Human telomerase reverse transcriptase-immortalized MRC-5 and HCA2 human fibroblasts are fully permissive for human cytomegalovirus

MRC-5 cells are a well-characterized human diploid fibroblast cell line approved for vaccine production and favoured for the routine propagation of human cytomegalovirus (HCMV). Ectopic expression of telomerase in fibroblasts is capable of overcoming replicative senescence induced by telomere shortening. Following delivery of the hTERT gene to MRC-5 cells using a retrovirus vector three clones were generated that (i) expressed functional telomerase activity, (ii) exhibited telomere extension and (iii) were sustained for > 100 population doublings. Immortalized MRC-5-hTERT and also HCA2-hTERT human fibroblasts were both fully permissive for HCMV as determined by plaque assay, studies of virus growth kinetics and measurement of virus yields. Furthermore, telomerase-immortalized HCA2 cells proved capable of supporting the stable maintenance of an EBV-based episomal vector with efficient transgene expression when driven by the HCMV immediate early promoter. An indicator cell line suitable for the efficient detection of HCMV infection was also generated using an episome containing a reporter gene (lacZ) under the control of the HCMV β-2.7 early promoter. Telomerase immortalization of human fibroblasts will thus facilitate the growth and detection of HCMV and also the generation of helper cell lines for the propagation of HCMV deletion mutants. Immortalization of fibroblasts by telomerase does not affect cell morphology or growth characteristics. The MRC-5-hTERT clones may therefore be suitable for additional applications in virology, cell biology, vaccine production and biotechnology.