Enhanced anti-glioblastoma activity of microglia by AAV2-mediated IL-12 through TRAIL and phagocytosis in vitro

Microglia have been found to infiltrate into malignant brain tumors. However, their function is usually reversed by cancerous cells thus contributing to cancer growth and metastasis. We propose that microglial immuno-activity can be modulated with interleukin-12, by which the anti-cancer ability might be restored. To this end, a strategy was designed using AAV2 carrying interleukin-12 to activate microglia to eliminate cancerous cells. Under this strategy, recombinant AAV2 encoding interleukin-12 was constructed and evaluated for its transduction efficacy on cancerous and CNS cells. The bioactivity of microglia modulated by interleukin-12 was examined and death receptors 4 and 5 were detected on cancerous cells. The effects of interleukin-12 on microglial cytotoxicity were evaluated by MTT assay. The human cell line DBTRG, surgical specimens of GBM and rat astrocytes expressed AAV2-mediated GFP quite strongly. Interleukin-12 secretion was detected in DBTRG, RG2 and astrocytes after the transduction of AAV2 encoding interleukin-12. TRAIL releasing and phagocytotic activity of microglia were significantly increased after interleukin-12 stimulation. MTT assay of microglial cytotoxicity elicited significant increase after the stimulation with interleukin-12 protein. In conclusion, AAV2 is an effective vector in transferring therapeutic genes such as interleukin-12 to enhance microglial anti-cancer activity and to eliminate cancerous cells.