Qualitative and quantitative polymerase chain reaction monitoring of minimal residual disease in relapsed chronic lymphocytic leukemia: early assessment can predict long-term outcome after reduced intensity allogeneic transplantation

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Abstract
The graft-versus-leukemia effect is able to induce clinical responses in patients with chronic lymphocytic leukemia treated with a reduced intensity conditioning regimen, followed by allogeneic stem cell transplantation. We investigated whether molecular remissions could be attained after reduced intensity conditioning and allogeneic stem cell transplantation in patients with relapsed chronic lymphocytic leukemia and whether the assessment of minimal residual disease might be used to predict the clinical outcome.Minimal residual disease was monitored by polymerase chain reaction using the immunoglobulin heavy-chain gene rearrangement as a molecular marker in 29 relapsed patients who achieved complete remission following reduced intensity conditioning and allogeneic stem cell transplantation. A nested-polymerase chain reaction with patient-specific primers derived from complementarity determining regions (CDR2 and CDR3) was carried out in all the patients. Real-time polymerase chain reaction was performed in patients whose nested reaction gave positive or mixed results.Three patterns of minimal residual disease were observed: negative (31%), mixed (24%), and always positive (45%). The cumulative incidence of relapse according to the minimal residual disease status at 6 and 12 months after transplantation was significantly different between polymerase chain reaction-negative and -positive patients (p=0.031 and p=0.04, respectively). Two-year disease-free survival was 93% and 46% for polymerase chain reaction-negative and -positive patients at 6 months after transplantation, respectively (p=0.012). Similarly, 2-year disease-free survival was 100% and 57% for polymerase chain reaction-negative and -positive patients at 12 months, respectively (p=0.037). No clinical or biological factors were predictive of the achievement of polymerase chain reaction negativity after allogeneic stem cell transplantation. Graft-versus-host disease was more frequent in patients who did not relapse (p=0.04). Quantitative monitoring of minimal residual disease was able to identify polymerase chain reaction-positive patients with a higher risk of relapse.These findings demonstrate that relapsed patients can achieve molecular remission after reduced intensity conditioning and allogeneic stem cell transplantation and suggest a minimal residual disease-driven intervention that might be useful to prevent overt hematologic relapse.

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