In vitro culture of fresh ATLL cells and long-term ATLL T-cell lines, constitutively express TGF-β (Transforming Growth Factor-β) mRNA and secrete TGF-β [97,124,125], although TGF-β levels in the serum of ATLL patients are not significantly different from that of healthy donors [53]. Here, TGFB1 is linked to adult T-cell leukemia/lymphoma.