Production of recombinant vesicular stomatitis virus-based vectors by tangential flow depth filtration

Cell culture-based production of vector-based vaccines and virotherapeutics is of increasing interest. The vectors used not only retain their ability to infect cells but also induce robust immune responses. Using two recombinant vesicular stomatitis virus (rVSV)-based constructs, we performed a proof-of-concept study regarding an integrated closed single-use perfusion system that allows continuous virus harvesting and clarification.

Using suspension BHK-21 cells and a fusogenic oncolytic hybrid of vesicular stomatitis virus and Newcastle disease virus (rVSV-NDV), a modified alternating tangential flow device (mATF) or tangential flow depth filtration (TFDF) systems were used for cell retention. As the hollow fibers of the former are characterized by a large internal lumen (0.75 mm; pore size 0.65 μm), membrane blocking by the multi-nucleated syncytia formed during infection could be prevented. However, virus particles were completely retained. In contrast, the TFDF filter unit (lumen 3.15 mm, pore size 2–5 μm) allowed not only to achieve high viable cell concentrations (VCC, 16.4–20.6×10⁶ cells/mL) but also continuous vector harvesting and clarification. Compared to an optimized batch process, 11-fold higher infectious virus titers were obtained in the clarified permeate (maximum 7.5×10⁹ TCID₅₀/mL).

Using HEK293-SF cells and a rVSV vector expressing a green fluorescent protein, perfusion cultivations resulted in a maximum VCC of 11.3×10₆ cells/mL and infectious virus titers up to 7.1×10¹⁰ TCID₅₀/mL in the permeate. Not only continuous harvesting but also clarification was possible. Although the cell-specific virus yield decreased relative to a batch process established as a control, an increased space-time yield was obtained.