Neutrophils Seeking New Neighbors - Radiotherapy Affects the Cellular Framework and the Spatial Organization in a Murine Breast Cancer Model

Neutrophils are known to contribute to many aspects of tumor progression and metastasis in cancer. The presence of neutrophils or neutrophil-derived mediators in the tumor microenvironment has been associated with poor prognosis in several types of solid tumors. Nonetheless, the effects of cancer treatments such as radiotherapy on neutrophils has not been studied yet. Furthermore, the cellular composition and distribution of immune cells in the tumor is of increasing interest in cancer research and new imaging technologies allow to perform more complex spatial analyses within tumor tissues. Therefore, we aim to offer novel insight into intra-tumoral formation of cellular neighborhoods and communities in murine breast cancer. We used the TS/A breast cancer tumor model for our analyses. We performed image mass cytometry and spatial neighborhood analyses of the tumor microenvironment and quantified NET-degradation products in serum. We show that radiotherapy of 2x8 Gy significantly alters the cellular composition and spatial organization in the tumor, especially of neutrophils. Locally applied radiotherapy further affects neutrophils in a systemic manner by decreasing the serum neutrophil extracellular trap concentrations which correlates positively with survival. In addition, the intercellular cohesion is maintained after radiotherapy as shown by E-Cadherin expression via the TGF-β/SMAD axis which potentially prevents metastasis. We conclude that radiotherapy-modulated cellular composition and spatial distribution of immune cells, particularly that of neutrophils and macrophages in connection to T cells has to be considered more. This sheds light on potential mechanisms that influence treatment outcomes and metastatic potential of solid tumors such as breast cancer.