Cancer cell SMAD4 loss promotes tumor progression by modulating the tumor immune microenvironment in pancreatic ductal adenocarcinoma 2803

Description Pancreatic cancer’s dismal 12% five-year survival rate urgently calls for a better understanding of the underlying tumor biology. KRAS, TP53, and SMAD4 mutations are frequent and are thought to be key disease drivers in the most common pancreatic cancer type, pancreatic ductal adenocarcinoma (PDAC). Recent literature has suggested KRAS and TP53 mutations can drive cancer progression by enhancing suppressive myeloid cell recruitment to the tumor microenvironment (TME). Thus, this prompts the need to understand if additional SMAD4-inactivating mutations can further contribute to an immunosuppressive PDAC TME. We hypothesize SMAD4 loss modulates the TME myeloid compartment to support tumor progression. We used CRISPR-Cas9 to delete Smad4 in an immunogenic murine PDAC cell line to generate SMAD4 knockout (SKO) and SMAD4-intact control lines (mock). SKO orthotopic implantation in C57BL/6 mice resulted in greater tumor burden compared to mock, but not in immunodeficient NSG mice. Single cell RNA-sequencing of tumors prior to tumor weight divergence revealed the greatest differences in the macrophage and granulocyte clusters. Notably, lipid-associated macrophages were enriched in SKO tumors, and this was accompanied by an influx of exhausted CD8+ T cells, highlighting a more immunosuppressive TME overall. Collectively, these results suggest a critical role for cancer cell SMAD4 loss in modulating the TME to subvert anti-tumor immunity and promote PDAC progression.