Binding of programmed death ligand-1 (PD-L1) to programmed cell death protein-1 (PD1) leads to cancer immune evasion via inhibition of T cell function. One of the defining characteristics of glioblastoma, a universally fatal brain cancer, is its profound local and systemic immunosuppression. Glioblastoma has also been shown to generate extracellular vesicles (EVs), which may play an important role in tumor progression. We thus hypothesized that glioblastoma EVs may be important mediators of immunosuppression and that PD-L1 could play a role. We show that glioblastoma EVs block T cell activation and proliferation in response to T cell receptor stimulation. PD-L1 was expressed on the surface of some, but not of all, glioblastoma-derived EVs, with the potential to directly bind to PD1. An anti-PD1 receptor blocking antibody significantly reversed the EV-mediated blockade of T cell activation but only when PD-L1 was present on EVs. When glioblastoma PD-L1 was up-regulated by IFN-g, EVs also showed some PD-L1-dependent inhibition of T cell activation. PD-L1 expression correlated with the mesenchymal transcriptome profile and was anatomically localized in the perinecrotic and pseudopalisading niche of human glioblastoma specimens. PD-L1 DNA was present in circulating EVs from glioblastoma patients where it correlated with tumor volumes of up to 60 cm3. These results suggest that PD-L1 on EVs may be another mechanism for glioblastoma to suppress antitumor immunity and support the potential of EVs as biomarkers in tumor patients.
Bibliographical noteFunding Information:
We thank M. Ericsson from the Harvard Electron Microscopy Core Facility for technical support. Funding: This work was funded, in part, by the following: NIH [National Cancer Institute (NCI) P01 CA69246 (to E.A.C. and B.S.C.), NCI 1R01 CA176203-01A1 (to J.G.), and NIH UH3 TR000931 (to B.S.C.)], Deutsche Forschungsgemeinschaft (scholarship to F.L.R.; RI 2616/1-1 and RI 2616/2-1), 1RO1NS097649-01, the Doris Duke Charitable Foundation Clinical Scientist Development Award, the Sontag Foundation Distinguished Scientist Award, the Kimmel Scholar Award, and BWF 1006774.01 (to C.C.C.). U19 CA179563 was supported by the NIH Common Fund through the Office of Strategic Coordination/Office of the NIH Director (to X.O.B.) and NIH/NCI P01 CA069246 (to X.O.B.) and by an American-Italian Cancer Foundation Postdoctoral Research Fellowship (to C.P.). S.R. acknowledges support from the Center for Immuno-Oncology, Dana-Farber Cancer Institute. Author contributions: F.L.R. designed, acquired, and analyzed overall assays; designed the study; and wrote the paper. Q.A. performed in vivo assays. H.K. acquired data and designed the study. A.B.M. acquired data and interpreted the results. M.C.S. acquired data and designed the study. J.L.H. performed bioinformatic analysis. K.L. and K.Y. performed ELISA-type sandwich fluorescent measurements. L.B. performed and analyzed droplet PCR. C.P. designed and performed the PD-L1/PD1 binding assay. A.K.R. performed short tandem repeat analysis and interpreted the data. S.K. performed confocal microscopy and interpreted the results. C.C.C. and I.N. obtained and controlled patient specimens. T.S. and J.T. analyzed MR data. S.R. performed and interpreted IHC staining. S.C., H.L., X.O.B., R.W., J.G., M.W., K.L., A.B., and G.J.F. assisted with the writing of the manuscript and with analysis and interpretation of the data. S.E.L. designed the study, analyzed the data, and wrote the manuscript. E.A.C. acquired patient specimens, designed the study, analyzed the data, and wrote the manuscript. All authors discussed the results and commented on the manuscript. Competing interest: G.J.F. has patents/pending royalties on the PD1 pathway from Roche, Merck, Bristol-Myers Squibb, EMD Serono, Boehringer Ingelheim, AstraZeneca, Dako, and Novartis. All other authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors. Correspondence and requests for materials should be addressed to S.E.L. and E.A.C.
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