Chimerism monitoring
Transplantation and monitoring
Pēdējo trīsdesmit gadu laikā kaulu smadzeņu un perifērisko asiņu cilmes šūnu transplantācija visā pasaulē kļuvusi par plaši pielietotu ārstēšanas procedūru vairāku saslimšanu gadijumā. Alogēnā transplantācija tiek izmantota, lai ārstētu sirpjveida anēmijas, smagu aplastisko anēmiju, talassēmijas, akūtas leikozes, hronisku mieloleikozi un citas slimības. Pēc transplantācijas ir ļoti būtiski zināt, vai jaunajām asinsrades šūnām ir donora vai recipienta (saņēmēja) izcelsme. No tā var secināt, cik veiksmīga bijusi transplantācija, cik ātri notiek un notiks recipienta asins šūnu aizvietošana ar donora izcelsmes šūnām. Asins šūnu izcelsmes pētīšanu pēc transplantācijas sauc par himērisma analīzi jeb monitoringu.
Since 2006, Latvia offers allogeneic transplantation for patients with serious diseases. It is very important to regularly monitor the ratio of recipient and donor cells in the recipient’s body — this allows the assessment of transplantation results and further adjustments in the treatment.
What is chimerism?
Chimerism can occur for a variety of reasons, such as an inheritance from the mother (maternal-foetal stem cell trafficking during gestation), blood vessel sharing in fraternal twin gestation, after blood transfusions, as a result of bone marrow transplantation, umbilical cord blood transplantation, and organ transplantation.
Initially, it was thought that after successful transplantation, all cells of the hematopoietic system would develop from the donor stem cells. In recent years, it has been shown that after transplantation donor and recipient haematopoiesis can coexist. This condition is called mixed chimerism and can result in autologous recovery. If, after transplantation, all hematopoietic cells are of donor origin, complete chimerism is considered and the patient is called a complete chimera.
Test description, reference values
The purpose of the method is to determine the degree and development of chimerism in the post-transplantation period. The method is based on chromosomal DNA analysis, in which specific genetic markers of specific loci, the so-called STR (from short tandem repeats), are tested and compared in recipient and donor tissue samples. Each individual inherits two STR sequences within one locus. In the population, the frequency of STR varies for different loci, so the more loci are analysed, the more informative alleles are obtained for chimerism analysis. The number of loci analysed is essential for the chimerism test, as donor and recipient samples are often of related origin, which limits the number of informative loci. We test 15 STR loci. The method allows the detection of the genome of another human—the donor—in the blood of the recipient even if there is as little as 1%.
If the percentage of donor cells in the recipient’s blood is less than 85%, it indicates a transplantation failure and signals the need for increased patient monitoring.
The following samples are required for testing:
Donor venous blood or saliva sample;
Recipient venous blood or saliva sample before transplantation;
Recipient venous blood sample — after transplantation, and thereafter at intervals determined by the physician.