Background. ATL is an HTLV-I-associated hematological malignancy. The majority of ATL patients are not curable using current chemotherapy with median survival time of 13 months. Recently, patients undergoing allo-SCT with conventional conditioning regimen were reported to have a 3-year overall survival (OS) rate of 45%, however, with high transplant-related mortality (TRM) rate as much as 40% (

Fukushima T. Leukemia 19:829, 2005
). Since most ATL patients are over 50 years old with various complications, limited numbers of patients are eligible for conventional transplant. We have already conducted a phase I multi-center trial testing the feasibility of RIST in ATL patients, where 2-year OS was 33% and some differences in the outcome were suggested among participating institutes. Hence, we investigated the efficacy of RIST performed exclusively in our single institute (NCCH, Japan).

Patients and Methods. Between Oct 2000 and Jun 2005, 16 ATL patients underwent RIST from a related donor. Since 3 have been enrolled into an on-going multi-center trial, 13 patients were analyzed in this retrospective study, including 3 who were enrolled into the above-mentioned multi-center trial (

Okamura J. Blood 105;4143, 2005
). Median age was 51 years old (range, 44–61), 8 males and 5 females, and 8 were of acute type and 5 of lymphoma. The disease status at transplant was 3 CR, 7 PR and 3 primary refractory. Three donors were HTLV-I healthy carriers. Eleven were HLA 6/6, 2 were 5/6, 12 were PBSCT and 1 was BMT. Conditioning regimen was fludarabine 30 mg/m2 x6, busulfan 4 mg/kg x2 with (n=5) or without (n=8) rabbit ATG 2.5 mg/kg x2. Prophylaxis of GVHD was CSP alone.

Results. Engraftment was rapid (median, 11 days) in all cases, and there was no TRM. Acute GVHD of grade II–IV developed in 7, and chronic extensive GVHD in 5. Eleven patients achieved CR after RIST, and 6 relapsed or progressed, among whom 2 achieved CR after cessation of CSP, donor lymphocyte infusion and local irradiation, and have been disease-free for more than 1 year. Ten patients are alive, 9 without disease, with median follow-up time of 26 mos (range, 4–45 mos). HTLV-I proviral titers determined using real time PCR decreased after RIST and became undetectable in 8 out of 13 patients. In 3, including one transplanted from an HTLV-I carrier donor, anti-HTLV-1 antibody transiently decreased and became nearly undetectable.

Conclusions. RIST is feasible and safe in ATL patients, and it has not only an anti-ATL but also an anti-HTLV-I activity. This is the first report documenting the efficacy of RIST for ATL in terms of survival and remission durability.

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Topics:
adult t-cell lymphoma/leukemia, disease remission, hematopoietic stem cell transplantation, htlv-i infections, human t-lymphotropic virus 1, leukemia, t-cell, leukemia-lymphoma, t-cell, acute, htlv-i-associated, lymphoma, radioimmunosorbent test, transplantation

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2005, The American Society of Hematology
2005
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