Towards a Clinical Application of Freeze-Dried Human Platelets

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Abstract
Storage of platelets remains a major problem for blood banks. In this study we describe the development of a lyophilization protocol for platelet concentrates obtained from a blood bank. In previous studies with small samples we reported some considerable success. We now confirm those earlier results, extend them to platelet concentrates, and scale up the process to a full unit of platelets. Platelets were loaded with trehalose and freeze-dried in a formulation of trehalose and albumin. Optimal survival rates were found, using a 1:1 weight ratio of trehalose and albumin in the lyophilization buffer. Survival rates of 90% were found when the platelets were freeze-dried in 1-mL aliquots, in vials. Freeze-drying 1 platelet concentrate unit in a specially designed lyophilization bag yielded 85% recovery after rehydration. Gradual rehydration from the vapor phase resulted in a mean platelet volume distribution similar to that of fresh control platelets, whereas directly rehydrated platelets were considerably larger in size and balloon shaped. The rehydrated platelets exhibited a normal response to thrombin and ristocetin. Scanning electron microscopy studies showed the absence of pseudopodia on the membrane surface of the rehydrated platelets; however, microvesicles were visible on the membrane surface. In addition, rehydrated cells were rounder than control cells. The platelets are stable for at least 22 months in the freeze-dried state at room temperature.