Early achievement of full donor chimerism after allogeneic hematopoietic stem cell transplantation predicts lower relapse risk in patients with acute lymphoblastic leukemia

Background: Acute lymphoblastic leukemia (ALL) remains one of the most difficult-to-cure hematological malignancies. Allogeneic hematopoietic stem cell transplantation (HSCT) provides curative potential but a substantial proportion of patients eventually will relapse. It is unknown if there are any modifiable factors exists that could improve survival or predict relapse immediately after HSCT is unknown. The aim of this study was to explore whether achieving early (<30 days) full donor chimerism (FDC) could predict disease relapse after allogeneic HSCT in ALL patients. A second objective is to examine the impact of achieving early donor chimerism on survival. Methods: This study retrospectively enrolled 55 ALL patients undergoing allogeneic HSCT during the 10-year period from 1999 to 2008. Analysis of short tandem repeats (STR) was used to determine donor chimerism, and was prospectively followed at the time of engraftment and on days 30. Patients with early treatment-related mortality (<30 days), without STR analysis, or who were lost to follow-up before FDC were excluded. Survival analyses were performed using Kaplan–Meier Methods. Cox proportional hazard analyses were performed for poor prognostic factors associated with overall survival (OS) and relapse-free survival (RFS). Results: The general characteristics were comparable between patients with early donor chimerism (n = 31) and those with late donor chimerism (n = 24). Survival analyses showed patients with early FDC had both lower probability of relapse (χ² = 5.770, p = 0.022) and longer RFS than those with late chimerism. The OS was not different according to the chimerism status on days 30. In the Cox proportional hazard analyses, early FDC is a significant factor predictive for longer RFS (HR = 0.264, p = 0.010). Conclusion: Our results indicate that the achievement of early FDC within 30 days after allogenic HSCT can be used as a significant predictor of RFS. The results underscored the need to improve outcome in ALL patients with late FDC.