Because both Smad3–Ser208 phosphorylation and Smad3–Foxo3a interaction were detectable only in LT-CML stem cells (Fig. 3e), we wondered whether the phosphorylation of Smad3–Ser208 might be involved in regulating Foxo3a's recently reported function in CML stem cell maintenance15. Here, FOXO3 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.