Introduction: Chronic pancreatitis is the most prevalent risk factor for the development of pancreatic cancer. Dendritic cells (DC) are known to augment inflammation in a range of clinically significant contexts, yet their role in chronic pancreatitis and pancreatic cancer development has not been intensely studied. We postulated a primary role for DC in pancreatic inflammation and the transition to carcinogenesis.
Methods: Chronic pancreatitis was induced using caerulein (50µg/kg, 3 weeks) in C57BL/6 mice. The p48Cre;KrasG12D model was used to study pancreatic carcinogenesis. Pancreatic DC populations were expanded by i.p. adoptive transfer of bone marrow-derived DC (1x106 cells, 3X/week) or using Flt3L (10µg/day x 10 days). MyD88 was inhibited in DC using CD11c-Cre MyD88 Floxed+/+ bone marrow chimeric p48Cre;KrasG12D mice.
Results: DC accounted for 1-3% of CD45+ leukocytes in normal pancreata, but increased to 10-15% during chronic pancreatitis. Moreover, the absolute number of pancreatic DC increased 100-fold. The number of DC was similarly increased in the pancreata of p48Cre;KrasG12D mice compared with aged matched WT or p48Cre controls. Furthermore, the surface phenotype of DC infiltrating p48Cre;KrasG12D pancreata differed from controls in that they were highly mature, expressing elevated CD40 and CD86. DC adoptive transfer to mice experiencing chronic pancreatitis resulted in severely exacerbated fibro-inflammatory disease, including greater than 60% reduction in acinar cell volume and a marked reduction in islet cell mass. Further, mice treated with Flt3L and simultaneous challenge with caerulein showed exacerbated acinar destruction, fibrosis, and inflammation. In addition to the fibroinflammatory changes, DC-overexpansion in pancreatitis led to widespread development of early PanIN lesions. Overall, approximately 40% of ducts were classified as PanINs in mice adoptively transferred with DC. Moreover, DC markedly accelerated malignant transformation when transferred for four weeks to p48Cre;KrasG12D mice as evidenced by a two-fold increase in tumor weight. Protein analysis revealed that DC transfer resulted in altered pancreatic expression of numerous cell cycle regulatory and tumor suppressor genes including upregulated expression of p21, p27, p-p27, p53, and Rb. DC effects in pancreatic fibroinflammation and carcinogenesis were mediated by induction of Th2-deviated CD4+ T cells. The number of intra-pancreatic CD4+ T cells and CD4:CD8 T cell ratio was markedly increased in mice adoptively transferred with DC. Additionally, intra-pancreatic CD4+ T cells in DC-treated mice exhibited a strong Th2 differentiation. Accentuation of the DCTh2 axis by inhibiting MyD88 signaling in DC further accelerated carcinogenesis in p48Cre;KrasG12D mice. CD4+ T cell depletion, protected p48Cre;KrasG12D mice adoptively transferred with DC from developing accelerated carcinogenesis. Further, adoptive transfer of Th2-deviated CD4+ T cells from pancreatitic mice that had previously been transferred with DC markedly accelerated carcinogenesis.
Conclusion: DC expand in chronic pancreatitis and pancreatic cancer. DC over-expansion in chronic pancreatitis exacerbates endocrine and exocrine destruction, induces marked inflammation, and early PanIN lesions. DC expansion in p48Cre;KrasG12D results in marked acceleration of tumor growth. DC effects on pancreatic fibroinflammation and neoplasia are mediated by induction of pancreatic-antigen-restricted Th2 cells.
Citation Format: Saman Zarbakhsh, Harry Mushlin, Raghavendra Rao, Sanna Badar, Mohsin Jamal, Dafna Bar-Sagi, George Miller, Adeel Rehman, Christopher Graffeo, Atsuo Ochi, Rocky Barilla, Constantinos Zambirinis, Nina Fallon, Cristina Hajdu, Yuliya Pylayeva-Gupta. Dendritic cells contribute to pancreatic fibroinflammatory disease and the transition to neoplasia. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr A102.