Induction and Maintenance of CX3CR1-Intermediate Peripheral Memory CD8⁺ T Cells by Persistent Viruses and Vaccines

The induction and maintenance of T cell memory is critical to the success of vaccines. A recently described subset of memory CD8⁺ T cells defined by intermediate expression of the chemokine receptor CX3CR1 was shown to have self-renewal, proliferative, and tissue-surveillance properties relevant to vaccine-induced memory. We tracked these cells when memory is sustained at high levels: memory inflation induced by cytomegalovirus (CMV) and adenovirus-vectored vaccines. In mice, both CMV and vaccine-induced inflationary T cells showed sustained high levels of CX3R1^int cells exhibiting an effector-memory phenotype, characteristic of inflationary pools, in early memory. In humans, CX3CR1^int CD8⁺ T cells were strongly induced following adenovirus-vectored vaccination for hepatitis C virus (HCV) (ChAd3-NSmut) and during natural CMV infection and were associated with a memory phenotype similar to that in mice. These data indicate that CX3CR1^int cells form an important component of the memory pool in response to persistent viruses and vaccines in both mice and humans.