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Age-Related Accumulation of a Novel CD44 + CD25low T-Cell Population in Hematopoietic Organs of the Mouse

Department for Gene and Cell Medicine, Mount Sinai School of Medicine, New York.

Address correspondence to Hans-Willem Snoeck, MD, PhD, Department for Gene and Cell Medicine, Mount Sinai School of Medicine, Box 1496, Gustave L. Levy Place, New York, NY 10029. E-mail: hans.snoeck{at}mssm.edu

We discovered a novel population of T cells in the mouse that accumulates with age in hematopoietic organs, but not in epithelia. These cells are CD25low (an unusual phenotype for T cells in the mouse); express higher levels of TCR and CD44 than do CD25– T cells; mainly express V2, V3, and V4 chains; and are largely quiescent. A very similar cell population appears in the late stages of fetal thymus organ cultures, suggesting that the accumulation of CD44 + CD25lowTCR + cells is a response to stress induced by aging in vivo or by culture in vitro. The precursors of CD44 + CD25lowTCR + cells are generated during fetal or very young adult life, as this population was undetectable in aged recipients of bone marrow from old or young donors. CD44 + CD25lowTCR + cells may be a biomarker of aging, but could also play a role in the inflammatory changes that accompany aging.