Modified Flow Cytometry Crossmatch Detecting Alloantibody-related Cytotoxicity as a Way to Distinguish Lytic Antibodies From Harmless in Allosensitised Kidney Recipients

The serological complement-dependent cytotoxicity crossmatch (CDC-XM) permits routine identification of anti-donor alloantibodies in the sera of allotransplant recipients. However, in a small group of recipients, antibodies below the threshold of detection may still be responsible for hyperacute rejection. For the same reason, approximately 20% of recipients develop acute rejection episodes. The flow cytometry crossmatch (FCXM) was designed to address these problems, but because of the presence of clinically insignificant antibodies (linked, non-lytic), the FCXM appears to be too sensitive yielding false-positive results. We compared FCXM with its modified version assessing cell viability (cytolytic flow cytometry crossmatch; cFCXM) using sera from previously sensitised kidney recipients. The presence of alloantibodies was detected using the Luminex platform. The cFCXM proved to be of greater sensitivity than CDC-XM, which was additionally confirmed with bead-based Luminex techniques. The cFCXM was also superior to FCXM because it distinguished lytic from non-lytic antibodies. The cFCXM was superior to assess donor specificity, sensitivity, and detection of clinically relevant lytic antibodies.