Genetic barcodes are increasingly used to track individual cells and to quantitatively assess their clonal contributions over time. Although barcode quantification relies entirely on counting sequencing reads, detailed studies about the method’s accuracy are still limited. We report on a systematic investigation of the relation between barcode abundance and resulting read counts after amplification and sequencing using cell-mixtures that contain barcodes with known frequencies (“miniBulks”). We evaluated the influence of protocol modifications to identify potential sources of error and elucidate possible limitations of the quantification approach. Based on these findings we designed an advanced barcode construct (BC32) to improved barcode calling and quantification, and to ensure a sensitive detection of even highly diluted barcodes. Our results emphasize the importance of using curated barcode libraries to obtain interpretable quantitative data and underline the need for rigorous analyses of any utilized barcode library in terms of reliability and reproducibility.

Intratumoral heterogeneity has been identified as one of the strongest drivers of treatment resistance and tumor recurrence. Therefore, investigating the complex clonal architecture of tumors over time has become a major challenge in cancer research. We developed a new fluorescent "optical barcoding" technique that allows fast tracking, identification, and quantification of live cell clones in vitro and in vivo using flow cytometry (FC). We optically barcoded two cell lines derived from malignant glioma, an exemplary heterogeneous brain tumor. In agreement with mathematical combinatorics, we demonstrate that up to 41 clones can unambiguously be marked using six fluorescent proteins and a maximum of three colors per clone. We show that optical barcoding facilitates sensitive, precise, rapid, and inexpensive analysis of clonal composition kinetics of heterogeneous cell populations by FC. We further assessed the quantitative contribution of multiple clones to glioblastoma growth in vivo and we highlight the potential to recover individual viable cell clones by fluorescence-activated cell sorting. In summary, we demonstrate that optical barcoding is a powerful technique for clonal cell tracking in vitro and in vivo, rendering this approach a potent tool for studying the heterogeneity of complex tissues, in particular, cancer.

Highlights d Xenografted HNSCC comprises multiple unevenly propagating clones d Postsurgical recurrences reproducibly show a substitution of dominating clones d Clones enriched in recurrences are initially sparse in primary tumors d Clones enriched in recurrences feature distinct phenotypic and genetic traits