In vitro CDC activity of patient 13 serum. The serum was collected (A) before infusion 1, (B) before infusion 2, and (C) before infusion 3 of 20 mg/m² KM871 doses. CDC analyses were performed in the presence of 0.001-10 µg/mL exogenous KM871 (solid circles) and the isotype matched control antibody KM966 (gray squares) on target SK-MEL-28 cells. High background cytolytic activity was observed due to the presence of circulating KM871 in the patient sera. Based upon ELISA pharmacokinetic measurements, the data were corrected for KM871 concentration for (D) before infusion 2 and (E) before infusion 3 CDC analyses. (F) High background CDC activity of patient serum was not present in the control Lewis Y system in the presence of increasing hu3S193 (solid circles with lines) and isotype control (circles with white dot) antibodies.