Human melanoma-reactive CD4+ and CD8+ CTL clones resist Fas ligand-induced apoptosis and use Fas/Fas ligand-independent mechanisms for tumor killing.
Tumor cells have been shown recently to escape immune recognition by developing resistance to Fas-mediated apoptosis and acquiring expression of Fas ligand (FasL) molecule that they may use for eliminating activated Fas+ lymphocytes. In this study, we report that tumor-specific T lymphocytes isolated from tumor lesions by repeated in vitro TCR stimulation with relevant Ags (mostly represented by normal self proteins, such as MART-1/Melan A and gp100) can develop strategies for overcoming these escape mechanisms. Melanoma cells (and normal melanocytes) express heterogeneous levels of Fas molecule, but they result homogeneously resistant to Fas-induced apoptosis. However, CD4+ and CD8+ CTL clones kill melanoma cells through Fas/FasL-independent, granule-dependent lytic pathway. In these lymphocytes, Ag/MHC complex interaction with TCR does not lead to functional involvement of FasL, triggered, on the contrary, by T cell activation with nonspecific stimuli such as PMA/ionomycin. Additionally, melanoma cells express significant levels of FasL (detectable on the cell surface only after treatment with metalloprotease inhibitors), although to a lesser extent than professional immune cells such as Thl clones. Nevertheless, antimelanoma CTL clones resist apoptosis mediated by FasL either in soluble form or expressed by Thl lymphocytes or FasL+ melanoma cells. These results demonstrate that CD4+ and CD8+ antimelanoma T cell clones can be protected against Fas-dependent apoptosis, and thus be useful reagents of immunotherapeutic strategies aimed to potentiate tumor-specific T cell responses.
Division of Experimental Oncology D, Istituto Nazionale Tumori, Milan, Italy.
L
L
Rivoltini
M
M
Radrizzani
P
P
Accornero
P
P
Squarcina
C
C
Chiodoni
A
A
Mazzocchi
C
C
Castelli
P
P
Tarsini
V
V
Viggiano
F
F
Belli
M P
MP
Colombo
G
G
Parmiani
D017209:Apoptosis / Q000276:immunology*; D015704:CD4 Antigens / Q000032:analysis*; D016827:CD8 Antigens / Q000032:analysis*; D002478:Cells, Cultured; D002999:Clone Cells; D003601:Cytotoxicity Tests, Immunologic; D003602:Cytotoxicity, Immunologic; D053222:Fas Ligand Protein; D006801:Humans; D007113:Immunity, Innate; D008544:Melanocytes / Q000166:cytology / Q000276:immunology; D008545:Melanoma / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology* / Q000378:metabolism; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000096:biosynthesis / Q000502:physiology*
D015704:CD4 Antigens; D016827:CD8 Antigens; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D011948:Receptors, Antigen, T-Cell; D019014:fas Receptor