Molecular basis of improved immunogenicity in DNA vaccination mediated by a mannan based carrier

Receptor mediated gene delivery is an attractive non-viral method for targeting genetic material to specific cell types. We have previously utilized oxidized (OMPLL) and reduced mannan poly-l-lysine (RMPLL) to target DNA vaccines to antigen presenting cells and demonstrated that it could induce far stronger immune responses in mice compared to naked DNA immunization. In this study, we describe the immune enhancing attributes of mannan-PLL mediated DNA vaccination at the molecular level. Several attributes observed in similar gene delivery conjugates, such as entry via the endocytic pathway, low toxicity, protection from nucleases and compaction of particle size, were also evident here. In addition, OMPLL and RMPLL conjugates had profound effects on the antigen presentation functions of dendritic cells and macrophages, through the stimulation of cytokine production and maturation of dendritic cells. Interestingly, we demonstrate that OMPLL–DNA and RMPLL–DNA are able to mediate dendritic cell activation via toll-like receptor 2 as opposed to mannan alone which mediates via toll-like receptor 4. Overall, this report leads to greater understanding of how oxidized and reduced mannan mediated gene delivery could augment immune responses to DNA vaccination and provide insights into ways of further improving its immunogenicity.