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

ABSTRACT

Background: The combination of an anti-CD38 monoclonal antibody, Dara, to the main induction protocols (VRd, VTd,VCd) significantly improved the response rate of TE NDMM before transplantation. However, there is a concern regardingthe possible interference in the SC collection and bone marrow engraftment, since SC, to some degree, express CD38on their surface. In the MAX Dara study, Dara-CTd protocol was used sequentially close to the pre- and post-autologousstem cell transplantation-(ASCT) (D-30 and D + 30), in order to take advantage of the molecule's action as an in vivopurge. Aims: In this analysis, we examine the impact of the number of Dara doses administered pre-mobilization on CD34 cellcount, SC apheresis yield, and post-ASCT engraftment. Methods: 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-1500 mg oral (PO) per cycle, duringcycles 1 to 4, T at 100-200 mg PO on days 1 to 28, during cycles 1-8, (d) at 160 mg PO per cycle, during cycles 1 - 8 andDara at 16 mg/kg/dose intravenous (IV) on days 1,8,15 and 22 during cycles 1 - 2 and every other week in cycles 3 – 8. Because of the Covid pandemic we had to adapted the protocol and moving 5-6 consolidation cycles to be used asinduction, increasing the total dose of Dara from 12 to 16 and the number of cycles from 4 to 6 before ASCT. Granulocytecolony-stimulating factor (G-CSF) was administered alone for SC mobilization and plerixafor added based on day 4 preharvestperipheral blood CD34 counts. The target of SC collection was to enable the performance of one ASCT (>2,5 x 106/kg). PMN and platelet engraftment post-ASCT was defined as the first day with sustained PMN count >1000 x 106/L andindependence from platelet transfusion in the preceding 7 days with a count >20 x 109/L, respectively Results: From a total of 21 pts that were included, 19 pts completed mobilization. 12 pts received 12and 7 pts received 16 induction Dara doses, respectively. The median number (range) of daysbetween the last dose of Dara infusion and SC harvest was 23 (16-63) days. A total of five (26%) ptsreceived plerixafor during mobilization. More pts from Dara 16 doses needed plerixafor comparingwith Dara 12 doses (42% vs 16%), but without difference between the groups. Pts underwent amedian (range) of 1 (1-2) days of apheresis. The median number of CD34+ cells collected in the totalgroup was 3.94×106/kg, and no difference was found between Dara 12 vs 16 doses (3.61×106/kg vs4.01x106/kg), p = 0.27. There was no difference in the number of SC collected considering theresponse rate after induction > or < VGPR, and the last day of Dara use > or < 30 days, before SCharvesting. Hematopoietic reconstitution rates were similar for Dara 12 vs 16 doses, a median(range) of 11.0 (9-13) vs 11.0 (11-14) days was required to achieve sustained ANC > 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. Summary/Conclusion: SC mobilization was feasible with Dara-CTd induction. Despite the more doses of Dara usebefore mobilization increases the need of plerixafor use, the SC number difference was not significant comparing Dara 12vs 16 doses (p = 0.3). The infusion of Dara close to harvest did not interfere with SC collection. Adding DARA to CTdallowed successful transplantation in pts with TE NDMM.