Human bone marrow: a reservoir for "enhanced effector memory" CD8+ T cells with potent recall function.

The role of human bone marrow (BM) CD8+ T cells in the immune response to viral Ags is poorly defined. We report here the identification and characterization of a functionally enhanced effector memory CD8+ T cell population (TEM) in the BM of patients undergoing total joint replacement for osteoarthritis. These BM-derived TEM differ strikingly from correlate cells in peripheral blood (PB), expressing elevated levels of CD27, HLA-DR, CD38, CD69, and unique patterns of chemokine receptors. Interestingly, while BM TEM have low levels of resting perforin and granzyme B, these molecules evidence profound up-regulation in response to TCR stimulation resulting in enhanced cytotoxic potential. Moreover, compared with the TEM subset in PB, BM CD8+ TEM cells demonstrate a more vigorous recall response to pooled viral Ags. Our results reveal that human BM serves as a repository for viral Ag-specific TEM with great therapeutic potential in vaccine development.