Low-Dose Plerixafor and Granulocyte Colony-Stimulating Factor for First-Line Autologous Peripheral Blood Stem Cell Mobilization in Lymphoma and Multiple Myeloma

Introduction: Approximately 10-30% of candidates to autologous hematopietic stem cell transplant (HSCT) are unable to collect an adequate yield of CD34+ cells/kg to support high-dose chemotherapy and autologous HSCT. Peripheral blood stem cell (PBSC) mobilization strategies vary considerably but the optimal methodology for mobilizing PBSC is not well defined. Plerixafor (Mozobil®) is approved for the mobilization of PBPC in combination with G-CSF at a dose of 0.24 mg/kg once daily for up to 4 consecutive days; however, it is an expensive drug and is expected to increase costs associated with PBSC harvest. Failure of peripheral blood (PB) mobilization and harvest is a critical issue for multiple myeloma (MM) and non hodgkin´s lymphoma (NHL) since the correlation between successful engraftment and the number of CD34+ cells infused is well established. We aim to investigate the safety and efficacy of the administration of low-dose plerixafor in mobilizing CD34+ cells plus G-CSF in MM and NHL.

Methods: It is a preliminary report of a single-institution, open-label, phase II trial to test the feasibility and efficacy for mobilization of low-dose plerixafor added to daily G-CSF administration in adult patients with MM or NHL undergoing autologous HSCT. Institution ethic board approved the trial and all patients provided written informed consent. Consecutive patients in autologous transplant protocol with MM or NHL were included. The mobilization protocol consisted of G-CSF (10 μg/kg) subcutaneously daily for 4 days and plerixafor (0.12 mg/kg) administered subcutaneously 11 hours prior to initiation of apheresis. Stem cells collection was performed with a Cobe Spectra® or Spectra Optia® apheresis system. The planned target blood volume to be processed was 4-fold total blood volume calculated according to patients' weight and size. Peripheral blood CD34+ counts were analyzed using flow cytometry. Primary endpoint was the proportion of patients achieving at least 2 x 10⁶ CD34+cells/kg in 1 apheresis harvest. Secondary end points included the rate of successful CD34+ cell mobilization, defined as a peak of CD34+ cells in PB >20 cells/mL. We measure PB CD34+ cells the day 4 and 5 after plerixafor administration. Toxicities and engraftment were documented.

Results: Between april 2017 and july 2017, nine patients has been enrolled. Six with MM and 3 with NHL. The median PB CD34+ cell count for patients on day 4 before receiving plerixafor was 12.3/mL (range, 2.2-168.8) and 65.4/mL (range, 8.2-360.7) on day 5 after plerixafor (P=0.103). The median collection yield was 4.9 x 10⁶ CD34+ cells/Kg (range, 1.4 - 24.5 million CD34+ cells/Kg). Plerixafor was well tolerated in most patients, only 2 referred moderate diarrhea. Eight of the 9 patients reached the target cell count (88.8%) with only 1 day of collection. Seven of nine patients had hematopoietic recovery with median neutrophil and platelet engraftment of 14 (range, 10-16) and 12 days (range, 10-16), respectively. Two patients are on day +1 and +5 and waiting for engraftment.

Conclusions: Failure of PBSC mobilization is a critical issue for MM and NHL patients undergoing autologous HSCT. The combination of low-dose plerixafor with G- CSF in this study achieved 88% of successful yields, and appears to be an efficient and safe approach in first-line to improve the success of the yield. Aside of the costs related to plerixafor, this strategy can be counterweighed by reducing other resources as reducing number of apheresis and possibly reducing the impact on quality of life for patients.