Both Delta1 and Jagged1 inhibit B-cell development in DN1 thymocytes, but only Delta1 promotes their maturation into CD4⁺CD8⁺ T cells. (A) Flow cytometric analysis for B-cell markers after 21 days of coculture of BM-HSCs (top row), or 11 days of coculture of thymus DN1 (bottom row) on OP9-MigR1, OP9-Jagged1, or OP9-Delta1. (B) Maturation of DN1 thymocytes into T cells after 26 days of coculture on OP9-MigR1, OP9-Jagged1, or OP9-Delta1. Early DN stages are distinguished by expression of CD44 and CD25, and maturation to the DP stage is monitored by expression of CD4 and CD8. (C) Differentiation of DN1 thymocytes into non–T-cell lineages after 26 days of coculture on OP9-MigR1, OP9-Jag1, or OP9-Delta1 by expression of CD11c and NK1.1. Numbers in quadrants refer to the percentage of gated populations in that quadrant.