New crossmatch technique eliminates interference by humanized and chimeric monoclonal antibodies

Humanized and chimeric antilymphocyte antibodies (Ab) are used to prevent and treat rejection and for treatment of human disease. Rituximab (RIT, anti-CD20), daclizumab (DAC; anti-CD25), alemtuzumab (ALE; anti-CD52), or infliximab (IFX) may interfere with Ab detection methods such as complement-dependent cytotoxicity (CDC) and flow cytometric crossmatch (FCXM). These agents are recognized as anti-human Ab or fix complement and are not differentiated from anti-allo-Ab. A new enzyme-linked immunosorbent assay crossmatch (XM) utilizing class I and II HLA antigens from donor cells called Transplant Monitoring System (TMS; GTI, Waukesha, Wisc) potentially precludes interference by eliminating non-major histocompatability complex antigens. To test this, normal sera (nonsensitized volunteers) were supplemented with 0.1 or 10 microg/mL of RIT, DAC, IFX or ALE, and were tested using three methods: the TMS T-cell CDCXM with antihuman globulin (AHG); and B-cell CDCXM without AHG; and FCXM with mean channel shifts of 45 and 150 indicating positive T-cell and B-cell crossmatch, respectively. No reactivity occurred with normal sera using any crossmatch technique. At 0.1 and 10 microg/mL, RIT interfered with CDC B-cell, but not T-cell crossmatch. RIT at 10, but not 0.1 microg/mL interfered with B-cell FCXM. No interference occurred with RIT in T-cell FCXM or TMS. ALE interfered with B-cell and T-cell CDC and FCXM but neither class I nor II TMS. DAC did not interfere with CDC or FCXM at 0.1 microg/mL, but gave false positive B-cell FCXM and CDCXM with some samples. No interference by DAC occurred using TMS. TMS may be useful to differentiate de novo donor-specific Ab after treatment with humanized or chimeric Ab.