Management of visceral leishmaniasis with therapeutic vaccines

Abstract

Visceral leishmaniasis (VL), a phlebotomine-borne neglected tropical disease, is caused by parasites of the Leishmania donovani complex. While L. donovani infection is restricted to the Indian subcontinent and East Africa, where transmission is anthroponotic, Leishmania infantum occurs in Europe, North Africa, and parts of Latin America, where it is zoonotic in nature with dogs as reservoir hosts. Though the incidence of VL caused by L. infantum has been on the decline, L. donovani continues to cause epidemics periodically. By and large, a small proportion of L. donovani infection manifests as clinical disease but majority of the infected individuals remain asymptomatic and contribute to the perpetuation of the VL transmission cycle via the sand fly vector. This is one of the major stumbling blocks to World Health Organization initiatives to eliminate this deadly disease by 2020. These parasites reside within the host macrophages and impair the immune system of the infected individual, which ultimately results in marked immunosuppression. In the absence of any safe and effective vector control measure, attempts have been made to design therapeutic vaccine(s) that can exclusively target infected macrophages. So far, two vaccines – a glycoprotein complex from L. donovani promastigote, fucose–mannose ligand with saponin, commercialized as Leishmune®, as well as a polyprotein vaccine formulation, Leish-111f + monophosphoryl lipid A plus squalene emulsion in combination with glucantime, have been successfully evaluated for their immunotherapeutic potential against canine VL. However, encouraging results obtained from several experimental trials so far against human VL are still to be translated clinically. This review provides an overview on the various strategies tried and tested for developing therapeutic vaccines against this dreaded disease.