Department of Pathology

Chimerism testing

Dr. Shyla Chikkamuniyappa

Chimerism testing (AKA Engraftment studies) is a routine diagnostic test performed after allergenic stem cell or bone marrow transplantation. Monitoring assesses the relative ratio of donor and recipient cell populations in the post-transplant peripheral blood and/or bone marrow of the patient. It is based on the detection of differences in allele types between the donor and recipient cells at several short tandem repeat (STR) loci.

Short tandem repeats are short sequences of DNA, normally of length 2-5 base pairs, that are repeated numerous times in a head-tail manner. They are abundant throughout the entire genome and highly polymorphic. They are easy to amplify and quantitate and therefore are useful as genetic markers to obtain an unambiguous individual identification.

Engraftment is defined as a rise in white cell and platelet count with studies showing complete donor cells. This usually occurs between Days 15-30. Platelets are the last hemopoietic cells to engraft. Causes for delayed engraftment are infection, immunosuppression, graft failure, low stem cell dose at transplant and if it’s a cord transplant.
Chimerism testing can be done on a peripheral blood or bone marrow sample. Stored pretransplant WBC pellets are available for comparison from both the donor and recipient. DNA is first extracted from the samples using a standard Qiagen protocol. The chimerism analysis is done using the ABI 310 Genetic analyzer, Genescan software and AmpFISTR SGM plus kit. Results are obtained from ~ 1ng of DNA in less than 5 hours. 10 polymorphic STR system alleles and the X and Y chromosome marker, labeled with different fluorescent dyes is analyzed at the same time using the technique of capillary electrophoresis. Based on the results of either a full or mixed chimerism, complete vs delayed engraftment vs. relapse of primary disease or Graft vs. Host disease (GVHD), further management of the patient is done.

In essence, it is a powerful technique which provides rapid diagnosis of engraftment and identity testing.

Short Tandom Repeats, An Introduction

Short Tandom Repeats, References (1); References (2)

1. The information in the DOLS web site is developed for and intended to help the clinicians of our academic medical community: The University Health System; The University of Texas Health Science Center at San Antonio; The South Texas Veterans Healthcare System: Audie Murphy Memorial Veterans Hospital.
2. If you are from outside of our community and you find that the information is helpful, you are welcome to it, however, we encourage you to consult with your local experts and your health science center libraries for more information.

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Last updated on 26 July, 2005 by John D. Olson, M.D., Ph.D.