MGAH22-induced IL-6 release in vivo and in vitro. (a) Serum IL-6 levels in single- and repeat-dose studies in cynomolgus monkeys. When MGAH22-treated groups were compared with RES120-treated groups (single-dose study) or with vehicle control group (repeat-dose study), there were no statistically significant changes in IL-6 levels. (b) In vitro IL-6 release from human peripheral blood mononuclear cells (PBMCs) incubated with the indicated antibodies on uncoated plates or plates coated with recombinant HER2 antigen. Statistically significant changes in IL-6 levels (P = 0.0313) were noted for MGAH22 compared with RES120 at concentrations of 1 or 10 μg/mL in the presence of immobilized HER2, but there were no significant differences between MGAH22 and trastuzumab. Data are presented as mean ± standard error of the mean. IL-6, interleukin-6; MGAH22, chimeric anti-HER2 monoclonal antibody with an optimized Fc domain; RES120, chimeric anti-HER2 monoclonal antibody with wild-type human immunoglobulin G 1 Fc domain.