Myeloid-derived suppressor cells express the death receptor Fas and apoptose in response to T cell–expressed FasL

Abstract

IntroductionTumor progression in patients and mice is associated with increasing levels of a population of suppressor cells known as myeloidderived suppressor cells (MDSCs). MDSCs suppress antitumor immunity by blocking the activation of CD4 ϩ and CD8 ϩ T cells, 1-3 skewing cytokine production toward a type 2 phenotype, 4 inhibiting natural killer-cell cytotoxicity, 5,6 promoting the accumulation of immune suppressive regulatory T cells, 7,8 and perturbing lymphocyte trafficking. 9 As a result, MDSCs are a significant obstacle to cancer immunotherapies that require activation of the host's immune system.A hallmark of tumor-driven MDSCs is their elevated presence in the BM, spleen, blood, lymph nodes, and primary and metastatic tumor sites. 1,10 Their accumulation is attributed to multiple proinflammatory factors, including IL-1␤, 11,12 IL-6, 13 prostaglandin E 2 (PGE 2 ), 14,15 S100A8/A9 proteins, 10, 17 and VEGF,18,19 driving their differentiation from hemopoietic progenitor cells. These inflammatory mediators are produced by tumor cells 13,[20][21][22] or host cells 23,24 or both. In persons with cancer, tumor cells are the predominant inducers because removal of tumor causes a rapid decrease in MDSCs. 25,26 In contrast to induction of MDSCs, the factors that regulate MDSC maintenance and turnover are not well understood.Accumulation For personal use only. on May 11, 2018. by guest www.bloodjournal.org From Mass spectrometryMDSCs were obtained from the peripheral blood of tumor-bearing mice 14 (Ͼ 90% Gr1 ϩ CD11b ϩ cells; 5 ϫ 10 6 -10 7 cells/mouse) and lysed at a final concentration of 0.1% Rapigest acid-cleavable detergent (Waters) in 100mM NH 4 HCO 3 , pH 8.4. Cell lysates were digested with sequencing grade-modified trypsin (1:50 trypsin-to-protein ratio; Promega) for 1 hour at 37°C, after which trifluoroacetic acid was added to a final pH of ϳ 3. Lysates were incubated for 1 hour at 37°C, freeze-thawed at Ϫ80°C, and microfuged at 13 200 rpm for 5 minutes (Eppendorf 5415 D), and the trifluoroacetic acid-precipitated material was discarded. 27 Supernatant fluid containing tryptic peptides was collected and brought to pH 7, and peptide concentration was measured by OD 280. Peptides (30 g) were desalted (C18 spin cartridges; Pierce) and analyzed with a LTQ-FT Ultra mass spectrometer (ThermoFischer) interfaced with an Agilent 1100 nanoLC system. Tandem mass spectra were searched against the National Center for Biotechnology Information (NCBI) mouse protein database 28 with the use of MASCOT data analysis software (v2.1; Matrix Science) with the following conditions: peptide mass tolerance at 10 ppm; fragment mass tolerance at 1.5 Da; a maximum of 2 allowed missed cleavages; and methionine oxidation and disulfide as the variable modifications. Proteins identified by Ն 2 peptides with a MASCOT MOWSE (molecular weight search) score Ͼ 30 were considered reliable identifications. 29 Antibodies, flow cytometry, confocal microscopyFluorescently coupled mAbs to Gr1, CD11b, Fas, FasL, CD69, CD3, CD4, DO11.10 TCR (clon...

TNF signaling drives myeloid-derived suppressor cell accumulation

“…Blockade of factors such as S100A8/9 impairs MDSC accumulation (34). Besides, recent researches report that activation of the Fas/FasL pathway (38) or blockade of the IL-4Rα/STAT6 pathway (39) also promote MDSC apoptosis. It is not presently clear whether these factors function separately or synergistically or interact with TNF in MDSC accumulation.…”

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

“…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.…”

Myeloid-derived suppressor cell development is regulated by a STAT/IRF-8 axis

“…Intriguingly, granulocytic MDSCs outnumber monocytic MDSCs in numerous mouse tumor models (3,5), although the basis for this subset dichotomy remains unclear. The phenotypes in humans are more complex and vary with tumor type.…”