Using directed evolution, Zhou, Damsky and Weizman et al. created functional murine and human IL-18 variants with high binding affinity for IL-18Rα, but not for the secreted decoy receptor IL-18BP, which is upregulated in the tumor milieu. mIL-18 variant DR-18, but not mIL-18, induced T cells to inhibit syngeneic tumor growth, enhance host mouse survival, and synergize with anti-PD-1. Post-treatment analyses of tumors showed that DR-18 expanded TCF1+ stem-like and CD8+ TEFF cells, CD4+ T cells, NK cells, and granulocytes, whereas mIL-18 induced TEX cells and immune-suppressive macrophages. DR-18 promoted NK cell/IFNγ responses against Β2m-/- tumors.
Contributed by Paula Hochman
ABSTRACT: Cytokines were the first modern immunotherapies to produce durable responses in patients with advanced cancer, but they have only modest efficacy and limited tolerability(1,2). In an effort to identify alternative cytokine pathways for immunotherapy, we found that components of the interleukin-18 (IL-18) pathway are upregulated on tumour-infiltrating lymphocytes, suggesting that IL-18 therapy could enhance anti-tumour immunity. However, recombinant IL-18 previously did not demonstrate efficacy in clinical trials(3). Here we show that IL-18BP, a high-affinity IL-18 decoy receptor, is frequently upregulated in diverse human and mouse tumours and limits the anti-tumour activity of IL-18 in mice. Using directed evolution, we engineered a 'decoy-resistant' IL-18 (DR-18) that maintains signalling potential but is impervious to inhibition by IL-18BP. Unlike wild-type IL-18, DR-18 exerted potent anti-tumour effects in mouse tumour models by promoting the development of poly-functional effector CD8(+) T cells, decreasing the prevalence of exhausted CD8(+) T cells that express the transcriptional regulator of exhaustion TOX, and expanding the pool of stem-like TCF1(+) precursor CD8(+) T cells. DR-18 also enhanced the activity and maturation of natural killer cells to effectively treat anti-PD-1 resistant tumours that have lost surface expression of major histocompatibility complex class I molecules. These results highlight the potential of the IL-18 pathway for immunotherapeutic intervention and implicate IL-18BP as a major therapeutic barrier.