Cutaneous leishmaniasis (LC) is a parasitic tropical disease transmitted by insects with a high incidence in Colombia and the world. The prophylactic and therapeutic tools available for its management and control are deficient, and new alternatives are required. Although clinical, epidemiological, and experimental evidence suggests that vaccination would be a possible option, there is currently no effective vaccine available for human use. Previous studies conducted by our group in an ulcerative LC murine model by Leishmania (Viannia) panamensis (LVp), the species of greater distribution in Colombia, have identified a synthetic oligonucleotide containing CpG motifs (CpG) and liposomes as promising protective adjuvants for the development of an effective vaccine. Moreover, using a reverse vaccinology strategy, we have identified the protein trypanothione reductase (TR) as a potential antigen to be formulated with those adjuvants in a vaccine. Considering this background and the need to develop a molecularly defined vaccine with transfer potential for human use, we proposed that prophylactic administration of TR using a particulate delivery system such as liposomes, with or without CpG, would effectively protect mice from an infectious challenge. To determine this, first, we standardized the production of the CpG or TR liposomes, considering the impact of different factors involved in their preparation, according to various response variables such as particle size, charge, and encapsulation efficiency. We optimized the development of cationic (+65 mV), micro/nanometric (800-1600 nm) liposomes, which were physically stable and loaded with CpG or TR with an encapsulation efficiency of ~65% or ~20%, respectively. Subsequently, the prophylactic efficacy of several formulations composed of CpG and/or TR, both soluble and liposomal, was tested and compared to prevent an infectious challenge with LVp in the animal model. The results of five independent experiments indicated that a formulation composed of liposomal TR (1 μg) and soluble CpG (12.5 μg) was the most promising since it induced significant immunity both clinically and parasitologically in most of the vaccinated mice. Interestingly, the protection entirely depended on the liposomal formulation of the TR and the dose of soluble CpG used. Furthermore, mice vaccinated with only 1 μg of liposomal rTR without any other adjuvant, although with lesser magnitude, were also significantly protected against the infectious challenge. Our results, in addition to allowing progress in the development of an effective vaccine, 1) demonstrate the potential of liposomes as an antigen release system and as intrinsic adjuvants, 2) confirm CpG as a potent protective adjuvant, and 3) evidence the importance of the delivery system of vaccine components and its complex influence on efficacy.

Formulation and preclinical test of a liposomal vaccine against cutaneous leishmaniasis

LatinXChem

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.