library_construction_protocol: To sort hAPCs for scRNA-sequencing, thymi were harvested and enzymatically digested with an enzymatic solution comprising LiberaseTM (Roche) and DNAse I in PBS at 37°C. Isolated cells were centrifuged and immunostained with a panel of fluorescently-labeled antibodies prior to resuspension in FWB+ EDTA  + propidium iodide (Enzo). HAPCs were FACS purified as MHCII lo to + CD45+ Thy1.2- non-thymic epithelial cells (Epcam+CD11c-). Purified hAPCs  were then centrifuged and resuspended in FWB without EDTA, counted and resuspended at a concentration of 700-1200 cells/µL prior to submission to the University of Texas Genomic Sequencing and Analysis Facility. Cell suspensions were loaded on the Chromium Controller (10X Genomics) and processed for cDNA library generation following the manufacturer's instructions for the Chromium NextGEM Single Cell 3' Reagent Kit v3.1 (10X Genomics). Libraries were examined for size and quality using the Bioanalyzer High Sensitivity DNA Kit (Agilent) and their concentrations were measured using the KAPA SYBR Fast qPCR kit (Roche).