Abstract 1651: Contextual immune sensitisation of pancreatic ductal adenocarcinoma to anti GITR agonist
Authors: Desai Krisha , Ragulan Chanthirika , Lawrence Patrick Varun , Box Gary , Fontana Elisa , Young Kate , Larkin James , Cunningham David , Starling Naureen , Sadanandam Anguraj 
Published: July 2021

Abstract
Introduction: Harnessing the potential of immune-activating agents like glucocorticoid-induced TNF receptor (GITR) agonists, especially in highly aggressive pancreatic ductal adenocarcinoma (PDAC) presents an attractive opportunity. The success of immune targeting has, however, been met with limited clinical success. This warrants careful selection of pre-clinical models that efficiently recapitulate the immune heterogeneity within human PDAC for testing and developing immunotherapeutic strategies.
Experimental Procedures: Syngeneic mouse models established using cell lines derived from genetically engineered mouse models were characterized into T cell high (TCH) and T cell low (TCL) groups using putative T cell genes. Subcutaneous tumors from one TCH and another TCL syngeneic model were treated with mouse anti-GITR agonist (DTA-1; n=10) or isotype control (IgG; n=10). Tumors were profiled using a multi-parametric approach utilizing custom-designed NanoString panel, 12-colour flow cytometry (FACS), immunohistochemistry (IHC) and Luminex to assess immune-associated changes.
Results: Clustering analysis categorized syngeneic models into TCH and TCL, which was similar to patient PDAC. A significant survival benefit (p&lt;0.05) along with reduced tumor burden was observed in DTA-1 treated TCH model compared to IgG control. This was supported by significant (p&lt;0.05) enrichment of GranzymeB+ CD8+ T cells by co-immunostaining and increased interferon (IFN) gamma expression by Luminex (p&lt;0.05). PDL1 expression, by mRNA and FACS, was also significantly upregulated in DTA-1 treated TCH tumors. On the other hand, treatment with DTA-1 led to poorer survival (p&lt;0.05) and significantly higher tumor burden than IgG in the TCL model. Apart from the downregulation of T cell genes, DTA-1 led to increased Ly6C expression (monocyte/macrophage marker) and stark enrichment of IFN gamma expression. More importantly, treatment with DTA-1 in the TCH model resulted in a switch to the classical PDAC subtype genes in contrast to quasi-mesenchymal gene upregulation in DTA-1 treated TCL model.
Conclusions: Our results indicate differential anti-tumor immune response mediated by DTA-1 in models with distinct immune composition. The study highlights the importance of patient selection for maximal treatment benefit and reducing the risk of unnecessary cytotoxicity. Finally, our models prove useful for personalized testing and validation of existing and novel immunotherapeutic modalities.
Citation Format: Krisha Desai, Chanthirika Ragulan, Patrick Varun Lawrence, Gary Box, Elisa Fontana, Kate Young, James Larkin, David Cunningham, Naureen Starling, Anguraj Sadanandam. Contextual immune sensitisation of pancreatic ductal adenocarcinoma to anti GITR agonist [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1651.