Development of a novel metallo-lipid microparticle delivery system for a leishmania mexicana vaccine

 Cutaneous leishmaniasis (CL) is a globally distributed parasitic disease. No effective vaccine currently exists and the complex epidemiology of CL limits vector/reservoir control. Development of a safe, effective vaccine would represent an important public health advance.  DNA vaccine development has been hindered by weak immunogenicity. Encapsulating DNA within degradable liposome or nanoparticle delivery systems can reduce risk for its degradation. We designed a DNA vaccine candidate against Leishmania mexicana. The biopterin transporter (bt), cell adhesion molecule-like (icam-l), orff, and amastin genes were amplified from L. mexicana cDNA and inserted on pVax backbone. The p-orff-amastin and p-bt-icam plasmids were then encapsulated within a synthetic metallo-lipid microparticle (MLM). The major objective was to investigate MLM delivery system effectiveness. Seventy-two BALB/c mice were randomized to one of 9 experimental groups (8/group): naked p-bt, naked p-orff-amastin, naked p-bt-icam, naked p-orff-amastin and p-bt-icam, MLM + p-orff-amastin and p-bt-icam, MLM Zn + p-orff-amastin and p-bt-icam, MLM Cu + p-orff-amastin and p-bt-icam, MLM alone (control), PBS alone (control). Each group was given three doses of one formulation administered at 3-week intervals. Mice subsequently underwent footpad challenge with L. mexicana. Lesion progression and vaccine immunogenecity (IFN-γ, IL-4, IL-10, IL-12) were evaluated for 10 weeks. The results suggested that plasmid encapsulation with MMR enhanced delivery to target cells and improved its immunogenicity. This novel delivery system shows promise for future use in a human DNA vaccine for CL.