Pleural Effusion of Patients with Malignant Mesothelioma Induces Macrophage-Mediated T Cell Suppression

Our plain-English summary of Pleural Effusion of Patients with Malignant Mesothelioma Induces Macrophage-Mediated T Cell Suppression, by L.A. Lievense, R. Cornelissen, K. Bezemer, et al (Journal of Thoracic Oncology, 2016).

The study

• Authors: L.A. Lievense, R. Cornelissen, K. Bezemer, M.E. Kaijen-Lambers, J.P. Hegmans, J.G. Aerts
• Journal: Journal of Thoracic Oncology
• Published: 2016;11(10):1755-64
• Cited by: 75 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: Clinical studies have demonstrated beneficial effects of immunotherapy in malignant pleural mesothelioma. The pleural cavity seems an attractive compartment to administer these types of therapies; however, local immunosuppressive mechanisms could hamper their efficacy. Macrophages are abundantly present within the mesothelioma microenvironment. This study investigates the influence of the macrophage phenotype, macrophages' capacity to inhibit local immune responses, and the decisive role of pleural effusion (PE) in this regard.

Methods: We cultured macrophages in the presence of PEs and investigated their phenotype. Macrophages and T cells were cocultured in the presence of PEs and tumor cell line supernatants. The levels of 11 cytokines and the prostanoid prostaglandin E2 were measured in PEs and supernatants. The presence and phenotype of macrophages and T cell subsets was measured in the PE of patients with mesothelioma.

Results: PE induced a tumor-promoting M2 phenotype in macrophages, which was confirmed by the suppressive activity of macrophages on T cell proliferation during coculture. Prostanoid prostaglandin E2 was identified as a potential inducer of the suppressive capacity of macrophages in PE. Macrophages isolated from PEs displayed an M2 phenotype and were negatively correlated with T cells in vivo.

Conclusions: The current study demonstrates that macrophages in PE can play a pivotal role in directly hampering the antitumor T cell immune response. This emphasizes the potential of macrophages as a therapeutic target in mesothelioma and indicates that the presence and phenotype of macrophages in PE should be taken into consideration in the application of (intrapleural) immunotherapies.

Copyright © 2016 International Association for the Study of Lung Cancer. Published by Elsevier Inc. All rights reserved.

In plain English

This laboratory study examined how pleural effusion (fluid around the lungs) from people with malignant pleural mesothelioma affects immune cells called macrophages. Asbestos exposure was not studied. Macrophages made from a healthy donor's blood cells, exposed for two days to 10% cell-free effusion fluid from six patients, showed gene activity typical of tumor-promoting (M2) macrophages. When macrophages and T cells, another immune cell, were cultured together for four days in 10% effusion fluid, the macrophages significantly reduced T cell growth. In 30% fluid from tumor cell lines made from the same effusions, they instead increased it. Prostaglandin E2 was 80-fold higher in effusions than in cell line fluid. Added at 30 ng/mL to cell line cocultures, it reduced T cell growth by 50.4%. In stored effusions from 30 untreated patients, macrophages averaged 46.8% of live cells; a higher macrophage percentage went with a lower T cell percentage (correlation minus 0.90). The authors concluded that the effusion is an immunosuppressive compartment where macrophages play a pivotal role in hampering anti-tumor immunity. They noted the results apply to the effusion, not the tumor itself.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) experiments on healthy-donor macrophages and T cells exposed to patient pleural effusion fluid, plus flow cytometry analysis of stored pleural effusion cells from 30 patients, with clinical data retrieved retrospectively
• Who was studied: 30 untreated patients with malignant pleural mesothelioma, selected from the Erasmus Medical Center (Rotterdam, The Netherlands) immunotherapy-trial data bank based on availability of stored pleural effusions. 29 were male, and 26 had epithelioid tumors. Effusion fluid from 6 patients, and cell lines grown from those effusions, was used in the lab experiments, together with monocytes and T cells from one healthy blood donor.
• Exposure: No asbestos or fiber exposure was studied. In the laboratory, healthy-donor monocytes were first differentiated into macrophages over 6 days. For the gene expression experiments, they were then cultured for 2 days in 10% pleural effusion supernatant. For the T cell experiments, macrophages and T cells were cocultured for 4 days in 10% normal human serum, 10% pleural effusion supernatant, or 30% mesothelioma cell line supernatant. Cytokines and prostaglandin E2 were measured in the effusion and cell line fluids.
• Main results:
  • Macrophages cultured in pleural effusion supernatants showed M2-type gene expression: high CD163 and IL-10, and low CD80, PD-L1 and HLA-DR.
  • During 4-day cocultures with 10% pleural effusion supernatant present, macrophages significantly reduced T cell proliferation (6 effusions, p = 0.03). During cocultures with 30% mesothelioma cell line supernatant present, macrophages enhanced T cell proliferation.
  • None of the attempts to restore T cell proliferation worked. Adding normal human serum did not restore it, and neither did lowering the effusion concentration to 5% or adding the M1 stimuli IFN-g and lipopolysaccharide.
  • Measured cytokines were about threefold higher in the effusions than in the cell line supernatants, while prostaglandin E2 was 80-fold higher. Adding synthetic prostaglandin E2 at 30 ng/mL (the average level measured in the effusions) to cocultures in cell line supernatant reduced T cell proliferation by 50.4%.
  • In effusions from the 30 patients, tumor-associated macrophages were the most common immune cell measured, at a mean of 46.8% (SD 32.2%) of live cells. Mean CD3 T cells were 26.7% (SD 27.9%), and mean CD8 T cells were 8.5% (SD 8.8%).
  • In the 30 patients' effusions, measured as percentages of live cells, macrophages were negatively correlated with all T cells (r = minus 0.90, p less than 0.001), with CD4 T cells (r = minus 0.89) and with CD8 T cells (r = minus 0.85). Regulatory T cells, as a percentage of CD4 T cells, were positively correlated with macrophages (r = 0.58, p less than 0.01).
  • B cells were not significantly correlated with macrophages (r = minus 0.06, p = 0.75). Prostaglandin E2 levels in the 30 effusions were not correlated with macrophages or T cells.
• The authors' conclusion: The authors concluded that pleural effusion is an important immunosuppressive compartment in malignant pleural mesothelioma, and that tumor-associated macrophages play a pivotal role in hampering the antitumor immune response.
• Limitations the authors state:
  • The results are restricted to the pleural effusion and cannot be taken to apply to the tumor itself or to macrophages inside the tumor.
  • Patient macrophages were classified as M2 by the surface markers CD163 and/or CD206, which do not demonstrate how the cells actually function.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Pleural Effusion, Malignant Mesothelioma, Macrophage, Immunotherapy, Pleural Mesothelioma, Pleural Cavity, Mesothelioma, Cytokine.

Related studies

• Are macrophages, myeloid derived suppressor cells and neutrophils mediators of local suppression in healthy and cancerous tissues in aging hosts? — C. Jackaman, D.J. Nelson (2014)
• Heterogeneity in immunologic functions of rat alveolar macrophages--their accessory cell function and IL-1 production — Y. Oghiso (1987)
• Pleural Effusions from Patients with Mesothelioma Induce Recruitment of Monocytes and Their Differentiation into M2 Macrophages — A.L. Chéné, S. d'Almeida, et al. (2016)
• Precision immunotherapy; dynamics in the cellular profile of pleural effusions in malignant mesothelioma patients — L.A. Lievense, K. Bezemer, et al. (2017)
• Intrapleural interleukin-2 induces nitric oxide production in pleural effusions from malignant mesothelioma: a possible mechanism of interleukin-2-mediated cytotoxicity? — C. Porta, V. Rizzo, et al. (2002)
• Tumor-associated macrophages in thoracic malignancies — L.A. Lievense, K. Bezemer, et al. (2013)

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