Abstract 211P
Background
The type and activity of immune cells infiltrating solid tumors influence patient prognosis and survival. Cancer cells secrete molecules such as chemoattractants and immunomodulatory mediators that attract and polarize the infiltrating immune cells. The combination of such compounds contributes to forming an immunosuppressive tumor microenvironment that promotes tumor growth. Therefore, we hypothesized that non-metastatic and metastatic cancer cells will recruit and polarize different types of immune cells. Our aim was to investigate the potential differences in immune cell recruitment to tumors with different metastatic potential and to uncover signaling compounds that contribute to making an immunosuppressive environment.
Methods
Using RNA sequencing, we compared non-metastatic 67NR and metastatic 66cl4 cells and primary tumors, originating from the 4T1 mammary tumor model. We used several molecular biological methods, including flow cytometry and immunohistochemistry to determine the immune cell heterogeneity within the tumors. Further, we performed qPCR, ELISA and shRNA-mediated knockdown to elucidate the role of our proteins of interest.
Results
Analysis of primary tumor transcriptomes and flow cytometry of dissociated tumors formed by 67NR cells and 66cl4 cells revealed clear differences in tumor landscapes of the two tumors. The most striking difference was the high infiltration of myeloid cells in the metastatic tumors. Consistent with this result, we found that 66cl4 cells produce and secrete high levels of the chemokine CXCL3, a potent chemoattractant of neutrophils. We used CXCL3 knock-down to determine its role in tumors. The loss of CXCL3 expression resulted in a significant decrease in infiltrating neutrophils and a shift in the macrophage polarization in the primary tumors.
Conclusions
Our results highlight the essential role of CXCL3 in shaping the tumor microenvironment. When CXCL3 is knocked-down it shifts the tumor microenvironment towards a less immunosuppressive state, making CXCL3 a potential new therapeutic target.
Legal entity responsible for the study
The authors.
Funding
Norges Forskningsråd, Norske Kvinners Sanitetsforening, Helse Midt-Norge.
Disclosure
All authors have declared no conflicts of interest.