Optimizing Progenitor Cell Mobilization in Patients with Myeloma: Effect of a Pre-Emptive Day 4 Plerixafor-Based Mobilization Algorithm
Authors: Fasan Omotayo O. , Usmani Saad Z , Sun Danyu , Jacobs Ryan , Lee Carlos , Trivedi Jigar , Chow Eric , Plesca Dragos , Bhutani Manisha , Avalos Belinda R. , Copelan Edward A. 
Published: October 2019

Abstract
BACKGROUND: Peripheral blood progenitor cell (PBPC) mobilization strategies vary considerably. Optimization of this critical aspect of autologous hematopoietic stem cell transplantation (ASCT) requires efficient use of resources including apheresis kits, machine run time, nursing and cell processing time and consumables. Equally important is the patient experience, which is strongly influenced by collection days and caregiver time that reduces their economic productivity and raises their expenses. We developed a mobilization algorithm designed to collect the target number of cells on day 1 of collection. The algorithm utilizes pre-emptive day 4 plerixafor to maximize collection day peripheral blood (PB) CD34+ cell numbers.
METHOD: We analyzed data on all patients with multiple myeloma undergoing PBPC mobilization between March 2014 and July 2016. All patients were mobilized with the intent of collecting sufficient numbers of progenitor cells to permit two ASCT procedures. Patients received filgrastim 10 mcg/kg daily x 4 days. Patients in whom the PB white blood cell (WBC) count was < 50K/uL on day 4 received an extra dose of filgrastim that evening and plerixafor at 0.24 mg/Kg (Figure 1) or a fixed dose of 12mg (Figure 2) if the PBCD34 was < 50/uL. A fixed dose was administered if a patient could be paired with another patient simultaneously undergoing PBPC mobilization. The number of days of apheresis, run time, collection efficiency (CE2) and other relevant variables were analyzed and compared between the standard and fixed dose cohorts. We defined successful mobilization as ≥ 8 million CD34+ cells/Kg (based on our institutional ideal dose of 4 million CD34+ cells/Kg for a single ASCT), optimal mobilization as ≥ 6 million CD34+ cells/Kg (based on the International Myeloma Working Group (IMWG) recommended minimum dose of 3 million CD34+ cells/Kg for an ASCT), suboptimal mobilization as ≥ 2 million but < 6 Million CD34+ cells/Kg, and mobilization failure as < 2 million CD34+ cells/Kg.
RESULTS: We identified 105 patients with MM. Median age was 61 years (range, 25 - 76) and 57% were female. Disease status at mobilization included: 7 CR, 14 stringent CR, 5 unconfirmed CR, 52 very good PR (VGPR), and 27 PR. The median day 4 PBCD34+ cell number was 19.9/uL (range, 0.8 - 118.7/uL), and median day 5 PBCD34+ count was 107.8/uL (range, 15.6 - 307.8/uL). Ninety percent of patients required plerixafor of which 16% (n = 17) received the 12 mg fixed dose. The median increase in day 4 to day 5 PBCD34+ cell count for patients receiving plerixafor was 6.6 fold (range, 1.5 - 56.4 fold). In patients not receiving plerixafor, the median increase was 1.8 fold (range, 1.5 - 2.6 fold). The median collection yield was 10.95 million CD34+ cells/Kg (range, 2.9 - 22.5 million CD34+ cells/Kg) no significant difference between patients who received standard dose or fixed dose plerixafor. By the criteria outlined above 96.2% of patients had an optimal mobilization i.e. ≥ 6 million CD34+ cells/Kg sufficient for 2 ASCT procedures with 94.2% achieving this with only 1 day of collection. Per our institutional criteria, 71.4% achieved a successful collection (> 8 million CD34+ cells/Kg) in 1 day. There was no significant difference in days of collection among patients receiving 4 or less cycles of lenalidomide versus those receiving more than 4 cycles (p value = 0.104). The median duration of collection was 399 minutes (range, 180 - 495 minutes) with a median collection efficiency (CE2) of 42.3%. The mean number of days of collection was 1.23 days (range, 1 - 2 days). The median transplanted CD34+ cell dose was 5.48 million CD34+ cells/Kg. All patients had hematopoietic recovery with median neutrophil and platelet engraftment of 11 days and 18 days, respectively.
CONCLUSION: The pre-emptive use of plerixafor on day 4 is effective and results in a high percentage of optimal day 1 collections. The cost of a more liberal plerixafor algorithm is offset by the savings incurred from reduced collection day numbers with the majority of patients requiring only 1 day of collection. Cost savings include limiting days away from work and family for the patient and caregiver and decreasing expenses for travel and overnight stays. Reducing collection day numbers also reduces the impact on quality of life for patients, caregivers and family members. Collectively, these data demonstrate utility of the pre-emptive day 4 plerixafor-based mobilization algorithm described here.

Disclosures
Usmani: Amgen: Consultancy, Research Funding, Speakers Bureau; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Onyx: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; BioPharma: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pharmacyclics: Research Funding; Britsol-Myers Squibb: Consultancy, Research Funding; Skyline: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Array: Research Funding; Millenium: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Speakers Bureau. Jacobs:Magellan Health: Consultancy; Pharmacyclics: Consultancy, Speakers Bureau. Bhutani:Onyx, an Amgen subsidiary: Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Takeda Oncology: Research Funding, Speakers Bureau; Prothena: Research Funding. Avalos:Seattle Genetics: Membership on an entity's Board of Directors or advisory committees.