Frequency and distribution of chromosomal integration sites of the Epstein-Barr virus genome

Human lymphocytes can be transformed in vitro by integration of the Epstein-Barr virus (EBV) into the host genome. To study whether integration sites are stable or changeable in the course of long-term cultivation, three EBV-transformed lymphoblastoid cell lines, along with positive control (Namalwa cell line) and negative control (noninfected lymphocytes) cells were studied. A biotinylated Bam H1W EBV-DNA fragment was used as the probe for fluorescence in situ hybridization to count the numbers and to localize the sites of integrated EBV-DNA. Among these cell lines, the percentage of cells with integrated signals varied from 58% to 91%, with a mean of 1.43 to 2.66 signals per cell. No consistent tendency of increasing or decreasing number of signals was observed for the three cell lines harvested at four different cultivation intervals (86-204 days after infection). Although the integration was not site-specific, high frequencies of integration did occur in all three cell lines at the following chromosomal sites: 1p31, 1q31, 2q32, 3q13, 6q24 and 7q31. Because there were multiple integration sites present, it was difficult to draw any conclusion on integration site stability.