Characterization of Platelet factor 4-Polyanion complexes and corresponding pathogenic antibodies

• Applicant: Dr. Thi Huong Nguyen, Ph.D.
• Subject Area: Immunology ; Hematology, Oncology
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 269095734

After we have successfully characterized biophysical properties of anti-PF4/polyanion antibodies (aPF4/P Abs), which induce the adverse drug effect heparin-induced thrombocytopenia (HIT), we now aim to build on this information to further understand the pathogenesis of HIT. We have shown in our previous proposal that clinically relevant aPF4/P Abs have a higher binding affinity to PF4/heparin complexes than clinically non-relevant Abs, we now aim to widely investigate the interaction of Abs to PF4/P complexes using different physicochemical environments and mutated/recombinant PF4s. As second approach, we want to establish a detection method for aPF4/P Abs using a cell membrane mimicking system because the clinically relevant Abs bind with much higher avidity to PF4/P complexes on cell membranes than clinically non-relevant antibodies. With both approaches we aim to establish a tool to differentiate clinically relevant (platelet activating) and non-relevant aPF4/P Abs, which can be further developed for clinical application.Monoclonal antibodies are very helpful tool for pathogenicity studies, but the two available monoclonal antibodies mimicking human aPF4/P Abs, namely KKO and 5B9 are not well-characterized in comparison to patient-derived antibodies. With the tools we have developed during the last 3 years, we aim to characterize both monoclonal Abs in comparison to human, patient-derived aPF4/P Abs to facilitate interpretation of future in vitro and in vivo studies (animal studies) with these antibodies.In the third part of our proposal we address the pathogenesis of HIT. We build on the observation that PF4 binds to von Willebrand factor which opens the possibility that aPF4/P Abs interfere with von Willebrand factor cleavage by ADAMTS13 causing thrombotic microangiopathy. Based on our clinical observations, we assume that autoimmune group-3 antibodies interfere with ADAMTS 13 cleavage of von Willebrand factor, as patients with these antibodies show symptoms of thrombotic microangiopathy. Closely linked to this question is the final part of this proposal in which we aim to further investigate the mechanisms by which aPF4/P Abs interfere and activate endothelial cells.Taken together, this proposal will provide deeper understanding on the pathogenesis of HIT, and may provide the basic information to solve one of the most important clinical issues associated with HIT, i.e. improving the specificity of tests applicable in the clinical laboratory for clinically relevant aPF4/P Abs.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Andreas Greinacher