Alzheimer's disease abeta vaccine reduces central nervous system abeta levels in a non-human primate, the Caribbean vervet.

Amyloid beta (Abeta) protein immunotherapy lowers cerebral Abeta and improves cognition in mouse models of Alzheimer's disease (AD). Here we show that Caribbean vervet monkeys (Chlorocebus aethiops, SK) develop cerebral Abeta plaques with aging and that these deposits are associated with gliosis and neuritic dystrophy. Five aged vervets were immunized with Abeta peptide over 10 months. Plasma and cerebral spinal fluid (CSF) samples were collected periodically from the immunized vervets and five aged controls; one monkey per group expired during the study. By Day 42, immunized animals generated plasma Abeta antibodies that labeled Abeta plaques in human, AD transgenic mouse and vervet brains; bound Abeta1-7; and recognized monomeric and oligomeric Abeta but not full-length amyloid precursor protein nor its C-terminal fragments. Low anti-Abeta titers were detected in CSF. Abetax-40 levels were elevated approximately 2- to 5-fold in plasma and decreased up to 64% in CSF in immunized vervets. Insoluble Abetax-42 was decreased by 66% in brain homogenates of the four immunized animals compared to archival tissues from 13 age-matched control vervets. Abeta42-immunoreactive plaques were detected in frontal cortex in 11 of the 13 control animals, but not in six brain regions examined in each of the four immunized vervets. No T cell response or inflammation was observed. Our study is the first to demonstrate age-related Abeta deposition in the vervet monkey as well as the lowering of cerebral Abeta by Abeta vaccination in a non-human primate. The findings further support Abeta immunotherapy as a potential prevention and treatment of AD.

Evidence for peripheral clearance of cerebral Abeta protein following chronic, active Abeta immunization in PSAPP mice.

Immunization with amyloid-beta (Abeta) peptide in mouse models of Alzheimer's disease has been reported to decrease cerebral Abeta levels and improve behavioral deficits. Several mechanisms have been proposed, including antibody-induced phagocytosis of Abeta by cerebral microglia and increased efflux of Abeta from the brain to the periphery. The latter mechanism was suggested in mice undergoing acute, passive transfer of an Abeta monoclonal antibody. Here, PSAPP transgenic mice were actively immunized by a single intraperitoneal injection of synthetic Abeta followed by chronic intranasal administration of Abeta with the mucosal adjuvant, Escherichia coli heat-labile enterotoxin, LT, twice weekly for 8 weeks. Serum from Abeta-immunized mice had an average of 240 microg/ml of anti-Abeta-specific antibodies; these antibodies had epitope(s) within Abeta1-15 and were of immunoglobulin (Ig) isotypes IgG2b, IgG2a, and IgG1. Immunization led to a 75% decrease in plaque number (P < 0.0001) and a 58% decrease in Abetax-42 levels (P < 0.026) in brain, and gliosis and neuritic dystrophy were diminished. No pathological effects of the immunization were observed in kidney, spleen, or snout. Serum Abeta levels increased 28-fold in immunized mice (53.06 ng/ml) compared to controls (1.87 ng/ml). Most of the Abeta in the serum of the immunized mice was bound to antibodies. We conclude that following active immunization, anti-Abeta antibodies sequester serum Abeta and may increase central nervous system to serum Abeta clearance.

Amyloid-beta immunization in Alzheimer's disease transgenic mouse models and wildtype mice.

Alzheimer's disease is the most prevalent form of dementia worldwide. Therapies are desperately needed to prevent and cure the disease. Mouse models of amyloid-beta deposition [APP and PSAPP transgenic (tg) mice] have been useful in determining the role of amyloid-beta (A beta) in both the pathogenesis and cognitive changes in AD. In addition, they have allowed scientists to investigate potential AD therapies in living animals. Active and passive A beta immunizations have been employed successfully in APP and PSAPP tg mice to lower cerebral A beta levels and improve cognition. Optimization of immunization protocols and characterization of immune responses in wildtype mice have been reported. Based on the promising results of A beta immunization studies in mice, a clinical trial was initiated for A beta vaccination in humans with AD. Although no adverse effects were reported in the Phase I safety trials, about 5% of AD patients in the phase II clinical trial developed meningoencephalitis, ending the trial prematurely in March 2002. Studies in AD mouse models and wildtype mice may help elucidate the mechanism for these unwanted side effects and will be useful for testing newer, safer vaccines for future use in human clinical trials.

Abeta1-15 is less immunogenic than Abeta1-40/42 for intranasal immunization of wild-type mice but may be effective for "boosting".

Immunizing mouse models of Alzheimer's disease (AD) against beta-amyloid (Abeta) leads to a decrease in cerebral Abeta burden as well as an improvement in behavioral deficits. Circulating Abeta-antibodies may be responsible for interfering with Abeta deposition. In the present study, we attempted to initiate more robust antibody production in wild type (WT) mice. Three immunization strategies were examined: intranasal (i.n.) immunization with Abetal-15 or full-length Abeta1-40/42, i.n. administration of Abeta combined with mucosal adjuvants, native labile enterotoxin (LT) or its non-toxic form, LT(R192G), and prime-boost regimes. Using Abeta1-15 as the primary immunogen for intranasal immunization did not initiate strong antibody production. When Abeta1-15 or Abeta1-40/42 was combined with native LT or LT(R192G), antibody production was significantly increased. Nasal immunization with Abeta1-15 and native LT successfully "boosted" an immune response "primed" by an intraperitoneal (i.p.) injection of Abeta1-40/42, producing moderately high Abeta titers that remained stable for at least 6 months. Serum anti-Abeta antibodies, regardless of the length of the Abeta immunogen, consistently detected human AD plaques, had epitopes within Abeta1-15, and were predominantly of the IgG2b, IgG1, and IgG2a isotypes. The adjuvants were well-tolerated in the mice. Thus, Abeta1-15 may have potential as a safer, more cost-effective "boosting" immunogen than the full-length Abeta peptide for chronic, active Abeta immunization.

Intranasal immunotherapy for the treatment of Alzheimer's disease: Escherichia coli LT and LT(R192G) as mucosal adjuvants.

Alzheimer's disease (AD) is the most common form of dementia worldwide, yet there is currently no effective treatment or cure. Extracellular deposition of amyloid-beta protein (Abeta) in brain is a key neuropathological characteristic of AD. In 1999, Schenk et al. first reported that an injected Abeta vaccine given to PDAPP mice, an AD mouse model displaying Abeta deposition in brain, led to the lowering of Abeta levels in brain. In 2000, we demonstrated that intranasal (i.n.) immunization with human synthetic Abeta1-40 peptide for 7 months led to a 50-60% reduction in cerebral Abeta burden in PDAPP mice; serum Abeta antibody titers were low (approximately 26 microg/ml). More recently, we have optimized our i.n. Abeta immunization protocol in wild-type (WT) mice. When low doses Escherichia coli heat-labile enterotoxin (LT) were given as a mucosal adjuvant with Abeta i.n., there was a dramatic 12-fold increase in Abeta antibody titers in WT B6D2F1 mice treated two times per week for 8 weeks compared to those of mice receiving i.n. Abeta without adjuvant. A non-toxic form of LT, designated LT(R192G), showed even better adjuvanticity; anti-Abeta antibody titers were 16-fold higher than those seen in mice given i.n. Abeta without adjuvant. In both cases, the serum Abeta antibodies recognized epitopes within Abeta1-15 and were of the immunoglobulin (Ig) isotypes IgG2b, IgG1, IgG2a and low levels of IgA. This new and improved Abeta vaccine protocol is now being tested in AD mouse models with the expectation that higher Abeta antibody titers may be more effective in reducing cerebral Abeta levels.

The generation and characterization of potentially therapeutic Abeta antibodies in mice: differences according to strain and immunization protocol.

Previous studies have shown that in various mouse models of Alzheimer's disease (AD), amyloid beta-protein (Abeta) antibodies generated by Abeta peptide immunization resulted in the prevention of Abeta plaque formation in brains of young mice, decreased Abeta plaque burdens in older mice and improved cognition. The purpose of this study was to optimize Abeta immunization protocols for future trials in transgenic mouse models of AD. The timing and titers of Abeta antibody production, as well as epitope(s) and imunoglobulin isotypes, were compared between two different mouse strains (C57BL/6 and B6D2F1) and five treatment protocols: (1). chronic Abeta nasal administration, (2). repeated Abeta intraperitoneal (i.p.) injection, (3). one i.p. injection followed by chronic Abeta nasal administration, (4). chronic and concurrent Abeta nasal administration + Abeta i.p. injection, and (5). untreated controls. B6D2F1 mice generated Abeta antibodies earlier and in higher quantities than the C57BL/6 mice, indicating that B6D2F1 mice are more responsive to Abeta immunization. For both strains, mice that received the combination of Abeta nasal + Abeta i.p. injection showed the highest antibody titers. Epitope mapping experiments indicated that the mouse anti-Abeta antibodies recognize residues within Abeta1-15. Immunoglobulin isotyping demonstrated that the Abeta antibodies are of the Th-2 anti-inflammatory type, IgG1 and IgG2b, with a few IgM. Currently there is no effective therapy for Alzheimer's disease; thus if Abeta immunization proves effective, it would be a significant step in the prevention and/or treatment of this devastating disease.