Consolidation with Alemtuzumab in First Remission Induces Pronounced MRD Reduction and Clinical Remissions - Update on a Randomized Phase III Trial of the German CLL Study Group (GCLLSG).

The monoclonal antibody alemtuzumab is known to be effective in combination or alone in patients with late stage chronic lymphocytic leukaemia. Flow cytometric studies on minimal residual disease (MRD) showed the high potency beyond clinical response criteria even in late stage chronic lymphocytic leukaemia (CLL). The aim of the phase III trial of the GCLLSG was to investigate the role of alemtuzumab as consolidation therapy in CLL patients in first clinical remission after fludarabin (F) or F plus cyclophosphamide (FC).

Patients in partial or complete clinical remission were randomized to either arm A (alemtuzumab 3 x 30 mg i.v. for up to 12 wks) or no further treatment (arm B). From 21 eligible patients 11 (1CR, 1 nPR, 9PR) were randomized to arm A. All patients received standard infection prophylaxis with famciclovir and trimethoprim/sulfamethoxazole. Before, at 6 and 12 weeks after start of consolidation therapy and regulary during follow up blood and bone marrow samples were send for molecular MRD assessment by allele specific real time PCR. The PCR allowed MRD assessment with a sensitivity of at least 10E-4 in 11 eligible cases.

Results: MRD analysis showed clear reduction of CLL content by first line treatment to a median MRD level of 2.2E-3. Short after alemtuzumab treatment all treated patients showed pronounced MRD reduction to a median MRD level of 5.0E-5. During molecular follow-up median MRD level remained below 1E-4 for one year with a tendency to increase afterwards. After a median follow-up of 31.3 months from start of initial treatment occurred one relapse in the treatment arm compared to 7 of 10 in arm B. The median progression free survival (PFS) calculated from start of consolidation therapy was significantly shorter in the control group versus the treatment group (pfs 25.2; p= 0.04). Nevertheless due to severe acute infections (CTC III and IV) this study had to be stopped prematurely.

Conlusion: The addition of alemtuzumab as a consolidation regimen after remission induction by F or FC is highly effective and leads to sustained MRD reduction below 10E-4. This translates into significant improved clinical outcome even in this small patient cohort compared to the control group. Encouraged by the molecular responses the GCLLSG initiated a new phase I/II trial as a dose finding study in CLL patients after F based induction of clinical remission.