Cysteine proteinase type I, encapsulated in solid lipid nanoparticles induces substantial protection against Leishmania major infection in C57BL/6 mice.

Appropriate adjuvant, proper antigen(s) and a suitable formulation are required to develop stable, safe and immunogenic vaccines. Leishmanial cysteine proteinase type I (CPB) is a promising vaccine candidate; nevertheless, it requires a delivery system to induce a potent immune response. Herein, solid lipid nanoparticles (SLN) have been applied for CPB [with and without C-terminal extension (CTE)] formulation to utilize as a vaccine against Leishmania major infection in C57BL/6 mice. Therefore, SLN-CPB and SLN-CPB(-CTE) formulations were prepared from cetyl palmitate and cholesterol, using melt emulsification method. After intraperitoneal vaccination and subsequent L. major challenge, a strong antigen-specific T-helper type 1 (Th1) immune response was induced compared to control groups. Lymph node cells from immunized mice displayed lower parasite burden, higher IFN-γ, IgG2a and lower IL-4 production, indicating that robust Th1 immune response had been induced. Our results revealed that CTE is not necessary for inducing protective responses against L. major infection as the IFN-γ/IL-4 ratio was significantly higher, whereas IgG1 responses were lower in the SLN-CPB(-CTE) vaccinated group, post-challenge. Thus, SLN-CPB(-CTE) was shown to induce specific Th1 immune responses to control L. major infection, through effective antigen delivery to the peritoneal antigen presenting cells.