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Glioblastoma multiforme (GBM) is the most frequent and lethal primary brain tumor in adults. Despite intense biomedical research, the median survival after diagnosis is 15 months. One factor contributing to this poor prognosis is the immune protection afforded by the tumor microenvironment. Tumors have a diverse repertoire of immune-evasive techniques. One method of evasion not well explored is the release of tumor-derived exosomes. Exosomes are tiny membrane-bound vesicles of endocytic origin that contain viable mRNA and functional proteins that can affect the physiology of recipient cells. Exosome release has been reported for numerous cancer types, including GBM. Exosomes from colon cancer have been shown to carry Fas ligand (FasL) and to induce apoptosis of activated T cells. The aim of this study was to elucidate whether the same immune-evasive technique is used in GBM. GBM exosomes were isolated from the serum-free culture medium of U87 MG and U138 MG cells by using differential ultracentrifugation and were then resuspended in phosphate-buffered saline. The protein concentration of the resulting exosome pellet was determined, and subsequent exosome treatments were based on protein concentration. A3T T cells were plated at a concentration of 10,000 cells per well in 96-well plates and were treated with quantified exosome fractions or with recombinant FasL, and T cell proliferation was determined. Our data demonstrated that tumor-derived exosomes significantly inhibited the proliferation of T cells and that the cellular inhibition resulting from the exosomes was comparable to that seen with the recombinant FasL. These results suggest that targeting FasL in GBM could greatly decrease the amount of immune suppression that occurs at the tumor site.
Keith Z. Sabin, Danny Lebert, Vanessa Thibado, Richard A. Rovin, Johnathan E. Lawrence, and Robert J. Winn. "Glioblastoma derived exosomes contribute to tumor immune evasion" Neuro-Oncology 13.suppl 3 (2011): iii30-iii33. Available at: http://works.bepress.com/johnathan_lawrence/7