Three hybridomas producing monoclonal antibodies (IgG), reacting with components of the human mammary milk fat globule have been isolated. When tested for binding to a wide range of human cell lines and strains, all three antibodies show negative reactions with fibroblasts, lymphoblastoid cells, and a large number of epithelial cell lines of non-breast origin. Two of the antibodies (1.10.F3 and 3.14.A3) reacted with seven out of eight breast cancer lines tested, and with epithelial cells cultured from human milk. The other antibody (3.15.C3) reacted with only two of the breast cancer cell lines.

Two monoclonal antibodies, 3.14.A3 and 1.10.F3, raised against a delipidated preparation of the human milk fat globule and characterized as epithelium-specific (Taylor-papadimitriou et al., 1981) were assayed histologically, by an indirect immunoperoxidase technique, against formalin-fixed, paraffin-embedded, normal and tumour tissue sections, in order to establish their in vivo specificity. Both antibodies bound to less than 10% of the alveoli and ducts in the resting breast, but bound to all areas of alveoli, ducts and secretion in the lactating breast. Binding was to the luminal surface of the alveolar and ductal epithelium. Antibody 3.14.A3 showed positive reactions with each of 20 primary breast carcinomas tested, and with metastatic lesions in lymph nodes from six of these. Antibody 1.10.F3 also reacted with most of the primary carcinomas but not with those of the mucoid type nor with metastatic lesions in lymph nodes. When tested against a variety of normal tissues, 1.10.F3 bound only to the luminal epithelial surface of classically defined exocrine glands, to their associated ducts and to the collecting tubules of kidney and bronchioles of the lung. 3.14.A3 showed a similar pattern of binding to 1.10.F3 but also bound to sweat glands, the alveolar epithelium of lung and the luminal epithelium of the ductuli efferentes of the epididymis. The only tumours, other than breast, showing a positive reaction with the antibodies were adenocarcinomas of the lung, uterus and ovary.

Summary.-Monoclonal antibodies to epithelial -cell antigenic determinants, labelled with 1231 and 1251, were administered parenterally to immunodeficient mice bearing human tumours derived from a human cancer cell line. Anterior, posterior and lateral radioscans of the body were taken with a gamma scintillation camera at various times from immediately to 65 days after injection. Visual displays of the images were processed by standard computer techniques. The model used a human colon-cancer cell line, HT29, and the monoclonal antibody, AUA1, which is specific to an epithelial proliferating antigen. Tumour detection was achieved in all the mice. The smallest tumour detectable appeared to be about 1 mm in diameter. The degree of antibody uptake in a tumour depended on its size and the blood supply of its surrounding tissues We believe that the technology and skills are now available for accurate radioimmunodetection of cancer in man.

A monoclonal antibody (AAP1) to human intestinal alkaline phosphatase (ALP) was produced by immunizing a mouse with D98/AH‐2 (HeLa) cells, which produce the enzyme ectopically. The antibody, which did not inhibit enzyme activity using p‐nitrophenyl phosphate as the substrate, was of the IgG2A class and did not show complement‐dependent cytotoxicity. In trace binding assays AAP1 bound only to cells that expressed an intestinal‐like form of human ALP, including some human intraspecific (D98/AH‐2 × human lymphocyte or fibroblast) hybrids. Immuno‐precipitation of immune complexes from cell‐free extracts of D98/AH‐2 cells, using protein A containing 5. aureus and AAP1 antibody, resulted in precipitation of all the ALP activity. The precipitated material had a subunit molecular weight of 80,000 daltons, as estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. In non‐denaturing conditions, AAP1 antibody prevented the migration of ALP activity into the gel when cell‐free extracts were made from human adult or fetal intestine, or D98/AH‐2 cells. Similarly, AAP1 could be used to precipitate ALP activity from these extracts but not from extracts of human liver, kidney or placenta.