Previously we have demonstrated that amphiphilic peptide consisting of a poly (hydrophobic amino acid) sequence such as poly-leucine, and a hydrophilic sequence could help elicit stronger humoral immune responses against peptide antigens [1]. Such amphiphilic peptide sequence can self-assemble into nanoparticles or nanoaggregates, which is beneficial for its recognition by antigen-presentation cells like dendritic cells (DCs), as the size resembles that of natural pathogens like viruses. However, the adjuvant properties of poly (hydrophobic amino acid) have yet to be tested for protein antigens. Current study focuses on the usage of peptide consisting of 10 or 15 leucine residues, and multiple lysine residues synthesized through solid-phase peptide synthesis (SPPS), as an immune stimulator or a delivery system for model protein antigen ovalbumin (OVA).
When mixed physically with such peptide, OVA induced higher total IgG titer in mice compared to that of OVA emulsified in widely used protein antigen adjuvant, alum. As the complexes of protein and peptide formed by electrostatic interaction might not be stable under complicated in vivo conditions, a conjugate of amphiphilic peptide and protein antigen can be more beneficial. Of the variety of conjugation methods [2], maleimide-thiol chemistry was performed to graft these peptides with OVA covalently, however, there was no clear evidence showing the conjugation was successful. It was hypothesized that the electrostatic interaction between positively-charged peptide and negatively-charged protein has blocked the conjugation site, therefore, charged-modified amphiphilic peptide are currently being investigated for the conjugation with OVA.