Three phases in transformation of human lymphocytes by Epstein-Barr virus, as revealed by colony formation in soft agar.

Human cord lymphocytes were examined for colony formation in soft agar medium at various times after infection with Epstein-Barr virus (EBV). The transformation process could be divided into the following three sequential phases: (1) A pre-early phase, lasting about 10 hr post infection (pi), during which the number of transformed colonies was virus dose dependent. (2) An early phase, between about 10 and 60 hr pi, during which cloning efficiency was markedly lower than that of the pre-early phase. (3) A later phase, starting at about 60 hr pi, during which cloning efficiency was restored and the number of colony formers increased in an exponential fashion. EBV-associated nuclear antigen-positive cells first appeared at the beginning (12 hr pi) of the early phase and increased continuously thereafter. Increased DNA synthesis began at about 48 hr pi. These results suggest that the cloning efficiency of the infected cells changes during the transformation process, possibly reflecting altered cell sensitivity to agar.