Nonepitopic antibody binding sequence: implications in screening and development of peptide vaccines

Phage display: selecting straws instead of a needle from a haystack

An increasing number of peptides with specific binding affinity to various protein and even non-protein targets are being discovered from phage display libraries. The power of this method lies in its ability to efficiently and rapidly identify ligands with a desired target property from a large population of phage clones displaying diverse surface peptides. However, the search for the needle in the haystack does not always end successfully. False positive results may appear. Thus instead of specific binders phage with no actual affinity toward the target are recovered due to their propagation advantages or binding to other components of the screening system, such as the solid phase, capturing reagents, contaminants in the target sample or blocking agents, rather than the target. Biopanning experiments on different targets performed in our laboratory revealed some previously identified and many new target-unrelated peptide sequences, which have already been frequently described and published, but not yet recognized as target-unrelated. Distinguishing true binders from false positives is an important step toward phage display selections of greater integrity. This article thoroughly reviews and discusses already identified and new target-unrelated peptides and suggests strategies to avoid their isolation.

Peptide dendrimers: applications and synthesis

Peptide dendrimers are radial or wedge-like branched macromolecules consisting of a peptidyl branching core and/or covalently attached surface functional units. The multimeric nature of these constructs, the unambiguous composition and ease of production make this type of dendrimer well suited to various biotechnological and biochemical applications. Applications include use as biomedical diagnostic reagents, protein mimetics, anticancer and antiviral agents, vaccines and drug and gene delivery vehicles. This review focuses on the different types of peptide dendrimers currently in use and the synthetic methods commonly employed to generate peptide dendrimers ranging from stepwise solid-phase synthesis to chemoselective and orthogonal ligation.

A DNA vaccine encoding a peptide mimic of Streptococcus pneumoniae serotype 4 capsular polysaccharide induces specific anti-carbohydrate antibodies in Balb/c mice

Streptococcus pneumoniae is a leading cause of morbidity and mortality in both the developing and developed world. The T-independent nature of the current polysaccharide vaccine renders it ineffective in elderly adults and children <2 years of age. Although the recently licensed conjugate vaccines are capable of producing T-cell-dependent immunity, they also have their limitations, namely a lack of response in certain populations. Our laboratory has focused on a different approach, DNA vaccination. We have defined a peptide sequence (pep4) that mimics the S. pneumoniae serotype 4 capsular polysaccharide (PPS4) using a monoclonal antibody to PPS4 (mAb4) and phage display library. Pep4 was synthesized, complexed to proteosomes and used to immunize mice. We have shown by ELISA that this peptide mimic is capable of eliciting an anti-PPS4 immune response significantly higher than in negative control mice (P<0.05). A PPS4-DNA vaccine was made by cloning an oligodeoxynucleotide encoding pep4 into the HBcAg vector. Following epidermal immunization with the PPS4-DNA vaccine, mice produced an anti-PPS4 antibody response significantly higher than in mice immunized with an impertinent DNA vector (P<0.05). Our results demonstrate the feasibility of peptide mimicry in DNA vaccine development.