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

Background: Microglial cells are the predominant immune cells in malignant brain Tumors, but Tumors may release some factors to reduce their defensive functions. Restoration of the anti-cancer function of microglia has been proposed as a treatment modality for Glioblastoma. We examined the effect of intra-cranially administered Recombinant adeno-associated virus encoding interleukin-12 (rAAV2/IL12) on transfection efficiency, local immune activity and survival in a rat model of Glioblastoma Multiforme.

Methods: 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.

Results: 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.

Conclusion: 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.