Abstract 123: Genetic Deficiency Of The Ectoenzyme CD73 Increases Neutrophil Extracellular Trap Formation In Patients With ACDC

Background/Purpose: CD73 is a ecto-5′-nucleotidase located on the plasma membrane that generates adenosine from AMP in the extracellular space, and functions as a checkpoint against immune and vascular activation. CD73 inhibitors that eliminate this immune checkpoint blockade are being studied in phase 2/3 cancer clinical trials. We recently identified that lack of CD73 promotes vascular thromboinflammation and neutrophil extracellular trap (NET) formation in mice. The role of CD73 in human NETosis, however, remains to be studied. Arterial calcification due to deficiency of CD73 (ACDC) is a rare, autosomal recessive condition (~20 patients globally) that results in occlusive peripheral vascular disease. We hypothesized that the congenital absence of CD73 and its function as an immune checkpoint would heighten innate immune activation in patients with ACDC.

Methods: To test this hypothesis, six patients with molecularly confirmed ACDC were recruited to the NIH for mechanistic studies. Using purified neutrophils from ACDC patients and healthy controls, spontaneous and LPS-induced NET formation was quantified by both Sytox extracellular DNA (eDNA) labeling and NET-associated MPO activity.

Results: Absence of surface CD73 was confirmed by flow cytometry. Relative to healthy controls, four of six (4/6) patients with ACDC demonstrated increased ex vivo spontaneous NET formation, but not LPS-triggered NETosis. The four ACDC patients with increased spontaneous NETosis had a mean 1.7-fold increase in Sytox-stained eDNA and 2-fold increase in MPO activity compared with contemporary healthy controls.

Conclusion: These data reveal marked, spontaneous NETosis in patients deficient in the ectoenzyme CD73. Comparison with LPS-stimulated neutrophils demonstrates near maximal NETosis at baseline in patients with ACDC, consistent with a model where CD73 tonically suppresses neutrophil activation to maintain vascular and immune homeostasis. Ongoing studies are exploring the mechanism of spontaneous NETosis, thrombin formation, and fibrinolysis in patients with ACDC. Taken together, these data will have relevance to patients with ACDC, and inform the thromboinflammatory risk of cancer patients receiving CD73 inhibitors.