Development of T cells in vitro from UCB- but not from hESC-derived hematopoietic progenitor cells. (A) CD34⁺ UCB cells or (B) CD34⁺ hESC-derived cells were cocultured with OP9-DL1 or OP9-GFP stromal cells. Cells were harvested at the indicated time points and analyzed by flow cytometry for surface expression of CD4, CD8, CD7, and CD1a. (C) FTOC culture of UCB- and hESC-derived hematopoietic progenitors. CD34⁺ cells from UCB and hESC/S17 sources were cultured for 12 days in mouse fetal thymic lobes. Cultured cells were analyzed by flow cytometry for expression of CD4 and CD8 using antibodies specific for human proteins. (D) CD34⁺ CD45⁺ hESC-derived progenitors were cocultured with OP9-DL1 for 14 days and analyzed by flow cytometry for expression of CD4, CD8, CD11c, CD123, CD33, CD45, and CD56.