Relapse of hematological malignancy remains a major complication after allogeneic stem cell transplantation. This is especially true for patients receiving minimal or reduced-intensity conditioning therapy. Analysis of donor chimerism (DC) is an important diagnostic tool to assess the risk of relapse after allogeneic stem cell transplantation, especially in patients lacking a specific marker suitable for monitoring of minimal residual disease. The sensitivity of a standard PCR assay amplifying short-tandem-repeat sequences can be improved significantly by investigating sorted CD34+ peripheral blood cells. We prospectively compared the serial analysis of DC in selected CD34+ cells and unmanipulated whole blood (WB) within a randomised study in 131 patients with CD34+ hematological malignancies (AML, ALL and MDS) surviving more than 100 days after transplantation. The primary end-point was the association between decreasing CD34+ DC and haematological relapse. Whenever a decreasing CD34+ or WB DC was confirmed and no signs of active GvHD were present, a rapid taper of CsA or tracolimus (50% every 5–7 days) was suggested. If no GvHD occurred within 14 days after the stop of CsA or tacolimus, patients were scheduled to receive donor lymphocyte infusions (DLI) in incremental doses. The cumulative incidence of relapse was significantly increased in patients with decreasing or incomplete CD34+ DC (62% vs. 38%, p=0.01). This was associated with a lower probability of overall survival (20% vs. 39%, p=0.03). The interval between the decrease in CD34+ DC and hematological relapse was 35 days (range 0–567) in the study group compared to only 8 days (range 0–63) in the control group monitored by WB DC analysis (p=0.05). The median time between a decrease in CD34+ DC and WB DC was 14 days (range, 0 to 445). Patients receiving preemptive therapy triggered by decreasing CD34+ DC had a significantly higher probability of disease-free survival compared to cases monitored and treated according to WB DC (19% vs. 0%, p=0.009). Multivariate analysis revealed age, disease-risk and decreasing CD34+ DC as independent risk-factors for overall survival in the study group. In summary, we could demonstrate that the quantification of DC in CD34+ selected cells is a sensitive method to predict relapse and survival after allogeneic SCT. Although this technology opens a window for preemptive therapy, new treatment approaches have to be employed to improve the overall outcome of patients with recurrence of residual disease after allogeneic stem cell transplantation.

Disclosures: Bornhaeuser:Deutsche Krebshilfe: Research Funding. Thiede:Deutsche Krebshilfe: Research Funding.

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