Featured Poster: The impact of CD73 immune checkpoint blockade on procoagulant tissue factor

Description of Background: Monocytes play a key role in initiating immune-mediated thrombosis through expression of tissue factor (TF) and release of TF-bearing extracellular vesicles. Extracellular adenosine is a key intravascular brake on the self-amplifying cycle of thromboinflammation following tissue injury. CD73, an immune checkpoint ectoapyrase, hydrolyzes the terminal phosphate group from extracellular AMP to generate adenosine. Genetic or post-natal inhibition of CD73 exacerbates venous and arterial thromboinflammation in animal models. Recent studies have also identified CD73 as an immune checkpoint on tumor cells, leading to many phase 2 clinical trials with CD73 inhibitors in patients already at high risk of thrombosis.

Methods: To assess the impact of CD73 inhibition on monocyte tissue factor expression, we incubated THP-1 monocytes and healthy hPBMCs with the CD73 inhibitor, adenosine 5'-(α, β-methylene) diphosphate (AMPCP). We then examined PBMCs and plasma from a cohort of patients with ultrarare, loss-of-function gene mutations that result in loss of CD73 (ACDC) and who present with premature peripheral artery calcific disease and occlusions.

Results: In a human monocytic cell line in vitro, CD73 inhibition increased surface tissue factor expression in a time-dependent manner (p=0.01). However, hPBMCs treated with CD73 inhibitor did not demonstrate changes in tissue factor expression at baseline or following cytotoxic challenge with LPS (p=0.17, p=0.98). In a pilot study comparing PBMCs from patients with ACDC (n=8) and healthy controls (n=6), surface tissue factor expression was similar between the groups at baseline and after LPS challenge (p=0.31). Correspondingly, analysis of plasma-derived extracellular vesicle tissue factor activity from ACDC and controls revealed no differences (p=0.145).

Conclusion: These findings suggest exogenous suppression or innate deficiency of CD73 does not increase monocyte tissue factor expression or extracellular vesicle tissue factor activity at baseline or following exposure to LPS. Together, these data provide insight into the molecular mediators of thromboinflammation and may inform thrombotic risk in patients with ACDC or patients with cancer receiving CD73 inhibitors.

Learning Objective: To assess the impact of CD73 blockade on monocyte tissue factor expression and activity.