UK approach to assessing assays and filters designed to reduce the risk of transfusion-transmitted vCJD

• Published in: Transfusion clinique et biologique (Paris) 2013-09, Vol.20 (4), p.405-411
• Main Authors: Thomas, S., Turner, M.L., Williamson, L.M.
• Format: Article
• Language: English
• Subjects: Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Assays; Biological and medical sciences; Blood. Blood and plasma substitutes. Blood products. Blood cells. Blood typing. Plasmapheresis. Apheresis; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Filters; Filtres; Medical sciences; Neurology; Risk; Risques; Royaume-Uni; Tests; Transfusions. Complications. Transfusion reactions. Cell and gene therapy; vCJD; vMCJ
• ISSN: 1246-7820
• DOI: 10.1016/j.tracli.2013.05.002

Three cases of vCJD transmission by blood transfusion have been reported in the UK, and a fourth case discovered at post-mortem. Modelling has been conducted to predict the number of cases that may occur in the future through transfusion, based on estimates of prevalence, infectivity and susceptibility, and a number of steps have been taken to reduce the risk of transmission. These include deferral of previously transfused donors, leucocyte depletion of all components, importation of plasma for certain patient groups and for fractionation, and the collection of the majority of platelets from single donors (by apheresis). However, even with these interventions, some future cases are still predicted. The UK-wide Advisory Committee on the Safety of Blood, Tissues and Organs (SaBTO) considers the evidence for clinical and cost-effectiveness of any proposed intervention, such as prion assays and filters, and makes recommendations to the governments of the UK. The development of prion assays is challenging as prions do not generate an immune response, do not have nucleic acid and are present in blood in very low concentrations against a high background of normal prion protein. It is critically important that prion assays show high levels of sensitivity and — especially —specificity for a healthy blood donor population. Assessment is impacted by the very short supply of positive human samples, necessitating the use of animal models. Filters that are capable of removing prions from blood components have been developed and CE marked, but it is again necessary to use animal models to study their efficacy. Guidelines have been produced for the assessment of the quality of red cells filtered through these devices, and a clinical safety study has recently been completed. In conclusion, the evaluation of screening assays and prion filters is challenging, time-consuming and costly, but these evaluations are critical to policy making. Trois cas de transmission transfusionnelle de la vMCJ ont été rapportés au Royaume-Uni et un quatrième cas a été identifié en post-mortem. La prédiction du nombre de futurs cas de futurs transmissions secondaires par transfusion sanguine été estimée par une modélisation basée sur plusieurs paramètres : l’estimation de la prévalence, de l’infectivité, de la susceptibilité à l’infection et des mesures préventives mises en place pour réduire le risque de transmission. Les mesures de prévention comprennent l’exclusion des sujets transfuses, la l