Identification of an HLA-A*0201-restricted CD8+ T-cell epitope encoded within Leptospiral immunoglobulin-like protein A

Leptospirosis is an important zoonosis in humans. Immunity against leptospiral infection was thought to be primarily humoral, and limited studies have addressed the role of CD8+ T cells. Leptospiral immunoglobulin-like protein A (LigA) is an important protective antigen of Leptospira and a potential target for Leptospira-specific cell-mediated immunity. In this study, twenty LigA-derived peptides were tested their binding affinity and stability for the HLA-A*0201 molecule. Peptides with high binding affinity and stability for HLA-A*0201 were then assessed their capacity to elicit specific cytotoxic T-lymphocyte (CTL) responses using cytotoxicity, ELISPOT assays for IFN-γ and HLA-A*0201-peptide tetramer assays. We identified a HLA-A*0201-restricted epitope, LigA305–313 KLIVTPAAL in Leptospira LigA. CTLs specific for LigA305–313 were elicited both in HLA-A2.1/Kb transgenic mice and in patients with a clinical and/or laboratory diagnosis of leptospirosis. Staining of the HLA-A*0201–LigA305–313 tetramer revealed the presence of LigA305–313-specific CTLs in peripheral blood mononuclear cells (PBMCs) sourced from five patients infected with three different serovars of Leptospira. In conclusion, we report the existence of specific cytotoxic CD8+ T cells in patients with leptospirosis and we suggest that the newly identified epitope, LigA305–313, will be helpful in enhancing the understanding of the mechanism of immunity to leptospirosis.