Fig. 1. Abundant murine virus sequence reads found in RNA-Seq data generated from PDX tumor cells.

a The proportion of murine virus reads in the total virome in various PDX tumor samples and corresponding controls, wild-type mice and NSG mice. Box limits: 25th and 75th percentiles; center line: median; whiskers: 1.5x interquantile range from box limits; dots: outliers. b Major categories of murine virus as identified by sequence reads from all PDX cancer samples. c Assembly of full viral genome from RNA-Seq reads. A-G: murine leukemia virus from seven types of PDX. H. Zika-virus-infected human brain organoids as positive control. d Sequence reads from breast cancer PDX (top) but not from non-PDX samples (bottom) cover the entire murine leukemia virus genome. e Amplification of XMLV ENV, XMRV GAG, and MLV GPP gene fragments from genomic DNA preparations of two breast cancer PDX tumor samples. The human GAPDH gene was used as a control to validate the experimental system. Reaction without template is considered as negative control. f Amplification of the MLV GPP gene fragment from 4 breast cancer PDX models with duplicates (A, B). PCR amplicfication was performed twice for each experiment. Source data for (a, b, e, and f) are provided in Source Data File.