Conformation-sensitive antibodies against Alzheimer amyloid-β by immunization with a thioredoxin-constrained B-cell epitope peptide

Immunotherapy against the amyloid-beta(A beta) peptide is a valuable potential treatment for Alzheimer disease ( AD). An ideal antigen should be soluble and nontoxic, avoid the C-terminally located T-cell epitope of A beta, and yet be capable of eliciting antibodies that recognize A beta fibrils and neurotoxic A beta oligomers but not the physiological monomeric species of A beta. We have described here the construction and immunological characterization of a recombinant antigen with these features obtained by tandem multimerization of the immunodominant B-cell epitope peptide A beta 1-15 (A beta 15) within the active site loop of bacterial thioredoxin (Trx). Chimeric Trx(A beta 15)(n) polypeptides bearing one, four, or eight copies of A beta 15 were constructed and injected into mice in combination with alum, an adjuvant approved for human use. All three polypeptides were found to be immunogenic, yet eliciting antibodies with distinct recognition specificities. The anti-Trx(A beta 15)(4) antibody, in particular, recognized A beta 42 fibrils and oligomers but not monomers and exhibited the same kind of conformational selectivity against transthyretin, an amyloidogenic protein unrelated in sequence to A beta. We have also demonstrated that anti-Trx(A beta 15)(4), which binds to human AD plaques, markedly reduces A beta pathology in transgenic AD mice. The data indicate that a conformational epitope shared by oligomers and fibrils can be mimicked by a thioredoxin- constrained A beta fragment repeat and identify Trx(A beta 15)(4) as a promising new tool for AD immunotherapy.