Flow Cytometric Detection of Minimal Residual Disease One Year Post Allogeneic Stem Cell Transplantation Predicts Outcome in Patients with B-CLL.

In a completed study (NCT00337519), patients with advanced B-CLL received allogeneic stem cell transplantation (SCT) after cytoreductive treatment with alemtuzumab followed by a wash-out period for the antibody and conditioning with fludarabine/busulfan. Aim of the present investigation was to correlate flow cytometric levels of minimal residual disease (MRD) in the peripheral blood at different time points after transplantation with patient outcome.

In 58 CLL patients 900 flow cytometric MRD investigations (at least 4 measurements/patient: at day 30, between days 31–100, 101–180, and 181–365 after SCT) were performed measuring the following CLL phenotype: CD19^posCD5^posCD20^dimCD79b^neg. Therefore, a 4-color-approach (FACSCalibur, until 2006) or an 8-color-approach then in combination with T- and NK cell antigens (FACSCanto) was performed. A patient was defined as MRD negative if less than 0.05% CLL cells were detectable or as relapse if more than 0.05% CLL cells were again redetectable in at least two successive investigations. For assessment of progression-free survival (PFS), clinical progress was defined according to the NCI criteria.

The median follow up time after SCT was 536 days (range: 44d –1758d). Considering all 58 transplanted patients the probability of one-year overall survival (OS) including the 95% confidence interval was 83% ± 10% (2-year OS: 76%±12%) and of one-year PFS 74% ± 12% (2-year PFS: 50%±16%). In the majority of cases flow cytometric MRD negativity was achieved within the first year post SCT with a cumulative incidence of 36%±13% at day 100 and of 73%±12% at one year, respectively. Only two additional patients became MRD negative within the second year post SCT. Patients who achieved MRD negativity until day 365 showed a significantly better 2-year OS compared to the MRD positive group (96%±7% vs. 56%±49%; p=0.009). Remarkably, the 2-year PFS of patients achieving flow cytometric MRD negativity until day 365 was also significantly better than in the MRD positive cases (83%±16% vs. 0%, 3-year: 75%±20% vs. 0%; p=0.002). Of note, early flow cytometric MRD negativity until day 100 was not informative concerning OS or PFS at one year (88%±13% vs. 79%±15% and 77%±18% vs. 72%±18%). The flow cytometric MRD status was one trigger to speed the taper of cyclosporine or to give DLI. Interestingly, this kind of immunomodulation resulted in flow cytometric MRD negativity in eight out of nine patients after a median of 130 days. The probability of relapse in the investigated patient cohort was 15%±10% after 1 year and 31%±14% after 2 years. Thus, 8/14 patients showed a clinical relapse in parallel with flow cytometric MRD positivity. Two patients featured an isolated flow relapse with MRD at two successive investigations. Four patients showed a mere nodal relapse, all but one occurring within the first year post SCT.

In summary, the present flow cytometric MRD study in B-CLL patients elucidates the dynamics of remission induction and relapse in the first year post SCT. In the majority of patients MRD is eradicated between day +100 and day +365 which is the time interval when chronic GvHD occurs in most cases. Therefore, close monitoring of MRD status in the first year after SCT is necessary. Once patients are flow cytometrically MRD negative at day 365, they seem to have a high probability of long term survival.

Schetelig:Schering-Bayer: Research Funding.