Hematopoietic Progenitor Cell (HPC) Collection Is Feasible in Previously Transplanted Multiple Myeloma Patients and Plerixafor Improves Collection

Abstract ⁴¹²⁷

Autologous hematopoietic progenitor cell transplant (aHPCT) as salvage treatment in relapse is a therapeutic modality proven to induce response and improve overall survival (OS) in Multiple Myeloma (MM). However, many previously transplanted MM patients who might benefit from this intervention no longer have cryopreserved stem cells in storage. For these patients, it is important to know if HPC can be collected again adequate to support further aHPCT.

Records of MM patients treated at the Myeloma Institute for Research and Therapy (MIRT), University of Arkansas for Medical Sciences, between 06/22/2005 – 11/16/2011 were reviewed to identify patients undergoing attempted remobilization following at least one previous aHPCT. HPC collection was performed using a Spectra (TerumoBCT) apheresis device to perform large volume leukapheresis (30L processed). Collection was guided by our predictive formula (Rosenbaum ER et al., Cytotherapy 2012;14(4) :461–6) and was continued until the collection goal was met or the daily collection contained less than 0.5×10⁶ CD34+ cells/kg.

We identified 48 patients (median age 58, range 38–82) who underwent at least one HPC collection, for a total of 98 collections (19 patients underwent one collection, 17 two collections, 6 three collections, 3 four collections, 3 five collections). The median time from previous APSCT was 3.25 years (range 0–8.8). Mobilization regimen information was available in all collections but two (Table 1). Plerixafor (Mozobil®) was used in 34 patients, for a total of 44 collections. For the total cohort of patients the median number of CD34+ cells per collection was 3.15×10⁶ CD34+ cells/kg (0.1– 21.56), with a median of 4 days for each collection (1–10). No statistically significant correlation was seen for age, sex, number of previous aHPCT, time elapsed from previous aHPCT, or chemotherapy regimen used for previous aHPCT relative to the number of CD34+ cells collected. While the median number of CD34+ collected cells with or without plerixafor did not differ significantly (3.15 vs. 3.35×10⁶ CD34+ cells/kg, p=0.701), the addition of plerixafor yielded a statistically significant increase if there was a poor previous mobilization (1.73 vs. 2.94×10⁶ CD34+ cells/kg, p=0.004). Of 48 patients collected, 30 then underwent a subsequent aHPCT. Of these, 16 received cells procured after an aHPCT and 14 with cells procured prior to an aHPCT. No treatment related mortality was recorded in these aHPCT. Median number of CD34+ infused cells was 5.12×10⁶ CD34+ cells/kg and 4.70×10⁶ CD34+ cells/kg (p=0.583) for the before and after aHPCT procured stem cells. Median time for neutrophil engraftment (>500/mm³) was 10 days in both (p=0.897). Median time for platelet engraftment >20.000/mm³ was 12 and 11 days respectively (p=0.234), while for platelet engraftment >50.000/mm³ it was 24 and 15 days, with the difference being statistical significant (p=0.035). Nevertheless, all patients but one eventually achieved adequate platelet recovery (>100.000/mm³).

In conclusion, collection of CD34+ cells following aHPCT is feasible and the addition of plerixafor can yield enough cells for a subsequent aHPCT even in cases where the initial attempt failed. HPC collected after a previous aHPCT provide a safe graft for another transplant.