Abstract 4584: Malignant pancreatic cancer cells respond to immune selection pressure to foster immunosuppression

Abstract

Abstract Background: Host immunity is relevant to pancreatic cancer (PC). Pancreatic tumors are infiltrated with a high number of immune cells, and they play a potential important role in disease evolution. However, there is no FDA approved immunotherapy for PC yet, suggesting that a deeper understanding of immune-cancer interaction is needed. The aim of this study was to investigate the effects of immune selection pressure on malignant pancreatic epithelial cells and on subsequent cancer immune evasion mechanisms. Materials and Methods: 1 X105 mT3-2D murine pancreatic cancer cells (Kras+/G12D, p53+/-R172H (Boj et al. 2015)) were injected subcutaneously into syngeneic C57BL/6J (WT), B6.CB17-Prkdcscid/SzJ (SCID) and T cell-depleted WT mice (10 mice/group). Tumor growth was monitored over time. 1 cm3 tumors then were harvested, processed and studied. To consider the complex biology of pancreatic cancer immunology, we analyzed tumor specimens in their entirety by histopathological evaluation, multiple color flow cytometry, NanoString nCounter, and global proteomics profiling. Furthermore, to evaluate the influence of immune selection pressure on neoplastic cells, we selectively analyzed malignant epithelial cell gene expression in the cell line, and in cells isolated from tumors grown in WT and SCID mice, respectively, by RNAseq on mT3-2D-GFP+ fluorescence-activated cell sorter (FACS)-sorted cells. Also, whole exome sequencing was performed on WT tumors. Results Here we demonstrate that mT3-2D tumors engrafted in WT mice grow more slowly as compared with syngeneic SCID and T cell-depleted tumors, demonstrating that the reduced mT3-2D tumor growth rate in WT mice is T cell dependent. Putative cancer neoantigens were identified from whole exome sequences with pVACtools. Supporting evidence of tumor immunogenicity came from the observation that WT tumors are moderately infiltrated with T cells, by IHC and flow cytometry. Proteomics and NanoString nCounter analysis demonstrated the selective presence of myeloid suppressive cells in WT tumors, supporting their role in immune evasion. Notably, RNAseq showed selective upregulation of malignant epithelial cell-derived genes known to stimulate this immunosuppressive phenotype, including myeloid- and complement-related genes. Conclusion Despite the immunogenicity of the WT tumors and the infiltration of T cells in this PC model, T cell immunity incompletely controls tumor growth. Malignant epithelial cells mediate this cancer immunosuppressive phenotype in response to immune selection pressure, suggesting novel translational opportunities.