Absence of MIF delays CLL development and prolongs overall survival. (A) WBC (top panel) and malignant (IgM⁺CD5⁺) B cells (bottom panel) over time in TCL1^+/wtMIF^wt/wt (●) and TCL1^+/wtMIF^−/− (○) mice. Y-axis modified to accommodate high cell counts in leukemic mice. TCL1^+/wtMIF^wt/wt mice have higher WBC and malignant B cells than TCL1^+/wtMIF^−/− mice. (B) Incidence of CLL over time. TCL1^+/wtMIF^wt/wt mice develop leukemia with a WBC > 20 × 10⁹/L more frequently than TCL1^+/wtMIF^−/− mice (P = .02, log rank test). Y-axis truncated at 50% because not all animals develop WBC > 20 × 10⁹/L. (C) Increased spleen and liver weight in TCL1^+/wtMIF^wt/wt versus TCL1^+/wtMIF^−/− mice at month 12. (D) Prolonged overall survival of TCL1^+/wtMIF^−/− (n = 60) versus TCL1^+/wtMIF^wt/wt mice (n = 60). The difference of 80 days was significant with P = .0003 (log-rank test). + indicates censored events (not caused by CLL).