Forensic implications of the presence of chimerism after hematopoietic stem cell transplantation.

Biological vestiges are used in forensic science to resolve a large number of cases by typing the genetic profile and identifying the individual to whom it belongs. However, chimeric persons that possess cells with two or more different DNA make these types of analyses difficult. This situation can occur naturally, by errors in the fertilization or early embryogenesis, or in an artificial way, for example after hematopoietic stem cell transplantation (HSCT), when host and donor cells coexist in the patient. In this paper, we will specially focus on the latter. The vestiges from transplant patients represent a challenge from a forensic perspective since the interpretation of the genetic fingerprint can be misleading because of the presence of chimerism. Due to the high number of transplant patients (and their increase over the years) and the existence of natural chimeras (probably many of them hidden), it is necessary to consider whether we are facing a possible chimeric person or someone who has been a donor of hematopoietic stem cells in a forensic context. In this review, the presence of donor bone marrow derived cells in some tissues of forensic interest will be discussed. Finally, to emphasize the importance of chimerism after HSCT in forensic genetics, some real-life cases will be examined.

The genetic profile of bone marrow transplant patients in different samples of forensic interest.

Humans constantly lose epithelial cells, and these biological traces are frequently studied in the context of criminal investigations. The objective of this work was to examine the genetic profile in samples of forensic interest (nail and skin epithelial cells) of bone marrow transplant patients and discuss its forensic and clinical implications. The genetic profile of nail, epidermal cells and blood samples of patients receiving HSCT was analyzed by the amplification and sequencing of 38 insertion/deletion polymorphisms and 15 short tandem repeat polymorphisms. In this analysis, the age of patients and donors, the time elapsed from the transplant, the type of conditioning prior to the transplant and whether the patient suffered graft-versus-host disease were considered. Donor chimerism can be detected in the DNA extracted from nail and skin epithelial cells of transplant patients. No statistically significant correlation was found between the type of conditioning and the percentage of donor DNA in nail (p > 0.05). A positive correlation, without statistical significance, was encountered when we analyzed the relationship between the time elapsed from the transplant with the percent donor chimerism found in epithelial cells of the epidermis and in nails. We conclude that within a judicial context (e.g. when testifying as an expert witness) it is necessary to consider whether we are facing a possible transplant patient or a person who has been a bone marrow donor.