Prior Treatment with Alemtuzumab Interferes with T-Cell Engraftment After Allogeneic Stem Cell Transplantation in Patients with Chronic Lymphocytic Leukemia.

The majority of patients with chronic lymphocytic leukemia (CLL) who receive allogeneic hematopoietic cell transplantation (HCT) have fludarabine-refractory disease. The most active single agent in this disease stage is alemtuzumab. Alemtuzumab has a long half-life and induces profound T-cell depletion (TCD). Since TCD may mitigate graft-versus leukemia effects we evaluated „pre-conditioning“ with alemtuzumab followed by a washout period in order to minimize in vivo T-cell depletion of the graft in a phase II study (NCT 00337519).

Patients received cytoreductive treatment with 3 × 30 mg alemtuzumab weekly prior to HCT. The scheduled interval between last dose of alemtuzumab and HCT was increased from two weeks to one month during the study. The antibody level at the day of HCT was measured with an ELISA with a lower limit of detection of 31.25 ng/mL (BioAnaLab lim., Oxford, UK). The conditioning regimen contained fludarabine (150 mg/m²) and busulfan (8 mg/kg). Cyclosporine (CSA) and methotrexate (MTX) were applied as GVHD-prophylaxis. Medically fit patients with relapsed CLL were elible.

62 patients with a median age of 57 years were included between April, 2004 and October, 2008. A median of 3 prior regimens had been given. 55% of the patients had fludarabine-resistant disease. Two patients failed to reach HCT due to progressive disease during alemtuzumab therapy. Donors were matched siblings for 26 and matched unrelated donors for 34 patients. The median level of alemtuzumab in peripheral blood after a washout period of two weeks was 62 ng/mL (interquartile range, 45 to 196 ng/mL; minimum below the limit of detection; maximum 490 ng/mL) compared to a median level below the limit of detection after a delay of four weeks (interquartile range, between the limit of detection and 77 ng/mL, maximum 256 ng/mL) (p=0.005). Despite one month time between the last dose of alemtuzumab and HCT 4 out of 30 patients (13%) had alemtuzumab levels greater than 200 ng/mL. No primary or secondary graft failure occurred. A linear relationship between the alemtuzumab level at HCT and the time to complete CD4-T-cell chimerism (TCC) was observed (p=0.003). At day +100 a CD4 positive T-cell-chimerism (TCC) >95% had been achieved by 84% of patients with alemtuzumab levels <100 ng/mL, 83% of patients with antibody levels between 100 and 200 ng/mL and 25% of patients with antibody levels >200 ng/mL (p=0.006). All patients had a complete neutrophil-chimerism at day +100. After early taper of immunosuppression (N=2) or the application of donor lymphocyte infusions in incremental doses (N=5) mixed TCC has been converted to complete TCC in all patients. The median follow-up is 17 months (1 to 61 months). Day +100 non-relapse mortality was 2%. At two years non-relapse mortality and relapse incidence were 21% and 29%, respectively. Two-year overall survival and progression-free survival were 67% (95% CI, 51% to 83%) and 50% (95% CI, 31% to 69%).

In patients who received alemtuzumab prior to HCT, residual drug levels may interfere with T-cell engraftment. Lineage specific T-cell chimerism should therefore be assessed prospectively in this group of patients. Persistent mixed T-cell chimerism can be converted by an early taper of immunosuppression and incremental doses of donor lymphocyte infusions.

Schetelig:Bayer Schering: Research Funding. Platzbecker:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.