Communicated by W.Doerfler BL67 and BL18 are Burkitt's lymphoma cell lines with t(8;14) translocations (the breakpoint is in the first exon and first intron, respectively) in which the A-heavy chain switch region is fused to the c-myc gene in head to head orientation. In both cell lines only aberrant c-myc RNAs are found. BL67 cells contain two c-myc RNA species of 2.4 and 3.5 kb. The 2.4-kb RNA is initiated at several cryptic promoters in the first intron. The 3.5-kb RNA is transcribed from the immunoglobulin heavy chain anti-sense strand across the breakpoint of the translocation into the first exon of the c-myc gene and is then normally spliced using the physiological splice donor and acceptor sites of the c-myc gene. BL18 contains c-myc RNA of 2.4 kb initiated at cryptic promoters in the first intron and additional RNAs of 0.90 kb and 0.74 kb transcribed from the dual c-myc promoters on the reciprocal fragment of the translocation. The cytoplasmic turnover of these RNAs differs significantly from that of the normal c-myc message. The 3.5-kb RNA of BL67 cells and the 0.90-kb and 0.74-kb RNAs of BL18 cells, which are both hybrid molecules consisting of c-myc and immunoglobulin sequences, have a halflife of several hours in contrast to the normal c-myc message with a half-life of 15 min. The aberrant 2.4-kb c-myc RNAs of BL67 and BL18 cells are also more stable than the normal c-myc message and disappear with a half-life of 50 min. The results are compatible with the model that the secondary structure of the normal c-myc RNA is required for the fast, regulated decay of the c-myc message in the cytoplasm.

Attempts were made to superinfect epithelial explant cell cultures prepared from nasopharyngeal carcinomas with Epstein-Barr virus. Virus-specific markers were observed in such cultures 3 days after superinfection. In addition, expression of Epstein-Barr virus early antigens was observed in epithelial cell explant cultures treated with iododeoxyuridine. The (2), early antigen(s) (3), soluble antigen(s) (4), and nuclear antigen (5). In addition, EBV-specific antibody levels have been shown to be related to the clinical stage of the tumor (1, 5).When NPC tumor biopsy specimens were assayed for EBV DNA by nucleic acid hybridization, virus-specific DNA was found in the specimens (6). Moreover, it has now been shown that both EBV genomes (7) and the EBV-associated nuclear antigen (EBNA) (8) are associated with the epithelial elements of NPC (9, 10) rather than with the infiltrating lymphoid cells (11).We have studied the expression and regulation of EBV in mammalian cells. To circumvent the inability of EBV to lytically infect (or transform) cells other than B (bone-marrow-derived) lymphocytes (12) 75-1525, 75-1531-1, 75-1531-2, and 75-1576) were cut into approximately 1 mm pieces. The tumor specimens were placed on glass coverslips in 13 mm plastic tissue culture plates (Falcon) which had been pretreated with calf serum to aid in attachment of explants. A small volume of RPMI 1640 medium supplemented with 20% fetal calf serum, 100 units of penicillin per ml, and 100 ,ug of streptomycin per ml was added to the tissue culture plates. Epithelial cells from the explants were allowed to grow out on glass coverslips prior to treatment or superinfection.Superinfection of NPC Epithelial Cells with EBV. Seven days after preparation of the NPC explants, the medium was changed and cells were grown in fresh RPMI 1640 medium, as previously described, for 24 hr. Coverslip explant cell cultures were infected with 0.2 ml aliquots containing 105 fluorescence-forming units (18)

The recurrent loss of genetic material from a specific chromosomal region in a given tumor type suggests the presence of a tumor- suppressor gene, the loss or inactivation of which may be relevant for tumorigenesis. In this study, we provide molecular evidence for the recurrent association between deletions on the long arm of chromosome 6 and B-cell non-Hodgkin lymphoma (B-NHL). Normal and tumor DNAs from 71 cases of B-NHL were studied for loss of constitutional heterozygosity (LOH) at 19 loci on chromosome 6 using a panel of restriction fragment length polymorphism (RFLP) probes. LOH, indicating deletion of all or part of 6q, was detected in 16 of 71 cases (22.5%), ranging from low- grade to high-grade B-NHL. The isolated loss of 6p or the loss of other chromosomes (8, 17, 22) tested as controls for specificity was not observed in any case. Comparison of the extent of the deletions among different cases allowed the identification of two distinct regions of minimal deletion (RMD) at 6q25 to 6q27 (RMD-1) and at 6q21 to 6q23 (RMD- 2), respectively, suggesting the existence of two tumor-suppressor genes. These data support a role for 6q deletions in B-NHL pathogenesis and provide a basis for identifying the corresponding tumor-suppressor genes.

This paper reports a unique type of interaction of Epstein-Barr virus (EBV) with an EBV receptor-positive, genome-negative human lymphoid T cell line (Molt 4), which can be summarized as follows. Although Molt 4 cells express receptors for EBV, they appear to block the penetration of this virus. These observations are derived from combined studies with immunofluorescence and electron microscopy. It is possible that T cell lines bearing receptors for EBV may express such a control on virus penetration.

APO-1 is a cell surface molecule that induces apoptosis when ligated with the monoclonal antibody anti-APO-1. Expression of APO-1 and response to anti-APO-1 was investigated in a number of Epstein-Barr virus (EBV)-positive and -negative Burkitt lymphoma (BL) cell lines, in EBV-immortalized lymphoblastoid cell lines, and in cells from fresh BL biopsies. APO-1 was not expressed in EBV-negative cell lines and in EBV- positive BL cell lines with a phenotype corresponding to BL tumor biopsy cells (CD10+, CD21-, CD23-, CD30-, CD39-, CDw70-, CD77+). Accordingly, fresh BL cells obtained from three BL biopsies were APO-1 negative. EBV-positive BL cell lines that had acquired a lymphoblastoid phenotype (CD10-, CD21+, CD23+, CD30+, CD39+, CDw70+, CD77-) upon prolonged in vitro cultivation, as well as normal B-lymphoblastoid cell lines, expressed a high density of APO-1. APO-1 may, therefore, be regarded as a B-cell activation marker. APO-1 expression is not the only prerequisite for anti-APO-1-induced apoptosis because 6 of 7 APO-1- expressing EBV-positive BL cell lines were not sensitive to anti-APO-1, whereas all lymphoblastoid cell lines were killed by anti-APO-1. The sensitivity of lymphoblastoid cell lines to anti-APO-1-mediated apoptosis may open a new therapeutic approach for the treatment of EBV- induced lymphoproliferative lesions in immunocompromised individuals, because these are composed of cells with a lymphoblastoid phenotype.