Refinement of a DNA based Alzheimer disease epitope vaccine in rabbits

Abstract

We previously demonstrated that our second-generation DNA-based Alzheimer disease (AD) epitope vaccine comprising three copies of a short amyloid-β (Aβ) B cell epitope, Aβ₁₁ fused with the foreign promiscuous Th epitope, PADRE (p3Aβ₁₁-PADRE) was immunogenic in mice. However, since DNA vaccines exhibit poor immunogenicity in large animals and humans, in this study, we sought to improve the immunogenicity of p3Aβ₁₁-PADRE by modifying this vaccine to express protein 3Aβ₁₁-PADRE with a free N-terminal aspartic acid fused with eight additional promiscuous Th epitopes. Generated pN-3Aβ₁₁-PADRE-Thep vaccine has been designated as AV-1955. We also delivered this vaccine using the TriGrid electroporation system to improve the efficiency of DNA transfection. This third-generation DNA epitope vaccine was evaluated for immunogenicity in rabbits in comparison to the parent construct p3Aβ₁₁-PADRE. AV-1955 vaccination induced significantly stronger humoral immune responses in rabbits compared with p3Aβ₁₁-PADRE vaccine. Anti-Aβ₁₁ antibodies recognized all forms of human β-amyloid peptide (monomers, oligomers and fibrils), bound to amyloid plaques in brain sections from an AD case and reduced oligomer- and fibril-mediated cytotoxicity ex vivo. These findings suggest that AV-1955 could represent an effective DNA epitope vaccine for AD therapy, pending safety and efficacy studies that are currently being conducted in Rhesus monkeys.

Keywords: :

• Alzheimer disease
• DNA vaccine
• T helper epitope
• electroporation
• humoral immune responses

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We would like to thank A. Poghosyan, B. Ellefsen, M. Valenzuela, T. Marquez and L. Chau for technical help. We also thank Dr Annette Marleau, Dr Claire F. Evans and Drew Hannaman for help with editing and valuable comments. This work was supported by funding from NIH (NS-50895, NS-065518, AG-20241 and NS-057395). H.D. and N.M. were supported by NIA T32 training grant (AG000096). Additional support for AD case tissues was provided by University of California, Irvine Alzheimer Disease Research Center Grant P50 AG16573.