Targeting of immunostimulatory DNA cures experimental visceral leishmaniasis through nitric oxide up-regulation and T cell activation

Active targeting of CpG-containing oligodeoxynucleotide (CpG-ODN) to macrophages was studied by incorporating it in mannose-coated liposomes, using visceral leishmaniasis as the model macrophage disease. Mannosylated liposomal CpG-ODN was more effective than liposomal or free CpG-ODN in inhibiting amastigote multiplication within macrophages. Moreover, in a 60-day mouse model of visceral leishmaniasis, complete elimination of spleen parasite burden was achieved by mannosylated liposomal CpG-ODN, compared to 62% and 81% parasite suppression by free and liposomal ODN, respectively, at a similar dose. Although in vitro exposure of CpG-ODN did not induce marked nitric oxide (NO) generation by macrophages, considerably enhanced amount of NO was generated by macrophages of CpG-ODN-treated animals. Their splenocytes secreted soluble factors required for the induction of NO generation, and the increased NO generation was paralleled by an increase in antileishmanial activity. Inducible NO generation was suppressed by treating splenocyte supernatants with anti-IFN-gamma or anti-IL-12 antibodies, whereas in vivo administration of these anti-cytokine Ab along with CpG-ODN reversed protection against infection. CpG-ODN treatment resulted in reduced levels of IL-4 but increased levels of IFN-gamma, IL-12 and inducible NO synthase in infected spleen cells, which was magnified by encapsulation in mannose-coated liposomes. This targeted treatment was not only curative, but it also imparted resistance to reinfection. These results represent a general approach for intracellular targeting of CpG-ODN, which effectively enhances its therapeutic potential in redirecting curative Th1 responses in Th2-driven disorders.