Production and characterization of mouse monoclonal antibodies to human bladder tumor-associated antigens

Monoclonal antibodies (McAbs) to human bladder carcinoma were generated by fusion of NS-1 mouse myeloma cells with spleen cells from BALB/c mice immunized with either cultured human bladder cancer cells or cells obtained from a fresh surgically removed bladder tumor. Four hybridomas which reacted strongly with bladder tumor cells and not to normal skin fibroblasts or urothelial cells were identified and cloned by limiting dilution to obtain monoclonality. One McAb, 3G2-C6, raised with cultured tumor bladder cells MGH-U1 (EJ) as the immunogen reacted more strongly to the bladder tumor lines tested than any of the other McAbs resulting from various fusion experiments. Hybridoma 3G2-C6 was found to secrete murine immunoglobulin G1 and to produce high titer ascites fluid when grown in BALB/c mice. Results from quantitative enzyme-linked immunosorbent assays on a panel of more than 35 cell lines demonstrated that McAb 3G2-C6 reacted with several bladder tumor cell lines 50 to 90 times more than with normal transitional urothelium. Two kidney and two testicular tumor lines also bound 10 times more 3G2-C6 than with normal cells. The 3G2-C6 antigen was only marginally detected on a number of other cancer and noncancerous cells tested such as breast and lung tumor cells, melanoma, fetal cells, and peripheral blood lymphocytes. To identify the antigen 125I-labeled membrane components from MGH-U1 cells were extracted with detergent, immunoprecipitated with Protein-A bound 3G2-C6, and analyzed by sodium dodecyl sulfate-gel electrophoresis. This revealed that McAb 3G2-C6 binds to a Mr 90,000 cell surface component. Indirect immunofluorescence microscopy with fluorescein isothiocyanate-anti-mouse immunoglobulin G also identified the antigen on the surface of cultured and fresh tumor cells and detected the antigen on 16 of 17 Grade 3 bladder tumor specimens as well as on some kidney and testicular tumor cells. This study confirms the potential of the hybridoma technique for producing McAbs capable of identifying tumor associated antigens which may be useful in the diagnosis and treatment of bladder cancer.