The treatment of glioblastoma multiforme through activation of microglia and TRAIL induced by rAAV2-mediated IL-12 in a syngeneic rat model

F344 rats were injected with rAAV2/IL12 and implanted with syngeneic RG2 cells (glioblastoma cell line). Intracerebral interleukin-12 and interferon-γ concentrations were determined by ELISA. Activation of microglia was determined by expressions of ED1 and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) which were evaluated by Western blotting and immunohistochemistry. The proliferation of cancer cells was evaluated with Ki67 immunohistochemistry and apoptosis of cancer cells with TUNEL.The brains treated with rAAV2/IL-12 maintained high expression of interleukin-12 and interferon-γ for at least two months. In syngeneic tumor model, brains treated with rAAV2/IL12 exhibited more infiltration of activated microglia cells as examined by ED1 and TRAIL stains in the tumor. In addition, the volume of tumor was markedly smaller in AAV2/IL12-treated group and the survival time was significantly longer in this group too.The intra-cerebrally administered rAAV2/IL-12 efficiently induces long lasting expression of IL-12, the greater infiltration of activated microglia cells in the tumor associated improved immune reactions, resulting in the inhibited growth of implanted glioblastoma and the increased survival time of these rats.Interleukin-12 (IL-12) is a potent anti-cancer cytokine that enhances innate and adaptive immune-responses. At the molecular and cellular level, IL-12 facilitates maturation of natural killer cells and cytotoxic T cells, stimulates secretion of interferon-γ (IFN-γ) leading to anti-angiogenesis, enhances secretion of the tumor necrosis factor (TNF) superfamily leading to apoptosis, and provokes antigen-specific adaptive immunity of tumors via the TH1 pathway [1-4]. However, systemic administration of recombinant IL-12 protein is associated with a high risk of injury to vital organs [5,6]. Several preclinical studies, therefore, have attempted to transfer IL-12 by direct injection into tumors or tumor environments to reduce systemic toxicit