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  • Title: Fas ligand-positive membranous vesicles isolated from sera of patients with oral cancer induce apoptosis of activated T lymphocytes.
    Author: Kim JW, Wieckowski E, Taylor DD, Reichert TE, Watkins S, Whiteside TL.
    Journal: Clin Cancer Res; 2005 Feb 01; 11(3):1010-20. PubMed ID: 15709166.
    Abstract:
    OBJECTIVE: In patients with oral squamous cell carcinoma, a high proportion of T cells in the tumor undergo apoptosis, which correlates with Fas ligand (FasL) expression on tumor cells. The present study was done to identify mechanisms responsible for apoptosis of T cells seen in the peripheral circulation of these patients. METHODS: Sera of 27 patients, normal donor sera, and supernatants of cultured normal or tumor cells were fractionated by size exclusion chromatography and ultracentrifugation to isolate microvesicles. The presence of microvesicle-associated FasL was studied by Western blots, blocking with anti-Fas reagents, and immunoelectron microscopy. Biological activities of microvesicles were tested including the ability to induce apoptosis of Jurkat and T-cell blasts. Semiquantitative analysis of FasL in microvesicles was correlated with caspase-3 activity, DNA fragmentation, cytochrome c release, loss of mitochondrial membrane potential, and TCR-zeta chain expression in lymphocytes. RESULTS: FasL-positive (FasL+) microvesicles were detected in sera of 21 of 27 patients. Microvesicles contained 42 kDa FasL. These microvesicles induced caspase-3 cleavage, cytochrome c release, loss of mitochondrial membrane potential, and reduced TCR-zeta chain expression in target lymphocytes. Biological activity of the FasL+ microvesicles was partially blocked by ZB4 anti-Fas monoclonal antibody. Microvesicle-associated FasL levels correlated with the patients' tumor burden and nodal involvement. CONCLUSION: Sera of patients with active oral squamous cell carcinoma contain FasL+ microvesicles, which induce the receptor and mitochondrial apoptotic pathways in Jurkat and activated T cells.
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