Bootcongres

The early events of human CD8 T cell differentiation upon viral infection still remain poorly understood. Bucholtz recently postulated a linear developmental path progressing from slowly-proliferating long-lived to rapidly-expanding short-lived subsets, based on experiments in mice (Science, 2013). We aimed to study the early changes within the CD27^brightCD45RA^bright, naïve CD8 T cell subset upon viral infection. Longitudinal flowcytometric analysis of the transcription factors (TF) T-bet, eomesodermin (Eomes) and hobit, proliferation marker Ki-67, granzyme content and other phenotypical markers was performed on PBMC’s of two patients experiencing a primary hCMV and a patient experiencing hCMV-reactivation after kidney transplantation. Prior to the primary infection the percentage of TF-expressing naïve CD8 T cells (defined as CD27^brightCD45RA^bright) did not exceed 2%. The majority of these cells were Ki-67ˉ IL-7Rα⁺ KLRG1⁺ granzyme K⁺ granzyme Bˉ. During the acute phase of an anti-hCMV response the percentage of TF-expressing CD27^brightCD45RA^bright CD8 T cells kept rising steadily, to a staggering 20%, until cessation of hCMV replication. Up to a quarter of these TF-expressing-CD27^brightCD45RA^bright CD8 T cells expressed ki-67, more than half lost IL7Ra-expression and up to one third contained granzyme B. No rise of TF-expressing-CD27^brightCD45RA^bright cells was seen during hCMV reactivation. After cessation of viral replication the percentage of TF-expressing cells within the CD27^brightCD45RA^bright CD8 T cells declined rapidly. Although these cells no longer expressed Ki-67, their phenotype during latency remained highly divers.
In conclusion, during primary hCMV infection the CD27^brightCD45RA^bright CD8 T cell compartment contains a variety of actively dividing cells with memory- and effector-cell traits. Our study demonstrates that especially during acute viral infections, cell surface phenotyping is not an accurate way to separate naïve from antigen-experienced cells.