ICAM-1-targeted thrombomodulin mitigates tissue factor-driven inflammatory thrombosis in a human endothelialized microfluidic model

Diverse human illnesses are characterized by loss or inactivation of endothelial thrombomodulin (TM), predisposing to microvascular inflammation, activation of coagulation, and tissue ischemia. Single-chain antibody fragment (scFv)/TM) fusion proteins, previously protective against end-organ injury in murine models of inflammation, are attractive candidates to treat inflammatory thrombosis. However, animal models have inherent differences in TM and coagulation biology, are limited in their ability to resolve and control endothelial biology, and do not allow in-depth testing of "humanized" scFv/TM fusion proteins, which are necessary for translation to the clinical domain. To address these challenges, we developed a human whole-blood, microfluidic model of inflammatory, tissue factor (TF)-driven coagulation that features a multichannel format for head-to-head comparison of therapeutic approaches. In this model, fibrin deposition, leukocyte adhesion, and platelet adhesion and aggregation showed a dose-dependent response to tumor necrosis factor-alpha activation and could be quantified via real-time microscopy. We used this model to compare hTM/R6.5, a humanized, intracellular adhesion molecule 1 (ICAM-1)-targeted scFv/TM biotherapeutic, to untargeted antithrombotic agents, including soluble human TM (shTM), anti-TF antibodies, and hirudin. The targeted hTM/R6.5 more effectively inhibited TF-driven coagulation in a protein C (PC)-dependent manner and demonstrated synergy with supplemental PC. These results support the translational prospects of ICAM-targeted scFv/TM and illustrate the utility of the microfluidic system as a platform to study humanized therapeutics at the interface of endothelium and whole blood under flow.