Sanne de Bruin

179 Biotinylation of platelets for transfusion purposes: a novel method to label platelets in a closed system Introduction Labeling of platelets is required to distinguish transfused platelets from the recipient’s own circulating platelets. This enables the measurement of recovery and survival of transfused platelets in vivo . Radiolabeling of platelets with the radioactive isotopes 111 Indium-oxin and/or 51 Chro- mium is currently the golden standard to test for survival and recovery of platelets. 1 This method is used to evaluate the effects of donor-, recipient- and platelet storage factors on platelet survival after transfusion in the recipient. 2 Also, radiolabeling is re- quired by the FDA to analyze the effect of altered platelet storage protocols, such as new additive solutions and pathogen-reduction technologies. 3. However, radiolabeling exposes the recipient to potential harmful ionization. Therefore, this method cannot be used in vulnerable patients, in particular pediatric patients and neonates. Moreover, the use of radiolabeled platelets is strictly regulated, which limits it’s applicability for research purposes. In Europe, radiolabeling is restricted to studies in healthy volun- teers only. Therefore, a non-radioactive alternative to label platelets is desired. Biotin, a water-soluble vitamin (B8) can be used as a non-radioactive label for various cells. 4-9 The N-hydroxysuccinimide ester of the biotin reagent binds in a non-specific manner to cellsurface proteins of the platelet (Figure 1A, biotinylation of platelets). Unlike radiola- beling, biotin-labeling has the major advantage that it is possible to selectively isolate biotin-labeled platelets from the recipients’ circulation. Also, a biotin label can even be used to trace multiple platelet populations concurrently by using different densities of the biotin label per platelet. Recently, our group reported a protocol for the biotinylation of red cell concentrates, according to Good Practice Guidelines (GPG). 10 This product is currently available for clinical use and the first trials have started recruiting patients. (Registered at trialreg- ister.nl: NTR 6596, NTR6492). However, labeling of platelets is difficult compared to erythrocytes, due to their propensity to become activated. Biotin-labeling of platelets has been used in various animal models 7,11,12 and twenty years ago, biotin-labeled platelets (bioPLTs) were safely infused in humans for the first time. 13 In this pilot study, platelet recovery wasmeasured after infusion of biotinylated platelets in ten healthy male subjects. However, this study was hampered by activation of the platelets during biotinylation. We developed a method to minimize platelet activation during biotinylation. Because platelets concentrates are particularly prone to bacterial 7