Visceral leishmaniasis (VL) in the Americas is a chronic systemic disease caused by infection with Leishmania infantum parasites. The toxicity of antileishmanial drugs, long treatment course and limited efficacy are significant concerns that hamper adequate treatment against the disease. Studies have shown the promise of an immunotherapeutics approach, combining antileishmanial drugs to reduce the parasitism and vaccine immunogens to activate the host immune system. In the current study, we developed an immunotherapy using a recombinant T cell epitope-based chimeric protein, ChimT, previously shown to be protective against Leishmania infantum, with the adjuvant monophosphoryl lipid A (MPLA) and amphotericin B (AmpB) as the antileishmanial drug. BALB/c mice were infected with L. infantum stationary promastigotes and later they received saline or were treated with AmpB, MPLA, ChimT/Amp, ChimT/MPLA or ChimT/MPLA/AmpB. The combination of ChimT/MPLA/AmpB significantly reduced the parasite load in mouse organs (p < 0.05) and induced a Th1-type immune response, which was characterized by higher ratios of anti-ChimT and anti-parasite IgG2a:IgG1 antibodies, increased IFN-γ mRNA and IFN-γ and IL-12 cytokines and accompanied by lower levels of IL-4 and IL-10 cytokines, when compared to other treatments and controls (all p < 0.05). Organ toxicity was also lower with the ChimT/MPLA/AmpB immunotherapy, suggesting that the inclusion of the vaccine and adjuvant ameliorated the toxicity of AmpB to some degree. In addition, the ChimT vaccine alone stimulated in vitro murine macrophages to significantly kill three different internalized species of Leishmania parasites and to produce Th1-type cytokines into the culture supernatants. To conclude, our data suggest that the combination of ChimT/MPLA/AmpB could be considered for further studies as an immunotherapy for L. infantum infection.

Current treatment for visceral leishmaniasis (VL) is associated with toxicity, a high cost, and the emergence of drug-resistant parasite strains. Moreover, no human vaccine is available. In this context, immunotherapeutics combining vaccination and chemotherapy have emerged as a promising alternative. In this study, we combined a recombinant chimeric protein (ChimT) with the adjuvant 3-O-desacyl–monophosphoryl lipid A (MPLA) and the antileishmanial drug miltefosine (Milt) and used it to treat Leishmania infantum-infected mice. Parasitological, immunological, and toxicological assays were performed at 1 and 30 days post treatment. The ChimT/MPLA/Milt combination was the most effective therapeutic regimen, inducing robust Th1-type cellular and humoral immune responses, as demonstrated by increased levels of IFN-γ, IL-12, and TNF-α cytokines, nitrite, and IgG2a antibodies. These responses were associated with significant reductions in parasite load across various organs. Furthermore, the treatment showed low renal and hepatic toxicity at both evaluation time points. By contrast, ChimT alone, ChimT/MPLA, and Milt induced lower immunological and parasitological responses when compared with the ChimT/MPLA/Milt group. The results observed at 1 and 30 days post treatment demonstrated the potential of ChimT/MPLA/Milt combination against VL.