Short amyloid-β immunogens with spacer-enhanced immunogenicity without junctional epitopes for Alzheimer's disease...

Induction of an immune response to amyloid-β (Aβ) protein is effective in treating animal models of Alzheimer's disease. The Aβ1-15 sequence contains the antibody epitope(s), but lacks the T-cell reactive sites of full-length Aβ1-42. We tested two alternative peptide immunogens encompassing either a tandem repeat of GPGPG-linked Aβ1-15 sequences (2Aβ15-linker) or a tandem repeat Aβ1-15 without the spacer sequence (2Aβ15). Titers of the immunized sera were measured by indirect ELISA. We analyzed the production of interferon-γ and interleukin-4 cytokine by lymphocytes and CD4 T-cells using ELISPOT and FACS assays; we then measured CD4 T-cell proliferation using a CFSE-based lymphoproliferation assay. Immunization with 2Aβ15-linker resulted in a high anti-Aβ titer of the noninflammatory T-helper 2 isotype, a lack of lymphocyte proliferation against the spacer part peptide. We observed much lower titers against the Aβ protein after immunization with 2Aβ15. Restimulation of lymphocytes with the corresponding immunogens resulted in proliferative responses, which showed that the sequential arrangement of the epitopes created junctional epitopes. The disruption of junctional epitopes through the introduction of a GPGPG spacer restored the immunogenicity against all the epitopes. Our novel immunogen with spacer may be a safer alternative to a peptide-based vaccine.