BM dissemination model with DNA-barcoded MM cells. (A) Schematic diagram illustrating the study procedures. Twelve-base random DNA sequences were inserted into the pCW307 lentivirus backbone with RFP as selection marker. MM.1S cells were transduced with the DNA-barcode library and injected into the cavity of femurs freshly harvested from donor mice. Myeloma-bearing bone chips were subcutaneously transplanted under the dorsal skin of recipient mice. (B) Pie chart of barcode diversity in preinjection cell pool shows absence of major clone bias. (C) The proportions of barcoded clones in the implanted bone chip (primary site), left and right femur BM, and CTCs. (D) Cumulative ranking of barcodes from primary tumor site, distant BM site, and CTCs from 4 representative mice. Dotted cutoff lines indicate a threshold, which represents 90% of the total reads. Colored numbers are the number of barcodes that represents 90% of total reads in different sample types. LTR, long terminal repeat.