Tissue-resident memory T cells are defined by their expression of the surface marker CD69 and the lack of sphingosine-1-phosphate receptor 1 (S1PR1), a chemokine receptor which senses sphingosin-1-phophate in the blood and promotes exit of cells from tissues into the blood. In a recent publication, researchers at the German Rheumatology Research Center (DRFZ) compared single-cell transcriptomes and T cell receptor (TCR) repertoires of memory T cells from the blood and bone marrow of human donors.<\/p>\n\n\n\n
Emilia Schneider Revueltas and colleagues found that memory T cells from blood and bone marrow show similar, but distinct gene expression profiles, but have different repertoires of antigen receptors. This identifies memory T cells of the bone marrow as a distinct, tissue-resident compartment of memory T cells.<\/p>\n\n\n\n
A minority of bone marrow-resident memory T cells expresses the marker CD69, but not the S1PR1 chemokine receptor, and thus is not attracted to the blood. The majority does not express CD69 on the cell surface and it had been unclear whether they are true residents of the bones. The DRFZ researchers found that these cells do express CD69, and also S1PR1, but both molecules dimerize and the dimer is internalized by the cells, neither molecule is expressed on the cell surface, so that the cells are also blindfolded for egress into the blood. This mechanism may also contribute to the retention of inflammation-driving T cells in chronically inflamed tissues and presents a potential target to prevent the systemic spread of inflammation.<\/p>\n\n\n\n
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