Decoy-resistant IL-18 reshapes the tumor microenvironment and enhances rejection by anti-CTLA-4 in renal cell carcinoma

The cytokine interleukin-18 (IL-18) has immunostimulatory effects but is negatively regulated by a secreted binding protein, IL-18BP, that limits IL-18's anti-cancer efficacy. A "decoy-resistant" form of IL-18 (DR-18), that avoids sequestration by IL-18BP while maintaining its immunostimulatory potential, has recently been developed. Here, we investigated the therapeutic potential of DR-18 in renal cell carcinoma (RCC). Using pan-tumor transcriptomic data, we found that clear cell RCC had among the highest expression of IL-18 receptor subunits and IL18BP of tumor types in the database. In samples from RCC patients treated with immune checkpoint inhibitors, IL-18BP protein expression increased in the tumor microenvironment and circulating in plasma in non-responding patients and decreased in the majority of responding patients. We used immunocompetent RCC murine models to assess the efficacy of DR-18 in combination with single- and dual-agent anti-PD-1 and anti-CTLA-4. In contrast to preclinical models of other tumor types, in RCC models DR-18 enhanced the activity of anti-CTLA-4 but not anti-PD-1 treatment. This activity correlated with intra-tumoral enrichment and clonal expansion of effector CD8+ T cells, decreased regulatory T cell levels, and enrichment of pro-inflammatory, anti-tumor myeloid cell populations. Our findings support further clinical investigation of the combination of DR-18 and anti-CTLA-4 in RCC.