LCMV gp (33-41)

The role of IRF7 in the host response to lymphocytic choriomeningitis virus (LCMV) Armstrong 53b infection of mice was investigated. Intracranial infection of IRF7 KO mice was associated with delayed onset of LCM, increased survival and significantly reduced expression of the Ifng gene in the brain but not in the periphery. IRF7 KO mice showed impaired control of LCMV replication and delayed clearance of LCMV. Similar numbers of activated anti-LCMV-GP(33-41) CD8+ T cells were present in the brain and spleens of infected WT and IRF7 KO mice. While plasma IFN-β was increased to similar levels, IFN-α was markedly reduced in IRF7 KO compared with WT mice. Compared with IFN-β, IFN-α was a less potent inhibitor of LCMV infection in vitro. In conclusion, IRF7 (1) is required for the early innate control of LCMV infection, likely through the regulation of the appropriate type I IFN response, and (2) is not required for the antiviral CD8+ T cell-dependent clearance of LCMV from infected tissues.

It has recently been demonstrated that a recombinant replication-deficient human adenovirus 5 (Ad5) vector expressing lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) fused to the p31 invariant (Ii) chain confers broad, long-lasting T-cell immunity that completely protects C57BL/6 mice against lethal peripheral challenge. The current study questioned whether the same strategy, i.e. linkage of GP to an Ii chain, could be applied to a naked DNA vaccine. Following gene-gun immunization with the linked construct (DNA-IiGP), GP-specific CD4(+) T cells could not be detected by flow cytometry. However, inclusion of the Ii chain augmented the priming of GP-specific CD8(+) T cells directed towards both immunodominant (GP(33-41)) and subdominant (GP(276-286) and GP(92-101)) epitopes, and vaccination with DNA-IiGP conferred significantly improved protection against systemic LCMV infection compared with the unlinked construct. In contrast, substantial protection against peripheral challenge was not observed. Additional experiments with T-cell subset-depleted or perforin-deficient mice revealed that virus control in vaccinated mice depends critically on cytotoxic CD8(+) T cells. Finally, priming with the naked DNA vaccine was shown to augment the immune response raised by subsequent immunization with the Ad5 vector. In conclusion, this study showed that the immunoenhancing effect of Ii chain linkage is not limited to the Ad5 vector, but is also relevant with a DNA platform. Furthermore, given the fact that the Ii chain enhances the presentation of more than one epitope, this suggests that Ii-chain-based DNA vaccines may be promising candidates for various heterologous prime-boost regimes.

We have shown that PLG nanoparticles loaded with peptide antigen can reduce disease in animal models of autoimmunity and in a phase 1/2a clinical trial in celiac patients. Clarifying the mechanisms by which antigen-loaded nanoparticles establish tolerance is key to further adapting them to clinical use. The mechanisms underlying tolerance induction include the expansion of antigen-specific CD4+ regulatory T cells and sequestration of autoreactive cells in the spleen. In this study, we employed nanoparticles loaded with two model peptides, GP33-41 (a CD8 T cell epitope derived from lymphocytic choriomeningitis virus) and OVA323-339 (a CD4 T cell epitope derived from ovalbumin), to modulate the CD8+ and CD4+ T cells from two transgenic mouse strains, P14 and DO11.10, respectively. Firstly, it was found that the injection of P14 mice with particles bearing the MHC I-restricted GP33-41 peptide resulted in the expansion of CD8+ T cells with a regulatory cell phenotype. This correlated with reduced CD4+ T cell viability in ex vivo co-cultures. Secondly, both nanoparticle types were able to sequester transgenic T cells in secondary lymphoid tissue. Flow cytometric analyses showed a reduction in the surface expression of chemokine receptors. Such an effect was more prominently observed in the CD4+ cells rather than the CD8+ cells.