The amyloid-β (Aβ) peptide has a central role in the neurodegeneration of Alzheimer disease (AD). Immunization of AD transgenic mice with Aβ1–42 (Aβ42) peptide reduces both the spatial memory impairments and AD-like neuropathologic changes in these mice. Therapeutic immunization with Aβ in patients with AD was shown to be effective in reducing Aβ deposition, but studies were discontinued owing to the development of an autoimmune, cell-mediated meningoencephalitis. We hypothesized that gene vaccination could be used to generate an immune response to Aβ42 that produced antibody response but avoided an adverse cell-mediated immune effect.
To develop an effective genetic immunization approach for treatment and prevention of AD without causing an autoimmune, cell-mediated meningoencephalitis.
Mice were vaccinated with a plasmid that encodes Aβ42, administered by gene gun. The immune response of the mice to Aβ42 was monitored by measurement of (1) antibody levels by enzyme-linked immunosorbent assay (ELISA) and Western blot and (2) Aβ42-specific T-cell response as measured by interferon-γ enzyme-linked immunospot (ELISPOT) assay.
Gene-gun delivery of the mouse Aβ42 dimer gene induced significant humoral immune responses in BALB/c wild-type mice after 3 vaccinations in 10-day intervals. All 3 mice in the treated group showed significant humoral immune responses. The ELISPOT assay for interferon-γ release with mouse Aβ42 peptide and Aβ9–18 showed no evident cytotoxic T-lymphocyte response. We further tested the responses of wild-type BALB/c mice to the monomer Aβ42 gene vaccine. Western blot evaluation showed both human and mouse Aβ monomer gene vaccine elicited detectable humoral immune responses. We also introduced the human Aβ42 monomer gene vaccine into AD double transgenic mice APPswe/PSEN1(A246E). Mice were vaccinated with plasmids that encode Aβ1–42 and Aβ1–16, or with plasmid without the Aβgene. Treated mice showed significant humoral immune responses as demonstrated by ELISA and by Western blot. These mice also showed no significant cellular immune response as tested by ELISPOT. One of the treated mice was killed at 7 months of age for histological observations, and scattered amyloid plaques were noted in all layers of the cerebral cortex and in the hippocampus in both Aβ42- and control-vaccinated mice. No definite difference was discerned between the experimental and control animals.
Gene-gun–administered genetic immunization with the Aβ42 gene in wild-type BALB/c and AD transgenic mice can effectively elicit humoral immune responses without a significant T-cell–mediated immune response to the Aβ peptide. This immunotherapeutic approach could provide an alternative active immunization method for therapy and prevention of AD.