Retroviral aspects of the characterisation of avian and mammalian cell substrates.

There have been no reported incidents of adventitious retroviral infection of cell lines used for the production of vaccines and other biologicals. However, due to the unique molecular biology of retroviruses, cell lines may contain endogenous retroviral genomes and these can give rise to defective retroviral particles, e.g. murine hybridomas and CHO cells. Recently, a similar situation was reported for a cell substrate in use for decades for vaccine production, namely chick embryo fibroblasts, and this raised some concern regarding the safety of these vaccines.