Deletion of MIF gene from live attenuated LdCen-/- parasites enhances protective CD4+ T cell immunity.

Vaccination with live attenuated Leishmania parasites such as centrin deleted Leishmania donovani (LdCen-/-) against visceral leishmaniasis has been reported extensively. The protection induced by LdCen-/- parasites was mediated by both CD4+ and CD8+ T cells. While the host immune mediators of protection are known, parasite determinants that affect the CD4+ and CD8+ T cell populations remain unknown. Parasite encoded inflammatory cytokine MIF has been shown to modulate the T cell differentiation characteristics by altering the inflammation induced apoptosis during contraction phase in experimental infections with Leishmania or Plasmodium. Neutralization of parasite encoded MIF either by antibodies or gene deletion conferred protection in Plasmodium and Leishmania studies. We investigated if the immunogenicity and protection induced by LdCen-/- parasites is affected by deleting MIF genes from this vaccine strain. Our results showed that LdCen-/-MIF-/- immunized group presented higher percentage of CD4+ and CD8+ central memory T cells, increased CD8+ T cell proliferation after challenge compared to LdCen-/- immunization. LdCen-/-MIF-/- immunized group presented elevated production of IFN-γ+ and TNF-α+ CD4+ T cells concomitant with a reduced parasite load in spleen and liver compared to LdCen-/-group following challenge with L. infantum. Our results demonstrate the role of parasite induced factors involved in protection and long-term immunity of vaccines against VL.

Induction of immunogenicity by live attenuated Leishmania donovani centrin deleted parasites in dogs.

Zoonotic visceral leishmaniasis, caused by the intracellular protozoan parasite Leishmania infantum, is a neglected tropical disease that is often fatal when untreated. Dogs are considered the main reservoir of L. infantum in zoonotic VL as the presence of infected dogs may increase the risk for human infection. Canine visceral leishmaniasis (CVL) is a major veterinary and public health problem in Southern Europe, Middle East and South America. Control of animal reservoirs relies on elimination of seropositive dogs in endemic areas. However, treatment of infected dogs is not considered a favorable approach as this can lead to emergence of drug resistance since the same drugs are used to treat human infections. Therefore, vaccination against CVL remains the best alternative in control of the animal reservoirs. In this study, we present data on the immunogenicity profile of a live attenuated parasite LdCen(-/-) in a canine infection model and compared it to that of Leishmune(®), a commercially available recombinant vaccine. The immunogenicity of the LdCen(-/-) parasites was evaluated by antibody secretion, production of intracytoplasmic and secreted cytokines, activation and proliferation of T cells. Vaccination with LdCen(-/-) resulted in high immunogenicity as revealed by the higher IgGTotal, IgG1, and IgG2 production and higher lymphoproliferative response. Further, LdCen(-/-) vaccinated dogs showed higher frequencies of activated CD4+ and CD8+ T cells, IFN-γ production by CD8+ T cells, increased secretion of TNF-α and IL-12/IL-23p40 and decreased secretion of IL-4. These results contribute to the understanding of immunogenicity elicited by live attenuated L. donovani parasites and, consequently, to the development of effective vaccines against visceral leishmaniasis.