Chimerism monitoring

Transplantsation and monitoring

 

During the last three decades, transplantation of bone marrow and peripheral blood stem cells has become a widely used treatment method for several diseases worldwide. Allotransplantation is used to treat sickle cell anaemia, severe aplastic anaemia, thalassemia, acute leukaemia, chronic myeloid leukaemia and other conditions. After the transplantation, it is very important to determine whether the new hematopoietic cells have a donor or recipient origin. This is the basis for evaluating the success of the transplantation and the current and expected rate of recipient blood cell replacement with donor cells. Investigation of the origins of blood cells after the transplantation is called chimerism analysis or chimerism monitoring.

 

Since 2006, allotransplantation has also been offered to patients with severe conditions in Latvia. Regular monitoring of the recipient–donor cell proportion in the body is crucial. It helps to assess the outcome of a transplantation and adjust further treatment.

 

What is chimerism?

Initially it was believed that after a successful transplantation, all the cells in the hematopoietic system developed from donor stem cells. However, in recent years it has been proven that donor and recipient haematopoiesis may co-exist after transplantation. This condition is called mixed chimerism, and it may lead to a predominance of autologous cells (autologous recovery). If all the hematopoietic cells after the transplantation are donor cells, this condition is called complete (full) chimerism.

 

Description of the test and reference values

 

The objective of the test is to establish the degree and proportion of chimerism in the post-transplantation period. The method is based on chromosomal DNA testing where specific genetic markers called STR (short tandem repeats) of particular loci are analysed and compared in recipient and donor tissue samples. Each person inherits two STR sequences within one locus. The STR prevalence rate in population varies depending on the locus. Therefore, the higher the number of analysed loci, the more information can be obtained for chimerism analysis of alleles. The number of analysed loci plays an essential role in chimerism analysis, because donor and recipient samples often originate from close relatives, which limits the number of informative loci. We test 15 STR loci. This method detects the presence of even 1% of foreign – or donor – genome in the recipient’s blood sample.

 

If the proportion of donor cells in the recipient’s blood is lower that 85%, it indicates an unsuccessful transplantation and marks the need for closer monitoring of the patient.

 

Samples required for the test

  • A donor sample of venous blood or saliva

  • A recipient sample of venous blood or saliva, prior to transplantation

  • A recipient sample of venous blood – immediately following transplantation and later in intervals specified by the doctor

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