Fgf7 does not correct age-related declines in differentiation. (A) Cell recovery from fetal thymic organ cultures 2 weeks after seeding with ETPs isolated from 15- to 18-month-old Ffg7-treated mice. Cells were harvested from thymic lobes 15 days after treatment with 1 round of Fgf7. Average ± SD total number of cells shown is pooled from 3 independent experiments. (B) Representative FACS plots from 1 of the experiments described in panel A showing CD4 and CD8 expression by cells harvested from the fetal thymic lobes.