Cytokine levels in cynomolgus monkeys receiving CLL1/CD3H (HA) and CLL1/CD3L (LA). (A) G-CSF, (B) tumor necrosis factor-α (TNFα), (C) IL-2, and (D) IL-6. Cytokine release typically occurred within 2 to 6 hours of administration of either molecule and was markedly increased in those animals that received 0.5 mg/kg CLL1/CD3H compared with those that received CLL1/CD3L. All animals that required unscheduled euthanasia had comparatively elevated cytokine levels compared with those that survived to scheduled necropsy. The one animal that received 0.5 mg/kg CLL1/CD3L and required unscheduled necropsy had perimortem increases in G-CSF, IL-6, and other innate cytokines such as MCP-1 (data not shown).