Author ORCID Identifier
0000-0001-9187-2022
Date of Graduation
8-2023
Document Type
Dissertation (PhD)
Program Affiliation
Immunology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Padmanee Sharma
Committee Member
James P Allison
Committee Member
Jennifer Wargo
Committee Member
Raghu Kalluri
Committee Member
Stephanie S. Watowich
Committee Member
Matthew M. Gubin
Abstract
The advent of immune checkpoint therapy (ICT) has transformed cancer treatment, but its effectiveness is limited in certain cancers like pancreatic ductal adenocarcinoma (PDAC), which exhibit resistance to this therapy. To overcome this challenge, it is crucial to understand the underlying mechanisms that determine tumor response to ICT and develop rational therapeutic combinations. The tumor microenvironment (TME), including suppressive myeloid cells, regulatory T cells (Tregs), and cancer-associated fibroblasts (CAFs), plays a pivotal role in ICT responses. Leveraging single-cell technologies, this study explores the role and function of immune subsets in the TME that induce therapy resistance.
Using single-cell RNA sequencing (scRNAseq), we performed comparative analyses on murine models sensitive (melanoma) and resistant (pancreatic) to ICT. Baseline analysis revealed the presence of specific subsets of suppressive myeloid cells and Tregs in pancreatic tumors, while melanoma tumors exhibited antigen-presenting myeloid cells and anti-tumor effector T cell subsets. These suppressive immune cells in pancreatic tumors persisted despite ICT intervention, leading to poor survival outcomes. Longitudinal assessment demonstrated the dominance of the suppressive microenvironment from early tumor stages, intensifying with tumor progression. Thus, we propose early intervention with agents targeting suppressive macrophages and Tregs to prime the environment before introducing checkpoint antibodies, enhancing ICT efficacy.
Through comprehensive analyses of the immune, tumor, and stromal compartments in both models, we identified two independent pathways of resistance. First, we discovered the recruitment of a distinct subset of ST2+Tregs mediated by IL-33 secreted by tumor cells. These ST2+Tregs were present in early-stage tumors and remained unaffected by ICT. Based on our patient data analyses, we propose ST2+Tregs as potential predictive biomarkers for therapeutic response.
Second, we uncovered a novel pathway of ICT resistance mediated by CAF-secreted TNF stimulated Gene 6 (TSG-6). Our findings in murine and human samples suggest that TSG-6 interacts with CD44+ myeloid cells in the TME, contributing to their suppressive phenotypes. High TSG-6 levels correlated with poor prognosis in patients treated with ICT, and in vivo inhibition of TSG-6 in combination with ICT improved survival. Therefore, we propose TSG-6 as a novel therapeutic target to enhance ICT responses in myeloid-rich and ICT-nonresponsive tumor types.
Keywords
Immunecheckpoint therapy, resistance, myeloid suppression, single cell RNA sequencing, high dimensional analyses, pancreatic cancer, stromal myeloid crosstalk, immunology, ST2 Tregs, TSG-6, cancer-associated fibroblasts