Growth phenotypes of cytomegalovirus isolates do not correlate with glycoprotein B, major immediate early genotypes or antiviral sensitivity

Human Cytomegalovirus (CMV) is generally described from in vitro experiments as a slowly replicating virus. A doubling time of one day in blood, however, has been shown in vivo. The growth phenotypes of CMV isolates and laboratory strains were studied in human fibroblasts. The viruses were found to replicate either rapidly or slowly. Comparison of CMV protein expression in lung and foreskin fibroblast cultures showed that two tissue culture adapted CMV strains (AD169 and Towne) and 3 clinical isolates belonged to the rapidly replicating viruses, whereas another 3 clinical isolates replicated slowly. CMV antigen concentrations were 6‐fold and virus yields were 10–1000‐fold higher for the rapidly replicating viruses than for the slow replicators. The antigen expression of two slowly replicating isolates was enhanced after 20 passages compared to the isolates at passage 5, but it was not as efficient as that of strain Towne. Slow or fast replication was related neither to major immediate early gene exon 4, and gB genotypes, nor to antiviral susceptibility. Proteins of the beta cascade may contribute to differences in the replication rate of CMV isolates. J. Med. Virol. 62:117–126, 2000. © 2000 Wiley‐Liss, Inc.