SPECIFIC INTERFERENCE WITH THE DETERMINATION OF THE TUMOR-ASSOCIATED GLYCOPROTEIN-72 BY HUMAN ANTIIDIOTYPIC ANTIBODIES FORMED AFTER TREATMENT WITH THE ANTI-TUMOR-ASSOCIATED GLYCOPROTEIN-72 ANTIBODY B72.3

Recorded concentrations of the tumour-associated glycoprotein 72 (TAG- 72) in ovarian cancer patients after repeated infusion of the antibody B72.3 were found to be falsely elevated when measured with an homolog ous immunometric assay involving the anti-TAG-72 antibody B72.3 (Test 1), or with an heterologous assay involving CC49 capture and B72.3 det ector antibodies (Test 2). Test 1 yielded falsely elevated values up t o 10(4) kU/l. Test 2 gave slightly false positive elevations up to 10( 2) kU/l for only some of the samples with very high false-positive val ues in Test 1. The interfering serum components bound to Protein G-Sep harose and could be precipitated with perchloric acid or by heating se rum samples to 100 degrees C. Addition of non-specific murine immunogl obulins only partly suppressed false-positive values in both tests. Ou r results suggest that this interference is caused by human anti-B72.3 IgG induced by B72.3 application, which to some extent specifically b inds to determinants of the B72.3 antibody. Heat extraction of serum s amples effectively eliminated interferences probably caused by anti-id iotypic antibodies, but did not affect real TAG-72.