gms | German Medical Science

Objective: Interleukin-12 (IL12) has shown to have potent anti-tumor activity by stimulation of the glioma-suppressed cytotoxic T-cell system. However, systemic therapy is limited by severe side effects. Local adenoviral-mediated gene transfer has the potential to overcome this obstacle but vector systems are needed which result in a high and controllable transgene expression with minimized viral toxicity.

Methods: Therapeutic efficiency of local interleukin-12 gene therapy was evaluated by intratumoral injection of adenoviral vectors in the well-established syngenic orthotopic glioma xenograft model (GL261 - C56/BL6). The adenoviral IL12 transgene was under the control of a bi-directional promoter and a tetracycline-suppressible transactivator which was cloned into the E1-region of a E1-deleted recombinant adenoviral vector (Ad.3rmIL12). This vector system was compared to a conventional CMV-promoter controlled IL12-expressing adenoviral vector system.

Results: One week after intratumoral injection of Ad.3rmIL12 glioma growth was inhibited by 73% (p<0.05) as assessed by T1-Gd-enhanced MRI when compared to tumors injected with NaCl or control adenovirus (n=12/group). Survival was significantly prolonged in Ad.3rmIL12 treated animals and CD3-immunohistochemistry demonstrated a significantly higher intratumoral T-cell infiltration (>4-fold, p<0.001). Transgene expression in vivo was localized in close vincinity to the viral injection site as demonstrated by eGFP staining. In vitro expression of IL12 by GL261 glioma cells was significantly higher after infection with Ad.3rmIL12 when compared to an adenoviral vector with transgene expression under the control of a conventional CMV-promoter (Ad.CMV-IL12) and highly suppressed in the presence of tetracyclin. Local in vivo gene therapy with Ad.3rmIL12 resulted in a higher reduction of tumor burden when compared to Ad.CMV-IL12 at the same dosage (6x107 pfu) (n=5/group, not significant). In vivo treatment with tetracyclin led to reduction of glioma growth inhibition due to the in vivo suppression of IL12.

Conclusions: Here, we demonstrated that local interleukin-12 gene therapy is counterbalancing the glioma-induced immunosupression by inducing intratumoral T-cell infiltration which results in a significant reduction of tumor growth. This new adenoviral vector system can contribute to the safety of viral gene therapy by controllable and higher transgene expression than conventional CMV-promoter driven vectors.