Reduced Intensity Stem Cell Transplantation and Donor Lymphocyte Infusion after Imatinib Induction To Eradicate Residual Disease in Chronic Myeloid Leukaemia.

Recommended first-line therapy for patients with chronic phase (CP) CML is imatinib mesylate (IM). Although IM induces complete cytogenetic responses (CCR) in the majority of patients, disease often remains detectable by Q-RT-PCR, likely reflecting stem cell persistence. Furthermore, primary and acquired resistance to IM have led to concerns about response durability. Allogeneic stem cell transplantation (SCT) remains the only curative option and with reduced intensity conditioning (RISCT) is less toxic and may be offered to a broader patient group. Our novel approach used IM to establish disease control (CCR) in patients with newly diagnosed CP CML prior to RISCT (fludarabine/melphalan/MabCampath). Prophylactic escalating DLI was given for residual disease. 18 patients (4 centres) were recruited between 2001 and 2006. Of these, 3 received myeloablative SCT, 2 for progression to blast crisis prior to SCT and the third for failing to reach a major cytogenetic response. 15 patients with a median age of 39y (21–56y) received sibling RISCT. Hasford scores were 38% low, 54% intermediate and 8% high risk. EBMT risk scores were 1–2 (13 patients) and 3–4 (2 patients). 5 patients required IM dose escalation to achieve CCR prior to RISCT. Follow-up data extends to a median of 31 (12–61) months (m) post RISCT. The RISCT procedure was well tolerated with rapid engraftment and short in-patient stays. 53% had infective episodes post RISCT, including CMV reactivation (86% patients at risk), EBV+ post transplant lymphoproliferative disease (2 patients) and PCP (1 patient). 1 patient developed aGvHD (grade III) and 8 cGvHD (6 limited, 2 extensive). DLI was given to 13 patients (87%), 6 for elevated Bcr-Abl, 4 for mixed chimerism and 2 for both. The median total dose was 0.65 × 10⁷CD3+cells/kg (0.1–6.65 × 10⁷cells/kg) in a median of 2 infusions. GvHD was seen in 6 of 12 patients receiving DLI (50%). IM was required in 4 patients with residual disease and all discontinued IM once disease control was re-established (4–13m of IM). 1 of 15 transplanted has died (at 12m with GvHD and infection). Of surviving patients median Bcr-Abl measurements fell as follow-up progressed. 8 patients currently have sustained undetectable Bcr-Abl. 7 of these 8 received DLI, the other had GvHD. The interval between last DLI and first proof of disease eradication was median 2m (range 1–28m). Only 2 of these 8 patients received IM post-transplant. In this study, the patients receiving RISCT were in early CP with a CCR to IM. It is likely that the majority would have maintained CCR if not offered transplantation. However the number of patients who achieved undetectable Bcr-Abl following RISCT and DLI compares favourably with the response expected with IM alone. The patients have tolerated the transplant procedure well and are currently off all treatment for CML. Regular monitoring remains necessary, however if relapse occurs it should be DLI responsive. Currently IM is the accepted first line therapy in the majority of patients however we would highlight the importance of RISCT in selected groups and believe our approach is effective and well tolerated.