Peripheral blood cells chimerism after unrelated cord blood transplantation in children: kinetics, predictive factors and impact on post-transplant outcome.
Résumé
This study aimed to describe kinetics of complete donor chimerism occurrence (cDC, >99*9% donor) after unrelated cord blood transplantation (UCBT), to identify its predictive factors and its impact on post-transplant outcome. Ninety-four children who received single UCBT after a myeloablative conditioning regimen had blood chimerism evaluation at predefined post-transplant dates, using a real-time polymerase chain reaction method with 0*1% sensitivity. Cumulative incidence of cDC at 1 year post-transplantation was 61*8%. Three predictive factors were identified in multivariate analysis: history of malignant disease (P = 0*03), older age (above 2*16 years, the first quartile of age, P = 0*0055) and higher level of cord/recipient human leucocyte antigen mismatch (4/6 vs. 5-6/6, P < 0*001) increased the probability of post-transplant cDC. Although graft cell dose had a strong impact on haematological recovery, it did not apparently influence cDC occurrence. Early cDC (i.e. more than 99*9% donor chimerism on days 15-30 post-transplant) appeared useful to predict engraftment (P = 0*003) as well as acute and chronic graft-versus-host disease (GvHD). Severe acute or chronic GvHD never occurred in patients with DC ≤99*9%, suggesting than even minimal residual host haematopoiesis is associated with a very low risk of GvHD after UCBT.