In a groundbreaking advancement for the treatment of hereditary thrombophilia, scientists have successfully demonstrated the therapeutic potential of adeno-associated virus (AAV) vectors to restore protein C levels in a murine model of protein C (PC) deficiency. This inherited disorder, driven by mutations in the PROC gene, severely compromises the natural anticoagulant pathway, significantly elevating risks of venous thromboembolism with limited options for effective long-term intervention. The novel study, recently published in Gene Therapy, leverages AAV serotype 8 vectors engineered to deliver functional murine or human PROC genes, setting the stage for transformative gene therapy approaches.
Protein C is a crucial vitamin K-dependent protein synthesized primarily by the liver, playing a pivotal role in controlling blood coagulation by inactivating factors Va and VIIIa. Deficiency in PC tips the hemostatic balance toward hypercoagulability, predisposing individuals to recurrent thrombotic events. Although conventional anticoagulant therapies offer some mitigation, they fail to address the underlying genetic cause and carry risks of bleeding complications. This pressing clinical challenge underscores the need for a targeted, long-lasting corrective strategy.
The investigators engineered AAV8 vectors containing either murine (mPROC) or human protein C (hPROC) coding sequences and administered these via tail vein injections into PROC knockout mice, a well-established preclinical model mimicking human hereditary PC deficiency. AAV8 is renowned for its hepatotropic properties and robust transgene expression, making it an ideal vector for liver-directed gene therapy aimed at plasma proteins such as protein C.
Dose-escalation experiments revealed that the highest administered dose of AAV8-mPROC, quantified as 6.00 × 10^12 vector genomes per kilogram (vg/kg), elicited extraordinary increases in plasma PC activity and antigen levels. Quantitatively, PC activity surged to 200.7% of normal baseline by week 4 post-injection, maintaining a remarkable sustaining level of 171.8% by week 48. Protein C antigen levels mirrored this pattern, reaching 190.1% initially and stabilizing at 165.2% long-term, demonstrating the vector’s potent and durable expression kinetics.
Similarly, administration of the AAV8-hPROC vector at a slightly higher dose of 8.00 × 10^12 vg/kg engendered robust expression of human protein C in the mouse circulation. Initial PC activity peaked at an impressive 295.4%, with antigen concentrations reaching 3.72 μg/ml. These values remained substantially elevated after 48 weeks, with activity maintained at 195.1% and antigen at 1.13 μg/ml. The sustained expression observed underscores the potential clinical viability of AAV-mediated gene therapy as a one-time treatment yielding long-term correction.
Importantly, the functional ramifications of restored protein C levels were validated in two rigorous thrombosis models. In a vein thrombosis assay designed to recapitulate pathological clot formation, both murine and human PROC expressions conferred significant protection. Thrombus weights—a direct measure of clot burden—were substantially reduced from a control average of 12.11 mg to 7.19 mg and 6.81 mg in the AAV8-mPROC and AAV8-hPROC treated groups, respectively. This outcome confirms the biological activity of the transgenic protein C in modulating coagulation cascades in vivo.
The protective effect extended to a murine pulmonary embolism model, where elevated protein C levels corresponded with a marked reduction in embolized lung vessels. Control animals displayed a high embolization rate of 88.53%, while the AAV8-mPROC and AAV8-hPROC treated mice exhibited significant decreases to approximately 60.62% and 62.33%, respectively. This amelioration of thromboembolic complications further substantiates the therapeutic promise of this gene transfer approach.
Notably, the gene therapy approach was well tolerated without adverse effects reported within the 48-week observation period, suggesting a favorable safety profile. The stable and sustained expression of the protein C transgenes indicates that immune responses against the vector or transgene product were minimal or absent, a critical factor for translation into human therapy.
The research harnesses the natural tropism of AAV8 for hepatocytes to ensure targeted expression of protein C in the liver, the physiological site of its synthesis. This strategic targeting optimizes physiological regulation and secretion into the bloodstream, thus restoring homeostasis while minimizing off-target effects. The study’s dual approach—employing both murine and human PROC sequences—also provides important translational insights, demonstrating the potential for cross-species gene delivery and functional restoration.
This extensive investigational work stands as a preclinical milestone. It offers a robust foundation to propel clinical development of AAV-assisted gene therapies for patients suffering from inherited PC deficiency, a condition that currently imposes lifelong therapeutic burdens and a persistent risk of life-threatening thrombotic events.
Looking ahead, further studies integrating long-term safety, immunogenicity, and dose optimization are required to transition from animal models to human trials. The ability to sustainably elevate protein C levels via a minimally invasive, single administration gene therapy could revolutionize management paradigms for hereditary thrombophilia and related coagulopathies.
Moreover, this therapeutic platform may be adaptable to other hepatic-derived anticoagulant proteins, broadening the horizon for genetic correction of various hemostatic disorders. Given the widespread clinical challenge posed by venous thromboembolism, the successful application of AAV-based gene therapy to protein C deficiency represents a significant stride toward personalized, curative medicine.
In conclusion, the use of AAV8 vectors encoding murine or human PROC holds enormous promise to correct the molecular deficit in hereditary PC deficiency. The demonstrated efficacy in elevating functional protein C activity, curbing thrombus formation, and reducing embolization in rigorous targeted models heralds a new era for gene therapy interventions addressing coagulation disorders. These findings invite optimism that previously intractable genetic risks for thrombosis may soon be amenable to durable correction with an innovative and safe vector-based approach.
Subject of Research: Hereditary protein C deficiency and gene therapy correction using AAV8 vectors encoding mouse and human PROC genes.
Article Title: AAV8-mediated mouse/human PROC expression rescues thrombophilia in hereditary protein C-deficient mice.
Article References:
Wu, T., Tao, Y., Lu, H. et al. AAV8-mediated mouse/human PROC expression rescues thrombophilia in hereditary protein C-deficient mice. Gene Ther (2026). https://doi.org/10.1038/s41434-026-00624-2
Image Credits: AI Generated
DOI: 01 June 2026
