Impaired development of both αβ and γδ T cells from the earliest human thymic precursors in hu/mo FTOCs treated with the γ-secretase inhibitor DFK167. Fetal murine thymic lobes seeded with normal TN1 human thymocytes were cultured in the presence of DFK167 γ-secretase inhibitor (50 μM) or DMSO, added fresh every 12 hours for 19 days. Absolute numbers of cells for the indicated subsets were normalized to 2 × 10³ cells/lobe. Results are representative of 2 independent experiments.