BacMam transduction technology combines the ability of baculoviruses to maintain and amplify large gene inserts with the desirable post-translational characteristics of proteins expressed in mammalian cell lines. Improved versions of BacMam expression vectors demonstrate increased transduction efficiencies and wider ranges of permissible, mammalian host cells. BacMam technology has been used successfully in the fields of cell-based assays for drug discovery and for imaging of subcellular structures and functions. The development of a large-scale platform for the transient expression of recombinant proteins using BacMam transduction would significantly improve the current transient transfection methodology. We report our initial results obtained using BacMam constructs expressing a humanized rIgG. Serum-free suspension cultures of HEK-293 and CHO-S cells were cotransduced with BacMam viruses at total multiplicity of infection ratios between 10 and 20. Purified yields of 18.9 mg/L were obtained for shake-flask cultures of HEK-293 cells under nonoptimized conditions. These results illustrate the potential of the BacMam system to produce significant quantities of recombinant proteins in mammalian host cells…