Membrane-associated Hsp72 from tumor-derived exosomes mediates STAT3-dependent immunosuppressive function of mouse and human myeloid-derived suppressor cells
Fanny Chalmin, … , Cédric Rébé, François Ghiringhelli
Fanny Chalmin, … , Cédric Rébé, François Ghiringhelli
Published January 19, 2010
Citation Information: J Clin Invest. 2010;120(2):457-471. https://doi.org/10.1172/JCI40483.
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Research Article Immunology

Membrane-associated Hsp72 from tumor-derived exosomes mediates STAT3-dependent immunosuppressive function of mouse and human myeloid-derived suppressor cells

Abstract

Myeloid-derived suppressor cells (MDSCs) have been identified in humans and mice as a population of immature myeloid cells with the ability to suppress T cell activation. They accumulate in tumor-bearing mice and humans and have been shown to contribute to cancer development. Here, we have isolated tumor-derived exosomes (TDEs) from mouse cell lines and shown that an interaction between TDE-associated Hsp72 and MDSCs determines the suppressive activity of the MDSCs via activation of Stat3. In addition, tumor-derived soluble factors triggered MDSC expansion via activation of Erk. TDE-associated Hsp72 triggered Stat3 activation in MDSCs in a TLR2/MyD88-dependent manner through autocrine production of IL-6. Importantly, decreasing exosome production using dimethyl amiloride enhanced the in vivo antitumor efficacy of the chemotherapeutic drug cyclophosphamide in 3 different mouse tumor models. We also demonstrated that this mechanism is relevant in cancer patients, as TDEs from a human tumor cell line activated human MDSCs and triggered their suppressive function in an Hsp72/TLR2-dependent manner. Further, MDSCs from cancer patients treated with amiloride, a drug used to treat high blood pressure that also inhibits exosome formation, exhibited reduced suppressor functions. Collectively, our findings show in both mice and humans that Hsp72 expressed at the surface of TDEs restrains tumor immune surveillance by promoting MDSC suppressive functions.

Authors

Fanny Chalmin, Sylvain Ladoire, Grégoire Mignot, Julie Vincent, Mélanie Bruchard, Jean-Paul Remy-Martin, Wilfrid Boireau, Alain Rouleau, Benoit Simon, David Lanneau, Aurélie De Thonel, Gabriele Multhoff, Arlette Hamman, François Martin, Bruno Chauffert, Eric Solary, Laurence Zitvogel, Carmen Garrido, Bernhard Ryffel, Christophe Borg, Lionel Apetoh, Cédric Rébé, François Ghiringhelli

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Figure 6

pStat3 expression in MDSCs is dependent on Hsp72 on TDEs.

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pStat3 expression in MDSCs is dependent on Hsp72 on TDEs. (A) Purified m...
(A) Purified myeloid cells from naive WT or TLR2-deficient mice were either untreated or treated as indicated. (B) Naive mice were i.v. injected with TDEs from shRNA mock CT26 cells or Hsp72 shRNA CT26 clones H96 or H97. 18 hours later, spleen cells were harvested and pStat3 expression was determined by FACS. (C) Naive BALB/c mice were s.c. injected with 1 × 106 H96, H97, or mock CT26 cells. 2 weeks later, spleens were harvested and pStat3 expression determined by FACS. For A–C, pStat3 was determined by FACS analysis on MDSC gated cells. Data represent MFI ± SD. Experiments were performed in triplicate (n = 3 mice per group). Inset shows immunoblot of pStat3 expression in sorted MDSCs from mice bearing mock CT26 or Hsp72 shRNA CT26 clone H96. (D) Mice were vaccinated with frozen/thawed CT26 cells 1 week before i.v. injection of live CT26 cells admixed or not with MDSCs isolated from mice bearing shRNA mock-transfected or Hsp72 shRNA-transfected (clone H96) CT26 tumors. Twelve days later, lung metastasis numbers were evaluated. Experiments were performed in triplicate (n = 5 mice per group). For box and whisker plots, bottoms and tops of boxes show the 25th and 75th percentiles, respectively, and middle bands show the median; whiskers show extrema. *P < 0.05. Error bars represent mean + SD.