Chimerism testing in myeloid malignancies: techniques, considerations, and connections to post-transplant outcomes

Relapse represents the most significant cause of death post-allogeneic stem cell transplant (aSCT) for patients with myeloid malignancies. Early intervention among patients deemed high risk for relapse is one focus to improve aSCT-related outcomes. As such, the early identification of residual malignant cell burden is of critical importance. Chimerism testing, the assessment of the relative percentage of donor to recipient haematopoietic cells based on genetic differences, offers one practical means to assess for residual host haematopoietic cells, which could be indicative of leukaemic cell burden. The purpose of this review paper is to discuss the use of chimerism testing to better understand the risk of relapse. Important consideration will be given to the various laboratory techniques used to compute donor chimerism percentage and their relative limitations, the external factors that may influence the relative value of donor to recipient chimerism ​and its importance among the major myeloid malignancy diagnostic categories. Special attention will be paid to strategies to improve the sensitivity and specificity of chimerism testing, namely its concurrent use with measurable residual disease and the use of lineage-specific chimerism to both improve relapse detection and guide therapy decisions.