An Epstein-Barr virus that expresses only the first 231 LMP1 amino acids efficiently initiates primary B-lymphocyte growth transformation

An Epstein-Barr virus (EBV) recombinant (MS231) that expresses the first 23 1 amino acids (aa) of LMP1 and is truncated 155 aa before the carboxyl term inus transformed resting B lymphocytes into lymphoblastoid cell lines (LCLs ) only when the infected cells were grown on fibroblast feeder cells (K. M. Kaye et al., J. Virol. 69:675-683, 1995). Higher-titer MS231 virus has now been compared to wild-type (WT) EBV recombinants for the ability to cause resting primary B-lymphocyte transformation. Unexpectedly, MS231 is as pote nt as WT EBV recombinants in causing infected B lymphocytes to proliferate in culture for up to 5 weeks. When more than one transforming event is init iated in a microwell, the MS231 recombinant supports efficient long-term LC L outgrowth and fibroblast feeder cells are not required. However, with lim ited virus input, MS231-infected cells differed in their growth from WT vir us-infected cells as early as 6 weeks after infection. In contrast to WT vi rus-infected cells, most MS2S1-infected cells could not be grown into long- term LCLs. Thus, the LMP1 amino-terminal 231 aa are sufficient for initial growth transformation but the carboxyl-terminal 155 aa are necessary for ef ficient long-term outgrowth. Despite the absence of the carboxyl-terminal 1 55 aa, MS231- and WT-transformed LCLs are similar in latent EBV gene expres sion, in ICAM-1 and CD23 expression, and in NF-kappa B and c-jun N-terminal kinase activation. MS231 recombinant-infected LCLs, however, require 16- t o 64-fold higher cell density than WT-infected LCLs for regrowth after limi ting dilution. These data indicate that the LMP1 carboxyl-terminal 155 aa a re important for growth at lower cell density and appear to reduce dependen ce on paracrine growth factors.