Interleukin-12 has been elucidated as a powerful anti-cancer factor in pre-clinical research. However, the obstacles of this modality that emerged from human clinical trails included the toxicity of repeated large dose administration and short effective duration. Therefore, a prolonged, constant therapeutic level of interleukin-12 is required to reduce the adverse effects and enhance the therapeutic efficacy. In this study, 54 nude mice were divided into three groups treated with rAAV2 encoding interleukin-12, rAAV2 vector, and PBS, respectively. All nude mice received human glioblastoma multiforme cell line DBTRG implantation. The biochemistry studies included serum levels of interleukin-12, isotypes of immunoglobulin, interferon-γ, and TNF-α. The activated NK cells were sorted from the spleen by flow cytometry and the cytotoxicity of NK cells were evaluated by LDH assay. In the rAAV2 encoding interleukin-12 group, substantial expression of interleukin-12 was obtained with a serum level of 120-150 pg/ml through the experimental course and a significant increase of activated NK cells was achieved. The splenocytes extracted from the spleen in rAAV2 encoding IL-12 mice strongly exhibited cytotoxic activity compared to the control groups (p<0.001). The IgG1, IgG2a, and IgM also showed a significant increase in the rAAV2 encoding IL-12 group compared to the control groups (p<0.05). The tumor growth rate decreased obviously in the rAAV2 encoding IL-12 group with a significant difference from the control groups (p<0.001). This study demonstrated an encouraging result of immunomodulative therapy in malignant brain tumors by rAAV2 carrying IL-12 through activating NK cells.

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