59.09 T_H17 Cells Mediate Cancer Progression and Development Due to Neutrophil Extracellular Traps in Liver

V. Sud¹, S. Tohme¹, H. Huang^1,2, D. J. Van Der Windt¹, A. Tsung^{1  1}University Of Pittsburg,General Surgery,Pittsburgh, PA, USA ²Huazhong University Of Science And Technology,Surgery,Wuhan, HUBEI, China

Introduction:
Colorectal cancer is the third leading cause of cancer in the United States, a majority of which is due to liver metastasis. In liver metastasis of colorectal cancer, surgical resection is superior to chemotherapy alone. However, the rate of recurrence of metastasis after surgical resection is 50-60%, a major cause of treatment failure. It has been shown that the Neutrophil Extracellular Traps (NETs), a unique method of neutrophil apoptosis, contribute significantly to this process of cancer growth and development. We hypothesized that NETs influence the growth of metastasis by altering the tumor immune environment to a more pro-tumorigenic state.

Methods:
C57BL/6J wild-type mice (WT) and global genetic knockouts for peptidylarginine deaminase 4 (PAD4) gene (PAD4 KO mice), a gene which codes for an integral enzyme for NET formation, hence preventing the formation of NETs in the mice, were used. At 12wks of age both groups were injected through the portal vein with 0.5 million cells of Murine colorectal cancer cell line (MC-38). After 3 weeks, livers from both groups were harvested and underwent flow cytometry to analyze the innate and adaptive cell populations. 

Results:
Flow cytometry analysis was run on mice from both groups and the samples from the background liver and tumor of the mice were independently assessed. On examination, there were far fewer tumors in the PAD4KO mice than the WT. Flow analysis on the liver demonstrated a 5.6 fold decrease in the T_H17 cell population in the PAD4KO mice as compared to the WT (0.082% PAD4KO; 0.448% WT). Which was accompanied by an increase in the CD8+ population (66.1% WT v 33.4% PAD4KO of total T cells) and a small decrease in the CD4+ population (18.9% WT v 20.6% PAD4KO of total T cells). 

Conclusion:

We found that absence of NETs leads to an anti-tumorigenic environment by a decrease in T_H17 cells and increase in CD8 cells. Further studies are underway to further characterize the crosstalk between NET’s and immune cells in the tumor microenvironment.