Development of LIPL32 DNA vaccine for leptospirosis using modified chitosan nanoparticles

Abstract

Leptospirosis is a global zoonotic disease and public health problem in Thailand. In this study, we have developed a DNA vaccine by using mannosylated chitosan nanoplaticle-encapsulating plasmid carrying lipL32. The efficiency of the system was evaluated in vitro and in vivo. After transfection of plasmid containing full-length lipL32 gene (pVITRO-lipL32) into HEK293T cells, LipL32 was expressed in both the cell lysate and culture supernatant. The chitosan nanoparticles were modified by mannosylation to specifically target antigen presenting cells expressing mannose receptors, such as macrophages and dendritic cells. The chitosan and mannosylated chitosan nanoparticles were able to completely encapsulate the lipL32 DNA vaccine (CS-pVITRO-lipL32 and MC-pVITRO-lipL32, respectively). When RAW 264.7 cells were transfected with CS-pVITRO-lipL32 or MC-pVITRO-lipL32, no cytotoxicity was observed, and expression of LipL32 was detected. To evaluate immunogenicity, BALB/c mice were immunized with CS-pVITRO-lipL32 and MC-pVITRO-lipL32. Total IgG level of mice immunized with MC-pVITRO-lipL32 was significantly higher than that of CS-pVITRO-lipL32 and naked plasmid (pVITRO-lipL32) at 8 week of immunization (p<0.05). In addition, mice immunized with MC-pVITRO-lipL32 vaccine tended to develop toward Th1 response but at the lower extent than that of chitosan-conjugated vaccine. Our results suggest that CS and MC nanoparticles are efficient delivery systems for lipL32 DNA vaccine to specifically induce humoral and Th1-predilected cell-mediated immune responses.