CpG-Adjuvanted Virus-like Particle Vaccine Induces Protective Immunity Against <i>Leishmania donovani</i> Infection

Visceral leishmaniasis poses a significant public health challenge due to the lack of an approved human vaccine. We attempted to enhance the efficacy of virus-like particle (VLP) vaccines expressing the Leishmania donovani promastigote surface antigen (LdPSA) by adjuvanting with CpG oligodeoxynucleotide. Here, we evaluated adjuvanted vaccine-induced immune responses and their efficacies in mice challenged with mCherry-expressing L donovani promastigotes. Adjuvanted LdPSA-VLP vaccination significantly elevated parasite-specific IgG serum antibody levels. Additionally, vaccinated mice exhibited enhanced germinal center B cells and splenic T-cell activities as compared with unimmunized mice. Importantly, adjuvanted LdPSA-VLPs reduced the levels of inflammatory cytokines interferon γ and interleukin 6 in visceral organs, leading to decreased total parasite burden and protection against L donovani challenge. Our findings indicate that CpG oligodeoxynucleotide enhanced the protection conferred by LdPSA-VLPs, offering a promising step toward effective visceral leishmaniasis vaccine development.