Table VIII presents a short résumé on cell lines of biotechnological interest which contain endogenous viruses or latent proviruses and are therefore producers or potential producers of these viruses. Whereas plasmacytomas, hybridomas, CHO and BHK cells contain endogenous viruses which integrated into the genome Table VII . Characteristics of C-type particles isolated from CHO cells (Dinowitz et al., 1992) Reversed transcriptase activity Detected in highly concentrated (4000-7000-fold) culture fluids from some cell lines; Mn 2+ preferring.