Simultaneous expression of fas and nonfunctional Fas ligand in Ewing's sarcoma

Fas-Fas ligand interactions play a central role in the regulation of the im mune response. Fas ligand expression by tumors has been implicated in the a brogation of the host antitumor response by killing of Fas-positive effecto r lymphocytes. We have studied the presence and functional status of Pas an d Pas ligand in Ewing's sarcoma. All Ewing's sarcoma cell lines tested expr essed Fas on their surface. Three of the cell lines were readily killed aft er ligation of the Fas receptor. Four additional cell lines exhibited Pas-m ediated apoptosis after preincubation with IFN-gamma and/or cycloheximide, whereas two cell lines were resistant to Fas-mediated killing. With regard to Fas ligand, all cell lines examined were positive for protein by immunob lot, and specificity was confirmed by reverse transcription-PCR. However, u sing flow cytometric analysis, Fas ligand could only be detected in Ewing's sarcoma cells after permeabilization, Furthermore, the cell lines were not capable of inducing apoptosis of Pas-sensitive Jurkat cells. In addition, Ewing's sarcoma cell lines were able to serve as stimulators for the genera tion of cytotoxic effector lymphocytes and were susceptible to lysis by the m. Therefore, Pas ligand is expressed in Ewing's sarcoma but is not functio nal, suggesting that Ewing's sarcoma is a potential target for immunotherap y.