Potential for artifacts in monitoring for the detection of tumor associated antigens (TAG-72 and CEA) in serum from patients undergoing MAb-based diagnostic and therapeutic protocols

The administration of murine monoclonal antibodies (MAbs) induces, in many patients, an immunological response represented by the development of human anti-mouse antibodies (HAMA). HAMA have been previously shown to interfere in some assays for the detection of CEA, as well as other non tumor related analytes. The present study was performed to determine whether the CA 72-4 assay is affected by the presence of HAMA, and to establish conditions capable of overcoming this artifact. Serum samples obtained from 8/9 patients entered into a therapeutic protocol using ¹³¹I-labeled MAb B72.3 showed the development of apparently high levels of TAG-72 during the clinical follow-up concurrent with the appearance of elevated titers of HAMA. Heat treatment at 90°C at pH 5.0 sodium acetate, previously reported as a method of abolishing HAMA interference without affecting CEA levels, resulted in a considerable loss of detectable TAG-72. However, treatment of these samples at 90°C in pH 6.5 Bis Tris abolished the artifact due to HAMA and resulted in the reversion of reported TAG-72 levels to those observed prior to any MAb administration. As the use of murine MAbs, for both diagnostic and therapeutic applications continues to expand, the identification of this artifactual increase in reported antigen levels due to the development of HAMA has become an important factor in the use of tumor markers, e.g. TAG-72 and CEA, in the follow-up of carcinoma patients.