Cytokine Gene Therapy of Cancer Using Gene Gun Technology: Superior Antitumor Activity of Interleukin-12

Abstract

We compared the antitumor effect of several transgene expression plasmids encoding specific cytokines, including interleukin-2 (IL-2), IL-4, IL-6, IL-12, interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), and granulocyte-macrophage colony-stimulating factor (GM-CSF), following gene gun-mediated DNA delivery into the epidermis overlying an established intradermal murine tumor. IL-12 gene therapy was much more effective than treatment with any other tested cytokine gene for induction of tumor regression. Strong activation of antitumor immunity in response to IL-12 gene therapy was evidenced by an augmented CD8⁺ T cell-mediated cytolitic activity in the draining lymph nodes of tumor-bearing mice. Furthermore, following the IL-12 gene therapy protocol, test mice were able to eradicate not only the treated but also the untreated solid tumors at distant sites. This systemic antitumor effect of IL-12 gene therapy was not associated with visible signs of toxicity or significantly elevated systemic levels of IFN-γ. These results show that gene gun-mediated in vivo delivery of IL-12 cDNA clearly distinguishes itself from the other cytokine gene therapy approaches tested in parallel, suggesting that this delivery system may be employed as an efficient model for comparative studies of in vivo cytokine gene therapy. The results also suggest that the current IL-12 gene therapy strategy may provide a safer alternative to IL-12 protein therapy for clinical treatment of cancers.

Overview summary

Interleukin 12 (IL-12) has been shown to exhibit a powerful antitumor effect in murine models. However, IL-12 therapy may pose a significant risk to human patients due to the toxicity of the recombinant IL-12 protein. Using a nonviral gene therapy approach, we show in this study that a localized, gene gun-mediated in vivo delivery of IL-12 cDNA led to the activation of antitumor immunity, which could result in eradication of solid tumors at distant sites. This IL-12 gene therapy protocol was apparently nontoxic and, in the comparative study, superior to those using other cytokine genes such as interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-2, IL-4, or IL-6. Thus, gene gun-mediated IL-12 gene therapy may be an effective and safe alternative to IL-12 protein therapy for human cancers.