Background: Myeloid-derived suppressor cells (MDSCs) are heterogenic population of multipotent progenitors of myeloid lineage. For their immunosuppressive effect, MDSC are responsible for tumour escape from the host immune surveillance. Furthermore, MDSCs support tumour by promotion of angiogenesis and metastasis. Membrane markers of human MDSCs are myeloid markers CD11b and CD13, these cells are HLA-Drlow/- and expression of CD15 or CD14 differentiate them into granulocytic (Gr-MDSCs) and monocytic (Mo-MDSCs), resp.
Patients and methods: Using flow cytometry, we investigated Mo-MDSC counts in peripheral blood of non-cancer individuals - control group (n = 61), breast (n = 39) and colorectal (n = 52) cancer patients. These cells were detected as CD45+CD11b+CD33+CD14+HLA-Drlow/- and quantified as percentage of total white blood cells and as absolute count.
Results: In control group, circulating Mo-MDSCs was gender-and age-independent and the average value was 1.09% and 0.073 × 109/l. Breast cancer patients had higher circulating Mo-MDSCs compared to control group with average values: 3.57% and 0.229 × 109/l (p < 0.001) and we also observed increase in Mo-MDSC number after granulopoietic growth factors administration (p = 0.043). Colorectal cancer patients had higher average number of circulating Mo-MDSCs compared to control group: 1.71% a 0.125 × 109/l (p = 0.003) and its number did not correlate with tumour clinicopathological stage, localization of primary tumour (colon vs. rectum), site (left vs. right) and microsatellite instability.
Conclusion: Increased number of MDSCs in circulation and within tumour microenvironment has been associated with immune suppression and tumour progression. Colorectal cancer patients at diagnosis showed higher circulating Mo-MDSCs possibly reflecting immunosuppressive effect of tumour microenvironment. Change of Mo-MDSC number from baseline level need to be evaluated in the context of CRC patients outcome. Recombinant granulopoietic growth factors increase number of circulating Mo-MDSCs and the effect of this phenomenon on cancer prognosis remains to be elucidated.Key words: myeloid-derived suppressor cells - colorectal cancer - breast cancer - immunology - immunosuppression - G-CSF This work was supported by MEYS by NPU I (LO1413), grant AZV 16-31966A and MH DRO 00209805. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers.Submitted: 11. 3. 2017Accepted: 26. 3. 2017.