The Effective Use of Plerixafor as a Real-Time Rescue Strategy for Patients with Poorly Mobilizing Autologous CD34+ Cells

Plerixafor has been demonstrated to enhance peripheral blood CD34+ cell mobilization and apheresis yields in combination with G-CSF and has been shown to salvage patients who have failed prior harvests. However, the optimal use of plerixafor is unknown as the vast majority of patients can be successfully collected without the use of this agent. We hypothesized that plerixafor could effectively be employed as a “rescue” strategy in the midst of mobilization for patients with factors indicating a likely poor CD34+ cell yield.

Between Feb 2009 and May 2010, 522 aphereses were performed as part of 295 autologous peripheral blood stem cell (PBSC) collections at our center. Of these, 39 (13%) utilized plerixafor as rescue strategy based on treating physicians’ interpretation of clinical factors predictive of poor mobilization/collection. These included: pre-collection blood CD34+ cell concentration <10/μL (n=30, 77%, median CD34+ cell count = 5.95/μL, range 1.12– 8.64), low CD34+ cell yield from first apheresis day (n=7, 18%, median prior day's apheresis yield= 1.06 ×10⁶ CD34+ cells/kg, range .54-1.7 ×10⁶/kg), waning CD34+ cell yield (n=1), and clinical delay of apheresis (n=1). Baseline characteristics of these 39 patients included: median age = 62yrs (range 26–73 yrs), 23 Non-Hodgkin lymphoma, 14 multiple myeloma, 1 Hodgkin lymphoma, and 1 amyloidosis; median # of prior treatment regimens 2 (range 1–8), prior lenalidomide 14 (36%), prior fludarabine 2 (5%), prior pelvic or spinal radiation 6 (15%), prior failed mobilization 8 (21%), prior transplant 1. Twenty-six (67%) patients received chemotherapy + G-CSF for mobilization and 13 (33%) G-CSF alone prior to plerixafor.

Patients received a median of 1 standard dose of plerixafor (range 1–4 doses) 10–12 hours prior to apheresis. These patients had a median of 2 total days of apheresis and a median of 1 day of apheresis immediately following plerixafor. The median total CD34+ cells collected for the entire group was 5 ×10⁶/kg (range 0.5–14.54) and 34 (87%) collected > 2 × 10⁶ CD34/kg, 26 (67%) collected > 4 × 10⁶ CD34/kg, and 7 (18%) collected > 8 × 10⁶ CD34/kg. The median collections for lymphoma and myeloma patients were 4.1 × 10⁶ and 8.3 × 10⁶ CD34/kg, respectively. A single dose of plerixafor was associated with an increase in the mean peripheral blood precollection CD34+ cell concentration of 17.2 cells/μL (p=.005) and mean CD34+ cell yield following a single apheresis of 5.11 × 10⁶/kg (p=.01,Table). Engraftment kinetics of 26 patients that went on to transplant included a median time to ANC>500 and plts >50K of 16 days (range 14–38 days) and 19 days (range 14–33 days), respectively.

These data indicate that a real-time rescue strategy of adding plerixafor to G-CSF with or without prior chemotherapy in poorly mobilizing patients significantly increases the blood CD34+ cell concentration and can result in adequate PBSC collections in the majority of patients resulting in acceptable engraftment kinetics. Such an approach may provide a cost and time-effective policy by employing this agent only in those that require its use yet obviating the need for a second distinct mobilization attempt. These data suggest that a prospective validation of such a rescue method using plerixafor in autologous PBSC harvests is warranted.

Gopal: Genzyme: Consultancy. Off Label Use: Rescue use of plerixafor. Bensinger: Genzyme: Research Funding. Holmberg: Genzyme: Research Funding.