Proliferation of ROR1⁺ and ROR1^– cell populations. Cells from BCP-ALL (Pts 16, 17, and 19) (A), T-ALL (Pts 20, 22, and 27) (B), and 3 NBM cases (C) were stained with proliferation marker, CTV before being cultured for 7 days. CTV MFI of ungated, ROR1⁺ and ROR1^– cells and subpopulations was compared between day 0 (undivided) and day 7 cells and analyzed by Kruskal-Wallis test. ∗P = .04. Data are expressed as mean ± standard deviation (SD). MFI, median fluorescence intensity.