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Primary nasopharyngeal carcinoma (NPC) cells were fused to hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-defective cells derived from adenoid tissues using Sendai virus. Some of the fused cells developed into epithelial-like hybrid cells in a selective HAT medium. The hybrid cells (NPC-KT) were Epstein-Barr virus (EBV)-associated nuclear antigen (EBNA)-positive cells. There have been no reports on the establishment of EBNA-positive epithelial cell lines derived from NPC. Thus, the epithelial-like hybrid cells might serve as an in vitro model for studying the biologic activity of NPC-associated EBV.

Epstein-Barr virus (EBV) preparations from both NPC-KT cells (NPC-EBV) and P3HR-1 cells (HR-1-EBV) can induce cell fusion between EBV receptor (EBVR)-positive Raji cells and EBVR-negative cells, but other strains of EBV cannot induce cell fusion. The effect of these two EBV isolates on ability of cells to fuse has been studied to determine if there are differences in the biological properties of the different EBV isolates, particularly the isolates obtained from nasopharyngeal carcinoma such as NPC-EBV. The frequency of cell fusion between NPC-EBV-superinfected Raji cells and EBVR-negative epithelial cells (Ad-AH) was increased more than 30-fold in the presence of medium containing 1% dimethylsulfoxide (DMSO). However, the frequency of cell fusion between HR-1-EBV-superinfected Raji cells and Ad-AH cells was unaffected under the same conditions. The data show that differences in the ability of cells to fuse are induced by variants of EBV in response to DMSO. These differences may be important in elucidating the different biological properties of EBV isolates and might have implications for the pathophysiology of EBV-associated illness.

An epithelial-like hybrid cell line was established by cell fusion of 8-azahypoxanthine-resistant epithelial cells (Ad-AH) with lymphoblastoid cells (A2L), derived from the human nasopharynx. The nasopharyngeal hybrid cells, designated as A2L/AH, were Epstein-Barr virus (EBV)-associated nuclear antigen (EBNA)-positive by the anticomplement immunofluorescence method. Furthermore, the treatment of the hybrid cells with 5-Iodo-2' -deoxyuridine (IUDR) induced early antigen (EA) and viral capsid antigens (VCA), while the treatment of nonproducer lymphoblastoid cells, A2L, induced EA but not VCA. The appearance of IUDR-induced VCA in the hybrid cells suggests that some factor produced by the Ad-AH cells might neutralize a repressed state of VCA and thus activate these antigens with the treatment of IUDR. These established nasopharyngeal hybrid cells might be useful for studies of in vitro nasopharyngeal carcinoma (NPC) since no EBV-carrying NPC cell lines have been established.

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