The new generation of T cell-based cancer immunotherapeutics, best exemplified by the checkpoint inhibitors anti-CTLA-4 and anti-PD-1/PD-L1, can elicit therapeutic antitumor immunity in cancer patients. Nevertheless, these therapeutic responses are often not durable or only experienced in a subset of patients, likely owing to a variety of immunosuppressive mechanisms employed by tumors to subvert the action of antitumor T cells. For instance, T cells expressing antigen receptors (TCRs) that recognize MHC restricted-tumor epitopes with high avidity/affinity have a propensity to undergo functional inactivation or deletion, and hence cytolytic effector T cells (CTL) localized within tumors generally have a limited ability to recognize and be triggered by tumor epitopes. Hence, strategies to amplify weak tumor epitope recognition, or even induce TCR-independent T cell activation intratumorally, might boost T cell-mediated antitumor efficacy. In this regard, we previously found that effector T cells programmed with antitumor promoting costimulatory agonists can be triggered to degranulate and secrete the tumoricidal cytokine IFN-? through a TCR-independent process that involves stimulation with a STAT-activating cytokine (IL-2 or IL-12) plus an IL-1 family member (IL-33 or IL-36). This ?innate-like? response is akin to how innate immune cells such as NK cells can be triggered through cytokine combinations such as IL-12 plus IL-18, and may help explain why the presence of IL-36 in the tumor microenvironment limits tumor growth. Further, engaging this 2-cytokine triggering pathway will be an effective means to boost the efficacy of cancer immunotherapies. In analyzing the mechanism of this 2-cytokine pathway using costimulated CD8+ T cells treated with the IL-2 + IL-36 combination, it was found that IL-2 primes for IL-36 responsiveness by rapidly inducing IL-36R mRNA (encoded by the Il1rl2 gene) in a JAK/STAT-dependent manner. Chromatin immunoprecipitation with high throughput sequencing (ChIP-seq) revealed that IL-2 induces STAT5 binding to five separate STAT/GAS consensus elements located throughout a large ~75 kb intergenic region between Il1rl2 and Il1rl1 (encoding IL-33R that is also induced by IL-2). Strikingly, RNA polymerase II bound the same sites prior to IL-2 stimulation. These results, in concert with a previous bioinformatic analysis of publically available ChIP-seq data sets generated from IFN-?-expressing T cells, forms the basis of the novel overarching hypothesis that will be tested in this project that the Il1rl2-Il1rl1 intergenic region contains a super-enhancer (SE) that serves as a molecular hub to facilitate cross-talk between STAT-activating and IL-1 family cytokines during ?innate-like? antitumor T cell responses.
Immune-based cancer therapies can program effector T cell migration into tumors, however, tumor cell killing is typically limited by immunosuppressive mechanisms that diminish T cell recognition of tumor antigens. A potential strategy to bypass this issue is to stimulate effector T cells with particular cytokine combinations (e.g., IL-2 plus IL-33 or IL-36) that elaborate tumoricidal function even in the absence of antigen. This project will test the novel hypothesis that an IL-2-responsive super-enhancer located between the genes encoding the IL-33 and IL-36 receptors functions as a molecular hub to facilitate this 2-cytokine T cell triggering process.
