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.
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