In vitro IFN-α activity. Specific activities (IU/pmol) measured using (A) cell-based reporter gene assay and (B) in vitro viral protection assay with EMC virus and A549 cells. The activity of known concentrations of each test article was extrapolated from a rhIFN-α2b standard curve. In vitro lymphoma proliferation assays were performed using (C) Daudi and (D) Jeko-1 cells. Cultures were grown in the presence of increasing concentrations of 20-2b (●), 734-2b (■), v-mab (○), v-mab plus 734-2b (□), PEGASYS (▾), PEG-Intron (▴), or 1R-2b (▿), and the relative viable cell densities were measured with MTS. The percentage of the signal obtained from untreated cells was plotted versus the log of the molar concentration. Dose-response curves and EC₅₀ values were generated using Prism software. Error bars represent SD.