Defining the mechanism(s) of protection by cytolytic CD8 T cells against a cryptic epitope derived from a retroviral alternative reading frame

Abstract

The goal of this study was to determine the functional properties of protective cytolytic CD8 T cells (CTL) specific for an MHC class I cryptic epitope, SYNTGRFPPL, during infection with the LP‐BM5 murine retrovirus. Disease‐susceptible CD8−/ − BALB/c mice reconstituted with SYNTGRFPPL‐specific CTL were able to clear the retrovirus and were therefore protected from disease. Since the mechanism(s) involved in the protective response against this alternative epitope were uncertain, perforin (pfp) −/ −, IFNγ−/ −, pfp−/−/IFNγ−/ − (DKO) and wild‐type (WT) BALB/c mice were infected with LP‐BM5 and assessed for disease. A subset of infected pfp−/ − mice had reduced splenomegaly and immunosuppression, compared to CD8−/ − mice. However, IFNγ−/ − and DKO mice were resistant to disease. SYNTGRFPPL‐specific CTL were generated from all strains of mice by priming with a Vaccinia construct expressing LP‐BM5 gag followed by in vitro restimulation with SYNTGRFPPL peptide. Effector CTL were then transferred into CD8−/ − mice following infection with LP‐BM5. Compared to CD8−/ − recipients protected with WT CTL, CD8−/− mice receiving DKO CTL had moderate disease whereas CD8−/− mice receiving Pfp−/ − CTL developed more severe disease. CD8−/− mice receiving IFNγ−/− CTL were fully protected from disease. These results indicate pfp, but not IFNγ, as a critical component of the CTL response against cryptic epitope SYNTGRFPPL.