The EuroChimerism Concept for a Standardized Approach to Chimerism Analysis Following Allogeneic Stem Cell Transplantation.
Authors: Lion Thomas , Tilanus Marcel , Cavé Hélène , Lawler Mark , Serra Anna , Biondi Andrea , van Dongen Jacques , González Marcos , Barbany Gisela , Roosnek Eddy , Steward Colin , Bader Peter 
Published: October 2019

Abstract
Transplantation of hematopoietic stem cells from related and unrelated donors is becoming an increasingly important approach in the successful treatment of different malignant and non-malignant disorders. There is thus growing demand for clinical diagnostic methodologies permitting the surveillance of chimerism during the post-transplant period. The techniques currently employed are rather heterogeneous, rendering uniform evaluation and comparison of diagnostic results between centers difficult. Leading laboratories from ten European countries have therefore performed a collaborative study supported by a grant from the European Commission, the EuroChimerism Concerted Action. The aim of this Concerted Action was the development of a standardized diagnostic methodology for the detection and monitoring of chimerism in patients undergoing allogeneic stem cell transplantation. A set of microsatellite markers, selected on the basis of their excellent performance in chimerism analysis at the reference centers involved, have been carefully evaluated and optimized for quantitative chimerism testing under standardized experimental conditions. A EuroChimerism panel designed to optimally meet the specific requirements of quantitative chimerism analysis was established utilizing 13 markers (D2S1360, D7S1517, D8S1132, D9S1118, D10S2325, D11S554, D12S1064, D12S391, D17S1290, D19S253, MYCL1, P450CYP19 and SE-33), which best satisfied the criteria of the EuroChimerism consortium. Individual microsatellites from the panel can be analyzed in multiplex reactions to facilitate the identification of one or more markers optimally suited for the monitoring of chimerism during the post-transplant period. Extensive testing of related individuals (>500 pairs) revealed that the EuroChimerism marker panel will provide at least two informative markers which meet the stringent criteria of eligibility defined by the EuroChimerism consortium (Watzinger et al., Leukemia 2006) in >99% of all patient/donor constellations. In addition to the outstanding informativeness of the marker panel, chimerism testing by singleplex assays permitted sensitive detection of residual cells of patient or donor origin at levels ranging between 0.8–1.6% in about 90% of instances. The assay also facilitates accurate and reproducible quantification of donor and recipient hematopoietic cells in peripheral blood or bone marrow specimens and in specific cell lineages isolated by flow-sorting. The precision in determining the relative contribution of donor/recipient cell populations to mixed chimerism was high within the range between 10–90% donor- or recipient-derived cells, while there was a tendency to overestimate the percentage of the subdominant cell population within the range between 1–10%.
Wide use of the EuroChimerism assay will provide a basis for international standardization of chimerism testing, which will ultimately contribute to improved clinical management of patients undergoing allogeneic stem cell transplantation.