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Chimerism Monitoring by Short Tandem Repeat (STR) Markers in Allogeneic Stem Cell Transplantation.

BACKGROUND
Allogeneic hematopoietic stem cell (allo-HSC) transplantation is used in the treatment of malignant hematological diseases. An important tool in monitoring post-transplantation evolution is represented by the percentage of donor's blood cells found in recipient's blood, known as chimersim. This is useful in predicting the graft rejection and the risk of disease relapse. In this study, we present the importance of multiplex STR markers in chimerism monitoring of a 8 year old girl diagnosed with acute lymphoblastic leukemia (ALL).


METHODS
In the pre-transplant stage, saliva on buccal swabs and blood samples in EDTA were collected from the donor and recipient and used as reference samples. The DNA extraction from saliva and blood samples was done using the Pure Link Genomic DNA kit (Invitrogen, USA). For the DNA quantification, the Quantifiler Human DNA kit (Applied Biosystems, USA) was used on an ABI 7500 Real-time PCR system (Applied Biosystems, USA). Amplification of the STR markers was performed using the AmpFLSTR NGM SElect kit (Applied Biosystems, USA) on a ProFlex PCR System. The PCR products were separated and detected on an ABI 3500 Genetic Analyzer (Applied Biosytems, USA).


RESULTS
One month post-transplantation of HSC, a mixed chimerism (MC) containing 38% of donor's cells was obtained from a bone marrow aspiration sample. On the 45th day, a new transplantation was performed. On the 15th day after 2nd transplantation, a MC with 91% donor's cells was obtained. On the 21st day after the 2nd transplantation, a complete chimerism (CC) with 100% donor's cells was obtained.


CONCLUSIONS
Chimerism monitoring is useful in identifying those patients in risk for relapse or graft rejection.