Background: The transcription factor STAT3 is a negative regulator of myeloid inflammatory immune responses, leading to profound suppression of dendritic cell (DC) and T cell function, and anti-tumor immunity. Blockade of STAT3 signaling in tumor models results in activation of innate immune cells, DCs, and tumor infiltration of T cells. We hypothesized that tumor associated macrophages (TAMs) from breast cancer patients were dysfunctional, due to IL-6-mediated activation of STAT3.

Methods: To isolate sufficient numbers of CD14+ TAMs and CD3+ tumor infiltrating lymphocytes (TILs) for functional assays, 10 malignant effusions were obtained from breast cancer patients and peripheral blood was obtained from 8 healthy controls. Levels of up to 22 cytokines in the effusions and the blood were determined by Luminex cytokine assay. CD14+ TAMs and CD3+ TILs were magnetically sorted, and functional mixed lymphocyte reaction (MLR) assays were performed. Quantitation of STAT3 and tyrosine-phosphorylated STAT3 (pSTAT3) were determined by immunoblotting. RNA expression analysis of TILs and healthy donor CD3+ cells was performed using Affymetrix U133 microarrays.

Results: Malignant effusions from breast cancer patients have high levels of IL-6 (mean 3188 pg/ml; range 966-5235), compared with serum from healthy donors (mean 88 pg/ml; p<0.0001). TAMs isolated from malignant effusions, but not peripheral blood, poorly stimulated healthy T cells in MLR, and showed increased expression of pSTAT3 and total STAT3 on immunoblot. A 30 minute exposure to a malignant effusion containing high levels of IL-6 markedly induced STAT3 activation in healthy donor CD14+ monocytes. Compared with CD3 cells from healthy donors (n=3), RNA microarray analysis of CD3+ TILs (n=3) showed downregulation in TCR signalling (Zap70, fyn, PI3K), NK/CTLs (CD160, KLRF1), and chemokines for T cell trafficking (CXCR4). Immunosuppressive factors (IL10, PDIA4, IL13R, STAT1, and VEGF) were upregulated (p<0.05).

Conclusions: High levels of IL-6 in breast cancer malignant effusions are associated with both antigen presenting cell and T cell dysfunction. Inhibition of STAT3 is a potential target to enhance immune activation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1906.

©2010 American Association for Cancer Research
2010