Immunotherapy against visceral leishmaniasis with the nucleoside hydrolase-DNA vaccine of Leishmania donovani

The nucleoside hydrolase (NH36) of Leishmania (L.) donovani is a vital enzyme which releases purines or pyrimidines of foreign DNA to be used in the synthesis of parasite DNA. As a bivalent DNA vaccine, the VR1012-NH36 was immunoprotective against visceral and cutaneous murine leishmaniasis. In this work we tested the immunotherapy against Leishmania (L.) chagasi infection, using two doses of 100 or 20 μg VR1012-NH36 vaccine (i.m. route), and, as a possible immunomodulator, aqueous garlic extract (8 mg/kg/day by the i.p. route), which was effective in immunotherapy of cutaneous murine leishmaniasis. Liver parasitic load was significantly reduced following treatment with 100 μg (91%) and 20 μg (77%) of the DNA vaccine, and by 20 μg DNA vaccine and garlic extract (76%) (p = 0.023). Survival was 33% for saline controls, 100% for the 100 μg vaccine, and 83 and 67% for the 20 μg vaccine with and without garlic extract addition, respectively. Garlic treatment alone did not reduce parasite load (p > 0.05), but increased survival (100%). The NH36-DNA vaccine was highly effective as a new tool for the therapy and control of visceral leishmaniasis, while the mild protective effect of garlic might be related to an unspecific enhancement of IFN-γ secretion.