Adaptive immunity to Lymphocytic choriomeningitis virus: new insights into antigenic determinants

Difference of two new LCMV strains in lethality and viral genome load in tissues

More than 30 strains of lymphocytic choriomeningitis virus (LCMV) have been isolated from mice, hamsters and humans in the United States, Europe and Japan. Experimentally infected mice exhibit different clinical signs and lethality depending on a combination of LCMV epitope peptides and host major histocompatibility complex (MHC) class I molecules. This study examined the pathogenicity, clinical signs and lethality, of two new LCMV strains (BRC and OQ28) using three inbred mouse strains with different genetic backgrounds having different H-2D haplotypes. Strain OQ28 (OQ28) infected mice exhibited clinical signs and lethality, whereas strain BRC (BRC) infected mice showed no clinical signs of infection. The viral genome load in tissues of C57BL/6 mice infected with two strains was determined using one-step real time RT-PCR. In C57BL/6 mice, higher levels of OQ28 viral genome load were detected in all tissues rather than were present in BRC infected mice. The viral genome load in lungs of both virus strains remained higher levels than in other tissues at 28 days post infection. Comparing sequences of the three LCMV epitope peptide regions revealed one non-conservative amino acid substitution codon in OQ28 and two amino acid differences in BRC. These results suggest that the varied pathogenicity and viral genome load of LCMV strains are not based only on differences in the host MHC class I molecule.

A multivalent vaccination strategy for the prevention of Old World arenavirus infection in humans

Arenaviruses cause severe human disease ranging from aseptic meningitis following lymphocytic choriomeningitis virus (LCMV) infection to hemorrhagic fever syndromes following infection with Guanarito virus (GTOV), Junin virus (JUNV), Lassa virus (LASV), Machupo virus (MACV), Sabia virus (SABV), or Whitewater Arroyo virus (WWAV). Cellular immunity, chiefly the CD8(+) T-cell response, plays a critical role in providing protective immunity following infection with the Old World arenaviruses LASV and LCMV. In the current study, we evaluated whether HLA class I-restricted epitopes that are cross-reactive among pathogenic arenaviruses could be identified for the purpose of developing an epitope-based vaccination approach that would cross-protect against multiple arenaviruses. We were able to identify a panel of HLA-A*0201-restricted peptides derived from the same region of the glycoprotein precursor (GPC) of LASV (GPC spanning residues 441 to 449 [GPC(441-449)]), LCMV (GPC(447-455)), JUNV (GPC(429-437)), MACV (GPC(444-452)), GTOV (GPC(427-435)), and WWAV (GPC(428-436)) that displayed high-affinity binding to HLA-A*0201 and were recognized by CD8(+) T cells in a cross-reactive manner following LCMV infection or peptide immunization of HLA-A*0201 transgenic mice. Immunization of HLA-A*0201 mice with the Old World peptide LASV GPC(441-449) or LCMV GPC(447-455) induced high-avidity CD8(+) T-cell responses that were able to kill syngeneic target cells pulsed with either LASV GPC(441-449) or LCMV GPC(447-455) in vivo and provided significant protection against viral challenge with LCMV. Through this study, we have demonstrated that HLA class I-restricted, cross-reactive epitopes exist among diverse arenaviruses and that individual epitopes can be utilized as effective vaccine determinants for multiple pathogenic arenaviruses.

A multivalent and cross-protective vaccine strategy against arenaviruses associated with human disease

Arenaviruses are the causative pathogens of severe hemorrhagic fever and aseptic meningitis in humans, for which no licensed vaccines are currently available. Pathogen heterogeneity within the Arenaviridae family poses a significant challenge for vaccine development. The main hypothesis we tested in the present study was whether it is possible to design a universal vaccine strategy capable of inducing simultaneous HLA-restricted CD8⁺ T cell responses against 7 pathogenic arenaviruses (including the lymphocytic choriomeningitis, Lassa, Guanarito, Junin, Machupo, Sabia, and Whitewater Arroyo viruses), either through the identification of widely conserved epitopes, or by the identification of a collection of epitopes derived from multiple arenavirus species. By inoculating HLA transgenic mice with a panel of recombinant vaccinia viruses (rVACVs) expressing the different arenavirus proteins, we identified 10 HLA-A02 and 10 HLA-A03-restricted epitopes that are naturally processed in human antigen-presenting cells. For some of these epitopes we were able to demonstrate cross-reactive CD8⁺ T cell responses, further increasing the coverage afforded by the epitope set against each different arenavirus species. Importantly, we showed that immunization of HLA transgenic mice with an epitope cocktail generated simultaneous CD8⁺ T cell responses against all 7 arenaviruses, and protected mice against challenge with rVACVs expressing either Old or New World arenavirus glycoproteins. In conclusion, the set of identified epitopes allows broad, non-ethnically biased coverage of all 7 viral species targeted by our studies.

Arenaviruses cause significant morbidity and mortality worldwide and are also regarded as a potential bioterrorist threat. CD8⁺ T cells restricted by class I MHC molecules clearly play a protective role in murine models of arenavirus infection, yet little is known about the epitopes recognized in the context of human class I MHC (HLA). Here, we defined 20 CD8⁺ T cell epitopes restricted by HLA class I molecules, derived from 7 different species of arenaviruses associated with human disease. To accomplish this task, we utilized epitope predictions, in vitro HLA binding assays, and HLA transgenic mice inoculated with recombinant vaccinia viruses (rVACV) expressing arenavirus antigens. Because our analysis targeted two of the most common HLA types worldwide, we project that the CD8⁺ T cell epitope set provides broad coverage against diverse ethnic groups within the human population. Furthermore, we show that immunization with a cocktail of these epitopes protects HLA transgenic mice from challenge with rVACV expressing antigens from different arenavirus species. Our findings suggest that a cell-mediated vaccine strategy might be able to protect against infection mediated by multiple arenavirus species.