Abstract
A sensitive assay for antibody‐dependent cell‐mediated cytotoxicity (ADCMC) was developed utilizing serum from a patient with gestational choriocarcinoma and the ^3^H‐proline microcytotoxicity test for detection of destruction of monolayer target cells. Conditions for optimal expression of ADCMC were investigated using serum from this patient and skin fibroblasts from her husband and daughter as target cells with semi‐purified blood leukocytes from normal donors as effector cells. Factors critical for optimal expression of ADCMC in this assay are the selection of effector cell donors possessing high levels of activity in the presence of serum with known lymphocyte‐dependent antibody (LDA), the effector cell preparative technique, and incubation for up to 40 h. Tris‐NH~4~Cl lysis of red blood cells was found significantly to reduce effector cell activity. Under optimal conditions, the LDA titer of this patient's serum was >10^−4^. The sensitivity of the assay was confirmed by the detection of LDA activity of an anti‐blood‐group antibody at dilutions not demonstrating hemagglutination, and by the induction of ADCMC for blood group A antigen‐bearing target cells by normal sera of B and O blood groups. In a preliminary study of sera from 16 melanoma patients on the corresponding autologous tumor target cells, four had significant LDA. Further studies are under way to determine specificity, incidence, and relationship of LDA‐positive autologous sera to course of disease.