This study demonstrates the novel use of the HeLaS3 human tumor cell line for propagating ONYX-411, a recombinant oncolytic adenoviral vector. HeLaS3 cells enabled high levels of vector production without the risk of generating vector recombinants, which is possible with HEK293 cells. The development of a high-cell-density perfusion process using ATF technology yielded production levels as high as 6 × 1011 vp/mL, which was approximately sevenfold greater than the titers achieved in fed-batch bioreactors. Several experiments were performed at the bench (15 L) and pilot (70 L) scales to demonstrate the robust and scalable nature of this industrially relevant technology. © 2004 Wiley Periodicals, Inc.