Short amyloid-beta immunogens show strong immunogenicity and avoid stimulating pro-inflammatory pathways in bone marrow-derived dendritic cells from C57BL/6J mice in vitro

Abstract

Amyloid beta peptide 1–15 (Aβ1–15) and its derivatives have attracted the attention of the scientific community as candidate vaccines for Alzheimer's disease (AD) immunotherapy. Recent studies suggested that Aβ1–42 modulated the immune system by inducing pro-inflammatory dendritic cells (DCs) with reduced antigen-presenting function. However, it remains elusive how Aβ1–15 impacts DCs function. We therefore investigated the modulation by short Aβ peptides of DCs from C57Bl/6J mice. Two new immunogens, a tandem repeat of two-lysine-linked Aβ1–15 sequences with or without an addition of a RGD motif, were tested. Chemotaxis, endocytosis, antigen presenting function and producing cytokines were measured. Both peptides increased migration/endocytosis of immature DCs and MHC II molecule expression/alloreactive T cell activation in TNF-α-matured DCs. In addition, they exhibited decreased production of Th1/Th2 cytokines and pro-inflammatory cytokines. Overall, the two peptides demonstrated strong immunogenicity but did not stimulate pro-inflammatory pathways. These results support the use of short Aβ immunogens in AD immunotherapy.

Introduction

The pathological hallmarks of Alzheimer's disease (AD) are intracellular neurofibrillary tangles consisting of hyperphosphorylated tau protein and extracellular senile plaque deposits, comprised mainly of amyloid beta (Aβ) peptide. Aβ, the main constituent of amyloid plaques, is believed to be the main causative factor of AD pathogenesis [11], [21]. Aβ is formed after sequential cleavage of the amyloid precursor protein by β- and γ-secretases. The most common isoforms are Aβ₄₀ and Aβ₄₂.

Aβ immunotherapy has attracted significant attention since the first dramatic success in a mouse model of AD [29]. Initial human trials of active Aβ1–42 vaccination (AN1792), however, were halted early because of meningoencephalitis in 6% of subjects [25]. The failure might be ascribed to a promiscuous T cell epitope, which is located within Aβ15-42 and known to activate Aβ specific T cells [8], [22], [23], [39]. Short immunogens, which include B cell epitopes but lack T cell epitopes, such as Aβ1–15 and its derivatives, have shown promise as immunogens. Recent studies suggest that Aβ1–42 modulates the immune system by inducing pro-inflammatory dendritic cells (DCs) with reduced antigen-presenting function [4], [5]. It was therefore of interest to investigate how Aβ1–15 or its derivatives would impact DCs function.

We tested two immunogens, which were a tandem repeat of two-lysine-linked Aβ1–15 sequences (P1) with the addition of an Arg-Gly-Asp (RGD) motif (P2). The aim of this study was to analyze safety and immunogenicity of the peptides by examining DC function.