On the use of adenovirus dodecahedron as a carrier for glycoconjugate vaccines.

Virus-Like Particles (VLPs) have been used as immunogenic molecules in numerous recombinant vaccines. VLPs can also serve as vaccine platform to exogenous antigens, usually peptides incorporated within the protein sequences which compose the VLPs or conjugated to them. We herein described the conjugation of a synthetic tetrasaccharide mimicking the Streptococcus pneumoniae serotype 14 capsular polysaccharide to recombinant adenoviral type 3 dodecahedron, formed by the self-assembling of twelve penton bases and investigated the induced immune response when administered subcutaneously (s.c.). Whether formulated in the form of a dodecahedron or disassembled, the glycoconjugate induced an anti-protein response after two and three immunizations equivalent to that observed when the native dodecahedron was administered. On the other hand, the glycoconjugate induced a weak anti-IgM response which diminishes after two doses but no IgM-to-IgG switch was observed in mice against the serotype 14 capsular polysaccharide. In definitive, the whole conjugation process preserved both particulate nature and immunogenicity of the adenoviral dodecahedron. Further studies are needed to fully exploit adenoviral dodecahedron potential in terms of plasticity towards sequence engineering and of its capacity to stimulate the immune system via the intranasal route of administration as well as to shift the response to the carbohydrate antigen by playing both with the carbohydrate to protein ratio and the length of the synthetic carbohydrate antigen.

Semisynthetic glycoconjugate based on dual role protein/PsaA as a pneumococcal vaccine.

Pneumococcal infections remain a major public health concern worldwide. The currently available vaccines in the market are based on pneumococcal capsular polysaccharides but they still need to be improved to secure an optimal coverage notably in population at risk. To circumvent this, association of virulence pneumococcal proteins to the polysaccharide valencies has been proposed with the hope to observe an additive - if not synergistic - protective effect. Along this line, the use of the highly conserved and ubiquitous pneumococcal surface adhesin A (PsaA) as a protein carrier for a synthetic pneumococcal oligosaccharide is demonstrated herein for the first time. A tetrasaccharide mimicking functional antigenic determinants from the S. pneumoniae serotype 14 capsular polysaccharide (Pn14TS) was chemically synthesised. The mature PsaA (mPsaA) was expressed in E. coli and purified using affinity chromatography. The Pn14PS was conjugated to mPsaA using maleimide-thiol coupling chemistry to obtain mPsaA-Pn14PS conjugate (protein/sugar molar ratio: 1/5.4). The mPsaA retained the structural conformation after the conjugation and lyophilisation. The prepared glycoconjugate adjuvanted with α-galactosylceramide, a potent activator of invariant Natural Killer T cells, was tested in mice for its immunological response upon subcutaneous injection in comparison with mPsaA alone and a model BSA conjugate (BSA-Pn14PS, used here as a control). Mice immunised with the mPsaA-Pn14TS produced a robust IgG response against mPsaA and against the capsular polysaccharide from pneumococcal serotype 14. These data provide the basis for novel pneumococcal vaccine development.