Identification of murine leukemia virus in xenograft cultures. A. PCR detection of murine type C retrovirus (MTCR) in brain tumor xenograft cultures and nude mouse, but not primary tumors. B. Comparison between DK-MICROBE tag counts and quantitative real-time PCR (qPCR) data. Amplicons surrounding MTCR DK-MICROBE tags were quantified by Q-PCR in xenografts GBMX1 and GBMX2 and in negative control primary tumor GBM16. DK-MICROBE tag counts are indicated above each bar.