Establishing the method of chimerism monitoring after allogeneic stem cell transplantation using multiplex polymerase chain reaction amplification of short tandem repeat markers and Amelogenin.

We describe the implementation, optimization, sensitivity determination and first clinical results of polymerase chain reaction (PCR) amplification of polymorphic short tandem repeat (STR) markers and Amelogenin locus coupled with fluorescent detection and capillary electrophoresis in chimerism monitoring of patients transplanted at three different transplant centers using a commercially available multiplex microsatellite assay. The chimerism analysis was performed with genomic DNA extracted from unselected peripheral blood leukocytes of one hundred pediatric and adult patients, who underwent allogeneic stem cell transplantation (SCT) from human leukocyte antigen (HLA) matched or one antigen mismatched related or unrelated donors for malignant (70 patients) and non-malignant (30 patients) diseases. Tested were 79 donor recipient pairs for 15 STR systems and identified an informative marker in all but one of them (98,7%), using 6 selected systems out of these fifteen, that appeared highly informative in our patients population. In 21 sex-mismatched donor recipient pairs we used the Amelogenin locus to distinguish the X and Y chromosome. In sixty-three out of these 100 patients chimerism was regularly analyzed from blood samples taken at various time points after SCT with the median follow up of 17 months. Complete chimerism (CC), maintained over the whole follow-up period, was detected in 24 (38, 1%), stable and decreasing mixed chimerism (MC) in 28 (44, 4%) and increasing MC in 11 patients (17, 5%). Patients with CC, stable and decreasing MC showed a significantly better (p 0,005) overall survival rate (0, 81), compared to those with increasing MC (0, 24). These results demonstrate that STR-based chimerism monitoring with sensitivity above 1% and high informativity (98, 7% of donor recipient pairs) is necessary in establishing the origin of engrafted cells after an allogeneic SCT, in detecting graft rejection and that it may contribute in identifying patients with imminent leukemia relapse.