(P-CB-9) Cryopreserved Platelets Promote Hemostatic Clot Formation and Extend Platelet Shelf Life

Background/Case Studies: Cryopreserved platelets (CPP) are an investigational 6% DMSO frozen platelet product manufactured from pooled apheresis platelets (from ≤10 donors) that have ~90% of the plasma removed, with an extended shelf life of 5 years. CPP is being investigated for the treatment of acute bleeding as an alternative to conventional platelets in a phase 2/3 clinical trial in the US (NCT04709705). Conventional room-temperature apheresis platelets (RTP) have a short shelf life of 5-7 days. Cold stored platelets (CSP), which are intended for the treatment of active bleeding when conventional platelets are not available or not practical, provides a storage condition to extend the shelf life to 14 days. This work evaluates these platelet products’ secondary hemostatic potential, platelet protein and surface marker characteristics, and activation potential over time.

Study

Design/Methods: CPP, CSP, and RTP were evaluated in vitro by platelet count, pH, thrombin generation assay (TGA), clot formation assay, aggregation, thromboelastography (TEG), and flow cytometry. RTP were evaluated on Day 1 (24 hours post collection), Day 4, and Day 7. Matched CSP units were prepared by sampling RTP units on Day 1 and subsequent storage at 4°C without agitation; CSP units were evaluated on Day 7 and Day 14. CPP were produced from 10-12 pooled RTP units (not matched) and evaluated at 0, 3, and 6 months after storage at -80°C.

Results/Findings: CPP had a greater proportion of activated, phosphatidylserine (PS) positive particles than CSP or RTP (81 vs. 21 vs. 9% respectively, p < 0.0001). Greater activation trended with secondary hemostatic potential. CPP had approximately 3X higher activity than RTP or CSP in the Thrombin Generation Assay and accelerated time to peak thrombin production (Figure A); CSP had intermediate activity to RTP and CPP. Similarly, CPP reduced R-time in donor whole blood by approximately 40% in the TEG assay (p < 0.0001) while RTP and CSP did not. Greater activation appeared inversely correlated with aggregation potential; CPP had reduced aggregation response relative to RTP; CSP had intermediate aggregation.
RTP and CSP characterization changed over time. RTP thrombin generation, lactadherin expression, and microparticle content increased modestly with storage time. RTP aggregation potential decreased with storage time. CSP thrombin generation, lactadherin expression, and microparticle content increased with time. CSP platelet count decreased with time.

Conclusions: CPP presents a more activated phenotype, as demonstrated by PS expression and the higher secondary hemostatic activity, compared to CSP or RTP. CPP has less aggregation response and activation potential than CSP or RTP, as it is already activated. CSP and RTP evolve over time while CPP retains a consistent profile.