The effect of mobilizing large numbers of CD34 + cells (super-mobilizers) on the engraftment and survival in patients undergoing autologous stem cell transplantation.

With the use of plerixafor in addition to growth factor for peripheral blood stem cell mobilization, the yield of autologous stem cell harvest has been higher while the length of apheresis days has become shorter. There is still debate whether higher cell collection efficacy in autologous stem cell transplant (ASCT) affect outcomes. In this retrospective study, we defined two groups of patients, group 1, super-mobilizers, with more than double the target cell dose collected (n = 15), while group 2 included all other patients (n = 75). Multiple myeloma (MM) and lymphoma patients were combined. Patients with chemo-mobilization, those needed more than one day apheresis, or with less than 100 days after ASCT were excluded. Correlations were performed between cell collection efficacy and post thaw CD34 cell viability (by 7AAD flow cytometry method), product HCT, and engraftment of neutrophils and platelets. We performed multiple linear regression using the above variables in addition to age, sex and disease type. We used Kaplan Meier's curves to show effect of cell collection efficacy on 1-year overall survival (OS). Our results show that all super-mobilizers received plerixafor in addition to G-CSF, while 83% did in group 2. Correlations between cell collection efficacy and neutrophil and platelet engraftment in group 1 and 2 was modest and better in group 1 (R=0.449 Vs 0.233 for neutrophils; R=0.464 Vs 0.110 for platelets, respectively). However, multiple linear regression showed statistically significant association between cell collection, as a continuous variable, with disease type (P < 0.001), product HCT (P < 0.001), post thaw viability (P = 0.003), and age (P = 0.013). MM patients were more likely to be super-mobilizers, while the product HCT was higher in the super-mobilizers. No significant effect of cell collection efficacy was found on engraftment of neutrophils or platelets. With relatively short post ASCT follow up, 6 patients in group 2 died of any cause while no deaths were recorded in the super-mobilizers group (P = 0.1892 by log-rank test). In conclusion, stem cell collection efficacy in ASCT is more frequent in MM than lymphoma patients, but is not predictive of faster engraftment. On the other hand, 1-year OS was 100% in the super-mobilizers group versus 93% in the other group.