THE EXAMINATION OF CELL CHIMERISM AS A NONSPECIFIC MARKER IN POST-TRANSPLANT PERIOD BY MOLECULAR GENETICS METHODS

Background:

Allogeneic bone marrow or peripheral blood stem cell transplantation (allo-HSCT) is an important medical procedure in the treatment of malignant and nonmalignant disorders in children. After the transplantation it leads in the recipient to the development of chimerism (cells from genetically different individuals coexist in one body). The detection of only donor´s genotype in blood cells is called the complete chimerism (CC). The coexistence of recipient’s and donor’s  haematopoiesis in different proportions (mixed chimerism – MC) augments the risk of relapse.

Aims:

The early detection of mixed chimerism or microchimerism (less than 1% of recipient´s genotype) is important for individual approach to the patient care. The ability to detect early the recurrence of recipient’s  haematopoiesis followed by disease depends on the sensitivity of the used method.

Methods:

The most of the samples are quantitatively determined by the short tandem repeat polymerase chain reaction (STR-PCR). Currently, sex-specific loci and a method based on SNP (Single Nucleotide Polymorphism) or short insertion and deletion (indel) are also used; less frequently  the length polymorphisms of VNTR type (Variable Number of Tandem Repeats) are determined. The sensitivity of the used methods is the following: VNTR 1-5%, STR 1% and SNP or indels 0.01%. We have regularly received the samples of pediatric patients after allo-HSCT from The University Hospital Motol  since 1992. Informed consents were obtained from all patients, or from their legal guardian.

Results:

The informativity was determined in 356 children´s patients indicated for allo-HSCT during the years 1992-2012, including 112 cases of acute lymphoblastic leukemia (ALL), 49 cases of acute myeloid leukemia (AML), 58 cases of aplastic anemia, 26 cases of chronic myeloid leukemia (CML), 40 cases of immunodeficiency, 41 cases of  myelodysplastic syndromes (MDS) and 30 cases of other diagnoses. It was also investigated 23 cases of maternal engraftment and 2 detections of twins zygocy. In total, 67% of transplantations were provided from unrelated donors and 33% from related donors. Patients achieved CC in a median of 21 (range, 7-543) days after allo-HSCT, 9% of all patients never reached CC and they still have MC. Altogether, 77% of all monitored patients survive and they are constantly monitored, while 23% of all patients died. Five years after HSCT 80% of patients with CC and 74% of patients with MC continue to survive. Relapse was the cause of death in 37%, infection in 23%, graft versus host disease (GVHD) in 16%, organ failure in 13% and the other causes in 11%. In 29 patients who died because of relapse MC was detected in 20 of them (69%). In the other 9 patients with relapse CC was detected. These patients died before the year 2005 when the samples were analysed only by VNTR polymorphisms, that´s sensitivity is 1-5%. According to the selected examples of the patients who died because of relapse the increasing of cell chimerism corresponds with the other results (increasing of blast number).

Summary / Conclusion:

Analysis of individual haematopoietic chimerism in the time period after transplantation is a nonspecific marker for post-transplant haematopoiesis for all diagnoses and it provides diagnostic evidence for clinical decisions. With this analysis it is possible to predict negative events, such as graft rejection or relapse in the early stage of disease. Subsequently quick therapeutic intervention can efficiently reduce the number of autologous cells before clinical manifestation of the disease.

Email address: Monika.Holicka@uhkt.cz

Keywords: Allo-SCT, Chimerism, Molecular markers

Abstrakta v časopise Haematologica 2013, Suppl1

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