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

Abstract

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.

Human Cytomegalovirus UL131-128 Genes Are Indispensable for Virus Growth in Endothelial Cells and Virus Transfer to Leukocytes

“…In addition, both laboratory strains, currently considered to be Huv Ϫ Leuk Ϫ , were shown to be able to reacquire both properties, and thus to become Huv ϩ Leuk ϩ after adaptation to growth in HUVECs, as recently reported (9,10). In parallel, the Toledo strain (originally obtained from E. Gonczol, Wistar Institute), which is considered a low-passage wild-type HCMV strain, could never be adapted to growth in ECs despite repeated attempts and was thus considered Huv Ϫ Leuk Ϫ , whereas the reported EC-tropic variant (18) of Toledo was shown to be a different virus strain that possibly originated from a recombination event (2).…”

The pentameric complex of human Cytomegalovirus: cell tropism, virus dissemination, immune response and vaccine development

“…These results suggested that it was probably only minor variations in the viral genome of the two strains that were responsible for the loss/reacquisition of the two biological properties. In addition, the Toledo strain, commonly considered a prototype of wild-type strains, was shown to lack both EC-and leuko-tropism [51].…”

“…At the beginning of this study, the following findings were critical in directing interest to the ULb¢ region as a prime candidate: (i) the loss of EC-and leuko-tropism in the laboratory strains, Towne and AD169, was associated with the loss of the great majority of ULb¢ [52,53]; (ii) the low-passaged strain Toledo, which was shown to be tropism-deficient [51], was found to display an inversion of ULb¢ [53]; and (iii) extensive propagation of EC-and leuko-tropic clinical isolates in HELFs was found to be consistently associated with the selection of tropism-deficient variants [37,45,[54][55][56] in the presence of only minor variations in the relevant viral genomes.…”

Coding potential of laboratory and clinical strains of human cytomegalovirus

“…Like AD169, it was passaged extensively in fibroblasts as a vaccine candidate. Toledo, isolated from the urine of a congenitally infected child (12); FIX (VR1814), isolated from a pregnant woman with a primary HCMV infection (13,14); PH, isolated from a bone marrow transplant patient (15,16); and TR, an ocular isolate from an AIDS patient with retinitis (17) (19).…”