Bone Marrow Engraftment Analysis

In genetics, chimerism is defined as the state where an organism is comprised of genetically distinct cell populations that arise from different zygotes. In hematopoietic progenitor cell transplantation (HPCT), hematopoietic progenitor cells (HPCs) from a donor are infused into a patient (recipient) with the intention of reconstituting normal hematopoietic function through the donor cells. One primary goal of HPCT is engraftment, which is characterized by neutrophil (myeloid) engraftment, platelet engraftment, erythroid engraftment, and T-cell (CD3+) engraftment. The main objective of chimerism testing is to detect and quantify the presence or absence of recipient and donor cell populations post-HPCT, thereby allowing for chimerism assessment of engraftment of these different cell lineages. Chimerism testing can also be useful in monitoring for risk of relapse in high-risk patients and thus permitting for preemptive interventions such as donor lymphocyte infusions (DLI) or withdrawal of immunosuppressive therapies (IST). Other uses of chimerism testing include, but are not limited to, forensic testing to identify suspects or unidentified victims, parentage and/or kinship testing, and zygosity testing for twin studies. Herein, the different methodologies used in chimerism testing will be presented with a particular focus on short tandem repeat (STR) analysis, which is the most commonly employed method in clinical laboratories. Emphasis will be placed on STR nomenclature, allele designation, categorization, and testing interpretation to determine percent recipient and donor contributions of post-HPCT laboratory samples. Finally, the limitations in STR testing will be highlighted along with strategies to mitigate their effects.