The fate of CD4^-8^- T cell receptor-αβ⁺ thymocytes

CD4^-8^- TCR-αβ⁺ thymocytes represent a distinct population whose fate and function have remained a mystery. We show here that this thymocyte subset bears NK1, a surface Ag previously thought to be expressed exclusively by TCR^- NK cells. Analysis of peripheral lymphocytes for the coexpression of TCR-αβ and NK1 revealed a subset with similar characteristics to the NK1⁺ thymocytes: a large fraction that are CD4^-8^- and a skewed TCR repertoire in which Vβ8 is overrepresented. Thymus transplant experiments into congenically marked athymic (nude) mice revealed that the NK1⁺TCRαβ⁺ subset was exclusively thymus derived and represented a distinct subset from the thymus-independent NK1⁺TCR^- population. Finally, the NK1⁺TCRαβ⁺ population preferentially localizes to the bone marrow. These results demonstrate that this T cell subset is exported to the periphery after developing in the thymus. Their unique surface Ag expression and tissue localization suggest an immune function distinct from classical T cells.