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Monoclonal Antibody Recognizing a Carcinoembryonic Antigen Epitope Differentially Expressed in Human Colonic Carcinoma versus Normal Adult Colon Tissues¹

Departments of Tumor Biology [H. Z. Z., J. C. C.] and Anatomic Pathology [N. G. O., J. G. B.], The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030

Murine hybridomas were generated against purified carcinoembryonic antigen (CEA), and their monoclonal antibodies (MAb) were assayed for their ability to recognize specific CEA epitopes. One of the MAb, designated 7F, was found to recognize an epitope of CEA that was expressed in human colonic carcinoma tissues but not in normal colonic tissues. When extracts of 13 colonic carcinoma tissues and 9 normal colonic tissues were examined with the Western blot technique using MAb 7F, 11 colonic carcinoma tissues (85%) reacted with 7F, but none of the 9 normal colonic tissues (including many obtained from the areas adjacent to the colonic carcinomas) did. Western blot analysis indicated a M_r 180,000 band in 11 of 13 (85%) colonic carcinoma extracts. The limit of detectability of CEA was 0.5 µg/lane. According to immunohistochemical tochniques, 16 of 18 (89%) formalin-fixed paraffin-embedded sections of colonic carcinomas reacted with MAb 7F, whereas 9 of 9 (100%) frozen sections of colonic carcinomas reacted with the antibody. Of the 32 paraffin-embedded and frozen sections of normal colonic tissues examined, none showed any reactivity with MAb 7F. MAb 7F did not react with nonspecific cross-reacting antigen either. This antibody has been examined for its usefulness in detecting CEA in suspension and has been found to work both in sandwich enzyme-linked immunosorbent assays and in sandwich radioimmune assays. The detection of CEA in colon tumors but not in normal colonic tissues may be attributed to two possible explanations. It is possible that the level of CEA expression in normal colonic tissue is below the sensitivity of the assays employed. Alternatively, MAb 7F may recognize a "specific" epitope of CEA which was found in colon tumors but not in CEA of normal colonic tissues. At the present time, it is not possible to discern between these two possibilities. Nevertheless, MAb 7F was capable of detecting the differential expression of CEA in colonic carcinomas and, therefore, may be useful for the immunodiagnosis, radioimaging, and immunotherapy of colon cancer.

¹ This project was supported by the University Cancer Foundation Grants 175409 and 174391 of The University of Texas M. D. Anderson Cancer Center in Houston, by Korea Green Cross Foundation Grant 170366, and by The Council for Tobacco Research—USA, Inc. Grant 2264M.

² To whom requests for reprints should be addressed, at The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030.

Received 9/13/88. Revised 1/27/89. Revised 6/12/89. Accepted 7/21/89.

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