Prevention of Thrombocytopenia and Thrombosis in Heparin-Induced Thrombocytopenia (HIT) Using Deglycosylated KKO: A Novel Therapeutic for HIT?
Amrita Sarkar, Ph.D.
Children’s Hospital of Philadelphia
On Tuesday, July 20, 2021, Amrita Sarkar, Ph.D., of the University of Pennsylvania and Children's Hospital of Philadelphia in Philadelphia presented research about heparin-induced thrombocytopenia (HIT) and a potential new therapeutic. HIT is a clinicopathological syndrome that occurs when heparin-dependent, IgG antibodies bind to heparin/platelet factor 4 (PF4) complexes to activate platelets and produce a hypercoagulable state. KKO is a mouse monoclonal antibody that mimics the sentinel biological features of pathogenic antibodies that cause HIT, when it is injected into “HIT mice” lacking mouse PF4 and transgenic for human (h) PF4 and FcγRIIA. Previous research has demonstrated that KKO activates platelets, neutrophils, and monocytes through Fcγ receptor (FcγR)-mediated mechanisms, primarily FcγRIIA, and induces complement-dependent cytotoxicity after binding to complexes of hPF4 and polyanions. Sarkar commented that they aimed to determine whether deglycosylation of the Fc portion of KKO (DGKKO) would either compete with HIT antibodies, eliminate FcγR and complement activation, or be protective in HIT. Via ELISA, dynamic light scattering, and flow cytometry, Sarkar observed that deglycosylation did not affect KKO binding to multimolecular PF4-polyanion complexes but eliminated its interaction with FcgRIIA, abrogated platelet activation, and decreased complement activation. Treating HIT mice with DGKKO did not induce thrombocytopenia or thrombosis. Infusion of DGKKO post KKO reversed thrombocytopenia induced by KKO when infused up to six hours after the KKO. In a microfluidic injury model, she showed that the infusing of DGKKO 15 minutes after infusing healthy whole blood activated with either KKO or HIT IgG from two different patients prevented thrombosis, further supporting that such Fc-modified KKO may be a novel therapeutic agent to prevent or treat HIT. Future studies examining the effect of DGKKO on additional polyspecific HIT patient IgG will continue.