[1] MRC, Cambridge Ctr Brain Repair, Cambridge CB2 2SR, England
[2] Univ Cambridge, Addenbrookes Hosp, Neurol Unit, Cambridge CB2 1TN, England
[3] Univ Cambridge, Dept Vet Med, Cambridge CB2 1TN, England
[4] Inst Neurol, Multiple Sclerosis Lab, London WC1N 3BG, England
[5] Ludwig Inst Canc Res, S-75124 Uppsala, Sweden