The timing of plerixafor addition to G-Csf and chemotherapy affects immunological recovery after autologous stem cell transplant in multiple myeloma

Plerixafor inhibits CXCR4, thus inducing the mobilization of hematopoietic stem/progenitor cells in lymphoma and multiple myeloma (MM) patients eligible for autologous stem cell transplantation (ASCT). However, the kinetics of plerixafor-induced mobilization of lymphocyte subsets is poorly known. Here, we evaluated the graft content, the engraftment, and the immunological reconstitution of MM patients receiving plerixafor. Thirty-seven patients undergoing one or tandem ASCT were enrolled. After mobilization with cyclophosphamide plus G-CSF, plerixafor was added at hematological recovery regardless of CD34⁺ cell count. We evaluated the number of CD34⁺, CD34⁺/CD38⁻, CD3⁺, CD4⁺, CD8⁺, CD19⁺, CD56⁺/CD3⁻, CD4⁺/CD25⁺/FOXP3⁺, and CD138⁺/CD38⁺ cells on each apheresis. Hematological and immunological recovery were determined at 30 days, 3, 6, 9, and 12 months after ASCT. Overall, 34/37 patients mobilized a median of 10.1 × 10⁶ CD34⁺ cells/Kg (IQ 7.7–13.4). Patients with <20/µL CD34⁺ cells at plerixafor administration (18/33) had a significantly higher CD34⁺ cell fold increase, but not a higher absolute number, than 16/33 patients with ≥20/µL CD34⁺ cells. A similar CD34⁺ and immune graft composition was reported. A higher number of CD3⁺ and CD8⁺ cells/µL was observed at 3 months after first ASCT (p < 0.05) in the group with ≥20 CD34⁺ cells/µL. Thus, in MM patients, the timing of plerixafor administration influences immunological recovery.