1.2000
#28
RITUXIMAB DOES NOT INTERFERE IN DONOR-SPECIFIC MHC TAMS(ELISA) ASSAY.
Patrick W. Adams, MS,CHS and Charles G. Orosz, PhD. Columbus OH, American Samoa, Ohio State University Medical Center, 43210, Clinical Histocompatibility Laboratory.

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Rituximab, a monoclonal antibody employed in antibody desensitization protocols, can persist up to 6 months in patient samples, and severely confounds the interpretation of B cell crossmatches. We reasoned that since the TAMS ELISA consists of a plastic matrix coated with murine “capture” antibody and donor MHC proteins, this assay should minimize the binding of extraneous antibodies like Rituximab that can bind to non-MHC related molecules on the surface of donor cells. To test this, normal human serum was spiked with low (10ug/ml), medium (100ug/ml) and high (1000ug/ml) concentrations of Rituximab , and tested for binding activity in the TAMS assay. At all Rituximab concentrations tested, detectable IgG binding was similar to the binding observed with the negative control serum that is included in the kit. To further demonstrate lack of Rituximab interference in the TAMS assay, serum from 8 patients who exhibited varying degrees of alloantibody reactivity were selected for TAMS analysis. Either 10ul of Rituximab (100mg/ml) or 10ul PHS were added to 90ul patient serum. These spiked sera were tested for MHC Class I and II alloantibodies in the TAMS assay using lysate antigen from a single donor. The OD values did not differ by more than 10% for each sample, whether treated with drug or PHS. The TAMS assay has also been used to determine anti-donor MHC alloantibody in 2 patients who were treated with Rituximab during the early post transplant period. In both cases, donor-specific TMS results agree with PRA specificity results using solid-phase Luminex technology. We conclude that the TAMS assay offers a unique opportunity to easily determine the presence or absence of donor-reactivie MHC Class II alloantibodies in the presence of circulating Rituximab.