Pancreatic Ductal Adenocarcinoma (PDA) is the most commonly diagnosed form (~90%) of pancreatic cancer with a dismal 5-year survival rate of ~8%. PDA features a prominent pro-tumorigenic microenvironment rich in immunosuppressive cells that inhibit functions of anti-tumor immunity. Current immunotherapeutic approaches have been unsuccessful in improving PDA patient outcomes, leaving a need for a better understanding of the immunomodulatory signaling mechanisms within pancreatic tumor microenvironment. We have identified infiltrating regulatory B cells as being key contributors to pancreatic tumorigenesis through their expression of the regulatory cytokine IL-35, which directly inhibits anti-tumor immune responses. The mechanisms that cause B cells to produce IL-35 in cancer and promote pancreatic tumor growth are not known. Using a mouse model harboring a monoclonal fixed B cell receptor (BCR), or mice with a B cell-specific deletion of the Toll-Like Receptor (TLR) adaptor protein MyD88, I found that orthotopically implanted pancreatic tumors were drastically reduced in size as compared to WT mice. I have also conducted in vitro analysis of TLR and BCR activation and found that co-stimulation of endosomal TLRs and the BCR leads to a robust increase of IL-35 expression in B cells. Based on my preliminary data, I hypothesize that cancer-driven upregulation of IL-35 in B cells is dependent on crosstalk between BCR and endosomal TLRs, which promotes pancreatic tumor growth through immunosuppression. I propose two specific aims to test my hypothesis.
In Aim 1, I will determine how BCR and endosomal TLR signaling via Bruton's tyrosine kinase (BTK) contributes to expression of IL-35 expression in B cells, using analysis of signaling pathways in primary regulatory B cells and established B cell lines.
In Aim 2, I will investigate how activation of both BCR and TLR signaling in B cells promotes PDA tumor growth in vivo. To accomplish this task, I will analyze mouse models expressing a fixed BCR specificity with or without specific antigen exposure, mouse models lacking MyD88 signaling in B cells, as well as a cross of the two models. Our proposed research will provide an understanding of a previously uncharacterized facet of B cell-mediated function in PDA and use state-of-the-art PDA murine models to test strategies that block immune suppressive pathways. Ultimately, I anticipate my findings will reveal a targetable mechanism to inhibit B cell-mediated immunosuppression in pancreatic tumors and provide a multi-faceted training experience to help advance my scientific career.
Pancreatic cancer results in the third-leading cause of cancer related deaths in the United States as most current treatment modalities, including immunotherapies, fail to improve patient survival. Completion of this research proposal will advance our understanding of the mechanisms that activate the functions of immunosuppressive B cells in pancreatic cancer. Information gained from these studies will provide targetable mechanisms to increase sensitivity to immunotherapies in pancreatic cancer as well as increasing our collective understanding of B cell biology.