Fas/Apo-1 (CD95)-Fas ligand (FasL) system has been implicated in the suppression and stimulation of immune responses. We examined the induction of antitumor immunity with neuroblastoma Neuro-2a cells transfected with FasL cDNA (Neuro-2a+ FasL). Neuro-2a+ FasL cells expressed FasL on the cell surface and secreted soluble FasL. Histologic and flow cytometric analyses revealed that Neuro-2a+ FasL cells caused neutrophils to infiltrate into the injected site, resulting in strong inflammation. Neutrophil infiltration was inhibited by treatment with anti-FasL mAb and did not occur in Fas-deficient lpr mice. Normal syngeneic mice rejected Neuro-2a+ FasL cells after the inflammation and acquired tumor-specific protective immunity. CD8+ T cells were responsible for the antitumor immunity. Neuro-2a+ FasL cells formed tumors after far longer latency compared with mock-transfected Neuro-2a+ Neo cells in nude mice, and immune competent mice rejected Neuro-2a cells but not sarcoma S713a cells when they were injected with Neuro-2a+ FasL cells in a mixture. These results suggest that neutrophils attracted through the Fas-FasL system may impair tumor cells by inflammation at the initial step, followed by development of CD8+ T cell-dependent tumor-specific antitumor immunity, leading to complete eradication of tumor cells. Importantly, the treatment with Neuro-2a+ FasL cells exhibited therapeutic efficacy against growing tumors.