Membrane-associated antigens on tumor cells from transitional-cell carcinoma of the human urinary bladder. I. Immunological characterization by xenogeneic antisera.

An antiserum was raised in rabbits by immunization with a human tumor cell line, T-24, derived from transitional cell carcinoma (TCC) of the urinary bladder. The specificity of the IgG fraction was assessed by antibody-dependent cellular cytotoxicity (ADCC), using purified blood lymphocytes from healthy human donors as effector cells and seven human cell lines as target cells (T-24 and two additional TCC-lines, two normal urothelial lines, one colon carcinoma and one malignant melanoma). The IgG induced strong lysis of all seven target cell types. However, lysis of the five urothelial lines was significantly stronger than that of the control tumors. Conversely, antisera to either of the control tumors induced a significantly stronger lysis of the homologous tumors than of the urothelial cells. All antisera contained antibodies to fetal bovine serum but removal of these by absorption did not change the specificity of the ADCC reactions. When the anti T-24 serum was exhaustively absorbed with glutaraldehyde-fixed spleen homogenate, the cytotoxicity to the control tumor targets was abolished. Although absorption reduced the antibody titer of the IgG preparation, ADCC to the TCC targets remained at a high level. There was no difference in the degree of lysis of the three TCC targets. Lysis of the two target lines from normal urothelium was slightly lower than that of the tumor cells. The results indicate that the anti-TCC serum contained antibodies to one or several antigens shared by five urothelial cell lines but not by the control tumors. Whether or not it also contained antibodies to TCC-associated antigens remains to be established. The molecular basis for these findings will be given in the accompanying paper.