CM-01. Effect of HSC mobilization procedure in patients with multiple myeloma on the level of myeloid suppressor cells in peripheral blood

Summary

Introduction

The aim of our study was to investigate the influence of hematopoietic stem cell (HSC) mobilization on frequencies of different subsets of myeloid-derived suppressor cells (MDSCs) in peripheral blood (PB) of multiple myeloma (MM) patients.

Patients and methods

The study included 35 patients with MM before and following HSC mobilization courses. The counts of granulocytic (G-MDSCs; Lin^–HLA-DR^–CD33⁺CD66b⁺), monocytic (М-MDSCs; CD14⁺HLA-DR^low/–) and early MDSCs (Lin^–HLA-DR^–CD33⁺CD66b^–) were assessed by flow cytometry.

Results

Relative contents of G-MDSCs and M-MDSCs were increased in MM patients before mobilization of HSCs compared with donors. The relative and absolute amounts of M-MDSCs were significantly higher than the frequency and absolute count of G-MDSCs. Counts of the studied MDSC subsets did not differ from patients with complete/very good partial response (CR/VGPR) and the ones with partial response (PR). There was a statistical trend to higher relative count of G-MDSCs in PB of the patients after 2-3 lines of chemotherapy. After a course of HSC mobilization (cyclophosphamide 2-4 g/m² + G-CSF 5 μg/kg/day), the median values of the relative count of P-MDSCs and M-MDSCs increased 2.3- 2.0 times, respectively, whereas the relative content of G-MDSCs was increased by 46 times.

Conclusion

The percentage of G-MDSCs, as well as relative and absolute levels of M-MDSCs were increased in MM patients compared to donors. Heavy pre-treatment of the patients was associated with higher G-MDSC frequencies. Treatment response (CR/VGPR vs PR) was not associated with any differences in quantitative MDSC indices. HSC mobilization with G-CSF led to a significant increase of all analyzed MDSC populations.

Keywords

Multiple myeloma, myeloid-derived suppressor cells, hematopoietic stem cell mobilization, G-CSF.