The formation of neutrophil extracellular traps (NETs), known as NETosis, was first observed as a novel immune response to bacterial infection, but has since been found to occur abnormally in a variety of other inflammatory disease states including cancer. Breast cancer is the most commonly diagnosed malignancy in women. In breast cancer, NETosis has been linked to increased disease progression, metastasis, and complications such as venous thromboembolism. NET-targeted therapies have shown success in preclinical cancer models and may prove valuable clinical targets in slowing or halting tumor progression in breast cancer patients. We will briefly outline the mechanisms by which NETs may form in the tumor microenvironment and circulation, including the crosstalk between neutrophils, tumor cells, endothelial cells, and platelets as well as the role of cancer-associated extracellular vesicles in modulating neutrophil behavior and NET extrusion. The prognostic implications of cancer-associated NETosis will be explored in addition to development of novel therapeutics aimed at targeting NET interactions to improve outcomes in patients with breast cancer.

In patients with sickle cell disease (SCD), the polymerization of intraerythrocytic hemoglobin S promotes downstream vaso-occlusive events in the microvasculature. While vaso-occlusion is known to occur in the lung, often in the context of systemic vaso-occlusive crisis and the acute chest syndrome, the pathophysiological mechanisms that incite lung injury are unknown. We used intravital microscopy of the lung in transgenic humanized SCD mice to monitor acute vaso-occlusive events following an acute dose of systemic lipopolysaccharide sufficient to trigger events in SCD but not control mice. We observed cellular microembolism of precapillary pulmonary arteriolar bottlenecks by neutrophil-platelet aggregates. Blood from SCD patients was next studied under flow in an in vitro microfluidic system. Similar to the pulmonary circulation, circulating platelets nucleated around arrested neutrophils, translating to a greater number and duration of neutrophil-platelet interactions compared with normal human blood. Inhibition of platelet P-selectin with function-blocking antibody attenuated the neutrophil-platelet interactions in SCD patient blood in vitro and resolved pulmonary arteriole microembolism in SCD mice in vivo. These results establish the relevance of neutrophil-platelet aggregate formation in lung arterioles in promoting lung vaso-occlusion in SCD and highlight the therapeutic potential of targeting platelet adhesion molecules to prevent acute chest syndrome.

Rationale: Intraerythrocytic polymerization of Hb S promotes hemolysis and vasoocclusive events in the microvasculature of patients with sickle cell disease (SCD). Although platelet–neutrophil aggregate–dependent vasoocclusion is known to occur in the lung and contribute to acute chest syndrome, the etiological mechanisms that trigger acute chest syndrome are largely unknown. Objectives: To identify the innate immune mechanism that promotes platelet–neutrophil aggregate–dependent lung vasoocclusion and injury in SCD. Methods: In vivo imaging of the lung in transgenic humanized SCD mice and in vitro imaging of SCD patient blood flowing through a microfluidic system was performed. SCD mice were systemically challenged with nanogram quantities of LPS to trigger lung vasoocclusion. Measurements and Main Results: Platelet–inflammasome activation led to generation of IL-1β and caspase-1–carrying platelet extracellular vesicles (EVs) that bind to neutrophils and promote platelet–neutrophil aggregation in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro. The inflammasome activation, platelet EV generation, and platelet–neutrophil aggregation were enhanced by the presence of LPS at a nanogram dose in SCD but not control human blood. Inhibition of the inflammasome effector caspase-1 or IL-1β pathway attenuated platelet EV generation, prevented platelet–neutrophil aggregation, and restored microvascular blood flow in lung arterioles of SCD mice in vivo and SCD human blood in microfluidics in vitro. Conclusions: These results are the first to identify that platelet–inflammasome–dependent shedding of IL-1β and caspase-1–carrying platelet EVs promote lung vasoocclusion in SCD. The current findings also highlight the therapeutic potential of targeting the platelet–inflammasome–dependent innate immune pathway to prevent acute chest syndrome.

Sickle cell disease (SCD) is a genetic disorder that leads to red blood cell (RBC) sickling, hemolysis and the upregulation of adhesion molecules on sickle RBCs. Chronic hemolysis in SCD results in...