library_construction_protocol: Mouse lungs were harvested after perfusion through the right ventricle with PBS. After mincing with razor blades, tissues were suspended in protease solution [0.25 % Collagenase A, 1 U/ml Dispase II, 2000 U/ml Dnase I in DMEM containing 10 mM HEPES and 2% FBS. The suspension was incubated at 37°C for 25 min with trituration by glass Pasteur pipette every 8 minutes. The digestion was then quenched for 5 minutes in ice-cold PBS containing 5% FBS and 2 mM EDTA, and cells were passed through a 100 μm cell strainer. Cells were pelleted and resuspended in RBC lysis buffer for 5 minutes. RBC lysis was quenched with 5% FBS/PBS and cells were passed through a 70 μm cell strainer, washed, and resuspended in 5% FBS/PBS containing antibodies for FACS purification. Approximately 100k CD45+ cells, 100k CD31+ cells, and 1x10e6 CD45-/CD31- cells were sorted for each sample and collected in 10% FBS/PBS. Sorted cells were then counted and labeled with oligonucleotide tags for multiplexing using 10x Genomics 3' CellPlex Kit Set A. All 8 biologic samples for P7 timepoint were pooled and 60,000 cells / lane were loaded onto 2 lanes of a Chromium Next GEM Chip (10x Genomics). The same workflow was used for P14 samples with all 8 P14 biologic samples pooled together and loaded onto 2 lanes as well. Each lane therefore represents a technical replicate for each biologic sample. Chromium Single Cell 3' v3.1 (10x Genomics) reagents were used for library preparation according to the manufacturer's protocol. The libraries were sequenced on an Illumina NovaSeq 6000 S4 flow cell.