title: A direct relationship between the partitioning of the pathogenic prion protein and transmissible spongiform encephalopathy infectivity during the purification of plasma proteins.
abstract: BACKGROUND
  Experimental evidence from rodent models indicates that blood can contain transmissible spongiform encephalopathy (TSE) infectivity, which suggests a potential risk for TSE transmission via proteins isolated from human plasma. Because methods that can reduce TSE infectivity typically are detrimental to protein function, infectivity must be removed to ensure the safety of these therapeutic proteins. Animal bioassays are conventionally used to detect infectivity, but the pathogenic form of the prion protein (PrP(Sc)) can serve as a marker for TSE infectivity.
  
  
  METHODS
  Seven plasma protein-purification steps were performed after the plasma intermediates were spiked with TSE-infected material. Resulting fractions were analyzed for PrP(Sc) by using a Western blot assay and for TSE infectivity by using an animal bioassay. Western blots were quantitated by an endpoint dilution analysis, and infectivity titers were calculated by the Spearman-Kärber method.
  
  
  RESULTS
  PrP(Sc) partitioning paralleled TSE infectivity partitioning, regardless of the nature of the protein-purification step. The detection ranges for PrP(Sc) and infectivity were 0 to 5.3 log and 1.1 to 8.9 log median infectious dose per unit, respectively. Clearance of PrP(Sc) and infectivity ranged from 1.0 to 6.0 log.
  
  
  CONCLUSIONS
  Purification steps for isolating therapeutic proteins from human plasma showed the removal of both PrP(Sc) and TSE infectivity. PrP(Sc) partitioning coincided with infectivity partitioning, which showed a close relationship between PrP(Sc) and TSE infectivity. By exploiting this association, the in vitro Western blot assay for PrP(Sc) was valuable for estimating the partitioning of TSE infectivity during plasma protein purification.
authors.affiliation: Department of Pathogen Safety Research/Biological Products, Bayer Corporation, Research Triangle Park, North Carolina 27709, USA. doug.lee.b@bayer.com
authors.forename: D C
authors.initials: DC
authors.lastname: Lee
authors.forename: C J
authors.initials: CJ
authors.lastname: Stenland
authors.forename: J L
authors.initials: JL
authors.lastname: Miller
authors.forename: K
authors.initials: K
authors.lastname: Cai
authors.forename: E K
authors.initials: EK
authors.lastname: Ford
authors.forename: K J
authors.initials: KJ
authors.lastname: Gilligan
authors.forename: R C
authors.initials: RC
authors.lastname: Hartwell
authors.forename: J C
authors.initials: JC
authors.lastname: Terry
authors.forename: R
authors.initials: R
authors.lastname: Rubenstein
authors.forename: M
authors.initials: M
authors.lastname: Fournel
authors.forename: S R
authors.initials: SR
authors.lastname: Petteway
mesh_terms: D000818:Animals; D015415:Biomarkers; D001798:Blood Proteins / Q000009:adverse effects* / Q000302:isolation & purification; D006224:Cricetinae; D006801:Humans; D017096:Prion Diseases / Q000635:transmission*; D011328:Prions / Q000032:analysis*
chemical_list: D015415:Biomarkers; D001798:Blood Proteins; D011328:Prions