CD8 T Cells Are More Frequent in CMV Seropositive Bone Marrow Grafts and Display Phenotype of an Adaptive Immune Response.

The role of gamma delta () T cells in human cytomegalovirus (HCMV) immune surveillance has been the focus of research interest for years. Recent reports have shown a substantial clonal proliferation of T cells in response to HCMV, shedding light on the adaptive immune response of T cells. Nevertheless, most efforts have focused on V2 T cell subset while less attention has been given to investigate other less common T cell subsets. In this regard, a distinct subpopulation of T cells that expresses the CD8 coreceptor (CD8 T cells) has not been thoroughly explored. Whether it is implicated in HCMV response and its ability to generate adaptive response has not been thoroughly investigated. In this study, we combined flow cytometry and immune sequencing of the TCR -chain () to analyze in-depth bone marrow (BM) graft T cells from CMV seropositive (CMV+) and CMV seronegative (CMV-) donors. We showed that the frequency of CD8 T cells was significantly higher in CMV+ grafts compared to CMV- grafts ( < 0.001). Further characterization revealed that CD8 T cells from CMV+ grafts express V9 and preferentially differentiated from a naive to terminal effector memory phenotype (CD27CD45RO). In line with these findings, immune sequencing revealed clonal focusing and reduced usage of the V9/JP gene segment in a CMV+ graft. Furthermore, CD8 T cells showed an enhanced response to TCR/CD3 and cytokine stimulation in contrast to CD8 T cells. We conclude that T cells in BM grafts are reshaped by donor CMV serostatus and highlight the potential adaptive role of CD8 T cells in HCMV immune response.