Timing Of Daratumumab Administered Pre-Mobilization In Multiple Myeloma Impacts Pre-Harvest Peripheral Blood Cd34+Cell Counts And Plerixafor Use

Background: Daratumumab (DARA) is a monoclonal antibody which targets CD38 on plasma cells and B cell progenitors. DARA has been effectively combined with other therapies in newly diagnosed and relapsed/refractory multiple myeloma (RRMM), while DARA-based induction regimens in transplant-eligible patients (pts) are increasingly being used in clinical practice. Given that hematopoietic stem cells also express CD38, DARA may potentially affect stem cell mobilization and hematopoietic reconstitution following autologous stem cell transplant (ASCT). Although no clinically significant impact of DARA on stem cell mobilization or hematopoietic recovery was described in large phase 3 trials of triplet induction regimens +/- DARA in newly diagnosed MM, stem cell yields were lower and plerixafor more commonly used in the DARA-containing arms [Moreau et al, Lancet 2019; Voorhees et al, Blood 2020]. Significantly longer time to neutrophil (PMN) engraftment was also reported in pts receiving DARA-based induction who underwent upfront ASCT [Al Saleh et al, Am J Hematol 2020]. In this study, we examine the impact of timing of DARA administration pre-mobilization on day 4 pre-harvest peripheral blood CD34 cell count, stem cell apheresis yield, and post-ASCT engraftment.