Abstract 4462: Immunoregulatory effects of NNMT-expressing cancer-associated fibroblasts

Abstract Nicotinamide N-methyltransferase (NNMT) is highly expressed in the stroma of several malignancies and has been shown to drive the transformation of resting fibroblasts into cancer-associated fibroblasts (CAFs) through epigenetic changes. Given that CAFs can promote immunosuppression in cancer, the aim of our study was to investigate the effect of NNMT-expressing CAFs on the tumor-immune environment. Using a co-culture system of normal fibroblasts and activated PBMCs, we found that IFN-γ produced by PBMCs upregulates NNMT expression in fibroblasts. We confirmed this mechanism in vivo in IFN-γ knockout mice and identified T cells as the main source of IFN-γ in the tumor. Gene expression and protein analysis showed that upregulation of NNMT in CAFs induces the secretion of the chemokine CXCL1, a critical chemoattractant for immunosuppressive myeloid-derived suppressor cells (MDSCs). Upregulation of NNMT induces CXCL1 secretion directly through promoter hypomethylation, and in vitro migration assays show that NNMT-expressing CAFs recruit high numbers of MDSCs. Using spectral flow cytometry, we analyzed the tumor-immune cell infiltration in whole-body NNMT-knockout mice and discovered that NNMT knockout of the stroma significantly reduced the abundance of MDSCs and increased the number of functional CD8+ T cells. Increased T cell cytotoxicity was associated with a significant reduction in tumor burden in the syngeneic ID8 ovarian and MC38 colon cancer models. These findings were confirmed after adoptive transfer of NNMT-wildtype immune cells into irradiated whole-body NNMT-knockout mice. Moreover, in scRNA-seq data of various human malignancies, we found a strong correlation between NNMT and CXCL1 expression in CAFs. In summary, our results support a model in which cancer cells induce IFN-γ secretion by T-cells, thereby upregulating NNMT expression in fibroblasts, leading to CXCL1 secretion. CXCL1 secreted by CAFs recruits MDSCs to the tumor, which in turn suppress the anti-tumor T cell response. Citation Format: Janna Heide, Andras Piffko, Agnes J. Bilecz, Ethan A. Teich, Lisa Schweizer, Sayed R. Alhunayan, Kaiting Yang, Ernst Lengyel. Immunoregulatory effects of NNMT-expressing cancer-associated fibroblasts. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4462.