Use of Plerixafor to Overcome Stem Cell Mobilization Failure: Long Term Follow up of Patients Proceeding to Transplant Using Plerixafor Mobilized Stem Cells
Authors: Deol Abhinav , Abrams Judith , Masood Ashiq , Al-Kadhimi Zaid , Abidi Muneer H. , Ayash Lois , Ratanatharathorn Voravit , Lum Lawrence G , Uberti Joseph P. 
Published: October 2019

Abstract
Abstract 4390

Background:
Plerixafor is a CXCR 4 antagonist which is now approved for use for stem cell (SC) mobilization with granulocyte colony stimulating factor (GCSF) in patients with non Hodgkin lymphoma (NHL) or multiple myeloma (MM). Prior to the approval of plerixafor, we enrolled 49 patients in a compassionate use protocol at our institution to mobilize SC for patients who previously failed at least one mobilization attempt.

Methods:
Patients received 0.24 mg/kg of plerixafor subcutaneously 9 –11 hrs prior to apheresis in addition to twice daily GCSF.

Results:
Median age of the patients was 64 years (range, 23–74 years). NHL was the most common diagnosis in 27 (55%) patients, followed by MM with 17(35%) patients and HD with 5 (10%) patients. Thirty nine patients (80%) had been treated with more than 2 chemotherapeutic regimens prior to the first attempt at stem cell collection. Thirty seven patients (76%) failed one previous mobilization attempt, while 12 (24%) had failed 2 or more previous attempts. Using the combination of Plerixafor and GCSF we collected ≥ 2.5 × 106 CD34+ cells/Kg in 33 patients (67%). The median days for pheresis were 1 day with a range of 1 to 3 days. The median SC dose collected was 4 × 106 CD34+ cells/Kg, with a range 2.5 – 14.3. The median CD-34+ peripheral blood count on the 1st day of their collection with plerixafor was 22.4/uL. In contrast the median peripheral blood CD-34+ cell count in these patients on the day of their first collection which failed was 6.2 /uL. The median increase using G-CSF and plerixafor was 14.9 CD-34+ cells/uL. We collected ≥ 2.5 × 106 CD34+ cells/Kg on 4/5 (80%) patients with HD, 13/17 (76%) patients with MM and 16/27 (59%) patients with NHL. Sixteen patients (33%) collected < 2.5 × 106 CD34+ cells/Kg. The median cell dose collected in these patients was 1.4 × 106 CD34+ cells/Kg with a range, 0.4–2.2. The median number of days of pheresis was 2 days (range, 1–4 days). In these16 patients the median CD-34+ count on the day of their previous failed collection was11.2/uL. Their CD-34+ cell count on their first day of collection after the use of G-CSF and plerixafor was 8.3/ul. Figure 1 shows the change in peripheral CD34 counts with the prior mobilization attempt and after plerixafor mobilization, for 38 patients in whom data was available. The most common side effects attributed to plerixafor were diarrhea, fatigue, thrombocytopenia and bone pain; observed in 12%, 8%, 8% and 6% patients, respectively. Forty three of the 49 patients proceeded to an autologus peripheral blood SC transplant, 34 patients received ≥ 2.5 × 106 CD34+ cells/Kg. Thirty two of these patients used the plerixafor collection as the only source of SC. Two patients had their plerixafor mobilized SC combined with a previous suboptimal SC collection. Nine patients received < 2.5 × 106 CD34 + cells/Kg; 4 patients received plerixafor mobilized SC alone, 5 patients received plerixafor mobilized SC combined with their previously mobilized SC. The preparative regimens used were R- BEAM (20 patients), Melphalan (16 patients), BEAM (6 patients) and Etoposide+TBI (1 patient). All patients received GCSF from day +6 till WBC engraftment. The median days of WBC and platelet engraftment were day +11 (range, 9–13 days) and day +16 (range, 11–77 days), respectively. There was no significant difference in days to engraftment between the patients who collected greater or less than 2.5 × 106 CD34 + cells/Kg. With a median follow up 13.7 months, long term engraftment data is available on 27 patients. The median white cell count, hemoglobin and platelet count 1 year after transplant was 4.7 × 109/L, 12.2 g/dL and 109 ×109/L, respectively. There was no significant difference in counts at the 1 year mark between patients who collected more or less than 2.5 × 106 CD34 + cells/Kg. To date 15 patients have evidence of disease progression. Two patients have developed MDS/AML post transplant.

Conclusion:
Overall, plerixafor leads to mobilization of sufficient stem cells in a vast majority of patients who have failed previous mobilization attempts and allows more patients to proceed to an autologous SC transplant. Plerixafor is well tolerated with minimal side effects, acceptable time to engraftment and acceptable peripheral blood counts at 1 yr after the transplant. Our analysis suggests that failure to increase peripheral CD34 count after plerixafor when compared to previous attempts may predict unsuccessful mobilization.

Disclosures:
Lum: Transtarget Inc: Equity Ownership, Founder of Transtarget.