PB2445 PRE‐TRANSFUSION IMMUNOHEMATOLOGY TESTING INTERFERENCE WITH DARATUMUMAB: PRELIMINARY EXPERIENCE FROM THE FIRST PATIENTS TREATED AT ASST GOM NIGUARDA

Background: Daratumumab is a human anti‐CD38 monoclonal antibody approved for the treatment of relapsed or refractory multiple myeloma (MM). Due to the physiological presence of the antigen CD38 on the red blood cell (RBC) membrane, Daratumumab (DARA) inteferes with the classical pre‐transfusion tests, impairing the identification of potential auto‐ or alloantibodies whenever present. The duration of this interference has been reported to be of 2‐6 months after the last DARA administration [Oostendorp M, Transfusion 2015]. Aims: The present analysis aims at evaluating the duration of DARA‐related pre‐transfusion testing interference after the end of treatment at our Center, in order to better define an optimal strategy to assign compatible packed RBCs for transfusion therapy. Methods: According to our policy, all patients were typed for AB0, full Rh phenotype, K/k, direct/indirect antiglobulin tests and extended sierological RBCs typing before starting with DARA [2016 SIMTI recommendations]; the identification of compatible packed RBCs was obtained after crossmatching using dithiothreitol‐treated patient's blood sample. Results: From October 2017, a total of n = 7 MM patients received DARA at a median age of 68y (range: 50‐79); median number of previous therapeutic lines was 3 (range: 1‐7) and the median number of weekly administrations was 7 per patient (range: 1‐12). Two patients are still receiving DARA (1 and 12 administrations respectively). As expected, both direct and indirect antiglobulin tests were positive for all patients; moreover, one patient had also a well‐identified allo anti‐D antibody. Among the n = 5 ongoing patients, n = 4 are evaluable because they underwent the subsequent pre‐transfusion tests after the end of DARA treatment: n = 1 still presents interference 50 days after the end of DARA whereas interference disappeared in n = 3 patients at 48, 65 and 111 days after the last treatment. Summary/Conclusion: Our preliminary data confirm the persistence of DARA‐related pre‐transfusion testing interference after the end of treatment for a median period of 2 months in this cohort of MM patients treated at our Institution. Futher follow‐up and the analysis of additional patients in the next future will allow to better determine the duration of interference; we believe these data are worthy of note due to increasing use of DARA, even for other clinical situations [Chapuy CI, NEJM 2018; Kwun JEB, Am J Transplant 2017]