Abstract 2873: Evolution of immune cell composition and functionality as pancreatic intraepithelial neoplasia progresses to pancreatic ductal adenocarcinoma
Authors: Lyman Melissa R. , Mitchell Jacob T. , Kagohara Luciane T. , Barrett Benjamin , Huff Amanda , Shin Sarah , Longway Gabriella , Gupta Anuj , Andaloori Lalitya , Armstrong Todd D. , Haldar Daniel , Anders Robert , Thompson Elizabeth , Azad Nilo , Ho Won Jin , Jaffee Elizabeth , Fertig Elana J. , Zaidi Neeha 
Published: April 2023

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is most often diagnosed at an advanced stage. Newly diagnosed patients therefore have a dismal five-year survival rate of 11%. However, PDAC progresses from pre-invasive pancreatic intraepithelial neoplasia (PanIN) over at least a decade. Throughout this transition, the tissue microenvironment becomes increasingly immunosuppressive. Early PanINs may therefore be more amenable to immune-based interception strategies; however, little is known about the pre-malignant lesion immune microenvironment in PDAC. We hypothesized that the identification of the immune landscape of PanINs will elucidate the immuno-dynamic changes that occur during PanIN-to-PDAC progression and identify novel strategies for intercepting PDAC. Here, we use an inducible mouse model to study the evolution of immunosuppression from PanINs to PDAC. We pair spatial molecular profiling of our mouse model with profiling of human tissue in a cohort of patients with normal tissue, chronic pancreatitis, PanIN, and PDAC. To examine the evolution of the immune microenvironment throughout PanIN-to-PDAC progression, we first optimized a tamoxifen-inducible Pdx1-CreERT2 mouse that controls KRASG12D expression and knocks out p53. The impact of KRASG12D expression on the immune cell landscape in PanIN and PDAC lesions was examined by immunohistochemistry (IHC) and RNA in situ hybridization on mouse pancreas. We used imaging mass cytometry (IMC) of 35 immune markers to better classify and quantify the immune cell subtypes. Our analyses thus far reveal increased Tregs as PanINs progress to PDAC. Furthermore, although CD3+ T cells are recruited to tumors, these immune cells are strictly restricted to the immediate edge of the tumor and predominantly consist of Tregs. For our human analyses, FFPE pancreas sections from treatment naïve patients who had undergone surgical resection without neoadjuvant chemotherapy were evaluated. Each section contained regions of normal tissue, chronic pancreatitis, PanIN and PDAC. These were evaluated using IHC, IMC, and spatial transcriptomics to allow us to spatially evaluate the immune populations associated with lesions and PDAC. The relative density and localization of myeloid and lymphoid cell types in both PanIN and PDAC regions revealed an initial influx of CD8+ and CD4+ T cells to PanINs and a progressively immunosuppressive microenvironment in subsequent stages. While PanINs and PDAC both recruited immune cells, the phenotypes of the immune infiltrates were distinct and revealed unique immune pathways that could contribute to immunosuppression as PanINs develop into PDACs. Our proteomic and transcriptomic data from mouse and human pancreas show that mutant KRAS driven premalignant lesions recruit an evolving immune response that readily becomes immunosuppressive as progression to PDAC occurs.
Citation Format: Melissa R. Lyman, Jacob T. Mitchell, Luciane T. Kagohara, Benjamin Barrett, Amanda Huff, Sarah Shin, Gabriella Longway, Anuj Gupta, Lalitya Andaloori, Todd D. Armstrong, Daniel Haldar, Robert Anders, Elizabeth Thompson, Nilo Azad, Won Jin Ho, Elizabeth Jaffee, Elana J. Fertig, Neeha Zaidi. Evolution of immune cell composition and functionality as pancreatic intraepithelial neoplasia progresses to pancreatic ductal adenocarcinoma [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 2873.