Basic study for. Cancer Gene Therapy by Antitumor Effects Using Fas-Fas Ligand-Mediated Apoptosis

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In the immunologically privileged sites, FasL (ligand) is constitutively expressed and causes prompt apoptosis of infiltrating lymphoid cells. FasL can protect the grafted tissue from immune-mediated damage. However, we and other researchers reported that various types of tumors, when genetically manipulated to express FasL, were rejected after inducing marked inflammation with extensive neutrophil infiltrate. Thus, we investigated cancer therapy using FasL-transfected tumor cells.Four kinds of FasL cDNA-transfected murine tumor cells (neuroblastoma Neuro-2a, lung carcinoma 3LL, hepatoma MH134, fibrosarcoma MethA) were rejected when injected into mice, and induced strong antitumor immunity. Thus, the antitumor activity of FasL did not depend on tumor type. To address how FasL-expressing tumors induce neutrophil emigration and abrogate tumorigenicity, we investigated the behavior of G2 (MHl34+FasL) cells injected into +/+, lpr^<cg>/lpr^<cg>(lpr^<cg> and gld/gld Ipr/lpr (gld/lpr) mice. G … More 2 cells were eradicated after extensive infiltration of neutrophils around them in +/+ mice but formed tumors without such infiltration in lpr^<cg> and gld/lpr mice. These results indicate that apoptosis of neutrophils with FasL-expressing tumors depends on Fas and may trigger the extensive infiltration of neutrophils resulting in violent inflammation and ultimately in eradication of tumor cells in + mice. The antitumor effect was examined by mixing G2 cells with MH134 cells (model of Fas/FasL-negative tumor) or F6b (MH134+Fas) and injecting into mice. The mixture of tumor cells was eradicated after extensive infiltration of neutrophils around them. The antitumor effect of G2 cells against F6b cells was extremely stronger than that against parent cells (MH134). These results suggested that FasL-expressing tumor exerted antitumor activity against un-transfected tumor cells by-stander effects. This seems to be useful for the clinical application, because all tumor cells could not be always transfected with transfected cDNA. On the other hand, the suppression of resistant cells which appear in treatment is important for augmentation in tumor-gene therapy. To solve this problem, we examined the antitumor effect of F6b cells and anti-Fas Mab-resisant F6b cells by anti-Fas Mab. The resistant cells could survive by modulating Fas cDNA which resulted in the decrease or the depletion of Fas expression for the attack by the anti-Fas Mab.Collectively, our results indicate that transfection of FasL into tumor cells is a good method for the induction of strong antitumor effects and might be much useful for clinical application. Less