Utility Of An Algorithm For Use Of Plerixafor In Filgrastim-based Hematopoietic Progenitor Cell Mobilization In Patients With Plasma Cell Myeloma Treated With Carfilzomib-Lenalidomide-Dexamethasone.

Mobilization of hematopoietic progenitor cells (HPC) for subsequent autologous transplantation is difficult in patients with plasma cell myeloma (PCM) due to poor marrow reserve. Targeted HPC yields are generally not achieved in a single apheresis procedure without use of plerixafor as a supplement to standard filgrastim. Strategies to limit use of plerixafor, due to its expense, to cases of poor CD34 mobilization have been developed, but their applicability in patients receiving the novel induction regimen carfilzomib-lenalidomide-dexamethasone (CRD) (Blood 2012;120:1801) has not been described. We prospectively studied the CD34 cell mobilization responses of PCM patients following CRD induction, using a CD34 cell predictive algorithm to determine when plerixafor should be added to the mobilization regimen. Thirty patients, including 23 with PCM and 7 with smoldering PCM, mean age 55 (range 40-72), 47% male, received 4 to 7 cycles of CRD (median, 5 cycles), with the last dose of lenalidomide given at least one week prior to mobilization. Filgrastim 10-16 mcg/kg/day was given as a single evening dose for 5 days, with circulating CD34 count assessed 12 hours after the 4^th dose. The pre-apheresis CD34 count after the 5^th dose of filgrastim was predicted to be 10% greater than that after the 4^th dose; this prediction was validated with an actual pre-apheresis CD34 count obtained the following day. Prior mobilization data derived from healthy HPC apheresis donors was used to generate a regression formula, y=0.45x+0.86, where x=the pre-apheresis circulating CD34 count after the 5^th dose of filgrastim, and y=the expected yield of the apheresis procedure, expressed as millions of CD34 cells harvested per liter processed. Targeted yield was ≥ 4 x 10⁶ CD34 cells/kg, with minimum acceptable yield ≥ 2 x 10⁶ CD34 cells/kg. Plerixafor 240 mcg/kg was given with the 5^th dose of filgrastim, 8-10 hours prior to apheresis, if the regression equation predicted a CD34 cell yield of < 4 x 10⁶ CD34 cells/kg in a single procedure with a maximum of 30 liters processed. The actual volume processed was based on the stat blood CD34 count drawn immediately prior to apheresis. Procedures were performed on the Cobe Spectra device; continuous intravenous calcium was used to mitigate citrate toxicity. Central lines were required in 67% of subjects.

Mean CD34 cell count in the entire group after the 4^th dose of filgrastim was 29/uL (range 2-88/uL). Using the regression formula as a guide, 17/30 (57%) of patients received plerixafor. CD34 counts increased 4.2-fold in patients receiving plerixafor, from 15 ± 9/uL (m ± SD) on the day prior to apheresis to 53 ± 30/uL immediately pre-apheresis; CD34 counts did not change in patients who received filgrastim alone (from 48 ± 17/uL to 45 ± 19/uL). Guided by the stat pre-apheresis CD34 count, the volume processed in the first apheresis procedure was the same, 23 ± 7 (range 12-30) liters, with or without plerixafor. CD34 cells were collected with 72 ± 14% efficiency. First-procedure CD34 cell yields were 6.4 ± 2.5 x 10⁶/kg (range 2.5-10.1) with supplemental plerixafor vs 5.8 ± 2.5 x 10⁶/kg (range 1.1-9.3) with filgrastim alone. Only 2/30 patients underwent a second procedure; neither received plerixafor prior to the first procedure, and both received it prior to the second. In one patient, criteria for plerixafor administration were met, but the drug was inadvertently not given prior to the first procedure; in the second patient, an unexpectedly low pre-apheresis CD34 count was traced to inadequate self-administration of the 5^th dose of filgrastim. All 30 patients achieved the minimum CD34 collection goal of ≥ 2 x 10⁶ cells/kg and 29/30 did this in one procedure. The higher targeted collection goal of ≥ 4 x 10⁶ CD34 cells/kg was achieved in a single procedure by 76% of patients in both the plerixafor group and the filgrastim-alone group. There was a trend for higher cumulative lenalidomide and carfilzomib doses to be associated with lower CD34 mobilization responses to filgrastim.

Induction treatment with CRD does not appear to impair HPC mobilization response to filgrastim in patients with PCM, compared to older regimens. An algorithm that uses the CD34 cell count after 4 doses of filgrastim to predict the following day’s pre-apheresis CD34 count and thus determine whether plerixafor supplementation is needed, was useful in identifying the 40% of CRD-treated myeloma patients who do not need plerixafor.