Studies on the removal of abnormal prion protein by processes used in the manufacture of human plasma products.

BACKGROUND AND OBJECTIVES: To identify if any process steps used in plasma fractionation may have a capability of removing agents of human transmissible spongiform encephalopathy (TSE).

MATERIALS AND METHODS: Sixteen fractionation steps were investigated separately by adding a preparation of hamster adapted scrapie 263K to the starting material at each process step and determining the distribution into resultant fractions of protease-K-resistant (abnormal) prion protein by Western blot analysis.

RESULTS: A number of process operations were found to remove abnormal prion protein to the limit of detection of the assay. These were cold ethanol precipitation of fraction IV (log reduction, LR, >/=3.0) and a depth filtration (LR >/=4.9) in the albumin process; cold ethanol fraction I+III precipitation (LR >/=3.7) and a depth filtration (LR >/=2.8) in the immunoglobulin processes and adsorption with DEAE-Toyopearl 650M ion exchanger (LR >/=3.5) in the fibrinogen process. In addition, a substantial degree of removal of abnormal prion protein was observed across DEAE-Toyopearl 650M ion exchange (LR = 3.1) used in the preparation of factor-VIII concentrate; DEAE-cellulose ion exchange (LR = 3.0) and DEAE-sepharose ion exchange (LR = 3.0) used in the preparation of factor-IX concentrates and S-sepharose ion exchange (LR = 2.9) used in the preparation of thrombin.

CONCLUSIONS: Plasma fractionation processes used in the manufacture of albumin, immunoglobulins, factor-VIII concentrate, factor-IX concentrates, fibrinogen and thrombin all contain steps which may be capable of removing causative agents of human TSEs.