Effectiveness of leucoreduction for removal of infectivity of transmissible spongiform encephalopathies from blood

Risk of variant Creutzfeldt-Jakob disease in a simulated cohort of Canadian blood donors

BACKGROUND AND OBJECTIVES

No transfusion-associated cases of variant Creutzfeldt-Jakob disease (vCJD) have occurred in more than 20 years. Yet, many countries have maintained blood donor deferral criteria for vCJD. We developed a risk simulation model to reassess the need for vCJD-related deferral criteria in Canada.

MATERIALS AND METHODS

The model provides results separately for Héma-Québec (HQ) and Canadian Blood Services (CBS). The model used a Monte Carlo simulation approach to estimate the risk of having a vCJD-contaminated blood donation ('risk of vCJD') in a simulated cohort of 10 million donors followed for up to 85 years. The model assumed current deferral criteria for vCJD were lifted, which would allow new 'at-risk' donors to give blood. The model accounted for disease prevalence, donors' travel/immigration history, PRNP genotype at codon 129, demographics and the type of labile blood product.

RESULTS

In the base case, the risk of vCJD was estimated at zero at both blood services. In the most pessimistic scenario, the risk of vCJD was 6.4 × 10-9 (i.e., 1 in 157 million donations) at HQ, or ≤1 in 77 million based on the upper bound of the 95% confidence interval (CI). At CBS, this risk was 4.8 × 10-8 (i.e., 1 in 21 million donations), or ≤1 in 16 million based on the upper bound of the 95% CI.

CONCLUSION

vCJD poses minimal risks to the Canadian blood supply. Current vCJD deferral criteria may, therefore, be lifted with virtually no impact on safety, while significantly expanding the donor base.

Human leukocyte antigen alloimmunization prevention mechanisms in blood transfusion

In many fields of clinical medicine and blood transfusion, the human leukocyte antigen (HLA) system is crucial. Alloimmunization happens as a result of an immune response to foreign antigens encountered during blood transfusion. This gives rise to alloantibodies against red blood cells (RBCs), HLA, or human platelet antigen (HPA). HLA alloimmunization following allogeneic transfusion was shown to be a result of contaminating white blood cells (WBCs) present in the product. It is a common complication of transfusion therapy that leads to difficulties in clinical intolerance and refractoriness to platelet transfusion during patient management. Single-donor platelets, prophylactic HLA matching, leukoreduction, and irradiation of cellular blood products are some of the mechanisms to prevent HLA alloimmunization during a blood transfusion. Now, the best approach to reduce the occurrence of primary HLA alloimmunization is the removal of WBCs from the blood by filtration.

Transmission of Variant Creutzfeldt-Jakob Disease Through Blood Transfusion and Plasma-Derived Products: A Narrative Review of Observed and Modeled Risks

Secondary transmission of variant Creutzfeldt-Jakob disease (vCJD) can occur through blood transfusion or receipt of plasma-derived products. However, published reviews on this topic are outdated, focused on a single country or product type, or did not comprehensively review modeling studies on the risk of transfusion-transmission. We reviewed existing data on observed and modeled risks of transfusion-transmission of vCJD. To date, five patients are suspected to have acquired clinical vCJD or a vCJD infection after receiving a blood or plasma-derived product from a donor who later developed clinical vCJD. All of these cases received a nonleukodepleted blood-derived product in the United Kingdom between 1994 and 1999. Thus, all transfusion-associated cases occurred before the adoption of universal leukodepletion in 1999, which supports the preferential tropism of vCJD for leukocytes. In descriptive cohort studies, no cases of clinical vCJD were observed over ∼13 years of follow-up. In modeling studies, the risk of collecting a contaminated donation was generally <23 per million donations, that of infection was generally <10 per million transfusions or doses, and that of clinical vCJD was generally <2 per million transfusions or doses. These low risk estimates and the two-decade long absence of new cases of transfusion-associated vCJD suggest vCJD poses minimal risks to the safety of the blood supply. Furthermore, despite concerns of a second wave driven by individuals harboring a non-MM genotype at codon 129 of PRNP, there has been only 1 autopsy-confirmed case of clinical vCJD in an MV individual in 2016. The current trend to reassess or (in some countries) fully withdraw the blood donation criteria related to vCJD therefore seems justified, safe, and may significantly expand the donor base.

Risk of variant Creutzfeldt-Jakob disease transmission by blood transfusion in Australia

Background and Objectives

Most of the 233 worldwide cases of variant Creutzfeldt–Jakob disease (vCJD) have been reported in the United Kingdom and 3 have been associated with transfusion‐transmission. To mitigate the potential vCJD risk to blood safety, Australian Red Cross Lifeblood imposes restrictions on blood donation from people with prior residency in, or extended travel to, the United Kingdom during the risk period 1980–1996. We have modified a previously published methodology to estimate the transfusion‐transmission risk of vCJD associated with fresh component transfusion in Australia if the UK residence deferral was removed.

Materials and Methods

The prevalence of current pre‐symptomatic vCJD infection in the United Kingdom by age at infection and genotype was estimated based on risk of exposure to the bovine spongiform encephalopathy agent for the period 1980–1996. These results were used to estimate the age‐specific prevalence of undiagnosed, pre‐symptomatic vCJD in the Australian population in the current year due to prior UK residency or travel. The primary model outputs were the 2020 vCJD risks/unit of vCJD contamination, transfusion‐transmission (infections) and clinical cases.

Results

The overall (prior UK residency in and travel to United Kingdom, 1980–1996) mean risk of contamination per unit was 1 in 29,900,000. The risks of resulting vCJD transmission (infection) and clinical case were 1 in 389,000,000 and 1 in 1,450,000,000, respectively.

Conclusion

Our modelling suggests that removing the Lifeblood donation deferral for travel to, or UK residence, would result in virtually no increased risk of vCJD transfusion‐transmission and would be a safe and effective strategy for increasing the donor base.

Preclinical Detection of Prions in Blood of Nonhuman Primates Infected with Variant Creutzfeldt-Jakob Disease

Variant Creutzfeldt-Jakob disease (vCJD) is caused by prion infection with bovine spongiform encephalopathy and can be transmitted by blood transfusion. Protein misfolding cyclic amplification (PMCA) can detect prions in blood from vCJD patients with 100% sensitivity and specificity. To determine whether PMCA enables prion detection in blood during the preclinical stage of infection, we performed a blind study using blood samples longitudinally collected from 28 control macaques and 3 macaques peripherally infected with vCJD. Our results demonstrate that PMCA consistently detected prions in blood during the entire preclinical stage in all infected macaques, without false positives from noninfected animals, when using the optimized conditions for amplification of macaque prions. Strikingly, prions were detected as early as 2 months postinoculation (>750 days before disease onset). These findings suggest that PMCA has the potential to detect vCJD prions in blood from asymptomatic carriers during the preclinical phase of the disease.

Preclinical transmission of prions by blood transfusion is influenced by donor genotype and route of infection

Variant Creutzfeldt-Jakob disease (vCJD) is a human prion disease resulting from zoonotic transmission of bovine spongiform encephalopathy (BSE). Documented cases of vCJD transmission by blood transfusion necessitate on-going risk reduction measures to protect blood supplies, such as leucodepletion (removal of white blood cells, WBCs). This study set out to determine the risks of prion transmission by transfusion of labile blood components (red blood cells, platelets, plasma) commonly used in human medicine, and the effectiveness of leucodepletion in preventing infection, using BSE-infected sheep as a model. All components were capable of transmitting prion disease when donors were in the preclinical phase of infection, with the highest rates of infection in recipients of whole blood and buffy coat, and the lowest in recipients of plasma. Leucodepletion of components (<10⁶ WBCs/unit) resulted in significantly lower transmission rates, but did not completely prevent transmission by any component. Donor PRNP genotype at codon 141, which is associated with variation in incubation period, also had a significant effect on transfusion transmission rates. A sensitive protein misfolding cyclic amplification (PMCA) assay, applied to longitudinal series of blood samples, identified infected sheep from 4 months post infection. However, in donor sheep (orally infected), the onset of detection of PrP^Sc in blood was much more variable, and generally later, compared to recipients (intravenous infection). This shows that the route and method of infection may profoundly affect the period during which an individual is infectious, and the test sensitivity required for reliable preclinical diagnosis, both of which have important implications for disease control. Our results emphasize that blood transfusion can be a highly efficient route of transmission for prion diseases. Given current uncertainties over the prevalence of asymptomatic vCJD carriers, this argues for the maintenance and improvement of current measures to reduce the risk of transmission by blood products.

Variant Creutzfeldt-Jakob disease (vCJD) resulted from zoonotic transmission of bovine spongiform encephalopathy (BSE), and has also been transmitted by blood transfusion. One of the most important risk reduction measures introduced by human transfusion services to safeguard the blood supply is leucodepletion (removal of white blood cells) of blood components. This study represents the largest experimental analysis to date of the risks of prion infection associated with transfusion of labile blood components, and the effectiveness of leucodepletion in preventing transmission. Using a BSE-infected sheep model, we found that red blood cells, platelets and plasma from preclinical donors were all infectious, even after leucodepletion, although leucodepletion significantly reduced transmission rates. In addition, the time course of detection of prions in blood varied significantly depending on the route and method of infection. This has important implications for the risk of onward transmission, and suggests that further improvements in sensitivity of diagnostic tests will be required for reliable preclinical diagnosis of vCJD and other prion diseases. The results of this study support the continuation of current measures to reduce the risk of vCJD transmission by blood products, and suggest areas for further improvement.

Infusion of blood from mice displaying cerebral amyloidosis accelerates amyloid pathology in animal models of Alzheimer's disease

Previous studies showed that injection of tissue extracts containing amyloid-β (Aβ) aggregates accelerate amyloid deposition in the brain of mouse models of Alzheimer's disease (AD) through prion-like mechanisms. In this study, we evaluated whether brain amyloidosis could be accelerated by blood infusions, procedures that have been shown to transmit prion diseases in animals and humans. Young transgenic mice infused with whole blood or plasma from old animals with extensive Aβ deposition in their brains developed significantly higher levels brain amyloidosis and neuroinflammation compared to untreated animals or mice infused with wild type blood. Similarly, intra-venous injection of purified Aβ aggregates accelerated amyloid pathology, supporting the concept that Aβ seeds present in blood can reach the brain to promote neuropathological alterations in the brain of treated animals. However, an amyloid-enhancing effect of other factors present in the blood of donors cannot be discarded. Our results may help to understand the role of peripheral (amyloid-dependent or -independent) factors implicated in the development of AD and uncover new strategies for disease intervention.

Experimental inoculation of CD11c+ B1 lymphocytes, CD68+ macrophages, or platelet-rich plasma from scrapie-infected sheep into susceptible sheep results in variable infectivity

Many studies have demonstrated prion infectivity in whole blood and blood components in a variety of transmissible spongiform encephalopathies of livestock and rodents, and variant Creutzfeldt–Jakob disease in humans, as well as an association between pathogenic prion protein (PrP^Sc) and different immune cells (e.g. follicular dendritic cells, T and B lymphocytes, monocytes and tingible body macrophages). To further investigate the role of various blood components in prion disease transmission, we intracranially inoculated genetically susceptible VRQ/ARQ and ARQ/ARQ sheep with inocula composed of CD11c⁺ B1 lymphocytes, CD68 +macrophages, or platelet-rich plasma derived from clinically ill sheep infected with the US no. 13–7 scrapie agent. At the completion of the study, we found that VRQ/ARQ and ARQ/ARQ sheep inoculated with CD11c⁺ B1 lymphocytes and CD68⁺ macrophages developed scrapie with detectable levels of PrP^Sc in the central nervous system and lymphoreticular system, while those inoculated with platelet-rich plasma did not develop disease and did not have detectable PrP^Sc by immunohistochemistry or enzyme immunoassay. This study complements and expands on earlier findings that white blood cells harbour prion infectivity, and reports CD11c⁺ B1 lymphocytes and CD68⁺ macrophages as additional targets for possible preclinical detection of prion infection in blood.

Creutzfeldt-Jakob disease and blood transfusion safety

Transmissible spongiform encephalopathies (TSEs) are untreatable, fatal neurologic diseases affecting mammals. Human disease forms include sporadic, familial and acquired Creutzfeldt-Jakob disease (CJD). While sporadic CJD (sCJD) has been recognized for near on 100 years, variant CJD (vCJD) was first reported in 1996 and is the result of food-borne transmission of the prion of bovine spongiform encephalopathy (BSE, 'mad cow disease'). Currently, 230 vCJD cases have been reported in 12 countries, the majority in the UK (178) and France (27). Animal studies demonstrated highly efficient transmission of natural scrapie and experimental BSE by blood transfusion and fuelled concern that sCJD was potentially transfusion transmissible. No such case has been recorded and case-control evaluations and lookback studies indicate that, if transfusion transmission occurs at all, it is very rare. In contrast, four cases of apparent transfusion transmission of vCJD infectivity have been identified in the UK. Risk minimization strategies in response to the threat of vCJD include leucodepletion, geographically based donor deferrals and deferral of transfusion recipients. A sensitive and specific, high-throughput screening test would provide a potential path to mitigation but despite substantial effort no such test has yet appeared. The initial outbreak of vCJD appears to be over, but concern remains about subsequent waves of disease among those already infected. There is considerable uncertainty about the size of the infected population, and there will be at least a perception of some continuing risk to blood safety. Accordingly, at least some precautionary measures will remain in place and continued surveillance is necessary.

Human transmissible spongiform encephalopathies: historic view

The first of several pivotal moments leading to current understanding of human transmissible spongiform encephalopathies (TSEs) occurred in 1959 when veterinary pathologist W.J. Hadlow first recognized several similarities between scrapie-a slow infection of sheep caused by an unusual infectious agent-and kuru, a fatal exotic neurodegenerative disease affecting only people of a single language group in the remote mountainous interior of New Guinea, described two years earlier by D.C. Gajdusek and V. Zigas. Based on the knowledge of scrapie, Gajdusek, C.J. Gibbs, Jr., and M.P. Alpers soon initiated efforts to transmit kuru by inoculating kuru brain tissue into non-human primates, that-although requiring several years-ultimately proved successful. In the same year that Hadlow first proposed that kuru and scrapie might have similar etiology, I. Klatzo noted that kuru's histopathology resembled that of Creutzfeldt-Jakob disease (CJD), another progressive fatal neurodegenerative disease of unknown etiology that A.M. Jakob had first described in 1921. Gajdusek and colleagues went on to demonstrate that not only the more common sporadic form of CJD but also familial CJD and a generally similar familial brain disease (Gerstmann-Sträussler-Scheinker syndrome) were also transmissible, first to non-human primates and later to other animals. (Other investigators later transmitted an even rarer brain disease, fatal familial insomnia, to animals.) Iatrogenic CJD (spread by human pituitary-derived hormones and tissue grafts) was also transmitted to animals. Much later, in 1996, a new variant of CJD was attributed to human infection with the agent of bovine spongiform encephalopathy; vCJD itself caused an iatrogenic TSE spread by blood transfusion (and probably by a human-plasma-derived clotting factor). Starting in the 1930s, the scrapie agent was found to have a unique constellation of physical properties (marked resistance to inactivation by chemicals, heat and radiation), eventually interpreted as suggesting that it might be an unconventional self-replicating pathogen based on protein and containing no nucleic acid. The work of S.B. Prusiner led to the recognition in the early 1980s that a misfolded form of a ubiquitous normal host protein was usually if not always detectable in tissues containing TSE agents, greatly facilitating the diagnosis and TSEs and understanding their pathogenesis. Prusiner proposed that the TSE agent was likely to be composed partly if not entirely of the abnormal protein, for which he coined the term "prion" protein and "prion" for the agent. Expression of the prion protein by animals-while not essential for life-was later found to be obligatory to infect them with TSEs, and a variety of mutations in the protein clearly tracked with TSEs in families, explaining the autosomal dominant pattern of disease and confirming a central role for the protein in pathogenesis. Prusiner's terminology and the prion hypothesis came to be widely though not universally accepted. A popular corollary proposal, that prions arise by spontaneous misfolding of normal prion protein leading to sporadic cases of CJD, BSE, and scrapie, is more problematic and may serve to discourage continued search for environmental sources of exposure to TSE agents.

How do PrPSc Prions Spread between Host Species, and within Hosts?

Prion diseases are sub-acute neurodegenerative diseases that affect humans and some domestic and free-ranging animals. Infectious prion agents are considered to comprise solely of abnormally folded isoforms of the cellular prion protein known as PrP^Sc. Pathology during prion disease is restricted to the central nervous system where it causes extensive neurodegeneration and ultimately leads to the death of the host. The first half of this review provides a thorough account of our understanding of the various ways in which PrP^Sc prions may spread between individuals within a population, both horizontally and vertically. Many natural prion diseases are acquired peripherally, such as by oral exposure, lesions to skin or mucous membranes, and possibly also via the nasal cavity. Following peripheral exposure, some prions accumulate to high levels within the secondary lymphoid organs as they make their journey from the site of infection to the brain, a process termed neuroinvasion. The replication of PrP^Sc prions within secondary lymphoid organs is important for their efficient spread to the brain. The second half of this review describes the key tissues, cells and molecules which are involved in the propagation of PrP^Sc prions from peripheral sites of exposure (such as the lumen of the intestine) to the brain. This section also considers how additional factors such as inflammation and aging might influence prion disease susceptibility.

Experimental transfusion of variant CJD-infected blood reveals previously uncharacterised prion disorder in mice and macaque

Exposure of human populations to bovine spongiform encephalopathy through contaminated food has resulted in <250 cases of variant Creutzfeldt-Jakob disease (vCJD). However, more than 99% of vCJD infections could have remained silent suggesting a long-term risk of secondary transmission particularly through blood. Here, we present experimental evidence that transfusion in mice and non-human primates of blood products from symptomatic and non-symptomatic infected donors induces not only vCJD, but also a different class of neurological impairments. These impairments can all be retransmitted to mice with a pathognomonic accumulation of abnormal prion protein, thus expanding the spectrum of known prion diseases. Our findings suggest that the intravenous route promotes propagation of masked prion variants according to different mechanisms involved in peripheral replication.

Plasma cholesterol level determines in vivo prion propagation

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases with an urgent need for therapeutic and prophylactic strategies. At the time when the blood-mediated transmission of prions was demonstrated, in vitro studies indicated a high binding affinity of the scrapie prion protein (PrP^Sc) with apoB-containing lipoproteins, i.e., the main carriers of cholesterol in human blood. The aim of the present study was to explore the relationship between circulating cholesterol-containing lipoproteins and the pathogenicity of prions in vivo. We showed that, in mice with a genetically engineered deficiency for the plasma lipid transporter, phospholipid transfer protein (PLTP), abnormally low circulating cholesterol concentrations were associated with a significant prolongation of survival time after intraperitoneal inoculation of the 22L prion strain. Moreover, when circulating cholesterol levels rose after feeding PLTP-deficient mice a lipid-enriched diet, a significant reduction in survival time of mice together with a marked increase in the accumulation rate of PrP^Sc deposits in their brain were observed. Our results suggest that the circulating cholesterol level is a determinant of prion propagation in vivo and that cholesterol-lowering strategies might be a successful therapeutic approach for patients suffering from prion diseases.

Leucoreduction of blood components: an effective way to increase blood safety?

Over the past 30 years, it has been demonstrated that removal of white blood cells from blood components is effective in preventing some adverse reactions such as febrile non-haemolytic transfusion reactions, immunisation against human leucocyte antigens and human platelet antigens, and transmission of cytomegalovirus. In this review we discuss indications for leucoreduction and classify them into three categories: evidence-based indications for which the clinical efficacy is proven, indications based on the analysis of observational clinical studies with very consistent results and indications for which the clinical efficacy is partial or unproven.

Preclinical detection of infectivity and disease-specific PrP in blood throughout the incubation period of prion disease

Variant Creutzfeldt-Jakob disease (vCJD) is a fatal neurodegenerative disorder characterised by accumulation of pathological isoforms of the prion protein, PrP. Although cases of clinical vCJD are rare, there is evidence there may be tens of thousands of infectious carriers in the United Kingdom alone. This raises concern about the potential for perpetuation of infection via medical procedures, in particular transfusion of contaminated blood products. Accurate biochemical detection of prion infection is crucial to mitigate risk and we have previously reported a blood assay for vCJD. This assay is sensitive for abnormal PrP conformers at the earliest stages of preclinical prion disease in mice and precedes the maximum infectious titre in blood. Not only does this support the possibility of screening asymptomatic individuals, it will also facilitate the elucidation of the complex relationship that exists between the ensemble of abnormal PrP conformers present in blood and the relationship to infectivity.

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.

Prion strains are differentially released through the exosomal pathway

Cell-to-cell transfer of prions is a crucial step in the spreading of prion infection through infected tissue. At the cellular level, several distinct pathways including direct cell-cell contacts and release of various types of infectious extracellular vesicles have been described that may potentially lead to infection of naïve cells. The relative contribution of these pathways and whether they may vary depending on the prion strain and/or on the infected cell type are not yet known. In this study we used a single cell type (RK13) infected with three different prion strains. We showed that in each case, most of the extracellular prions resulted from active cell secretion through the exosomal pathway. Further, quantitative analysis of secreted infectivity indicated that the proportion of prions eventually secreted was dramatically dependent on the prion strain. Our data also highlight that infectious exosomes secreted from cultured cells might represent a biologically pertinent material for spiking experiments. Also discussed is the appealing possibility that abnormal PrP from different prion strains may differentially interact with the cellular machinery to promote secretion.

Evaluation of the protection of primates transfused with variant Creutzfeldt-Jakob disease-infected blood products filtered with prion removal devices: a 5-year update

BACKGROUND

Analysis of archived appendix samples reveals that one in 2000 individuals in the United Kingdom may carry the infectious prion protein associated with variant Creutzfeldt-Jakob disease (vCJD), raising questions about the risk of transfusion transmission from apparently healthy carriers. Blood leukoreduction shows limited efficiency against prions. Therefore, in absence of antemortem diagnostic tests, prion removal filters, including the P-Capt filter were designed to improve blood transfusion safety.

STUDY DESIGN AND METHODS

We evaluated the performances of two filters, the P-Capt and one prototype (PMC#005), with blood-borne infectivity in two independent experiments. Blood was drawn twice from prion-infected macaques. Corresponding RBCCs were prepared according to two different procedures: in Study A, the leukoreduction step was followed by the filtration through the P-Capt. In Study B, the leukoreduction and prion removal were performed simultaneously through the PMC#005. For each study, two groups of three animals were transfused twice with samples before or after filtration.

RESULTS

Among the six macaques transfused with nonfiltered samples, five developed neurologic signs but only four exhibited peripheral detectable protease-resistant prion protein (PrPres) accumulation. In Study A, the three animals transfused with P-Capt-filtered samples remain asymptomatic and devoid of PrPres in lymph node biopsies 6 years after the transfusion. In Study B, one animal transfused with PMC#005-filtered samples developed vCJD.

CONCLUSION

After 5 to 6 years of progress, this ongoing study provides encouraging results on the prion blood removal performances of the P-Capt filter in macaques, an utmost relevant model for human prion diseases.

Variant CJD. 18 years of research and surveillance

It is now 18 years since the first identification of a case of vCJD in the UK. Since that time, there has been much speculation over how vCJD might impact human health. To date there have been 177 case reports in the UK and a further 51 cases worldwide in 11 different countries. Since establishing that BSE and vCJD are of the same strain of agent, we have also shown that there is broad similarity between UK and non-UK vCJD cases on first passage to mice. Transgenic mouse studies have indicated that all codon 129 genotypes are susceptible to vCJD and that genotype may influence whether disease appears in a clinical or asymptomatic form, supported by the appearance of the first case of potential asymptomatic vCJD infection in a PRNP 129MV patient. Following evidence of blood transfusion as a route of transmission, we have ascertained that all blood components and leucoreduced blood in a sheep model of vCJD have the ability to transmit disease. Importantly, we recently established that a PRNP 129MV patient blood recipient with an asymptomatic infection and limited PrP(Sc) deposition in the spleen could readily transmit disease into mice, demonstrating the potential for peripheral infection in the absence of clinical disease. This, along with the recent appendix survey which identified 16 positive appendices in a study of 32,441 cases, underlines the importance of continued CJD surveillance and maintaining control measures already in place to protect human health.

Development of a bifunctional filter for prion protein and leukoreduction of red blood cell components

BACKGROUND

Leukofiltration of blood components is currently implemented worldwide as a precautionary measure against white blood cell-associated adverse effects and the potential transmission of variant Creutzfeldt-Jakob disease (vCJD). A newly developed bifunctional filter (Sepacell Prima, Asahi Kasei Medical) was assessed for prion removal, leukoreduction (LR), and whether the filter significantly affected red blood cells (RBCs).

STUDY DESIGN AND METHODS

Sepacell Prima's postfiltration effects on RBCs, including hemolysis, complement activation, and RBC chemistry, were compared with those of a conventional LR filter (Sepacell Pure RC). Prion removal was measured by Western blot after spiking RBCs with microsomal fractions derived from scrapie-infected hamster brain homogenate. Serially diluted exogenous prion solutions (0.05 mL), with or without filtration, were injected intracerebrally into Golden Syrian hamsters.

RESULTS

LR efficiency of 4.44 log with the Sepacell Prima was comparable to 4.11 log with the conventional LR filter. There were no significant differences between the two filters in hemoglobin loss, hemolysis, complement activation, and RBC biomarkers. In vitro reduction of exogenously spiked prions by the filter exceeded 3 log. The titer, 6.63 (log ID50 /mL), of prefiltration infectivity of healthy hamsters was reduced to 2.52 (log ID50 /mL) after filtration. The reduction factor was calculated as 4.20 (log ID50 ).

CONCLUSION

With confirmed removal efficacy for exogenous prion protein, this new bifunctional prion and LR filter should reduce the residual risk of vCJD transmission through blood transfusion without adding complexity to component processing.

Preparation, quality criteria, and properties of human blood platelet lysate supplements for ex vivo stem cell expansion

Most clinical applications of human multipotent mesenchymal stromal cells (MSCs) for cell therapy, tissue engineering, regenerative medicine, and treatment of immune and inflammatory diseases require a phase of isolation and ex vivo expansion allowing a clinically meaningful cell number to be reached. Conditions used for cell isolation and expansion should meet strict quality and safety requirements. This is particularly true for the growth medium used for MSC isolation and expansion. Basal growth media used for MSC expansion are supplemented with multiple nutrients and growth factors. Fetal bovine serum (FBS) has long been the gold standard medium supplement for laboratory-scale MSC culture. However, FBS has a poorly characterized composition and poses risk factors, as it may be a source of xenogenic antigens and zoonotic infections. FBS has therefore become undesirable as a growth medium supplement for isolating and expanding MSCs for human therapy protocols. In recent years, human blood materials, and most particularly lysates and releasates of platelet concentrates have emerged as efficient medium supplements for isolating and expanding MSCs from various origins. This review analyzes the advantages and limits of using human platelet materials as medium supplements for MSC isolation and expansion. We present the modes of production of allogeneic and autologous platelet concentrates, measures taken to ensure optimal pathogen safety profiles, and methods of preparing PLs for MSC expansion. We also discuss the supply of such blood preparations. Produced under optimal conditions of standardization and safety, human platelet materials can become the future 'gold standard' supplement for ex vivo production of MSCs for translational medicine and cell therapy applications.

Advances in screening test development for transmissible spongiform encephalopathies

The blood of patients with transmissible spongiform encephalopathy or prion disease can no longer be considered free of infectivity. There have been two recent reports of highly probable transfusion-associated iatrogenic variant Creutzfeldt-Jakob disease infections, and there is supporting experimental evidence of scrapie transmission by the transfusion of blood from sheep with naturally occurring disease. In the absence of a preclinical diagnostic test for transmissible spongiform encephalopathy, the main precautionary measures undertaken by blood agencies employ donor exclusion criteria, ensuring that the number of any further iatrogenic cases will be small. The development of a sensitive, specific and reliable diagnostic test is urgently needed for early identification of infected individuals in order to ensure the safety of blood supplies. During the past 5 years, significant progress has been made in improving the sensitivity and specificity of tests using brain and lymphoreticular tissues to identify Creutzfeldt-Jakob disease-infected individuals. However, the quest for a blood test is still in its infancy and requires extensive further research.

In vitro detection of prionemia in TSE-infected cervids and hamsters

Blood-borne transmission of infectious prions during the symptomatic and asymptomatic stages of disease occurs for both human and animal transmissible spongiform encephalopathies (TSEs). The geographical distribution of the cervid TSE, chronic wasting disease (CWD), continues to spread across North America and the prospective number of individuals harboring an asymptomatic infection of human variant Creutzfeldt-Jakob Disease (vCJD) in the United Kingdom has been projected to be ~1 in 3000 residents. Thus, it is important to monitor cervid and human blood products to ensure herd health and human safety. Current methods for detecting blood-associated prions rely primarily upon bioassay in laboratory animals. While bioassay provides high sensitivity and specificity, it requires many months, animals, and it is costly. Here we report modification of the real time quaking-induced conversion (RT-QuIC) assay to detect blood-borne prions in whole blood from prion-infected preclinical white-tailed deer, muntjac deer, and Syrian hamsters, attaining sensitivity of >90% while maintaining 100% specificity. Our results indicate that RT-QuIC methodology as modified can provide consistent and reliable detection of blood-borne prions in preclinical and symptomatic stages of two animal TSEs, offering promise for prionemia detection in other species, including humans.

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

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.

Assessment of prion reduction filters in decreasing infectivity of ultracentrifuged 263K scrapie-infected brain homogenates in "spiked" human blood and red blood cells

BACKGROUND

The safety of red blood cells (RBCs) is of concern because of the occurrence of four transfusion-transmitted variant Creutzfeldt-Jakob disease (vCJD) cases in the United Kingdom. The absence of validated screening tests requires the use of procedures to remove prions from blood to minimize the risk of transmission. These procedures must be validated using infectious prions in a form that is as close as possible to one in blood.

STUDY DESIGN AND METHODS

Units of human whole blood (WB) and RBCs were spiked with high-speed supernatants of 263K scrapie-infected hamster brain homogenates. Spiked samples were leukoreduced and then passed through prion-removing filters (Pall Corporation). In another experiment, RBCs from 263K scrapie-infected hamsters were treated as above, and residual infectivity was measured by bioassay.

RESULTS

The overall removal of infectivity by the filters from prion-spiked WB and RBCs was approximately two orders of magnitude. No infectivity was detected in filtered hamster RBCs endogenously infected with scrapie.

CONCLUSION

The use of prion-removing filters may help to reduce the risk of transfusion-transmitted vCJD. To avoid overestimation of prion removal efficiency in validation studies, it may be more appropriate to use supernates from ultracentrifugation of scrapie-infected hamster brain homogenate rather than the current standard brain homogenates.

Transfusion of prion-filtered red cells does not increase the rate of alloimmunization or transfusion reactions in patients: results of the UK trial of prion-filtered versus standard red cells in surgical patients (PRISM A)

This study, conducted for the UK Blood Transfusion Services (UKBTS), evaluated the clinical safety of red cells filtered through a CE-marked prion removal filter (P-Capt™). Patients requiring blood transfusion for elective procedures in nine UK hospitals were entered into a non-randomized open trial to assess development of red cell antibodies to standard red cell (RCC) or prion-filtered red cell concentrates (PF-RCC) at eight weeks and six months post-transfusion. Patients who received at least 1 unit of PF-RCC were compared with a control cohort given RCC only. About 917 PF-RCC and 1336 RCC units were transfused into 299 and 291 patients respectively. Twenty-six new red cell antibodies were detected post-transfusion in 10 patients in each arm, an overall alloimmunization rate of 4.4%. Neither the treatment arm [odds ratio (OR) 0.93, 95% confidence interval (CI) 0.3, 2.5] nor number of units transfused (OR 0.95, 95% CI 0.8, 1.1) had a significant effect on the proportion of patients who developed new alloantibodies. No pan-reactive antibodies or antibodies specifically against PF-RCC were detected. There was no difference in transfusion reactions between arms, and no novel transfusion-related adverse events clearly attributable to PF-RCC were seen. These data suggest that prion filtration of red cells does not reduce overall transfusion safety. This finding requires confirmation in large populations of transfused patients.

Adverse effects of plasma transfusion

Plasma utilization has increased over the past two decades, and there is a growing concern that many plasma transfusions are inappropriate. Plasma transfusion is not without risk, and certain complications are more likely with plasma than other blood components. Clinical and laboratory investigations of the patients suffering reactions after infusion of fresh-frozen plasma (FFP) define the etiology and pathogenesis of the panoply of adverse effects. We review here the pathogenesis, diagnosis, and management of the risks associated with plasma transfusion. Risks commonly associated with FFP include: 1) transfusion-related acute lung injury, 2) transfusion-associated circulatory overload, and 3) allergic and/or anaphylactic reactions. Other less common risks include 1) transmission of infections, 2) febrile nonhemolytic transfusion reactions, 3) red blood cell alloimmunization, and 4) hemolytic transfusion reactions. The effects of pathogen inactivation or reduction methods on these risks are also discussed. Fortunately, a majority of the adverse effects are not lethal and are adequately treated in clinical practice.

Highly efficient prion transmission by blood transfusion

It is now clearly established that the transfusion of blood from variant CJD (v-CJD) infected individuals can transmit the disease. Since the number of asymptomatic infected donors remains unresolved, inter-individual v-CJD transmission through blood and blood derived products is a major public health concern. Current risk assessments for transmission of v-CJD by blood and blood derived products by transfusion rely on infectious titers measured in rodent models of Transmissible Spongiform Encephalopathies (TSE) using intra-cerebral (IC) inoculation of blood components. To address the biological relevance of this approach, we compared the efficiency of TSE transmission by blood and blood components when administrated either through transfusion in sheep or by intra-cerebral inoculation (IC) in transgenic mice (tg338) over-expressing ovine PrP. Transfusion of 200 µL of blood from asymptomatic infected donor sheep transmitted prion disease with 100% efficiency thereby displaying greater virulence than the transfusion of 200 mL of normal blood spiked with brain homogenate material containing 10³ID₅₀ as measured by intracerebral inoculation of tg338 mice (ID₅₀ IC in tg338). This was consistent with a whole blood titer greater than 10^3.6 ID₅₀ IC in tg338 per mL. However, when the same blood samples were assayed by IC inoculation into tg338 the infectious titers were less than 32 ID per mL. Whereas the transfusion of crude plasma to sheep transmitted the disease with limited efficacy, White Blood Cells (WBC) displayed a similar ability to whole blood to infect recipients. Strikingly, fixation of WBC with paraformaldehyde did not affect the infectivity titer as measured in tg338 but dramatically impaired disease transmission by transfusion in sheep. These results demonstrate that TSE transmission by blood transfusion can be highly efficient and that this efficiency is more dependent on the viability of transfused cells than the level of infectivity measured by IC inoculation.

In the UK, several v-CJD cases have been identified in patients that received blood or blood-derived products prepared from incubating asymptomatic donors. Since there is no screening test to identify infected donors, procedural risk reduction measures remain the only protection against v-CJD transfusion risk. These measures rely, in part, on the assumptions that (i) the level of infectivity in blood is low and (ii) the risk of blood borne transmission is directly correlated with the infectious titer of blood and blood products. Using a transmissible spongiform encephalopathy (TSE) animal model, we have provided evidence that despite a very low infectious titer in blood as measured by inoculation into brain, the transfusion of 0.2 mL of blood from asymptomatic infected donors is sufficient to transmit the disease with a 100% efficacy. We further demonstrated that this high efficiency of disease transmission is crucially dependant on the viability of the transfused white blood cells rather than on their infectious titer. These findings provide new insights into the pathogenesis of TSE diseases and require revision of some of the key assumptions of the v-CJD blood borne risk assessments.

Assessing prion infectivity of human urine in sporadic Creutzfeldt-Jakob disease

Prion diseases are neurodegenerative conditions associated with a misfolded and infectious protein, scrapie prion protein (PrP(Sc)). PrP(Sc) propagate prion diseases within and between species and thus pose risks to public health. Prion infectivity or PrP(Sc) presence has been demonstrated in urine of experimentally infected animals, but there are no recent studies of urine from patients with Creutzfeldt-Jakob disease (CJD). We performed bioassays in transgenic mice expressing human PrP to assess prion infectivity in urine from patients affected by a common subtype of sporadic CJD, sCJDMM1. We tested raw urine and 100-fold concentrated and dialyzed urine and assessed the sensitivity of the bioassay along with the effect of concentration and dialysis on prion infectivity. Intracerebral inoculation of transgenic mice with urine from 3 sCJDMM1 patients failed to demonstrate prion disease transmission, indicating that prion infectivity in urine from sCJDMM1 patients is either not present or is <0.38 infectious units/mL.

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.

Candidate cell substrates, vaccine production, and transmissible spongiform encephalopathies

Transmissible spongiform encephalopathy (TSE) agents have contaminated human tissue-derived medical products, human blood components, and animal vaccines. The objective of this study was to determine the potential susceptibility to infection of 5 cell lines used or proposed for manufacture of biological products, as well as other lines. Cell lines were exposed to the infectious agents of sporadic and variant Creutzfeldt-Jakob disease and bovine spongiform encephalopathy (BSE). Exposed cultures were tested for TSE-associated prion protein (PrP(TSE)) and TSE infectivity by assay in rodents and nonhuman primates. No PrP(TSE) or infectivity has been detected in any exposed cell line under study so far. Animals inoculated with BSE brain homogenate developed typical spongiform encephalopathy. In contrast, animals inoculated with cells exposed to the BSE agent remained asymptomatic. All cell lines we studied resisted infection with 3 TSE agents, including the BSE agent.

All clinically-relevant blood components transmit prion disease following a single blood transfusion: a sheep model of vCJD

Variant CJD (vCJD) is an incurable, infectious human disease, likely arising from the consumption of BSE-contaminated meat products. Whilst the epidemic appears to be waning, there is much concern that vCJD infection may be perpetuated in humans by the transfusion of contaminated blood products. Since 2004, several cases of transfusion-associated vCJD transmission have been reported and linked to blood collected from pre-clinically affected donors. Using an animal model in which the disease manifested resembles that of humans affected with vCJD, we examined which blood components used in human medicine are likely to pose the greatest risk of transmitting vCJD via transfusion. We collected two full units of blood from BSE-infected donor animals during the pre-clinical phase of infection. Using methods employed by transfusion services we prepared red cell concentrates, plasma and platelets units (including leucoreduced equivalents). Following transfusion, we showed that all components contain sufficient levels of infectivity to cause disease following only a single transfusion and also that leucoreduction did not prevent disease transmission. These data suggest that all blood components are vectors for prion disease transmission, and highlight the importance of multiple control measures to minimise the risk of human to human transmission of vCJD by blood transfusion.

Prions and protein-folding diseases

Prions represent a group of proteins with a unique capacity to fold into different conformations. One isoform is rich in beta-pleated sheets and can aggregate into amyloid that may be pathogenic. This abnormal form propagates itself by imposing its confirmation on the homologous normal host cell protein. Pathogenic prions have been shown to cause lethal neurodegenerative diseases in humans and animals. These diseases are sometimes infectious and hence referred to as transmissible spongiform encephalopathies. In the present review, the remarkable evolution of the heterodox prion concept is summarized. The origin of this phenomenon is based on information transfer between homologous proteins, without the involvement of nucleic acid-encoded mechanisms. Historically, kuru and Creutzfeldt-Jakob disease (CJD) were the first infectious prion diseases to be identified in man. It was their relationship to scrapie in sheep and experimental rodents that allowed an unravelling of the particular molecular mechanism that underlie the disease process. Transmission between humans has been documented to have occurred in particular contexts, including ritual cannibalism, iatrogenic transmission because of pituitary gland-derived growth hormone or the use in neurosurgical procedures of dura mater from cadavers, and the temporary use of a prion-contaminated protein-rich feed for cows. The latter caused a major outbreak of bovine spongiform encephalopathy, which spread to man by human consumption of contaminated meat, causing approximately 200 cases of variant CJD. All these epidemics now appear to be over because of measures taken to curtail further spread of prions. Recent studies have shown that the mechanism of protein aggregation may apply to a wider range of diseases in and possibly also outside the brain, some of which are relatively common such as Alzheimer's and Parkinson's diseases. Furthermore, it has become apparent that the phenomenon of prion aggregation may have a wider physiological importance, but a full understanding of this remains to be defined. It may involve maintaining neuronal functions and possibly contributing to the establishment of long-term memory.

Prion disease blood test using immunoprecipitation and improved quaking-induced conversion

A key challenge in managing transmissible spongiform encephalopathies (TSEs) or prion diseases in medicine, agriculture, and wildlife biology is the development of practical tests for prions that are at or below infectious levels. Of particular interest are tests capable of detecting prions in blood components such as plasma, but blood typically has extremely low prion concentrations and contains inhibitors of the most sensitive prion tests. One of the latter tests is quaking-induced conversion (QuIC), which can be as sensitive as in vivo bioassays, but much more rapid, higher throughput, and less expensive. Now we have integrated antibody 15B3-based immunoprecipitation with QuIC reactions to increase sensitivity and isolate prions from inhibitors such as those in plasma samples. Coupling of immunoprecipitation and an improved real-time QuIC reaction dramatically enhanced detection of variant Creutzfeldt-Jakob disease (vCJD) brain tissue diluted into human plasma. Dilutions of 10(14)-fold, containing ~2 attogram (ag) per ml of proteinase K-resistant prion protein, were readily detected, indicating ~10,000-fold greater sensitivity for vCJD brain than has previously been reported. We also discriminated between plasma and serum samples from scrapie-infected and uninfected hamsters, even in early preclinical stages. This combined assay, which we call "enhanced QuIC" (eQuIC), markedly improves prospects for routine detection of low levels of prions in tissues, fluids, or environmental samples.

IMPORTANCE

Transmissible spongiform encephalopathies (TSEs) are largely untreatable and are difficult to diagnose definitively prior to irreversible clinical decline or death. The transmissibility of TSEs within and between species highlights the need for practical tests for even the smallest amounts of infectivity. A few sufficiently sensitive in vitro methods have been reported, but most have major limitations that would preclude their use in routine diagnostic or screening applications. Our new assay improves the outlook for such critical applications. We focused initially on blood plasma because a practical blood test for prions would be especially valuable for TSE diagnostics and risk reduction. Variant Creutzfeldt-Jakob disease (vCJD) in particular has been transmitted between humans via blood transfusions. Enhanced real-time quaking-induced conversion (eRTQ) provides by far the most sensitive detection of vCJD to date. The 15B3 antibody binds prions of multiple species, suggesting that our assay may be useful for clinical and fundamental studies of a variety of TSEs of humans and animals.

Infusion of P-Capt prion-filtered red blood cell products demonstrate acceptable in vivo viability and no evidence of neoantigen formation

BACKGROUND

Transmission of variant Creutzfeldt-Jacob disease (vCJD) is a major concern in blood transfusion. The P-Capt filter has been shown to remove around 4 log ID(50) prion infectivity from prion-spiked human red blood cells (RBCs).

STUDY DESIGN AND METHODS

Two independent, single-center, randomized, open-label studies were designed to analyze the safety of P-Capt-filtered RBCs. RBCs prepared from leukoreduced whole blood from 43 eligible subjects were randomly assigned to P-Capt filtration and/or storage in plasma or SAGM and stored for 28 or 42 days. Stored RBCs were analyzed for in vivo 24-hour recovery, hemolysis, metabolic variables, blood group antigen expression, neoantigen formation, and safety after autologous infusion.

RESULTS

Mean P-Capt filtration times for leukoreduced RBCs were 41 (SAGM) to 51 (plasma) minutes. Thirteen of 14 subjects receiving P-Capt-filtered RBCs had 24-hour RBC recoveries of 75% or more after 42-day storage, with a mean hemolysis of less than 0.6%. No loss of RBC antigen expression or formation of neoantigens was observed. In both studies, RBCs had white blood cell counts of less than 1 × 10(6)/unit after leukofiltration. P-Capt prion filtration provided an additional greater than 0.8 log leukoreduction. No serious or unexpected adverse events were observed after infusion of P-Capt-filtered full-volume RBC units.

CONCLUSIONS

P-Capt-filtered, stored RBCs demonstrated acceptable viability and no detectable neoantigen expression, immunogenic responses. or safety issues after infusion of a complete unit. The additional filtration time and modest reduction in RBC content are within acceptable levels for implementation in countries with transfusion transmission of vCJD.