Multiplexed enrichment and tracking of lineages with CloneSweeper

A fundamental challenge in studying therapy resistance is understanding whether it results from pre-existing cellular states ("priming") or drug-induced changes ("adaptation"). While lineage barcoding enables retrospective analysis of cells before and after treatment, current methods struggle to efficiently capture rare lineages in single-cell RNA sequencing (scRNA-seq) or isolate multiple specific lineages simultaneously for functional study. To overcome these limitations, we developed CloneSweeper, a multiplexed lineage tracking platform that pools enrichment libraries to isolate or enrich multiple rare lineages. CloneSweeper utilizes a dual-function barcode expressed as both a Cas9 gRNA for live-cell sorting and a 3 UTR transcript for high-recovery detection in 10x Genomics scRNA-seq. We applied CloneSweeper to a model of BRAF V600E melanoma, where we identified that resistance to targeted therapy emerges from a polyclonal population of rare, pre-existing lineages. By simultaneously targeting and enriching 21 distinct rare lineages prior to treatment, we defined a heritable, primed state characterized by de-differentiation and elevated mesenchymal markers. We demonstrate that these primed cells are not quiescent but instead exhibit upregulated inflammatory and stress response signaling, specifically via the AP-1 and NF-{kappa}B1 pathways. CloneSweeper thus provides a robust framework for dissecting the molecular mechanisms of rare biological phenomena through simultaneous, multiplexed lineage isolation.