Abstract
Background:
Interleukin-18 (IL-18), or interferon (IFN)-γ-inducing factor, potentiates T helper 1 and natural killer cell activation as well as CD8+ T-cell proliferation. Recombinant IL-18 has displayed limited clinical efficacy in part due to the expression of the decoy receptor, IL-18 binding protein (IL-18BP). A series of IL-18 variants that are devoid of IL-18BP binding, termed DR18 (decoy-resistant IL-18), was developed via directed evolution. We tested DR18 using oncolytic adenovirus (oAd) as a platform for delivery in syngeneic mouse tumor models.
Methods:
oAd harboring wild-type IL-18 or DR18 (oAdDR18) was constructed by inserting IL-18 mutant into modified oAd backbone with Ad5/3 chimeric fiber. The delivery effect and IFN-γ induction were determined by ELISA. The antitumor efficiency of oAdDR18 was tested in CT26, B16BL6 and 4T1 tumor-bearing mice, or athymic nude mice and compared with recombinant DR18 protein (rDR18). 4T1 lung metastasis model was used to evaluate the antitumor efficiency of local and distant tumors. Antitumor memory and synergistic effect with an anti-programmed cell death protein-1 (PD-1) antibody was evaluated. The phenotypes of the immune cells in tumor microenvironment were analyzed by flow cytometry and immunohistochemistry.
Results:
Mice received oAdDR18 maintained stable production of IL-18 and IFN-γ compared with those received rDR18. Intratumoral delivery of oAdDR18 significantly reduced tumor growth across several tumor models, but not in the athymic nude mouse model. Mice that had tumor remission showed antitumor memory. The antitumor effect was associated with intratumor infiltration of CD4+ and CD8+ T cells. DR18 delivered by oAd demonstrated long-lasting and enhanced antitumor activities against local and distant tumors compared with that received rDR18 or wild-type IL-18 delivered by oAd (oAdwtIL-18). oAdDR18 treatment also reduced 4T1 lung metastasis. In addition, combination of this virotherapy with immune checkpoint inhibitors (ICIs)like the anti-PD-1 antibody further enhanced the antitumor activity as compared with respective monotherapy.
Conclusions:
oAdDR18 demonstrates enhanced antitumor activities through the induction of stronger local and system immunities and modulation of the tumor microenvironment compared with those of oAdwtIL-18 and rDR18. A combination of oncolytic virotherapy with cytokine engineering would lead to cytokine-based therapeutics for cancer and other diseases.