IL-7Rα expression correlates with ability to differentiate into pro-B cells in short-term culture. Adherent stromal layers were seeded with sorted subpopulations of CD34⁺-enriched marrow stained with anti–IL-7Rα FITC v CD19 PE v CD3 ECD. The percentage of TdT⁺ cells after a 2-week culture expressing each differentiation marker is indicated (mean ± SEM, n = 3). The IL-7Rα⁺ population gave rise to TdT⁺ cells with significantly lower CD34 but higher CD10 and CD19 expression than the IL-7Rα⁻ population (P < .05, paired t-test).