Activation-independent, antibody-mediated removal of GPVI from circulating human platelets: development of a novel NOD/SCID mouse model to evaluate the in vivo effectiveness of anti–human platelet agents

• Published in: Blood Vol. 108; no. 3; pp. 908 - 914
• Main Authors: Boylan, Brian, Berndt, Michael C., Kahn, Mark L., Newman, Peter J.
• Format: Journal Article
• Language: English
• Published: Washington, DC Elsevier Inc 01.08.2006; The Americain Society of Hematology; The American Society of Hematology
• Subjects: Animals; Antibodies, Monoclonal - pharmacology; Antibodies, Monoclonal - therapeutic use; Biological and medical sciences; Blood Platelets - drug effects; Blood. Blood coagulation. Reticuloendothelial system; Cell Survival - drug effects; Hemostasis, Thrombosis, and Vascular Biology; Humans; Medical sciences; Mice; Mice, Inbred NOD; Mice, SCID; Models, Animal; Pharmacology. Drug treatments; Platelet Activation - drug effects; Platelet Aggregation - drug effects; Platelet Aggregation Inhibitors - pharmacology; Platelet Membrane Glycoproteins - immunology; Human; In vivo; Animal model; Platelet; Platelet function; NOD/SCID mouse; Glycoprotein VI; Monoclonal antibody; Antiplatelet agent
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2005-07-2937

GPVI is a 62-kDa membrane glycoprotein expressed in noncovalent association with the Fc receptor γ chain on human and murine platelets and serves as the major activating receptor for collagen. GPVI-specific antibodies have the capacity to specifically deplete GPVI from mouse and human platelets in vivo, rendering them unresponsive to collagen and GPVI-specific agonists. Such antibodies do not remove GPVI from noncirculating platelets in vitro, however, making it difficult to evaluate their antithrombotic potential and mechanism of action, particularly in human platelets. We devised a model system in which human platelets are introduced into the retroorbital plexus of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice, allowed to circulate, and evaluated for the effects of GPVI-specific murine monoclonal antibodies (mAbs) on platelet survival and function. GPVI-specific mAbs triggered depletion of GPVI from human, but not murine, platelets. Soluble truncated human GPVI appeared concomitantly in mouse plasma. GPVI-depleted human platelets had markedly diminished responses to GPVI-specific agonists and unexpectedly exhibited somewhat depressed responses to G-protein–coupled agonists. The ability to evaluate in living mice the in vivo function and survival of circulating human platelets may prove valuable for determining mechanisms of antibody-mediated platelet passivation and aid in the development of novel anti-platelet therapeutics.