Abstract PO-014: Harnessing the Heterogeneity of Circulating Hybrid Cells in Pancreatic Adenocarcinoma

Pancreatic adenocarcinoma (PDAC) remains one of the most lethal malignancies in the United States and tumor heterogeneity has major implications on the effectiveness of systemic therapies. Comprehensive tumor analysis at the single cell level offers an in-depth examination of neoplastic cells with metastatic potential and supports development of individualized treatment strategies to ultimately improve survival. Hybrid cells are a novel cell population derived from immune-cancer cell fusion within solid tumors and disseminate into peripheral blood, where they can be detected as circulating hybrid cells (CHCs) based on their dual expression of tumor and immune cell epitopes. Compared to conventionally-defined circulating tumor cells (CTCs), CHCs are found in patients at higher levels which allows for more robust phenotypic analyses of tumor cell features and collection for downstream multi-omic profiling. To investigate heterogeneity among disseminated CHCs in patients with PDAC, we assessed for tumor cell features using immunohistochemical analyses of single cells from peripheral blood mononuclear cell smears and by single cell RNA sequencing (scRNA-seq) from FACS-isolated cells. Downstream image analyses was performed Zeiss Zen blue software and scRNA-seq was analyzed using the Seurat analysis package. We determined that PDAC patients harbored heterogeneous populations of CHCs with differential protein expression that mirrored expression in corresponding primary tumors. Further, scRNA-seq analyses identified CHC populations with varying degrees of retained tumor identity, as well as subsets derived from different immune cell lineages. Unsupervised clustering of CHCs with tumor-dominate phenotypes demonstrated high differential expression of cancer related genes with known implications in PDAC tumors and treatment resistant pathways. Inference copy number variation analysis revealed chromosomal amplifications of 1q and 19q along with deletions of 6p, 12q, and 22q, characteristic of PDAC tumors. Additionally, a myriad of KRAS mutations were identified in patient CHCs but absent in normal leukocytes. As the product of tumor and immune cell fusion, CHCs provide a rich source for assessing PDAC heterogeneity through genetic and protein expression analyses. Ultimately, CHCs have great potential as a liquid biopsy in pancreatic cancer which could be harnessed to guide therapy. Citation Format: Brett Scott Walker, Sidharth Sengupta, Michael Parappilly, Aysegul Ors, Jared Fischer, Thomas Sutton, Brett Sheppard, Skye Mayo, Melissa Wong. Harnessing the heterogeneity of circulating hybrid cells in pancreatic adenocarcinoma [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-014.