The delivery of exogenous antigen to antigen presenting cells (APC) for processing and presentation is the first step in the generation of immune responses. We have utilized mannan or mannose as a vehicle to target protein and peptide antigens to mannose binding receptors on antigen presenting cells. In these studies antigen (protein or peptides) conjugated to oxidized mannan (OxMan) generated cellular immune responses in mice whilst antigen conjugated to reduced mannan (RedMan) gave humoral immune responses. These differential immune responses are due to the ability of OxMan to deliver exogenous conjugated antigen to the cytoplasm of APC (macrophages and DC). We have now used OxMan and RedMan to deliver DNA and RNA to APC. Mannan conjugates of poly-lysine (PLL) and polyethyleneimine (PEI) successfully complexed with DNA and RNA as evidenced by retardation on agarose gel electrophoresis. OxMan-PEI or PLL complexed with DNA or RNA transfected mannose receptor expressing J774 cells as well as bone marrow-derived dendritic cells. Mice immunized with OxMan-PLL-DNA conjugate were protected from a challenge of OVA expressing tumour cells. The combination of mannose receptor targeting and immunomodulating properties of OxMan results in an excellent adjuvant/delivery system.