SB431542, which is considered to be a TGF-β receptor (ALK4/5/7) inhibitor, could partly abolished the protective effects of the CAFs for the tumor cells from chemotherapy (Fig. 3i), indicating that the chemo-protection for AML cells from CAF was mediated by some soluble substances, most likely TGF-β superfamily. The gene discussed is ACVR1B; the disease is acute myeloid leukemia.