Mechanisms of JAG1-mediated immune suppression in the pancreatic cancer microenvironment

Pancreatic cancer (PanCan) is notorious for its resistance to therapy including immunotherapy, which is largely contributed by a suppressive tumor microenvironment. Targeting molecular pathways integral to PanCan resistance to current therapy remains an unmet need. Notch signaling regulates PanCan growth, metastasis, and the tumor microenvironment. While other

studies have shown that Notch signaling in macrophage and myeloid derived suppressor cells plays an immune-suppressive role in breast cancer and lung cancer, for example, our proposal will study previously unrecognized role of JAG1 in the regulation of the metabolic fitness of conventional dendritic cells (cDCs) that underlies the poor anti-tumor responses to

immunotherapy. The overarching objective of this application is to define if targeting Jagged1 (JAG1), a Notch ligand, whose expression correlates with a worse prognosis and inversely correlates with BATF3, essential for type I cDC (cDC1) development, could reverse the immunotherapy resistance in tumors with poor tumor-infiltrating cDC1 and T cells. cDC1 cells

present tumor antigens to tumor-killing T cells and thus play a critical role in supporting T cell anti- tumor immunity in immunotherapy. However, dendritic cells are present in low numbers and often display functional suppression in pancreatic cancer patients. Our recent work revealed that JAG1 functions as an inhibitory Notch ligand for cDC1 development as well as cDC metabolic fitness.

We also found that ablating JAG1 induced marked tumor regression and prolonged tumor-bearing mice long-term survival by increasing and reviving tumor-infiltrating DCs and Notch-activated tumor-killing T cells. We will test our central hypothesis that JAG1 promotes PanCan therapy resistance by suppressing cDC1 metabolic fitness and CD8 T cell anti-tumor response through

three interrelated aims. In aim 1, we will test if anti-JAG1 blocking antibody could sensitize resistant tumors to immunotherapy. In aim 2, we will investigate the mechanism by which JAG1 impairs cDC metabolic fitness essential for anti-tumor activation. Aim 3 will focus on the mechanism of anti-tumor T cell reinvigoration mediated by JAG1 ablation/blockade. We will use

a combination of the autochthonous KPC mouse model, immunophenotypically defined KPC orthotopic tumors, human PanCan organoids/myeloid cell coculture, and human PanCan specimens. We will employ cutting-edge mass cytometry to investigate the interplay between tumor cells and the surrounding immune cells and the tumor stroma. We will integrate the

immunophenotyping and the spatial transcriptomics of rare immune cell populations with clinical and histopathological information to correlate molecular findings with patient outcomes. This work is innovative as we illuminate a novel function of JAG1 in the maintenance of PanCan therapy resistance and explore its potential as a novel immunomodulatory treatment for this deadly

disease.