Sanne de Bruin

192 Chapter 7 but not by biotin itself. The processing steps are similar to the steps in obtaining platelet volume reduced products, which have been in use for several years and showed, after correction for platelet loss during preparation, similar cell count increment as standard platelet concentrates. 20-22 Centrifugation of platelets has previously been suggested to activate platelets 23 , which is not completely prevented by the addition of ACD-A. Radio- labeling of platelets also requires centrifugation steps. 24 Since the processing steps, and not the biotin led to platelet activation, similar results can be expected for radiolabeling. We found that exposure to saline or PBS is detrimental to platelet quality; incubating platelets in a PBS-sulfo-NHS-biotin or saline solution led to unacceptable high activa- tion of platelets (data not shown). Therefore the PBS-biotin was diluted in PAS-E. To our knowledge, no data are available on the effect of radiolabeling on platelet quality parameters. However, in previous labeling studies, platelets were incubated in saline, both for radiolabeling and biotin-labeling, 13,24 which might be not optimal with respect to platelet quality. We recommend a comparative study to assess platelet activation in both bioPLTs and radiolabeled platelets. An important limitation of our study is that biotin labeling has not yet been compared to radioactive labeling in humans. However, in dogs, survival of bioPLTs was compa- rable to platelets labeled with both 111 Indium-oxine or 51 Chromium. 7 BioPLTs survived normally after transfusion, and could be used for determining platelet life spans in vivo. The platelet lifespan curves of bioPLTs were in agreement with radiolabeled platelets. Red blood cell labeling studies showed modification of antigens and the risk of anti- body-formation against the biotin. 25,26 These antibodies did not affect red blood cell recovery and survival in the recipient. However, this limits the possibility of repeated transfusions with bioPLTs for clinical research. To minimize the risk of antibody forma- tion we labeled at the lowest possible traceable biotin density. Future research should include the assessment of the formation of antibodies against bioPLTs. BioPLTs will be first administered in an autologous transfusionmodel in healthy volunteers (registered at trialregister.nl, NTR6493). In conclusion, we developed a standardized, simple, reproducible, protocol according to GMP standards for biotin-labeling of platelets, as non-radioactive alternative to trace and isolate transfused platelets in vivo .