Polyfunctional CD4+ T cell responses to a set of pathogenic arenaviruses provide broad population coverage

Background. Several arenaviruses cause severe hemorrhagic fever and aseptic meningitis in humans for which no licensed vaccines are available. A major obstacle for vaccine development is pathogen heterogeneity within the Arenaviridae family. Evidence in animal models and humans indicate that T cell and antibody-mediated immunity play important roles in controlling arenavirus infection and replication. Because CD4+T cells are needed for optimal CD8+T cell responses and to provide cognate help for B cells, knowledge of epitopes recognized by CD4+T cells is critical to the development of an effective vaccine strategy against arenaviruses. Thus, the goal of the present study was to define and characterize CD4+T cell responses from a broad repertoire of pathogenic arenaviruses (including lymphocytic choriomeningitis, Lassa, Guanarito, Junin, Machupo, Sabia, and Whitewater Arroyo viruses) and to provide determinants with the potential to be incorporated into a multivalent vaccine strategy. Results. By inoculating HLA-DRB1*0101 transgenic mice with a panel of recombinant vaccinia viruses, each expressing a single arenavirus antigen, we identified 37 human HLA-DRB1*0101-restricted CD4+T cell epitopes from the 7 antigenically distinct arenaviruses. We showed that the arenavirus-specific CD4+T cell epitopes are capable of eliciting T cells with a propensity to provide help and protection through CD40L and polyfunctional cytokine expression. Importantly, we demonstrated that the set of identified CD4+T cell epitopes provides broad, non-ethnically biased population coverage of all 7 arenavirus species targeted by our studies. Conclusions. The identification of CD4+T cell epitopes, with promiscuous binding properties, derived from 7 different arenavirus species will aid in the development of a T cell-based vaccine strategy with the potential to target a broad range of ethnicities within the general population and to protect against both Old and New World arenavirus infection. © 2010 Kotturi et al; licensee BioMed Central Ltd

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

Dissociation between epitope hierarchy and immunoprevalence in CD8 responses to vaccinia virus Western Reserve

Understanding immunity to vaccinia virus (VACV) is important for the development of safer vaccines for smallpox- and poxvirus-vectored recombinant vaccines. VACV is also emerging as an outstanding model for studying CD8+ T cell immu-nodominance because of the large number of CD8+ T cell epitopes known for this virus in both mice and humans. In this study, we characterize the CD8+ T cell response in vaccinated BALB/c mice by a genome-wide mapping approach. Responses to each of 54 newly identified H-2d-restricted T cell epitopes could be detected after i.p. and dermal vaccination routes. Analysis of these new epitopes in the context of those already known for VACV in mice and humans revealed two important findings. First, CD8+ T cell epitopes are not randomly distributed across the VACV proteome, with some proteins being poorly or nonimmunogenic, while others are immunoprevalent, being frequently recognized across diverse MHC haplotypes. Second, some proteins constituted the major targets of the immune response by a specific haplotype as they recruited the majority of the specific CD8+ T cells but these proteins did not correspond to the immunoprevalent Ags. Thus, we found a dissociation between immunoprevalence and immunodominance, implying that different sets of rules govern these two phenomena. Together, these findings have clear implications for the design of CD8+ T cell subunit vaccines and in particular raise the exciting prospect of being able to choose subunits without reference to MHC restriction

Lymphocytic Choriomeningitis Virus Infection Yields Overlapping CD4+ and CD8+ T-Cell Responses▿

Activation of CD4+ T cells helps establish and sustain other immune responses. We have previously shown that responses against a broad set of nine CD4+ T-cell epitopes were present in the setting of lymphocytic choriomeningitis virus (LCMV) Armstrong infection in the context of H-2d. This is quite disparate to the H-2b setting, where only two epitopes have been identified. We were interested in determining whether a broad set of responses was unique to H-2d or whether additional CD4+ T-cell epitopes could be identified in the setting of the H-2b background. To pursue this question, we infected C57BL/6 mice with LCMV Armstrong and determined the repertoire of CD4+ T-cell responses using overlapping 15-mer peptides corresponding to the LCMV Armstrong sequence. We confirmed positive responses by intracellular cytokine staining and major histocompatibility complex (MHC)-peptide binding assays. A broad repertoire of responses was identified, consisting of six epitopes. These epitopes originate from the nucleoprotein (NP) and glycoprotein (GP). Out of the six newly identified CD4+ epitopes, four of them also stimulate CD8+ T cells in a statistically significant manner. Furthermore, we assessed these CD4+ T-cell responses during the memory phase of LCMV Armstrong infection and after infection with a chronic strain of LCMV and determined that a subset of the responses could be detected under these different conditions. This is the first example of a broad repertoire of shared epitopes between CD4+ and CD8+ T cells in the context of viral infection. These findings demonstrate that immunodominance is a complex phenomenon in the context of helper responses