Genomes of the endothelial cell-tropic variant and the parental Toledo strain of human cytomegalovirus are highly divergent

The low-passage Toledo strain of human cytomegalovirus (HCMV) and fresh clinical HCMV isolates have been reported to share the capacity to propagate efficiently in endothelial cell cultures. In the laboratory, however, repeated attempts to adapt the Toledo strain to growth in endothelial cells have been unsuccessful. Southern blot analysis of the entire viral genome and restriction length polymorphism analysis of multiple genome regions amplified by PCR demonstrated that the reported endothelial cell-tropic viral variant of the Toledo strain and the parental Toledo strain are highly divergent. In fact, the restriction profile of the genome of the endothelial cell-tropic variant seems highly distinct from that of the parental strain. In conclusion, the degree of dissimilarity between the two genomes suggests that the endothelial cell-tropic variant of the Toledo strain could have originated from a recombination event.