Direct cytotoxic potential of αCD20-IL-21 fusokine in DLBCL and MCL cell lines and primary tumors. (A) DLBCL (RCK8) and MCL (Mino) cell lines sensitive to IL-21 alone, (B) MCL cell lines (G-519, L-128, UPN-1, and Jeko-1) resistant to IL-21 alone, and (C) primary B-cells isolated from lymphoma patients were incubated with αCD20-IL-21 (1 µg/mL) or the molar equivalent of IL-21, αCD20-IgG1, or rituximab for 72-96 hours, followed by staining with YO-PRO-1 and PI to measure cell death. Cells positive for both dyes were considered dead. Data presented as mean ± SD. *P < .05. FL, follicular lymphoma; MCL, mantle cell lymphoma; MZL, marginal zone lymphoma.