EPSTEIN-BARR-VIRUS (EBV) CAN IMMORTALIZE B-CLL CELLS ACTIVATED BY CYTOKINES

B-type of chronic lymphocytic leukemia (B-CLL) cells are inert to the potent transforming action of Epstein-Barr virus (EBV). The mitogenic action of Staphylococcus aureus Cowan I (SAC), MP6-thioredoxin, and in terleukin 2 (IL-2), agents previously shown to induce proliferation in normal as well as in B-CLL cells, lifted this block, and EBV-positive cell lines could be established. It was not possible to establish cel l lines of leukemic origin from cultures that were incubated with EBV alone or cytokine mix alone. CLL-cells infected with EBV only, express ed the viral nuclear antigen complex (EBNA), but not the viral latent membrane protein (LMP). They were not activated as measured by cell si ze and H-3-thymidine incorporation. In contrast, cells incubated withE BV and cytokine mix expressed both EBNA and LMP in parallel with enlar gementand increased H-3-thymidine incorporation. These results emphasi ze that LMP expression is a prerequisite for growth transformation and immortalization and that cytokine activation signals are required for its expression in B-CLLs. Cells incubated with SAC/MP6-thioredoxin/IL -2 did not express any of the viral antigens, but were activated with regard to the mentioned parameters.Nine cell lines were established fr om six patients. From each of the three patients, we obtained 'twin'-p air lines: one corresponding to the malignant celland the other to a n ormal B-lymphoblastoid cell. Thus, malignant and normal B-cell counter parts, from the very same donor, are at hand for comparative studies. The cell lines have been carried out for more than 12 months in cultur e. We conclude that B-CLL that are refractory to EBV-transformation ca n be rendered susceptible through in vitro cytokine activation.