Background and objectives: Leucoreduced platelet concentrates (LR-PCs) can be stored at 20-24 degrees C for 5-7 days. When LR-PCs are cryopreserved they can be stored for several years. For cryopreservation to become applicable in blood-bank practice, an off-the-shelf cryoprotectant is needed that can be added to the LR-PC in a sterile manner. For this, we varied the composition of the cryopreservation medium and studied various parameters of cryopreserved LR-PCs for up to 24 h after thawing at room temperature.
Materials and methods: LR-PCs in plasma or Composol were concentrated and divided into 2 units. To each unit, an equal part of 10% dimethylsulfoxide (DMSO) in plasma, Composol with or without 5% albumin, or GPO (pasteurized plasma-protein solution) was added. Freezing occurred at 1 degrees C/min and LR-PCs were placed in the vapour phase of nitrogen. LR-PCs were thawed at 37 degrees C and stored at room temperature. LR-PCs were tested for morphology, platelet recovery, swirling effect, and activation antigens at various time-points thereafter.
Results: LR-PCs in 100%, 65% and 50% plasma supplemented with Composol showed good morphology scores (>250), limited CD62P expression (<35%), low CD63 expression (<20%) and a swirling effect of about 2, at 24 h after thawing. At the same time-point, platelet recovery was >80% under all conditions and CD42b expression varied between 70 and 85%. Results of LR-PCs in 15% plasma and Composol, with or without plasma substitutes, were not acceptable at 24 h after thawing, i.e. the morphology score was <200 and the CD62P expression was >40%.
Conclusions: A minimum of 50% plasma in the cryopreserved LR-PC is necessary to maintain an acceptable in vitro quality of platelets up to 24 h after thawing. Composol is a good candidate for using to prepare an off-the-shelf cryoprotectant.