Abstract B044: Durable T-cell-mediated anti-tumor immune response to pancreatic cancer cells overexpressing interleukin 6

Abstract Tumor immune resistance contributes to low survivorship in patients with pancreatic ductal adenocarcinoma (PDAC). To understand how tumor-secreted factors might impact anti-tumor immunity, we developed a model of PDAC tumor overexpressing interleukin-6 (IL-6), a known driver of pancreatic tumorigenesis and cancer cachexia, in orthotopically implanted PDAC cancer cells (OT-PDACIL6). This model utilized codon-optimized IL6 to accurately detect tumor cells in the pancreas and distal organs via qPCR. OT-PDACIL6 tumors developed poorly- differentiated, infiltrative carcinomas, which were histologically similar to the PDAC cell line they were derived from (OT-PDACparental). Surprisingly, OT-PDACIL6 tumors were present at 5 days post implantation, but undetectable by histology or qPCR by 10 days post implantation. OT- PDACIL6 and sham mouse survival were equivalent (87. 5%) at 76 days post-implantation. OT- PDACparental mortality was 100% at day 13. We concluded that OT-PDACIL6 tumors resolve spontaneously. IL-6 is well-established as a driver of cachexia, and we saw that OT-PDACIL6 tumors induced a rapid cachexia phenotype that began to resolve as the tumor was cleared. Plasma IL-6 levels tracked with tumor burden. At 5 days, plasma IL-6 was 100-fold higher in OT-PDACIL6 mice than in OT-PDACparental mice, but undetectable in OT-PDACIL6 mice after 12 days. We hypothesized that high levels of IL-6 were driving an anti-tumor immune response. To assess changes in tumor immune infiltrate that could lead to tumor clearance, we measured a broad range of immune cells using flow cytometry and immunofluorescent histology. At peak tumor burden, we observed exacerbated splenomegaly, and increased tumor-infiltrating T cells and NK cells in OT-PDACIL6 mice. T regulatory cells were decreased in OT-PDACIL6 tumors. CD4/CD8 antibody-based depletion prevented tumor clearance and significantly decreased survival of OT-PDACIL6 mice, indicating that T cells are necessary for IL-6-driven PDAC tumor clearance. We then tested whether the anti-tumor T cell response was durable using a secondary tumor challenge with PDACparental cells. This revealed that the anti-tumor T cell response elicited by mice bearing OT-PDACIL6 tumors was sufficient to prevent development of OT-PDACparental tumors, likely due to induction of long-term memory T cells during the initial tumor challenge. We assessed the effect of the anti-tumor immune response on metastases and found that PDACIL6 cells were detected by qPCR in lungs of 58% of mice at day 5, and not detected at day 12. We conclude that extremely high levels of tumor-derived IL-6 are sufficient to drive an anti-tumor T cell response that rapidly and durably clears the tumor. The combination of increased tumor-infiltrating T cells and decreased T regulatory cells are likely both important aspects of the immune response observed in OT-PDACIL6 mice. This surprising finding highlights the pleiotropic effects of IL-6, which is known to promote tumorigenesis and cachexia, and yet, in this work, is the driving force underlying tumor clearance. Citation Format: Paige C Arneson-Wissink, Alexandra Q Bartlett, Heike Mendez, Xinxia Zhu, Jessica Dickie, Matthew McWhorter, Peter R Levasseur, Parham Diba, Katelyn T Byrne, Gregory D Scott, Robert Eil, Aaron J Grossberg. Durable T-cell-mediated anti-tumor immune response to pancreatic cancer cells overexpressing interleukin 6 abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84 (17 Suppl₂): Abstract nr B044.