A Modification-Specific Peptide-Based immunization Approach Using CRM197 Carrier Protein: Development of a Selective Vaccine Against Pyroglutamate Aβ Peptides

Abstract

Strategies aimed at reducing cerebral accumulation of the amyloid-β (Aβ) peptides have therapeutic potential in Alzheimer's disease (AD). Aβ immunization has proven to be effective at promoting Aβ clearance in animal models but adverse effects have hampered its clinical evaluation. The first anti-Aβ immunization clinical trial, which assessed a full-length Aβ1-42 vaccine, increased the risk of encephalitis most likely because of autoimmune pro-inflammatory T helper 1 (Th1) response against all forms of Aβ. Immunization against less abundant but potentially more pathologically relevant Aβ products, such as N-terminally-truncated pyroglutamate-3 Aβ (AβpE3), could provide efficacy and improve tolerability in Aβ immunotherapy. Here, we describe a selective vaccine against AβpE3, which uses the diphtheria toxin mutant CRM197 as carrier protein for epitope presentation. CRM197 is currently used in licensed vaccines and has demonstrated excellent immunogenicity and safety in humans. In mice, our AβpE3:CRM197 vaccine triggered the production of specific anti-AβpE3 antibodies that did not cross-react with Aβ1-42, non-cyclized AβE3, or N-terminally-truncated pyroglutamate-11 Aβ (AβpE11). AβpE3:CRM197 antiserum strongly labeled AβpE3 in insoluble protein extracts and decorated cortical amyloid plaques in human AD brains. AntiAβpE3 antibodies were almost exclusively of the IgG1 isotype, suggesting an anti-inflammatory Th2 response bias to the AβpE3:CRM197 vaccine. To the best of our knowledge, this study shows for the first time that CRM197 has potential as a safe and suitable vaccine carrier for active and selective immunization against specific protein sequence modifications or conformations, such as AβpE3.

Recent developments in chemical conjugation strategies targeting native amino acids in proteins and their applications in antibody–drug conjugates

“…CRM 197 is used as a carrier protein for vaccines, for epitope presentation. 148 The in vivo study showed that the antibodies generated by the oxetane-stapled CRM 197 had a 3-fold higher avidity (avidity index ¼ 0.8 : 0.4 M) for the protein antigen compared to the intact CRM 197 (avidity index ¼ 0.3 : 0.1 M).…”

Cognizance of posttranslational modifications in vaccines: A way to enhanced immunogenicity

“…The vaccine for Alzheimer's AN1792, composed of full‐length Aβ1‐42, has come up with the threat of meningoencephalitis due to the autoimmune Th1 response in contrast to all forms of Aβ (Fox et al, 2005 ; Orgogozo et al, 2003 ). To overcome this risk and minimize the accumulation of Aβ, the authors have utilized the chemically synthesized AβpE3‐8 and AβpE11‐16 peptides that were having C‐terminal amidated and cysteine bridged with two‐glycine residues (pEFRHDSGGC and pEVHHQKGGC, respectively) (Vingtdeux et al, 2016 ). Targeting the N‐terminal truncated pyroglutamate‐3 Aβ (AβpE3), a potential Aβ product could be a possible way for the acceptability of immunotherapy in Aβ of amyloid plaques.…”