.

Myeloid bronchoalveolar landscape
A total of 129280 myeloid cells were analyzed across all timepoints which distributed into 17 distinct clusters across the 3 timepoints studied (Fig 3A-B, Fig S3a). The populations were homogenously distributed across all animals at all timepoints ( Fig S3b). We noted distinctive cluster alignment of all myeloid populations based on key myeloid phenotype markers (Fig 3c-d) that differed between different conditions ( Figure 3d).
As expected, due to limitation of the 10x Genomics scRNAseq pipeline to detect neutrophils 17 , this population was not detected in our analysis. As reported earlier in various NHP studies 4,18,19 , BAL landscape mostly comprised of macrophages, which are distributed into alveolar (CD206 + ) or interstitial (CD206 -) phenotypes 4,19 . Our prior scRNAseq analysis using the 10x platform in single cells isolated from lungs of rhesus macaques with tuberculosis had identi ed novel macrophage phenotypes exhibiting distinct TREM2 and IFN-responsive gene signatures 17 . Here, we found 3 distinct IFNresponsive macrophages populations which were predominantly present on 3dpi (Fig 4a,b), one of which also expressed high levels of Triggering Receptor Expressed On Myeloid Cells (TREM) 2 gene expression (Fig 4a). For reference, we annotated the most abundant IFN-responsive macrophage population as Mac_IFN_1, second IFN responsive macrophage population was annotated Mac_IFN_2 and the third IFN responsive macrophages with a TREM2 expression module were annotated Mac_TREM2_IFN (Fig 4a).
pDCs are considered the chief drivers and source of Type I IFN signature. Our prior data suggested a signi cant in ux of pDCs in BAL compartment and lungs of SARS-CoV-2 infected macaques 4 . The pDC cluster in our current scRNAseq data was identi ed by expression of classic pDC markers like IL3RA/CD123, CLEC4C and Transcription Factor (TCF) 4. This cluster was only modestly increased at 3dpi. However, the pDC cluster contained genes associated with innate response to viral pathogens like Toll-like receptors (TLR)7, TLR9 etc. along with induction of Type I IFN response like Interferon Regulatory Factor (IRF) 1, IRF3, IRF7, IRF8, IRF9, Derlin (DERL) 3, Solute Carrier Family 15 Member 4 (SLC15A4), with signi cant induction in expression levels. In addition, expression of an IFN responsive transcriptional signature (MX1, MX2, ISG15, ISG20, IFI6, IFI16, IFI27) was also signi cantly elevated in this pDC cluster (Fig 4c, d). Multilabel confocal microscopy analysis validated the higher expression of IFN-a by pDCs in lung tissues isolated from infected macaques at 3dpi (Fig 4e) when compared to 14-17dpi and healthy macaques (Fig4e, S4).
Among macrophage subclusters, mac_IFN_1 was the most abundant population found in 3dpi BAL samples, comprising 70 percent of myeloid cells; this population was completely absent in pre-infection and during resolution at endpoint. IFN-responsive gene signature was strongly upregulated in this population and the key genes which were most differentially upregulated in this population were MX1, MX2, IFIT1, IFIT2, IFIT3, IFIT5, IFI6, IFI16, IFI44, ISG15, HERC5, SIGLEC1, OAS1, OAS2, OAS3 etc. (Fig 4a). MX1 encodes a guanosine triphosphate (GTP)-metabolizing protein called IFN-induced GTP-binding protein Mx1 which is induced by Type I and Type II IFNs, antagonizes the replication process of several RNA and DNA viruses and participates in the cellular antiviral responses [20][21][22][23] . MX2, a paralog of MX1, is another IFN-induced GTP-binding protein that induces innate antiviral immune responses. IFIT genes encode IFN-induced antiviral proteins which acts as an inhibitor of cellular as well as viral processes, cell migration, proliferation, signaling, and viral replication 24,25 . IFI6 is one of the earliest identi ed IFN induced gene encoding the IFN-a -inducible protein 6 which has been shown to exert antiviral activity towards viruses by inhibiting the EGFR signaling pathway [26][27][28][29] . IFI16 gene encodes the Interferon Gamma Inducible Protein 16 which has been shown to be involved in the sensing of intracellular DNA and inducing death of virus infected cells [30][31][32][33] . IFI44 encodes the Interferon-Induced Protein 44 which is induced by Type 1 but not Type II IFNs and has been reported to suppress viral transcription 34,35 . IFIT genes encodes for the IFIT proteins (Interferon Induced proteins with Tetratricopeptide repeats) which confer antiviral state in a cell by either directly binding to the viral RNA or by binding to eukaryotic initiation factor 3 (eIF3) and preventing eIF3 from initiating viral translational processes [36][37][38] . All four classes of IFIT i.e. IFIT1, IFIT2, IFIT3 and IFIT5 were upregulated in the mac_IFN_1 population (Fig 4a). ISG15 also called Ubiquitin-like protein ISG15 is an early mediator of signaling induced by Type I IFNs and elicits innate immune response to viral infections by conjugation/ISGylation of its targets like MX and IFIT [39][40][41][42] . OAS encodes IFN-induced, dsRNA-activated antiviral enzyme which plays a critical role in cellular innate antiviral responses 43,44 . HERC5 is an E3 ligase for ISG15 conjugation which acts as a positive regulator of innate antiviral response in cells induced by IFNs and functions as part of the ISGylation machinery [45][46][47] . SIGLEC1 (CD169) is an IFN-inducible gene that acts as an endocytic receptor mediating clathrin dependent endocytosis and has been reported to be upregulated in circulating monocytes in COVID-19 patients [48][49][50][51] . Gene set enrichment analysis (GSEA) analysis revealed defense response to virus, negative regulation of viral genome replication, response to IFN-a and innate immune response as enriched gene ontology (GO) terms in this population (Fig 5a). SARS-CoV-2 infection in CD169 + macrophages has been reported in COVID-19 15,52 . To validate our ndings of SARS-CoV-2 infection in CD169 + macrophages, lung tissues from rhesus macaques following SARS CoV-2 infection and healthy controls were stained for CD68, ACE2, SIGLEC1, MX1, MX2, ISG15, Complement component 1q (C1q) and SARS CoV-2 nucleocapsid antibody (Fig5 b-h, j, S5-12). Lung macrophages expressing SIGLEC1/CD169 were enriched and expressed high levels of ACE2 at 3dpi (Fig  5b, S5). Another independent study has established that human macrophages and monocytes can be infected by SARS-CoV-2 but that the infection is abortive 53 . The macrophage population was further studied for detecting IFN responsive elements: MX1 (Fig 5c,S6), MX2 (Fig 5e, S8), ISG15 (Fig 5g, S10) and viral antigens (Fig 5d,S7,5f, S9, 5h, S11) and were found to be abundantly harboring SARS-CoV-2 in vivo as shown by multicolor confocal staining for SARS-CoV-2 Nucleocapsid/Spike protein in lung sections. MX1/MX2/ISG15 staining with viral antigen clari ed that the IFN-responsive signature was mostly restricted to macrophages harboring SARS-CoV-2, con rming an early IFN-driven innate immune response in lung macrophages.
Mac_IFN_2 cluster was mostly identical to Mac_IFN_1 but expressed a comparatively higher expression  (Fig 4a). While the Mac_IFN_TREM2 cluster showed an upregulation of IFN-responsive gene signature comprising of SIGLEC1, MX, IFIT, IFI, ISG and OAS genes (Fig 4a), suggesting defense response to virus as signi cantly enriched geneset (Fig5i). In vivo validation in lungs of macaques con rmed abundance of TREM2 macrophages with IFN-responsive phenotype on 3dpi (Fig 5j, S12).\ Mac_FOS cluster was abundant in BAL at baseline and constituted ~40-50% of myeloid cells. However, this cluster was depleted at 3dpi and not restored at the endpoint tested. Mac_FOS expressed high CXCL8 expression along with FOS, FOSB, NFKBIA, NFKBIZ AHR, lysozyme (LYZ) and CD69. GSEA revealed that this subset expressed an in ammatory and neutrophil chemotactic nature (Fig S13a), even in absence of infection in healthy macaques.
Mac_S100A8 cluster constituted 10% of the myeloid cells at pre-infection baseline, but was absent on 3dpi and abundantly represented at the endpoint suggesting a potential role for these cells in SARS-CoV-2 mediated pathology (Fig 3d). The key genes upregulated in this cluster were S100 Calcium Binding Protein (S100) A4, S100A6, S100A8, S100A9, Cathelicidin Antimicrobial Peptide (CAMP), Carboxypeptidase Vitellogenic Like (CPVL) (Fig4a) which represent innate in ammatory immune responses, neutrophil aggregation and chemotaxis pathways (Fig S13b). Mac_S100A8 cluster has four genes signi cantly upregulated from the S100 family of genes that involves low molecular-weight proteins considered as potent damage-associated molecular pattern molecules (DAMPs). DAMPs are also called danger signals or alarmins as they serve as a warning sign for the innate immune system to alert ambient damage or infection. S100A8 protein also called calgranulin A forms a heterodimer with S100A9 protein called calgranulin B, to form a heterodimer called Calprotectin which stimulates Tlymphocyte chemotaxis by acting as a chemoattractant complex with Peptidoglycan Recognition Protein 1 (PGLYRP1) that promotes lymphocyte migration via C-C chemokine receptor (CCR) 5/ C-X-C motif chemokine receptor (CXCR) 3 receptors 56,57 ; neutrophil recruitment along with TLR4 and/or receptor for advanced glycation end products 58 -mediated multiple in ammatory pathways 59,60 . Intracellular functions of S100A6 includes regulation of several cellular functions, such as proliferation, apoptosis, cytoskeleton dynamics, response to different stress factors etc. but when secreted into extracellular milieu it also RAGE (receptor for advanced glycation end products) and integrin β1 mediated in ammatory responses 61 . S100A4 has been reported to synergize with vascular endothelial growth factor (VEGF) in a RAGE dependent manner to promoting endothelial cell migration by increasing KDR (kinase insert domain receptor)/Vascular Endothelial Growth Factor Receptor 2 (VEGFR2) expression and MMP-9 activity 62 . S100A4 also plays a major role in high-density collagen deposition 63 .
Three other populations of macrophages lacking IFN signature (annotated Mac, Mac_2 & Mac_3) are present in healthy macaques at pre-infection timepoint. These populations were non-existent at 3dpi but are replenished at the endpoints (Fig 3d, 4a).
To further understand the in uence of macrophages on ambient immunocytes, we analyzed the ligandreceptor interactions between the most abundant macrophage population and other immunocytes based on cell speci c transcripts read at respective timepoint. The ligand-receptor interactions between Mac_IFN_1 and other immunocytes present at 3dpi depicted as Circos plot (Fig 6a) (Fig 6b) and the Mac_S100A8 cluster with Mast cells, cDCs, pDCs in addition to Mac_TREM2_IFN (Fig 6c).

Lymphoid bronchoalveolar landscape
A total of 38160 lymphoid cells were analyzed across all timepoints which distributed into 13 distinct clusters across the 3 timepoints studied (Fig 7a, Fig S14a,b). The populations were homogenously distributed across all animals at each timepoint (Fig S14c). We noted distinctive cluster alignment of all lymphoid populations based on key lymphocyte phenotype markers (Fig 7a,b) that differed between different conditions (Figure 7c,d). The only distinct lymphocyte cluster found to be upregulated at Day 3 post infection was a T cell cluster with IFN responsive gene signature spanning MX1, MX2, ISG15, ISG20, IFI27, IFI44, IFIT1, IFIT2, IFIT3, IFIT5, OAS1, OAS2, HERC5 HERC6 genes and was annotated T_IFN (Fig  7d,e). Confocal analysis in lung sections validated the abundance of IFN responsive T cells at 3dpi in macaque lungs (Fig7 f, S15).  74 . This is an important paradox to resolve, as it could lead to better therapeutic approaches for COVID-19 as well as for long-term persistent COVID-19 sequelae. Elegant approaches are available to modulate the signaling of this pathway in macaques 75  Our results unequivocally show that in protected, immunocompetent hosts, SARS-CoV-2 infection is characterized by an acute in ammatory response leading to a myeloid cell in ux into the lung compartment 4 and a strong Type I IFN response 5 . Using state-of-the-art scRNAseq approach in longitudinal BAL samples, we now demonstrate that the robust Type I IFN and related cytokine response observed in the lungs of infected macaques is mediated by myeloid cell subpopulations that are alveolar rather than tissue-resident in nature. In particular, macrophage subpopulations Mac_IFN_1, Mac_IFN_2 and Mac_TREM2_IFN subpopulations expressed high levels of IFN downstream genes both in magnitude and frequency (Fig 2). Our results clearly show that induction of a robust IFN response in macrophages strongly correlates with viremia (Fig S16a,b) and subsequent clearance of SARS-CoV-2 from the airways of macaques (Fig S16c,d).

Materials And Methods
Macaques. No live Indian origin rhesus macaques were used in this study. Samples obtained from young Rhesus macaques (Macaca mulatta) infected with 1.05x10 6 pfu SARS-CoV-2 isolate USA-WA1/2020 (BEI Resources, NR-52281, Manassas, VA) enrolled in a previously described (approved by the Animal Care and Use Committee of the Texas Biomedical Research Institute) study 4 were used for further analysis (Table S1).
Isolation of BAL single cells from macaques. Single cell suspensions from BAL obtained at different time points were collected as described earlier 4,76 and cryopreserved in Cryostor-CS10 (Biolife Solutions, USA) at -70ºC and then used for downstream processing of scRNAseq.
Single cell RNA: Library generation and sequencing. scRNAseq was done according to the manufacturer instructions (10x genomics) and as previously described 77 . Brie y, after quickly thawing the frozen BAL single cell suspension in water bath, 2X10 6 cells were taken for downstream processing. BAL single cell suspensions were subjected to droplet-based massively parallel single-cell RNA sequencing using Chromium Single Cell 3' (v3.1) Reagent Kit in the BSL-3 laboratory as per manufacturer's instructions (10x Genomics). Brie y, cell suspensions were loaded at 1,000 cells/μL with the aim to capture 10,000 cells/lane. The 10x Chromium Controller generated GEM droplets, where each cell was labeled with a speci c barcode, and each transcript labeled with a unique molecular identi er 78 during reverse transcription. The barcoded cDNA was isolated and removed from the BSL-3 space for library generation. The cDNA underwent 11 cycles of ampli cation, followed by fragmentation, end repair, A-tailing, adapter ligation, and sample index PCR as per the manufacturer's instructions. Libraries were sequenced on a NovaSeq S4 (200 cycle) ow cell, targeting 30,000 read pairs/cell. Single cell RNAseq: data processing. The Cell Ranger Single-Cell Software 3.0 available at 10x website was used to perform sample demultiplexing. We aligned resulting fastq les on mmul10 genome (Genebank, https://www.ncbi.nlm.nih.gov/assembly/GCF _003339765.1/), with addition of Ensembl mmul8 mitochondrial genes for GTF le with cellranger count. For each sample the recovered-cells parameter was set to 10,000 cells that we expected to recover for each individual library.
We used R package Seurat 3 79 for downstream analysis of count matrixes that we got as output from cellranger count 77 . We ltered cells that (1) had more than 10% of mitochondrial gene content and 80  clusters. For each cluster, only genes that were expressed in more than 15% of cells with at least 0.15-fold difference were considered. Heatmap representations were generated as described earlier with Phantasus software (https://artyomovlab.wustl.edu/phantasus/) 77 , using the mean expression of markers inside each cluster for each sample was used.

Circos Plots
Circos plots depicting possible cell interactions were created using SingleCellSignalR 81 .
Immunohistochemistry and Confocal Imaging: To validate the ndings of BAL single cell sequencing, multilabel immuno-histochemistry was performed on Naïve and SARS CoV-2 infected Rhesus macaque lungs at Day 3 and Day 14 post infection as described 4 . The lung sections were stained for macrophages with anti-CD68 antibody, SIGLEC1 with anti-CD169 antibody, Mac_IFN_1 signature markers with anti-MX1, MX2 and ISG15 antibodies; Mac-TREM2 with anti C1q-FITC conjugated antibody and pDCs with anti-HLA-DR and anti-CD123 antibodies to validate the in-vivo expression of these markers in SARS CoV-2 infected lung tissue (Table S2). SARS CoV-2 nucleocapsid antibody was used to detect SARS CoV-2 and ACE-2 expression was con rmed using human anti-ACE2 antibody. DAPI was used for nuclear staining. Images were captured using Ziess LSM-800 confocal microscope.

Statistical Analysis:
Graphs were prepared and statistical comparisons were applied using GraphPad Prism v8.4.3. Statistical comparisons were performed as outlined in respective methods. One-way repeated measure ANOVA with Geisser Greenhouse correction for sphericity and Tukey post hoc correction for multiple testing (GraphPad Prism 8.4.3) was applied for statistical comparison of population clusters across timepoints as described in the gure legends. For correlation analysis, Spearman's rank tests were applied. Statistical differences between groups were reported to be signi cant when the P value was less than or equal to 0.05. Data are presented as mean + standard error of mean (SEM).

Declarations
Reporting Summary: Further information on research design is available in the Nature Research Reporting Summary linked to this article.

Data availability:
All data supporting the ndings of this study are available within this manuscript and its Supplementary Information. Any additional data can be requested from the corresponding authors upon reasonable request. Figure 1 Immune landscape of BAL in SARS-CoV-2 infected macaques. Study outline of scRNAseq analysis of BAL cells from rhesus macaques infected with SARS-CoV-2. BAL single cell suspensions from 6 young rhesus macaques infected with SARS-CoV-2 from pre-infection (-7dpi), 3dpi and endpoint (14-17dpi) were subjected to scRNAseq (A). Immuno uorescence confocal images of the lungs stained with nucleocapsid (N)-speci c antibodies (turquoise) and 4,6-diamidino-2-phenylindole (DAPI) (blue). Shown are the images at 10x, 20x and 63x magni cation from naïve lungs (uninfected) as well as lungs infected with SARS-