Comparison of the optimized expression vectors for transient production in HEK293-6E cells. Two pCMV-oriP1 and pCSE vectors expressing the CD30 specific antibody scFv-Fc-4E3 and the corresponding immunoRNase, respectively, as well as the pCSE2.5-hIgG1-XP vector that expresses only the hIgG1-Fc fragment were transiently transfected into HEK293-6E cells in 25 mL scale and shake flasks. After 48 h one volume fresh medium and 0.5% tryptone TN1 was added. After 5 days additional 0.5% TN1 was fed. A) Volumetric yields were determined by gel densitometry from supernatants. B) Transfection efficiency was measured by co-transfection with YFP reporter plasmid (1/20 of the total plasmid DNA) using flow cytometry. C) Viability of the cells was also measured by flow cytometry with PI staining.