EXPRESSION AND TUMORIGENICITY OF THE EPSTEIN-BARR-VIRUS BARF1 GENE INHUMAN LOUCKES B-LYMPHOCYTE CELL-LINE

We previously showed that the Epstein-Barr virus, which encodes the BA RF1 gene, could transform rodent fibroblasts. In this work, the expres sion of the BARF1 gene was studied in the human Louckes B-lymphocyte c ell line. Introduction of the BARF1 open reading frame under the contr ol of the Mo-MuLV LTR promotor into nontumorigenic Louckes lymphoid ce lls led to the activation of the c-myc protooncogene and increased exp ression of the B-cell surface proteins, the transferrin receptor, CD21 , and CD23. BARF1-expressing cells induced a diffuse lymphoma-like tum or in newborn rats treated with anti-thymocyte serum that was, however , transient and regressed after 3-4 weeks as the immune system recover ed. The tumor induction was similar to that observed with lymphoid cel l lines in vitro generated by infection with the B95-8 virus strain, i n which lytic antigens are expressed at low levels. After long-term cu lture, Louckes cell clones lost expression of the BARF1 gene and were unable to induce tumors.