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Amyloid-beta (Abeta) immunotherapy has received considerable attention as a promising approach for reducing the level of Abeta in the CNS of Alzheimer's disease patients. However, the first Phase II clinical trial, for the immune therapy AN1792, was halted when a subset of those immunized with Abeta(42) developed adverse events in the central nervous system. In addition, data from the trial indicated that there was a low percentage of responders and generally low to moderate titers in the patients that received the vaccine. Generated antibodies reduced beta-amyloid deposits in the parenchyma of patients' brains, but no reduction in soluble Abeta or significant improvements in cognitive function of patients were observed. These data and data from pre-clinical studies suggest that reduction in the most toxic oligomeric forms of Abeta is important for prevention or slowing down of the progression of cognitive decline, and that vaccination should be started prior to irreversible accumulation of the oligomeric Abeta, at the early stages of AD. Protective immunotherapy requires a development of safe and effective strategy for Abeta immunotherapy. In this review, the rationale for developing epitope vaccines for the treatment of AD will be discussed. We believe that an epitope vaccine will induce an adequate anti-Abeta antibody response in the absence of potentially adverse self T cell-mediated events, making it possible to start immunization at the early stages of AD.

In a seminal report in 1999, Schenk and colleagues demonstrated that vaccination of a mouse model of Alzheimer's disease (AD) with amyloid-beta(1-42) peptide (Abeta(1-42)) and adjuvant resulted in striking mitigation of AD-like pathology - giving rise to the field of AD immunotherapy. Later studies confirmed this result in other mouse models of AD and additionally showed cognitive improvement after Abeta vaccination. Based on these results, early developmental clinical trials ensued to immunize AD patients with Abeta(1-42) plus adjuvant (so-called "active" Abeta immunotherapy; trade name AN-1792; Elan Pharmaceuticals, Dublin, Ireland). However, the phase IIa trial was halted after 6 % of patients developed aseptic meningoencephalitis. Despite occurrence of this adverse event, many individuals demonstrated high serum antibody titres to Abeta and histological evidence of clearance of the hallmark AD pathology, beta-amyloid plaques. While raising justifiable safety concerns, these important results nonetheless demonstrated the feasibility of the active Abeta immunotherapy approach. This review focuses on alternative approaches to active Abeta vaccination that are currently in various stages of development - from pre-clinical studies in animal models to current clinical trials. Specifically, the focus is on those strategies that target inflammatory and immune aspects of AD, and can therefore be classified as immunotherapeutic in a broad sense.

Alzheimer disease (AD) is the most common form of dementia in the elderly and the number of individuals developing the disease is rapidly rising. Interventions focused on reducing beta-amyloid (Abeta), a component of senile plaques within the AD brain offer a promising approach to prevent or slow disease progression. In this review, we describe the immune system and cognitive and neurobiological features of a natural model of human brain aging, the beagle. The immune system of dogs shares many features of the human immune system, including developmental and aging characteristics. Further, dogs naturally accumulate human sequence Abeta as they age, which coincides with declines in learning and memory. A longitudinal study (approximately 2 years) of the response of aged beagles to vaccination with fibrillar Abeta1-42 indicated that despite significant clearance of Abeta, there were limited benefits in cognitive function. However, there was evidence for maintenance of executive function over time. These results are strikingly similar to reports of human clinical immunotherapy trials. We propose that the canine model complements existing animal models and will be helpful in developing new vaccine approaches to slowing or preventing Abeta pathology that can be translated to human clinical trials.