Prion diseases like variant Creutzfeldt-Jakob disease (vCJD) in humans1, BSE in cattle and scrapie in sheep are fatal brain diseases caused by an infectious agent, known as a prion. Prions are thought to be composed of abnormal forms (generally referred to as PrPSc) of a protein which is a normal constituent of brain cells, known as the cellular prion protein (PrPC). These disease-associated forms of prion protein form clumps or plaques in the brain and this process causes damage to, and then loss of, brain cells.
In vCJD, prions first infect lymphoreticular tissues (such as the spleen and lymph nodes) outside the brain (tissues that are normally involved in the body’s defences against infection) and then spread to the brain where they cause damage leading to symptoms of the disease. Since these abnormal prion proteins are formed form one of the body’s own proteins, they are not recognised as being foreign by the immune system (as a virus or bacteria would be) which normally tends to produce antibodies and protect against infection. This “immune tolerance” means there is a lack of natural defence against prion infection.
In addition to ingestion of BSE-contaminated food products, it is thought that vCJD may be transmitted by contaminated surgical instruments and it is now known that it can be spread through blood transfusion or treatment with blood products that were derived from a donor who was incubating vCJD2. It is unknown at present how many healthy people may be infected with vCJD prions. Several thousand people in the UK have been notified that they are at increased risk of developing CJD because of exposure to blood, blood products or surgical instruments that may have been contaminated.
We have used prion proteins we have made in the laboratory to immunise mice to produce a large range monoclonal antibodies (mAb) that recognise PrPC and PrPSc3. The mAbs recognise native PrPC and PrPSc from many species4 and have proved very useful in research. We have also demonstrated that some of these antibodies are very effective in curing prion-infected cells and two have been shown to be protective against prion disease in mice, preventing PrPSc accumulation and delaying onset of prion disease in mice5. The blood-brain-barrier limits the entry of large molecules such as antibodies into the brain from the circulation, and so to investigate the therapeutic potential of these mAbs against neurodegeneration, we are investigating methods for them to gain entry into the brain where they may be effective in treating the disease. The mAbs are thought to work by binding to PrPC and preventing its conversion into PrPSc. We are studying the relationship between the immune system and the normal (PrPC) and diseased (PrPSc) forms of prion protein6, in the hope of developing a mAb treatment with minimal side effects.
The MRC Unit has been funded by MRC to “humanise” two of these mice monoclonal antibodies with a view to their trial in human to see if they may be useful to treat prion infection and disease. The therapeutic molecular interaction between one of these antibodies (known as ICSM18) and the prion protein has been characterised by X-ray crystallography7. This translational work is well underway, as are parallel studies to better understand how these antibodies might be used and to study any potential side effects. Currently, many mAbs are used in clinical trials in the treatment of various diseases, such as cancer, rheumatoid arthritis, multiple sclerosis and Alzheimer's disease.
Figure 1. Monoclonal antibodies detecting PrPSc (shown as brown deposits) in a Prion infected brain.
Collinge J., et al. (1996) Nature 383:685-690.
Wroe S. J., et al. (2006) Lancet 368:2061-2067.
Khalili-Shirazi, A., et al. (2005) J. Gen. Virol. 86:2635-2644.
Khalili-Shirazi A., et al. (2007) Biochimica et Biophysica Acta 1774:1438-50.
White A. R., et al. (2003) Nature 422:80-83.
Khalili-Shirazi A., et al. (2005) J.Immunol. 174:3256-3263.
Antonyuk S. V., et al. (2009) Proc Natl Acad Sci USA. 106:2554-8.
Peter-Christian Klöhn, Michael Farmer, Jacqueline M. Linehan, Catherine O'Malley, Mar Fernandez de Marco, William Taylor, Mark Farrow, Azy Khalili-Shirazi, Sebastian Brandner, John Collinge
Nature Reviews Genetics 13, 14-20 ( Jan 2012 )
Tattum MH, Jones S, Pal S, Khalili-Shirazi A, Collinge J, Jackson GS. .
Transfusion. 2010 Jun 18
Crystal structure of human prion protein bound to a therapeutic antibody
Antonyuk, S.V., Trevitt, C. R., Strange, R. W., Jackson, G. S., Sangar, D., Batchelor, M., Cooper, S., Fraser, C., Jones, S., Georgiou, T., Khalili Shirazi, A., Clarke, A. R., Hasnain, S. S. and Collinge, J.
Proc Natl Acad Sci, (2009) 106:2554-2558.
A novel pathogenic pathway of immune activation detectable before clinical onset in Huntington's disease
Maria Björkqvist, Edward J. Wild, Jenny Thiele, Aurelio Silvestroni, Ralph Andre, Nayana Lahiri, Elsa Raibon, Richard V. Lee, Caroline L. Benn, Denis Soulet, Anna Magnusson, Ben Woodman, Christian Landles, Mahmoud A. Pouladi, Michael R. Hayden, Azadeh Khalili-Shirazi, Mark W. Lowdell, Patrik Brundin, Gillian P. Bates, Blair R. Leavitt, Thomas Möller, and Sarah J. Tabrizi
J Exp Med, (2008) 205: 1869-1877.
b-PrP form of human prion protein stimulates production of monoclonal antibodies to epitope 91-110 that recognise native PrPSc.
Azadeh Khalili-Shirazi, Maria Kaisar, Gary Mallinson, Samantha Jones, Daljit Bhelt, Carol Fraser, Anthony R. Clarke, Simon S. Hawke, Graham S. Jackson & John Collinge.
Biochimica et Biophysica Acta, (2007) 1774:1438-1450.
Elongated PrP Dimers Assemble into Prion Amyloid Fibrils.
M. Howard Tattum, Sara Cohen-Krausz, Azadeh Khalili-Shirazi, Graham S. Jackson, Elena V. Orlova, Anthony R. Clarke, John Collinge, Helen R. Saibil.
J Mol Biol, (2006) 357:975-985.
Protein conformation influences immune responses to prion protein.
A. Khalili-Shirazi, S. Quaratino, M. Londei, G. Jackson and J. Collinge.
Immunology, (2005) 116 Suppl 1:42.
PrP glycoforms are associated in a strain-specific ratio in native PrPSc.
A. Khalili-Shirazi, L. Summers, J. Linehan, G. Mallinson, D. Anstee, S. Hawke, G. Jackson and J. Collinge.
J Gen Virol, (2005) 86:2635-2644.
Protein conformation significantly influences immune responses to prion protein.
A. Khalili-Shirazi, S. Quaratino, M. Londei, L. Summers, A. Clarke, S. Hawke, G. Jackson and J. Collinge.
J Immunol, (2005) 174:3256-3263.
Immune response to α- and β conformations of the prion protein
A. Khalili-Shirazi, G. S. Jackson, G. Mallinson, A. R. Clarke, S. Hawke and J. Collinge.
Clinical Investigative Medicine (2004).