RAPID DETECTION OF ANTI-OKT3 ANTIBODIES WITH THE TRANSTAT ASSAY

The ability to successfully reuse OKT3, a mouse monoclonal antibody, is dependent upon the host's response to the antibody during and following the first treatment course. Antiidiotypic and/or antiisotypic antibodies may develop after exposure to OKT3. Antiidiotypic antibodies will bind OKT3, rendering it ineffective, while antiisotypic antibodies do not influence the efficacy of OKT3. A new membrane-based immunoassay, Transtat OKT3 (Sangstat Medical Corp, Menlo Park, CA) detects anti-OKT3 antibodies in less than 15 min. It allows simultaneous detection of antiidiotype and antiisotype antibodies. A total of 180 serum samples were initially analyzed by ELISA; results were negative, low-titer (1:100), or high-titer (greater-than-or-equal-to 1:1000). Retrospectively, these same samples were analyzed by Transtat for both anti-OKT3 (idiotype) and IgG2a (isotype). A total of 109 samples of 180 (60.6%) tested negative by ELISA and Transtat, while 71 (39.4%) tested positive. Of the negative samples by ELISA, 98 of 109 (89.9%) also tested anti-OKT3-negative by Transtat. Of the 109 specimens that were anti-OKT3 negative by Transtat, 98 (89.9%) tested negative by ELISA. There were 22 discrepant samples between the two methods; all were low-titer-positive (ELISA and Transtat). The 71 positive ELISA samples consisted of 53 low-titer (1:100) and 18 high-titer (greater-than-or-equal-to 1:1000), while the 71 anti-OKT3 positive Transtat samples consisted of 44 low-titer (1:10) and 27 high-titer (1:50). Sixty of 71 (84.5%) ELISA-positive samples were also positive by Transtat. Similarly, 60 of 71 (84.5%) Transtat-positive samples were also positive by ELISA. Of 71 patient samples positive for anti-OKT3 antibodies, 63 had an antiisotypic component present by Transtat. In conclusion, the Transtat OKT3 assay for measuring OKT3 and IgG2a antibodies offers a rapid and accurate assay for OKT3 monitoring.