Partial downregulation of platelet Glycoprotein VI by low affinity antibodies confers sustained and safe antithrombotic protection

Using a humanized GPVI (hGP6tg/tg) mouse model, we show that high-affinity anti-human GPVI IgGs (Emf1 KD 0.490 nM, Emf2) induce a GPVIKO-like phenotype with antithrombotic efficacy. In contrast, JAQ1 IgG, which binds hGPVI with low affinity (KD: 9.6 nM), induces only partial (~50%) GPVI downregulation, generating a stable low-density GPVI (GPVILO) phenotype lasting up to 10 days. GPVILO platelets showed impaired aggregation, abolished procoagulant activity, and—similar to Fab-mediated inhibition—conferred protection from arterial thrombosis and LPS-induced thrombo-inflammation without increasing bleeding, even when combined with high-dose aspirin.

The low-affinity anti-mouse GPVI antibody JAQ4 (KD = 21 nM) induced a comparable GPVILO phenotype in wild-type mice. Transfusion of human platelets in NOD/SCID mice showed that complete and partial GPVI depletion, respectively, also occurs in human platelets in vivo. These findings establish that partial, affinity-dependent GPVI downregulation can provide sustained antithrombotic protection while preserving hemostasis, offering a promising strategy for long-term platelet inhibition.