Use of a transfection method to demonstrate a monolayer cell transforming agent from the EB3 line of Burkitt's lymphoma cells.

Primary human amnion cell monolayers which had been treated with DEAE-dextran, washed, and then inoculated with sonicated cells of the EB3 line of Burkitt's lymphoma cells developed foci of transformed amnion cells 7 to 14 days later. When either the DEAE-dextran or the sonicate was omitted, no significant transformation was found. The foci consisted of enlarging mounds of rapidly dividing cells, which upon subculturing continued their high miotic activity; and strains or lines of the transformed amnion cells were thus readily established. The modal number of chromosomes in such lines was 65 instead of the normal 46. Not all human amnions yielded cells transformable by EB3 cell sonicate, as determined by direct comparisions using the same cultural conditions and testing with the same fresh sonicate preparation in the same experiment. Overall, it appeared that only about 40 to 50% of the amnions yielded transformable cell monolayers; the rest gave monolayers apprently completely refractory to the transformation. The transformed amnion cells contained nuclear and cytoplasmic Epstein-Barr virus (EBV) antigen(s), as revealed by indirect immunofluorescence tests. EB3 cell sonicate also caused the appearance of rapidly growing transformed cell foci on secondary rat embryo cell monolayers which had been sensitized with DEAE-dextran. Calcium in the cell maintenance medium decreased the number of transformed foci found, both on the human and on the rat cell monlayers. Sonicates of cultured normal human leucocytes had no such transforming activity for either the human or the rat cells. The transforming agent in EB3 cell sonicate was completely destructible by either deoxyribonuclease or trypsin, but not by ribonuclease, and was not neutralizable by anti-EBV serum. The simplest interpretation of these results is that the transforming agent is part of all of the EBV DNA plus some necessary protein, with both the DNA and the protein accessible to hydrolytic enzyme action.