Testis imaging with 111In-labeled anticarcinoembryonic antigen monoclonal antibody: identification of carcinoembryonic antigen in normal germ cells.

A monoclonal antibody to carcinoembryonic antigen (CEA) labeled with 111In (Indacea) was used to image tumors in patients with colorectal cancer. The anti-CEA antibody has a high affinity (2.6 X 10(10) M-1) for CEA and does not cross-react with normal cross-reacting antigen, biliary glycoprotein-1, or tumor-extracted, CEA-related antigen. During the course of these studies, it was noted that a significant number of male patients (20 of 27, 74%) showed uptake of Indacea in the testes. In order to determine if the Indacea uptake was specific, 20 testicular specimens were analyzed by immunohistological methods using five different anti-CEA CEA monoclonal antibodies recognizing five different epitopes on CEA. In 18 cases (90%) germ cells were uniformly stained by all five antibodies. Fresh frozen testis tissue was homogenized in water and precipitated with 1.0 M perchloric acid. The supernatant contained a CEA-like material as measured by an enzyme immunoassay specific for CEA. The same supernatant was radiolabeled with 125I and immunoprecipitated with anti-CEA monoclonal antibodies. Sodium dodecyl sulfate:polyacrylamide gel electrophoresis of the immunoprecipitates revealed a single species (Mr 180,000) which was indistinguishable from CEA. This study documents the first description of CEA in the germ cells of normal testis. The CEA in the testis was accessible to circulating monoclonal antibodies in the majority of male patients tested.