CD70 defines a subset of proinflammatory and CNS-pathogenic T

CD70 is the unique ligand of CD27 and is expressed on immune cells only upon activation. Therefore, engagement of the costimulatory CD27/CD70 pathway is solely dependent on upregulation of CD70. However, the T cell-intrinsic effect and function of human CD70 remain underexplored. Herein, we describe that CD70 expression distinguishes proinflammatory CD4(+) T lymphocytes that display an increased potential to migrate into the central nervous system (CNS). Upregulation of CD70 on CD4(+) T lymphocytes is induced by TGF-β1 and TGF-β3, which promote a pathogenic phenotype. In addition, CD70 is associated with a T(H)1 and T(H)17 profile of lymphocytes and is important for T-bet and IFN-γ expression by both T helper subtypes. Moreover, adoptive transfer of CD70(−/−)CD4(+) T lymphocytes induced less severe experimental autoimmune encephalomyelitis (EAE) disease than transfer of WT CD4(+) T lymphocytes. CD70(+)CD4(+) T lymphocytes are found in the CNS during acute autoimmune inflammation in humans and mice, highlighting CD70 as both an immune marker and an important costimulator of highly pathogenic proinflammatory T(H)1/T(H)17 lymphocytes infiltrating the CNS.