Rapid CD8+ T cell repertoire focusing and selection of high-affinity clones into memory following primary infection with a persistent human virus:: Human Cytomegalovirus

To investigate the mechanism of selection of individual human CD8(+) T cell clones into long-term memory following primary infection with a persistent human virus (human CMV (HCMV)), we undertook a longitudinal analysis of the diversity of T cell clones directed toward an immunodominant viral epitope: we followed this longitudinally from early T cell expansion through the contraction phase and selection into the memory pool. We show that following initial HCMV infection, the early primary response against a defined epitope was composed of diverse clones possessing many different TCR V beta segments. Longitudinal analysis showed that this usage rapidly focused predominantly on a single TCR V beta segment within which dominant clones frequently had public TCR usage, in contrast to subdominant or contracted clones. Longitudinal clonotypic analysis showed evidence of disproportionate contraction of certain clones that were abundant in the primary response, and late expansion of clones that were subdominant in the primary response. All dominant clones selected into memory showed similar high functional avidity of their TCR, whereas two clones that greatly contracted showed substantially lower avidity. Expression of the IL-7R is required for survival of murine effector CD8(+) T cells into memory, but in primary HCMV infection IL-7R was not detected on circulating Ag-specific cells until memory had been established. Thus, the ofigocional T cell repertoire against an immunodominant persistent viral epitope is established early in primary infection by the rapid selection of public clonotypes, rather than being a stochastic process.