Anti–CD20-hIFNα fusion protein has proapoptotic activity against the human B-cell lymphoma Daudi. (A) Daudi lymphoma cells were incubated with various concentrations of the indicated proteins for 72 hours. Staining with annexinV-FITC and PI was performed to distinguish necrotic (annexin⁻PI⁺), early apoptotic (annexin⁺PI⁻), and late apoptotic (annexin⁺PI⁺) cell populations. The percentage of total apoptotic cells was quantified for each sample as the sum of early apoptotic and late apoptotic cells. Experiments were performed in triplicate, and error bars indicate mean ± SD. *P = .001. **P = .003.