Interference of therapeutic antibodies used in desensitization protocols on lymphocytotoxicity crossmatch results

Therapeutic antibodies used to desensitize patients awaiting a human leukocyte antigen (HLA) or ABO-mismatched graft are suspected to interfere with the lymphocytotoxicity crossmatch (LCT-XM) test when they are present in the tested sera because of their potential ability to activate or inhibit the complement.

The most frequent therapeutic antibodies (Abs) used in desensitization protocols (intravenous immunoglobulins, rituximab, basiliximab, eculizumab, antithymocyte globulin) were added to a negative- or a positive-control serum at various concentrations, and tested in vitro in a LCT-XM test.

Rituximab turned the LCT-XM positive on B cells at 0.2 μg/mL and antithymocyte globulin turned the LCT-XM positive with T and B cells at 20 μg/mL and 200 μg/mL, respectively. Treatment with dithiothreitol sera, supplemented with rituximab (0.2 and 2 μg/mL) and antithymocyte globulins (20 and 200 μg/mL), partially or totally reduced this positive interference. Intravenous immunoglobulin, eculizumab, and basiliximab did not trigger any interference with the negative control serum. In a positive LCT-XM, eculizumab did not annihilate activation of the rabbit complement. Intravenous immunoglobulins (25 g/L) could partially or totally reduced lysis score of positive crossmatch with weak lysis scores.

If eculizumab within the serum did not annihilate rabbit complement activation and basiliximab did not interfere with the crossmatch reaction, treatments based on rituximab, antithymocyte globulin and intravenous immunoglobulins need to be taken into account when interpreting a positive or negative crossmatch test.