Daratumumab Interference in Pretransfusion Testing Is Overcome by Addition of Daratumumab Fab Fragments to Patients' Plasma.

BACKGROUND: Daratumumab (DARA), an IgG1κ human monoclonal anti-CD38 antibody, is used for the treatment of refractory myeloma for example. Binding of DARA to CD38 on red blood cells (RBCs), however, leads to panagglutination in indirect antiglobulin testing and possibly masks clinically relevant alloantibodies. Dithiothreitol eliminates panreactivity by destroying CD38 but has the drawback of modifying certain blood group antigens and, thereby, impairs the detection of alloantibodies.
METHODS: DARA was digested for 16 h at 37°C using immobilized papain in a spin column, centrifuged, and washed, and the DARA-Fab fragments in pooled flow-throughs were stored at -20°C. DARA-Fab and test cells (ID-DiaCell I-II-III or ID-DiaPanel; BioRad) were incubated with human plasma spiked with DARA (plasma concentration up to 1,000 mg/L) or plasma from patients under DARA therapy at 37°C for 15 min. Thereafter, ID-Cards LISS/Coombs were used.
RESULTS: Immunofixation electrophoresis showed complete fragmentation of DARA into Fc and Fab fragments by papain proteolysis. DARA-Fab efficiently prevented RBC agglutination by patients' plasma and by plasma spiked with DARA. Moreover, DARA-Fab did not interfere with the detection of alloantibodies.
CONCLUSION: We present a quite easy, reproducible, and cost-effective method for DARA-Fab fragment preparation. Blocking CD38 epitopes with DARA-Fab easily overcomes DARA interference in pretransfusion testing without affecting alloantibody detection.