M. Hundeyin1, S. Pushalkar1, D. Daley1, G. Werba1, N. Mohan1, S. Lall1, B. Wadowski1, B. Aykut1, E. Kurz1, U. Soni1, E. Morales-Vicente1, D. Saxena1, G. Miller1 1New York University School Of Medicine,Surgery,New York, NY, USA
Introduction:
Pancreatic ductal adenocarcinoma (PDA) is the 3rd most lethal cancer in the United States and accounts for 85% of all pancreatic malignancies. The gut microbiome has emerged as an important regulator in the balance between health and disease, including oncogenesis. However, the microbiome has not been directly linked to pancreatic oncogenesis. We postulated that hosts with PDA harbor an altered pancreatic and gut microbiome and that dysbiosis influences PDA progression.
Methods:
To determine whether endoluminal gut bacteria can access the pancreas, we administered fluorescently-labeled Enterococcus faecalis to WT mice via oral gavage. To determine whether bacteria promote the progression of pancreatic oncogenesis, we employed the slowly progressive p48Cre;LSL-KrasG12D (KC) mouse model of PDA and rederived KC mice in a germ-free environment. To identify possible perturbations in the gut microbiome associated with the progressive pancreatic oncogenesis, we evaluated the composition of the gut microbial community of KC mice compared with age-matched WT littermate controls by performing 16S gene sequencing. Lastly to determine the mechanism of immunosuppression; we injected F21242 pancreatic tumor cell line orthotopically into the pancreas of WT mice after bacterial ablation and vehicle, isolated the pancreatic leukocytes and analyzed them by flow cytometry.
Results:
In the pre-morbid state the intestinal microbiome is similar in mice bearing pancreas-specific oncogenic mutations and in controls; however, as mice age, PDA-bearing hosts develop a unique gut microbiome including expansion of Actinobacteria and Deferribacteres. We found that gut bacteria access the pancreas and the cancerous pancreas harbors a distinct microbiome in mice. Further, genotypically identical PDA-bearing mice that exhibit divergent disease phenotypes harbor stage-specific microbiomes suggesting that microbial structure is associated with disease aggressiveness. Germ-free or ablative antibiotic treated mice were protected against PDA whereas transfer of gut bacteria from PDA-bearing mice, but not from control mice, reversed the tumor-protection. Bacterial ablation was associated with innate and adaptive immunogenic reprogramming of the PDA tumor microenvironment including a marked reduction in myeloid-derived suppressor cells and immune-suppressive macrophages, increased Th1 differentiation of CD4+ T cells, and expansion and activation of cytotoxic CD8+ T cells. In addition, we show that gut bacterial ablation and PD-1 blockade offer synergistic efficacy.
Conclusion:
These data suggest that endogenous microbiota promote the crippling immune-suppression characteristic of PDA and that the microbiome has marked potential as a biomarker and therapeutic target in PDA.