Computational mapping and in vitro/in vivo evaluation of immunogenic epitopes for Lassa fever virus

Lassa Fever Virus (LFV) causes severe hemorrhagic fever in humans with a high fatality rate. Currently, there are no effective treatments for LFV infections or vaccines to prevent infection with this virus. Cellular responses mediated by cytotoxic T lymphocytes (CTL) play a primary role in neutralizing LFV during infection. Identification of the immunogenic LFV epitopes capable of generating CTLs may lead to new strategies for LFV-directed therapies, diagnostic tools, and, more importantly, protective vaccines.We performed computational analyses using BIMAS and SYFPEITHI algorithms to map immunogenic epitopes present within LFV glycoprotein (GP) and nucleoprotein (NP). Studies focused on the identification of CTL epitopes with binding affinity for the MHC class I allele HLA*0201. Five candidate CTL epitopes derived form GP and two derived from NP were identified and tested for their ability to stabilize class I MHC expression using HLA*0201+ T2 cells. Three of the five GP peptides stabilized class I expression none of the NP peptides tested stabilized HLA*0201.Three LFV GP peptides (GP258--266, GP441--449, and GP60--68) that were shown to stabilize class I and one peptide (GP386--394) that did not stabilize HLA*0201 were tested for their potential to generate CTLs in vivo. HLA*0201-transgenic mice were immunized with peptides together with a T-helper peptide specific for I-Ab for Hepatitis B virus core protein. Lymphoid cells from immunized mice were tested for their cytolytic activity. Three out of four peptides induced IFN-gamma and CTL responses. Peptide-specific CD8+ CTL responses generated by two of the tested peptides (GP258--266 and GP60--68) were essentially of the same magnitude as those seen in mice immunized with a positive control peptide. The third peptide (GP441--449) induced moderate responses. Finally, the peptide that failed to stabilize class I (GP386--394) also failed to induce the CTL responses. We also enumerated LFV peptide-specific CD8 + cells for one of the peptides (GP258--266) using class I tetramer staining and showed a small but significant population of peptide-binding CD8+ cells in immunized mice as compared with control mice. We conclude that computational prediction of virus-specific epitopes is a valid and useful tool for epitope mapping.