Transition of adult T-cell leukemia/lymphoma clones during clinical progression.

Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell neoplasm caused by the transformation of HTLV-1-infected T cells. ATLL, especially its aggressive form, is known for its poor prognosis, even with intensive chemotherapy. ATLL cells are considered to be monoclonal; however, multiclonal proliferation or emergence of a new clone over time has been reported based on Southern blot analysis, although direct molecular evidence remains elusive. Furthermore, it is thought that clonal change may be a cause of early drug resistance in ATLL. To directly analyze potential clonal changes in ATLL during its clinical course, we used inverse PCR to detect integration sites in combination with a newly developed method using next-generation sequencing, and compared ATLL cell clonality at different time points. The results of inverse PCR indicated that the major clone was altered in three of 19 patients. Together with results from five patients, using this new method, we found direct evidence of clonal change occurring during the clinical course or in response to chemotherapy in ATLL. These results also highlight the importance of clonality analysis for understanding the mechanisms of ATLL development and drug resistance.