Immunotherapy against experimental canine visceral leishmaniasis with the saponin enriched-Leishmune® vaccine

Abstract

In order to assess the immunotherapeutic potential on canine visceral leishmaniasis of the Leishmune® vaccine, formulated with an increased adjuvant concentration (1 mg of saponin rather than 0.5 mg), 24 mongrel dogs were infected with Leishmania (L.) chagasi. The enriched-Leishmune® vaccine was injected on month 6, 7 and 8 after infection, when animals were seropositive and symptomatic. The control group were injected with a saline solution. Leishmune®-treated dogs showed significantly higher levels of anti-FML IgG antibodies (ANOVA; p < 0.0001), a higher and stable IgG2 and a decreasing IgG1 response, pointing to a TH1 T cell mediated response. The vaccine had the following effects: it led to more positive delayed type hypersensitivity reactions against Leishmania lysate in vaccinated dogs (75%) than in controls (50%), to a decreased average of CD4+ Leishmania-specific lymphocytes in saline controls (32.13%) that fell outside the 95% confidence interval of the vaccinees (41.62%, CI95% 43.93–49.80) and an increased average of the clinical scores from the saline controls (17.83) that falls outside the 95% confidence interval for the Leishmune® immunotherapy-treated dogs (15.75, CI95% 13.97–17.53). All dogs that received the vaccine were clustered, and showed lower clinical scores and normal CD4+ counts, whereas 42% of the untreated dogs showed very diminished CD4+ and higher clinical score. The increase in clinical signs of the saline treated group was correlated with an increase in anti-FML antibodies (p < 0.0001), the parasitological evidence (p = 0.038) and a decrease in Leishmania-specific CD4+ lymphocyte proportions (p = 0.035). These results confirm the immunotherapeutic potential of the enriched-Leishmune® vaccine. The vaccine reduced the clinical symptoms and evidence of parasite, modulating the outcome of the infection and the dog's potential infectiosity to phlebotomines. The enriched-Leishmune® vaccine was subjected to a safety analysis and found to be well tolerated and safe.