Oncolytic vaccinia virus expressing non-secreted decoy-resistant IL-18 mutein elicits potent antitumor effects with enhanced safety.

Cytokines are promising for cancer treatment but face challenges like short half-lives, high-dose requirements, and systemic toxicity. Oncolytic viruses provide an ideal platform to overcome these limitations by delivering cytokines directly to tumor sites, enabling high local concentrations within the tumor microenvironment (TME). This study utilized an oncolytic vaccinia virus (oVV) to deliver interleukin-18 (IL-18) and its variants and assessed their antitumor effects across different tumor models. The non-secreted mature IL-18 mutein (nsmDR-18)-expressing oVV demonstrated potent antitumor efficacy with reduced systemic toxicity. It increased the expression of antitumor factors, including IL-2, interferon gamma (IFN-γ), granzyme B, and perforin, while expanding tumor-reactive CD39(+)CD103(+)CD8(+) T cells and reducing severely exhausted PD-1(+)TIM-3(+)CD8(+) T cells, thereby transforming immunologically "cold" tumors into "hot" tumors. However, nsmDR-18-expressing oVV treatment also elevated regulatory T cells (Tregs) and upregulated immune checkpoint molecules (PD-1, PD-L1, and CTLA-4). Combining nsmDR-18-expressing oVV with anti-CTLA-4 antibody significantly improved overall survival and induced systemic, tumor-specific antitumor immunity. These results highlight the potential of nsmDR-18-expressing oVV as a therapeutic strategy, supporting further exploration in clinical trials.