Tumor-infiltrating myeloid cells induce tumor cell resistance to cytotoxic T cells in mice
Tangying Lu, … , Michael B. Sporn, Dmitry Gabrilovich
Tangying Lu, … , Michael B. Sporn, Dmitry Gabrilovich
Published September 12, 2011
Citation Information: J Clin Invest. 2011;121(10):4015-4029. https://doi.org/10.1172/JCI45862.
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Research Article Immunology

Tumor-infiltrating myeloid cells induce tumor cell resistance to cytotoxic T cells in mice

Abstract

Cancer immunotherapeutic approaches induce tumor-specific immune responses, in particular CTL responses, in many patients treated. However, such approaches are clinically beneficial to only a few patients. We set out to investigate one possible explanation for the failure of CTLs to eliminate tumors, specifically, the concept that this failure is not dependent on inhibition of T cell function. In a previous study, we found that in mice, myeloid-derived suppressor cells (MDSCs) are a source of the free radical peroxynitrite (PNT). Here, we show that pre-treatment of mouse and human tumor cells with PNT or with MDSCs inhibits binding of processed peptides to tumor cell–associated MHC, and as a result, tumor cells become resistant to antigen-specific CTLs. This effect was abrogated in MDSCs treated with a PNT inhibitor. In a mouse model of tumor-associated inflammation in which the antitumor effects of antigen-specific CTLs are eradicated by expression of IL-1β in the tumor cells, we determined that therapeutic failure was not caused by more profound suppression of CTLs by IL-1β–expressing tumors than tumors not expressing this proinflammatory cytokine. Rather, therapeutic failure was a result of the presence of PNT. Clinical relevance for these data was suggested by the observation that myeloid cells were the predominant source of PNT in human lung, pancreatic, and breast cancer samples. Our data therefore suggest what we believe to be a novel mechanism of MDSC-mediated tumor cell resistance to CTLs.

Authors

Tangying Lu, Rupal Ramakrishnan, Soner Altiok, Je-In Youn, Pingyan Cheng, Esteban Celis, Vladimir Pisarev, Simon Sherman, Michael B. Sporn, Dmitry Gabrilovich

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Figure 4

Effect of MDSCs on the protection of tumor cells from CTLs depends on ROS production.

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Effect of MDSCs on the protection of tumor cells from CTLs depends on RO...
(A) MDSCs are resistant to PNT. MDSCs or EL-4 cells were treated for 10 minutes with 0.1 mM PNT. The levels of H-2Kb expression and NT after treatments were examined by flow cytometry (left panels). Cells were labeled with SIINFEKL peptide (SIIN) conjugated with FITC; peptide binding was performed by flow cytometry, and MFI was compared. Four experiments with similar results were performed. (B) Binding of FITC-SIINFEKL peptide was measured in EL-4 cells incubated with untreated MDSCs isolated from EL-4 tumor–bearing mice, in the presence of 250 nM CDDO-Me, or MDSCs isolated from EL-4 tumor–bearing gp91phox–/– mice. As a control EL-4 cells were treated with CDDO-Me (250 nM). The background was set as 100% of peptide binding to untreated EL-4 cells. The graph shows the percentages of changes in MFI compared with background. Different concentrations of peptide were tested and showed similar results. One concentration, 4 μg/ml, is shown. Mean ± SEM of 4 experiments is shown. *P < 0.05 versus background. (C) EL-4 cells isolated from culture with MDSCs were loaded with control or specific peptides as target cells in CTL assays described in Figure 1C. MDSCs were from EL-4 tumor–bearing mice treated for 5 days with 150 mg/kg CDDO-Me or control diets. Representative 1 experiment and mean ± SEM of 3 performed experiments are shown. *P < 0.05 versus IMC-treated EL-4 cells. (D and E) Binding of peptides to tumor cells after treatment with CDDO-Me. EL-4 tumors were established in congenic (CD45.1+) mice. Mice were treated with control or CDDO-Me diets for 5 days. EL-4 (CD45.2+) cells were isolated by magnetic beads, and H-2Kb expression on tumor cells was examined by flow cytometry (D). Peptide binding was analyzed by incubation with FITC-SIINFEKL and evaluated by flow cytometry (E). Data are representative of 3 experiments with similar results.