Prototype Alzheimer’s Disease Vaccine Using the Immunodominant B Cell Epitope from -Amyloid and Promiscuous T Cell Epitope Pan HLA DR-Binding Peptide 1 Michael G. Agadjanyan, 2 * Anahit Ghochikyan,* Irina Petrushina, † Vitaly Vasilevko, † Nina Movsesyan,* Mikayel Mkrtichyan,* Tommy Saing, † and David H. Cribbs 2,3†‡ Immunization of amyloid precursor protein transgenic mice with fibrillar -amyloid (A) prevents Alzheimer’s disease (AD)-like neuropathology. The first immunotherapy clinical trial used fibrillar A, containing the B and T cell self epitopes of A, as the immunogen formulated with QS21 as the adjuvant in the vaccine. Unfortunately, the clinical trial was halted during the phase II stage when 6% of the participants developed meningoencephalitis. The cause of the meningoencephalitis in the patients that received the vaccine has not been definitively determined; however, analysis of two case reports from the AN-1792 vaccine trial suggest that the meningoencephalitis may have been caused by a T cell-mediated autoimmune response, whereas production of anti-A Abs may have been therapeutic to the AD patients. Therefore, to reduce the risk of an adverse T cell-mediated immune response to A immunotherapy we have designed a prototype epitope vaccine that contains the immunodominant B cell epitope of A in tandem with the synthetic universal Th cell pan HLA DR epitope, pan HLA DR-binding peptide (PADRE). Importantly, the PADRE-A 1–15 sequence lacks the T cell epitope of A. Immunization of BALB/c mice with the PADRE-A 1–15 epitope vaccine produced high titers of anti-A Abs. Splenocytes from immunized mice showed robust T cell stimulation in response to peptides containing PADRE. However, splenocytes from immunized mice were not reactivated by the A peptide. New preclinical trials in amyloid precursor protein transgenic mouse models may help to develop novel immunogen-adjuvant configurations with the potential to avoid the adverse events that occurred in the first clinical trial. The Journal of Immunology, 2005, 174: 1580 –1586. A lzheimer’s disease (AD) 4 is the most common form of dementia in the elderly and is characterized by a pro- gressive loss of memory and a general cognitive decline. The neuropathological features of the disease include neurofibril- lary tangles, deposition of -amyloid (A) in senile plaques, and neuronal loss in affected brain regions (1). The A peptide is cleaved from the amyloid precursor protein (APP) by - and -secretases (2– 4) and is believed to play an important role in the onset and progression of AD (5, 6). Many strategies currently be- ing proposed as therapies for AD are aimed at reducing the level of A in the brain or blocking the assembly of the peptide into pathological forms (7). One potentially powerful strategy for reducing the level of A in the brain is immunotherapy, where A-specific Abs facilitate the clearance of A. Active immunization of APP transgenic mice (APP/Tg) with fibrillar A peptide blocked the deposition of A in plaques, prevented the development of dystrophic neurites, and reduced astrogliosis in the mouse brain (8, 9). In addition, when older mice with established A deposits were immunized with A, they were able to clear A plaques from the brain. Other research- ers have reported that active immunization protected mice from developing functional memory deficits (10 –12), and that passive administration of anti-A mAbs to APP/Tg mice also reduced A levels in the brain (13, 14) and reversed memory deficits (15). These results suggest that the generation of Abs against A in humans might provide similar benefits to patients with AD. There were no reported adverse inflammatory events after A immuno- therapy in several animal models, including rabbits, guinea pigs, and monkeys. The only documented adverse incidence to A im- munotherapy was an increase in cerebral hemorrhages in very old, hemorrhage-prone, APP/Tg-23 mice injected with multiple high doses of anti-A mAb (16). Based on the impressive preclinical results, Elan Corp. in col- laboration with Wyeth-Ayerst began the first A immunotherapy clinical trial with their AN-1792 vaccine, a mixture of fibrillar A 42 and the saponin adjuvant QS-21, on AD patients. Unfortu- nately, the phase IIa trial was halted when 6% of the participants in the clinical trial developed aseptic meningoencephalitis (9, 17– 20). The cause of the meningoencephalitis in a subset of the pa- tients has not been definitively determined. However, postmortem examination of brains from two patients who suffered an adverse event to the vaccine revealed the presence of T lymphocyte infil- tration in the leptomeninges, cerebrovasculature, and cerebral neo- cortex (21, 22). This has provided support for the theory that the adverse response to the vaccine was due to a T cell-mediated au- toimmune response (9, 21–23). *Institute for Molecular Medicine, Department of Immunology, Huntington Beach, CA 92647; † Institute for Brain Aging and Dementia, ‡ Department of Neurology, University of California, Irvine, CA 92697 Received for publication July 20, 2004. Accepted for publication November 5, 2004. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported by National Institutes of Health Grants R01AG20241, R01NS050895 (to D.H.C. and M.G.A.) and R01AI44809 (to M.G.A.) and Alzhei- mer’s Association IIRG Grant 03-6279 (to M.G.A. and D.H.C.). 2 M.G.A. and D.H.C. contributed equally to this work. 3 Address correspondence and reprint requests to Dr. David H. Cribbs, Department of Neurology, Institute for Brain Aging and Dementia, 1207 Gillespie NRF, University of California, Irvine, CA 92697-4540. E-mail address: cribbs@uci.edu 4 Abbreviations used in this paper: AD, Alzheimer’s disease; A, -amyloid; APP, amyloid precursor protein; APP/Tg, APP transgenic mice; PADRE, Pan HLA DR- binding peptide; A 42 ,A peptides spanning aa 1– 42, 1– 40 (A 40 ), 1–33 (A 1–33 ), 1–15 (A 1–15 ), and 20–31 (A 20 –31 ); MAP, multiple antigenic peptides; PADRE- A 1–15 -MAP; A 1–33 -MAP; A 1–15 -MAP; A 20 –31 -MAP, peptides attached to PADRE and/or MAP. The Journal of Immunology Copyright © 2005 by The American Association of Immunologists, Inc. 0022-1767/05/$02.00