PB0529 - Investigations of the impact of different bleeding disorders using a humanized in vivo mouse model

Background: Immune thrombocytopenia (ITP) is a bleeding disorder due to multiple alterations. The immune system leads to increased platelet (PLT) clearance and bleeding in patients. Currently, no in vivo model system exists to predict the impact of autoantibodies on human platelets function in ITP.

Aims: To establish a humanized mouse model to investigate antibody–mediated destruction of human PLTs in vivo and to assess the impact on bleeding.

Methods: A monoclonal antibody against CD42b was injected in a NOD/SCID mouse model in order to deplete the murine platelets. Next, human PLTs were administrated into the tail vain and their survival was determined 1 and 5 hours post injection by flow cytometry (FC). The presence of human PLT was investigated by FC and calculated as % of circulating human PLTs. Finally, the functionality of human PLT in vivo was assessed by measuring the bleeding time.

Results: The CD42b antibody induced a drastic reduction of murine PLTs in the mouse bloodstream ( < 5 %) without affecting the survival of the animals. Subsequently, human PLTs were injected into the mouse bloodstream via the tail vein, and 30 minutes post injection approximately 90% of the circulating PLTs were human. Next, IgGs from ITP patients were injected into the mouse circulation in order to investigate PLT clearance and function. Interestingly. A rapid decrease in PLT survival was observed compared to the control IgG (% survival of human PLT after 5 h, mean±SEM: ITP vs. control IgG: 54.75 ± 6.7 vs. 27.51 ± 5.14, n=5 p=0.0133). Bleeding time in the humanised mouse model was established to assess platelet function. A significant reduction in bleeding time was observed following injection of human PLTs (360.8±20.5 vs 126±10.73 seconds, n=4, p= 0.0001).

Conclusion(s): Our results suggest that the NGS mouse model may be a promising tool to study human platelet function in different bleeding disorders.