Biomarkers in chronic graft-versus-host disease: quo vadis?

Biomarkers are increasingly used for diagnosis and treatment of transplant-related complications including the first biomarker-driven interventional trials of acute graft-versus-host disease (GvHD). In contrast, the development of biomarkers of chronic GvHD (cGvHD) has lagged behind due to a broader variety of manifestations, overlap with acute GvHD, a greater variation in time to onset and maximum severity, and lack of sufficient patient numbers within prospective trials. An international workshop organized by a North-American and European consortium was held in Marseille in March 2017 with the goal to discuss strategies for future biomarker development to guide cGvHD therapy. As a result of this meeting, two areas were prioritized: the development of prognostic biomarkers for subsequent onset of moderate/severe cGvHD, and in parallel, the development of qualified clinical-grade assays for biomarker quantification. The most promising prognostic serum biomarkers are CXCL9, ST2, matrix metalloproteinase-3, osteopontin, CXCL10, CXCL11, and CD163. Urine-proteomics and cellular subsets (CD4⁺ T-cell subsets, NK cell subsets, and CD19⁺CD21^low B cells) represent additional potential prognostic biomarkers of cGvHD. A joint effort is required to verify the results of numerous exploratory trials before any of the potential candidates is ready for validation and subsequent clinical application.