Immune recovery over time and CDH17 expression in thymic epithelial cells. (A) T-cell numbers. (B) CD8 T-cell subsets. (C) CD4 T-cell subsets. (D) TRECs. (E) B and NK cell numbers. (F) Immunoglobulin levels. (G) CDH17 expression in the human thymus is restricted to the population of mature medullary epithelial cells (mTEC^hi) as shown by quantitative reverse transcription PCR analysis. mTEC^hi is a heterogeneous population of thymic epithelial cells that primarily consists of functionally mature, AIRE-expressing cells.