Abstract
Neutrophils are thought to be critical to the process whereby breast cancers establish an immunosuppressive and tumour cell nurturing ‘pre-metastatic’ niche before overt metastasis can be detected. However, the spatial localization of neutrophils and their interaction with other cell types in the lung pre-metastatic niche is not well described. We used a spontaneously metastatic mammary cancer model combined with a multiplexed three- and four-dimensional imaging approach to investigate the behaviour of neutrophils in the pre-metastatic niche. Volume fixed tissue three-dimensional imaging showed that approximately 40% of CD8+ T cells are adjacent to neutrophils at this stage. In live tissue, we found neutrophils with impaired intravascular motility congested the capillaries of pre-metastatic lungs potentially obstructing CD8+ T cells. Slowed neutrophil transit was dependent on the conformation of β2-integrin and could be recapitulated by treating non-tumour bearing mice with G-CSF, a potent systemic mediator of granulopoiesis. We found a decrease in L-selectin (CD62L) on neutrophils in the lungs of both mammary tumour bearing and G-CSF treated mice. Finally, we observed differential accumulation of intravenously injected micro-beads in the lung, suggestive of transient circulatory dead spaces which were also dependent on β2-integrin inactivation. Overall, our study proposes that integrin-mediated neutrophil congestion of the alveolar capillaries could contribute to the generation of the pulmonary pre-metastatic niche.
Competing Interest Statement
LMC has consulted for Ono Pharmaceuticals UK, JBGM has subsequently become an employee of AstraZeneca, AJM has subsequently become an employee of Antibody Analytics
Footnotes
↵# Joint first authors
We have added additional data on CD62L expression (in Figure 3) and refined our description and interpretation in the text.
