OC 61.4 - Supercharged platelets as a novel therapy for reducing blood loss post-cardiac surgery

Background: Cardiovascular surgery is one of the surgical disciplines that requires the most blood components for transfusion. In addition to surgical techniques, the transfusion of blood components and pharmacological interventions, measures to restore haemostasis in actively bleeding patients include the administration of concentrated coagulation factors including recombinant FVIIa (rFVIIa). However, this has huge cost implications given the very short half-life of clotting factors and an inherent risk of adverse thrombotic events, resulting in increases in hospital, morbidity and mortality.

Aims: We sought to determine whether loading donor MK’s and subsequently MK’s generated in vitro from iPSC’s with FVIIa, would enhance the haemostatic ability of their platelet progeny, with a view to translating this to the clinic.

Methods: Immunofluorescence and flow cytometry were used to determine whether donor platelets endocytose extracellular rFVIIa. Using the bleeding time NRG mouse model, made profoundly thrombocytopenic through antibody depletion, we intravenously administered donor-derived platelets loaded with rFVIIa.

Using viral transduction we over-expressed 3 specific transcription factors (FLI1, TAL1 and GATA1) (FoP) to generate MK’s from iPSC’s and virally transduced these MK’s with FVIIa.

Results: We have shown that donor platelets endocytose rFVIIa and target it to their alpha granules. We have also shown a reduction in early haemorrhage in the NRG mouse administered donor platelets loaded with FVIIa, compared with those administered donor platelets or PBS (Figure 1). We have also shown that we can generate MK’s from iPSC’s and that they express FVIIa (Figure 2).

Conclusion(s): We have demonstrated that donor platelets ‘supercharged’ with rFVIIa have an enhanced haemostatic ability and that we can ‘over-express’ FVIIa in our FOP platelets. We are currently determining whether FoP platelets, which over-express FVIIa, exhibit a greater haemostatic ability than FoP platelets, which will enable the clinic to have a more effective, safe, continuous and universal supply of platelets.