Characterization of a new monoclonal antibody to a cell surface antigen on colorectal cancer and fetal gut tissues.

Murine hybridoma were raised against the human colon carcinoma cell line CL-187. One clone was found to secrete a monoclonal antibody (ND-1) that recognizes a large external antigen (LEA) on human colon carcinoma cells. With indirect immunofluorescence on formaldehyde-fixed cells, more than 90% of the human colorectal carcinoma cell lines tested expressed LEA. Almost all of the 46 human noncolorectal and nonhuman cell lines tested did not express LEA, including cancer cell lines from other endodermally derived tissues. Staining of frozen sections from human colorectal tumors, noncolorectal tumors, normal adult, and normal fetal tissues showed expression of the antigen on colorectal cancer tissue, fetal colon, and fetal biliary epithelium. LEA can also be detected in the serum and ascites of colorectal cancer patients. Double indirect immunofluorescence with rabbit anti-carcinoembryonic antigen (CEA) antibody and ND-1 monoclonal antibody on a human colorectal carcinoma cell line showed that LEA is distinct from CEA. Physicochemical analysis of LEA showed that it has a large molecular weight, is resistant to extraction from the cell surface, and that sialic acid is an important component of the antigenic site. Because of the specificity for colorectal cancer tissue along with certain biochemical properties, LEA appears to be unique when compared with other tumor-associated antigens. Further research is needed to define the clinical usefulness of LEA in either the diagnosis or treatment of colorectal carcinoma.