Objective: To investigate the exact kinetics of donor chimerism (DC), outcome of mixed chimerism (MC) and prognostic role of chimerism in the evaluation of engraftment, disease relapse, GVHD and long term survival after nonmyeloablative stem cell transplantation (NST).
Methods: 18 patients who received HLA compatible NST were evaluated. Peripheral blood and bone marrow were collected before and after transplantation at different time. DNA was extracted using QIAmp blood mini kit. Nine different STR markers were co-amplified in a single reaction by commercial AmpF/STR profiler plus PCR amplification kit. Separation of the PCR products and fluorescence detection were performed with ABI prism 310 genetic analyzer with capillary electrophoresis. Genescan and genotype software were used for size calling and quantification of peak areas. The formula to calculate donor chimerism values was based on different allelic distribution types between the donor and recipient.
Results: (1) Serial STR-PCR analysis revealed that donor chimerism became dominant (DC > 60%) by day 8; it preceded the detection of hematologic engraftment by an average of 4 days. It was also shown that chronic myeloid leukemia (CML) patients frequently had more delayed donor engraftment as compared with patients of acute leukemia or nonmalignant hematological diseases because the pretransplantation immune status of these two kinds of patients was different. (2) After NST, chimeric status had a process of conversion from the mixed chimerism (MC) to full donor chimerism (FDC). (3) The incidence of graft versus host disease (GVHD) of FDC group was higher than that of MC group (90.0% vs 62.5%). The average time between establishment of FDC and appearance of GVHD was 9 days. (4) Full donor chimerism and stable mixed chimerism with a high level of donor cells were compatible with disease free survival. On the contrary, progressive decrease of donor chimerism value was always followed by hematological relapse or graft rejection.
Conclusions: Sequencial and quantitative detection of donor chimerism may be of great value to study the kinetics of engraftment of NST, to evaluate the status of engraftment, to predict the outcome and prognosis of patients posttransplant and to guide implementation of therapy at an early stage.