P-173: Impact of Daratumumab (DARA) administration during transplant-eligible newly diagnosed Multiple Myeloma (TE NDMM) induction on stem cell (SC) mobilization count and post-transplant engraftment

In the MAX Dara study, Dara-CTd was used sequentially close to the pre- and post-ASCT (D-30 and D + 30), in order to take advantage of the Dara as an in vivo purge. However, dara could interfer in the SC collection and bone marrow engraftment. In this analysis, we examine the impact of the number of Dara doses administered pre-mobilization on CD34 cell count, SC apheresis yield, and post-ASCT engraftment. This is a phase II, open-label single-center clinical trial. The original protocol was Dara-CTd for up to four 28- day induction cycles and Dara-Td for up to four 28 days consolidation cycles. C-1500mg PO per cycle, during cycles 1 to 4, T at 100-200mg PO on days 1 to 28, during cycles 1-8, (d) at 160mg PO per cycle, during cycles 1 - 8 and Dara at 16mg/Kg/dose IV QW during cycles 1 - 2 and QOW in cycles 3 – 8. Because of the COVID pandemic we had to adapted the protocol and moving 5-6 consolidation cycles to be used as induction, increasing the total dose of Dara from 12 to 16 and the number of cycles from 4 to 6 before ASCT. G-CSF was administered alone for SC mobilization and plerixafor added based on day 4 preharvest PB CD34 counts. The target of SC collection was (>2,5×106/kg). PMN and platelet engraftment post-ASCT was defined as the first day with sustained PMN count >1000×106/L and independence from platelet transfusion in the preceding 7 days with a count ≥20×109/L, respectively. From a total of 21 included pts, 19 pts completed mobilization. 12 pts received 12 and 7 pts received 16 induction Dara doses, respectively. The median number (range) of days between the last dose of Dara infusion and SC harvest was 23 (16-63) days. A total of five (26%) pts received plerixafor during mobilization. More pts from Dara 16 doses needed plerixafor comparing with Dara 12 doses (42% vs 16%), but without statistic difference. Pts underwent a median (range) of 1 (1-2) days of apheresis. The median number of CD34+ cells collected in the total group was 3.94×106/kg, and no difference was found between Dara 12 vs 16 doses (3.61×106/kg vs 4.01×106/kg), p=0.27. There was no difference in the number of SC collected considering the response rate after induction > or or 1000 cells/mm3, and a median (range) of 12.0 (9-14) vs 11.0 (8-16) days was required to achieve sustained platelets >20,000 cells/mm3 without transfusion, respectively. In summary, SC mobilization was feasible with Dara-CTd induction. Despite the more doses of Dara use before mobilization increases the need of plerixafor use, the SC number difference was not significant comparing Dara 12 vs 16 doses (p=0.3). The infusion of Dara close to harvest didn’t interfere with SC collection. Adding DARA to CTd allowed successful transplantation in pts with TENDMM.