[Indications for chimerism analysis on sorted cell populations after allogeneic hematopoietic stem cell...

Chimerism monitoring following allogeneic hematopoietic stem cell transplantation is a key component of post-transplant surveillance. While whole blood chimerism analysis remains the standard approach, lineage-specific chimerism assessment on sorted cell populations has become increasingly common over recent years. However, its actual clinical benefit remains controversial. As part of this SFGM-TC harmonization workshop, a survey of current practices was conducted among French-speaking transplant centers and complemented by a critical review of the literature. The specific objective was to evaluate the added value of lineage-specific chimerism compared with whole blood chimerism. Therefore, the analysis focused on studies directly comparing these two approaches. Indeed, many published studies have investigated chimerism in specific cell populations without direct comparison with whole blood chimerism, making it difficult to assess the true benefit of cell sorting. The available data highlight the widespread use of lineage-specific chimerism monitoring in French-speaking centers, but also reveal substantial heterogeneity in practices, analytical methods, and clinical indications. Although some evidence suggests a potential role for selected cell subsets in specific clinical settings, the limited number of comparative studies and the lack of standardized decision thresholds preclude the establishment of robust consensus recommendations. At present, only targeted use of lineage-specific chimerism can be recommended, whereas whole blood chimerism remains the reference approach. Prospective comparative studies are needed to better define the role of lineage-specific chimerism monitoring in post-transplant follow-up.