Identification of Human T-cell epitopes for Lassa Fever Virus

Recovery from Lassa virus (LV) infection usually occurs before the appearance of neutralizing antibodies, indicating that cellular immunity plays a primary role in viral clearance. To date, the role of LV-specific CD8+ T cells has not been evaluated in humans. To facilitate studies of T cell responses to LV infection, we sought to identify human cytotoxic T lymphocyte (CTL) epitopes from the glycoprotein precursor (GPC) and nucleoprotein (NP) genes of two genetically distinct strains of LV (Josiah and GA-391). We identified 130 potential HLA-A2, -A3, or -B7 supertype-restricted CTL epitopes in the GPC and NP genes through the use of an HLA binding motif-based epitope prediction algorithm. Each peptide was assayed for MHC binding on a panel of five purified human MHC class I molecules per supertype. We found 48 peptides that bound two or more alleles with affinities of ? 500 nM, values indicative of immunogenicity. To determine whether these peptides were immunogenic in vivo, we immunized HLA transgenic mice (A*0201, A2 supertype; A*1101, A3 supertype; B*0702, B7 supertype) with pools of three to five nonoverlapping peptides. CD8+ T cells were isolated from spleens and assayed for their ability to produce interferon-gamma in response to each peptide (presented by HLA-restricted target cells) via ELISPOT assay. Thus far, we have identified 20 A2 peptides (n=33), five A3 peptides (n=12), and one B7 peptide (n=3) that are immunogenic in the transgenic mouse system. Six of these immunogenic peptide sequences are conserved (100% homology) in other members of the arenavirus family (range of 1 to 5 viruses). We have also found that effector cells immunized against Lassa peptides can recognize variant peptides from other arenavirues. The immunogenic epitopes identified in this study will aid in the characterization of T cell responses against LV and the design of multi-epitope vaccines.