Closed Hollow-fiber Bioreactor: A New Approach to Retroviral Vector Production

Background: The ability to obtain high-titer and large quantities of retroviral vector production in a 'closed' system would have profound implications in clinical and experimental gene therapy. Methods: We studied the cell growth and vector production of three retroviral packaging cell lines in a variety of conditions using hollow-fiber bioreactors designed as an 'artificial capillary system' (ACS) and enhanced with the application of a hermetically sealing device for sterile welding of connecting plastic tubings. Vector titer, fetal bovine serum (FBS) concentration, volume and the duration of productivity were assessed to optimize vector production. Results: In this pilot study, we observed that retroviral vector production (frozen-and-thawed) from cultures containing as low as 2.5% FBS yielded titers up to 2.2 × 10⁷ cfu/ml, 14.4-fold higher than titers obtained from control dish cultures. Up to 3 liters of vector supernatant were generated during a 2-month large-scale production run. There was a potential to double this volume of higher-titer supernatant by increasing the frequency of harvest. It seemed that a lower metabolic rate (i.e. lactate production) in the packaging cell culture was associated with higher vector producing ability. Conclusions: These data demonstrated the feasibility of producing retroviral vector with enhanced titers and clinically useful quantities in a 'closed' ACS. Thus a new approach for large-scale retroviral vector production is developed.