Use of a Recombinant Cysteine Proteinase from Leishmania (Leishmania) infantum chagasi for the Immunotherapy of Canine Visceral Leishmaniasis

Abstract

Background

A recombinant cysteine proteinase from Leishmania (Leishmania) infantum chagasi (rLdccys1) was previously shown to induce protective immune responses against murine and canine visceral leishmaniasis. These findings encouraged us to use rLdccys1 in the immunotherapy of naturally infected dogs from Teresina, Piauí, a region of high incidence of visceral leishmaniasis in Brazil.

Methodology/Principal Findings

Thirty naturally infected mongrel dogs displaying clinical signs of visceral leishmaniasis were randomly divided in three groups: one group received three doses of rLdccys1 in combination with the adjuvant Propionibacterium acnes at one month interval between each dose; a second group received three doses of P. acnes alone; a third group received saline. The main findings were: 1) dogs that received rLdccys1 with P. acnes did not display increase of the following clinical signs: weight loss, alopecia, onychogryphosis, cachexia, anorexia, apathy, skin lesions, hyperkeratosis, ocular secretion, and enlarged lymph nodes; they also exhibited a significant reduction in the spleen parasite load in comparison to the control dogs; 2) rLdccys1-treated dogs exhibited a significant delayed type cutaneous hypersensitivity elicited by the recombinant antigen, as well as high IgG2 serum titers and low IgG1 serum titers; sera from rLdccys1-treated dogs also contained high IFN-γ and low IL-10 concentrations; 3) control dogs exhibited all of the clinical signs of visceral leishmaniasis and had low serum IgG2 and IFN-γ levels and high concentrations of IgG1 and IL-10; 4) all of the dogs treated with rLdccys1 were alive 12 months after treatment, whereas dogs which received either saline or P. acnes alone died within 3 to 7 months.

Conclusions/Significance

These findings illustrate the potential use of rLdccys1 as an additional tool for the immunotherapy of canine visceral leishmaniasis and support further studies designed to improve the efficacy of this recombinant antigen for the treatment of this neglected disease.

Author Summary

Visceral leishmaniasis (VL) is an important public health problem and dogs are the main domestic reservoirs of zoonotic VL which has resulted in an annual incidence of 40,100–75,500 new human cases. Because canine VL chemotherapy is limited by the low efficacy of drugs currently used for human VL treatment, immunotherapy may provide a viable alternative. We used a recombinant cysteine proteinase from L. (L.) infantum chagasi, rLdccys1, in combination with the adjuvant P. acnes for the treatment of naturally infected mongrel dogs from Teresina, Pauí a state in Brazil that has a high incidence of VL. Dogs treated with rLdccys1 showed a significant delayed type hypersensitivity reaction against the recombinant antigen and displayed high serum concentrations of IgG2 and IFN-γ and low concentrations of IgG1 and IL-10. Immunotherapy with rLdccys1 resulted in no increase of the clinical signs of canine VL and an extensive reduction of spleen parasite load. Furthermore, all of the dogs treated with rLdccys1 survived for at least 12 months after treatment, whereas those that received either saline or P. acnes alone died within 3 to 7 months. These findings support the potential of rLdccys1 immunotherapy as an additional option for the treatment of canine VL.