Poor Mobilizers in an Autologous Hematopoietic Stem Cell Transplantation Setting: Matched Pair Analysis Profiling G-CSF and Plerixafor-Mobilized Stem Cells

Abstract 4413

Granulocyte colony-stimulating factor (G-CSF; Neupogen) is by far the most commonly used agent for mobilization of stem cells for autologous peripheral blood stem cell transplantation (ASCT) of non-Hodgkin lymphoma (NHL), Hodgkin lymphoma (HL), and multiple myeloma (MM) patients. However, up to 30% of the patients will fail to mobilize the targeted amount of CD34+ cells. The addition of plerixafor has been shown to mobilize the stem cells when G-CSF fails to do so. However, no reports have hitherto addressed and compared the biology of the CD34+ stem cells obtained from an inadequate G-CSF mobilization and a subsequent plerixafor administration. Given these considerations, this study was aimed at assessing the proportion of stem cells by means of phenotype and colony-forming potential. Given that CD34 is at best only a surrogate marker for stemness, we here included the aldehyde dehydrogenase (ALDH) activity, an emerging crucial marker in stem cell biology, to evaluate the stem cell pool in paired samples obtained after G-CSF and plerixafor administration.

Cryopreserved samples of peripheral blood mononuclear cells (PBMC) from patients diagnosed with NHL (n=3), MM (n=4), and HL (n=1,) were directly compared. All patients were heavily treated with at least 3 cytoreductive regimens prior to the decision to proceed with ASCT. Different mobilizing regimens were applied, but all received one dose of plerixafor (0.24mg/kg sc) as a result of failed G-CSF mobilization (12mg/kg sc twice daily for 3–5 days). The PBMCs were obtained from the morning CD34+ screening sample taken 1) during G-CSF mobilization, typically 1–2- days before it was substituted with plerixafor, and 2) the morning after the plerixafor injection. The percentages of CD34+CD38+ and CD34+CD38- cells and the percentage of ALDH^bright CD34+ cells in the samples of the suboptimal G-CSF mobilization and the matched plerixafor/G-CSF mobilization were analyzed and calculated as percentage of PBMC. These samples were also subjected to semisolid culturing and colonies were quantified after 14 days, where CFU-GEMM, BFU-E, and CFU-GM were enumerated.

We found no significant difference in the percentage of CD34+CD38+ and CD34+CD38- cells in the cell pools recovered from G-CSF (mean 0.68%, SD 0.281 and mean 0.183%, SD 0.095, respectively) and plerixafor mobilization (mean 1.123%, SD 1.143 and mean 0.361%, SD 0.316, respectively) (n=8, Wilcoxon matched-pairs signed rank test, p=0.46 and p=0.15, respectively). Importantly, when comparing the percentage of ALDH^bright CD34+ cells (G-CSF: mean 0.071%, SD 0.048. Plerixafor: mean 0.261%, SD 0.298) in the same matching samples the difference between them was not significant (p=0.11). Finally, the numbers of CFU-GEMM (G-CSF: mean 12.13, SD 16.65. Plerixafor: mean 12.5, SD 14.23), BFU-E (G-CSF: mean 2.375, SD 3.926. Plerixafor: mean 4.125, SD 7.06), and CFU-C colonies (G-CSF: mean 9, SD 13.68. Plerixafor: mean 10.5, SD 11.45) originating from the matching G-CSF and plerixafor-mobilized cells were not significantly different (p=0.93, p=0.29, p=1, respectively).

Collectively, these data reveal that in poor G-CSF mobilizers, the ratios of CD34+CD38+ and CD34+CD38- cells to PBMCs were equal in the matching samples recovered from G-CSF and plerixafor mobilization clearly suggesting that successful plerixafor mobilization is the consequence of increased cell release only in otherwise poor mobilizers. Notably, plerixafor and G-CSF caused the release of stem cells with equal degrees of stemness and commitment as measured by ALDH activity, percentages of CD34+ cells, and colony forming potential.