The identification of immunogenic glycotopes that render glycoconjugate vaccines protective is key to improving vaccine efficacy. Synthetic oligosaccharides are an attractive alternative to the heterogeneous preparations of purified polysaccharides that most marketed glycoconjugate vaccines are based on. To investigate the potency of semi- synthetic glycoconjugates, we chose the least efficient serotype in the current pneumococcal conjugate vaccine Prevnar 13™, Streptococcus pneumoniae serotype 3 (ST3). Glycan arrays containing synthetic ST3 repeating unit oligosaccharides were used to screen a human reference serum for antibodies and to define the recognition site of two ST3-specific protective monoclonal antibodies. The glycan array screens identified a tetrasaccharide that was selected for in-depth immunological evaluation. The tetrasaccharide-CRM197 carrier protein conjugate elicited protective immunity as evidenced by opsonophagocytosis assays and protection against pneumonia caused by ST3 in mice. Formulation of the defined protective lead candidate glycotope has to be further evaluated to elicit optimal long-term immunity.

Fluorescein-labeled α- and β-octaarginine amides were synthesized. The route, by which these oligoarginine (OA) derivatives enter cells (hepatocytes, fibroblasts, macrophages), was investigated by confocal fluorescence microscopy. Comparisons (by co-localization experiments) with compounds of known penetration modes revealed that the β-octaarginine amide also uses multiple pathways to enter cells. There was no difference between the α- and the β-OAs. Like other cell-penetrating peptides (CPPs), the β-octaarginine eventually winds up in the nucleoli of the cell nuclei (cf. Chem. Biodiversity, 2004, 1, 65). Surprisingly, there was no entry of α- or β-OA into intact and healthy human erythrocytes (which do not possess a nucleus). Blood cells infected by Plasmodium falciparum (malaria parasite) were, however, entered readily, and the OAs went all the way through a couple of membranes into the parasite. The potential of these results for delivering specific antimalarial drugs directly into the parasite is discussed.

No abstract