Br. Gastman et al., Fas ligand is expressed on human squamous cell carcinomas of the head and neck, and it promotes apoptosis of T lymphocytes, CANCER RES, 59(20), 1999, pp. 5356-5364
Recent reports have variously described expression of Fas ligand (FasL) or
its absence in human tumors. The importance of the Fas-FasL mechanism for t
he immune evasion by tumors provided a strong rationale for the examination
of Fast expression and function in squamous cell carcinoma of the head and
neck (SCCHN), which is one of the most immunosuppressive human cancers. Us
ing immunostaining or immunoblotting, SCCHN cell lines and tumor biopsies w
ere examined for the presence of the components of the Fas-FasL pathway and
found to express Fas, as well as both the full-length and cleaved forms of
Fast. By reverse transcription-PCR, mRNA for FasL and Fas were detected in
all SCCHN tested, and cross-hybridization to radioactive Fas and Fast cDNA
probes confirmed the specificity of amplification, To demonstrate that Fas
t expressed on cell surface of SCCHN cells was biologically active, various
SCCHN lines were coincubated with the Fas-sensitive Jurkat T-cell lines or
activated peripheral blood mononuclear cells. Tumor-induced apoptosis of T
cells was dependent on the ratio of tumor cells: lymphocytes. It was signi
ficantly but only partially inhibited by neutralizing antibodies to Fast an
d antagonistic antibodies to FasR. Tumor-induced apoptosis was enhanced by
the pretreatment of tumor cells with metalloproteinase inhibitors, which in
creased expression of Fast on tumor cells. Supernatants of tumor cells tran
sduced with FasL also induced apoptosis of Jurkat cells. Thus, coincubation
of SCCHN with Fas-sensitive lymphocytes can induce apoptosis of these lymp
hocytes, and the Fas/FasL pathway appears to be responsible, at least in pa
rt, for tumor-induced lymphocyte death, The data suggest that the Fas/FasL
pathway is potentially immunosuppressive and may be involved in the escape
of human carcinoma cells from immune destruction.