library_construction_protocol: The sample was dissociated using the Human Whole Skin Dissociation Kit (Miltenyi Biotech Inc) with Enzyme P, with overnight incubation as per manufacturers guidelines. The dissociated cells were stored in CryoStor CS10 (StemCell Technologies) at −80°C, then transferred to liquid nitrogen after 24 hours. Thawing occurred just prior to 7-AAD staining (BioLegend 420404) and viable cell sorting by the SH800 Cell sorter (Sony Biotechnology). Viable cells in single-cell suspension were resuspended in 1% BSA in phosphate-buffered saline (PBS) at a concentration of 1000 cells/µL. A maximum of 20 000 cells were counted using the fluorescence cell counter LUNA-FX7 (Logos Biosystems) and loaded onto a single 10× lane and processed with the 10× Genomics Single Cell 3' kit (V.3.1) following manufacturer user guide (CG000330). Only 3 samples did not reach this target, and about 17 000 cells were loaded. Sequencing was carried out by the Oxford Genomics Centre, using Illumina NovaSeq 6000 (V.1.5 chemistry, 28 bp/98 bp) and libraries were sequenced to a minimum of 50 000 reads/cell. Cells were analysed in 2 batches.