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.