In MM patients with intermediate mobilization capacity (PB CD34+ counts of 15-40 cells/μL after G-CSF), the addition of plerixafor markedly improved stem cell mobilization efficiency and enriched grafts with functionally robust progenitor cells compared to placebo.
Plerixafor significantly increased peripheral blood CD34+ cell counts compared to placebo in moderately mobilizing multiple myeloma patients.
All patients receiving plerixafor achieved the primary endpoint of collecting ≥6.0 × 10^6 CD34+ cells/kg in a single apheresis session, whereas none in the placebo group achieved it.
Mean CD34+ cell yield was significantly higher in the plerixafor group compared to the placebo group.
Plerixafor-mobilized grafts contained significantly higher numbers of primitive hematopoietic progenitor subsets and demonstrated increased CFU-GM formation.
Despite marked differences in graft quantity and quality, engraftment kinetics, graft sustainability, and immune reconstitution were comparable between the plerixafor and placebo groups.
The study was terminated prematurely due to changes in first-line multiple myeloma therapy and the COVID-19 pandemic.
This research studied whether adding plerixafor (a drug that helps release stem cells from bone marrow into the blood) to the standard mobilization drug G-CSF could help multiple myeloma patients who are 'moderate mobilizers' — meaning they produce a middling number of stem cells in response to G-CSF alone. These patients, with blood CD34+ stem cell counts between 15 and 40 cells per microliter, are often in a gray zone: not poor enough mobilizers to routinely receive plerixafor, but potentially at risk of not collecting enough stem cells for two transplants. The trial randomly assigned these patients to receive either plerixafor or a placebo alongside G-CSF before stem cell collection. The results were striking: every patient who received plerixafor successfully collected enough stem cells for two transplants in a single collection session, while none of the placebo patients reached that threshold. The plerixafor group collected on average about 10.4 million CD34+ cells per kilogram of body weight, compared to only 2.9 million in the placebo group. Beyond quantity, the stem cells collected with plerixafor also appeared more 'primitive' and potent in laboratory tests, suggesting higher quality grafts. Importantly, despite these large differences in collection quantity and quality, both groups recovered similarly after transplantation in terms of how quickly their blood counts returned to normal and how their immune systems reconstituted. This research suggests that patients who fall into the intermediate mobilization category — not poor enough to automatically receive plerixafor but not reliably good enough to guarantee sufficient stem cell collection — could meaningfully benefit from plerixafor-assisted mobilization. The study was smaller than planned due to the COVID-19 pandemic and changes in myeloma treatment practices, but the differences observed were large and statistically significant. These findings may support revisiting which patients are offered plerixafor, potentially expanding its use beyond those currently defined as 'poor mobilizers.'
Nina W, Martin S, Andreas T, Martin K, Bianca H, Peter N, et al.. (2026). Plerixafor and G-CSF Versus Placebo and G-CSF in Moderately Mobilizing Patients With Multiple Myeloma to Optimize Hematopoietic Stem Cell Collection Results (OPTIMIZE).. Journal of clinical apheresis. https://doi.org/10.1002/jca.70188