The immunodominant CD8⁺ T cell epitope region of Theiler's virus in resistant C57BL/6 mice is critical for anti-viral immune responses, viral persistence, and binding to the host cells

Theiler's virus infection induces an immune-mediated demyelinating disease, providing a relevant animal model of human multiple sclerosis. VP2_121-130-specific CD8⁺ T cells in resistant H-2^b mice account for the majority of CNS-infiltrating CD8⁺ T cells. To further study the role of the CD8⁺ T cells, we generated a panel of mutant viruses substituted with L, G, or T at the anchor residue (M130) of the VP2_121-130 epitope. M130L virus (M130L-V) with a substitution of M with L displayed similar properties as wild-type virus (WT-V). However, M130G-V and M130T-V could not establish a persistent infection in the CNS. The level of both virus-specific CD8⁺ and CD4⁺ T cell responses is significantly reduced in mice infected with these variant viruses. While all mutant and wild-type viruses replicate comparably in BHK cells, replication of M130G-V and M130T-V in macrophages was significantly lower compared to those infected with WT-V and M130L-V. Interestingly, these mutant viruses deficient in replication in primary mouse cells showed drastically reduced binding ability to the cells. These results suggest that the anchor residue of the predominant CD8⁺ T cell epitope of TMEV in resistant mice is critical for the virus to infect target cells and this deficiency may result in poor viral persistence leading to correspondingly low T cell responses in the periphery and CNS. Thus, selection of the cellular binding region of the virus as the predominant epitope for CD8⁺ T cells in resistant mice may provide a distinct advantage in controlling viral persistence by preventing escape mutations.