library_construction_protocol: Cells were washed with PBS with 0.04% w/v bovine serum albumin (BSA, New England Biolabs), filtered through 40 µm FlowMi filter tips filter tips (Bel-Art), and counted according to the 10x Genomics protocol. Approximately 14,000 cells per sample were loaded into the 10x Genomics Chromium Single Cell 3' Library and Gel Bead Kit v2 or v3 kit, and cDNA was reverse-transcribed, amplified, and purified according to the manufacturer's protocol. Resulting cDNA libraries were quantified by BioAnalyzer, yielidng the expected size distribution described in the manufacturer's protocol. To prepare the Target Site amplicon sequencing library, resulting amplified cDNA libraries were further amplified with custom, Target Site-specific primers containing P5/P7 Illumina adapters and sample indices. PCR amplification was performed using Kapa HiFi HotStart ReadyMix according to the following program: melting at 95C for 3 minutes, then 14 cycles at 98C for 15 seconds and 70C for 20 seconds. Approximately 12 fmol of template cDNA were used per reaction; amplification was performed in quadruplicate to avoid PCR-induced library biases, such as jack-potting. PCR products were re-pooled and purified by SPRI bead selection at 0.9x ratio and quantified by BioAnalyzer.