Follow-up of chimerism in children with hematological diseases after allogeneic hematopoietic progenitor cell transplants

Using in situ hybridization with an X and Y chromosome probe mixture, 106 b one marrow samples from 38 patients with malignant and non-malignant hemato logical diseases who received sex-mismatched allogeneic hematopoietic proge nitor cell transplants (PCT) in a single institution within short-term inte rvals (1, 3, 6, 12, 24 and >24 months) have been sequentially studied. The patients received either HLA-identical (n = 31) or nonidentical (n = 7) PCT , Twenty-six children showed donor chimerism, 10 children showed mixed chim erism (MC) and two children presented autologous reconstitution. Chimerism status with different parameters has been related (age, sex, donor, disease status before PCT, conditioning regimen, GVHD prophylaxis, relapse, GVHD a nd survival), Our results indicate that female patients (P = 0.011) and a l ess intensive conditioning regimen (P = 0.039) are significantly associated with the MC status, Mixed chimerism is not, per se, significantly associat ed with leukemia relapse but an increase of the MC is indicative of clinica l relapse.