Flow cytometric analysis of CD34 and CD38 expression following isolation from human cord blood and long-term coculture with OP9-control cells or OP9-DL1 cells. (A) Human HSCs were isolated into CD34⁺ and CD34^– fractions from human cord blood following a CD34-positive selection protocol on AutoMACS. As a reference for fold enrichment, we show CD34 by CD38 expression on Ficolled cord blood before and after AutoMACS enrichment. The CD34⁺ fraction obtained following AutoMACS was then sorted for the expression of CD34⁺CD38⁺ and CD34⁺CD38^– cells. The CD34⁺CD38^– cell population was then seeded onto OP9-control cells or OP9-DL1 cells. (B) CD34⁺CD38^– cells sorted from human cord blood were cocultured with OP9-control (top 2 rows of histograms) or OP9-DL1 (bottom 2 rows of histograms) stromal cells for 49 days. Initiation of differentiation and maintenance of hematopoietic potential was evaluated approximately every 4 days of coculture through the loss and gain of CD34 and CD38 expression, respectively.