Detection of a circulating tumor-associated antigen with a murine monoclonal antibody, LISA 101, selected by reversed indirect enzyme-linked immunosorbent assay.

In the presence of a characterized monoclonal antibody recognizing a soluble molecule, additional monoclonal antibodies reactive with unknown antigenic determinants on the molecule can be easily selected by reversed indirect enzyme-linked immunosorbent assay. A novel murine monoclonal antibody, LISA 101, was selected by reversed indirect enzyme-linked immunosorbent assay against soluble antigens, which exist in sera and in pleural effusions derived from lung adenocarcinoma patients and which bear determinants recognized by the previously characterized murine monoclonal antibody KL-6. Antigenic determinants recognized by the LISA 101 antibody appear to be sialylated carbohydrate in nature and different from those recognized by previously reported monoclonal antibodies against sialylated carbohydrates, such as NS 19-9, FH-6, and KL-6, suggested by competitive inhibition assay and immunostaining of tissues. A circulating antigen, LISA 1-6, was detected by a bimonoclonal bideterminant assay using immobilized LISA 101 antibody and enzyme-labeled KL-6 antibody. It was found that serum LISA 1-6 levels were elevated in 63% (25 of 40) of patients with lung adenocarcinoma and in 92% (11 of 12) of patients with pancreatic carcinoma, but only in 6.5% (2 of 31) of patients with benign lung diseases and in 7.1% (1 of 14) of patients with pancreatitis. The present observations indicate that the LISA 1-6 antigen may serve as a new tumor marker for adenocarcinomas of the lung and the pancreas. Additionally, the reversed indirect enzyme-linked immunosorbent assay may be a widely applicable method for selecting new monoclonal antibodies against as yet unknown antigenic determinants on soluble molecules.