Modulating Tumor Immune Microenvironment Using Heterologous Proteins
Cancer immunotherapy has revolutionized cancer treatment with widely varying response rates among different cancers. Since, immune cells and the cancer cells share the same genetic background, tumor cells evolve to evade anti-tumor immune responses by either hijacking the pathways already present in the body to avoid overactivation of immune responses or creating a challenging tumor microenvironment for functioning of immune cells. Modulating the tumor microenvironment with heterologous non-human proteins opens avenues for enhanced therapeutic efficacies with a minimal chance of developing resistance . In this thesis we have explored therapeutic potential of engineered proteins derived from pathogenic bacteria Helicobacter. pylori and Borrelia. garinii. In the first part we have engineered Helicobacter. pylori gamma-glutamyl transferase (PEG-GGT) to have a prolonged half-life in serum and deplete circulating glutamine (an amino acid extensively used by cancer cells for proliferation) without depleting asparagine (an amino acid important for T cell activation). PEG-GGT treatment inhibits growth of cancer cells in vitro, but in vivo it increases myeloid derived suppressor cells (MDSC) and has no significant impact on tumor growth. By deriving a glutamine depletion signature, we analyze diverse human cancers within the TCGA and illustrate that glutamine depletion is not associated with favorable clinical outcomes and correlates with accumulation of MDSC. Broadly, our results help clarify the integrated impact of glutamine depletion within the TME and advance PEG-GGT as an enzymatic v tool for the systemic and selective depletion (no asparaginase activity) of circulating glutamine in live animals. In the second part of the thesis, we have engineered T cells to increase their adhesion to endothelial cells with the overall objective of increasing their tumor infiltration. We showed that biglycan, a proteoglycan, is significantly overexpressed in metastatic cancers. We drew inspiration from B. garinii, the causative agent of lyme disease, in which the bacterium spreads systemically to various organs via binding biglycan present on endothelial cells utilizing its cell adhesion molecules. We showed that heterologous expression of these adhesion molecules in T cells enabled their efficient adhesion to endothelial cells under both static and dynamic conditions.
Cancer metabolism, glutamine metabolism, immunotherapy, T cell infiltration
Portions of this document appear in: Kumar, Monish, Ankita Leekha, Suman Nandy, Rohan Kulkarni, Melisa Martinez-Paniagua, KM Samiur Rahman Sefat, Richard C. Willson, and Navin Varadarajan. "Enzymatic depletion of circulating glutamine is immunosuppressive in cancers." Iscience 27, no. 6 (2024).
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