Background: Active immunization against Aβ was reported to have a therapeutic effect in murine models of Alzheimer's disease. Clinical Aβ vaccination trial AN1792 was interrupted due to the development in 6 % of the patients of meningoencephalitis likely involving pro-inflammatory CD4(+) T cells. However, the potential implication of auto-aggressive anti-Aβ CD8(+) T cells has been poorly investigated.
Methods: Potential MHC-I-restricted Aβ-derived epitopes were first analyzed for their capacity to recruit functional CD8(+) T cell responses in mouse models. Their impact on migration of CD8(+) T cells into the brain parenchyma and potential induction of meningoencephalitis and/or neuronal damage was investigated upon vaccination in the APPPS1 mouse model of AD.
Results: We identified one nonamer peptide, Aβ33-41, which was naturally processed and presented in association with H-2-D(b) molecule on neurons and CD11b(+) microglia. Upon optimization of anchor residues for enhanced binding to H-2-D(b), immunization with the modified Aβ33-41NP peptide elicited Aβ-specific IFNγ-secreting CD8(+) T cells, which are cytotoxic towards Aβ-expressing targets. Whereas T cell infiltration in the brain of APPPS1 mice is dominated by CD3(+)CD8(-) T cells and increases with disease evolution between 4 and 7 months of age, a predominance of CD3(+)CD8(+) over CD3(+)CD8(-) cells was observed in 6- to 7-month-old APPPS1 but not in WT animals, only after vaccination with Aβ33-41NP. The number of CD11b(+) mononuclear phagocytes, which significantly increases with age in the brain of APPPS1 mice, was reduced following immunization with Aβ33-41NP. Despite peripheral activation of Aβ-specific CD8(+) cytotoxic effectors and enhanced infiltration of CD8(+) T cells in the brain of Aβ33-41NP-immunized APPPS1 mice, no clinical signs of severe autoimmune neuroinflammation were observed.
Conclusions: Altogether, these results suggest that Aβ-specific CD8(+) T cells are not major contributors to meningoencephalitis in response to Aβ vaccination.