| Summary: | Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2020 === Cataloged from student-submitted PDF of thesis. Vita. Page 191 blank. === Includes bibliographical references. === Insights into mechanisms of immune escape have fueled the clinical success of immunotherapy in many cancers. However, pancreatic cancer has remained largely refractory to checkpoint immunotherapy. To uncover mechanisms of immune escape, we have characterized two preclinical models of immunogenic pancreatic ductal adenocarcinoma (PDAC). In order to dissect the endogenous antigen-specific T cell response in PDAC, lentivirus encoding the Cre recombinase and a tumor specific antigen (SIINFEKL, OVA[subscript 257-264]) was delivered to Kras[superscript LSL-G12D/+]; Trp[superscript 53flox/flox] (KP) mice. We demonstrate that KP tumors show distinct antigenic outcomes: a subset of PDAC tumors undergoes clearance or editing by a robust antigen-specific CD8+ T cell response, while a fraction undergo immune escape. Subsequently, we have developed an immunogenic pancreatic tumor organoid orthotopic transplant model. === In this model, immunogenic pancreatic tumors manifest divergent tumor phenotypes; 40% of tumor organoids do not form tumors ("non-progressors"), whereas 50% of organoids form aggressive tumors despite maintaining antigen expression and a demonstrable T cell response ("progressors"). Additionally, a subset (10%) of tumors show an intermediate phenotype, possibly reflective of an immune equilibrium state. We have further phenotypically and transcriptionally characterized the CD8+ T cell response to understand immune escape in this model. Our analyses reveal unexpected T cell heterogeneity, and acquisition of T cell dysfunctionality. Therapeutic combinatorial targeting of co-inhibitory receptors identified on dysfunctional antigen-specific CD8+ T cells led to dramatic regression of aggressive pancreatic tumors. === Finally, we demonstrate that human CD8+ T cells isolated from pancreatic tumors co-express co-inhibitory receptors, suggesting that T cell dysfunction may be operational in human disease. This is the first demonstration of immunoediting in an autochthonous and organoid-based model of pancreatic cancer. Further characterization of these preclinical model systems will enable rational design of novel clinical immunotherapeutic strategies for treatment of this devastating disease. === by Laurens J. Lambert. === Ph. D. === Ph.D. Massachusetts Institute of Technology, Department of Biology
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