The Neonatal CD8+ T Cell Repertoire Rapidly Diversifies during Persistent Viral Infection.

CMV is the most common congenital infection in the United States. The major target of congenital CMV is the brain, with clinical manifestations including mental retardation, vision impairment, and sensorineural hearing loss. Previous reports have shown that CD8(+) T cells are required to control viral replication and significant numbers of CMV-specific CD8(+) T cells persist in the brain even after the initial infection has been cleared. However, the dynamics of CD8(+) T cells in the brain during latency remain largely undefined. In this report, we used TCR sequencing to track the development and maintenance of neonatal clonotypes in the brain and spleen of mice during chronic infection. Given the discontinuous nature of tissue-resident memory CD8(+) T cells, we hypothesized that neonatal TCR clonotypes would be locked in the brain and persist into adulthood. Surprisingly, we found that the Ag-specific T cell repertoire in neonatal-infected mice diversified during persistent infection in both the brain and spleen, while maintaining substantial similarity between the CD8(+) T cell populations in the brain and spleen in both early and late infection. However, despite the diversification of, and potential interchange between, the spleen and brain Ag-specific T cell repertoires, we observed that germline-encoded TCR clonotypes, characteristic of neonatal infection, persisted in the brain, albeit sometimes in low abundance. These results provide valuable insights into the evolution of CD8(+) T cell repertoires following neonatal CMV infection and thus have important implications for the development of therapeutic strategies to control CMV in early life.