Re-wiring PDAC Tumor Immunity Through Dendritic Cells

PROJECT SUMMARY The prognosis for pancreatic ductal adenocarcinomas (PDAC) patients is dismal. This is likely due to the presence of a uniquely suppressive tumor microenvironment (TME) that is dominant in most PDAC. Our data suggest immune priming by conventional dendritic cells (cDCs) may be a necessary barrier to overcome to generate lasting immunity in PDAC patients. cDCs are central for generating tumor antigen–specific T cell responses. Our new data show that cDCs are severely dysfunctional in patients with PDAC. This dysfunction is driven by two mechanisms: 1) We recently reported that PDAC patients have impaired cDC development in their bone marrow, and this leads to functional depletion of circulation pre-DCs, and poor response to checkpoint inhibitors. 2) We recently showed that even when cDC development is not fully impaired, cDC1s are physically/biochemically excluded from the PDAC TME. These mechanisms to the loss of stereotactic body radiation therapy (SBRT)-induced priming of tumor antigen-specific T cell responses and ultimately failed tumor control in animal models. We overcame both of these dysfunctional barriers by targeting cDC1s using a combination of systemic treatment with FMS-like tyrosine kinase 3 ligand (FLT3L) and CD40 agonists. Our pre- clinical data are exceptionally strong and have placed us in a unique position to translate these findings into PDAC patients. Our central hypothesis is that targeting cDC can unlock responsiveness to RT by generating lasting anti-tumor immunity. We will expand test this hypothesis in three specific aims. Aim 1. Determine the safety and efficacy of the combination of CDX-301 plus CDX-1140 and SBRT in locally advanced PDAC patients Aim 2. Determine the mechanisms by which FLT3L plus a CD40 agonist induce anti-tumor immunity. Aim 3. Determine if FLT3L plus CD40 agonists improves responsiveness to checkpoint immunotherapy. Impact. PDAC patient responses to conventional radiation therapy have been disappointing. Our data strongly support the use of FLT3L and CD40 agonist to enhance patient responsiveness to RT and generate long-term anti-tumor immunity. Our team is well-positioned to test our central hypothesis directly in clinical and experimental studies.