Enhanced Th2 immunity after DNA prime–protein boost immunization with amyloid β (1–42) plus CpG oligodeoxynucleotides in aged rats

Generation and accumulation of fibrillar amyloid β (Aβ) is widely considered as the pathogenic basis of neurodegeneration in Alzheimer's disease (AD). Both active immunization with fibrillar Aβ and passive immunization with anti-Aβ antibodies in transgenic mouse models of AD result in prevention/dissociation of Aβ plaque formation and restoration of cognitive functions. However, similar immunization studies in humans had to be halted because 6% of the AD patients developed acute meningoencephalitis, likely due to anti-Aβ specific autoimmune Th1 cells. Hence, making Aβ immunotherapy successful requires production of strong antibody responses without Th1-type immunity. In an attempt to develop safer vaccines, we examined the influence of oligodeoxynucleotides as adjuvant on the Th1 and Th2 immune response to Aβ in aged rats. We further investigated whether a DNA prime–protein boost strategy could elicit a more robust Th2 response. The results of the present study showed that all the animals injected with either Aβ peptide alone or Aβ encoding plasmid alone or plasmid DNA prime followed by peptide boost have elicited specific anti-Aβ antibodies. When co-administered, synthetic oligodeoxynucleotides (ODN) further enhanced the anti-Aβ titres. More importantly, the IgG subclasses of the antibodies generated by DNA prime–peptide boost regimen with ODN as adjuvant were primarily of IgG2b and IgG1 isotypes, suggesting that heterologous immunization strategy along with ODN would be advantageous in eliciting more beneficial Th2-type humoral immune response.