Abstract

The CXCR4 antagonist, AMD3100, has recently been shown to rapidly mobilize primitive hematopoietic cells into the circulation. Compared to the agent of choice for clinical mobilization, granulocyte-colony stimulating factor (G-CSF), AMD3100 increases the peripheral WBC count within 4–6 hours after injection, whereas G-CSF takes up to 5 days to reach the maximum WBC number. This difference in rapidity of mobilization makes AMD3100 an interesting alternative to G-CSF. However, due to the different mobilization mechanisms of the two agents, it is of importance to evaluate the extent of mobilization of other cell lineages in addition to the most immature, as defined by the stem cell marker CD34. The lymphocyte subsets are of importance in predicting immune recovery, as well as potential graft-versus-leukemia, or graft-versus-host disease outcomes, and the commited myeloid progenitors are important for evaluating time to neutrophil and thrombocyte recovery post transplant. Here we report a detailed multilineage study of paired AMD3100 and G-CSF Mobilized-Peripheral Blood (MPB) products from two healthy donors. The mobilization regimens included an initial leukapheresis after a single injection of 240ug/kg AMD3100, which in the two donors produced an enrichment of circulating CD34+ cells to 0.6% and 0.8% of the total mononuclear cells (MNC), respectively. Following 2 weeks of drug clearance, the same donors were mobilized with G-CSF (0.4% and 1.9 % CD34+ cells, respectively), allowing for a paired comparison of the cell lineages mobilized into the circulation by these two regimens. Multilineage analysis of the MPB products showed that AMD3100 and G-CSF MPB products contained a similar quantity of monocytes and myeloid cells, as defined by CD13 (28.7+/−11.7 with AMD vs. 44.65+/−16.5 with G-CSF), CD14 (26.3+/−10.4 vs. 45.8+/−25.9) and CD66 (53.2+/−19.6 vs. 50.7+/−17.0). Moreover, the T-lymphocyte content of the AMD3100 MPB products averaged 33.6 +/− 4.7% CD4+ T cells, whereas the G-CSF MPB products contained 12.2 +/− 1.2 % CD4+ T-cells. Similary, the population of CD8+ cells present in the two M-PBSC products averaged 29.1 +/− 16.8% CD8+ for the AMD3100 MPB products and 5.4 +/− 5.1% CD8+ for the G-CSF MPB products. Although this appears to constitute a trend towards a higher degree of T-cell mobilization by AMD3100 compared to G-CSF, this difference may be explained on the basis of polymorphic variations between donor 1 and 2. Finally, expression of CXCR4 has been proposed to play a critical role in stem cell homing and migration after transplantation. We have evaluated the extent of CXCR4 expression in the resulting MPB products from the two mobilization regimens and found that 13.4+/−1.9% of the AMD3100 MPB product expressed the CXCR4 receptor whereas the level of expression in the G-CSF MPB product was 0.85+/−1.2. This may suggest increased responsiveness to SDF-1, and thereby increased engraftment speed post transplantation. Overall, these preliminary data indicate that AMD3100 does not differentially mobilize any of the major cell lineages as compared to G-CSF, including the immature CD34 subset.

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