LAUSR

Incomplete donor chimerism (DC) after hematopoietic stem cell transplantation (HSCT) is associated with reduced overall and disease-free survival and decreasing DC can precede overt relapse of malignant diseases.1, 2 Sensitive chimerism quantification may therefore allow for early therapeutic intervention, potentially improving treatment response.3, 4 Frequently, post-HSCT chimerism monitoring involves bone marrow (BM) biopsies, although hematologic malignancies are frequently associated with risk factors for adverse events (for example, low platelet count) and dry taps can preclude chimerism analyses.5, 6 However, new PCR strategies for chimerism quantification have dramatically increased technical sensitivity with current methods enabling the detection of chimerism below 0.1%.7, 8, 9 Therefore, applying these methods for chimerism quantification in peripheral blood (PB) may reduce the need for BM analysis. The influence of sample source on the sensitivity of chimerism analysis in the context of highly sensitive quantification methods, however, is not well substantiated. In order to address this, we compared sensitive chimerism analyses performed on paired BM and PB samples from 219 HSCT patients (Supplementary Table 1). The detailed materials and methods are available as Supplementary Information.