Status and transcriptional activity of a bovine-papillomavirus-I-based expression vector in a recombinant production cell line.

We have analysed the status and transcriptional activity of the bovine papillomavirus-I (complete BPV-I genome)-based expression vector pCES in CI27i-cell-line-derived 3TI cells used for the industrial production of recombinant human erythropoietin (rhuEpo). Complete tandem head-to-tail integration of about 600 vector copies at a single site of the cellular genome was observed. Deletions, insertions or rearrangements of pCES-specific sequences or extrachromosomal copies of vector sequences were not detected. Transcriptional analyses demonstrated that rhuEpo was abundantly expressed. BPV-I early transcription was detected, as expected from a BPV-I-transformed cell line; however, compared with the mouse metallothionein-I-promoter-driven rhuEpo-specific transcription, it was very weak. Late BPV-I transcription was also not detected in 3TI cells under conditions of large-scale rhuEpo production. Therefore this expression system proved to be safe and suitable for the production of rhuEpo.