In vitro comparison of cryopreserved and liquid platelets: potential clinical implications

Platelet (PLT) concentrates can be cryopreserved in dimethyl sulfoxide (DMSO) and stored at -80°C for 2 years. These storage conditions improve availability in both rural and military environments. Previous phenotypic and in vitro studies of cryopreserved PLTs are limited by comparison to fresh liquid-stored PLTs, rather than PLTs stored over their clinically relevant shelf life. Further, nothing is known of the effect of reconstituting cryopreserved PLTs in plasma stored at a variety of clinically relevant temperatures.

Apheresis PLTs were either stored at room temperature for 5 days or cryopreserved at -80°C with 5% DMSO. Cryopreserved PLTs were thawed at 37°C and reconstituted in plasma (stored at different temperatures) and compared to fresh and expired liquid-stored PLTs. In vitro assays were performed to assess glycoprotein expression, PLT activity, microparticle content, and function.

Compared to liquid PLTs over storage, cryopreserved PLTs had reduced expression of the key glycoprotein receptors GPIbα and GPIIb. However, the proportion of PLTs expressing activation markers CD62P and CD63 was similar between cryopreserved and liquid-stored PLTs at expiry. Cryopreserved PLT components contained significantly higher numbers of phosphatidylserine- and tissue factor-positive microparticles than liquid-stored PLTs, and these microparticles reduced the time to clot formation and increased thrombin generation.

There are distinct differences between cryopreserved and liquid-stored PLTs. Cryopreserved PLTs also have an enhanced hemostatic activity. Knowledge of these in vitro differences will be essential to understanding the outcomes of a clinical trial comparing cryopreserved PLTs and liquid PLTs stored for various durations.