αCD20-IL-21 fusokine extends serum half-life of IL-21 and induces tumor regression in rituximab insensitive A20-hCD20 tumor model. (A) Serum clearance of human IL-21 after intravenous injections of αCD20-IL-21 fusokine or IL-21 in CD20-Tg BALB/c mice was assayed by an ELISA. N = 3/group. (B and C) Tumor growth (B) and Kaplan-Meier survival curves. (C) of CD20-Tg mice bearing A20-hCD20 tumors treated with 2 µg/mL αCD20-IL-21 fusokine, the equivalent molar concentration of αCD20-IgG1, and/or IL-21, or PBS. N = 10/group.