CLONAL VERSUS POLYCLONAL EPSTEIN-BARR-VIRUS INFECTION IN NASOPHARYNGEAL CARCINOMA CELL-LINES

In most nasopharyngeal carcinoma (NPC) biopsy specimens, the Epstein-B arr virus (EBV), particularly in the terminal repeat region genomic st ructure, reveals a clonal pattern. To evaluate this phenomenon in vitr o, we infected EBV-negative NPC cell lines, which express secretory co mponent (SC) protein on their cell surface, with EBV particles. The vi ral particles were obtained either from a subcloned single cell or fro m the original B95-8 cell line. EBV infection was performed by incubat ing IgA anti-EBV and EBV particles with NPC cells and confirmed by dir ect in situ PCR hybridization. Southern blot analysis of EBV terminal repeat in EBV-infected NPC cell lines was performed using a XhoI 1.9-k b DNA fragment from the right terminus of the EBV genome as a probe. W e found that all four NPC cell lines (ie, NPC-TW01, 03, 04, and 06) ex pressed SC protein on their surfaces and could be infected by EBV thro ugh the EBV IgA-SC complex. Southern blot analysis in the single cell- subcloned B95-8 cell line showed a clonal EBV terminal repeat with a h igher molecular size; whereas the original B95-8 line revealed the pol yclonal EBV DNA pattern. A similar clonal EBV genomic pattern with low er molecular size was seen in all EBV-infected NPC cell lines. For com parison, six NPC biopsy specimens were also examined; of these, five s howed a single band, and the remaining showed one major band and sever al lower molecular-sized bands. The EBV genomic DNA in the infected ce lls was shown to be an episomal form. We conclude, therefore, that a s ingle (clonal) form of EBV genome can be obtained from a mixed populat ion of epithelial tumor cells, even when they are infected by multiple virions with single or multiple form(s) of the EBV genomic pattern.