Immunosuppressive CD14+HLA-DRlow/- monocytes in prostate cancer

Abstract

Objective: To determine if the levels of circulating myeloid-derived suppressor cells increase with progression of prostate cancer (PCa); to determine if such cells could contribute to the relative inefficiency of PCa immunotherapy.

Materials and methods: We analyzed peripheral blood mononuclear cells isolated from untreated PCa patients (uPCa; N = 18; mean age +/- SD: 72.1 +/- 6.9 years), tPCa (N = 22; 72.8 +/- 9.8 years) and age matched controls (AMC; N = 12; 68.8 +/- 7.5 years). We quantified surface marker phenotype, differentiation potential, effects on T cell proliferation and intracellular cytokines.

Results: We observed an unexpectedly high percentage of a type of myeloid-derived suppressor cells, CD14(+)HLA-DR(low/-) monocytes, in tPCa (30.7 +/- 15.0% of CD14(+) cells) relative to AMC (4.1 +/- 6.5%, P < 0.0001) and uPCa (10.6 +/- 14.3%, P = 0.0001). The levels of CD14(+) HLA-DR(low/-) cells were significantly correlated with circulating PSA levels and treatment with LHRH-agonist leuprolide in combination with either an antiandrogen or dexamethasone. Monocytes from tPCa inhibited autologous T cell proliferation statistically significantly more effectively than AMC monocytes and were defective in their ability to differentiate into phenotypically mature dendritic cells. Isolated CD14(+)HLA-DR(low/-) cells expressed higher levels of intracellular interleukin-10 and suppressed T cell proliferation more effectively than isolated CD14(+)HLA-DR(+) cells.

Conclusions: This is the first report of CD14(+) cells exhibiting reduced expression of HLA-DR molecules in PCa patients. These cells suppress immune cell function in vitro and, plausibly, in vivo, a finding that must be factored into the design of immunotherapy protocols for PCa patients.

Fig. 1

Percentage of HLA-DR^low/− cells among CD14⁺ cells in peripheral blood of AMC subjects (white circles), newly diagnosed untreated prostate cancer patients (uPCa; gray circles) and tPCa patients (black circles). Horizontal lines indicate mean values. The differences between AMC and tPCa and between uPCa and tPCa are statistically significant (P < 0.0001 and P = 0.001, respectively).

Fig. 2

a: Percentage of mature CD83⁺ dendritic cells in the final preparation and (b) viable cell yield expressed as percentage of the initially plated CD14⁺ cells for age-matched non-cancerous controls (AMC; white circles) and prostate cancer patients treated by androgen suppression (tPCa; blackcircles). Horizontal lines indicate mean values; the difference between CD83⁺ cell levels from AMC and tPCa in panel a is statistically significant (P = 0.0541); the difference in yields (b) is not (P = 0.543). c: Percentage of CD83⁺ cells and (d) CD83 mean fluorescence intensity (MFI) of cells after DC maturation from the CD14⁺ cells plotted as functions of the percentage of HLA-DR^low/− cells among CD14⁺ cells.

Fig. 3

T cell proliferation in the presence of autologous monocytes. a: CD4⁺ cells; (b) CD8⁺ cells. White circles, AMC; blackcircles, tPCa. T cells were stimulated by CD3/CD28 ligation in the absence or presence of autologous monocytes. All data were corrected by subtracting the corresponding values measured in unstimulated T cells in the absence of monocytes. There was no difference in proliferation of CD4⁺ cells (P = 0.515) or CD8⁺ cells (P = 0.995), but tPCa monocytes inhibited proliferation of autologous CD4⁺ cells and CD8⁺ cells more potently than AMC monocytes (P = 0.0036 and P = 0.0044, respectively). c, Left panel: A representative scattergram of mononuclear cells isolated from the blood of a treated PCa patient (P29 in Table II). CD14⁺ cells in the rightmost peak (monocytes) were sorted into HLA-DR^low/− cells and HLA-DR⁺ cells (right panel). d: Comparison of the effects of sorted HLA-DR^low/− cells and HLA-DR⁺ cells (shown in panel c) on proliferation of autologous T cells (measured as DNA synthesis) at the 1:1 ratio. Numbers in the panel designate the P-values for differences between bracketed pairs of groups (two-sided Student's t-test).

Fig. 4

T cells in PBMCs of subjects described in the legend to Figure 1. a: Percent of CD4⁺ cells (circles) and CD8⁺ cells (squares) among CD3⁺ cells. The percentage of CD4⁺ cells in AMC differed statistically from uPCa(P < 0.05). b: CD4⁺CD25⁺CD127^low/− T regulatory cells as percent of CD4⁺ cells. Horizontal lines indicate mean values. The percentage of cells in uPCa differed statistically from tPCa (P < 0.05).

Fig. 5

HLA-DR expression on CD19⁺ B cells from subjects described in the legend to Figure 1. Horizontal lines indicate mean values; these values did not differ statistically.

Fig. 6

Percent of CD4⁺ cells among CD3⁺ cells (upper panel), CD4⁺CD25⁺CD127^lo/− cells among CD4⁺ cells (middle panel) and HLA-DR^low/− cells among CD14⁺ cells (lower panel) plotted as a function of PSA concentrations measured in the blood of all subjects in this study. For statistical details, see the text.