Predominant clonal accumulation of CD8⁺ T cells with moderate avidity in the central nervous systems of Theiler's virus-infected C57BL/6 mice

Induction of antigen-specific CD8⁺ T cells bearing a high-avidity T-cell receptor (TCR) is thought to be an important factor in antiviral and antitumor immune responses. However, the relationship between TCR diversity and functional avidity of epitope-specific CD8⁺ T cells accumulating in the central nervous system (CNS) during viral infection is unknown. Hence, analysis of T-cell diversity at the clonal level is important to understand the fate and function of virus-specific CD8+ T cells. In this study, we examined the Vβ diversity and avidity of CD8⁺ T cells specific to the predominant epitope (VP2_121-130) of Theiler's murine encephalomyelitis virus. We found that Vβ6⁺ CD8⁺ T cells, associated with epitope specificity, predominantly expanded in the CNS during viral infection. Further investigations of antigen-specific Vβ6 ⁺ CD8⁺ T cells by CDR3 spectratyping and sequencing indicated that distinct T-cell clonotypes are preferentially increased in the CNS compared to the periphery. Among the epitope-specific Vβ6⁺ CD8⁺ T cells, MGX-Jβ1.1 motif-bearing cells, which could be found at a high precursor frequency in naïve mice, were expanded in the CNS and tightly associated with gamma interferon production. These T cells displayed moderate avidity for the cognate epitope rather than the high avidity normally observed in memory/effector T cells. Therefore, our findings provide new insights into the CD8⁺ T-cell repertoire during immune responses to viral infection in the CNS.