Semiquantitative analysis of residual disease in patients treated for adult T-cell leukaemia/lymphoma (ATLL) I NDIA L ECLERCQ, 1 F RANCK MORTREUX , 1 F RANCK MORSCHHAUSER , 1,2 PATRICK D UTHILLEUL , 3 C LAUDE D ESGRANGES , 4 A NTOINE G ESSAIN, 5 MARIELLE C AVROIS , 1 *J EAN-PAUL V ERNANT, 6 O LIVIER H ERMINE 7 AND E RIC WATTEL 1,2,8 1 Unite ´ 124 INSERM, Institut de Recherche sur le Cancer de Lille, 2 Service des Maladies du Sang, CHU, Lille, 3 De ´partement d’He ´matologie, Immunologie et Cytoge ´ne ´tique, Centre Hospitalier, Valencienne, 4 U271 INSERM, Lyon, 5 Unite ´ d’Epide ´miologie des Virus Oncoge `nes, Institut Pasteur, Paris, 6 Service d’He ´matologie, Ho ˆpital de la Pitie ´ Salpe ˆtrie `re, Paris, 7 Service d’He ´matologie, Ho ˆpital Necker, Paris, and 8 Unite ´ d’Oncogene `se Virale, Centre Oscar Lambret, Lille, France Received 9 October 1998; accepted for publication 12 February 1999 Summary. Many adult T-cell leukaemia/lymphoma (ATLL) patients who respond to induction treatment, then relapse. Knowing the clonality pattern of residual tumourous clones during treatment could help understand disease evolution and aid therapeutic decisions. We developed a sensitive and semi-quantitative molecular analysis of these clones in ATLL patients. DNA samples from PBMCs derived from eight ATLL patients were studied over time by quadruplicate linker mediated PCR (LMPCR) amplification of HTLV-1 integration sites. Patients were treated with combination chemotherapy, zidovudine–interferon-alpha and/or by peripheral stem cell transplantation or allogeneic bone marrow transplantation. Persistence of tumourous clones at a high frequency (>1/ 300 PBMCs) was frequently observed, even in complete responders, and was invariably correlated with relapse and/ or poor outcome. Fluctuation in the frequency of some tumourous clones was observed with evidence for clonal change under treatment in one patient, indicating that treatment of ATLL can result in the selection of resistant clones. Finally, allogeneic bone marrow transplantation (BMT) using an HTLV-1 infected sibling as donor was found to be associated with long-lasting disappearance of tumourous clones and a possible cure of the disease. Long- term persistent clonal expansion of circulating HTLV-1 bearing T cells which derived from the donor bone marrow was evidenced in this patient. In conclusion,variable success in treatment of ATLL is probably due to the clonal heterogeneity which results in the selection of resistant clones. Semi-quantitative assessment of residual disease (RD) through LMPCR may predict treatment failure. Accordingly, additional therapy may be tailored to the clonality pattern observed after first-line therapy. Keywords: adult T-cell leukaemia/lymphoma, HTLV-1, clonality, residual disease, bone marrow transplantation. Adult T-cell leukaemia/lymphoma (ATLL) is a malignant T- cell disorder caused by HTLV-1 (Poiesz et al, 1980; Yoshida et al, 1982). About 30–50% of patients treated for ATLL achieve complete remission after combination chemo- therapy or treatment by zidovudine and interferon-alpha (Shimamoto et al, 1990; Gill et al, 1995; Hermine et al, 1995). Many of these patients relapse and the overall survival remains short (Shimamoto et al, 1990). However, long-term disease-free survival can be obtained after consolidation by allogeneic bone marrow transplantation (BMT) (Borg et al, 1996; Sobue et al, 1987). Routine molecular techniques, such as Southern blotting or PCR amplification of the VDJ segment of the TCR gene, are inadequate for extensive monitoring of residual disease (RD) in ATLL, due to their low sensitivity or their inability to detect clonal change (Shimamoto et al, 1993; Shimoyama et al, 1991). Accordingly, therapeutic decision making, especially regarding intensive consolidation (Borg et al, 1996; Sobue et al, 1987), remains difficult for the patients who respond to induction therapy, calling for a test which creates a better understanding of disease evolution at the molecular level. We used a sensitive and semi-quantitative linker mediated British Journal of Haematology , 1999, 105, 743–751 743  1999 Blackwell Science Ltd *Present address: Institute of Human Virology, Medical Biotech- nology Center, University of Maryland at Baltimore, 725 West Lombard Street, Baltimore, MD 21201, U.S.A. Correspondence: Dr E. Wattel, Service des Maladies du Sang, CHU, Ho ˆpital Huriez, 1 place de Verdun, 59037 Lille, France. e-mail: wattel@ lille.inserm.fr.