Polymeric Delivery Systems as a Potential Vaccine against Visceral Leishmaniasis: Formulation Development and Immunogenicity

Recent studies suggest that the association of antigens in microparticles increases the anti-Leishmania vaccine immunogenicity. This study aims to investigate the in situ effect of the adjuvant performance consisting of chitosan-coated poly(D,L-lactic) acid submicrometric particles (SMP) and analyze the inflammatory profile and toxicity. Two formulations were selected, SMP¹, containing poly(D,L-lactide) (PLA) 1% wt/v and chitosan 1% wt/v; and SMP², containing PLA 5% wt/v and chitosan 5% wt/v. After a single dose of the unloaded SMP¹ or SMP² in mice, the SMPs promoted cell recruitment without tissue damage. In addition, besides the myeloperoxidase (MPO) activity having demonstrated similar results among the analyzed groups, a progressive reduction in the levels of N-acetyl-β-_D-glucosaminidase (NAG) until 72 h was observed for SMPs. While IL-6 levels were similar among all the analyzed groups along the kinetics, only the SMPs groups had detectable levels of TNF-α. Additionally, the Leishmania braziliensis antigen was encapsulated in SMPs (SMP¹Ag and SMP²Ag), and mice were vaccinated with three doses. The immunogenicity analysis by flow cytometry demonstrated a reduction in NK (CD3^-CD49⁺) cells in all the SMPs groups, in addition to impairment in the T cells subsets (CD3⁺CD4⁺) and CD3⁺CD8⁺) and B cells (CD19⁺) of the SMP² group. The resulting data demonstrate that the chitosan-coated SMP formulations stimulate the early events of an innate immune response, suggesting their ability to increase the immunogenicity of co-administered Leishmania antigens.