DHTKD1 and infection: In contrast to HepG2 cells, E1a levels in untreated MCR5 cells infected with the E1b-fully-deleted viruses were higher even at 2 days post-infection compared to cells infected with the other replicating viruses, suggesting that mCMV promoter is much more active than the E1a promoter in MRC5 cells (Figure 5B).