Abstract 1194: Understanding radiation and immunotherapy induced cell state shifts in the pancreatic tumor microenvironment

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease with few effective treatment options. It is characterized by a highly desmoplastic tumor microenvironment and a paucity of dendritic cells, leading to low immune cell infiltration and poor outcomes with immunotherapy treatments that are highly effective in other cancers. In a recent pilot study, metastatic PDAC patients who had progressed on chemotherapy were treated with a combination of dual immune checkpoint blockade (ICB) therapy and radiation which resulted in an 18% overall response rate (ORR) and 29% disease control rate (DCR). This led to a phase 2 study in order to further test this combination with the goal of deep correlative analysis to understand the determinants of immunotherapy response and resistance. In this follow up there was a 3. 6% ORR, 10. 7% DCR, progression free survival (PFS) of 2. 3 months, and a single patient with complete response. We collected 36 samples from 23 patients including primary pancreas tumor tissue and liver metastases, and 13 pairs of pre and on treatment biopsies. We performed single-nucleus and paired single-cell RNA and TCR sequencing on these samples to provide comprehensive insight into the cell types and biology present in this unique tumor microenvironment. Using supervised non-negative matrix factorization we have identified both previously established and novel gene programs that co-vary between cell types. Within the various tissue sites we have identified differing proportions of basal to classical tumor cell types and a distinct shift towards the classical state post-radiation. Of particular interest is a group of interferon related gene programs present within epithelial cell subtypes, C1QC+ and MHCII+ macrophages, and CD14+/CD16+ monocytes that indicate cell type specific responses to treatment. Focusing on the T cells, we found a distinct shift towards exhausted or proliferating states on treatment and using TCR sequencing data we have identified novel and expanding clones on treatment, largely consisting of those same cell subtypes. We also collected spatial transcriptomics data on a subset of patient samples, and analysis is ongoing to further confirm the cell type relationships identified in single-cell resolution data, along with spatial localization of basal to classical tumor states. This vast multimodal dataset allows us novel insight into the radiation and dual ICB induced cellular state shifts in the tumor microenvironment. Citation Format: Milan Parikh, Ryan Park, Aparna R. Parikh, Julie L. Koenig, Leon Pappas, Moshe Sade-Feldman, Lynn Bi, Nicole Carzo, Tarin M. Grillo, Islam Baiev, Olanike Asupoto, Irena Gushterova, Tom LaSalle, Anna Gonye, Emily Blaum, David P. Ryan, David T. Ting, Theodore S. Hong, Dana Pe'er, Nir Hacohen, Arnav Mehta. Understanding radiation and immunotherapy induced cell state shifts in the pancreatic tumor microenvironment abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1194.