Combining Cationic Liposomal Delivery with MPL-TDM for Cysteine Protease Cocktail Vaccination against Leishmania donovani : Evidence for Antigen Synergy and Protection

Abstract

BackgroundWith the paucity of new drugs and HIV co-infection, vaccination remains an unmet research priority to combat visceral leishmaniasis (VL) requiring strong cellular immunity. Protein vaccination often suffers from low immunogenicity and poor generation of memory T cells for long-lasting protection. Cysteine proteases (CPs) are immunogenic proteins and key mediators of cellular functions in Leishmania. Here, we evaluated the vaccine efficacies of CPs against VL, using cationic liposomes with Toll like receptor agonists for stimulating host immunity against L. donovani in a hamster model.Methodology/Principal FindingsRecombinant CPs type I (cpb), II (cpa) and III (cpc) of L. donovani were tested singly and in combination as a triple antigen cocktail for antileishmanial vaccination in hamsters. We found the antigens to be highly immunoreactive and persistent anti-CPA, anti-CPB and anti-CPC antibodies were detected in VL patients even after cure. The liposome-entrapped CPs with monophosphoryl lipid A-Trehalose dicorynomycolate (MPL-TDM) induced significantly high nitric oxide (up to 4 fold higher than controls) mediated antileishmanial activity in vitro, and resulted in strong in vivo protection. Among the three CPs, CPC emerged as the most potent vaccine candidate in combating the disease. Interestingly, a synergistic increase in protection was observed with liposomal CPA, CPB and CPC antigenic cocktail which reduced the organ parasite burden by 1013–1016 folds, and increased the disease-free survival of >80% animals at least up to 6 months post infection. Robust secretion of IFN-γ and IL-12, along with concomitant downregulation of Th2 cytokines, was observed in cocktail vaccinates, even after 3 months post infection.Conclusion/SignificanceThe present study is the first report of a comparative efficacy of leishmanial CPs and their cocktail using liposomal formulation with MPL-TDM against L. donovani. The level of protection attained has not been reported for any other subcutaneous single or polyprotein vaccination against VL.

Cationic Liposomal Sodium Stibogluconate (SSG), a Potent Therapeutic Tool for Treatment of Infection by SSG-Sensitive and -Resistant Leishmania donovani

“…As Leishmania parasites are larger than bacteria and have a membrane structure that exposes negatively charged lipids on their surfaces, DDAB may be better suited for interactions with their membranes for subsequent killing. Cationic liposomes probably interact with macrophage surface receptors (34) and subsequently are endocytosed by them (35). Inside the macrophages, these cationic liposomes probably exert dual effects by interacting directly with the intracellular parasites and also activating macrophage microbicidal activity.…”

Noninvasive Diagnosis of Visceral Leishmaniasis: Development and Evaluation of Two Urine-Based Immunoassays for Detection of Leishmania donovani Infection in India

“…donovani strain AG83 (ATCC PRA-413) parasite was cultured according to the standard protocol [ 27 ]. Recombinant proteins of strain AG83 namely, rGP63 (a 63 kDa recombinant glycoprotein) and rCPA (a recombinant cysteine protease) were purified from its clones [ 28 , 29 ]. Soluble leishmanial antigens (SLA) extracted from L .…”

Vaccine potential of HLA‐A2 epitopes from Leishmania Cysteine Protease Type III (CPC)

“…Lysosomal cysteine proteases (CP) of Leishmania , including cysteine proteases type I (CPB), II (CPA) and III (CPC), are conserved and functionally important proteolytic enzymes regulating cell cycle and host‐parasite interactions that have been found to be immunogenic in mice . Amongst the cysteine proteases, the efficiency of type III (CPC) CP demonstrated stronger antigenicity than type I and II …”