Gold nanoparticles as carriers of streptococcus pneumoniae carbohydrate antigens fully synthetic vaccines

In the last years, gold nanoparticles have been largely evaluated as multivalent systems bearing biomolecules, thanks to their peculiarities. In particular, gold nanoparticles functionalized with (oligo)saccharides (gold glyconanoparticles, GNPs) have been developed in order to mimic the natural presentation of the carbohydrate coating which is present at the cell or pathogen surface. They are non-cytotoxic, soluble in biological media and easy to prepare and purify. Recently, GNPs coated with the tetrasaccharide Gal(β1-4)Glc(β1-6)[Gal(β1-4)]βGlcNAc repeating unit of Streptococcus pneumoniae (SP) 14 capsular polysaccharide, OVA323-339 peptide as T helper cell, and β-D-glucoside to assist water solubility, in different molar ratio, were developed as synthetic conjugate vaccine4. The GNP bearing SP14/Glc/OVAp in 45:50:5 ratio resulted in the most active, able to induce IgG antibodies against native polysaccharide of S. Pneumoniae serotype 14. According to this result, we decided to prepare different GNPs bearing an analogue of the trisaccharide repeating unit ManNAc(β1-4)Glc(α1-2)Rha(α1-OPO3-→) of the 19F serotype of S. pneumoniae, alone or together with the tetrasaccharide of serotype 14. The idea is to develop new multiantigenic systems displaying different carbohydrate antigens arranged on a single nanoparticle. To prepare these GNPs, we have first synthesized the analogue of the trisaccharide antigen and a β-D-glucoside suitably functionalized with a thiol-ending linker in order to load them on the gold surface. The GNPs obtained, have been characterized by Transmission Electron Microscopy (TEM), Ultraviolet-Visible (UV/Vis), Circular Dichroism (CD), and Nuclear Magnetic Resonance (NMR). They show an exceptionally small core and uniform dispersion. Also, they are well soluble and stable in water. All the GNPs herein reported will be tested in vivo in mice to evaluate their ability to induce specific IgG antibodies against native capsular polysaccharide of S. pneumoniae type 14 and 19F.