Journal of Forensic Medicine and Legal Affairs

Chimerism in Humans after Bone Marrow Transplantation: A New Challenge for Forensic DNA Experts

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Published Date: February 08, 2016

Chimerism in Humans after Bone Marrow Transplantation: A New Challenge for Forensic DNA Experts

Garima Chaudhary

Senior Forensic Examiner, DNA Division, Forensic Science Laboratory, New Delhi, India

Corresponding author: Garima Chaudhary, Senior Forensic Examiner, DNA Division, Forensic Science Laboratory, New Delhi, India, E-mail:

Citation: Chaudhary G (2016) Chimerism in Humans after Bone Marrow Transplantation: A New Challenge for Forensic DNA Experts. J For Med Leg Aff 1(1): 104. Doi:


Keywords: Chimerism; DNA Profiling; STRs

When DNA profiling technique is being performed using any biological specimen from the individual, it promises the correct and unambiguous individualization, but in certain cases the forensic scientist may encounter the problem of mixed or completely mismatched DNA profile of a single individual [1,2]. STR’s (short tandem repeat) may lead to erroneous conclusion when the source of the biological material being analyzed is from a person who is a genetic chimera. In forensic genetics context, such genetic peculiarity may prevent the association of the perpetrator of an offence with the stain left at the crime scene or lead to false Identification of any suspect [2].

Forensic science, also known as legal medicine is a specialism beginning at a crime scene and concluding in a court room to help judges and juries to solve legal issues, in criminal as well as in civil cases. Establishing individuality is an imperative aspect of investigative process in forensic cases. Forensic molecular biology is one of the key forensic disciplines that allow the unambiguous identification of any individual [3].

Over the past 30 years, DNA profiling technique has revolutionized the field of forensic science with the ability to match the perpetrators with crime scenes. The evolution of forensic genetics has been driven by the analysis of human genome variations. Discovery of the human ABO blood group polymorphism by Karl Landsteiner in 1900-1901 provided the platform for solving crime by placing individuals in different groups based on their blood groups. The genetic system of ABO and other blood groups (MNSs system, Rhesus, Lewis, Kell, haptoglobin; discovered between 1920s- 1950s) has provided the power of exclusion. Developments made in 1960s and 1970s enabled the scientists to examine DNA sequences by using the restriction enzyme, Sanger sequencing and southern blotting. Revolution in forensic genetics began in 1984 when Alec Jeffery from Leicester, UK realized the potential forensic application of the variable number tandem repeat (VNTR) loci. The technique used to examine VNTRs is called restriction fragment length polymorphism (RFLP) and the first case solved using this technique was an immigration case of UK [Jeffery, 1985] and shortly thereafter it was used to solve a double homicide case [Jeffery, 1986].

The genetic peculiarity chimerism poses a potential challenge to forensic scientist to solve the case successfully, because for any subject who has a history of successful allogenic bone marrow transplantation, blood is not suitable for personal identification or kinship study because of presence of donor cells in the recipient blood, e.g. if a male blood group A+ is transplanted with the peripheral blood from his sister having blood group AB+, post transplanted blood and genetic analysis will be a female sex and blood group AB+. Fast reorganization of chimeras, adapting sampling scheme, as well as careful interpretation of the data can help significantly in avoiding the possible incorrect interpretation DNA profiling outcomes.

The term chimerism originates from the Greek mythology and refers to the creature “Chimaera”. The definition of chimaera (in medicine called “Chimera”) was first described by Ford in 1969. According to him, Chimera is an organism whose cells are derived from the two or more distinct zygote lineages. In a chimera there are two or more distinct cell lines present in one individual [4].

Endler et al. [4], were the first to describe the donor and mix profile in mouth wash of the patients after Allo-BMT. They examined 17 patients who undergone bone marrow transplants. They extracted the DNA from mouthwash and epithelial cells from oral cavity, PCR amplification of STR loci in the vWF and THO1 gene were performed. PCR products were assayed on precast 6% polyacrylamide gel. Their results showed that even though the mouthwash cell pellets contained about 75% epithelial cells leukocytes (presumably of recipient origin) and only 25% leukocytes (presumably of donor origin). Three out of five patients showed donor genotype and only two patients exhibited chimeric DNA patterns, when cellular DNA was obtained by boiling of mouthwash pellets. They concluded that blood cells serve as preferred DNA source in mouthwash samples and cannot be removed by epithelial cell separation [4].

These results were supported by Thiede et al. [5]. They analyzed buccal swab and mouthwash samples in 13 patients who underwent Allo-BMT (Allogeneic bone marrow transplant). Samples were taken 1-24 year after transplant. They found that mouthwash sample contain high amount of donor DNA, and are sometime almost completely derived from the donor. DNA samples derived from buccal swab also contained donor DNA but in much lower amount (median 21% in buccal swab compared to 74% in mouthwash). They could not explain the factor which defines the number of donor cells present in mouthwash as well as in buccal swab samples.

In a very important finding, Tran et al. [6], for the first time described the concept of trans-differentiation of human bone marrow derived cells into buccal epithelial cells. They performed in-situ hybridization with Y and X chromosome probes with 35-sulphar or digoxigenin, or labeled fluorescently Immuno-histochemistry with anti-Cytokeratin 13 along with fluorescence in-situ hybridization was performed to identify Y chromosome positive buccal epithelial cells in cheek scrapping obtained from five females who had received either bone marrow transplant or an allogenic mobilized peripheral blood progenitor cell transplant from male donors. They found that all female recipient had Y chromosome positive buccal swab (0.8-12.7%), when examined four to six years after male-to-female marrow cell transplantation. They concluded that male bone marrow derived cells migrate into the cheek and differentiate into epithelial cells and it does not depend on fusion of Bone marrow derived cells to recipient cells [6].

Dauber EM et al., 2004, also found donor cells in blood and buccal swab samples of patients who underwent Allo-BMT. They studied two STR loci SE33 and D12S3911 and further analysis was carried out on an ABI Prism 310 genetic analysis. They found complete chimerism in blood and in buccal swab, median of donor cells found was 32.1% (16.6%-76.3%) similar type of results were showed by Hong et al. [7], who studied chimerism in buccal swab using a panel of STR markers in Ampflstr profiler plus kit and found donor chimerism range 10-96%, Zhou et al. [8], studied STR markers of Ampflstr SGM Plus kit and found donor chimerism level in buccal swab ranging between 2-90%. Berger et al. [2], also studied 162 buccal swabs from 77 adults who underwent allo-BMT. They estimated the chimeric recipient/donor DNA ratios through analysis of 15 autosomal STR markers (Ampflstr identifiler kit) and found donor chimerism between 0 -100% with maximal frequency 10-30%.

Other commonly used biological sources for forensic DNA profiling are fingernails and hair follicles. Imanishi et al. [9], conducted a study to check whether donor derived cells could exist in non-haematopoietic tissue of recipient after allo-HSCT. They examined 21 patients. Ampflstr SGM Plus kit having ten STR regions was used to amplify the DNA extracted from fingernails of the patients of allo-HSCT (Allogeneic Hematopoietic Stem Cell Transplantation). Results showed coexistence of the donor pattern of the STRs, sharing from 89% to 72.9% of the total STR areas. Time from transplant to sampling was from 305-2399 days. These results were supported by Pearce et al. [10], they analyzed fingernails samples from eight adult patients undergoing allo-HSCT. Median time of sampling was 1048 days post HSCT (range 68-3353days). They showed median level of donor chimerism in the fingernails samples of these patients was 22% (range 14-58%).

In 2005, Rovo et al. conducted a study to analyze the chimerism in hair samples of the patients of allo-HSCT. In total 115 patients were studied by them and they found hair follicle remain exclusively of recipient type despite full whole blood donor type chimerism. Hair supposed to be the ideal specimen to retrieve the recipient pre-transplant genetic profile until a study by Jacewicz et al. [11], showed donor chimerism when analyzed with sex determining region Y (SRY). They studied ten female patients, who received Allo-HSCT from male donors (nine from their brothers and one from father). Extracted DNA from hair samples were amplified using Ampflstr Yfiler PCR amplification kit. They observed complete donor chimerism in hair samples of recipients [12]. Similar type of results were again reported by Jacewicz et al. [13], with the increase in the number of samples analyzed (32 patients) and donor chimerism was observed in hair samples of recipients of Allo-HSCT. 

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Copyright: © 2016 Garima Chaudhary. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.