CMV-specific central memory T cells reside in bone marrow

CMV-specific CD8(+) T cell responses in peripheral blood (PB) are characterized by a preponderance of effector and effector memory T cells. CMV-specific central memory T cells (T-CM), which are considered crucial in maintaining long-term immunity, are rarely detectable in PB. In this study we have analyzed differentiation and function of CMV pp65-specific CD8(+) T cells in paired samples of human PB and BM using intracellular cytokine and tetramer staining. Overall frequencies of CMV pp65-specific T cells were similar in PB compared to BM; however, CMV-specific CD45RA(-)CCR7(+) T-CM were almost exclusively detectable in BM, which was not related to a general accumulation of T-CM in BM. In vitro, CMV-specific T cells could be more efficiently expanded from BM (median 128-fold, n=6) than from PB (median 72-fold, p=0.01). Taken together, these data show that the BM is a compartment harboring CMV-specific T-CM and underline the concept of the BM as a secondary immune organ. CMV specific BM-derived T-CM might be a valuable source for generating T cells for adoptive transfer.