Due to lack of reliable markers that determine metastatic potential and guide cancer treatment; metastasis remains a major cause of cancer-related deaths. Immune cells, especially myeloid cells, contribute significantly to metastasis and could function as potential prognostic markers. However, due to their tremendous heterogeneity and plasticity; no reliable and clinically translatable markers to define pro-metastatic immune cell subsets have been identified. With this study we aim to gain deeper insights into myeloid immune cell activities in metastatic tumors to reveal potential markers that define pro-metastatic immune cells. We expect such markers will improve assessment of prognosis and further help devise therapeutic strategies.
To identify pro-metastatic functions and markers, we performed RNA sequencing on immune cells of 67NR (non-metastatic) and 66cl4 (metastatic) primary tumors, derived from the syngeneic 4T1 mouse breast cancer model. After data analysis, we validated the candidate of interest using flow cytometry, immunoblotting, ELISA, qPCR among other techniques. The translational potential of the identified marker was studied by immunohistochemistry on 487 breast cancer patient biopsies.
We identified several biological processes specifically upregulated in immune cells of metastatic tumors. Interestingly, a metabolic enzyme- arginase1 (ARG1), with known wound healing and immunosuppressive functions was associated with the top enriched processes. Therefore, we investigated it further and found that ARG1 was expressed in myeloid cells, specifically immature neutrophils and macrophages, infiltrating the metastatic tumors but not in non-metastatic ones. This indicated the potential of myeloid cells that express ARG1 to serve as prognostic markers. Further, we analyzed breast cancer patient biopsies and showed that a higher number of ARG1+ infiltrating cells were associated with breast cancer tumors that are more prone to metastasis (basal and HER2 type).
We identified ARG1-containing myeloid immune cells as pro-metastatic markers and indicated their translational potential to clinic.
The authors.
NTNU and Helse Midt-Norge.
All authors have declared no conflicts of interest.