T-ALL 5178 CD7⁺CD1a⁺ cells from NS122 xenograft proliferated in OP9-DL1 coculture. T-ALL 5178 cells recovered from the BM of engrafted NS122 recipients were sorted for the CD7⁺CD1a⁺ subset using flow cytometry-based cell sorting. 5 × 10⁴ Cells (5 × 10⁴) were placed into OP9-DL1 or OP9-GFP stroma for coculture. Cells were counted weekly with trypan blue for dead cell exclusion. CD7⁺CD1a⁺ cells from NS122 xenografts proliferated in excess of 50 days in OP9-DL1 coculture, but cell numbers declined rapidly in control OP9-GFP coculture.