Chimerism
Haematology Overview / Directory
Purpose of the test
The Chimerism investigation is carried out to monitor the engraftment of Bone Marrow (BM), Peripheral Blood (PB), CD3 T-cells, CD15 Granulocytes and CD19 B-Cells following haemopoietic stem cell transplant.
The microsatellite regions which the individual primer sets are designed to amplify, consist of repetitive sequences (short tandem repeats STRs) of DNA 3-7 base pairs in length. These STRs are well distributed throughout the human genome and are highly polymorphic. There are many advantages of STR typing. It is more tolerant of the use of degraded DNA templates than other typing methods because the amplification products are less than 500bp long. STR typing is also amenable to a variety of rapid DNA purification techniques, which are compatible with PCR but do not provide enough DNA of appropriate quality for Southern blot-based analyses.
Donor and Pre-transplant recipient samples must be obtained before the Post transplant sample can be analysed. The donor and recipient samples are run in conjunction with all post transplant specimens (BM, PB or fractionated cells) to illustrate the individual polymorphic alleles which distinguish the donor population from the recipient.
Analysis of chimerism is valuable in assessing patients response to transplantation. Observing a complete donor profile in the post transplant samples indicates a successful transplant. Chimeric profiles, (the presence of both donor and recipient allelic peaks) depending on the donor to recipient ratio (%), may indicate a less successful engraftment or progression to relapse.
Following analysis, donor and recipient profiles can be semi-quantified in the post transplant sample by obtaining the values for the areas underneath respective peaks and calculating the percentages of each. A value is obtained for each of the informative genes and the mean is calculated to give a more accurate indication of the recipient status. The 16 gene profiles for each patient are printed and handed to the consultant haematologist at least 24 hours before the weekly chimerism meeting, where the individual cases are discussed with the BMT co-ordination team.
Sample Requirements
500µl BM and 5-10ml PB for fractionation.
Presence of heparin anticoagulant will inhibit PCR applications. Clotted samples are unsuitable for DNA analysis.
Samples must be clearly labelled with the patient's first name, surname, D.O.B, hospital number and the date the sample was taken.
Storage and Transport
Samples must be in EDTA and transported to the MRD Laboratory within 24 hours.
First class postage is adequate but samples must be shipped with packaging appropriate for UN 3373 samples following packing instruction 650. See link below for further details.
Samples should be addressed to:
Central Specimen Reception,
Ground Floor, Bessemer Wing,
King's College Hospital,
Denmark Hill,
London SE5 9RS,
United Kingdom
Turnaround Time
10 working days.
Time Limit for Extra Tests
Dependent upon additional tests - please enquire
Factors affecting results or interpretation
Post-transplanted samples can only be assessed alongside a donor and pre-transplant DNA profile. These samples must be provided as a one-off prior to the sending of post-transplant material.
Price
Please contact the laboratory for prices
(* Discounts available for significant workloads)
Contacts
Dr Nicholas Lea
T 020 7848 5821
Dr Atiyeh Abdallah
T 020 7848 5821 / 5809
References
Edwards, A. et al. (1991) DNA typing with trimeric and tetrameric tandem repeats;; polymorphic loci, detection systems and population genetics. In:The Second International Symposium on Human Identification 1991, Promega Corporation, 31 - 52.
Edwards, A. et al. (1991) DNA typing and genetic mapping with trimeric and tetrameric tandem repeats. Am Journal Hum. Genetics. 49, 746 - 56
Warne, D. et al. (1991) Tetranucleotide repeat polymorphism at the human B-actin related pseudogene 2 detected using the polymerase chain reaction. Nucl Acids Res. 19, 6980
