Use of an in‐house trypsin‐based method to resolve the interference of daratumumab

Abstract

Background Daratumumab (DARA) is a monoclonal antibody for treatment of plasma cell myeloma targeting CD38, a surface molecule expressed on plasma cells and red blood cells (RBCs). This complicates blood bank testing, requiring dithiothreitol (DTT) to remove DARA interference. A simple in‐house method of removing DARA interference without use of DTT, a potentially hazardous chemical, is desirable. We demonstrate a trypsin‐based method to remove interference in antibody testing at a medical center (MC), with parallel testing at an immunohematology reference laboratory (IRL). Study design and methods Pre‐DARA type and screen (T&S) samples were obtained from 61 patients for antibody testing and RBC phenotyping using untreated reagent RBCs. Subsequent post‐DARA T&S testing was performed with untreated reagent RBCs to demonstrate interference and repeated after trypsin treatment. Positive trypsin‐treated antibody screens were reflexed to antibody identification using trypsin‐treated panel cells. Parallel testing was performed on the same post‐DARA samples at IRL. Results DARA interference was detected in 61/61 (100%) samples by MC and IRL. After trypsin treatment, DARA interference was eliminated in 60/61 (98.4%) antibody screens by both institutions with an overall percent agreement of 96.7% (95% confidence interval [CI] 88.7%–99.6%). Identification of known alloantibodies was confirmed in 3/3 patients with 100% concordant results between MC and IRL. There were no false‐negative results demonstrated by IRL's functionally CD38‐negative controls. Conclusion Our in‐house trypsin‐based method enables pretransfusion testing of patients receiving DARA in an accurate and cost‐effective manner without missing clinically significant alloantibodies. This presents an additional testing option where DTT use is undesirable.

Efficient neutralization of daratumumab in pretransfusion samples using a novel recombinant monoclonal anti‐idiotype antibody

“…Lower concentrations of DTT (e.g., 0.01 M, as in the Osaka method 8,9 ) can be used to preserve K antigen expression. 10 Other approaches to mitigate the anti-CD38 interference include: denaturing RBC CD38 with other thiol reagents 11 or trypsin; 3,12 using phenotyped cord blood cells 13 or In(Lu) cells, 14 which express low or no serologically detectable CD38; blocking RBC CD38 using F(ab') 2 fragments 15 or antihuman globulin 16 ; using the manual polybrene method; 17 adsorbing plasma with Daudi cell stroma 18 or MEL-745A cells engineered to express high levels of CD38; 19 or providing phenotypically or genotypically matched RBC units. 11,20 One of the first approaches to resolve the anti-CD38 interference was to neutralize DARA in plasma with soluble CD38 or anti-DARA idiotype antibodies.…”