Immuno-informatics based approaches to identify CD8+ T cell epitopes within the Leishmania donovani 3-ectonucleotidase in cured visceral leishmaniasis subjects

Leishmaniases are vector-borne diseases for which no vaccine exists. These diseases are caused by the Leishmania species complex. Activation of the CD8+ T cell is crucial for protection against intracellular pathogens, and peptide antigens are attractive strategies for the precise activation of CD8+ T in vaccine development against intracellular infections. The traditional approach to mine the epitopes is an arduous task. However, with the advent of immunoinformatics, in silico epitope prediction tools are available to expedite epitope identification. In this study, we employ different immunoinformatics tools to predict CD8+ T cell specific 9 mer epitopes presented by HLA-A*02 and HLA-B40 within the highly conserved 3′-ectonucleotidase of Leishmania donovani. We identify five promiscuous epitopes, which have no homologs in humans, theoretically cover 85% of the world's population and are highly conserved (100%) among Leishmania species. Presentation of selected peptides was confirmed by T2 cell line based HLA-stabilization assay, and three of them were found to be strong binders. The in vitro peptide stimulation of peripheral blood mononuclear cells (PBMC) from cured HLA-A02+ visceral leishmaniasis (VL) subjects produced significantly higher IFN-γ, IL-2 and IL-12 compared to no peptide control healthy subjects. Further, CD8+ cells from treated VL subjects produced significantly higher intracellular IFN-γ, lymphocyte proliferation and cytotoxic activity against selected peptides from the PBMCs of treated HLA-A02+ VL subjects. Thus, the CD8+ T cell specific epitopes shown in this study will speed up the development of polytope vaccines for leishmaniasis.