Remobilization with G-CSF Is Less Effective Than the Initial Mobilization in Healthy Donors Undergoing Peripheral Blood Stem Cell Collection for Allogeneic Transplantation

Background: The need to repeat peripheral blood stem cell (PBSC) mobilization and collection arises infrequently in healthy donors, but may be required due to insufficient initial collection, graft failure, or relapse of the recipient’s disease. Currently no published data exists on the efficacy of remobilization of healthy PBSC donors. Studies of remobilization in patients undergoing autologous transplantation (ASCT) have largely focused on the use of alternative mobilization agents such as chemotherapy or plerixafor. Boeve et al (Bone Marrow Transplant, 2004) reported that remobilization with G-CSF in patients undergoing ASCT who failed initial mobilization with G-CSF, resulted in higher numbers of CD34+ cells collected than the initial collection, though this required a doubling of the dose of G-CSF.

Patients/Methods: We performed retrospective chart review of 977 consecutive adult (>18 yrs) donors who underwent apheresis for PBSC donation at Washington University School of Medicine from 1995 through 2013. We identified 66 donors who had undergone more than one mobilization. Two cohorts of donors were identified for analysis: Group 1 included donors mobilized initially and again subsequently with G-CSF (10 ug/kg/day), or GM-CSF (5 ug/kg/day) + G-CSF (10 ug/kg/day). Group 2 consisted of donors mobilized with a CXCR4 antagonist, plerixafor (240-320 ug/kg) or POL6326 (1000-2500 ug/kg), and subsequently were remobilized with G-CSF (10 ug/kg/day).

Statistical Analysis: Spearman correlations were performed to analyze the relationship between peak peripheral blood (PB) CD34⁺/uL level; the number of CD34⁺ cells collected per kg (recipient weight); and the number of CD34⁺ cells per L of apheresis collected during initial mobilization (MOB1) and remobilization (MOB2); and the interval (days) between MOB1 and MOB2. One-way ANOVA with repeated measures analyses were performed to determine the relationship of PB CD34⁺/uL, CD34⁺/kg and CD34⁺/L during MOB1 and MOB2.

Results: Group 1 included 30 donors. The median age was 49 years (range 18-75) and 15 were male. The median number of days between MOB1 and MOB2 was 140 (range 26-2238). All 30 donors were remobilized due to graft failure or relapse of the recipient’s disease. PB CD34⁺/uL, CD34⁺/kg and CD34⁺/L all correlated between MOB1 and MOB2. The mean PB CD34/uL at MOB1 was 69 compared to 37 at MOB2 (p= 0.029); the mean CD34/kg collected at MOB1 was 5.6x10⁶ compared to 3.3x10⁶ at MOB2 (p= 0.002); and the mean CD34/L collected at MOB1 was 24.0x10⁶ compared to 17.6x10⁶at MOB2 (p= 0.023). The interval between MOB1 and MOB2 did not correlate with any of the MOB2 variables. Results from the analysis are summarized in Table 1.

Group 2 included 32 donors. The median age was 51 years (range 21-67) and 18 were male. The median number of days between MOB1 and MOB2 was 20 (range 4-1123). 18 donors were remobilized due to mobilization failure, while 14 were remobilized due to graft failure or relapse of the recipient’s disease. The mean PB CD34/uL at MOB1 was 15 compared to 68 at MOB2 (p< 0.001); the mean CD34/kg collected at MOB1 was 2.5x10⁶ compared to 7.1x10⁶ at MOB2 (p< 0.001); and the mean CD34/L collected at MOB1 was 10.6x10⁶ compared to 30.1x10⁶at MOB2 (p< 0.001). The interval between MOB1 and MOB2 did not correlate with any of the MOB2 variables. Results from the analysis are summarized in Table 2.

Conclusion: Remobilization with G-CSF or GM-CSF and G-CSF after initial successful mobilization with the same regimen results in poorer mobilization while remobilization with G-CSF after initial mobilization with a CXCR4 antagonist results in dramatically improved mobilization. The reason for this remains unclear, but in this study the interval between collections was not associated with successful remobilization.