Plerixafor and G-CSF For Autologous Stem Cell Mobilization In AL Amyloidosis: A Single Center Experience
Authors: Kaul Esha , Shah Gunjan L , Chaulagain Chakra P , Comenzo Raymond L. 
Published: October 2019

Background
Risk-adapted melphalan and stem cell transplant (SCT) is standard initial therapy for a minority of patients with systemic AL amyloidosis (Blood 2013;121: 5124; Blood 2011;118: 4298). Stem cell mobilization is often accomplished with high dose G-CSF (16μg/kg/d) (Blood 2011;118:4346). In the current era with effective new agents such as bortezomib, many AL patients are receiving initial therapy and achieving profound rapid cytoreduction with organ improvement (Blood 2012;119:4391; Blood 2011;118:86). But not all patients respond and in some cases the duration of response is limited. In addition, the use of SCT for consolidation after an initial response, although reasonable, has not been systematically evaluated. Whether SCT is employed as consolidation or as a second- or third-line option, the efficacy and tolerance of mobilization become important issues. Because AL patients have organ involvement limiting chemotherapy-based mobilization options, we decided to explore the option of Plerixafor and G-CSF for stem cell mobilization, based on the phase III experience in MM (Blood 2009;113:5720). We now report the first experience with this mobilization approach in AL.

Patients and Methods
Patients were evaluated and diagnosed by standard criteria including, in all cases, tissue biopsies showing amyloidosis. They were mobilized and collected between 4/16/12 and 6/19/13 with G-CSF 10μg/kg/d subcutaneously (SC) for 5 days (continued through collection process) and Plerixafor adjusted for renal function starting on day 4 and continuing until collection was completed.

Results
We report on 10 patients whose median age at mobilization was 58 years (range 46-72), 60% of whom were men. Median number of organs involved was 2 (range 1-3). Heart and kidneys were the most frequently involved organs (7 patients in each group). Median time from diagnosis to mobilization was 9 months (range 2-123). Eight patients had received prior bortezomib-based therapy. The median number of cycles was 3 (range 0-6). One had received a prior MEL 140 transplant 10 years prior and had relapsed, and 2 were treatment naïve, one of whom was 1 year status post orthotopic heart transplant. At the time of mobilization, 3 patients had non-responsive hematologic disease, 3 had achieved PR, 1 VGPR and 1 had achieved CR. Five patients had a creatinine ≥ 1.5 mg/dL including 2 patients on hemodialysis. The target cell dose was 10x106CD34/kg for all but one patient (with previous history of transplantation). The median number of collections was 2 (range 2-3). On day one, the median number of CD34+ cells collected per kg was 3.6 x106 (0.4-6x106) and on day two 6.4 x106 (2.7-19x106). The median total CD34+ cells collected per kg was 12.5x106 (5-18x106). Two patients had grade 1 bleeding from the catheter site during apheresis and one patient had dyspnea with suspected fluid overload which responded to a single dose of intravenous furosemide. There were no significant toxicities observed with Plerixafor in mobilization.
All patients went on to receive high dose chemotherapy with melphalan followed by autologous stem cell transplant. The median length of hospital stay was 25 days (18-32). The median stem cell dose infused was 7.6x106CD34/kg and median days to ANC > 500 was 11 (10-22), to platelets > 20K untransfused 22 (15-44) and to lymphocytes > 500/μl 14.5 (11-25). One patient who had VOD and persistent thrombocytopenia was given the remainder of his stem cells on day +31 with full recovery and normalization of the blood counts by day +65.

Conclusions
In the era of more effective initial therapies, an era in which AL patients are living longer, many with moderate organ damage, mobilization with Plerixafor and G-CSF was well tolerated and made it possible to collect ample numbers of CD34+ cells with limited leukaphereses in previously treated patients and in those with advanced renal failure. This approach not only allowed the collection of sufficient CD34+ cells for optimal immediate stem cell dosing but also permitted the cryopreservation of aliquots for post-SCT boost and potentially for future cell-based therapies.

Disclosures:
Comenzo: Millenium: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Prothena: Research Funding; Teva: Research Funding.