The present invention discloses novel saponin derivatives for use with nucleic acids that induce an immune response when administered to animals and humans. The novel saponin derivatives disclosed comprise (a) a saponin aglycone core, wherein the aglycone core is covalently linked to one or more oligosaccharide chains; (b) a positively charged cationic chain, and optionally (c) a naturally occurring or synthetic lipophilic chain. Pharmaceutical and veterinary compositions comprising one or more of the novel saponin derivatives and saponin derivative/polynucleotide complexes are also disclosed. Disclosed as well are methods of using the novel saponin derivatives to deliver a polynucleotide molecule to cells of an animal, to stimulate or generate an immune response in an animal, and to generate a detectable immune response in an animal.