R01HL151730

Complement and Thrombosis in HIT - Abstract

Heparin-induced thrombocytopenia (HIT) is a severe thrombotic disorder initiated by ultralarge immune complexes (ULICs) containing IgG antibodies to a multivalent antigen composed of platelet factor 4 (PF4) and heparin (H). Patients with HIT are at risk for death, amputation, recurrent thromboembolism, and bleeding while receiving maximally tolerated doses of factor Xa or direct thrombin inhibitors (DTIs). Thus, there is an unmet need for deeper insight into the pathobiology of thrombosis in HIT that will lead to targeted novel non-anticoagulant interventions to supplement contemporary therapy.

Our published and pilot data demonstrate that activation of the complement pathway fulfills this gap. Specifically, we show that HIT ULICs:

1) Interact and bind complement components and von Willebrand factor (VWF) multimers,
2) Generate soluble complement components via the classical pathway,
3) Deposit C3 on neutrophils, monocytes, and endothelial cells (ECs),
4) Trigger complement-dependent neutrophil degranulation, monocyte tissue factor (TF), and procoagulant activity upstream of C5,
5) Activate complement even in the presence of DTIs, and
6) Promote complement deposition in a murine thrombosis model of HIT.

Based on these findings, we hypothesize that complement activation by HIT ULICs contributes to the prothrombotic state in HIT through direct EC injury mediated by surface-expressed complement receptors (CRs) and by amplifying signaling by promoting cooperativity with FcγRIIA on neutrophils and monocytes.

We will address the following specific aims:

1) Examine HIT ULIC-complement interactions and effects of complement activation on ECs. We will test the hypothesis that incorporation of complement enlarges and stabilizes assembled ULICs, impairs complement regulatory function, and promotes EC injury leading to the release of VWF multimers that further amplify ULIC formation and complement activation.

2) Examine cooperative interactions of HIT ULICs, complement, and monocyte/neutrophil FcγR. We will test the hypothesis that complement-containing ULICs amplify FcγRIIA signaling by promoting cooperativity with cellular CRs on neutrophils and monocytes. We will examine the effects of ULIC composition on cell activation, identify CRs involved in binding HIT ULICs, study soluble and cellular complement regulatory mechanisms, and characterize complement activation in seropositive patients with and without HIT.

3) Examine complement inhibition as a therapeutic strategy for thrombosis in HIT. We will use microfluidic assays and murine thrombosis models to test the hypothesis that activation of the classical complement pathway by HIT ULICs promotes macrovascular thrombosis through the release of VWF from activated ECs and amplification of cellular procoagulant activity. We will examine the efficacy of proximal and terminal complement pathway inhibition as a strategy to lower the intensity of antithrombotic therapy needed to treat HIT.

Together, these studies will provide new insights into IC-mediated thrombosis broadly and provide a detailed mechanistic pathway for complement inhibition as a rationale, potent, and non-anticoagulant-dependent strategy for the treatment of HIT.

Duke University

THE DIVISION OF BLOOD DISEASES AND RESOURCES SUPPORTS RESEARCH AND RESEARCH TRAINING ON THE PATHOPHYSIOLOGY, DIAGNOSIS, TREATMENT, AND PREVENTION OF NON-MALIGNANT BLOOD DISEASES, INCLUDING ANEMIAS, SICKLE CELL DISEASE, THALASSEMIA, LEUKOCYTE BIOLOGY, PRE-MALIGNANT PROCESSES SUCH AS MYELODYSPLASIA AND MYELOPROLIFERATIVE DISORDERS, HEMOPHILIA AND OTHER ABNORMALITIES OF HEMOSTASIS AND THROMBOSIS, AND IMMUNE DYSFUNCTION. FUNDING ENCOMPASSES A BROAD SPECTRUM OF HEMATOLOGIC INQUIRY, RANGING FROM STEM CELL BIOLOGY TO MEDICAL MANAGEMENT OF BLOOD DISEASES AND TO ASSURING THE ADEQUACY AND SAFETY OF THE NATION'S BLOOD SUPPLY. PROGRAMS ALSO SUPPORT THE DEVELOPMENT OF NOVEL CELL-BASED THERAPIES TO BRING THE EXPERTISE OF TRANSFUSION MEDICINE AND STEM CELL TECHNOLOGY TO THE REPAIR AND REGENERATION OF HUMAN TISSUES AND ORGANS. SMALL BUSINESS INNOVATION RESEARCH (SBIR) PROGRAM: TO STIMULATE TECHNOLOGICAL INNOVATION, USE SMALL BUSINESS TO MEET FEDERAL RESEARCH AND DEVELOPMENT NEEDS, FOSTER AND ENCOURAGE PARTICIPATION IN INNOVATION AND ENTREPRENEURSHIP BY SOCIALLY AND ECONOMICALLY DISADVANTAGED PERSONS, AND INCREASE PRIVATE-SECTOR COMMERCIALIZATION OF INNOVATIONS DERIVED FROM FEDERAL RESEARCH AND DEVELOPMENT FUNDING. SMALL BUSINESS TECHNOLOGY TRANSFER (STTR) PROGRAM: TO STIMULATE TECHNOLOGICAL INNOVATION, FOSTER TECHNOLOGY TRANSFER THROUGH COOPERATIVE R&D BETWEEN SMALL BUSINESSES AND RESEARCH INSTITUTIONS, AND INCREASE PRIVATE SECTOR COMMERCIALIZATION OF INNOVATIONS DERIVED FROM FEDERAL R&D.

93.837 - Cardiovascular Diseases Research

National Heart Lung and Blood Institute (NHLBI) [HHS - NIH]

Durham, North Carolina 27710 United States

Single Zip Code

Research Project Grant (Parent R01 Clinical Trial Not Allowed) (PA-19-056)

Amendment Since initial award the total obligations have increased 408% from $633,189 to $3,216,929.