Figure 4.

(A) To determine whether the correlation between ADCC and antigen expression was due to cellular stress imparted by the binding of antibody to GD2, we examined the killing of neuroblastoma and Ewing's sarcoma lines opsonized with ch14.18/CHO (20 μg/mL). High levels of spontaneous cell death were only seen in the GD2⁺ neuroblastoma lines, despite GD2 expression being higher in some of the Ewing's sarcoma lines (n = 9–42, depending on cell line, ****p = <0.0001). (B) To confirm that killing of neuroblastoma cell lines was not simply due to the binding and activation of residual complement in the serum, we compared the effects in the presence or absence of serum, and saw no significant difference (n = 5). The data is expressed as the “% of maximum killing” and represents the ⁵¹Cr release from opsonized cells incubated in medium for 4 h as a percentage of the ⁵¹Cr release of the same cells treated with Triton X, minus the paired result from cells treated with control antibody.