Introduction: Glioblastoma multiforme deploys a number of weapons to thwart the immune system. Within the tumor microenvironment, cytotoxic T cells fall victim to Fas ligand (FasL) induced apoptosis. In prostate and colorectal cancer, exosomes can mediate this FasL induced T cell apoptosis. Exosomes are tiny, membrane bound vesicles that are released from a cell. They contain functional mRNA and protein and have cell surface molecules representative of their parent cell. It is not known if GBM derived exosomes can also mediate FasL triggered apoptosis. In this study, the role of tumor derived exosomes as the delivery vehicle for FasL is explored.
Methods: Exosomes are isolated from the T98 cell line using differential ultracentrifugation. FasL expression in the cell line and derived exosomes is determined using reverse transcription polymerase chain reaction (RT-PCR) and Western blotting. GBM derived exosomes, recombinant FasL, and exosomes treated with an anti-FasL antibody are co-cultured with Jurkat A3 T cells. Apoptosis is measured using a caspase-8 luminescent assay.
Results: FasL is expressed by the T98 cell line and is present on the surface of the cells and their exosomes. (Figure 1) Caspase-8 activation is seen in T cells treated with GBM derived exosomes and recombinant FasL, but not with exosomes treated with anti-FasL antibody or exosome free supernatant. (Figure 2)
Conclusions: GBM derived exosomes induce T cell apoptosis through a FasL mediated mechanism. This method of immune suppression has not previously been described. This research opens new avenues to antagonize GBM related immune system malfunction.
Patient Care: An understanding of the mechanisms causing immune system failure in GBM is needed in order to develop new treatments and improve current treatments such as dendritic cell vaccination. Exosome mediated T cell inhibition is a novel method of immune suppression and is thus an appropriate target for intervention.
Learning Objectives: At the conclusion of this session, participants will be able to: 1) describe the origin and function of exosomes, 2) discuss the mechanisms of T cell inhibition in GBM, and 3) describe how GBM derived exosomes affect T cells in both the tumor microenvironment and systemically.