Live-sorted CAR T cells (NGFR+) were tagged with MULTI-Seq barcodes (Sigma Aldrich), normalized and pooled, and processed using the Chromium Controller instrument (10x Genomics). Libraries were prepared according to manufacturer's instructions (10x Genomics 5' v2) with a separate MULTI-seq library preparation workflow performed following cDNA amplification, as described previously (McGinnis, Patterson, et al., Nature Methods, 2019).