Increased circulating myeloid-derived suppressor cells correlate with cancer stages, interleukin-8 and -6 in prostate cancer

Abstract

Aim: Myeloid-derived suppressor cells (MDSCs) are a population of cells which negatively regulate immune response during tumor progression. In this study, we assessed the accumulation of MDSCs (CD33(+)CD11b(+)HLA-DR(-)CD14(-)) in patients with prostate cancer and its clinical relevance.

Methods: We tested the frequency of MDSCs in the peripheral blood of patients with prostate cancer or benign prostate hyperplasia and healthy donors. Serumal interleukin-8, -6 and -10 were analyzed. Effects of MDSCs on the T cell response were determined.

Results: MDSCs increased in cancer patients, and there was an association between MDSCs and cancer stages or overall survival. Elevated serumal interleukin-8 and -6 in cancer patients correlated with MDSCs. Moreover, accumulation of MDSCs was associated with defective T cell function.

Conclusion: Our study showed an increased population of MDSCs in patients with prostate cancer. Interleukin-8 and -6 in serum may play a new important role companied with MDSCs in prostate cancer.

Keywords: IL-6; IL-8; MDSCs; prostate cancer.

Figure 1

MDSCs FACS and scatter plots of cancer patients and healthy controls. CD33⁺CD11b⁺HLA-DR^-CD14^- MDSCs FACS gating of PBMC of a patient with prostate cancer (A) and an age-matched normal control (B). Dot plots represent live gated events. The forward and side scatter gate was analyzed for CD33⁺HLA-DR^- cells. Then the CD33⁺HLA-DR^- gate was analyzed for cells expressing CD11b and CD14. MDSCs were calculated as a percentage of live cells in PBMCs. Markers analyzed are indicated in the axis of each FACS plot.

Figure 2

Significantly elevated MDSCs in patients with prostate cancer. A. Mean granulocytic CD33⁺CD11b⁺HLA-DR^-CD14^- MDSCs levels in patients with prostate cancer were significantly higher than age-matched controls and patients with BPH. B. Mean monocytic CD33⁺CD11b⁺HLA-DR^-CD14⁺ MDSCs levels in patients with prostate cancer were higher than controls and patients with BPH. C. Mean granulocytic CD33⁺CD11b⁺HLA-DR^-CD15⁺ MDSCs levels in patients with prostate cancer were higher than controls and patients with BPH. D. CD33⁺CD11b⁺HLA-DR^-CD14^- MDSCs is the the major phenotype of MDSCs in prostate cancer.

Figure 3

CD33⁺CD11b⁺HLA-DR^-CD14^- MDSCs correlated with clinical stages. Correlation between percentage of MDSCs and clinical stages (A), T classification (B), N classification (C) and distant metastasis (D) in patients with prostate cancer and normal controls (*P<0.05, **P<0.01).

Figure 4

IL-8, -6 and -10 are significantly higher expressed in patients with prostate cancer and correlated with stages of cancer. Serum cytokines levels including IL-8 (A), IL-6 (B) and IL-10 (C) in age-matched normal controls and patients with prostate cancer were measured using ELISA assays. Serum samples from patients had a significantly higher level of IL-8, 6 and 10 than control samples (left lanes) and the levels increased with clinical stages (right lanes) (*P<0.05, **P<0.01).

Figure 5

MDSCs correlated with serum IL-8 and IL-6 in patients with prostate cancer. MDSCs were associated with the poor prognosis of patients with prostate cancer. Spearman correlation analyses between percentages of MDSCs and serum levels of IL-8 (A, r=0.7149, P<0.0001) and IL-6 (B, r=0.6392, P<0.0001) in patients with prostate cancer. (C) Correlation between percentages of MDSCs and survival by Kaplan-Meier analysis of patients with the high (≥ the median) or low (< the median) MDSCs level.

Figure 6

MDSCs decreased T cell responses. Equal numbers of PBMCs from normal controls (N) and three patients with stage IV cancer (P) were assayed for cell proliferation (A), IL-2 (B) and IFN-γ(C) secretion in response to activation with anti-CD3/CD28-coated beads. Corresponding percentages of circulating MDSCs are shown above in bold. D. PBMCs were stained with CFSE, cultured for 5 days, and then stained with monoclonal antibodies against CD4 and CD8; proliferation was quantified as the percentages of CFSE^low cells. Left: Representative histogram of the FACS analysis. Right: Analysis of T cell proliferation. Myeloid cells (CD33⁺HLA-DR^-) were isolated from freshly drawn blood from three normal controls (N) and three patients with stage IV cancer (P). Direct contact of T cells with isolated myeloid cells (CD33⁺HLA-DR^-) from cancer patients inactivates T cell. E. Representative histograms of CD33⁺HLA-DR^- fractions before and after enrichment. F. Proliferation of isolated autologous T cells in response to CD3/CD28 activation in the presence of the indicated ratios of purified autologous CD33⁺HLA-DR^- cells.