Infectious prion protein in the filtrate even after 15nm filtration

Characterization of the 263K-derived microsomal fraction: a source of prions for nanofiltration validation studies

BACKGROUND

The manufacturing processes of plasma products include steps that can remove prions. The efficacy of these steps is measured in validation studies using animal brain-derived prion materials called spikes. Because the nature of the prion agent in blood is not known, the relevance of these spikes, particularly with steps that are based on retention mechanisms such as nanofiltration, is important to investigate.

STUDY DESIGN AND METHODS

The aggregation and sizes of PrPres assemblies of microsomal fractions (MFs) extracted from 263K-infected hamster brains were analyzed using velocity gradients. The separated gradient fractions were either inoculated to Tg7 mice expressing hamster-PrPc to measure infectivity or used in Protein Misfolding Cyclic Amplification for measuring seeding activity. The collected data allowed for reanalyzing results from previous nanofiltration validation studies.

RESULTS

A significant portion of MFs was found to be composed of small PrPres assemblies, estimated to have a size ≤24 mers (~22-528 kDa), and to contain a minimum of 20% of total prion infectivity. With this data we could calculate reductions of 4.10 log (15 N), 2.53 log (35 N), and 1.77 log (35 N) from validation studies specifically for these small PrPres objects.

CONCLUSION

Our gradient data provided evidence that nanofilters can remove the majority of the smallest PrPres entities within microsomes spikes, estimated to be in a size below 24 mers, giving insight about the fact that, in our conditions, size exclusion may not be the only mechanism for retention nanofiltration.

Integration of Planova filters in manufacturing processes of biologicals improve the virus safety effectively: A review of publicly available data

The capacity to remove viruses by Planova filters produced by Asahi Kasei, primarily by small virus-retentive filters, were compiled from data in peer-reviewed publications and, partly, publicly available data from presentations at conferences (Planova workshops). Data from more than 100 publications and presentations at conferences covering Planova filters were assessed. The data were grouped according to the different virus filters regarding mean pore sizes and viruses of different sizes for plasma and cell culture derived products. Planova 15N and 20N filters removed parvoviruses below the limit of detection of viruses in the filtrate in approx. 50% of all studies and mean LRFs (log reduction factors) for viruses detected in the filtrate were above 4, demonstrating effective parvovirus reduction. Parvovirus removal capacity increased for Planova BioEX filters as well as for 2 Planova 20N in series. Large viruses as retroviruses (e.g., HIV and MuLV), herpesviruses, flaviviruses and togaviruses were removed effectively by Planova 15N, 20N and BioEX filters and also by Planova 35N filters. Flow interruption, transmembrane pressure, volume and protein concentration per filter area had had no substantial impact on virus removal capacity at manufacturing specification. In conclusion, the incorporation of Planova filters in manufacturing processes of biologicals remove, depending on the filter pore size, small and large viruses from the feed stream reliably. This virus reduction step with an orthogonal mechanism integrated in the manufacturing processes of biologicals, based primarily on size exclusion of viruses, improves the virus safety of these biopharmaceutical products considerably.

Polyethyleneimine-modified resins effectively remove porcine circovirus and cellular prion protein

Polyethyleneimine (PEI) possesses various molecular weights (MWs), structures, and virus capture capacities. However, whether PEI can capture porcine circovirus (PCV) and animal cell-derived prion protein (PrP^C) that may contaminate source materials is unclear. Therefore, we conducted a feasibility study to assess the effectiveness of PEI in removing PCV and PrP^C as a model of pathogenic prions. The removal performance of PCV was evaluated by quantitative PCR using PEIs with various MWs, structures, and ion exchange capacities in Tris (pH 7.5) and acetate (pH 5.5) buffers under neutral (pH 7.5) to acidic (pH 5.5) conditions. Removal performances of PrP^C were also evaluated by western blotting using PEIs with various MWs and structures. Tris buffer did not affect the ability of PEI-modified resins to remove PCV, whereas acetate buffer affected removal performances, except those of PEI-10K-Br and PEI-70K-Br, which showed high ion-exchange capacities. PrP^C was captured by PEIs with high MWs, especially PEI-70K-Br, which was the most effective. The results of this feasibility study suggested that PEI-modified resin could remove PCV and PrP^C. PEI-70K-Br with an ion-exchange capacity of at least 0.3 meq/mL appears suitable as a PEI molecule for pathogen capture or removal of PCV or PrP^C from biological materials.

Unexpected prion phenotypes in experimentally transfused animals: predictive models for humans?

The recently reevaluated high prevalence of healthy carriers (1/2,000 in UK) of variant Creutzfeldt-Jakob Disease (v-CJD), whose blood might be infectious, suggests that the evolution of this prion disease might not be under full control as expected. After experimental transfusion of macaques and conventional mice with blood derived from v-CJD exposed (human and animal) individuals, we confirmed in these both models the transmissibility of v-CJD, but we also observed unexpected neurological syndromes transmissible by transfusion: despite their prion etiology confirmed through transmission experiments, these original cases would escape classical prion diagnosis, notably in the absence of detectable abnormal PrP with current techniques. It is noteworthy that macaques developed an original, yet undescribed myelopathic syndrome associating demyelination and pseudo-necrotic lesions of spinal cord, brainstem and optical tract without affecting encephalon, which is rather evocative of spinal cord disease than prion disease in human medicine. These observations strongly suggest that the spectrum of human prion diseases may extend the current field restricted to the phenotypes associated to protease-resistant PrP, and may notably include spinal cord diseases.

Are prions transported by plasma exosomes?

Blood has been shown to contain disease-associated misfolded prion protein (PrP(TSE)) in animals naturally and experimentally infected with various transmissible spongiform encephalopathy (TSE) agents, and in humans infected with variant Creutzfeldt-Jakob disease (vCJD). Recently, we have demonstrated PrP(TSE) in extracellular vesicle preparations (EVs) containing exosomes from plasma of mice infected with mouse-adapted vCJD by Protein Misfolding Cyclic Amplification (PMCA). Here we report the detection of PrP(TSE) by PMCA in EVs from plasma of mice infected with Fukuoka-1 (FU), an isolate from a Gerstmann-Sträussler-Scheinker disease patient. We used Tga20 transgenic mice that over-express mouse cellular prion protein, to assay by intracranial injections the level of infectivity in a FU-infected brain homogenate from wild-type mice (FU-BH), and in blood cellular components (BCC), consisting of red blood cells, white blood cells and platelets, plasma EVs, and plasma EVs subjected to multiple rounds of PMCA. Only FU-BH and plasma EVs from FU-infected mice subjected to PMCA that contained PrP(TSE) transmitted disease to Tga20 mice. Plasma EVs not subjected to PMCA and BCC from FU-infected mice failed to transmit disease. These findings confirm the high sensitivity of PMCA for PrP(TSE) detection in plasma EVs and the efficiency of this in vitro method to produce highly infectious prions. The results of our study encourage further research to define the role of EVs and, more specifically exosomes, as blood-borne carriers of PrP(TSE).

A prion reduction filter does not completely remove endogenous prion infectivity from sheep blood

BACKGROUND

Variant Creutzfeldt-Jakob disease (vCJD) is a transmissible spongiform encephalopathy affecting humans, acquired initially through infection with bovine spongiform encephalopathy (BSE). A small number of vCJD cases have been acquired through the transfusion of blood from asymptomatic donors who subsequently developed vCJD. Filter devices that selectively bind the infectious agent associated with prion disease have been developed for removal of infection from blood. This study independently assessed one such filter, the P-CAPT filter, for efficacy in removing infectivity associated with the BSE agent in sheep blood. The sheep BSE model has previously been used to evaluate the distribution of infectivity in clinically relevant blood components. This is the first study to assess the ability of the P-CAPT filter to remove endogenous infectivity associated with blood components prepared from a large animal model.

STUDY DESIGN AND METHODS

Paired units of leukoreduced red blood cells (LR-RBCs) were prepared from donors at the clinical stage of infection and confirmed as having BSE. One cohort of recipients was transfused with LR-RBCs alone, whereas a parallel cohort received LR and P-CAPT-filtered RBCs (LR-RBCs-P-CAPT).

RESULTS

Of 14 recipients, two have been confirmed as having BSE. These sheep had received LR-RBCs and LR-RBCs-P-CAPT from the same donor.

CONCLUSIONS

The results indicate that, after leukoreduction and P-CAPT filtration, there can still be sufficient residual infectivity in sheep RBCs to transmit infection when transfused into a susceptible recipient.

Removal of TSE agent from plasma products manufactured in the United Kingdom

BACKGROUND AND OBJECTIVES

The outbreak of vCJD in the UK leads to concern regarding the potential for human-to-human transmission of this agent. Plasma-derived products such as albumin, immunoglobulin and coagulation factors were manufactured by BPL from UK plasma up until 1999 when a switch to US plasma was made. In the current study, the capacity of various manufacturing processes that were in use both prior to and after this time to remove the TSE agent was tested.

MATERIALS AND METHODS

Small-scale models of the various product manufacturing steps were developed. Intermediates were spiked with scrapie brain extract and then further processed. Samples were assayed for the abnormal form of prion protein (PrP(SC) ) by Western blotting, and the reduction in the amount of scrapie agent determined.

RESULTS

Many of the manufacturing process steps produced significant reduction in the scrapie agent. Particularly effective were steps such as ethanol fractionation, depth filtration, ion-exchange and copper chelate affinity chromatography. Virus retentive filters, of nominal pore size 15 or 20 nm, removed >3 log. The total cumulative reduction capacity for individual products was estimated to range from 7 to 14 log. In the case of factor VIII (8Y), the total removal was limited to 3 log.

CONCLUSION

All the processes showed a substantial capacity to remove the TSE agent. However, this was more limited for the intermediate purity factor VIII 8Y which included fewer manufacturing steps.

Virus safety of plasma products using 20 nm instead of 15 nm filtration as virus removing step

During the manufacture of human plasma derivatives, a series of complementary measures are undertaken to prevent transmission of blood-borne viruses. Virus filtration using 15 nm (Planova15N) filters has successfully been implemented in manufacturing processes for various plasma derivatives primarily because virus filtration is a technique, mild for proteins, that can effectively remove even small non-lipid-enveloped viruses, such as HAV and parvovirus B19. However, the use of 15 nm filters has limitations with regard to protein capacity of the filters and the process flow, resulting in an expensive manufacturing step. Therefore, studies were performed to test whether the use of 20 nm (Planova20N) filters, having different characteristics compared to 15 nm filters, can be an alternative for the use of 15 nm filters. It is shown that 20 nm filtration can be an alternative for 15 nm filtration. However, the virus removal capacity of the 20 nm filters depends on the plasma product that is filtered. Therefore, an optimisation study must be performed with regard to process parameters such as pressure, pH and protein concentration for each plasma product. In this study, using optimised conditions, the virus removal capacity of 20 nm filters appears to be comparable or even better when compared to that of 15 nm filters.

Detection of prion protein particles in blood plasma of scrapie infected sheep

Prion diseases are transmissible neurodegenerative diseases affecting humans and animals. The agent of the disease is the prion consisting mainly, if not solely, of a misfolded and aggregated isoform of the host-encoded prion protein (PrP). Transmission of prions can occur naturally but also accidentally, e.g. by blood transfusion, which has raised serious concerns about blood product safety and emphasized the need for a reliable diagnostic test. In this report we present a method based on surface-FIDA (fluorescence intensity distribution analysis), that exploits the high state of molecular aggregation of PrP as an unequivocal diagnostic marker of the disease, and show that it can detect infection in blood. To prepare PrP aggregates from blood plasma we introduced a detergent and lipase treatment to separate PrP from blood lipophilic components. Prion protein aggregates were subsequently precipitated by phosphotungstic acid, immobilized on a glass surface by covalently bound capture antibodies, and finally labeled with fluorescent antibody probes. Individual PrP aggregates were visualized by laser scanning microscopy where signal intensity was proportional to aggregate size. After signal processing to remove the background from low fluorescence particles, fluorescence intensities of all remaining PrP particles were summed. We detected PrP aggregates in plasma samples from six out of ten scrapie-positive sheep with no false positives from uninfected sheep. Applying simultaneous intensity and size discrimination, ten out of ten samples from scrapie sheep could be differentiated from uninfected sheep. The implications for ante mortem diagnosis of prion diseases are discussed.

Comparison of nanofiltration efficacy in reducing infectivity of centrifuged versus ultracentrifuged 263K scrapie-infected brain homogenates in "spiked" albumin solutions

BACKGROUND

The safety of plasma-derived products is of concern for possible transmission of variant Creutzfeldt-Jakob disease. The absence of validated screening tests requires the use of procedures to remove or inactivate prions during the manufacture of plasma-derived products to minimize the risk of transmission. These procedures need proper validation studies based on spiking human plasma or intermediate fractions of plasma fractionation with prions in a form as close as possible to that present in blood.

STUDY DESIGN AND METHODS

Human albumin was spiked with low-speed or high-speed supernatants of 263K scrapie-infected hamster brain homogenates. Spiked albumin was then passed through a cascade of filters from 100 nm down to 20 to 15 nm. Residual infectivity was measured by bioassay.

RESULTS

The overall removal of infectivity spiked into albumin through serial nanofiltration steps was 4 to 5 logs using low-speed supernatant and 2 to 3 logs with high-speed supernatant.

CONCLUSION

These findings confirm the utility of nanofiltration in removing infectivity from plasma (or other products) spiked with scrapie brain homogenate supernatants. However, efficiency is diminished using supernatants that have been ultracentrifuged to reduce aggregated forms of the infectious agent. Thus, filtration removal data based on experiments using "standard" low-speed centrifugation supernatants might overestimate the amount of prion removal in plasma or urine-derived therapeutic products.