Generation of anti-beta-amyloid antibodies via phage display technology

Applications of the phage display technology in molecular biology, biotechnology and medicine

The phage display technology is based on the presentation of peptide sequences on the surface of virions of bacteriophages. Its development led to creation of sophisticated systems based on the possibility of the presentation of a huge variability of peptides, attached to one of proteins of bacteriophage capsids. The use of such systems allowed for achieving enormous advantages in the processes of selection of bioactive molecules. In fact, the phage display technology has been employed in numerous fields of biotechnology, as diverse as immunological and biomedical applications (in both diagnostics and therapy), the formation of novel materials, and many others. In this paper, contrary to many other review articles which were focussed on either specific display systems or the use of phage display in selected fields, we present a comprehensive overview of various possibilities of applications of this technology. We discuss an usefulness of the phage display technology in various fields of science, medicine and the broad sense of biotechnology. This overview indicates the spread and importance of applications of microbial systems (exemplified by the phage display technology), pointing to the possibility of developing such sophisticated tools when advanced molecular methods are used in microbiological studies, accompanied with understanding of details of structures and functions of microbial entities (bacteriophages in this case).

Anti-Aβ antibodies induced by Aβ-HBc virus-like particles prevent Aβ aggregation and protect PC12 cells against toxicity of Aβ1-40

β-Amyloid peptide (Aβ) immunization is regarded as the most promising therapy to Alzheimer' s disease. The full length Aβ as antigen might induce meningoencepholontis adverse effect since the middle and C-terminal fragments of Aβ contain T cell epitopes. While N-terminal fragment of Aβ, containing B cell epitope, has weak or no immunogenicity. To improve the immunogenicity, we used HBV core antigen as carrier to make fusion protein containing 2 Aβ1-15. The fusion protein was expressed in Escherichia coli harboring the recombinant plasmid pET/c-2Aβ15-c. Transmission electron microscope (TEM) showed that fusion protein could form virus-like particles (VLPs). After 7-weeks immunization with Aβ-HBc VLPs through subcutaneous injection, the titer of anti-Aβ antibody in sera of BALB/c mice reached up to 10(5), higher than Aβ peptide immunization. Aβ-HBc VLPs immunization did not elicit Aβ-specific T cell proliferation. The main isotypes of antibody in mice immunized with Aβ-HBc VLPs were IgG1 and IgG2b, while isotype in mice immunized with Aβ1-42 was IgG2a. When the antisera from mice immunized with Aβ-HBc VLPs were co-incubated for 1 week at 37°C with Aβ, fibers of aggregated Aβ was reduced or diminished. The antibodies also prevented PC12 cells from injury by toxicity of Aβ. In conclusion, recombinant c-2Aβ15-c gene can be expressed in E. coli. The expressed protein could form VLPs and has strong immunogenicity. The antisera prevented Aβ fiber formation and protected the PC12 cells against toxicity of Aβ. This study lays the foundation for the experimental study of AD gene engineering vaccine.

Filamentous bacteriophage fd as an antigen delivery system in vaccination

Peptides displayed on the surface of filamentous bacteriophage fd are able to induce humoral as well as cell-mediated immune responses, which makes phage particles an attractive antigen delivery system to design new vaccines. The immune response induced by phage-displayed peptides can be enhanced by targeting phage particles to the professional antigen presenting cells, utilizing a single-chain antibody fragment that binds dendritic cell receptor DEC-205. Here, we review recent advances in the use of filamentous phage fd as a platform for peptide vaccines, with a special focus on the use of phage fd as an antigen delivery platform for peptide vaccines in Alzheimer's Disease and cancer.

Design and evaluation of a 6-mer amyloid-beta protein derived phage display library for molecular targeting of amyloid plaques in Alzheimer's disease: Comparison with two cyclic heptapeptides derived from a randomized phage display library

Amyloid plaques are the main molecular hallmark of Alzheimer's disease. Specific carriers are needed for molecular imaging and for specific drug delivery. In order to identify new low molecular weight amyloid plaque-specific ligands, the phage display technology was used to design short peptides that bind specifically to amyloid-beta protein, which is the principal component of amyloid plaques. For this purpose, a phage display library was designed from the amino acid sequence of amyloid-beta 1-42. Then, the diversity was increased by soft oligonucleotide-directed mutagenesis. This library was screened against amyloid-beta 1-42 and several phage clones were isolated. Their genomes were sequenced to identify the displayed peptides and their dissociation constants for amyloid-beta 1-42 binding were evaluated by ELISA. The two best peptides, which are derived from the C-terminus hydrophobic domain of amyloid-beta 1-42 that forms a beta-strand in amyloid fibers, were synthesized and biotinylated. After confirming their binding affinity for amyloid-beta 1-42 by ELISA, the specific interaction with amyloid plaques was validated by immunohistochemistry on brain sections harvested from a mouse model of Alzheimer's disease. The thioflavin T aggregation assay has furthermore shown that our peptides are able to inhibit the amyloid fiber formation. They are not toxic for neurons, and some of them are able to cross the blood-brain barrier after grafting to a magnetic resonance imaging contrast agent. To conclude, these peptides have high potential for molecular targeting of amyloid plaques, either as carriers of molecular imaging and therapeutic compounds or as amyloid fiber disrupting agents.

Immunogenicity and therapeutic efficacy of phage-displayed beta-amyloid epitopes

In vitro and in vivo studies indicate that Alzheimer's Disease (AD) could be prevented or treated by active immunization against self-peptide beta-amyloid. In this study, we compared the immunogenicity of different regions of beta-amyloid, displayed on filamentous phages. We established that a filamentous phage displaying epitope 2-6 (AEFRH) of beta-amyloid at the N-terminus of Major Capside Protein (phage fdAD(2-6)) is more immunogenic than a phage displaying epitope 1-7 (DAEFRHD) that differs only in flanking residues. Monthly injections of fdAD(2-6) trigger a robust anti-beta-amyloid antibody response, and afford a significant reduction of plaque pathology in a mouse model of AD, whereas the same treatment, performed with phage fdAD(1-7), induces a lower anti-beta-amyloid titer and does not protect from amyloid deposition. "Memory" anti-amyloid antibodies induced by a single prime-boost cycle with vaccine fdAD(2-6), that have a lower titer compared to antibodies induced by monthly restimulations, do not prevent plaque pathology. Our data show that optimization of epitope display is essential in vaccine design, and suggest that the titer of the anti-amyloid response is the crucial parameter to obtain therapeutic efficacy in vivo.

Mapping of immune responses following wild-type and mutant ABeta42 plasmid or peptide vaccination in different mouse haplotypes and HLA Class II transgenic mice

Although the recent clinical trial of the ABeta42 peptide vaccine against Alzheimer's Disease (AD) has been halted due to adverse events, the apparent clinical utility of this approach underscores the need to further improve the safety of the vaccine, as well as to understand the potential immunological basis for complications. In this study, we examine both humoral and cellular immune responses elicited by immunization with peptide or DNA encoding wild-type and the Flemish and Dutch mutations of ABeta42 (i.e. the beta amyloid peptide spanning amino acids 1-42) in mice of different immune haplotypes as well as HLA Class II transgenic mice. The Flemish and Dutch mutations have been associated with cerebrovascular hemorrhages in affected individuals. These data allow determination of potential immunological responses that could mediate pathology observed with mutant forms of amyloid beta, as well as lead to the generation of safer vaccine preparations. Following peptide or plasmid immunization, antibody responses were measured against the different ABeta42 peptides in an ELISA assay, while T cell epitopes were analyzed through interferon gamma ELISPOT and lymphocyte proliferation assays. B cell mapping studies indicated that sera from all of the haplotype mice vaccinated with any of the ABeta42 peptides reacted specifically to the first 10 amino acids of ABeta42 with the ABeta42 mutants eliciting higher immune responses. ELISPOT analysis, which accessed cellular immune responses indicated that mice expressed differences in Class I epitopes dependent on the different immune haplotypes. These results may have implications for the design of future ABeta42 based vaccines against Alzheimer's Disease.