Absence of Red Blood Cell Alloimmunization in Transfused Patients Receiving Daratumumab: Experience from a Single Center

<b>Background/Objectived:</b> Daratumumab is an anti-CD38 monoclonal antibody used in the treatment of multiple myeloma. Its use interferes with the indirect antiglobulin test (IAT). Treatment of reagent red blood cells (RBCs) with dithiothreitol (DTT) is one of the most validated techniques to resolve this interference. The objective of this study is to evaluate the rate of alloimmunization in transfused patients receiving daratumumab and the occurrence of hemolytic transfusion reactions. <b>Materials and Methods</b><i>:</i> We conducted a single-center, retrospective, descriptive analysis of all patients treated with daratumumab at our institution from October 2016 to April 2024. For daratumumab-treated patients requiring RBC transfusions, an IAT with DTT-pretreated RBCs (DTT-IAT) was performed using the automated Orthovision system. Transfusion was administered only with a previous negative DTT-IAT while respecting Rh and Kell phenotyping. We assessed the transfusion profile of our patient cohort, including their rates of alloimmunization before and after daratumumab initiation, as well as the incidence of hemolytic complications. Additionally, a literature review was performed on reported alloimmunization rates in daratumumab-treated patients. <b>Results:</b> Among all patients, 106 received RBC and/or platelet transfusions after starting daratumumab. Four had known pre-existing alloantibodies. None developed new alloantibodies or experienced hemolytic complications while receiving anti-CD38 therapy. There were four cases of false-positive DTT-IAT due to residual drug interference or technical variability, in which no alloantibodies or adverse transfusion reactions were detected. <b>Conclusions:</b> Patients receiving daratumumab exhibit a low risk of alloimmunization. This may be partly explained by adherence to Rh and Kell phenotyping and daratumumab's immunosuppressive effects on alloantibody production. These results support the conclusion that an extended red blood cell phenotype or genotype before starting daratumumab could be omitted if a fast and reliable technique for pretransfusion testing (such as automated DTT-IAT) is available 24 h.