Coestablishment of persistent infection and oncogenic transformation of hamster embryo cells by equine cytomegalovirus.

The study explores how equine cytomegalovirus (ECMV) infection can transform hamster embryo cells and establish a persistent infection that leads to cancerous growth.

Experimental Procedure and Results

• The researchers infected primary hamster embryo cells with UV-irradiated equine cytomegalovirus in vitro, which is a process conducted in a controlled environment outside a living organism.
• The result of the infection was that the cells were transformed, changing their morphology, losing their contact inhibition, increasing their saturation density, decreasing their generation time, and becoming immortal in culture. In essence, the cells adopted traits typically associated with cancerous cells.
• Three transformed cell lines, named EC-1 to EC-3, were independently cultivated from the focus of infection. The EC-2 and EC-3 cell lines were found to exhibit persistent infection, with 0.5 to 2% (EC-2) and 0.8 to 5% (EC-3) of the total cell populations producing infectious ECMV.
• All EC cell lines were found to cause cancer in healthy hamsters, and malignant fibrosarcoma cell lines were established from the resulting tumors. These transformed cell lines resisted further infection by ECMV and another virus, equine herpesvirus type 1 (EHV-1).

Evidence of Persistent ECMV Infection

• Even though the transformed cell line EC-1 and all tumor cell lines were not producing the virus, the researchers could still identify ECMV in the cell lines. The analysis of DNA reassociation found 8-32 ECMV genome equivalents per productive EC-2 cell and over 300 ECMV genome equivalents per productive EC-3 cell.
• Furthermore, the non-virus producing transformed cells and all tumor cell lines had small amounts of ECMV DNA sequences. Some of these sequences must be expressing because ECMV-specific polypeptides were found in all transformed and tumor cell lines.
• It’s also worth mentioning that the hamsters carrying tumors developed antibodies to ECMV. These antibodies could be identified by an ECMV plaque reduction assay.

Implications and Conclusion

• This study provides evidence that persistent infection with ECMV can transform non-cancerous cells into cancerous ones, which leads to the development of tumors in a living organism.
• The transformed cells exhibit typical characteristics of malignancy and the presence of ECMV DNA sequences, even in non-virus producing cells, demonstrates how the virus manipulates and persists within the host cells.
• Although this study used hamster embryo cells as a model, the results could have implications for understanding how other types of cytomegalovirus infections might similarly transform human cells and lead to cancer.