Tumor-infiltrating CD4⁺ T lymphocytes express APO2 ligand (APO2L)/TRAIL upon specific stimulation with autologous lung carcinoma cells: Role of IFN-α on APO2L/TRAIL expression and -mediated cytotoxicity

In the present report, we have investigated TRAIL/APO2 ligand (APO2L) expression, regulation, and function in human lung carcinoma tumor-infiltrating lymphocytes. Using a panel of non-small cell lung carcinoma cell lines, we first showed that most of them expressed TRAIL-R1/DR4, TRAIL-R2/DR5, but not TRAIL-R3/DcR1 and TRAIL-R4/DcR2, and were susceptible to APO2L/TRAIL-induced cell death. Two APO2L/TRAIL-sensitive tumor cell lines (MHC class I⁺/II⁺ or I⁺/II^-) were selected and specific CD4⁺ HLA-DR- or CD8⁺ HLA-A2-restricted CTL clones were respectively isolated from autologous tumor-infiltrating lymphocytes. Interestingly, although the established T cell clones did not constitutively express detectable levels of APO2L/TRAIL, engagement of their TCR via activation with specific tumor cells selectively induced profound APO2L/TRAIL expression on the CD4⁺, but not on the CD8⁺, CTL clones. Furthermore, as opposed to the CD8⁺ CTL clone which mainly used granule exocytosis pathway, the CD4⁺ CTL clone lysed the specific target via both perforin/granzymes and AP02L/TRAIL-mediated mechanisms. The latter cytotoxicity correlated with APO2L/TRAIL expression and was significantly enhanced in the presence of IFN-α. More interestingly, in vivo studies performed in SCID/nonobese diabetic mice transplanted with autologous tumor and transferred with the specific CD4⁺ CTL clone in combination with IFN-α resulted in an important APO2L/TRAIL-mediated tumor growth inhibition, which was prohibited by soluble TRAIL-R2. Our findings suggest that APO2L/TRAIL, specifically induced by autologous tumor and up-regulated by IFN-α, may be a key mediator of tumor-specific CD4⁺ CTL-mediated cell death and point to a potent role of this T cell subset in tumor growth control.