COW MULTIPLICITY INFECTION OF INSECT CELLS WITH A RECOMBINANT BACULOVIRUS - THE CELL YIELD CONCEPT

In vitro infection of insect cells with baculoviruses is increasingly considered a viable means for the production of biopesticides, recombi nant veterinary vaccines, and other recombinant products. Batch fermen tation processes traditionally employ intermediate to high multiplicit ies of infection necessitating two parallel scale-up processes-one for cells and one for virus. In this study, we consider the use of multip licities of infection as low as 0.0001 plaque-forming units per cell, a virus level low enough to enable infection of even large reactors (e .g., 10 m(3)) directly from a frozen stock. Using low multiplicities i n the Sf9/beta-gal-AcNPV system, recombinant protein titers comparable with the maximum titer observed in high multiplicity infections were achieved. Cultures yielding the maximum titer were characterized by re aching a maxim um cell density between 3 and 4 x 10(9) cell L(-1). Thi s optimal cell yield did not depend on the multiplicity of infection, supporting the existing view that batch cultures are limited by availa bility of substrate. Up to a certain cell density, product titer will increase almost linearly with availability of biocatalyst that is, cel ls. Beyond this point any further cell formation comes at the expense of final product titer. Low multiplicity infections were found not to cause any significant dispersion of the protein production process. He nce, product stability is not a major issue of concern using low multi plicities of infection. The sensitivity to initial conditions and dist urbances, however, remains an issue of concern for the commercial use of low multiplicity infections. (C) 1996 John Wiley & Sons, Inc.