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Dmitry Gabrilovich : Peregrine Pharmaceuticals KOL :

Dmitry stays busy as a bee for sure... Ultraviolet vision busy as a bee

JCI Impact (Journal of Clinical Investigation)
pg# 5 of 20

June 2014

ER stress regulates myeloid-derived suppressor cell fate through TRAIL-R–mediated apoptosis

Thomas Condamine, Vinit Kumar, Indu R. Ramachandran, Je-In Youn, Esteban Celis, Niklas Finnberg, Wafik S. El-Deiry, Rafael Winograd,
Robert H. Vonderheide, Nickolas R. English, Stella C. Knight, Hideo Yagita, Judith C. McCaffrey, Scott Antonia, Neil Hockstein, Robert Witt, Gregory Masters, Thomas Bauer, and Dmitry I. Gabrilovich

http://jci.me/74056

http://static.jci.org/impact/2014/jci_impact_2014_06.pdf

Direct link to the June 2014 Dmitry publication...
http://www.jci.org/articles/view/74056?utm_campaign=impact_2014_june&utm_content=short_url&utm_medium=pdf&utm_source=impact

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Dmitry is the MD of MDSC's, so just adding a little bit below.... extra credit if you read the rest and Quiz first thing Monday morning : )

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Research Article
ER stress regulates myeloid-derived suppressor cell fate through TRAIL-R–mediated apoptosis

Thomas Condamine1, Vinit Kumar1, Indu R. Ramachandran1, Je-In Youn1, Esteban Celis2, Niklas Finnberg3, Wafik S. El-Deiry3, Rafael Winograd4, Robert H. Vonderheide4, Nickolas R. English5, Stella C. Knight5, Hideo Yagita6, Judith C. McCaffrey2, Scott Antonia2, Neil Hockstein7, Robert Witt7, Gregory Masters7, Thomas Bauer7 and Dmitry I. Gabrilovich1

1The Wistar Institute, Philadelphia, Pennsylvania, USA.
2H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, USA.
3Penn State Hershey Cancer Institute, Hershey, Pennsylvania, USA.
4Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
5Antigen Presentation Research Group, Imperial College London, London, United Kingdom.
6Department of Immunology, Juntendo University School of Medicine, Tokyo, Japan.
7Helen F. Graham Cancer Center and Research Institute, Christiana Care Health System, Newark, Delaware, USA.

Address correspondence to: Dmitry I. Gabrilovich, The Wistar Institute, 3601 Spruce Street, Room 118, Philadelphia, Pennsylvania 19104, USA. Phone: [phone]; Fax: [phone]; E-mail: [e-mail].

First published May 1, 2014

Myeloid-derived suppressor cells (MDSCs) dampen the immune response thorough inhibition of T cell activation and proliferation and often are expanded in pathological conditions. Here, we studied the fate of MDSCs in cancer. Unexpectedly, MDSCs had lower viability and a shorter half-life in tumor-bearing mice compared with neutrophils and monocytes. The reduction of MDSC viability was due to increased apoptosis, which was mediated by increased expression of TNF-related apoptosis–induced ligand receptors (TRAIL-Rs) in these cells. Targeting TRAIL-Rs in naive mice did not affect myeloid cell populations, but it dramatically reduced the presence of MDSCs and improved immune responses in tumor-bearing mice. Treatment of myeloid cells with proinflammatory cytokines did not affect TRAIL-R expression; however, induction of ER stress in myeloid cells recapitulated changes in TRAIL-R expression observed in tumor-bearing hosts. The ER stress response was detected in MDSCs isolated from cancer patients and tumor-bearing mice, but not in control neutrophils or monocytes, and blockade of ER stress abrogated tumor-associated changes in TRAIL-Rs. Together, these data indicate that MDSC pathophysiology is linked to ER stress, which shortens the lifespan of these cells in the periphery and promotes expansion in BM. Furthermore, TRAIL-Rs can be considered as potential targets for selectively inhibiting MDSCs.


Introduction

Myeloid-derived suppressor cells (MDSCs) are widely considered as an important factor regulating immune responses to different pathologic conditions. Accumulation of these cells is a common occurrence in cancer and many other pathologic conditions (1). MDSCs constitute a heterogeneous group of cells consisting primarily of immature myeloid cells with morphological and phenotypic characteristics similar to those of monocytes and polymorphonuclear neutrophils (PMNs) (referred to herein as M-MDSCs and PMN-MDSCs, respectively) (1–3). MDSCs have a distinct gene expression profile and a number of biochemical and functional differences from normal monocytes and PMNs (4, 5). Expansion of MDSCs in cancer is controlled by several growth factors and cytokines, with GM-CSF being the most prominent (6, 7). However, the fate of MDSCs in tumor-bearing (TB) hosts remains poorly understood. The fact that MDSCs accumulate in large numbers could suggest that these cells have mechanisms protecting them from apoptosis. Indeed, studies have demonstrated several mechanisms that could promote MDSC survival. These mechanisms include TNFR2 signaling, which supports MDSC survival through upregulation of cellular FLICE-inhibitory protein (c-FLIP) and inhibition of caspase-8 activity (8), signaling mediated via IL-4a receptor (9), and decreased cell surface expression of FAS receptor, leading to diminished expression of IRF8 and BAX as well as increased levels of BCL-XL (10). MDSCs induced in highly inflammatory settings had increased resistance to FAS-mediated apoptosis (11). On the other hand, Sinha et al. demonstrated the possibility of CTLs killing MDSCs via FAS-FASL–mediated apoptosis (12). Nonetheless, unbiased analysis of the fate of MDSCs in cancer has been lacking. The initial goal of this study was to investigate the kinetics of MDSC homeostasis in different organs in vivo. To our surprise, our data revealed that MDSCs had much shorter lifespan than their counterpart PMNs and monocytes in tumor-free mice. Further investigation demonstrated that this effect was mediated by changes in the expression of TNF-related apoptosis–induced ligand receptors (TRAIL-Rs) caused by ER stress response in these cells.
Results

MDSC survival in TB mice. To monitor MDSC homeostasis, we administered BrdU to EL4 TB mice for 8 days in drinking water (pulse phase), followed by its withdrawal for 4 days (chase phase). PMNs and PMN-MDSCs (in naive and TB mice, respectively) were defined as CD11b+Ly6G+Ly6Clo, and monocytes and M-MDSCs as CD11b+Ly6G–Ly6Chi (Supplemental Figure 1A; supplemental material available online with this article; doi:10.1172/JCI74056DS1). TB mice had a dramatic increase of MDSCs in spleens and peripheral blood (PB), where PMN-MDSCs represented more than 90% of all MDSCs (2, 13). M-MDSCs incorporated BrdU significantly faster than monocytes (Figure 1A). PMN-MDSCs had the same rate of BrdU uptake as PMNs (Figure 1B). In contrast to M-MDSCs, PMN-MDSCs do not proliferate (13), which explains the different kinetics of BrdU accumulation observed between M-MDSCs and PMN-MDSCs (Figure 1, A and B). During the chase phase, we observed significantly accelerated loss of BrdU positivity by PMN-MDSCs compared with PMNs (Figure 1C). These differences were not due to different kinetics of replacement of labeled cells, since during the pulse phase, PMNs and PMN-MDSCs had similar rates of BrdU incorporation. Therefore, PMN-MDSCs either migrated to different organs or died faster than PMNs. To test these possibilities, we isolated the total population of Gr1+CD11b+ MDSCs from BM of EL4 TB mice and immature myeloid cells (IMCs), with the same phenotype and purity, from naive mice as a control (Supplemental Figure 1B). MDSCs and IMCs were separately labeled with 2 fluorescent cell trackers (CMFDA and DDAO, mixed at a 1:1 ratio), and then injected i.v. into EL4 TB mice. At 6 hours after transfer, the MDSC/IMC ratio in spleens and tumors in the recipients remained the same (1:1; Figure 1D). However, when cells were evaluated 20 hours after transfer, the presence of MDSCs in spleen, tumor, and lung was lower than that of IMCs (Figure 1, E and F). The same results were obtained when the 2 cell trackers were switched between the cells (data not shown), which indicates that the observed differences were not the artifact of the cell labeling. The total number of cells evaluated in each organ was relatively small. However, the large differences in MDSC/IMC ratios between different tissues suggests that blood contamination was not directly responsible for those changes.