Marianne L. Egan

Radioimmune assay of carcinoembryonic antigen

Abstract A double antibody technique for the detection and quantitation of carcino-embryonic antigen (CEA) in nanogram quantities is described. This antigen is characteristic of adenocarcinoma of digestive organs. The assay employs three γ-emitting radioisotopes. A computer program has been written to enable rapid calculation of results. The assay is of value in following the isolation and characterization of CEA and may also prove useful as a test for the detection of certain forms of cancer.

Isolation and characterization for carcinoembryonic antigen

Abstract Carcinoembryonic antigen (CEA) has been isolated from several tumors of the digestive tract. Comparisons of the products with one another and with CEA obtained from Dr. Gold have been made. CEA of two molecular sizes (6·8 S and 10·1 S) has been obtained, but the 6·8 S material is the one usually found. Considerable variation in yield has been observedp indicating that tumorsp may differ markedly in their content of CEA. Comparison of CEA isolated by Dr. Gold with material prepared by us has shown the two products to be immunologically indistinguishable.

The chemistry of carcin oembryonic antigen

The structure of carcinoembryonic antigen is being determined as an approach to greater diagnostic specificity in the radioimmune assay. Examination by combined gas chromatography–mass spectrometry of derivatized saccharides from CEA has given a general outline of its carbohydrate structure. Sialic acid and fucose were completely destroyed, and galactose and mannose were partially destroyed by a single periodate treatment. Serial periodate oxidation (Smith degradation) destroyed additional amounts of galactose and mannose, as well as significant amounts of N‐acetylglucosamine. Antigenic activity persisted, indicating that the residues destroyed played little, if any, part in the antigenicity of CEA.

Detection of circulating tumor antigens.

A wide variety of malignancies have associated tumor antigens. Two which have proven useful in the clinical detection and management of cancer are alphafetoprotein (AFP) and the carcinoembryonic antigen (CEA). These materials have been determined both by radioimmunoassay and by a newer technique employing enzymes to replace radioisotopes as markers. The interpretation of these immune assay results and the factors governing the shape of the standard curve are discussed. The advantages of 57Co over 22Na as a volume marker in radioimmunoassay are presented. Cancer 40:458–466, 1977.

57Co: a volume marker for the triple-isotope, double-antibody radioimmune assay.

Abstract A prototype triple-isotope, double-antibody radioimmune assay for the analysis of large numbers of samples on a routine basis has previously been reported (Egan et al., 1972). The major advantage of this technique is that almost instaneoeous computer calculations replace the tedious and often error-prone step of washing the precipitate as the last step in the assay procedure. The 22Na used as a volume marker in the original procedure can be replaced by 57Co provided a chelating agent is present to prevent its adsorption to serum proteins. Because of its decay pattern, 57Co can be counted with greater efficiency with less overlap into other channels. Other features which recommend its use are the lower gamma radiation level which results in reduced exporse of personnel to radioactivity.

Radioimmune assay for the diagnosis of human cancer

Radioimmune assay techniques based on tumor‐associated antigens are finding application in the diagnosis of human cancer. There are two basic forms of radioimmune assay. One is based on complete saturation of the antibodies with antigen, and the other is based on a progressive filling of the antibody binding sites. The specificity and sensitivity of any assay depend primarily on the antiserum used. For high sensitivity a high binding constant for the antibody is important. The preparation of a suitable antiserum is described. Specificity in a radioimmune assay is never absolute, but may be improved through knowledge of the structure of the antigen. These principles are illustrated with the carcinoembryonic antigen.

Isolation of carcinoembryonic antigen by an improved procedure

Abstract An improved procedure for the isolation of carcinoembryonic antigen (CEA) has been developed. Lengthy dialysis, ultrafiltration and lyophilization steps following perchloric acid extraction are replaced by a simple ethanol precipitation of the CEA prior to the Chromatographie purification steps. Chemical and immunochemical characterization of CEA prepared by this procedure showed no significant differences compared to CEA prepared by the more lengthy procedure not using ethanol precipitation.