Platelet concentrates were prepared in plastic packs of polyvinyl chloride with tri(2-ethylhexyl) trimellitate as plasticizer. They were stored, with gentle shaking, at room temperature for periods up to 7 days before labelling with isotope and reinfusing. In vivo survival studies, platelet counts, pH and electron microscopy indicated that platelet concentrates prepared in the new plastic were superior to those prepared in the standard pack currently in use. Oxygen was found to diffuse through the new pack more rapidly than through the standard pack. A shelflife of up to 1 week at room temperature seems possible for platelet concentrates prepared in the new plastic.

There is continuous need for blood components with long shelf life. To this end the 'circle' triple pack has been modified to provide 35-day red cell and 7-day platelet concentrates, in PVC bags of identical formulation and 0.4 mm thick. The plasticizer is a mixture of DEHP and TOTM (CLX Mark II). The primary pack contains 63 ml of CP 277.5 mM glucose. The third pack contains 100 ml of citric acid 2 mM, trisodium citrate 20 mM, NaH2PO4 20 mM, NaCl 123 mM, glucose 40 mM, and adenine 1.26 mM. Plasma is adenine-free. With these modifications both hard- and soft-spun red cells gave satisfactory biochemical and autologous survival indices up to 35 days of storage, the haematocrit not exceeding 60%. Platelet concentrates were acceptable at 7 days of shelf-life.

With the aim of reducing the damage to platelets while effectively removing class I HLA antigens from their surfaces, we developed a new method using acidified chloroquine diphosphate. Platelets were treated with a 0.2 M solution of chloroquine diphosphate (pH 4.0). More than 90% of the platelets remained viable after treatment. While a marked reduction in reactions of acidified chloroquine-treated platelets with multispecific HLA antisera was noted in comparison with phosphate-buffered-saline-(PBS)-treated platelets, reactions with platelet-specific antibodies were preserved. This was demonstrated by immunofluorescence tests and solid-phase and monoclonal antibody immobilization of platelet antigen assays. Aggregation responses, though reduced in comparison with PBS-treated platelets, were still preserved after acidified chloroquine treatment. Ultrastructural analysis did not show any significant difference from PBS-treated platelets. We conclude that treatment of platelets with acidified chloroquine diphosphate is a simple and effective method for removing class I HLA antigens from their surfaces with minimal damage to their structure and function.

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