Higher doses of CD34+ PBPC are associated with a rapid acquisition of full donor chimerism and lower risk of relapse after allogeneic transplantation in pediatric patients with hematological malignancies.

We conducted a retrospective study assessing the predictive value of early full donor chimerism status for relapse after allogeneic peripheral blood progenitor cell transplantation in 40 children aged between 1 and 16 years (median 8) with leukemia. The only variable that had a significant influence on chimerism status in either univariate or multivariate analysis was the number of CD34 cells infused. We found that the patients who were in complete donor chimerism by day +30 had a lower probability of relapse than those who were not (14% ± 6% versus 54% ± 15%; HR, 5.24; 95% confidence interval, 2.10-43.63; P = 0.003). Mixed chimerism by day +30, absence of chronic GvHD, and advanced disease at transplantation were significant risk factors for relapse in our patients. Children who presented early complete chimerism had a probability of developing chronic graft versus host disease significantly higher than patients with mixed chimerism (P = 0.04). Therefore, the analysis of chimerism kinetic in children undergoing peripheral blood progenitor cell transplantation would permit an early identification of patients at risk of relapse and patients with high risk of developing chronic graft versus host disease.