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  1. Biologics Research Projects

Transmissible Spongiform Encephalopathy Infectivity in Blood and Other Biologicals: Strategies for Detection, Decontamination and Removal

Principal Investigator: Luisa Gregori, PhD
Office / Division / Lab: OBRR / DETTD / LBTSEA

General Overview

Creutzfeldt-Jakob disease (CJD) and its variant form (vCJD) are rare, fatal, brain diseases known as transmissible spongiform encephalopathies (TSEs), or prion diseases. The term "spongiform" refers to the appearance of holes in the affected brain tissue, resembling a sponge, when observed under the microscope. In cows, a similar disease is popularly called "mad cow disease." Consumption of beef from cattle infected with mad cow disease caused the appearance of vCJD in humans.

TSEs are particularly insidious infections because the agents that cause them can remain undetected for decades, causing no noticeable illness. These agents are not like viruses and bacteria and they resist standard decontamination procedures. In addition, there are no tests that identify individuals who have CJD or vCJD before disease becomes apparent. As a consequence, these agents have on rare occasions been transmitted through corneal or neural tissue transplantations, blood transfusions, contaminated neurosurgical instruments or by treatment with plasma-derived products or drugs made from infected tissues (such as human pituitary-derived growth hormones).

vCJD is of particular concern because affected individuals can have the TSE agent in their blood for years before there are any signs of infection. In the meantime, these individuals represent a potential source of vCJD infection risk if they donate blood for transfusion.

Four transfusion-transmitted vCJD infections have already been reported in the United Kingdom (UK). One additional infection attributed to treatment with a protein called coagulation Factor VIII that was obtained from vCJD-contaminated human plasma and used to treat a patient with hemophilia. The number of silently infected blood donors in the UK is unknown, but estimates range from a few hundred to several thousand.

To reduce the risk of transmitting vCJD by blood and other biological sources, FDA has recommended deferring people who are at high risk for CJD and vCJD from donating blood and tissues. The deferral policies are based on the theoretical risk posed by eating contaminated beef. Individuals are deferred from donating blood if they have resided or traveled for a total of three or more months in the UK (the country with highest number of mad cow disease cases) between 1980 and 1996; or if they resided or traveled longer than 5 years from 1980 to the present in Western European countries. The recommendation is slightly different for plasma donations. Individuals are also deferred if they received blood transfusion in the UK from 1980 to present. In addition, permanent deferral is recommended for individuals who have been diagnosed with vCJD or other forms of CJD, individuals who received a high risk tissue transplant (e.g., cornea or neural tissue), and donors with one or more blood relatives diagnosed with CJD. While protecting the public from the risk of accidental exposure to the TSE agents, those policies have deferred many donors who are unlikely to have been infected with TSE agents and may have contributed to blood shortage in some cases. This situation could be improved if a TSE screening test is available to test donated blood for the presence of vCJD agents. FDA has also encouraged the development of such a test.

Several commercial companies are developing test methods to detect TSE. However, a major difficulty is lack of reference standards to validate the candidate tests; that is, there is no standard sample containing a known amount of vCJD agent against which to compare a new test to verify that it works properly. Our laboratory is trying to resolve this difficulty by producing infected animal blood as reference standards. We also developed new animal models of vCJD infection in order to study how TSE agents cause disease.

In addition, our laboratory is studying ways to reduce the risk of transmitting TSE agents that might be present in blood using a variety of devices, such as filters. A similar approach will be applied to remove other pathogens from blood as well. This investigation is highly critical to the FDA mission of protecting public health from the threat of blood-borne pathogens while maintaining an ample supply of blood.

Scientific Overview

While the risk of dietary vCJD transmissions has decreased, secondary transmissions of vCJD by blood transfusion remain the major threat to the blood supply and to public health. The newly reported case of transmission by Factor VIII derived from human plasma in the UK has broadened the risk to include soluble plasma products. An ante-mortem plasma-based vCJD test would offer a valuable tool for reducing this risk.

Our research program focuses on separate but complementary approaches to developing a TSE screening assay with the goal of enhancing the safety of blood and other biologics, reducing the risk of iatrogenic transmissions, and improving CJD diagnosis. These goals are highly relevant to the FDA mission to protect and improve public health. The research will also generate valuable material for studies of TSE transmission in transgenic mice and how the genetics of the animal host affects the pathology of TSE and the replication of the infectious agent.

Detection of TSE infectivity is currently conducted using PrPTSE (Amplification of pathological prion protein of transmissible spongiform encephalopathies) as a surrogate marker. Although there are reported cases in which the relationship between infectivity and PrPTSE is questionable, in most cases the presence of PrPTSE correlates with infectivity. Thus, in our studies, we use PrPTSE as biochemical marker of TSE infectivity, and when possible, infectivity is confirmed with the animal bioassay.

In previous studies, a test was developed in which PrPTSE was first captured using an immuno-affinity resin followed by detection with either a Western blot or an Origen Analyzer (an ELISA-like assay). FDA developed another assay format called DELFIA to detect PrPTSE in infected tissues. Both assay platforms are very sensitive and are currently available in the laboratory. However, PrPTSE concentrations in blood may be below the detection limit of both assays. Therefore, our program also envisions a different strategy to increase PrPTSE concentrations in blood using a relatively new technology called Protein Misfolding Cyclic Amplification (PMCA) which amplifies PrPTSE in vitro. This approach must be thoroughly investigated and demonstrated to have the necessary sensitivity and specificity. If successful, PMCA has the potential for detecting PrPTSE in infected blood.

Our laboratory is also developing vCJD-infected reference standard materials suitable for validating candidate TSE screening tests. We will titrate vCJD-infected blood using a panel of transgenic (Tg) mice expressing the human PrP gene ("humanized"Tg mice) and wild-type mice. We will test humanized Tg mice that over-express PrP and mice that do not over-express PrP. These mouse models must be experimentally evaluated and compared because mice sensitivity to low infectivity levels cannot be anticipated a priori. Control studies will be conducted to ensure that under the conditions tested the mice do not develop spontaneous neurological disease that could affect the results of the titrations.


Pharmacoepidemiol Drug Saf 2020 May;29(5):575-81
Assessment of risk of variant Creutzfeldt-Jakob disease (vCJD) from use of bovine heparin.
Huang Y, Forshee RA, Keire D, Lee S, Gregori L, Asher DM, Bett C, Niland B, Brubaker SA, Anderson SA, Yang H

PLoS One 2019 Dec 12;14(12):e0225904
Quaking-induced conversion of prion protein on a thermal mixer accelerates detection in brains infected with transmissible spongiform encephalopathy agents.
Kaelber N, Bett C, Asher DM, Gregori L

Biotechniques 2018 Dec;65(6):331-8
Rapid selection of single-stranded DNA aptamers binding Staphylococcus epidermidis in platelet concentrates.
Kaur SJ, Gilman V, Duong M, Asher DM, Gregori L

Handb Clin Neurol 2018;153:1-17
Human transmissible spongiform encephalopathies: historic view.
Asher DM, Gregori L

J Gen Virol 2018 Mar;99(3):422-33
Both murine host and inoculum modulate expression of experimental variant Creutzfeldt-Jakob disease.
Bett C, Piccardo P1, Cervenak J, Torres JM, Asher DM, Gregori L

AAPS J 2017 May;19(3):765-71
A heparin purification process removes spiked transmissible spongiform encephalopathy agent.
Bett C, Grgac K, Long D, Karfunkle M, Keire DA, Asher DM, Gregori L

Transplantation 2017 Apr;101(4):e120-4
Rapid testing for Creutzfeldt-Jakob disease in donors of cornea.
Gregori L, Serer A, McDowell KL, Cervenak J, Asher DM

Transfusion 2017 Apr;57(4):924-32
Geographic exposure risk of variant Creutzfeldt-Jakob disease in US blood donors: a risk-ranking model to evaluate alternative donor-deferral policies.
Yang H, Huang Y, Gregori L, Asher DM, Bui T, Forshee RA, Anderson SA

Transfusion 2015 Feb;55(2):405-12
Blood reference materials from macaques infected with variant Creutzfeldt-Jakob disease agent.
McDowell KL, Nag N, Franco Z, Bu M, Piccardo P, Cervenak J, Deslys JP, Comoy E, Asher DM, Gregori L


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