q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 79, 595±605 595 Journal of Neurochemistry, 2001, 79, 595±605 Vaccination with soluble Ab oligomers generates toxicity-neutralizing antibodies Mary P. Lambert,* ,1 Kirsten L. Viola,* ,1 Brett A. Chromy,* Lei Chang,* Todd E. Morgan,² Jiaxin Yu,³ Duane L. Venton,³ Grant A. Krafft,§ Caleb E. Finch² and William L. Klein* *Department of Neurobiology and Physiology, Northwestern University, Evanston, USA ²Andrus Gerontology Center and Department of Biological Sciences, University of Southern California, Los Angeles, California, USA ³Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The University of Illinois at Chicago, Chicago, USA §Evanston Northwestern Healthcare Research Institute, Evanston, USA Abstract In recent studies of transgenic models of Alzheimer's disease (AD), it has been reported that antibodies to aged beta amyloid peptide 1±42 (Ab 1242 ) solutions (mixtures of Ab monomers, oligomers and amyloid ®brils) cause conspicuous reduction of amyloid plaques and neurological improvement. In some cases, however, neurological improvement has been independent of obvious plaque reduction, and it has been suggested that immunization might neutralize soluble, non- ®brillar forms of Ab. It is now known that Ab toxicity resides not only in ®brils, but also in soluble proto®brils and oligomers. The current study has investigated the immune response to low doses of Ab 1242 oligomers and the characteristics of the antibodies they induce. Rabbits that were injected with Ab 1242 solutions containing only monomers and oligomers produced antibodies that preferentially bound to assembled forms of Ab in immunoblots and in physiological solutions. The antibodies have proven useful for assays that can detect inhibitors of oligomer formation, for immuno¯uorescence localization of cell-attached oligomers to receptor-like puncta, and for immunoblots that show the presence of SDS-stable oligomers in Alzheimer's brain tissue. The antibodies, moreover, were found to neutralize the toxicity of soluble oligomers in cell culture. Results support the hypothesis that immunizations of transgenic mice derive therapeutic bene®t from the immuno- neutralization of soluble Ab-derived toxins. Analogous immuno-neutralization of oligomers in humans may be a key in AD vaccines. Keywords: ADDLs, Alzheimer's disease, receptors, thera- peutic drugs, vaccination. J. Neurochem. (2001) 79, 595±605. Alzheimer's disease (AD) is the most common cause of dementia in older individuals. There is no effective treat- ment, and the molecular basis for pathogenesis remains uncertain. Multiple factors have been implicated, including CNS in¯ammation, oxidative damage, and cytoskeletal anomalies (Smith et al. 1995; Mandelkow and Mandelkow 1998; Spillantini and Goedert 1998; Finch et al. 2001). Increasing evidence, however, favors the hypothesis that a primary cause of AD is neuron dysfunction and death triggered by assembled forms of beta amyloid peptide 1±42 (Ab 1242 ; Pike et al. 1993; Lambert et al. 1998; Small 1998; Hartley et al. 1999; Golde et al. 2000; Klein 2001) While it has been known for many years that Ab monomers assemble into large neurotoxic amyloid ®brils Received May 29, 2001; revised manuscript received August 13, 2001; accepted August 13, 2001. Address correspondence and reprint requests to William L. Klein, Northwestern University, Department of Neurobiology and Physiology, 2153 N. Campus Dr, Evanston, IL 60208, USA. E-mail: wklein@northwestern.edu 1 These authors contributed equally to the manuscript. Abbreviations used:Ab, beta amyloid peptide; AD, Alzheimer's disease; ADDL, Ab-derived diffusible ligand; AFM, atomic force microscopy; APP, amyloid precursor protein; b-CD, b-cyclodextrin; BSA, bovine serum albumin; DEAE, diethylaminoethyl; DMSO, dimethyl sulfoxide; ELISA, Enzyme-Linked Immunosorbent Assay; HFIP, hexa¯uoro-2-propanol; IgG, immunoglobin G; MTT, 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; SDS±PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis.