Comparison of the effect of cytokines on the cycling status of LTC-IC present in the marrow of the same groups of (A) bone marrow and (B) cord blood-transplanted mice shown in Fig 1. Values shown represent the mean ± SEM of data obtained from the overnight³H-thymidine suicide assay described in Materials and Methods. Only the addition of TGF-β₁ (P < .001) was found to have a significant effect.