Release of inhibition with removal of hGM-CSF from FTOC. Day-14 fetal thymic lobes were harvested from hGMR-tg embryos and placed into FTOC with or without 50 ng/mL of hGM-CSF. After 7 days of culture, a set of lobes were harvested and analyzed for the expression of CD4 and CD8. The lobes cultured with hGM-CSF were further divided to two groups. One group of lobes was cultured without hGM-CSF, whereas the other group was left in 50 ng/mL of hGM-CSF. After 7 more days of culture, cultures were harvested and analyzed for the expression of CD4 and CD8.