In vitro production of stable Epstein-Barr virus-positive epithelial cell clones which resemble the virus:cell interaction observed in nasopharyngeal carcinoma.

The interaction of Epstein-Barr virus (EBV) with epithelial cells and the consequent role of the virus in the aetiology of undifferentiated nasopharyngeal carcinoma (NPC) is poorly understood. One important obstacle to work in this area has been the lack of an epithelial cell culture system in which EBV is stably maintained. Using a previously described approach in which CR2-transfected epithelial cells (SVK-CR2) are rendered susceptible to transient EBV infection (Li et al., Nature 356, 347, 1992), we now demonstrate that the pattern of EBV latent gene transcription in these acutely infected epithelial cells differs from that observed in virus-infected primary B cells. In addition, some of these epithelial cells spontaneously entered the EBV lytic cycle. By cloning Akata virus-infected SVK-CR2 cells we generated two stable lines which remained EBV positive for more than 1.5 years at which time further subclones were isolated. These cloned lines carry the EBV genome as an episome and exclusively use the FQp promoter for driving EBNA1 transcription, display no Cp/Wp promoter activity, and express low levels of the LMP mRNAs. Unlike acutely infected SVK-CR2 cells, the cloned lines responded poorly to suspension-induced terminal differentiation and were impaired in their ability to enter the virus lytic cycle. These results, showing similarities between the cloned EBV-positive SVK-CR2 lines and NPC tumour cells, suggest that stable maintenance of EBV in epithelial cells may require an undifferentiated cellular environment.