Gene mapping of an Epstein-Barr virus isolate obtained from a nasopharyngeal carcinoma

Epstein-Barr virus genotypes associated with nasopharyngeal carcinoma in southern China

We have used probes representing approximately two-thirds of the Epstein-Barr virus (EBV) genome to examine genetic polymorphism of wild-type EBV directly detected in 28 nasopharyngeal carcinoma (NPC) tissues from Southern China. In the hypervariable regions containing reiterated sequences, this analysis showed that while naturally occurring viruses are genetically diverse, only one genotype was detectable in each tumor specimen. Unique variants in NPC were detected in four regions of the EBV genome. Two of these appeared significant in their distribution. The type C variant resulting from loss of a BamHl site between the BamHl W1* and l1* regions was prevalent among isolates from Southern China, but not so common in the United States. An "f" variant having an extra BamHl site in the BamHl F region was almost exclusively detected in only Asian NPC biopsies.

Establishment and characterization of two epithelial tumor cell lines (HNE-1 and HONE-1) latently infected with Epstein-Barr virus and derived from nasopharyngeal carcinomas

Two epithelial tumor cell lines were established from biopsy specimens of 2 nasopharyngeal carcinomas (NPC) and designated HNE-1 and HONE-1. Uncloned HNE-1 cells were found to be Epstein-Barr virus (EBV) DNA-positive when examined by Southern blot analysis up to passage 35, after which the EBV genome could no longer be detected. A similar loss of EBV DNA took place in uncloned HONE-1 cells. However, HONE-1 clone 40 cells are still EBV DNA-positive up to passage 42 thus far and cell cultures contain 85-90% EBV nuclear antigen (EBNA)-positive cells. The HNE-1 cell line has been passaged more than 100 times and the uncloned HONE-1 cells more than 90 times. The tumorigenicity of the HNE-1 and HONE-1 cells was demonstrated by tumor induction in nude mice. Karyotypic analysis of the HNE-1 cells demonstrated an aneuploidy with a modal chromosomal number of 74 at passages 5 and 101 at passage 20; 18 marker chromosomes were identified. We have continued to map the EBV genome latently associated with the HNE-1 and HONE-1 cells using the Bam HI, EcoRI or Hind III restriction enzymes. Using EcoRI fragments A-K as probes, we found that HNE-1 EBV DNA is different from B95-8 and HR-1 EBV DNA in the EcoRI-C region. The Bam HI map for HONE-1 EBV DNA is very similar to the B95-8 map; it contains the Bam HI-Y fragment but without Bam HI B' and WI'. Differences were observed between HONE-1 EBV DNA and B95-8 DNA using the Hind III restriction enzyme. There was no evidence of spontaneous expression of the latent EBV genome in HNE-1 cells, and attempts to induce replication of the latent EBV genome and rescue infectious virus have failed, suggesting a tightly restricted virus genome.

Two epithelial tumor cell lines (HNE-1 and HONE-1) latently infected with Epstein-Barr virus that were derived from nasopharyngeal carcinomas

Two epithelial tumor cell lines were established from biopsy specimens of nasopharyngeal carcinomas (NPC). The specimens were taken from poorly differentiated squamous cell carcinomas of the nasopharynx. The tissues were prepared for cell culture and eventually two continuous epithelial cell lines were obtained and designated HONE-1 and HNE-1. Light and electron microscopic examination of these two cell lines demonstrated cells with an epithelial morphology including the presence of desmosomes. The HNE-1 cell line has been passaged more than 100 times and the HONE-1 cell line has been passaged more than 90 times. It was found that early-passage uncloned HNE-1 cells (passage 23) could be superinfected with the B95-8 and NPC-EBV isolates as demonstrated by the induction of Epstein-Barr virus (EBV)-specific early antigen(s) in a small percentage of the cells; HONE-1 cells could also be superinfected with EBV. Southern blot analysis detected EBV DNA in samples from uncloned HNE-1 cells at passages 12, 17, 21, 27, and 35. However, by passage 45, EBV DNA could no longer be detected in HNE-1 cells by Southern blot analysis. The EBV genome was detected in parental HONE-1 cells at subculture 9 and in clone 40 cells up to passage 40 thus far. When HNE-1 cells were examined for the expression of the EBV-encoded nuclear antigen (EBNA) at passage 12, only about 10% of the cells were found to be positive. The percentage of EBNA-positive HNE-1 cells decreased as the cells were passaged. A similar loss of EBNA was observed in uncloned HONE-1 cells, but not in HONE-1 clone 40 cells. In clone 40, which has been passaged 40 times thus far, 85-90% of the cells are still EBNA-positive. The data suggest that EBV genome-positive HNE-1 and HONE-1 cells were lost as the cells were cultivated in vitro and that cloning the cells at an early passage level may be critical in maintaining EBV genome-positive epithelial NPC cells. These EBV genome-positive epithelial NPC cell lines will be useful for studying the association of EBV and NPC.

Predilection of a nasopharyngeal carcinoma-derived isolate of Epstein-Barr virus for infection of specific subsets of B lymphocytes

It is important to know whether there are variants of Epstein-Barr virus (EBV) with biological properties that are different from the prototype viruses that have been studied in detail, such as P3HR-1 and B95-8. We have studied an EBV isolate derived from a nasopharyngeal carcinoma (NPC) tumor, designated NPC-EBV. We have examined the target B lymphocytes infected and growth-transformed with NPC-EBV as compared with two common EBV isolates, B95-8 and AG876 EBV, for stage of maturation using antibodies to several immunoglobulin chains. Typing of the NPC-EBV transformed lymphoblastoid cell lines revealed the predilection of the NPC-EBV isolate to infect immature B lymphocytes. This was not the case for the B95-8 and AG876 isolates. The reason for the predilection of NPC-EBV for immature B lymphocytes remains to be explored further. However, these results may be important in understanding the pathophysiology of EBV-associated diseases.

Epstein-Barr virus DNA in nasopharyngeal biopsies

The Epstein-Barr virus (EBV) has been closely associated with the undifferentiated form of nasopharyngeal carcinoma (NPC), which is particularly common in the high risk area in southeast China. We have examined 37 nasopharyngeal biopsies from patients within this high risk area, including 31 cases of undifferentiated NPC and 6 cases of patients with nasopharyngitis, for the presence of EBV DNA. We found that 26 of 31 biopsies from NPC patients were EBV DNA positive; 3 of the 6 biopsies from patients diagnosed with nasopharyngitis were also EBV DNA positive. Southern blot analysis of the DNAs obtained from the EBV genome positive biopsies, digested with EcoRI, showed that all preparations from the NPC tumors had only one band corresponding to the EcoRI A fragment when a BamHI W fragment was used as a probe. However, one tumor had an additional band with a molecular weight larger than EcoRI A. The presence of this novel band could indicate the integration of viral DNA into host cellular DNA. DNA from the same biopsies were restricted with BamHI and PstI restriction enzymes. The data obtained from these experiments suggest that the EBV genomes in both the NPC tumor biopsies and biopsies from nasopharyngitis patients obtained from an endemic area in South China may be similar to each other and to the B95-8 EBV isolate with respect to the BamHI Y region of the EBV genome. The data also demonstrate that infection of normal nasopharyngeal epithelial cells with EBV takes place in patients with nasopharyngitis.