Rituximab In Allogeneic Hematopoietic Stem Cell Transplantation for Advanced Chronic Lymphocytic Leukemia with Fludarabine + Total Body Irradiation Conditioning: Results of a Phase II Prospective Multicenter Study (ITAC 02-02)

CLL remains incurable with standard therapies. Myeloablative allogeneic SCT (allo-HSCT) is still associated with high TRM and few late relapses. Recently, the major focus of transplantation in CLL has been with reduced-intensity conditioning (RIC) allo-HSCT, which is applicable to the more elderly patient population and which attempts to exploit the graft-versus-leukemia (GVL) effect that was proved in CLL

To evaluate the efficacy and toxicity a RIC regimen including fludarabine and total body irradiation (TBI) with the introduction of rituximab for allo-HSCT in patients with a CLL stage B or C diagnosis.

This prospective study included adult CLL patients with age < 65 years in stage B or C in response after a salvage treatment either following at least 2 treatment lines (1 including fludarabine) or after a progressive disease after auto-HSCT, having a HLA identical sibling donor and a good performance status (Karnfosky >70%). Donors were mobilized by G-CSF and in case of collection failure, bone marrow aspiration was authorized. The conditioning included: rituximab 375mg/m² on day -5, fludarabine 30 mg/m² from day-4 to day-2, TBI 2grays (6-7 cGrays/minute) on day 0 and rituximab 500mg/m² on day1 and day8. GVHD prophylaxis used cyclosporine A (IV 3mg/kg/day) from day-2 and mycomofetil fenolate oral (2g/day) from day 1.

Between April 2003 and December 2008, 40 patients were included, 34 (85%) males and 6 females with a median age of 54 years (35-65), 38 (95%) were in B stage at diagnosis and 2 in stage C. Among 23 explored for cytogenetics, 8 were abnormal (3 del17, 1 trisomy12, 1 t(8-11) & 1 del13). Before transplantation, 17 patients received 2 lines treatment, 10 three lines, 5 four lines, and 8>4. Only 1 patient received a previous auto-HSCT. Among 18 explored for Matutes status, 1 was in score 1, 1 in score 2, 3 in score 3, 5 in score 4 & 9 in score 5. At time of allograft, 7 (17%) patients were in complete response (CR), 29 (73%) in partial response (PR) and 4 (10%) < PR. For sex-matching, 59% were mismatched (27%of them were F>M). For ABO matching, 68% were compatible, 19% major incomp. & 13% minor incopm. The median interval diagnosis-allo-HSCT was 58 months (6-177). Median CD34+ number was 7.64 (3.1-18.7). Seven (17%) patients did not receive rituximab during conditioning because the protocol did not include it at the beginning and has been amended later.

Thirty-nine (98%) patients engrafted with a median time to neutrophils recovery of 20 days (11-70), 79% of patients reached a total donor chimerism at day 90. Seventeen patients developed aGVHD grade ≥II (8 grII, 8 grIII & 1 grIV) with a cumulative incidence at 3 months of 44% (36-52). The cumulative incidence of cGVHD was, at 12 months: 29% (21-36) for limited and extensive; at 18 months: 32% (24-40) limited and 42% (34-50) extensive. After a median follow-up of 28 months (3-71), the median OS was not reached with 3 and 5-years probability of 55%(41-74). The median time of EFS was 30 months (15 - 70) with a 5-years probability of 46%(33-66). The cumulative incidence of relapse at 1 and 3 years was 17% (11-23) and 22% (15-29) respectively. The cumulative incidence TRM at 1 and 3 years was 10% (5-15) and 27% (20-35) respectively. At the last follow-up, 17 patients died, 6 due to relapse and 11 due to TRM. We noticed a high severe infection rate (56%) and 4% of deaths related only to infection. The univariate analysis showed a positive trend of rituximab on OS and relapse, and a significant protective effect on aGVHD>=2 (p=0.02). The multivariate analysis studying age, interval diagnosis-allo-HSCT, ABO and sex matching, disease status at allo-HSCT, CD34+ number, and rituximab, showed a positive significant impact of this last factor (rituximab) on OS and EFS [HR=0.1 [0-0.6] p=0.02 & HR=0.1[0-0.4] p=0.035 respectively].

We showed interesting results in terms of OS, relapse and TRM in patients with advanced CLL after Fludarabine/TBI allo-HSCT. The introduction of rituximab allowed a better outcome especially a significant reduction of incidence and severity of acute GVHD. Nevertheless there was still a high incidence of cGVHD, already known following the Fludarabine/TBI conditioning, leading us to propose either to increase the number of rituximab injections after allo-HSCT, or to test Fludarabine/busilvex/ATG associated to rituximab.

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No relevant conflicts of interest to declare.