Trials of an experimental vaccine against Alzheimer鈥檚 disease have been suspended, after four patients showed signs of what might be serious side-effects.
Safety trials on more than 80 people with mild to moderate Alzheimer鈥檚 disease in 2000 suggested Elan Pharmaceuticals鈥� vaccine, known as AN-1792, is safe. But four of 97 patients given the drug as part of Phase II trials in France have developed symptoms of inflammation of the central nervous system.
Traces of an unspecified virus have been found in the cerebrospinal fluid of 鈥渟ome鈥� of the patients, Elan says. Viral infection of the cerebrospinal fluid can cause CNS inflammation. Elan is refusing to release further details until it has completed its investigation. But it say the investigation should be completed by the date the patients鈥� next vaccine doses are due.
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Ivan Lieberburg, Elan鈥檚 chief scientific and medical officer, said in a statement: 鈥淥ur decision to temporarily suspend further dosing, pending the results of our evaluation, is a standard approach to protect the safety of patients in clinical trials. A decision will be made on resumption of dosing pending the outcome of this investigation.鈥�
The progress of Elan鈥檚 trial is being watched closely by Alzheimer鈥檚 researchers around the world, says Rebecca Wood, chief executive of the UK鈥檚 Alzheimer鈥檚 Research Trust. 鈥淭his is a very important trial of a potentially valuable vaccine against Alzheimer鈥檚 disease. It is most discouraging to hear that dosing has been temporarily suspended,鈥� she says.
Synthetic protein
AN-1792 contains a synthetic form of beta amyloid protein 鈥� the main component of the protein plaques that form in the brains of Alzheimer鈥檚 patients. The vaccine has been shown to clear beta amyloid plaques in mice brains by stimulating an immune response to the protein.
The new trials are designed to evaluate immune responses to the vaccine in human patients.
Richard Morris at Edinburgh University is involved in pre-clinical research on animals using the vaccine. 鈥淲e鈥檝e not seen any adverse effects with AN-1792,鈥� he says. He speculates that chemicals used to enhance the vaccine鈥檚 effects, rather than the vaccine itself, might have caused the central nervous system inflammation observed in the four patients.
But Paul Chapman, an expert on Alzheimer鈥檚 at Cardiff University, says it is not inconceivable that the vaccine itself could have been responsible.
鈥淭here was always a concern about what a patient鈥檚 response would be to administering a protein that is already in the brain,鈥� he told New 杏吧原创. 鈥淪ome people have voiced concerns that it might compromise the immune system or the blood brain barrier 鈥� which would normally keep viruses out.鈥�