Xanthan gum enhances humoral immune response elicited by a DNA vaccine against leptospirosis in mice

Background Traditional vaccines (killed or inactivated) played vital roles in controlling and eradicating infectious diseases for a long time. Antigen-specific T cell response can be induced when mice are intramuscularly inoculated with naked plasmid DNA. Therefore, DNA vaccines were evaluated in many studies, demonstrating its safety, stability and easy production. Furthermore, it has been reported that the gene expression lasted for one year after intramuscular injection of the plasmid DNA. However, some disadvantages such as the low transfection rate and low immunogenicity make the use of multiple doses necessary [1]. In light of this context, several studies have been performed to improve the immune response induced by DNA vaccines. The xanthan gum is an extracellular polysaccharide produced during fermentation of bacteria of the genus Xanthomonas and has been studied as a new vaccine adjuvant [2]. However, it has not yet been evaluated as an adjuvant for DNA vaccines. The aim of this study was to evaluate the capacity of the xanthan gum to increase the humoral immune response of mice inoculated with a DNA vaccine against a fragment of the leptospiral antigen LigAni cloned in the mammalian expression plasmid pTARGET.