Development of a novel adjuvant/delivery system to enhance the immunogenicity of sub-unit protein antigens

Infectious diseases encompass 25% of deaths in the world per year. The most effective approach in preventing deaths is vaccination. However, at present, the availability of vaccines for many infectious diseases is still scarce. For this reason, intensive studies are being carried out for the development of vaccines with high efficacy and protection rates. Current vaccines developed mainly are based on recombinant molecules or protein subunits of pathogenic organisms. In this approach, the antigens are safer and their manufacturing in large scale is possible. In spite of these advantages, they require adjuvants to provide effective and long-term immunity because of the inheritance of weak immunogenicity of the aforementioned antigenic structures. Adjuvant research has gained an extra dimension after better understanding of the immune system and immune response mechanisms. Depending on their structure, adjuvants trigger the innate immune response through different mechanisms by behaving or acting like specific pathogen associated molecular patterns. In this study, we combined Salmonella Typhi porin proteins and chitosan to develop a new adjuvant system to increase the immunogenicity of highly purified antigens. For this purpose, chitosan-based gel and nanoparticles having high porin proteins loading efficiency are prepared. The cellular uptake of the formulations was examined by confocal laser microscopy. In-vitro macrophage activation studies were performed by determining surface markers and cytokine release in the J774A.1 mouse macrophage cell line. A significant uptake of porins was observed when combined with chitosan, whilst the porins alone were not taken up by macrophage cells. Further, it was demonstrated in vitro that the porins+chitosan combination systems induced CD80 and MHC-II (p<0.1) expressions as well as TNF-α and IL-6 levels. Furthermore, in vivo studies performed in in BALB/c mice demonstrated that IgG and IgM levels were increased. In conclusion, we have demonstrated that the combination of chitosan+porins significantly increases the immune response, suggesting the developed combined system as a promising adjuvant for subunit vaccines.