Assessment of the potential of plasma fractionation processes to remove causative agents of transmissible spongiform encephalopathy.

Although there is no evidence that classical CJD (cCJD) can be transmitted by human blood or blood products in clinical practice, uncertainties surrounding new variant CJD (nvCJD) have led to the safety of plasma products derived from UK donors being questioned. To better define whether or not there is a risk of nvCJD being transmitted it is necessary to determine how the causative agent would partition across the separations processes used in the preparation of plasma products. The abnormal prion protein which is associated with transmissible spongiform encephalopathies (TSEs), such as CJD, has a low solubility, a high tendency to form aggregates and adheres to surfaces readily. If the physicochemical properties of the agent of nvCJD are similar to those of abnormal prion protein then nvCJD may be removed by precipitation and adsorption technologies used in plasma fractionation. Available data on the removal of TSE agents by such bioprocess technologies have been used to estimate the potential degree of reduction expected from each step in the plasma fractionation processes used by the SNBTS. The overall process reduction factors estimated are: 10(13) (albumin). 10(9) (immunoglobulins), 10(7) (factor IX, thrombin), 10(5) (fibrinogen), 10(4) (factor VIII) and 10(3) (factor II, IX and X); however, it will be necessary to establish the accuracy of these estimates by practical validation studies.